Molecular events in the cell types of the olfactory epithelium during adult neurogenesis
© Heron et al.; licensee BioMed Central Ltd. 2013
Received: 22 October 2013
Accepted: 15 November 2013
Published: 22 November 2013
Adult neurogenesis, fundamental for cellular homeostasis in the mammalian olfactory epithelium, requires major shifts in gene expression to produce mature olfactory sensory neurons (OSNs) from multipotent progenitor cells. To understand these dynamic events requires identifying not only the genes involved but also the cell types that express each gene. Only then can the interrelationships of the encoded proteins reveal the sequences of molecular events that control the plasticity of the adult olfactory epithelium.
Of 4,057 differentially abundant mRNAs at 5 days after lesion-induced OSN replacement in adult mice, 2,334 were decreased mRNAs expressed by mature OSNs. Of the 1,723 increased mRNAs, many were expressed by cell types other than OSNs and encoded proteins involved in cell proliferation and transcriptional regulation, consistent with increased basal cell proliferation. Others encoded fatty acid metabolism and lysosomal proteins expressed by infiltrating macrophages that help scavenge debris from the apoptosis of mature OSNs. The mRNAs of immature OSNs behaved dichotomously, increasing if they supported early events in OSN differentiation (axon initiation, vesicular trafficking, cytoskeletal organization and focal adhesions) but decreasing if they supported homeostatic processes that carry over into mature OSNs (energy production, axon maintenance and protein catabolism). The complexity of shifts in gene expression responsible for converting basal cells into neurons was evident in the increased abundance of 203 transcriptional regulators expressed by basal cells and immature OSNs.
Many of the molecular changes evoked during adult neurogenesis can now be ascribed to specific cellular events in the OSN cell lineage, thereby defining new stages in the development of these neurons. Most notably, the patterns of gene expression in immature OSNs changed in a characteristic fashion as these neurons differentiated. Initial patterns were consistent with the transition into a neuronal morphology (neuritogenesis) and later patterns with neuronal homeostasis. Overall, gene expression patterns during adult olfactory neurogenesis showed substantial similarity to those of embryonic brain.
KeywordsSmell Development Differentiation Neuritogenesis Immature neuron Transcription factor Stem cell Microarray Genomics
The evolutionary advantages of maintaining neurogenesis into adulthood seem substantial given the potential for repairing damage and forming memories, yet the mammalian nervous system has significant capacity for adult neurogenesis in only three locations. It contributes to learning and memory in the olfactory bulb and hippocampus [1–5] and is used to replace olfactory sensory neurons (OSNs) in the olfactory epithelium where the neurons are more exposed to external stressors than anywhere else in the nervous system.
Consistent with the conclusion that damage drives OSN replacement, the proliferation of new OSNs is accelerated by damage and slowed by protective manipulations [6, 7], events that are controlled by local signals impinging on the progenitor cells [8–16]. Analogous to the transition of embryonic neuroepithelial cells into astroglial-like adult neural stem cells located in the subventricular zone of the brain , these local progenitors derive from embryonic neuroepithelial cells that seed a layer, several cells thick, of basal cells located just above the basal lamina of the olfactory epithelium. Multipotent progenitor cells are present among both of the morphologically distinct classes of basal cells, horizontal basal cells and globose basal cells [11, 15, 18–23]. They give rise to neurally fated progenitor cells, marked first by expression of Ascl1 (Mash1) and then Neurog1 (Ngn1), which differentiate into immature OSNs. Differentiation of mature OSNs climaxes with the maturation of synapses at glomeruli in the olfactory bulb and the elaboration of cilia from the dendritic knob at the opposite pole of the neuron [24–27].
The several distinct cell types of the OSN cell lineage imply that a series of changes in gene expression programs must occur in order to produce differentiated OSNs. The molecular changes that have been described thus far [27–29] fall short of the complete characterization necessary to understand the networks of proteins that determine cellular functions . In addition, the cellular origins of most changes are unknown, a common shortcoming of expression profiling analyses of dynamic processes in complex tissues. However, this can now be overcome because the vast majority of genes expressed by mature OSNs, immature OSNs, and the summed population of the other cell types in the olfactory epithelium are known [31, 32]. We forced synchronous replacement of mature OSNs and characterized the molecular response, ascribing most of the molecular events to specific cell types, and in the case of immature OSNs, even to early or late stages of their differentiation.
Results and discussion
24% of olfactory epithelium mRNAs respond to bulbectomy
We caused selective loss of mature OSNs by unilateral bulbectomy, which severs all OSN axons on that side of the nasal cavity and evokes a well-characterized progression of cellular events [15, 27, 33–36]. Mature OSNs suffer apoptosis within three days. Macrophages infiltrate in response to OSN death, peaking around 3 days and persisting for several days thereafter. Proliferation of progenitor cells with a neural fate peaks at five days, and new mature OSNs begin to increase in number only after 10 days or more. We showed previously that the most informative point in the progression of changes after bulbectomy is at 5 days when progenitor cell proliferation is at its zenith, mature OSNs are at their nadir and the population of immature OSNs should be dominated by newly formed immature OSNs . Therefore, we profiled changes in mRNA abundance at this time point. Comparing olfactory epithelia ipsilateral and contralateral to bulbectomy, we detected transcripts from a total of 16,632 genes. Of these, 4,057 were significantly affected, with 1,723 increasing and 2,334 decreasing (Additional file 1: Table S1).
Overrepresented biological processes among mRNAs that decreased after bulbectomy
Gene ontology term
# of Genes
Olfactory transduction (3)
Odorant receptor (3)
Trace amine-associated receptor (1)
Neural functions (2)
Synaptic transmission (2)
Ion channels (2)
Overrepresented biological processes among mRNAs that increased after bulbectomy
Gene ontology term
# of Genes
Cell cycle, DNA replication, mitosis (27)
Regulation of transcription (14)
Protein phosphorylation (38)
Fatty acid metabolism (1)
Protein interaction domains (11)
Cell motion and migration (8)
Cytoskeletal organization (13)
Focal adhesion (3)
DNA binding (3)
Lipid metabolism (2)
Immune response (1)
Extracellular matrix (3)
Regulation of cell size (2)
FERM domain proteins (6)
Mature OSN transcripts decrease
Nine mRNAs had P(sp) values predicting expression in mature OSNs yet they increased rather than decreased after bulbectomy (Figure 2A). These mRNAs represented only 2.3% of the significantly affected mRNAs with P(sp) mature OSN values > 0.5, well within the error rate for P(sp) cell type assignments and therefore likely to be errors of this type. As expected, in situ hybridization for several of these mRNAs consistently revealed expression that was not restricted to mature OSNs but was instead primarily in other cell types (Additional file 2). In contrast, new in situ hybridization for 12 mRNAs with P(sp) values predicting expression in mature OSNs that decreased after bulbectomy all showed expression in mature OSNs: Arl3, Atrn, Bnip3, Cox5a, Fam179b, Fnbp1, Grip1, Ppme1, Ift80, Rab6b, Pafah1b1, and Tshz2 (Additional file 3).
Increased mRNAs identify active processes in non-OSN cell types
As expected, significantly affected mRNAs expressed primarily by the non-OSN cell types in the olfactory epithelium (P(sp) Other > 0.5) were nearly all increased, rather than decreased, after bulbectomy (Figure 2D). Existing in situ hybridization data for 28 mRNAs in this category revealed that all but one were expressed primarily by cell types that survive bulbectomy (anything other than mature OSNs): 16 in basal cells, 6 in sustentacular cells, 1 in scattered cells that may be infiltrating macrophages, 2 in immature OSNs and another 2 in a combination of basal cells, sustentacular cells, and immature OSNs. These data confirmed that mRNAs with P(sp) Other > 0.5 that increased after bulbectomy were indeed expressed primarily in cell types other than mature OSNs.
Increased mRNA abundance after the loss of mature OSNs, which constitute about half the cells in the adult olfactory epithelium, might result merely from increased prevalence of the remaining cell types. This is especially true for mRNAs expressed by infiltrating macrophages, whose abundance can increase many-fold after bulbectomy . However, for mRNAs expressed by the permanently resident cell types in the epithelium, the evidence suggests that increased cellular prevalence explains only a small fraction of the increased mRNAs. For example, of 10 documented markers of sustentacular cells and Bowman’s glands [31, 32, 37–43], only 2 were increased (Epas1 and Aqp5) while the other 8 were unaffected (Cbr2, Tyro3, Slc2a1, Slc2a3, Slc16a7, Aldh1a1, Cyp2a4/5 and Cyp2g1). These differences were not correlated with expression in neighboring respiratory epithelium (e.g., Epas1 and Cbr2 are expressed in respiratory epithelium, but Aqp5 is not), so contamination from respiratory epithelium did not obscure the effects of changes in cell type prevalence on mRNA abundance changes. Consistent with this interpretation, the canonical marker used to distinguish respiratory epithelium from olfactory epithelium, Reg3g , was not significantly increased after bulbectomy. Overall, only 39% of the mRNAs with P(sp) Other > 0.5 (552 of 1,398) were significantly affected by bulbectomy. These findings argue that increased prevalence of several cell types due to the loss of mature OSNs may not be the sole factor driving increased mRNA abundance. We hypothesize that increased transcriptional activation of the genes encoding proteins most critical for olfactory neurogenesis also contributes so that many of the largest and most consistent increases derive from genes actively responding to bulbectomy with increased transcription in the surviving cell types.
Overrepresented biological processes among non-OSN cell type transcripts that increased after bulbectomy
Gene ontology term
# of Genes
Cell cycle, cell division, mitosis, DNA replication (40)
Positive regulation of transcription (7)
Kinases; signaling, cell cycle control & transcription (18)
Sensory organ development (7)
Fatty acid metabolic processes (2)
Overrepresented biological processes among immature OSN RNAs that increased after bulbectomy
Gene ontology term
# of Genes
Focal adhesion (5)
ER, Golgi & vesicular trafficking (25)
Kinases & nucleotide binding (17)
Regulation of cytoskeletal organization (6)
As with the prediction of mature OSN mRNAs, there is an error rate in the prediction of genes expressed in non-OSN cell types (4%) that could account for the 15 mRNAs with P(sp) Other > 0.5 that decreased, rather than increased (Figure 2D). As predicted by their response to bulbectomy, in situ hybridization for several of these mRNAs consistently revealed disagreement with P(sp) values and expression primarily in the OSN layers of the olfactory epithelium (Additional file 4).
Early and late events during immature OSN differentiation
Overrepresented biological processes among immature OSN RNAs that decreased after bulbectomy
Gene ontology term
# of Genes
Protein catabolism (8)
Membrane coat, lysosomal sorting vesicles (4)
In contrast, the functional relationships among the immature OSN mRNAs that decreased were more closely associated with the other end of the lifespan of immature OSNs, especially processes that carry over into mature OSNs (Table 5). For example, increased energy production is a function shared by mature and immature OSNs , consistent with the overrepresentation of the mitochondrion category. Similarly, the axon category included several mRNAs encoding proteins important for axonal growth that are abundantly expressed in immature OSNs but also continue to be expressed in mature OSNs, such as Ncam1, Ncam2, Crmp1, Dpysl2, Mapk8ip1 [31, 55]. The protein catabolism category includes 27 mRNAs that encode ubiquitin ligases, ubiquitin proteases, or proteins that support ubiquitination in other ways; all functions that are likely to be required in both mature and immature OSNs.
Immature OSNs mRNAs that were differentially responsive to bulbectomy had distinct patterns of P (sp) and P (in) value averages
iOSN mRNA response
.00 ± .01
.41 ± .28
.48 ± .28
.48 ± .28
.89 ± .13
.11 ± .13
.01 ± .02
.24 ± .19
.73 ± .19
.74 ± .20
.97 ± .05
.02 ± .05
Transcripts expressed by both mature and immature OSNs (OSN) that were differentially responsive to bulbectomy had distinct patterns of P (sp) and P (in) value averages
Shared OSN mRNA response
.02 ± .05
.18 ± .13
.70 ± .14
.72 ± ,15
.88 ± . 12
.10 ± .12
.10 ± .12
.11 ± .12
.78 ± .11
.88 ± .13
.89 ± .12
.01 ± .04
Transcription factors and OSN differentiation
Transcription factors expressed in basal cells or immature OSNs should play critical roles in the shifts in gene expression programs that drive progression through the OSN cell lineage. Combining these new data with our previous study of the genomics of adult olfactory neurogenesis , we have detected a total of 203 transcription factor mRNAs that increased 5 – 7 days after bulbectomy when basal cell proliferation is peaking (Additional file 5). P(sp) and P(in) values predict that nearly all of these are expressed in cell types other than OSNs. Indeed, only four of them have their highest P(in) values in the immature OSN category. Given the expectation that adult neurogenesis recapitulates the primary neurogenesis that occurs when the embryonic olfactory epithelium first forms, we were not surprised to find increased abundance of several transcription factor mRNAs from genes whose germ line deletions cause defects in the development of OSNs: Neurog1, Emx2, Six1 and Runx1 [44, 47, 55, 68, 69].
Thousands of genes are expressed in the olfactory epithelium and hundreds of them are involved in transcriptional regulation. By identifying the transcriptional regulators that increased five days after bulbectomy and knowing whether these transcripts are present in immature OSNs or non-OSN cell types, we have predicted transcription factors involved in the shifts in gene expression programs that drive neural fate decisions and subsequent steps in OSN differentiation. The key role that basal cells play in driving the formation of OSNs is reflected in the evidence that 98% of the annotated transcriptional regulators that increased after bulbectomy are expressed primarily in non-OSN cell types. Many are already known to be expressed in basal cells, sometimes continuing into immature OSNs, so we hypothesize that others are likely to follow this same pattern of expression. The products of these genes probably help drive basal cells and immature OSNs along the process of OSN differentiation. The coexpression of these transcription factors across cell type and time help identify potential networks of transcriptional regulators.
A comprehensive catalog of the genes expressed by a cell type is a valuable tool, providing not only a long list of molecular functions performed by the products of each of the genes, but also revealing emergent properties formed by the functional relationships between the encoded proteins. By triggering apoptosis of mature OSNs and causing predictable changes in mRNA abundance, we confirmed the reliability of our previous identification of genes expressed in OSNs [31, 32] and were able to further parse genes expressed by immature OSNs into early and late categories – differences that correlate with functions associated with neurite outgrowth versus neuronal homeostasis, respectively. Cell lineages may look like distinct steps when viewed from the perspective of cell morphology or the expression of a few marker genes, but when viewed from the perspective of the entire transcriptome the progression of a cell through the OSN cell lineage appears more gradual. The genes expressed in any given cell type in the lineage initiate (and terminate) expression at widely different points in the lineage.
The molecular underpinnings of adult neurogenesis in the brain often appear to recapitulate events that drive embryonic neurogenesis [70–75]. In the case of the olfactory epithelium a comprehensive assessment of embryonic gene expression is lacking, so a direct comparison is not possible. However, we found extensive similarity with embryonic brain. Of the 1,723 mRNAs increased after bulbectomy, 54% of them were also significantly more abundant during the neurogenic phase of embryonic hippocampal development at age E10.5 – E11.5 compared to a 27% match during the gliogenic phase at age E16.5 . 100 of these shared genes are annotated as regulating transcription. They include Alx1, Ets1, Etv6, Eya2, Eya4, Foxc1, Foxn3, Hey1, Klf3, Meis1, Meis2, Msx1, Mybl1, Myc, Mycn, Neurod1, Neurog1, Otx1, Otx2, Pax3, Pax6, Rest, Runx1, Six1, Six2, Smad3, Smad5, Smad7, Stat1, Stat6, Tbl1x, Tead2, Tead3, and Trp63. The process of producing different types of neurons appears fundamentally similar across two widely different neural structures and ages. However, it would be premature to conclude that these shared genes have identical functions in embryonic brain development and adult olfactory neurogenesis because the integrative nature of transcriptional regulation would allow transcriptional regulators to contribute to distinctly different events in the development of different neural phenotypes.
C57Bl/6 mice were purchased from Harlan Laboratories, Inc. (Indianapolis, IN). Mice were housed in the Department of Laboratory Animal Resources at the University of Kentucky. All treatments and procedures used with mice were approved by the university’s institutional animal care and use committee and were consistent with National Institute of Health guidelines on animal use in research.
Male C57Bl/6 mice, age 6 weeks, were anesthetized with Ketamine/Xylazine (100 mg/kg; 10 mg/kg) i.p., the forehead was shaved, disinfectant applied to this site, and a lubricant (Artificial Tears, Butler Schein, Dublin, OH) was applied to the eyes. A midline incision was made between the eyes and a 1.5 mm hole above one olfactory bulb was drilled in the skull with a diamond-tipped burr. This bulb was removed by aspiration, the cavity filled with Gelfoam® (Pfizer, New York), and the skin was closed with 5-O Ethilon sutures (Ethicon, San Angelo, TX). To enhance recovery, 0.5 ml of warm saline was given subcutaneously. The mice were placed on a heating pad and allowed to recover, then given food and water ad libitum for 5 days.
RNA isolation and mRNA abundance measurement
Three mice previously subjected to unilateral bulbectomy were euthanized by inhalation of CO2, decapitated, and dissected to isolate olfactory epithelia ipsilateral and contralateral to the lesion. These were placed separately into ice-cold TriReagent (Molecular Research Center, Inc., Cincinnati, OH) for homogenization using a polytron. Total RNA was isolated according to the protocol supplied with the TriReagent and stored at -80°C. RNA quantity and quality was determined with a UV spectrophotometer and a model 2100 Bioanalyzer (Agilent Technologies, Palo Alto, CA).
Labeling of RNA samples, hybridization to Affymetrix GeneChip® Mouse Exon 1.0 Sense Target Arrays, and scanning of signals were done by the University of Kentucky Microarray Core Facility. Affymetrix Expression Console Software was used for generation of gene level robust multichip analysis values for transcript clusters. These were analyzed at the core annotation level to limit the data to probe sets that map to genes with annotated full-length open reading frames. These data were manipulated in Excel (Microsoft Corp., Redmond, WA). Data from the 10% of genes with the lowest average signal intensities were discarded. Statistical analyses via paired t-tests were done in SAS 9.2 (SAS Institute, Cary, NC). Setting α = 0.05 gave false discovery rates of 19.3% or less. Microarray data are available via the Gene Expression Omnibus (http://www.ncbi.nlm.nih.gov/geo/) under accession number GSE45931.
Functional bioinformatics to identify over-represented categories of biological processes, molecular functions and cytoplasmic compartments was done using DAVID (http://david.abcc.ncifcrf.gov/), with Benjamini corrected p-value criteria set at 0.05 . Statistically overrepresented categories supported by less than 10 genes (unless directly linked to other overrepresented functional categories) and extremely broad categories near the top of the Gene Ontology hierarchy were ignored.
Mouse genes and mRNAs are displayed according to the gene symbol conventions of Genbank, a repository of the National Center for Biotechnology Information (U.S.A). Gene accession numbers for the genes corresponding to all significantly affected mRNAs are provided (Additional file 1: Table S1).
In situ hybridization
As we have described previously, the in situ hybridization methods of Ishii and colleagues [82, 83] were followed meticulously, using 10–16 μm coronal cryosections of the nasal region of the head [27, 32, 43]. For each mRNA species, cDNA fragments of several hundred bp were amplified by PCR from olfactory epithelium cDNA and cloned into pBluescript (Additional file 6). The fragments chosen were selected to have less than 80% identity to any other mouse mRNA. Recombinant RNA probes labeled with digoxygenin were prepared for each mRNA species. Sense controls were invariably negative.
Wide-field images were obtained on a Nikon Diaphot 300 inverted microscope using a Spot 2e camera and Spot software version 4.0.6 through a 40x/0.75 numerical aperture Plan Fluor objective or a 4x/0.13 numerical aperture Plan objective. Images were processed in Adobe Photoshop by adjusting size and brightness. Images were combined and labeled in Deneba Canvas (version 8.0).
Cell type assignments
Examples of P (sp) and P (in) probabilities for olfactory epithelium cell type markers
Shared OSN P(sp)
Olfactory sensory neuron.
Funded by R01 DC007194 and R21 DC009624 to T.Mc., F32 DC011427 to P.M.H. and UL1TR000117 to A.J.S.
- Deng W, Aimone JB, Gage FH: New neurons and new memories: how does adult hippocampal neurogenesis affect learning and memory?. Nat Rev Neurosci. 2010, 11 (5): 339-350. 10.1038/nrn2822.PubMed CentralPubMedGoogle Scholar
- Livneh Y, Mizrahi A: Experience-dependent plasticity of mature adult-born neurons. Nat Neurosci. 2012, 15 (1): 26-28.Google Scholar
- Lledo PM, Alonso M, Grubb MS: Adult neurogenesis and functional plasticity in neuronal circuits. Nat Rev Neurosci. 2006, 7 (3): 179-193. 10.1038/nrn1867.PubMedGoogle Scholar
- Magavi SS, Mitchell BD, Szentirmai O, Carter BS, Macklis JD: Adult-born and preexisting olfactory granule neurons undergo distinct experience-dependent modifications of their olfactory responses in vivo. J Neurosci. 2005, 25 (46): 10729-10739. 10.1523/JNEUROSCI.2250-05.2005.PubMedGoogle Scholar
- Song J, Christian KM, Ming GL, Song H: Modification of hippocampal circuitry by adult neurogenesis. Dev Neurobiol. 2012, 72 (7): 1032-1043. 10.1002/dneu.22014.PubMed CentralPubMedGoogle Scholar
- Carr VM, Farbman AI: Ablation of the olfactory bulb up-regulates the rate of neurogenesis and induces precocious cell death in olfactory epithelium. Exp Neurol. 1992, 115 (1): 55-59. 10.1016/0014-4886(92)90221-B.PubMedGoogle Scholar
- Hinds JW, Hinds PL, McNelly NA: An autoradiographic study of the mouse olfactory epithelium: evidence for long-lived receptors. Anat Rec. 1984, 210 (2): 375-383. 10.1002/ar.1092100213.PubMedGoogle Scholar
- Bauer S, Rasika S, Han J, Mauduit C, Raccurt M, Morel G, Jourdan F, Benahmed M, Moyse E, Patterson PH: Leukemia inhibitory factor is a key signal for injury-induced neurogenesis in the adult mouse olfactory epithelium. J Neurosci. 2003, 23 (5): 1792-1803.PubMedGoogle Scholar
- Doyle KL, Karl T, Hort Y, Duffy L, Shine J, Herzog H: Y1 receptors are critical for the proliferation of adult mouse precursor cells in the olfactory neuroepithelium. J Neurochem. 2008, 105 (3): 641-652. 10.1111/j.1471-4159.2007.05188.x.PubMedGoogle Scholar
- Getchell TV, Shah DS, Partin JV, Subhedar NK, Getchell ML: Leukemia inhibitory factor mRNA expression is upregulated in macrophages and olfactory receptor neurons after target ablation. J Neurosci Res. 2002, 67 (2): 246-254. 10.1002/jnr.10090.PubMedGoogle Scholar
- Gokoffski KK, Wu HH, Beites CL, Kim J, Kim EJ, Matzuk MM, Johnson JE, Lander AD, Calof AL: Activin and GDF11 collaborate in feedback control of neuroepithelial stem cell proliferation and fate. Development. 2011, 138 (19): 4131-4142. 10.1242/dev.065870.PubMed CentralPubMedGoogle Scholar
- Hansel DE, Eipper BA, Ronnett GV: Neuropeptide Y functions as a neuroproliferative factor. Nature. 2001, 410 (6831): 940-944. 10.1038/35073601.PubMedGoogle Scholar
- Jia C, Hegg CC: NPY mediates ATP-induced neuroproliferation in adult mouse olfactory epithelium. Neurobiol Dis. 2010, 38 (3): 405-413. 10.1016/j.nbd.2010.02.013.PubMed CentralPubMedGoogle Scholar
- Lander AD, Gokoffski KK, Wan FY, Nie Q, Calof AL: Cell lineages and the logic of proliferative control. PLoS Biol. 2009, 7 (1): e15-10.1371/journal.pbio.1000015.PubMedGoogle Scholar
- Manglapus GL, Youngentob SL, Schwob JE: Expression patterns of basic helix-loop-helix transcription factors define subsets of olfactory progenitor cells. J Comp Neurol. 2004, 479 (2): 216-233. 10.1002/cne.20316.PubMedGoogle Scholar
- Wu HH, Ivkovic S, Murray RC, Jaramillo S, Lyons KM, Johnson JE, Calof AL: Autoregulation of neurogenesis by GDF11. Neuron. 2003, 37 (2): 197-207. 10.1016/S0896-6273(02)01172-8.PubMedGoogle Scholar
- Merkle FT, Alvarez-Buylla A: Neural stem cells in mammalian development. Curr Opin Cell Biol. 2006, 18 (6): 704-709. 10.1016/j.ceb.2006.09.008.PubMedGoogle Scholar
- Chen X, Fang H, Schwob JE: Multipotency of purified, transplanted globose basal cells in olfactory epithelium. J Comp Neurol. 2004, 469 (4): 457-474. 10.1002/cne.11031.PubMedGoogle Scholar
- Fletcher ML: Analytical processing of binary mixture information by olfactory bulb glomeruli. PLoS One. 2011, 6 (12): e29360-10.1371/journal.pone.0029360.PubMed CentralPubMedGoogle Scholar
- Huard JM, Youngentob SL, Goldstein BJ, Luskin MB, Schwob JE: Adult olfactory epithelium contains multipotent progenitors that give rise to neurons and non-neural cells. J Comp Neurol. 1998, 400 (4): 469-486. 10.1002/(SICI)1096-9861(19981102)400:4<469::AID-CNE3>3.0.CO;2-8.PubMedGoogle Scholar
- Iwai N, Zhou Z, Roop DR, Behringer RR: Horizontal basal cells are multipotent progenitors in normal and injured adult olfactory epithelium. Stem Cells. 2008, 26 (5): 1298-1306. 10.1634/stemcells.2007-0891.PubMed CentralPubMedGoogle Scholar
- Jang W, Lambropoulos J, Woo JK, Peluso CE, Schwob JE: Maintaining epitheliopoietic potency when culturing olfactory progenitors. Exp Neurol. 2008, 214 (1): 25-36. 10.1016/j.expneurol.2008.07.012.PubMed CentralPubMedGoogle Scholar
- Leung CT, Coulombe PA, Reed RR: Contribution of olfactory neural stem cells to tissue maintenance and regeneration. Nat Neurosci. 2007, 10 (6): 720-726. 10.1038/nn1882.PubMedGoogle Scholar
- Cuschieri A, Bannister LH: The development of the olfactory mucosa in the mouse: electron microscopy. J Anat. 1975, 119 (3): 471-498.PubMed CentralPubMedGoogle Scholar
- Marcucci F, Zou DJ, Firestein S: Sequential onset of presynaptic molecules during olfactory sensory neuron maturation. J Comp Neurol. 2009, 516 (3): 187-198. 10.1002/cne.22094.PubMed CentralPubMedGoogle Scholar
- Schwarzenbacher K, Fleischer J, Breer H: Formation and maturation of olfactory cilia monitored by odorant receptor-specific antibodies. Histochem Cell Biol. 2005, 123 (4–5): 419-428.PubMedGoogle Scholar
- Shetty RS, Bose SC, Nickell MD, McIntyre JC, Hardin DH, Harris AM, McClintock TS: Transcriptional changes during neuronal death and replacement in the olfactory epithelium. Mol Cell Neurosci. 2005, 30 (1): 90-107. 10.1016/j.mcn.2005.06.003.PubMedGoogle Scholar
- Krolewski RC, Jang W, Schwob JE: The generation of olfactory epithelial neurospheres in vitro predicts engraftment capacity following transplantation in vivo. Exp Neurol. 2011, 229 (2): 308-323. 10.1016/j.expneurol.2011.02.014.PubMed CentralPubMedGoogle Scholar
- Tietjen I, Rihel JM, Cao Y, Koentges G, Zakhary L, Dulac C: Single-cell transcriptional analysis of neuronal progenitors. Neuron. 2003, 38 (2): 161-175. 10.1016/S0896-6273(03)00229-0.PubMedGoogle Scholar
- Nurse P, Hayles J: The cell in an era of systems biology. Cell. 2011, 144 (6): 850-854. 10.1016/j.cell.2011.02.045.PubMedGoogle Scholar
- Nickell MD, Breheny P, Stromberg AJ, McClintock TS: Genomics of mature and immature olfactory sensory neurons. J Comp Neurol. 2012, 520: 2608-2609. 10.1002/cne.23052.PubMed CentralPubMedGoogle Scholar
- Sammeta N, Yu TT, Bose SC, McClintock TS: Mouse olfactory sensory neurons express 10,000 genes. J Comp Neurol. 2007, 502: 1138-1156. 10.1002/cne.21365.PubMedGoogle Scholar
- Calof AL: Intrinsic and extrinsic factors regulating vertebrate neurogenesis. Curr Opin Neurobiol. 1995, 5 (1): 19-27. 10.1016/0959-4388(95)80082-4.PubMedGoogle Scholar
- Gordon MK, Mumm JS, Davis RA, Holcomb JD, Calof AL: Dynamics of MASH1 expression in vitro and in vivo suggest a non-stem cell site of MASH1 action in the olfactory receptor neuron lineage. Mol Cell Neurosci. 1995, 6 (4): 363-379. 10.1006/mcne.1995.1028.PubMedGoogle Scholar
- Holcomb JD, Mumm JS, Calof AL: Apoptosis in the neuronal lineage of the mouse olfactory epithelium: regulation in vivo and in vitro. Dev Biol. 1995, 172 (1): 307-323. 10.1006/dbio.1995.0025.PubMedGoogle Scholar
- Suzuki Y, Schafer J, Farbman AI: Phagocytic cells in the rat olfactory epithelium after bulbectomy. Exp Neurol. 1995, 136 (2): 225-233. 10.1006/exnr.1995.1099.PubMedGoogle Scholar
- Asson-Batres MA, Smith WB: Localization of retinaldehyde dehydrogenases and retinoid binding proteins to sustentacular cells, glia, Bowman’s gland cells, and stroma: potential sites of retinoic acid synthesis in the postnatal rat olfactory organ. J Comp Neurol. 2006, 496 (2): 149-171. 10.1002/cne.20904.PubMed CentralPubMedGoogle Scholar
- Nunez-Parra A, Cortes-Campos C, Bacigalupo J, Garcia Mde L, Nualart F, Reyes JG: Expression and distribution of facilitative glucose (GLUTs) and monocarboxylate/H + (MCTs) transporters in rat olfactory epithelia. Chem Senses. 2011, 36 (9): 771-780. 10.1093/chemse/bjr052.PubMedGoogle Scholar
- Piras E, Franzen A, Fernandez EL, Bergstrom U, Raffalli-Mathieu F, Lang M, Brittebo EB: Cell-specific expression of CYP2A5 in the mouse respiratory tract: effects of olfactory toxicants. J Histochem Cytochem. 2003, 51 (11): 1545-1555. 10.1177/002215540305101114.PubMed CentralPubMedGoogle Scholar
- Sammeta N, Hardin DL, McClintock TS: Uncx regulates proliferation of neural progenitor cells and neuronal survival in the olfactory epithelium. Mol Cell Neurosci. 2010, 45 (4): 398-407. 10.1016/j.mcn.2010.07.013.PubMed CentralPubMedGoogle Scholar
- Sammeta N, McClintock TS: Chemical stress induces the unfolded protein response in olfactory sensory neurons. J Comp Neurol. 2010, 518 (10): 1825-1836. 10.1002/cne.22305.PubMed CentralPubMedGoogle Scholar
- Solbu TT, Holen T: Aquaporin pathways and mucin secretion of Bowman’s glands might protect the olfactory mucosa. Chem Senses. 2012, 37 (1): 35-46. 10.1093/chemse/bjr063.PubMedGoogle Scholar
- Yu TT, McIntyre JC, Bose SC, Hardin D, Owen MC, McClintock TS: Differentially expressed transcripts from phenotypically identified olfactory sensory neurons. J Comp Neurol. 2005, 483 (3): 251-262. 10.1002/cne.20429.PubMed CentralPubMedGoogle Scholar
- Cau E, Casarosa S, Guillemot F: Mash1 and Ngn1 control distinct steps of determination and differentiation in the olfactory sensory neuron lineage. Development. 2002, 129 (8): 1871-1880.PubMedGoogle Scholar
- Davis JA, Reed RR: Role of Olf-1 and Pax-6 transcription factors in neurodevelopment. J Neurosci. 1996, 16 (16): 5082-5094.PubMedGoogle Scholar
- Guo Z, Packard A, Krolewski RC, Harris MT, Manglapus GL, Schwob JE: Expression of pax6 and sox2 in adult olfactory epithelium. J Comp Neurol. 2010, 518 (21): 4395-4418. 10.1002/cne.22463.PubMed CentralPubMedGoogle Scholar
- Ikeda K, Kageyama R, Suzuki Y, Kawakami K: Six1 is indispensable for production of functional progenitor cells during olfactory epithelial development. Int J Dev Biol. 2010, 54 (10): 1453-1464. 10.1387/ijdb.093041ki.PubMedGoogle Scholar
- Sullivan SL, Bohm S, Ressler KJ, Horowitz LF, Buck LB: Target-independent pattern specification in the olfactory epithelium. Neuron. 1995, 15 (4): 779-789. 10.1016/0896-6273(95)90170-1.PubMedGoogle Scholar
- Kyrkanides S, Brouxhon SM, Tallents RH, Miller JN, Olschowka JA, O’Banion MK: Conditional expression of human beta-hexosaminidase in the neurons of Sandhoff disease rescues mice from neurodegeneration but not neuroinflammation. J Neuroinflammation. 2012, 9: 186-10.1186/1742-2094-9-186.PubMed CentralPubMedGoogle Scholar
- Kyrkanides S, Miller AW, Miller JN, Tallents RH, Brouxhon SM, Olschowka ME, O’Banion MK, Olschowka JA: Peripheral blood mononuclear cell infiltration and neuroinflammation in the HexB-/- mouse model of neurodegeneration. J Neuroimmunology. 2008, 203 (1): 50-57. 10.1016/j.jneuroim.2008.06.024.Google Scholar
- Menzel K, Hausmann M, Obermeier F, Schreiter K, Dunger N, Bataille F, Falk W, Scholmerich J, Herfarth H, Rogler G: Cathepsins B, L and D in inflammatory bowel disease macrophages and potential therapeutic effects of cathepsin inhibition in vivo. Clin Exp Immunol. 2006, 146 (1): 169-180. 10.1111/j.1365-2249.2006.03188.x.PubMed CentralPubMedGoogle Scholar
- Nepal RM, Mampe S, Shaffer B, Erickson AH, Bryant P: Cathepsin L maturation and activity is impaired in macrophages harboring M. avium and M. tuberculosis. Int Immunol. 2006, 18 (6): 931-939. 10.1093/intimm/dxl029.PubMedGoogle Scholar
- Blomster LV, Vukovic J, Hendrickx DA, Jung S, Harvey AR, Filgueira L, Ruitenberg MJ: CX(3)CR1 deficiency exacerbates neuronal loss and impairs early regenerative responses in the target-ablated olfactory epithelium. Mol Cell Neurosci. 2011, 48 (3): 236-245. 10.1016/j.mcn.2011.08.004.PubMedGoogle Scholar
- Fletcher RB, Prasol MS, Estrada J, Baudhuin A, Vranizan K, Choi YG, Ngai J: p63 regulates olfactory stem cell self-renewal and differentiation. Neuron. 2011, 72 (5): 748-759. 10.1016/j.neuron.2011.09.009.PubMed CentralPubMedGoogle Scholar
- McIntyre JC, Titlow WB, McClintock TS: Axon growth and guidance genes identify nascent, immature, and mature olfactory sensory neurons. J Neurosci Res. 2010, 88 (15): 3243-3256. 10.1002/jnr.22497.PubMedGoogle Scholar
- Chacon MR, Fazzari P: FAK: dynamic integration of guidance signals at the growth cone. Cell Adhes Migrat. 2011, 5 (1): 52-55. 10.4161/cam.5.1.13681.Google Scholar
- Chacon MR, Navarro AI, Cuesto G, del Pino I, Scott R, Morales M, Rico B: Focal adhesion kinase regulates actin nucleation and neuronal filopodia formation during axonal growth. Development. 2012, 139 (17): 3200-3210. 10.1242/dev.080564.PubMedGoogle Scholar
- Brackenbury WJ, Davis TH, Chen C, Slat EA, Detrow MJ, Dickendesher TL, Ranscht B, Isom LL: Voltage-gated Na + channel beta1 subunit-mediated neurite outgrowth requires Fyn kinase and contributes to postnatal CNS development in vivo. J Neurosci. 2008, 28 (12): 3246-3256. 10.1523/JNEUROSCI.5446-07.2008.PubMedGoogle Scholar
- Buchstaller A, Kunz S, Berger P, Kunz B, Ziegler U, Rader C, Sonderegger P: Cell adhesion molecules NgCAM and axonin-1 form heterodimers in the neuronal membrane and cooperate in neurite outgrowth promotion. J Cell Biol. 1996, 135 (6 Pt 1): 1593-1607.PubMedGoogle Scholar
- Erkman L, Yates PA, McLaughlin T, McEvilly RJ, Whisenhunt T, O’Connell SM, Krones AI, Kirby MA, Rapaport DH, Bermingham JR, et al: A POU domain transcription factor-dependent program regulates axon pathfinding in the vertebrate visual system. Neuron. 2000, 28 (3): 779-792. 10.1016/S0896-6273(00)00153-7.PubMedGoogle Scholar
- Guimond MO, Roberge C, Gallo-Payet N: Fyn is involved in angiotensin II type 2 receptor-induced neurite outgrowth, but not in p42/p44mapk in NG108-15 cells. Mol Cell Neurosci. 2010, 45 (3): 201-212. 10.1016/j.mcn.2010.06.011.PubMedGoogle Scholar
- Hammarlund M, Jorgensen EM, Bastiani MJ: Axons break in animals lacking beta-spectrin. J Cell Biol. 2007, 176 (3): 269-275. 10.1083/jcb.200611117.PubMed CentralPubMedGoogle Scholar
- Kerstein PC, Jacques-Fricke BT, Rengifo J, Mogen BJ, Williams JC, Gottlieb PA, Sachs F, Gomez TM: Mechanosensitive TRPC1 channels promote calpain proteolysis of talin to regulate spinal axon outgrowth. J Neurosci. 2013, 33 (1): 273-285. 10.1523/JNEUROSCI.2142-12.2013.PubMed CentralPubMedGoogle Scholar
- Lundquist EA, Herman RK, Shaw JE, Bargmann CI: UNC-115, a conserved protein with predicted LIM and actin-binding domains, mediates axon guidance in C. elegans. Neuron. 1998, 21 (2): 385-392. 10.1016/S0896-6273(00)80547-4.PubMedGoogle Scholar
- Sakane A, Honda K, Sasaki T: Rab13 regulates neurite outgrowth in PC12 cells through its effector protein, JRAB/MICAL-L2. Mol Cell Biol. 2010, 30 (4): 1077-1087. 10.1128/MCB.01067-09.PubMed CentralPubMedGoogle Scholar
- Treubert U, Brummendorf T: Functional cooperation of beta1-integrins and members of the Ig superfamily in neurite outgrowth induction. J Neurosci. 1998, 18 (5): 1795-1805.PubMedGoogle Scholar
- Varnum-Finney B, Reichardt LF: Vinculin-deficient PC12 cell lines extend unstable lamellipodia and filopodia and have a reduced rate of neurite outgrowth. J Cell Biol. 1994, 127 (4): 1071-1084. 10.1083/jcb.127.4.1071.PubMedGoogle Scholar
- Ikeda K, Ookawara S, Sato S, Ando Z, Kageyama R, Kawakami K: Six1 is essential for early neurogenesis in the development of olfactory epithelium. Dev Biol. 2007, 311 (1): 53-68. 10.1016/j.ydbio.2007.08.020.PubMedGoogle Scholar
- Theriault FM, Nuthall HN, Dong Z, Lo R, Barnabe-Heider F, Miller FD, Stifani S: Role for Runx1 in the proliferation and neuronal differentiation of selected progenitor cells in the mammalian nervous system. J Neurosci. 2005, 25 (8): 2050-2061. 10.1523/JNEUROSCI.5108-04.2005.PubMedGoogle Scholar
- Alvarez-Buylla A, Kohwi M, Nguyen TM, Merkle FT: The heterogeneity of adult neural stem cells and the emerging complexity of their niche. Cold Spring Harb Symp Quant Biol. 2008, 73: 357-365. 10.1101/sqb.2008.73.019.PubMedGoogle Scholar
- Jawerka M, Colak D, Dimou L, Spiller C, Lagger S, Montgomery RL, Olson EN, Wurst W, Gottlicher M, Gotz M: The specific role of histone deacetylase 2 in adult neurogenesis. Neuron Glia Biol. 2010, 6 (2): 93-107. 10.1017/S1740925X10000049.PubMedGoogle Scholar
- Ma DK, Marchetto MC, Guo JU, Ming GL, Gage FH, Song H: Epigenetic choreographers of neurogenesis in the adult mammalian brain. Nat Neurosci. 2010, 13 (11): 1338-1344. 10.1038/nn.2672.PubMed CentralPubMedGoogle Scholar
- Sohur US, Arlotta P, Macklis JD: Developmental Controls are Re-Expressed during Induction of Neurogenesis in the Neocortex of Young Adult Mice. Front Neurosci. 2012, 6: 12-PubMed CentralPubMedGoogle Scholar
- Steele AD, Emsley JG, Ozdinler PH, Lindquist S, Macklis JD: Prion protein (PrPc) positively regulates neural precursor proliferation during developmental and adult mammalian neurogenesis. Proc Natl Acad Sci U S A. 2006, 103 (9): 3416-3421. 10.1073/pnas.0511290103.PubMed CentralPubMedGoogle Scholar
- Suh H, Deng W, Gage FH: Signaling in adult neurogenesis. Annu Rev Cell Dev Biol. 2009, 25: 253-275. 10.1146/annurev.cellbio.042308.113256.PubMedGoogle Scholar
- Shimogori T, Lee DA, Miranda-Angulo A, Yang Y, Wang H, Jiang L, Yoshida AC, Kataoka A, Mashiko H, Avetisyan M, et al: A genomic atlas of mouse hypothalamic development. Nat Neurosci. 2010, 13 (6): 767-775. 10.1038/nn.2545.PubMed CentralPubMedGoogle Scholar
- Boutin C, Hardt O, de Chevigny A, Core N, Goebbels S, Seidenfaden R, Bosio A, Cremer H: NeuroD1 induces terminal neuronal differentiation in olfactory neurogenesis. Proc Natl Acad Sci U S A. 2010, 107 (3): 1201-1206. 10.1073/pnas.0909015107.PubMed CentralPubMedGoogle Scholar
- Hsieh J: Orchestrating transcriptional control of adult neurogenesis. Genes Dev. 2012, 26 (10): 1010-1021. 10.1101/gad.187336.112.PubMed CentralPubMedGoogle Scholar
- Karsten SL, Kudo LC, Jackson R, Sabatti C, Kornblum HI, Geschwind DH: Global analysis of gene expression in neural progenitors reveals specific cell-cycle, signaling, and metabolic networks. Dev Biol. 2003, 261 (1): 165-182. 10.1016/S0012-1606(03)00274-4.PubMedGoogle Scholar
- Petrik D, Jiang Y, Birnbaum SG, Powell CM, Kim MS, Hsieh J, Eisch AJ: Functional and mechanistic exploration of an adult neurogenesis-promoting small molecule. FASEB J. 2012, 26 (8): 3148-3162. 10.1096/fj.11-201426.PubMed CentralPubMedGoogle Scholar
- Huang DW, Sherman BT, Lempicki RA: Systematic and integrative analysis of large gene lists using DAVID bioinformatics resources. Nat Protoc. 2009, 4 (1): 44-57.Google Scholar
- Ishii T, Hirota J, Mombaerts P: Combinatorial coexpression of neural and immune multigene families in mouse vomeronasal sensory neurons. Curr Biol. 2003, 13 (5): 394-400. 10.1016/S0960-9822(03)00092-7.PubMedGoogle Scholar
- Ishii T, Omura M, Mombaerts P: Protocols for two- and three-color fluorescent RNA in situ hybridization of the main and accessory olfactory epithelia in mouse. J Neurocytol. 2004, 33 (6): 657-669. 10.1007/s11068-005-3334-y.PubMedGoogle Scholar
This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.