Fig. 1

Forebrain specific ELKS cKO by breeding with CaMKII-Cre mouse. a Forebrain size in ELKS cKO (ELKS flox; Cre⁺) mice was smaller than in control (ELKS flox; Cre⁻) mice, while the weight of the cerebellum did not differ significantly. Mean ± SD, n = 3 for each sample, **P < 0.01 (Student’s t-test). b Forebrain and cerebellum (Cb) brain homogenates were analyzed by western blot using the indicated antibodies. Cre recombinase was expressed specifically in the forebrain where ELKS expression was depleted. No truncated ELKS band was detected. c-d Exploration of novel environment was traced d and the distance traveled was measured between 0 and 10, 10–20, and 20–30 min in control (Cre-) and ELKS cKO (Cre+) mice. The distance travelled gradually decreased from 0 to 10 min to 20–30 min, which was not different between control and ELKS cKO mice. **P < 0.01 (one-way ANOVA, post-hoc Tukey’s test). e-g Immunohistochemistry using the indicated antibodies revealed that Cre expression in the hippocampal dentate gyrus DG granule cells and ELKS expression in the CA1 and CA3 regions was depleted. Ori, oriens; Py, pyramidale; Rad, radiatum; Luci, lucidum. h ELKS was not depleted in the cerebellum where Cre was not expressed. i-j Electron microscopy of the hippocampal CA1 stratum radiatum revealed numerous excitatory synapses on the pyramidal cell spines (asterisks). The synapse indicated by the # mark was excluded because mitochondria were present at the postsynaptic site. Presynaptic terminal area and AZ length were measured with high magnification as demonstrated by representative images j