Figure 3. Hevin is important for both the formation and long-term maintenance of thalamocortical synapses.
(A) Timeline of cortical synaptic development in mice. Axonal projections from the LGN reach their target areas in V1 shortly after birth. Around the time of eye opening, there is a period of intense synapse formation that gradually gives way to processes involved in synapse maturation and refinement, including synapse elimination. Multiple critical periods for different forms of plasticity in the visual system occur during this period of synapse formation and refinement. (B) At P7, the beginning of the synaptogenic period, co-localization of VGlut1 (green) and PSD95 (magenta) revealed a trend towards an increase in intracortical synapses (co-localized puncta; arrows) in the synaptic zone of hevin KO V1 (n = 3 z-stacks per animal, 3 animals per genotype; p = 0.082, nested ANOVA). (C) VGlut2 (red) and PSD95 (cyan) co-localization (arrows), representing thalamocortical synapses, was significantly decreased in P7 hevin KO compared to P7 WT (n = 3 z-stacks per animal, 3 animals per genotype; p < 0.05, nested ANOVA). Scale bars, 5 µm. (D) In the mature brain (12-weeks-old), hevin KO mice no longer have a discrepancy in VGlut1/PSD95 synaptic puncta when compared to WT (n = 3 z-stacks per animal, 5 animals per genotype; p > 0.05, Student's t test). (E) Deficient VGlut2/PSD95 synapse formation is still present in the mature hevin KO brains (n = 3 z-stacks per animal, 5 animals per genotype; p < 0.01, Student's t test). Scale bars, 5 µm.