Distribution of mRNA for the exocytotic calcium sensor, synaptotagmin 9, in mouse brain

The principal Ca^{2 +} sensors that control fusion of synaptic vesicles are synaptotagmins 1, 2 and 9. Synaptotagmin 9 (Syt9) has received the least attention. We applied RNAscope techniques to coronal sections of adult mouse brain to study the distribution of Syt9 mRNA. Our results showed weak Syt9 mRNA expression in many brain regions but elevated levels in a handful. Regions of strong expression were largely in limbic and sensory areas and included both excitatory and inhibitory neurons. Strongest expression in the brain was in the medial habenula. The interpeduncular nucleus that provides input to medial habenula and amygdala that receives medial habenula output also showed elevated Syt9 mRNA. Sensory regions with strong Syt9 mRNA expression included mitral and periglomerular cells in the olfactory bulb, thalamus, and sensory layers of the superior colliculus. A few putative layer 5 pyramidal cells in somatosensory, auditory and visual cortex were also strongly labeled. Neurons in motor regions including cortex did not generally show elevated expression with the exception of strong labeling of granular and molecular (but not Purkinje) cells in the cerebellum. Hippocampal neurons also showed only weak labeling.