Smad4 signaling establishes the somatosensory map of basal vomeronasal sensory neurons

Abstract

The accessory olfactory system is a unique model that can give insights on how the neurons can establish and maintain their identity, and connectivity. The vomeronasal organ (VNO) contains two distinct populations of vomeronasal sensory neurons (VSNs) each with specific innervation patterns to the accessory olfactory bulb (AOB). Though morphogenic signals are critical in defining various neuronal populations, the morphogenic signaling profiles that influence each VSN population remains unknown. Here, we found a pronounced BMP signaling gradient within the basal VSNs. By generating Smad4 conditional mutants, we disrupted canonical TGF-{beta}/BMP signaling in maturing basal VSNs and in all mature VSNs. We show that Smad4 loss-of-function in immature basal neurons leads to a progressive loss of basal VSNs, reduced activation of the remnant basal VSNs, and aberrant glomeruli formation in posterior AOB. However, Smad4 ablation in all mature VSNs does not affect neuronal activity nor survival but causes aberrant glomeruli formation only in the posterior AOB. Our study reveals that Smad4 signaling plays a critical role in mediating development, function, and circuit formation of basal VSNs.