Dynamic Expression of Sox2, Gata3, and Prox1 during Primary Auditory Neuron Development in the Mammalian Cochlea

Abstract

Primary auditory neurons (PANs) connect cochlear sensory hair cells in the mammalian inner ear to cochlear nucleus neurons in the brainstem. PANs develop from neuroblasts delaminated from the proneurosensory domain of the otocyst and keep maturing until the onset of hearing after birth. There are two types of PANs: type I, which innervate the inner hair cells (IHCs), and type II, which innervate the outer hair cells (OHCs). Glial cells surrounding these neurons originate from neural crest cells and migrate to the spiral ganglion. Several transcription factors are known to regulate the development and differentiation of PANs. Here we systematically examined the spatiotemporal expression of five transcription factors: Sox2, Sox10, Gata3, Mafb, and Prox1 from early delamination at embryonic day (E) 10.5 to adult. We found that Sox2 and Sox10 were initially expressed in the proneurosensory cells in the otocyst (E10.5). By E12.75 both Sox2 and Sox10 were downregulated in the developing PANs; however, Sox2 expression transiently increased in the neurons around birth. Furthermore, both Sox2 and Sox10 continued to be expressed in spiral ganglion glial cells. We also show that Gata3 and Prox1 were first expressed in all developing neurons, followed by a decrease in expression of Gata3 and Mafb in type I PANs and Prox1 in type II PANs as they matured. Moreover, we describe two subtypes of type II neurons based on Peripherin expression. These results suggest that Sox2, Gata3 and Prox1 play a role during neurogenesis as well as maturation of the PANs.

Hair Cell Mechanotransduction Regulates Spontaneous Activity and Spiral Ganglion Subtype Specification in the Auditory System

“…Previous studies had identified several genes that are expressed at different levels in mature type I and type II SGNs (Barclay et al, 2011; Hafidi, 1998; Lallemend et al, 2007; Mou et al, 1998; Nishimura et al, 2017; Vyas et al, 2017), and we have identified here many more. The functional consequences of these differences need to be explored, but one gene, Ngfr , provides an interesting example.…”

“…Mature type I SGNs can be distinguished from type II SGNs by high levels of Tubb3 expression while mature type II SGNs strongly express Prph (Barclay et al, 2011; Hafidi, 1998; Lallemend et al, 2007; Mou et al, 1998; Nishimura et al, 2017; Vyas et al, 2017). Unbiased clustering revealed groups of neurons that were separable on a t-Distributed Stochastic Neighbor Embedding (t-SNE) plot of all cells (Fig.…”

Opposing expression gradients of calcitonin‐related polypeptide alpha (Calca/Cgrpα) and tyrosine hydroxylase (Th) in type II afferent neurons of the mouse cochlea

“…The identity of peripherin − , GFP + SGNs is uncertain. Recent work suggested that peripherin immunolabels only a subset of type II SGNs (Maison, Liberman, & Liberman, ; Nishimura, Noda, & Dabdoub, ; Vyas et al, ). Therefore, some of the peripherin − , GFP + SGNs are most likely type II afferent neurons.…”

“…However, due to the graded expression of Th and Cgrp α in type II SGNs, genetic tools based on them would affect only a subset of type II SGNs. A recent work suggested Gata3, a transcription factor that is expressed in all SGNs during development, could be a marker for type II SGNs in the adult cochlea (Nishimura et al, ). However, it remains to be determined whether Gata3 labels the entire type II neuron population.…”

“…Mounting evidence suggests that the expression of the well‐established type II marker peripherin is also heterogeneous. Peripherin expression appears to be downregulated during development in a subset of Gata3 + type II SGNs (Nishimura et al, ). Previous work has shown that only a subset of TH‐positive type II afferent neurons were peripherin‐positive (Vyas et al, ).…”