ISL1 and POU4F1 directly interact to regulate the differentiation and survival of inner ear sensory neurons

Abstract

The inner ear sensory neurons play a pivotal role in auditory processing and balance control. Though significant progresses have been made, the underlying mechanisms controlling the differentiation and survival of the inner ear sensory neurons remain largely unknown. During development, ISL1 and POU4F transcription factors are co-expressed and are required for terminal differentiation, pathfinding, axon outgrowth and survival of neurons in the central and peripheral nervous systems. However, little is understood about their functional relationship and regulatory mechanism in neural development. Here, we have knocked outIsl1orPou4f1or both in mice of both sexes. In the absence ofIsl1, the differentiation of cochleovestibular ganglion (CVG) neurons is disturbed and thatIsl1-deficient CVG neurons display defects in migration and axon pathfinding. Compound deletion ofIsl1andPou4f1causes a delay in CVG differentiation and results in a more severe CVG defect with a loss of nearly all of spiral ganglion neurons (SGNs). Moreover, ISL1 and POU4F1 interact directly in developing CVG neurons and act cooperatively as well as independently in regulating the expression of unique sets of CVG-specific genes crucial for CVG development and survival by binding to thecis-regulatory elements including the promoters ofFgf10,Pou4f2andEpha5and enhancers ofEya1andNtng2. These findings demonstrate thatIsl1andPou4f1are indispensable for CVG development and maintenance by acting epistatically to regulate genes essential for CVG development.Significance StatementInner ear neurons play critical roles in hearing and balance by transmitting auditory information in the form of electric signals from sensory hair cells to the brain. To study the genetic basis underlying their development, we identified the direct interaction and roles of transcription factors ISL1 and POU4F1 in regulating the development and maintenance of cochleovestibular ganglion (CVG) neurons. Moreover, our expression analysis uncovered thatIsl1andPou4f1are involved in the feedback regulation of CVG pioneer genes and control CVG differentiation genes. Furthermore, we identified and validated the function of thecis-regulatory elements bound by ISL1 and POU4F1 in vivo. Together, these findings provide insights into the gene regulatory network controlling the development of the inner ear neurons.