Barhl1 Regulatory Sequences Required for Cell-Specific Gene Expression and Autoregulation in the Inner Ear and Central Nervous System

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Abstract
The development of the nervous system requires the concerted actions of multiple transcription factors, yet the molecular events leading to their expression remain poorly understood. Barhl1, a mammalian homeodomain transcription factor of the BarH class, is expressed by developing inner ear hair cells, cerebellar granule cells, precerebellar neurons, and collicular neurons. Targeted gene inactivation has demonstrated a crucial role for Barhl1 in the survival and/or migration of these sensory cells and neurons. Here we report the regulatory sequences of Barhl1 necessary for directing its proper spatiotemporal expression pattern in the inner ear and central nervous system (CNS). Using a transgenic approach, we have found that high-level and cell-specific expression of Barhl1 within the inner ear and CNS depends on both its 5′ promoter and 3′ enhancer sequences. Further transcriptional, binding, and mutational analyses of the 5′ promoter have identified two homeoprotein binding motifs that can be occupied and activated by Barhl1. Moreover, proper Barhl1 expression in inner ear hair cells and cerebellar and precerebellar neurons requires the presence of Atoh1. Together, these data delineate useful Barhl1 regulatory sequences that direct strong and specific gene expression to inner ear hair cells and CNS sensory neurons, establish a role for autoregulation in the maintenance of Barhl1 expression, and identify Atoh1 as a key upstream regulator.