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The development, maturation, and viability of inner ear neurosensory cells depend on the spatiotemporal expression of multiple transcriptional factors. Based on three mouse models [Tg(Pax2-Isl1)], Sox2CKO, and Neurod1CKO, this thesis investigates the function of three transcriptional factors ISL1, SOX2 and NEUROD1 in the neurosensory development of the inner ear. The mouse mutant [Tg(Pax2-Isl1)] carries transgenic sequence containing Isl1 gene under Pax2 regulatory sequence in its genome. ISL1 ectopic expression driven by Pax2 regulatory sequence resulted in the enlarged cochleovestibular ganglion and accelerated neurite extension in [Tg(Pax2- Isl1)] embryos. In adult mutants, we detected an early onset of age-related hearing loss correlating with the worsening function of outer hair cells. These changes were associated with the loss of medial olivocochlear efferent neuron fibers innervating outer hair cells. For the first time, we showed that the age-related hearing loss (presbyacusis) might be caused by efferent innervation defects besides hair cell loss and spiral ganglion degeneration. In addition to presbyacusis, [Tg(Pax2-Isl1)] mice suffered from hyperactivity that was diminished by the administration of picrotoxin - channel blocker for GABA receptor chloride channels. This indicates that...