Lmx1a is essential for marginal cell differentiation and stria vascularis formation

The transcription factor <i>Lmx1a</i> is widely expressed during early inner ear development, and mice lacking <i>Lmx1a</i> expression exhibit fusion of cochlear and vestibular hair cells and fail to form the ductus reuniens and the endolymphatic sac. <i>Lmx1a dreher</i> (<i>Lmx1a</i> ^<i>dr/dr</i> ), a recessive null mutation, results in non-functional <i>Lmx1a</i> expression, which expands from the outer sulcus to the stria vascularis and Reissner's membrane. In the absence of <i>Lmx1a</i>, we observe a lack of proteins specific to the stria vascularis, such as BSND and KCNQ1 in marginal cells and CD44 in intermediate cells. Further analysis of the superficial epithelial cell layer at the expected stria vascularis location shows that the future intermediate cells migrate during embryonic development but subsequently disappear. Using antibodies against pendrin (<i>Slc26a4</i>) in <i>Lmx1a</i> knockout (KO) mice, we observe an expansion of pendrin expression across the stria vascularis and Reissner's membrane. Moreover, in the absence of <i>Lmx1a</i> expression, no endocochlear potential is observed. These findings highlight the critical role of <i>Lmx1a</i> in inner ear development, particularly in the differentiation of cochlear and vestibular structures, the recruitment of pigment cells, and the expression of proteins essential for hearing and balance.