Homeostasis of retinal pigment epithelium essential for survival of photorecptor cells

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Microphthalmia-associated transcription factor (Mitf) is required for differentiation of retinal pigment epithelium. The mouse homozygous for the black-eyed white (Mitf-bw) allele is characterized by white-coat color and deafness with black eye, due to the loss of melanoblasts. The Mitf-bw allele carries an insertion of L1 element in the Mitf gene, causing the deficiency of the melanocyte-specific Mitf-M. Moreover, alternatively spliced Mitf-M mRNA species are expressed in developing melanoblasts: Mitf-M mRNA lacking exon 3, exon 4, or both exons 3 and 4. These aberrant mRNAs are also expressed in the bw mouse brain. Importantly, Mitf-M mRNA is expressed in the mouse and human brain. Moreover, the bw mice show the altered volitional motor activity under a stressful environment.We identified the MITF isoform expressed in the human retinal pigment epithelium. Moreover, the beta-catenin is responsible for maintaining the expression of MITF in the retinal pigment epithelium.