Microphthalmia Transcription Factor (MiTF)

There are two known isoforms of MiTF differing by 66 amino acids at the NH2 terminus. Shorter forms are expressed in melanocytes and run as two bands at 52kDa and 56kDa, while the longer Mi form runs as a cluster of bands at 60-70kDa in osteoclasts and in B16 melonoma cells (but not other melanoma cell lines), as well as mast cells and heart. It reacts with both melanocytic as well as the non- melanocytic isoforms of MiTF. This Ab does not cross-react with other b-HLH-ZIP factors by DNA mobility shift assay. Mi is a basic helix-loop-helix-leucin zipper (b-HLH-ZIP) transtripotion factor implicated in pigmentation, mast cells and bone development. The mutation of MiTF causes Waardenburg Syndrome type II in humans. In mice, a profound loss of pigmented cells in the skin eye and inner ear results, as well as osteopetrosis and defects in natural killer and mast cells. These melanocyte isoforms have been shown by two dimensional tryptic mapping to differ in c-Kit-induced phosphorylation. Osteopetrotic rat strain harbors a large genomic deletion encompassing the 3 prime end of TF including most of the b-HLH-ZIP region. Osteoclasts from these animals lack MiTF protein in contrast to wild-type rat, mouse, and human osteoclasts.