MiTF (Microphthalmia associated transcription factor) is a basic helix loop helix leucine zipper (b HLH ZIP) transcription factor implicated in pigmentation, mast cells and bone development. Mutations in MiTF cause auditory pigmentary syndromes, such as Waardenburg syndrome type II, type IIa and Tietz syndrome in humans. 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. MiTF plays a critical role in the differentiation of various cell types as neural crest-derived melanocytes, mast cells, osteoclasts and optic cup-derived retinal pigment epithelium.