Mutant mice: a useful tool for studying the development of mast cells

We have used various mouse mutants for studying the development of mast cells. The bone marrow origin of mast cells was shown by using giant granules of beige mice as a marker. Mast cell-deficient W/W(v) and Sl/Sl(d) mice are useful for investigation of the developmental processes. The mi locus encodes a member of the basic helix-loop-helix-leucine zipper protein family of transcription factors (MITF), and mast cells of mi/mi mice showed phenotypic abnormalities. Mast cells of mi/mi mice synthesized the mutant mi-MITF in normal amounts, and mi-MITF showed an inhibitory effect on the transcription of various mast cell-specific genes. On the other hand, mice of tg/tg possess the transgene insertional mutation in the 5' flanking region of the mi gene and do not express any MITFs. Genes whose transcription was suppressed were more numerous in mast cells of mi/mi mice than in those of tg/tg mice. The comparison between phenotypes of mi/mi mast cells and those of tg/tg mast cells gave some insights into the regulation of mast cell phenotypes by transcription factors.