Expression of the microphthalmia-associated basic helix-loop-helix leucinezipper transcription factor mi in avian neuroretina cells induces a pigmented phenotype

The microphthalmia gene (mi) appears to be required for pigment cell develo pment, based on its mutation in mi mice. The mi gene encodes a basic helix- loop-helix leucine zipper transcription factor (Mi) with tissue-restricted expression. To investigate the role of mi in cell proliferation and pigment ation, we transfected neuroretina (NR) cells with a recombinant virus expre ssing the murine mi cDNA, The virus induced the proliferation of chicken NR cells in response to fibroblast growth factor 2, which enabled them to for m colonies in soft agar, In contrast to control cultures, transfected chick en NR cells or quail NR cells became rapidly pigmented and strongly express ed the QNR-71 mRNA encoding a melanosomal protein. These results demonstrat e that Mi not only acts as pigmentation inducer but is also able to modulat e the response of cells to growth factors.