Expression of gene coding for a melanosomal matrix protein transcriptionally regulated in the transdifferentiation of chick embryo pigmented epithelial cells.

Chicken 115-kDa melanosomal matrix protein (MMP115) was purified from cultured pigmented epithelial cells (PECs), and mouse antiserum was raised to isolate cDNA clones. lambda gt11 expression library made from poly(A)+ RNA of the homogeneous population of PECs was screened with the antiserum. Nine positive clones were obtained from 5 X 10(5) independent phages, and inserts of them shared a common nucleotide sequence. The beta-galactosidase fusion protein from the longest insert (MM-2, 1.0 kb long) was recognized by the anti-MMP115 antiserum in immunoblotting, and the antibody, which was affinity-selected by the fusion protein, specifically reacted with the 115-kDa protein in PEC extracts. The RNA blot analysis with the MM-2 insert as a probe revealed that a transcript of 2.6 kb was expressed by the PEC in a tissue-specific manner. mRNA expressions in the process of in vitro transdifferentiation from PECs to lens cells were analyzed using the MM-2 insert. The transcripts were detected in neither transdifferentiating, transdifferentiated lens cells nor bipotent dedifferentiated PECs, although the 2.6 kb transcript was vigorously synthesized by redifferentiating into PECs.