Characterization of a new melanocyte‐specific gene (QNR‐71) expressed in v‐myc‐transformed quail neuroretina.

Quail neuroretina cells (QNR) infected with the v‐myc‐expressing retrovirus MC29 become pigmented after several passages in vitro. After differential screening of a cDNA library constructed from these cells, we have isolated a cDNA clone (QNR‐71) which identifies an RNA expressed only in the pigmented layer of the retina and in the epidermis. This gene can also be induced in other cell types transformed by MC29, suggesting that QNR‐71 may be regulated by the v‐myc protein. Sequence analysis showed that the QNR‐71 cDNA exhibits stretches of homologies with melanosomal proteins encoding genes. From bacterially expressed QNR‐71 peptides we obtained rabbit antisera able to specifically recognize two proteins of 95 and 100 kDa in pigmented retinal cells, but not in the neuroretina. To study the regulation of QNR‐71, we used promoter fragments linked to the CAT reporter gene, in transient co‐expression assay. We observed an increase in CAT expression with a c‐MYC and microphtalmia (mi) expression vectors. Both MYC and mi activate the QNR‐71 promoter through direct binding to a CATGTG site present in the promoter fragment.