A retroviral vector was constructed containing a cDNA for mouse tyrosinase under control of a modified (with intron removed) chick feather keratin promoter. Cultured chick embryo keratinocytes infected with this vector showed bright fluorescent labeling with an antibody (T1) specific to mouse tyrosinase, but did not produce visible pigment. Cultured chick embryo fibroblasts infected with the vector also showed positive fluorescent labeling with the T1 antibody, but the labeling appeared less bright than that seen in infected keratinocytes. Cultured albino (ca/ca) melanocytes infected with the vector developed dark, discrete pigment granules. Mock infected keratinocytes, fibroblasts, and melanocytes had little or no background immunofluorescence when labeled with T1. Chick hepatocytes infected with the keratin vector could not be distinguished from mock infected hepatocytes cultures, even by T1 labeling. These results suggest that the modified keratin promoter imparts partial tissue specificity to genes under its control. The tyrosinase expression seen in keratinocytes, and the pigment production seen in albino melanocytes infected with the keratin vector may make it a vector useful for tagging gene transfer in albino chickens.

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