Pmg-1 and Pmg-2 constitute a novel family of KAP genes differentially expressed during skin and mammary gland development

The epidermis, by invagination of the undifferentiated ectodermal cells, gives rise to several distinct structures including hair, sebaceous, eccrine sweat and mammary glands. We have recently isolated a novel gene, pmg-1, expressed in the pubertal mouse mammary gland. While investigating its genomic structure, we identified a related gene in close proximity, which we have termed pmg-2. pmg-1 and pmg-2 are intron-less, are transcribed in opposite directions and are separated by a potential promoter region of 2.8 kb containing putative binding motifs for the developmental transcription factors Lef-1, Sox5 and D-STAT. pmg-1 and pmg-2 encode small proteins rich in G, S, F, Y and Q and contain characteristic repeats reminiscent of the keratin-associated proteins (KAPs). Both genes are expressed in growing hair follicles in skin as well as in sebaceous and eccrine sweat glands. Interestingly, expression is also detected in the mammary epithelium where it is limited to the onset of the pubertal growth phase and is independent of ovarian hormones. Their broad, developmentally controlled expression pattern, together with their unique amino acid composition, demonstrate that pmg-1 and pmg-2 constitute a novel KAP gene family participating in the differentiation of all epithelial cells forming the epidermal appendages.