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Gene K51 probe isolated previously from the rat genomic library has been used to study the expression of its human counterpart by in situ hybridization and Northern blot analysis. A polyA-containing transcript of human gene K51 of 3 kb size has been detected in embryonic skin. The gene is also expressed in the epidermis of newborn humans and adults, but not in the adjacent mesenchymal tissues. Immunostaining with keratin antisera revealed predominantly earlier stage expression of K51 than cytokeratin markers. Sebaceous and sweat glands also contain cells expressing K51 gene. K51 expression was found in the cells of eight individual basal cell carcinomas tested, with the level of expression lower than in keratinocytes from normal human epidermis. We propose that K51 gene expression could serve as a convenient marker for the study of the process of skin keratinocyte development and the changes in this process associated with skin cancers and dysplasia.

A new method for studding gene expression--the histoblotting was used for the detection of k51 gene expression in rodent tissues. We have demonstrated several advantages of this method over in situ hybridization for the study of gene expression in epitelial tissues in particular. The transcription of the new gene k51 was detected in the upper layers of mouse and rat skin during epidermis development before and after rat birth. These data were confirmed by Northern hybridization analysis. We found that the expression of k51 occurs mainly in flat multilayer epithelium and is not simply connected with the degree of days of rat embryo development; it is high in newborn skin and lowers during hair growth. The expression of k51 can serve as a marker of a certain stage of adult skin development.

The nucleotide sequence of 686 bp from the cloned human genome locus gp5 has been determined. Analysis of this sequence has revealed a statistically significant homology with both the viral and murine mos genes. The region of mos homology contains two adjacent homologous domains, whereas their counterparts in viral mos gene are separated by 471 bp. The position of mos homologous region in the close vicinity to LTR of endogenous human viral-like repeat is in accordance with the hypothesis of retroviral involvement in the process of mos gene amplification.

AO region (884 b.p.) of ORAgp5 locus has been sequenced and proved to contain mos-related regions, as well as fragments structurally similar to proretroviral elements and Alu repeats. The data obtained are in accordance with earlier hypotheses on retroviral involvement in mos gene family generation and the role of Alu repeat insertion in the inactivation of mos-related genes. Molecular hybridisation studies showed the structural conservation of the segment in ORAgp5 locus comprising the AO region among higher primates. These data indicate that AO region of ORAgp5 was formed not later than 65-70 MYR ago and that the present structure of this region was kept during last 50 MYR.