SPECIFIC EXPRESSION IN ADULT MICE AND POSTIMPLANTATION EMBRYOS OF A TRANSGENE CARRYING THE HISTONE H1(0) REGULATORY REGION

Histone H1(0), a variant of the H1 group, has been found associated with the repressed state of chromatin and its content is increased in terminally differentiated cells. We have cloned a mouse H1(0) histone gene and introduced the promoter region, ligated to the beta-galactosidase reporter gene, into transgenic mice. By histochemistry we demonstrated a strong expression of the transgene in adult kidney, testis and brain. Intestine, uterus and ovarium were also positive. This expression followed the same pattern as that of the endogenous H1(0) gene, as demonstrated by in situ hybridization with a non-coding fragment of the mRNA, by Northern analysis, and by immunofluorescence with specific antibodies. In post-implantation embryos, the expression was very low up to day ten p.c. At this time, most of the X-Gal staining was found in the brain, retina and some of the large blood vessels. Hence, expression of the transgene as well as of the endogenous H1(0) gene is not exclusively linked to a differentiated phenotype or to a reduced cell proliferation capacity.