STAGE-SPECIFIC EXPRESSION OF B-CELL TRANSLOCATION GENE-1 IN RAT TESTIS

B Cell translocation gene 1 (BTG1) is a member of a new family of puta tive antiproliferative factors. They are characterized by their rapid, but transient, expression in response to factors that induce growth a rrest and subsequent differentiation. In immature rat Sertoli cell cul tures, BTG1 messenger RNA (mRNA) increases rapidly after FSH stimulati on. We obtained the full-length coding sequence of rat BTG1 complement ary DNA for Northern blot analysis and in situ hybridization to determ ine the temporal expression and spatial distribution of BTG1 mRNA in t he rat testis. Northern analysis of isolated adult germ cells and in s itu hybridization analysis of adult seminiferous epithelium demonstrat ed that BTG1 expression was first evident in late primary spermatocyte s. The level of BTG1 mRNA was also elevated in secondary spermatocytes , but was maximal in postmeiotic round spermatids where levels were 5 times the background. BTG1 mRNA was not detectable in cells in the M p hase of meiosis or spermatids undergoing nuclear elongation and conden sation. The oscillation of BTG1 expression from the late prophase of t he first meiotic division through spermatozoa release suggests BTG1 in volvement in spermatogenesis. High levels of BTG1 mRNA at entry into t erminal spermatid differentiation suggests a role consistent with that proposed for the BTG1 family of antiproliferative factors.