EXPRESSION OF TYPE-II ACTIVIN RECEPTOR GENES IN THE MALE AND FEMALE REPRODUCTIVE TISSUES OF THE RAT

In addition to the feedback regulation of pituitary FSH secretion, gon adal activins have been shown to modulate physiological functions in t he reproductive tissues. These observations suggested that activins an d the receptors for these peptides may be coexpressed in gonadal tissu es. In this study, we have cloned cDNAs encoding two species of type I I activin receptors (ActRII and ActRIIB) from rat testicular mRNA and have shown that the two rat activin receptors share 97% similarity in the nucleotide sequence with those reported in the mouse. Two species [6 and 3 kilobases (kb)] ActRII mRNA were identified in all reproducti ve tissues of adult male and female rats. The 6-kb ActRII mRNA was the abundant form in most of the reproductive tissues. In placenta, the 6 - and 3-kb mRNA were present in equal intensity. Interestingly, the ra tio of the expression of two species of ActRII mRNA in rat testis chan ged with age. The 6-kb mRNA was the predominant form in immature 15- a nd 20-day-old testis, while the 3-kb mRNA increased with age and becam e the major form in mature testis. In female rats, however, the 6-kb A ctRII mRNA was the abundant species in all of the ovaries examined, in cluding immature, normal cycling, and pregnant rats. One major 2.25-kb species of ActRIIB mRNA was identified in all of the reproductive org ans examined. Nucleotide sequence analysis of the isolated ActRIIB cDN A clones revealed that ActRIIB2 was the major isoform found in rat tes tis. The levels of expression of ActRIIB gene in rat testis or ovary w ere not changed during development. We conclude that 1) both type II a nd IIB activin receptor genes are widely expressed in the male and fem ale reproductive tissues; and 2) the expression of 6- and 3-kb ActRII mRNA is tissue dependent as well as age dependent in rat testis.