Developmental expression of activin/inhibin alpha- and beta(A)-subunit genes in the gonads of male and female chick embryos

The expression of inhibin alpha- and beta (A)-subunits was investigated in gonads of male and female chick embryos during the last week of their 21-da y incubation period. Fertilized Hisex brown laying hen eggs were incubated at 37.8 +/- 0.2 degrees and 60% relative humidity in an automatic forced-dr aft incubator with constant lighting. Embryos were killed after 14, 18, and 21 days of incubation, sexed by macroscopical inspection of the gonadal ph enotype, and further dissected to obtain the gonads. Total RNA was isolated using the ultraspec RNA method. The expression of alpha- and beta (A)-subu nits was evaluated by competitive RT-PCR. Significant differences were foun d within and between sexes in the expression of the alpha- and beta (A)-sub units. The level of the alpha -subunit in the testis was about 23-fold high er than that in the ovary at all ages. Testicular content of inhibin alpha mRNA levels was similar at days 14 and 18 but declined significantly at day 21 of incubation, whereas no significant differences were observed between the three age groups in the ovary. Testicular and ovarian inhibin beta (A) -subunit increased significantly from day 14 to day 18 followed by a signif icant decline before hatch. However, inhibin beta (A) level at day 14 was s ignificantly higher in the ovary than in the testis. At days 18 and 21, the re were no differences in the levels of the inhibin P, in the sexes. The ex pression of inhibin beta (A)-subunit in the ovary was significantly higher than that of the cu-subunit at. all ages. In the testis, however, the expre ssion of the beta (A)-subunit was higher at days 18 and 21 than at day 14. The sex difference in gonadal inhibin subunits expression suggests differen tial roles of inhibin/ activin in the development of the chicken gonads. Th e changing level of expression during incubation also suggests changing bio logical roles within sexes. (C) 20001 Academic Press.