Follicle stimulating hormone increases somatic and germ cell number in the ovary during chick embryo development

The aim of the present study was to evaluate the effect of human follicle stimulating hormone (hFSH) on cellular proliferation in the chick embryo ovary. Chick embryos (Babcock B300) were injected on chorioallantoic membrane with a single dose of hFSH (2.0 IU/ embryo) at Days 7, 9, or 13 of incubation or with hCG (2.0 IU/embryo) at Day 13 of incubation. At 17 days of incubation and within 24 h after hatching, left ovaries were dissected and completely dissociated. Cells from the whole ovary were classified into germ cells (primary oocytes), typical steroidogenic cells, and poorly differentiated somatic cells and counted with the aid of a hemocytometer. Aliquots of the cell suspension from the whole left ovary were analyzed by flow cytometry, in order to determine the percentage of cells at each phase of the cell cycle. In addition, samples of the suspension (1.0 x 10(6 )cells) were incubated for 2 h in basal and stimulated conditions measuring 17beta-estradiol secretion in the medium. The ovarian cell number at 17 days of incubation showed that hFSH treatment at Day 7 did not modify the cell number in any of the subpopulations evaluated; treatment at Day 9 resulted in an increase in poorly differentiated somatic cell number, without changes in steroidogenic and germ cells, whereas hFSH treatment at Day 13 augmented the number of poorly differentiated, steroidogenic, and germ cells. The percentage of cells in S-phase was increased 12 and 15 h after hFSH treatment (Day 13). Secretion of 17beta-estradiol was increased in the hFSH-treated group (Day 13) measured at 17 days of incubation. The increase in cell number of the three subpopulations was still observed in the left ovary of the newly hatched chicken. Treatment with hCG at Day 13 of incubation did not change the number of poorly differentiated, steroidogenic, and germ cells in the left ovary, neither in the 17-day-old chick embryo nor in the newly hatched chicken. The 17beta-estradiol secretion in hCG-treated embryos was similar to controls. The present study is the first evidence of an effect of FSH on somatic and germ cell number, together with an increase in 17beta-estradiol production during chick embryo ovary development.