OVARIAN MORPHOLOGY AND ENDOCRINE CHARACTERISTICS OF FEMALE SHEEP FETUSES THAT ARE HETEROZYGOUS OR HOMOZYGOUS FOR THE INVERDALE PROLIFICACY GENE (FECX(1))

The Inverdale gene (fecX'), located on the X chromosome, is a major ge ne affecting the ovulation rate of sheep. At each ovulation, ewes hete rozygous (I+) for the fecX' gene ovulate, on average, one more egg tha n noncarriers (++), whereas ewes that are homozygous (II) for this gen e are infertile and have ''streak'' ovaries. Since formation of the ov ary occurs in fetal life, it is possible that the fecX' gene influence s ovarian development before birth. The aims of this study were to exa mine the effects of the fecX' gene on germ cell development, follicula r formation and growth, and plasma gonadotropin concentrations at 5 di fferent days of gestation (i.e., Days 40, 90, 105, 120, and 135) and a lso in adult life. The results suggest that one copy of the X-linked m utation in female fetuses leads to a retardation of germ cell developm ent at Days 40 and 90 of gestation. However, from Day 105 of gestation , follicular formation and growth appear normal. By contrast, in femal es with two copies of the X-linked mutation, germ cell development and follicular formation appear normal, but thereafter follicular growth from the primary stage of development is impaired. During fetal life t he plasma concentrations of FSH and LH, although not measurable at Day 40, were similar between all the genotypes at Day 105, 120, and 135 o f gestation. The only exception was for LH at Day 90 in the I+ and II animals: in ewes with these genotypes the plasma concentrations of LH were similar but significantly lower (p < 0.01) than in the ++ genotyp e. In adult animals the plasma concentrations of FSH and LH were not d ifferent between the ++ and I+ genotypes, reflecting similar levers of ovarian follicular activity. However, in adult II animals, the plasma concentrations of FSH and LH were significantly higher (both p < 0.01 ) than in the ++ and If genotypes, reflecting the absence of normal se condary and antral follicles. In summary, these data show that the fec X' gene affects ovarian development before birth and that the nature o f the effect is influenced by whether the female fetus is a homozygous or heterozygous carrier of the X-linked mutation.