Ewes from the Booroola strain of Australian Mé rino sheep are characterized by high ovulation rate and litter size. This phenotype is due to the action of the FecB B allele of a major gene named FecB, as determined by statistical analysis of phenotypic data. By genetic analysis of 31 informative half-sib families from heterozygous sires, we showed that the FecB locus is situated in the region of ovine chromosome 6 corresponding to the human chromosome 4q22-23 that contains the bone morphogenetic protein receptor IB (BMPR-IB) gene encoding a member of the transforming growth factor-␤ (TGF-␤) receptor family. A nonconservative substitution (Q249R) in the BMPR-IB coding sequence was found to be associated fully with the hyperprolificacy phenotype of Booroola ewes. In vitro, ovarian granulosa cells from FecB B ͞FecB B ewes were less responsive than granulosa cells from FecB ؉ ͞FecB ؉ ewes to the inhibitory effect on steroidogenesis of GDF-5 and BMP-4, natural ligands of BMPR-IB. It is suggested that in FecB B ͞FecB B ewes, BMPR-IB would be inactivated partially, leading to an advanced differentiation of granulosa cells and an advanced maturation of ovulatory follicles.

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Freezing ovarian cortex is a new option to preserve the fertility of young patients undergoing cancer treatment or in women facing premature menopause. However, the best way to use this banked tissue remains unclear. The function of heterotopic and orthotopic autografts of frozen-thawed ovarian cortex of sheep was compared in the present study. Fresh and frozen-thawed fragments of ovarian cortex were autografted on the uterine horn of six ewes (orthotopic grafts) and under the skin of the belly in nine ewes (heterotopic grafts). In both orthotopic and heterotopic grafts, the resumption of follicular growth and ovulation was monitored. In orthotopically grafted ewes, fertility was recorded. Oocytes from both types of grafts were collected, matured and fertilized in vitro. In both fresh and frozen-thawed grafts follicular growth resumed normally; preantral and antral follicles were first detectable 4 and 10 weeks respectively following grafting but only 5% of the primordial follicles appeared to have survived. This confirms that grafting procedures are more deleterious for follicle survival than cryopreservation. Although ovulation resumed in most ewes, none of the ewes grafted orthotopically became pregnant at a synchronized mating. Seven months following grafting, oocytes could be collected from heterotopic and orthotopic grafts, matured and some of them fertilized, but none developed to the blastocyst stage. Heterotopic grafting may be an alternative to orthotopic grafting to preserve fertility provided follicle survival in the grafts is markedly improved.

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