Reproduction in Domestic Animals

398 P Mermillod, R Dalbie` s-Tran, S Uzbekova, A The´lie, J-M Traverso, C Perreau, P Papillier and P Mongetreceptor expression) as compared with oocytes fromprimary follicles.It appears finally that oocyte is able to regulate manyaspects of follicle somatic cells proliferation, differentiationand metabolic activities involved in late folliculargrowth regulation. This opens the way to a newhypothesis, i.e. that oocytes in early antral folliclesalready display intrinsic developmental competence.This competence may translate into differential abilityto drive proper follicular differentiation in a decreasingFSH support context and increasing interfollicularcompetition. Poorly differentiated oocytes (oocytesbearing some transcriptome abnormalities) fail in maintainingproper somatic cells differentiation status or toprotect these cells against apoptosis induced by increasinglychallenging hormonal environment and finallyleave their follicle degenerate on the way to atresia(Fig. 3). Hormonal stimulation of follicular growthpartly alleviates the selection pressure imposed onfollicles, and allows lower quality oocytes to drive theirfollicles to ovulation in these permissive conditions.The expression of many oocyte-specific genes duringoocyte growth in pre-antral follicles is coordinated bygermline-specific transcription factors such as FIGLAor NOBOX (Pangas and Rajkovic 2006). Interestingly,NOBOX regulates oocyte genes involved both in developmentalcompetence (Mater, Zar-1 and Mos) and incontrol of follicular function by oocyte (GDF-9 andBMP-15). This observation indicates that oocytes deficientin terms of competence may also be deficient intheir ability to properly drive their follicle to ovulation.ConclusionsDuring its early growth in pre-antral follicles, the oocytestores specific gene products that will be determinant forits ability to coordinate follicular growth and that willbe required during early embryo development afterfertilization. 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