Oocyte-specific gene signaling and its regulation of mammalian reproductive potential

Abstract

Oocyte-specific genes play important roles in regulating ovarian development, principally through the proper and timely progression of oogenesis and folliculogenesis. Development of transgenic mouse models has been critical in revealing how oocyte-specific transcripts influence oocyte development and growth, integrity of the oocyte-granulosa cell complex, oocyte maturation, fertilization, and early embryonic development. Oocyte-derived genes that mediate recombination of homologous chromosomes and DNA mismatch repair include Spo11, Atm, Dmc1, Msh5, Mlh1, and Msh4. Transcripts such as Dazla and Fig-alpha regulate initial proliferation of the primordial germ cell and follicle. Transition from the primordial to primary follicle relies on the expression of growth factors bFGF, Gdf9 and Bmp15, as well as on the expression of various transcripts that mediate oocyte-granulosa cell interactions. Oocyte growth is predominantly under exogenous control, however resumption of meiotic progression is dictated by genes that influence proper chromatin and spindle regulation, such as Cdk, Histone H1oo, Fmn-2, Mad2, and Bub3. Maintenance of meiotic metaphase II arrest prior to fertilization is mediated primarily by c-mos, and successful fertilization requires the expression of zona pellucida glycoproteins (Zp1, Zp2, and Zp3) and Cd9. Following fertilization, maternal-effect and maternally expressed 'imprinting' genes are necessary for the completion of meiosis and for patterning early embryonic development. Recent utilization of suppressive subtractive hybridization (SSH), PCR amplification, and cDNA microarray analysis techniques alongside established transgenesis models are expanding the classification of novel oocyte-specific genes required for reproductive fitness in various species, including human.