Mammalian female germ cells must successfully complete developmental programs to initial folliculogenesis that lead to mature gametes capable of fertilization and the transfer of genetic material to the next generation. At birth the ovary contains its full complement of germ cells, each surrounded by a single layer of granulosa cells which together form the primordial follicles. We have identified a novel, oocyte-specific, basic helix-loop-helix transcription factor, FIG-alpha (Factor In the Germline, alpha) and mouse lines have been established in which the single-copy Fig-alpha gene has been disrupted. Female mice lacking FIG-alpha are sterile because of germ cell depletion secondary to an inability to form primordial follicles. Identification of downstream targets of FIG-alpha should provide additional insights into the molecular basis of follicle formation. After the onset of folliculogenesis, FIG-alpha also modulates the expression of the single-copy genes that encode ZP1, ZP2 and ZP3. Normally, the three zona glycoproteins are secreted during folliculogenesis to form the zona pellucida, an extracellular matrix that mediates order-specific sperm binding to the egg (e.g., human sperm will not bind to the mouse zona pellucida). Using transgenesis, we have determined that mouse ZP1 is not required for formation of the zona pellucida, order-specific sperm binding or fertility. In contrast, both ZP2 and ZP3 are required for stable matrix formation without which mice are infertile. Although the replacement of either mouse ZP2, mouse ZP3 or both with their human homologue restores the zona pellucida matrix, it does not affect the specificity of sperm binding. Breeding studies to establish mouse lines expressing all three human zona proteins or mutant forms of the mouse zona proteins are being pursued to further investigate the molecular basis of sperm-egg interactions. Late in oogenesis the oocyte becomes transcriptionally inactive and much of the maternal RNA is degraded during meiotic maturation and ovulation. At fertilization, both gametes are transcriptionally inert and the major activation of the embryonic genome occurs at the two-cell stage. The sperm brings little but its genome to fertilization and the activation of early development programs must depend on maternal factors. MATER (Maternal Antigen That Embryos Require) is a cytoplasmic protein that is present in growing oocytes and persists in early embryos. Mice lacking MATER have normal folliculogenesis and ovulate eggs. Although fertilization takes place, embryos do not progress beyond the early cleavage stage. Males are unaffected and MATER represents a maternal effect gene product critical for mammalian development. Investigations are underway to determine its role in transition of the terminally differentiated germ cell into the totipotent stem cells of the early embryo.

Agency
National Institute of Health (NIH)
Institute
National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
Type
Intramural Research (Z01)
Project #
1Z01DK015506-18
Application #
6673348
Study Section
(LCDB)
Project Start
Project End
Budget Start
Budget End
Support Year
18
Fiscal Year
2002
Total Cost
Indirect Cost
Name
U.S. National Inst Diabetes/Digst/Kidney
Department
Type
DUNS #
City
State
Country
United States
Zip Code
Hoodbhoy, Tanya; Aviles, Manuel; Baibakov, Boris et al. (2006) ZP2 and ZP3 traffic independently within oocytes prior to assembly into the extracellular zona pellucida. Mol Cell Biol 26:7991-8
Hoodbhoy, Tanya; Joshi, Saurabh; Boja, Emily S et al. (2005) Human sperm do not bind to rat zonae pellucidae despite the presence of four homologous glycoproteins. J Biol Chem 280:12721-31
Hoodbhoy, Tanya; Dean, Jurrien (2004) Insights into the molecular basis of sperm-egg recognition in mammals. Reproduction 127:417-22
Dean, Jurrien (2004) Reassessing the molecular biology of sperm-egg recognition with mouse genetics. Bioessays 26:29-38
Zhao, Ming; Boja, Emily S; Hoodbhoy, Tanya et al. (2004) Mass spectrometry analysis of recombinant human ZP3 expressed in glycosylation-deficient CHO cells. Biochemistry 43:12090-104
Rankin, Tracy L; Coleman, Jenell S; Epifano, Olga et al. (2003) Fertility and taxon-specific sperm binding persist after replacement of mouse sperm receptors with human homologs. Dev Cell 5:33-43
Zhao, Ming; Gold, Lyn; Dorward, Heidi et al. (2003) Mutation of a conserved hydrophobic patch prevents incorporation of ZP3 into the zona pellucida surrounding mouse eggs. Mol Cell Biol 23:8982-91
Boja, Emily S; Hoodbhoy, Tanya; Fales, Henry M et al. (2003) Structural characterization of native mouse zona pellucida proteins using mass spectrometry. J Biol Chem 278:34189-202
Takasaki, N; Rankin, T; Dean, J (2001) Normal gonadal development in mice lacking GPBOX, a homeobox protein expressed in germ cells at the onset of sexual dimorphism. Mol Cell Biol 21:8197-202
Rankin, T L; O'Brien, M; Lee, E et al. (2001) Defective zonae pellucidae in Zp2-null mice disrupt folliculogenesis, fertility and development. Development 128:1119-26

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