RING OR ZINC FINGER PROTEINS DURING GAMETOGENESIS AND EMBRYONIC DEVELOPMENT

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This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Reproductive development and function are complex processes involving both genetically determined and physiological events. Identification of the critical genes involved in regulating these processes is necessary to characterize how these processes are coordinated. In particular, the generation of mature gametes involves many steps of development and differentiation, as well as the distinctive cellular process meiosis, that are collectively termed gametogenesis. In general, differentiation and development, and other processes that lead to the acquisition and maintenance of a cellular phenotype are dependent on the differential and coordinate regulation of gene expression. However, the regulation of gene expressioin many aspects of gametogenesis such as proliferation of spermatogonial stem cells, signals for meiotic arrest and meiotic exit, and spermiogenesis, and cross-talk between germ cells and adjacent somatic cells, are not clearly understood. In addition, the roles of maternal and paternal genes in zygotic development are also not well defined. Identification and functional characterization of germ cell-specific molecules such as zinc finger proteins during gametogenesis and early embryonic development would advance our knowledge regarding gamete and zygotic development, and will provide new leads for development of diagnostic reagents for reproductive diseases, novel therapeutic medicines for the treatment of infertility, gonadal cancers, pre-natal death, and novel contraceptive agents. The RING (Really interesting novel genes) finger is a specialized type of zinc finger proteins. It contains an evolutionarily conserved structure found in more than 300 proteins from the human genome database, in which two loops of amino acids are pulled together at their base by eight cysteine or histidine residues that bind two zinc ions. There are two different variants, the C3HC4-type and the C3H2C3-type, which is clearly related despite the different cysteine/histidine patterns. These ring finger domains are found in two major classes of proteins: (1) transcriptional activators, repressors or cofactors and (2) subunits of complexes that modulate chromatin. These proteins likely interact with other proteins, participate in ubiquitination, and play roles in cell growth control such as apoptosis, tumorigenesis, DNA damage repair, and gene expression. In silico analyses have demonstrated that a large number of ring/zinc finger proteins with human homologs are expressed in the germ cells or early embryos, indicating that these proteins may play a role in germ cell and zygotic development. Recent studies have shown that ring finger proteins, zygote arrest 1 (Zar1) and NEURL are critical for zygotic development, and male fertility and mammary gland maturation during pregnancy, respectively. Ablation of another ring finger protein, Siah1a, also caused male infertility due to defects in meiosis. In addition, another oocyte specific ring finger protein, RFPL4, interacts with oocyte proteins and likely functions as an E3 ubiquitin protein ligase to regulate protein degradation and meiotic cell cycle progression. Therefore, we are just in the beginning to understand the functional roles of these ring/zinc finger proteins during gametogenesis and early embryonic development. Having searched mouse and human genomic databases, I found that seven uncharacterized genes likely play a role during gametogenesis and zygotic development, as the expressed sequence tags (ESTs) of these genes are present in the cDNA libraries of mouse, human germ cells or early embryos. I am particularly interested in five of these genes (named unknown 1-5), which are located in different mouse chromosomes and all have human orthologs. Unknown-1, -2 and -3 are C3HC4 ring finger proteins, while unknown?4 and ?5 are C2H2 zinc finger proteins, similar to zfp148, nanos2 and nanos3, which are required for male or female germ cell development. I will combine genetic, molecular, and cellular approaches to address whether these genes are involved in the gametogenesis and early embryonic development.