Cloning and Characterization of Haploid Germ Cell-Specific Genes

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  • TANAKA Hiromitsu
    <I>Department of Science for Laboratory Animal Experimentation, Research Institute for Microbial Diseases, Osaka University</I>
  • IGUCHI Naoko
    <I>Department of Science for Laboratory Animal Experimentation, Research Institute for Microbial Diseases, Osaka University</I>
  • NISHIMUNE Yoshitake
    <I>Department of Science for Laboratory Animal Experimentation, Research Institute for Microbial Diseases, Osaka University</I>

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  • 男性不妊の疾患モデルと遺伝子工学的治療法　　１．精子形成遺伝子群の単離とその解析

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Abstract

In most multicellular organisms, fertilized eggs differentiate into somatic and germ cells. They become separated during the early developmental stages and have quite different roles. Germ cells maintain species continuity, whereas somatic cells ensure the constitution and activity of the individual. In other words, somatic cells help the germ cells to ensure survival and continuity of the species. Thus, germ cells play a fundamental role in multi-cellular organisms.<BR>To understand the unique mechanism of germ cell differentiation, the most straightforward strategy is to identify and characterize differentiation-specific molecules and their associated genes in germ cells. We have cloned haploid germ-cell-specific cDNAs from a subtracted cDNA library that was generated by subtracting the mRNA of 17-day-old mouse testes (before haploid germ cells develop) from the cDNA of 35-day-old mouse testes. Detailed mRNA expression analysis revealed that the genes corresponding to the cloned cDNAs were exclusively expressed in germ cells at all steps of differentiation, at specific steps of differentiation, or at specific steps in the development of haploid germ cells. The expression of all of these genes was developmentally controlled. The products of germ-cell-specific genes included various proteins having roles in spermatogenesis. Some germ-cell-specific isozymes of previously known enzymes for energy metabolism are interesting examples.<BR>We also isolated the genomic DNA of haploid-specific genes and identified a number of regulatory motifs in the gene-promoter regions that were essential for transcription. One of these motifs, the cyclic AMP response element, was present in the promoter regions of several testis-specific genes, and was deemed to be functionally important. However, the haspin gene-promoter region did not contain a CRE motif. Similarly, the promoter regions of the MMP-28 (Illman et al. 2001), Hormone-sensitive lipase (Blaise et al. 2001), ldhc (Jethanandani and Goldberg 2001), SP-10 (Reddi et al. 1999) genes, which were specifically expressed in haploid germ cells, did not have CRE motifs. These findings suggest the existence of haploid germ-cell-specific regulatory proteins specifically regulate the expression of haploid germ-cell-specific genes. Here, we describe our recent findings of germ-cell-specific genes and gene products, and discuss the relevance of our approaches to the study of germ cell differentiation mechanisms.

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