Cattaneo F, Pasini M E, Intra J, Matsumoto M, Briani F, Hoshi M, Perotti M E
Department of Biosciences and Informatics, Keio University, Kohoku Ku, Yokohama, Kanagawa 2238522, Japan.
Glycobiology. 2006 Sep;16(9):786-800. doi: 10.1093/glycob/cwl007. Epub 2006 May 29.
Sperm surface beta-N-acetylhexosaminidases are among the molecules mediating early gamete interactions in invertebrates and vertebrates, including man. The plasma membrane of Drosophila spermatozoa contains two beta-N-acetylhexosaminidases, DmHEXA and DmHEXB, which are required for egg fertilization. Here, we demonstrate that three putative Drosophila melanogaster genes predicted to code for beta-N-acetylhexosaminidases, Hexo1, Hexo2, and fdl, are all expressed in the male germ line. fdl codes for a homolog of the alpha-subunit of the mammalian lysosomal beta-N-acetylhexosaminidase Hex A. Hexo1 and Hexo2 encode two homologs of the beta-subunit of all known beta-N-acetylhexosaminidases, which we have named beta(1) and beta(2), respectively. Immunoblot analysis of sperm proteins indicated that the gene products associate in different heterodimeric combinations forming DmHEXA, with an alphabeta(2) structure, and DmHEXB, with a beta(1)beta(2) structure. Immunofluorescence demonstrated that all the gene products localized to the sperm plasma membrane. Although none of the genes was testis-specific, fdl was highly and preferentially expressed in the testis, whereas Hexo1 and Hexo2 showed broader tissue expression. Enzyme assays carried out on testis and on a variety of somatic tissues corroborated the results of gene expression analysis. These findings for the first time show the in vivo expression in insects of genes encoding beta-N-acetylhexosaminidases, the only molecules so far identified as involved in sperm/egg recognition in this class, whereas in mammals, the organisms where these enzymes have been best studied, only two types of polypeptide chains forming dimeric functional beta-N-acetylhexosaminidases are present in Drosophila three different gene products are available that might generate numerous dimeric isoforms.
精子表面的β-N-乙酰己糖胺酶是介导无脊椎动物和脊椎动物（包括人类）早期配子相互作用的分子之一。果蝇精子的质膜含有两种β-N-乙酰己糖胺酶，即DmHEXA和DmHEXB，它们是卵子受精所必需的。在此，我们证明，预测编码β-N-乙酰己糖胺酶的三个推定的黑腹果蝇基因Hexo1、Hexo2和fdl均在雄性生殖系中表达。fdl编码哺乳动物溶酶体β-N-乙酰己糖胺酶Hex A的α亚基的同源物。Hexo1和Hexo2分别编码所有已知β-N-乙酰己糖胺酶β亚基的两个同源物，我们分别将其命名为β(1)和β(2)。对精子蛋白的免疫印迹分析表明，基因产物以不同的异二聚体组合形式结合，形成具有αβ(2)结构的DmHEXA和具有β(1)β(2)结构的DmHEXB。免疫荧光显示，所有基因产物均定位于精子质膜。尽管没有一个基因是睾丸特异性的，但fdl在睾丸中高度且优先表达，而Hexo1和Hexo2的组织表达范围更广。在睾丸和多种体细胞组织上进行的酶活性测定证实了基因表达分析的结果。这些发现首次表明了编码β-N-乙酰己糖胺酶的基因在昆虫体内的表达，这类酶是迄今为止在该类别中唯一被确定参与精子/卵子识别的分子，而在对这些酶研究最为深入的哺乳动物中，仅存在形成二聚体功能性β-N-乙酰己糖胺酶的两种类型的多肽链，而在果蝇中，有三种不同的基因产物，它们可能产生众多的二聚体异构体。
