The Key Laboratory of Mammalian Reproduction Biology and Technology of Ministry of Education, College of Life Science, Inner Mongolia University, Hohhot 010021, People's Republic of China.
Mol Biol Rep. 2011 Mar;38(3):1995-2006. doi: 10.1007/s11033-010-0322-9. Epub 2010 Oct 21.
We cloned the cDNA and genomic DNA encoding for Izumo1 of cashmere goat (Capra hircus) and sheep (Ovis aries). Analysis of 4.6 kb Izumo1 genomic sequences in sheep and goat revealed a canonical open reading frame (ORF) of 963 bp spliced by eight exons. Sheep and goat Izumo1 genes share >99% identity at both DNA and protein levels and are also highly homologous to the orthologues in cattle, mouse, rat and human. Extensive cloning and analysis of Izumo1 cDNA revealed three (del 69, del 182 and del 217) and two (del 69 and ins 30) alternative splicing isoforms in goat and sheep, respectively. All of the isoforms are derived from splicing at typical GT-AG sites leading to partial or complete truncation of the immunoglobulin (Ig)-like domain. Bioinformatics analysis showed that caprine and ovine Izumo1 proteins share similar structure with their murine orthologue. There are a signal peptide at the N-terminus (1-22 aa), a transmembrane domain at the C-terminus (302-319 aa), and an extracellular Ig-like region in the middle (161-252 aa) with a putative N-linked glycosylation site (N(205)-N-S). Alignment of Izumo1 protein sequences among 15 mammalian species displayed several highly conserved regions, including LDC and YRC motifs with cysteine residues for potential disulfide bridge formation, CPNKCG motif upstream of the Ig-like domain, GLTDYSFYRVW motif upstream of the putative N-linked glycosylation site, and a number of scattered cysteine residues. These distinctive features are very informative to pinpoint the important gene motifs and functions. The C-terminal regions, however, are more variable across species. Izumo1 cDNA sequences of goat, sheep, and cow were found to be largely homologous, and the molecular phylogenetic analysis is consistent with their morphological taxonomy. This implies the Izumo1 gene evolves from the same ancestor, and the mechanism of sperm-egg fusion in mammals may be under the same principle in which Izumo1 plays an important role.
我们克隆了编码羊绒山羊（Capra hircus）和绵羊（Ovis aries）Izumo1 的 cDNA 和基因组 DNA。对绵羊和山羊 4.6 kb Izumo1 基因组序列的分析显示，一个典型的开放阅读框（ORF）由 8 个外显子拼接而成，长 963 bp。绵羊和山羊 Izumo1 基因在 DNA 和蛋白质水平上的同源性均超过 99%，与牛、鼠、大鼠和人类的同源物也高度同源。对 Izumo1 cDNA 的广泛克隆和分析显示，在山羊和绵羊中分别有三个（del 69、del 182 和 del 217）和两个（del 69 和 ins 30）选择性剪接异构体。所有异构体均源于在典型 GT-AG 位点的剪接，导致免疫球蛋白（Ig）样结构域的部分或完全截断。生物信息学分析表明，山羊和绵羊 Izumo1 蛋白与它们的鼠同源物具有相似的结构。在 N 端（1-22 aa）有一个信号肽，在 C 端（302-319 aa）有一个跨膜结构域，在中间（161-252 aa）有一个 Ig 样结构域，有一个潜在的 N-连接糖基化位点（N（205）-N-S）。在 15 种哺乳动物的 Izumo1 蛋白序列比对中，显示了几个高度保守的区域，包括 LDC 和 YRC 基序，其半胱氨酸残基用于潜在的二硫键形成，Ig 样结构域上游的 CPNKCG 基序，潜在的 N-连接糖基化位点上游的 GLTDYSFYRVW 基序，以及一些分散的半胱氨酸残基。这些独特的特征对于确定重要的基因基序和功能非常有信息。然而，C 端区域在物种间更为多样化。发现山羊、绵羊和牛的 Izumo1 cDNA 序列在很大程度上是同源的，分子系统发育分析与它们的形态分类学一致。这意味着 Izumo1 基因来自于同一个祖先，哺乳动物的精子-卵融合机制可能遵循相同的原则，其中 Izumo1 起着重要的作用。
