Kawahara Ryouka, Nishida Mutsumi
Department of Molecular Marine Biology, Ocean Research Institute, University of Tokyo, 1-15-1, Minamidai, Nakano-ku, Tokyo, 164-8639, Japan.
Gene. 2006 May 24;373:58-66. doi: 10.1016/j.gene.2006.01.008. Epub 2006 Feb 24.
The threespine stickleback (Gasterosteus aculeatus) is known to have a unique reproductive mode including male nest-building with a secreted glue-like protein named spiggin. Spiggin is a key character for studying the molecular mechanism in the evolution of this intriguing nest-building behavior, since the glue-like protein is essential for nest-building. However, it is unclear whether spiggin is encoded by a single gene or multiple genes; there are conflicting reports on this point. To resolve this discrepancy, we cloned this gene in a threespine stickleback collected in Japan. We found seven types of cDNAs including at least four genes, indicating that spiggin is encoded by a multi-gene family. On close inspection of the cDNAs, we found that one of these spiggin genes had four splicing variants. Although the cDNA sequences conserved functional domain structures, considerable diversity was observed in the sequence of each domain. Altogether, the current results imply that the structure and function of the spiggins are more complex than ever previously thought. Phylogenetic analysis of the cDNAs with related sequences including ninespine stickleback (Pungitius pungitius) spiggin genes and homologues of zebrafish (Danio rerio), torafugu (Takifugu rubripes), and spotted green pufferfish (Tetraodon nigroviridis) implied the existence of an ancestral "spiggin" gene and multiple duplication events of the gene in the stickleback lineage before and after the divergence of the threespine and ninespine sticklebacks.
三刺鱼（Gasterosteus aculeatus）具有独特的繁殖方式，包括雄性用一种名为spiggin的分泌型胶状蛋白筑巢。Spiggin是研究这种有趣筑巢行为进化过程中分子机制的关键特征，因为这种胶状蛋白对筑巢至关重要。然而，尚不清楚spiggin是由单个基因还是多个基因编码；在这一点上存在相互矛盾的报道。为了解决这一差异，我们在一条采集于日本的三刺鱼中克隆了该基因。我们发现了七种类型的cDNA，其中至少包括四个基因，这表明spiggin是由一个多基因家族编码的。在仔细检查这些cDNA时，我们发现其中一个spiggin基因有四种剪接变体。虽然cDNA序列保守了功能域结构，但在每个结构域的序列中观察到了相当大的多样性。总之，目前的结果表明spiggins的结构和功能比以前认为的更加复杂。对这些cDNA与相关序列进行系统发育分析，这些相关序列包括九刺鱼（Pungitius pungitius）的spiggin基因以及斑马鱼（Danio rerio）、红鳍东方鲀（Takifugu rubripes）和黑点绿河豚（Tetraodon nigroviridis）的同源物，这表明存在一个祖先“spiggin”基因，并且在三刺鱼和九刺鱼分化之前和之后，该基因在刺鱼谱系中发生了多次复制事件。
