Nishimura Yukiko, Sato Tokiharu, Morita Yasuhiro, Yamazaki Atsuko, Akasaka Koji, Yamaguchi Masaaki
Division of Life Science, Graduate School of Natural Science and Technology, Kanazawa University, Kakuma, Kanazawa, 920-1192, Japan.
Dev Genes Evol. 2004 Nov;214(11):525-36. doi: 10.1007/s00427-004-0442-0. Epub 2004 Oct 6.
The animal-vegetal axis of sea urchin embryos is morphologically apparent at the 16-cell stage, when the mesomeres, macromeres, and micromeres align along it. At this stage, the micromere is the only autonomously specified blastomere that functions as a signaling center. We used a subtraction PCR survey to identify the homeobox gene micro1 as a micromere-specific gene. The micro1 gene is a representative of a novel family of paired-like class homeobox genes, along with PlHbox12 from Paracentrotus lividus and pmar1 from Strongylocentrotus purpuratus. In the present study, we showed that micro1 is a multicopy gene with six or more polymorphic loci, at least three of which are clustered in a 30-kb region of the genome. The micro1 gene is transiently expressed during early cleavage stages in the micromere. Recently, nuclear beta-catenin was shown to be essential for the specification of vegetal cell fates, including micromeres, and the temporal and spatial coincidence of micro1 expression with the nuclear entry of beta-catenin is highly suggestive. We demonstrated that micro1 is a direct target of beta-catenin. In addition, we showed that micro1 is necessary and sufficient for micromere specification. These observations on the structure, regulation, and function of micro1 lead to the conclusion that micro1 and pmar1 (and potentially PlHbox12) are orthologous.
海胆胚胎的动植物轴在16细胞期在形态上就已明显可见，此时中节、大卵裂球和小卵裂球沿此轴排列。在此阶段，小卵裂球是唯一自主特化的卵裂球，充当信号中心。我们通过消减PCR筛选，鉴定出同源异型盒基因micro1为小卵裂球特异性基因。micro1基因是一个新的成对样类同源异型盒基因家族的代表，与紫球海胆的PlHbox12和红海胆的pmar1同属该家族。在本研究中，我们发现micro1是一个多拷贝基因，有六个或更多的多态性位点，其中至少三个聚集在基因组的一个30 kb区域内。micro1基因在小卵裂球的早期卵裂阶段短暂表达。最近研究表明，核β-连环蛋白对于包括小卵裂球在内的植物细胞命运的特化至关重要，而micro1表达与β-连环蛋白进入细胞核在时间和空间上的一致性极具启发性。我们证明micro1是β-连环蛋白的直接靶标。此外，我们还表明micro1对于小卵裂球的特化是必要且充分的。这些关于micro1的结构、调控和功能的观察结果得出结论，micro1和pmar1（可能还有PlHbox12）是直系同源的。
