Duncan Leonard, Nishii Ichiro, Howard Alicia, Kirk David, Miller Stephen M
Department of Biology, Washington University, St. Louis, MO 63130, USA.
Curr Genet. 2006 Jul;50(1):61-72. doi: 10.1007/s00294-006-0071-4. Epub 2006 Apr 19.
The multicellular green alga Volvox carteri forma nagariensis has only two cell types: terminally differentiated somatic cells and reproductive cells. The regA gene maintains the terminally differentiated state of the somatic cells, apparently by repressing transcription of genes required for chloroplast biogenesis and thereby preventing cell growth. Because the RegA protein sequence bore no obvious motifs, we are attempting to identify regions of functional importance by searching for strongly conserved domains in RegA orthologs. Here we report the cloning and characterization of regA from the most closely related known taxon, V. carteri f. kawasakiensis. Given the closeness of the relationship between these two formas, their regA genes are surprisingly different: they differ in the number of introns and by several lengthy indels, and they encode proteins that are only 80% identical. We also serendipitously discovered a paralogous gene immediately upstream of each regA locus. The two regA genes, both upstream paralogs and several genes in Chlamydomonas (the closest unicellular relative of Volvox) encode a conserved region (the VARL domain) that contains what appears to be a DNA-binding SAND domain. This discovery has opened up a new avenue for exploring how regA and the terminally differentiated state that it controls evolved.
终末分化的体细胞和生殖细胞。regA基因维持体细胞的终末分化状态，显然是通过抑制叶绿体生物发生所需基因的转录，从而阻止细胞生长。由于RegA蛋白序列没有明显的基序，我们试图通过寻找RegA直系同源物中高度保守的结构域来确定功能重要区域。在此，我们报告了从最密切相关的已知分类群——卡特氏团藻川崎变种中克隆和鉴定regA。鉴于这两个变种之间的亲缘关系很近，它们的regA基因却惊人地不同：它们在内含子数量和几个长插入/缺失方面存在差异，并且它们编码的蛋白质只有80%的同一性。我们还意外地在每个regA基因座的紧邻上游发现了一个旁系同源基因。这两个regA基因、上游旁系同源基因以及衣藻（团藻最接近的单细胞亲缘物种）中的几个基因都编码一个保守区域（VARL结构域），该区域包含一个看似DNA结合SAND结构域。这一发现为探索regA及其控制的终末分化状态是如何进化开辟了一条新途径。
