MCB Department, Division of Biomedicine, Brown University, Providence, Rhode Island, USA.
Mol Reprod Dev. 2023 May;90(5):310-322. doi: 10.1002/mrd.23684. Epub 2023 Apr 11.
Nanos genes encode essential RNA-binding proteins involved in germline determination and germline stem cell maintenance. When examining diverse classes of echinoderms, typically three, sometimes four, nanos genes are present. In this analysis, we identify and annotate nine nanos orthologs in the green sea urchin, Lytechinus variegatus (Lv). All nine genes are transcribed and grouped into three distinct classes. Class one includes the germline Nanos, with one member: Nanos2. Class two includes Nanos3-like genes, with significant sequence similarity to Nanos3 in the purple sea urchin, Strongylocentrotus purpuratus (Sp), but with wildly variable expression patterns. The third class includes several previously undescribed nanos zinc-finger genes that may be the result of duplications of Nanos2. All nine nanos transcripts occupy unique genomic loci and are expressed with unique temporal profiles during development. Importantly, here we describe and characterize the unique genomic location, conservation, and phylogeny of the Lv ortholog of the well-studied Sp Nanos2. However, in addition to the conserved germline functioning Nanos2, the green sea urchin appears to be an outlier in the echinoderm phyla with eight additional nanos genes. We hypothesize that this expansion of nanos gene members may be the result of a previously uncharacterized L1-class transposon encoded on the opposite strand of a nanos2 pseudogene present on chromosome 12 in this species. The expansion of nanos genes described here represents intriguing insights into germline specification and nanos evolution in this species of sea urchin.
纳米基因编码在生殖细胞决定和生殖干细胞维持中起关键作用的必需 RNA 结合蛋白。在研究不同种类的棘皮动物时，通常存在三个，有时四个纳米基因。在这项分析中，我们在绿海胆（Lytechinus variegatus）中鉴定并注释了九个纳米同源物。所有九个基因都转录并分为三个不同的类别。第一类包括生殖细胞 Nanos，其中一个成员是 Nanos2。第二类包括 Nanos3 样基因，与紫色海胆（Strongylocentrotus purpuratus）的 Nanos3 具有显著的序列相似性，但表达模式差异很大。第三类包括几个以前未描述的纳米锌指基因，它们可能是 Nanos2 重复的结果。九个纳米转录本占据独特的基因组位置，在发育过程中具有独特的时间表达谱。重要的是，在这里我们描述并表征了研究充分的 Sp Nanos2 的 Lv 同源物的独特基因组位置、保守性和系统发育。然而，除了保守的生殖细胞功能 Nanos2 外，绿海胆在棘皮动物门中似乎是一个异常现象，其有八个额外的纳米基因。我们假设，这种纳米基因成员的扩张可能是由于一种以前未被描述的 L1 类转座子，该转座子位于该物种 12 号染色体上 Nanos2 假基因的相反链上。这里描述的纳米基因的扩张代表了对该种海胆生殖细胞特化和纳米进化的有趣见解。
