Rebscher N, Zelada-González F, Banisch T U, Raible F, Arendt D
Institute of Zoology, Philipps University Marburg, Karl von Frisch Strasse 8, 35032 Marburg, Germany.
Dev Biol. 2007 Jun 15;306(2):599-611. doi: 10.1016/j.ydbio.2007.03.521. Epub 2007 Apr 1.
To elucidate the evolution of germ cell specification in Metazoa, recent comparative studies focus on ancestral animal groups. Here, we followed the germline throughout the life cycle of the polychaete annelid Platynereis dumerilii, by examining mRNA and protein expression of vasa and other germline-specific factors in combination with lineage tracing experiments. In the fertilised egg, maternal Vasa protein localises to the yolk-free cytoplasm at the animal pole. It then asymmetrically segregates first into the micromeres, then into the founder cells of the mesodermal posterior growth zone (MPGZ). Vasa transcripts initially show ubiquitous distribution, but then become progressively restricted to the MPGZ. The cells of the MPGZ are highly proliferative, as evidenced by BrdU pulse labelling experiments. Besides vasa, they express nanos along with the stem cell-specific genes piwi, and PL10. At 4 days of development, four primordial germ cells are singled out from within the MPGZ, and migrate into the anterior segments to colonise a newly discovered "primary gonad". Our data suggest a common origin of germ cells and of somatic stem cells, similar to the situation found in planarians and cnidarians, which may constitute the ancestral mode of germ cell specification in Metazoa.
为阐明后生动物中生殖细胞特化的进化过程，近期的比较研究聚焦于原始动物类群。在此，我们通过检测瓦萨蛋白（vasa）及其他生殖系特异性因子的mRNA和蛋白质表达，并结合谱系追踪实验，在多毛纲环节动物杜氏阔沙蚕（Platynereis dumerilii）的整个生命周期中追踪生殖系。在受精卵中，母源瓦萨蛋白定位于动物极不含卵黄的细胞质中。随后，它首先不对称地分离到小分裂球中，然后进入中胚层后生长区（MPGZ）的奠基细胞中。瓦萨转录本最初呈现普遍分布，但随后逐渐局限于MPGZ。MPGZ的细胞具有高度增殖性，5-溴脱氧尿嘧啶核苷（BrdU）脉冲标记实验证明了这一点。除了瓦萨蛋白，它们还表达纳米（nanos）以及干细胞特异性基因piwi和PL10。在发育4天时，从MPGZ中分离出四个原始生殖细胞，并迁移到前部体节中，定殖于一个新发现的“初级性腺”中。我们的数据表明生殖细胞和体干细胞有共同起源，类似于涡虫和刺胞动物中的情况，这可能构成了后生动物中生殖细胞特化的原始模式。
