Chang Chun-Che, Lee Wen-Chih, Cook Charles E, Lin Gee-Way, Chang Tschining
Laboratory for Genetics and Development, Department of Entomology, National Taiwan University, Taipei, Taiwan.
Int J Dev Biol. 2006;50(4):413-21. doi: 10.1387/ijdb.052100cc.
The germarium, oocytes and embryos of the parthenogenetic viviparous pea aphid Acyrthosiphon pisum are contained within a single ovariole. This species provides an excellent model for studying how maternally-inherited germ plasm is specified and how it is transferred to primordial germ cells. Previous studies have shown that germ cells are first segregated at the embryonic posterior after formation of the blastoderm. We used two cross-reacting antibodies against the conserved germline markers Vasa and Nanos, which specifically identified these presumptive germ cells, to investigate whether germ cells were determined during early development. We observed randomly-distributed weak expression of Vasa signals in the developing oocyte but no localization in the oocyte segregated from the germarium. Localized Vasa was not apparent until it was detected at the posterior in the embryo undergoing the second nuclear division. Nanos, on the other hand, was localized to a nuage-like structure surrounding the nucleus in the developing and segregated oocytes. At the beginning of the oocyte maturation division, Nanos localization shifted to the posterior and could be identified in successive stages until it was incorporated into the germ cells. Taken together, our results suggest that germ plasm is specified in the developing oocyte and that Nanos is an earlier germline marker than Vasa. Germ cells stained for Vasa remained at a dorsal location in the egg during mid-development and then were guided into abdominal segments A1 to A6 during germ-band retraction. We infer that germ cells coalesce with segmented gonadal mesoderm during this period.
孤雌胎生豌豆蚜（Acyrthosiphon pisum）的生殖腺、卵母细胞和胚胎包含在单个卵巢管内。该物种为研究母系遗传的生殖质如何被指定以及如何转移到原始生殖细胞提供了一个绝佳的模型。先前的研究表明，生殖细胞在胚盘形成后首先在胚胎后部被分离出来。我们使用了两种针对保守生殖系标记物Vasa和Nanos的交叉反应抗体，它们能特异性识别这些推定的生殖细胞，以研究生殖细胞是否在早期发育过程中就已被确定。我们观察到在发育中的卵母细胞中Vasa信号呈随机分布的弱表达，但在从生殖腺分离出的卵母细胞中没有定位。直到在进行第二次核分裂的胚胎后部检测到Vasa，其定位才变得明显。另一方面，Nanos定位于发育中和分离出的卵母细胞核周围的类核仁结构。在卵母细胞成熟分裂开始时，Nanos的定位转移到后部，并在连续阶段中都能被识别，直到它被整合到生殖细胞中。综上所述，我们的结果表明生殖质在发育中的卵母细胞中被指定，并且Nanos是比Vasa更早的生殖系标记物。在发育中期，用Vasa染色的生殖细胞在卵中保持在背侧位置，然后在胚带收缩期间被引导到腹部A1至A6节段。我们推断在此期间生殖细胞与分段的性腺中胚层合并。
