Department of Organismic and Evolutionary Biology, Harvard University, 16 Divinity Avenue, Cambridge, MA 02138, USA.
Department of Organismic and Evolutionary Biology, Harvard University, 16 Divinity Avenue, Cambridge, MA 02138, USA; Department of Zoology, University of Cambridge, Downing Street, Cambridge, Cambridgeshire, CB2 3EJ, England, UK.
Dev Biol. 2011 Nov 1;359(1):110-123. doi: 10.1016/j.ydbio.2011.07.029. Epub 2011 Jul 28.
The acquisition of specific cell fates throughout embryonic development is one of the core problems in developmental and evolutionary biology. In the amphipod Parhyale hawaiensis all three germ layers and the germ line are determined by the eight-cell stage. Despite this early fate determination, multiple cell types can be replaced following ablation of their founder cells, showing that this embryo also has significant regulative properties. Here we present a cellular-level resolution lineage analysis for P. hawaiensis embryos between fertilization and gastrulation, including analysis of cleavage patterns, division times, and clonal behaviors. We compare these cellular behaviors in wild type embryos with those in embryos where specific founder cells have been ablated, or where zygotic transcription has been inhibited. We observe that when germ line, endoderm or mesoderm founder cells are ablated, the remaining cells do not alter their cleavage or migration behaviors before the onset of gastrulation. In the absence of zygotic transcription, ingression movements proceed normally, but epibolic movements are disrupted. This indicates that the embryo's regulative response to germ layer founder loss, in the form of altered cell behavior, is realized in the ~32h between gastrulation and early germ band elongation, and is likely to require zygotic reprogramming rather than alternative deployment of maternally supplied determinants. Combining these data with the observations of previous studies, we propose a framework to elucidate the molecular mechanisms that regulate the determinative and regulative properties of the P. hawaiensis embryo.
胚胎发育过程中特定细胞命运的获得是发育和进化生物学的核心问题之一。在等足目动物 Parhyale hawaiensis 中，所有三个胚层和生殖系都是由八细胞阶段决定的。尽管存在早期命运决定，但在其创始细胞被消融后，仍然可以替换多种细胞类型，这表明该胚胎也具有显著的调节特性。在这里，我们呈现了 Parhyale hawaiensis 胚胎从受精到原肠胚形成之间的细胞水平分辨率谱系分析，包括对分裂模式、分裂时间和克隆行为的分析。我们将这些细胞行为与野生型胚胎进行比较，同时还比较了特定创始细胞被消融的胚胎和转录被抑制的胚胎。我们观察到，当生殖系、内胚层或中胚层创始细胞被消融时，在原肠胚形成之前，剩余细胞不会改变它们的分裂或迁移行为。在没有合子转录的情况下，内陷运动正常进行，但外包运动被打乱。这表明，胚胎对胚层创始细胞丢失的调节反应，以改变细胞行为的形式，是在原肠胚形成和早期生殖带伸长之间的约 32 小时内实现的，这可能需要合子重编程，而不是替代母体提供的决定因素的部署。将这些数据与之前研究的观察结果相结合，我们提出了一个框架来阐明调节 Parhyale hawaiensis 胚胎决定和调节特性的分子机制。
