Heikes Kira L, Game Mandy, Smith Frank W, Goldstein Bob
Biology Department, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA; Curriculum in Genetics and Molecular Biology, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA.
Biology Department, University of North Florida, Jacksonville, FL, USA.
Dev Biol. 2023 May;497:42-58. doi: 10.1016/j.ydbio.2023.02.008. Epub 2023 Mar 7.
Primordial germ cells (PGCs) give rise to gametes - cells necessary for the propagation and fertility of diverse organisms. Current understanding of PGC development is limited to the small number of organisms whose PGCs have been identified and studied. Expanding the field to include little-studied taxa and emerging model organisms is important to understand the full breadth of the evolution of PGC development. In the phylum Tardigrada, no early cell lineages have been identified to date using molecular markers. This includes the PGC lineage. Here, we describe PGC development in the model tardigrade Hypsibius exemplaris. The four earliest-internalizing cells (EICs) exhibit PGC-like behavior and nuclear morphology. The location of the EICs is enriched for mRNAs of conserved PGC markers wiwi1 (water bear piwi 1) and vasa. At early stages, both wiwi1 and vasa mRNAs are detectable uniformly in embryos, which suggests that these mRNAs do not serve as localized determinants for PGC specification. Only later are wiwi1 and vasa enriched in the EICs. Finally, we traced the cells that give rise to the four PGCs. Our results reveal the embryonic origin of the PGCs of H. exemplaris and provide the first molecular characterization of an early cell lineage in the tardigrade phylum. We anticipate that these observations will serve as a basis for characterizing the mechanisms of PGC development in this animal.
原始生殖细胞（PGCs）产生配子——这是多种生物体繁殖和生育所必需的细胞。目前对PGC发育的理解仅限于少数已鉴定和研究过其PGCs的生物体。将该领域扩展到包括研究较少的分类群和新兴模式生物，对于全面了解PGC发育的进化广度很重要。在缓步动物门中，迄今为止尚未使用分子标记鉴定出早期细胞谱系。这包括PGC谱系。在这里，我们描述了模式缓步动物典范高生熊虫（Hypsibius exemplaris）的PGC发育。最早内化的四个细胞（EICs）表现出类似PGC的行为和核形态。EICs的位置富含保守的PGC标记wiwi1（水熊piwi 1）和vasa的mRNA。在早期阶段，wiwi1和vasa mRNA在胚胎中均能均匀检测到，这表明这些mRNA并非PGC特化的定位决定因素。只有在后期，wiwi1和vasa才在EICs中富集。最后，我们追踪了产生四个PGC的细胞。我们的结果揭示了典范高生熊虫PGC的胚胎起源，并提供了缓步动物门早期细胞谱系的首次分子特征描述。我们预计这些观察结果将为表征这种动物中PGC发育的机制奠定基础。
