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EXPLORE ONTOLOGY GRAPH:
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All experimental data displayed here is from Davies et. al., 2017, Smed Embryogenesis Molecular Staging Resource
DESCRIPTION:
Zygote(s) and yolk cells are packaged into egg capsules laid by the parent. The single cell stage can be visualized in histological cross-sections: spherical zygotes, ~ 25-30 µm in diameter, are surrounded by a halo of yolk cells reminiscent of the corona radiata. During early cleavage divisions blastomeres cycle asynchronously, without retaining direct cell-cell contacts, within a yolk syncytium. Embryos are readily apparent in histologically stained sections but may be difficult to locate in live, unstained specimens.
Figure 1 - figure supplement 1: Histological cross-sections of Stage 1 embryos. A-D: Four independent examples of the single cell stage (S1), either metaphase II arrested oocytes or zygotes, in paraffin embedded, hematoxylin and eosin stained sectioned egg capsules fixed at 1-2 days post egg capsule deposition (20˚C). The entire capsule is shown in D. Black arrowheads: metaphase II arrested oocytes or zygotes, surrounded by a corona of yolk cells. Scale bars: 25 µm (A-C); 100 µm (D).
