Asymmetry is defined during meiosis in the oocyte of the parthenogenetic nematode Diploscapter pachys.
Dev Biol, 483:13-21.
Asymmetric cell division is an essential feature of normal development and certainpathologies. The process and its regulation have been studied extensively in theCaenorhabditis elegans embryo, particularly how symmetry of the actomyosin corticalcytoskeleton is broken by a sperm-derived signal at fertilization, upstream ofpolarity establishment. Diploscapter pachys is the closest parthenogenetic relativeto C. elegans, and D. pachys one-cell embryos also divide asymmetrically. Howeverhow polarity is triggered in the absence of sperm remains unknown. In post-meioticembryos, we find that the nucleus inhabits principally one embryo hemisphere, thefuture posterior pole. When forced to one pole by centrifugation, the nucleusreturns to its preferred pole, although poles appear identical as concerns corticalruffling and actin cytoskeleton. The location of the meiotic spindle also correlateswith the future posterior pole and slight actin enrichment is observed at that polein some early embryos along with microtubule structures emanating from the meioticspindle. Polarized location of the nucleus is not observed in pre-meiotic D. pachysoocytes. All together our results are consistent with the idea that polarity of theD. pachys embryo is attained during meiosis, seemingly based on the location of themeiotic spindle, by a mechanism that may be present but suppressed in C. elegans.
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