Authors: Piotr Świątek Janusz Kubrakiewicz Jerzy Klag
Publish Date: 2009/05/05
Volume: 337, Issue: 1, Pages: 137-148
Abstract
Animal germ cells tend to form clonal groups known as clusters or cysts Germ cells within the cyst cystocytes are interconnected by intercellular bridges and thus constitute a syncytium Our knowledge of the mechanisms that control the formation of germcell clusters comes from extensive studies carried on model organisms Drosophila Xenopus Germcell clusters have also been described in worms annelids flat worms and nematodes although their architecture differs significantly from that known in arthropods or vertebrates Their peculiar feature is the presence of a central anucleate cytoplasmic core cytophore rachis around which the cystocytes are clustered Each cystocyte in such a cluster always has one intercellular bridge connecting it to the central cytoplasmic core The way that such clusters are formed has remained a riddle for decades By means of light fluorescence and electron microscopy we have analysed the formation and architecture of cystocyte clusters during early stages of spermatogenesis and oogenesis in a few species belonging to clitellate oligochaetous annelids Our data indicate that the appearance of germ cells connected via a central cytophore is accompanied by a specific orientation of the mitotic spindles during cystocyte divisions Spindle long axes are always oriented tangentially to the surface of the cytophore In consequence cystocytes divide perpendicularly to the plane of the existing intercellular bridge Towards the final stages of cytokinesis the contractile ring of the cleavage furrow merges with the rim of the intercellular bridge that connects the dividing cystocyte with the cytophore and forces partition of the existing bridge into two new bridgesWe are grateful to Sylwia Nowak for her skillful technical assistance with the transmission electron microscopy and to Arnold Garbiec postgraduate student at the Zoological Institute University of Wrocław for his invaluable help with the fluorescence methods We also acknowledge the art work of Łukasz Simiczyjew Fig 2e f Fig 4
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