Elsevier

Developmental Biology

Volume 302, Issue 2, 15 February 2007, Pages 591-600
Developmental Biology

The Oikopleura coenocyst, a unique chordate germ cell permitting rapid, extensive modulation of oocyte production

https://doi.org/10.1016/j.ydbio.2006.10.021Get rights and content
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Abstract

The ability to adjust reproductive output to environmental conditions is important to the fitness of a species. The semelparous, chordate, Oikopleura dioica, is particularly adept in producing a highly variable number of oocytes in its short life cycle. Here we show that this entails an original reproductive strategy in which the entire female germline is contained in a single multinucleate cell, the “coenocyst”. After an initial phase of syncytial nuclear proliferation half of the nuclei entered meiosis whereas the other half became highly polyploid. The inner F-actin network, with associated plasma membranes, formed a highly ramified infrastructure in which each meiotic nucleus was contained in a pseudo-compartmentalized pro-oocyte linked to the common cytoplasm via ring canals. At a set developmental time, a subset of the pro-oocytes was selected for synchronous growth and the common coenocyst cytoplasm was equally partitioned by transfer through the ring canals. Examination of related species indicated that the coenocyst arrangement is a conserved feature of Appendicularian oogenesis allowing efficient numerical adjustment of oocyte production. As Appendicularia are the second most abundant class of zooplankton, with a world-wide distribution, the coenocyst is clearly a common and successful reproductive strategy on a global scale.

Keywords

Vasa
Nuage
Gamete
Larvacean
Germline cyst
Intercellular bridge
Clutch manipulator
Ascidian
Prophase I
Endoreplication

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