Oogenesis and oocytes |
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Authors: | Eckelbarger Kevin J |
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Institution: | (1) Darling Marine Center, School of Marine Sciences, University of Maine, 193 Clark’s Cove Road, Walpole, Orono, 04573, 04469, ME, U.S.A |
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Abstract: | The morphological features of polychaete ovarian morphology and oogenesis are reviewed. Some basic information on ovarian
structure and/or oogenesis is known for slightly more than half of recognized polychaete families although comprehensive studies
of oogenesis have been conducted on 0.1 of described species. Relative to other major metazoan groups, ovarian morphology
is highly variable in the Polychaeta. While some species appear to lack a defined ovary, most have paired organs that are
segmentally repeated to varying degrees depending on the family. Ovaries vary widely in their location but are most frequently
associated with the coelomic peritoneum, parapodial connective tissue, or elements of the circulatory system. The structural
complexity of the ovary is correlated with the type of oogenesis expressed by the species. In some polychaetes, extraovarian
oogenesis occurs in which previtellogenic oocytes are released into the coelom from a simple ovary where differentiation occurs
in a solitary fashion or in association with nurse cells or follicle cells. In other species, intraovarian oogenesis occurs
in which oocytes undergo vitellogenesis within the ovary, often in association with follicle cells that may provide nutrition.
Vitellogenesis probably includes both autosynthetic and heterosynthetic processes; autosynthesis involves the manufacture
of yolk bodies via the proteosynthetic organelles of the oocyte whereas heterosynthesis involves the extraovarian production
of female-specific yolk proteins that are incorporated into the oocyte through a receptor-mediated process of endocytosis.
Variation in the speed of egg production varies widely and appears to be correlated with the vitellogenic mechanism employed.
Mature ova display a wide range of egg envelope morphologies that often show some intrafamilial similarities. |
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Keywords: | oogenesis ultrastructure gametogenesis |
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