Spermatogenic columns, somatic cells, and the microenvironment of germinal cells in the testes of asteroids

Charles Wayne Walker

doi:10.1002/jmor.1051660107

An ultrastructural study of oogenesis, fertilization, and egg laying in a nemertean ectosymbiont of crabs, Carcinonemertes epialti (Nemertea, Hoplonemertea)

Canadian Journal of Zoology ◽

10.1139/z86-188 ◽

1986 ◽

Vol 64 (6) ◽

pp. 1256-1269 ◽

Cited By ~ 13

Author(s):

Stephen A. Stricker

Keyword(s):

Ultrastructural Study ◽

Gravid Female ◽

Somatic Cells ◽

Egg Laying ◽

Egg Mass ◽

Stages Of Development ◽

Endocytotic Vesicles ◽

Brachyuran Crabs ◽

Germinal Cells ◽

Sexually Mature

The nemertean worm Carcinonemertes epialti occurs ectosymbiotically on brachyuran crabs and becomes sexually mature while feeding on the eggs of its host. Gravid worms possess numerous saccular ovaries that lie among serially arranged diverticula of the intestine. The epithelium surrounding the lumen of each ovary contains germinal cells at various stages of development and somatic cells. Previtellogenic oocytes are typically situated in the subepidermal region of the ovarian epithelium, whereas vitellogenic oocytes tend to occur toward the intestine. The presence of numerous synthesizing organelles in vitellogenic oocytes indicates that at least some yolk constituents are produced within the ooplasm by an autosynthetic method. A supplemental form of heterosynthetic vitellogenesis may also occur, since somatic cells situated next to yolk-forming oocytes possess putative endocytotic vesicles that might help to transport yolk components derived from ingested crab eggs to the developing oocytes. Fully formed primary oocytes in the lumen of the ovary lack extracellular coats and typically measure 70–75 μm in diameter. Following fertilization, several egg strings that characteristically contain about 200 developing embryos are deposited by each gravid female in the egg mass of the crab.

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Embryological development of the cercarial tegument of Paramphistomum epiclitum in the planorbid snail, Indoplanorbis exustus

Journal of Helminthology ◽

10.1017/s0022149x00014668 ◽

1992 ◽

Vol 66 (4) ◽

pp. 243-254 ◽

Cited By ~ 4

Author(s):

T. S. Dunn ◽

P. H. Dang ◽

R. E. B. Hanna ◽

W. A. Nizami

Keyword(s):

Nurse Cell ◽

Somatic Cells ◽

Body Cavity ◽

Mechanical Support ◽

Nurse Cells ◽

Embryological Development ◽

Indoplanorbis Exustus ◽

Paramphistomum Epiclitum ◽

Cell Layers ◽

Germinal Cells

ABSTRACTCercariae develop from individual germinal cells occurring freely within the posterior body cavity of rediae. Individual germinal cells give rise to a germinal ball which becomes enveloped by increasing numbers of cytoplasmic extensions originating from specialized parenchyma-like cells, termed nursc cells. Up to eight cytoplasmic layers of nurse cells invest larger germinal balls. These layers may provide mechanical support for developing embryos and/or play a role in the provision of nutrients to them. The cercarial tegument develops from superficially located somatic cells in the germinal ball. Cytoplasmic extensions of presumptive tegumental cells fuse laterally to form a syncytial layer beneath the encapsulating nurse cell layers. As the cercarial tegument differentiates further, the cytoplasm of the nurse cell layers becomes vacuolated and ultimately these layers degenerate. The surface tegumental syncytia of intra-redial cercariae and newly released extra-redial cercariae are nucleated. Separate subtegumental perikarya develop with further differentiation of extra-redial cercariae.

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3-D examination of the cytoskeletal sheets of mammalian eggs

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100124975 ◽

1992 ◽

Vol 50 (1) ◽

pp. 914-915

Author(s):

Carolyn A. Larabell ◽

David G. Capco ◽

G. Ian Gallicano ◽

Robert W. McGaughey ◽

Karsten Dierksen ◽

...

Keyword(s):

Actin Filaments ◽

Somatic Cells ◽

Freeze Fracture ◽

Blastocyst Stage ◽

Cell Cytoplasm ◽

Planar Structures ◽

Cytoskeletal Network ◽

Entire Cell ◽

Cytoskeletal Networks ◽

Mammalian Eggs

Mammalian eggs and embryos contain an elaborate cytoskeletal network of “sheets” which are distributed throughout the entire cell cytoplasm. Cytoskeletal sheets are long, planar structures unlike the cytoskeletal networks typical of somatic cells (actin filaments, microtubules, and intermediate filaments), which are filamentous. These sheets are not found in mammalian somatic cells nor are they found in nonmammalian eggs or embryos. Evidence that they are, indeed, cytoskeletal in nature is derived from studies demonstrating that 1) the sheets are retained in the detergent-resistant cytoskeleton fraction; 2) there are no associated membranes (determined by freeze-fracture); and 3) the sheets dissociate into filaments at the blastocyst stage of embryogenesis. Embedment-free sections of hamster eggs viewed at 60 kV show sheets running across the egg cytoplasm (Fig. 1). Although this approach provides excellent global views of the sheets and their reorganization during development, the mechanism of image formation for embedment-free sections does not permit evaluation of the sheets at high resolution.

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