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

1980 ◽  
Vol 166 (1) ◽  
pp. 81-107 ◽  
Author(s):  
Charles Wayne Walker
Keyword(s):  
1986 ◽  
Vol 64 (6) ◽  
pp. 1256-1269 ◽  
Author(s):  
Stephen A. Stricker

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.


1992 ◽  
Vol 66 (4) ◽  
pp. 243-254 ◽  
Author(s):  
T. S. Dunn ◽  
P. H. Dang ◽  
R. E. B. Hanna ◽  
W. A. Nizami

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.


Author(s):  
Carolyn A. Larabell ◽  
David G. Capco ◽  
G. Ian Gallicano ◽  
Robert W. McGaughey ◽  
Karsten Dierksen ◽  
...  

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.


2014 ◽  
Author(s):  
Domenico Iuso ◽  
Paola Toschi ◽  
Debora Agata Anzalone ◽  
Marta Czernik ◽  
Grazyna Ewa Ptak ◽  
...  

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