ISSN:
0148-7280
Keywords:
spermatogenesis
;
Actinia fragacea
;
ultrastructure
;
testicular cyst
;
trophonema
;
Life and Medical Sciences
;
Cell & Developmental Biology
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Biology
Notes:
Spermatogenesis in the sea anemone Actinia fragacea takes place in numerous testicular cysts located in the mesoglea of the gonads. Prospermatogonia arise among the bases of the gonadal epithelial cells bordering the mesoglea, and later migrate into the mesoglea to establish the cysts. The prospermatogonia arise singly, but soon most are found as small groups within the endoderm. They are small cells, 6-7 μm in diameter, and have relatively large nuclei with a single nucleolus. Their cytoplasm is dense, and contains dense bodies and nuage material as well as Golgi, mitochondria, and individual cisternae of endoplasmic reticulum. Each prospermatogonium bears a flagellum, originating in a groove or channel in the cytoplasm.A small proportion of prospermatogonia enter the mesoglea singly, but most migrate as elongate groups or “slugs” of cells. As they enter, the groups often become constricted into hour-glass shapes, and they become covered by the endodermal basal lamina. During the later stages of entry, the last part of the group to enter retains contact with the bases of the epithelial cells, which are dragged into the mesoglea behind the germ cells. This contact between germ cells and endoderm persists throughout spermatogenesis and prevents closure of the mesoglea behind the group. The endodermal cells involved begin specialization to form the trophonema. Once entry is complete, the groups enlarge rapidly to form the testicular cysts. A small number of germ cells appear to remain behind in the endoderm after most have entered the mesoglea, and the possible significance of these cells is discussed.
Additional Material:
12 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/mrd.1120090307
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