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A histochemical and ultrastructural study of the ovary and vitellogenesis in the dogfish Squalus acanthias Reid, James Allen

Abstract

Protein yolk formation is being studied in an ever increasing number of organisms and in each the method of formation (i.e. intra-oocytic vs extraoocytic) and the organelles involved (Golgi, mitochondria etc.) differ even though the final product is markedly similar. Previous emphasis on elasmobranchs in this laboratory and the availability of the specimen favoured the selection of Squalus acanthias as the experimental animal as veil as the lack of any pertinent studies on its ovary or vitellogenic processes. While examining the problem of yolk formation with both histochemical and ultrastructural techniques, several other critical areas of investigation were pursued. As a result, the composition of the follicular envelope and the formation of its associated membranes, the surface epithelium, the tunica albuginea, the ovarian cortex and the lacunae border cells were also examined. An examination of representative oocytes from 0.1 to 4.0 mm in diameter revealed many important facts. First, these oocytes are in a prolonged diplotene with up to 100 nucleoli present, each rich in rRNA represented ultrastructurally by their granular nature. Secondly, a complex Balbiani body rich in protein and RNA and composed of mitochondria and SER is present. Here, this mitochondrial mass is the center for mitochondrial multiplication. Thirdly, lipid yolk is formed before proteinaceous yolk and it arises de novo in the ooplasm from extra-oocytically derived materials. Finally, proteid yolk arises from two sources. Initially, multigranular (MGB) and multivesicular (MVB) bodies form from Golgi, SER, micropinocytotic vesicles and vesicles derived from the nuclear membrane which fuse together forming granular-vesicular bodies (GVB). In oocytes larger than 0.k mm, distended Golgi lamellae, SER cisternae and loops of SER vesicles form limiting membranes and take up MGBs, MVBs and small GVBs. The contents of these large GVBs then dissolve, reaggregate and crystallize forming a mature yolk platelet. Of the other areas examined, the basal lamina, the vitelline membrane and the follicle cells were the most relevant to yolk formation. The follicle cells were implicated in the formation of both the lamina and the vitelline membrane. The former are predominantly acid and sulphated mucopolysaccharides while the latter is a protein-polysaccharide complex. Both membranes provide support and chemical selectivity. The evidence for steroid activity in the follicle cells of these stages was inconclusive.

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