Histochemical and ultrastructural studies of oogenesis, vitellogenesis and eggshell formation in acanthoparyphium spinulosum (trematoda: echinostomatidae), 1985

Moore, Revelyn M.

1980-1989

This investigation presents a composite of the cytolog-ical events of oogenesis, vitellogenesis and eggshell formation at the ultrastructural level in a poorly known echinostomid trematode, A. spinulosum. For comparison, histochemieal methods which demonstrate basic proteins, phenols and phenolase were used to identify reproductive structures which produce eggshell precursors of the quinone-tanning system. It was observed that the tanning, system is localized specifically in the shell globules of vitelline cells and eggshells. Through transmission electron microscopy (TEM), it was observed that organization of the granular endoplasmic reticulum and Golgi complex is associated with synthesis of cortical granules in dveloping oocytes. At the onset of maturation of ova, the cortical granules are characteristically arranged immediately beneath the plasma membrane. The nucleus of mature oocytes have dispersed chromatin, which suggests that oogenesis proceeds as far as the diplotene stage of the first division of meiosis. Furthermore, it was observed that "nucleolus-like bodies" occur in close association with mitochondria in these cells. However, the significance of this phenomenon is not clearly understood. The vitelline follicles contain cells in various stages of vitellogenesis and a number of nurse cells. In contrast to immature cells, maturing vitelline cells are characterized by a well-organized granular endoplasmic reticulum and Golgi complex, which are associated with the synthesis of shell globules. These globules are arranged beneath the plasma membrane of mature cells. These cells also contain copious amounts of lipid droplets and glycogen granules. In addition, it was observed that cytoplasmic extensions of nurse cells form junctional complexes with vitelline cells, suggesting that a mechanism of selective transport exists between these cells. There is evidence that initiation of eggshell formation occurs in the distal ootype and proximal uterus. Reticular secretions from membranous body cells of Mehlis * gland were seen on the inner and outer surfaces of egg capsules in these regions. Granular secretions from dense body cells of Mehlis* gland were also observed adhering to egg capsules in the distal uterus. In contrast to young eggs, the older shells are several times thicker and appear to be blotched with electron-lucid areas, some of which have finely granular cores. It is suggested that the appearance of the older capsules may represent some phase of the tanning process. In summary, egg formation in Acanthoparyphium spinulosum appears to follow the general pattern of most other trematodes. However, when comparing oogenesis and vitellogenesis of A_. spinulosum to those processes in other trematodes, particularly Schistosoma mansoni and Fasciola hepatica, a greater variance was observed in the histochemistry and ultrastructure of mature vitelline cells. The degree of variance among species may be a reflection of differences in environmental factors which affect development of the eggs.

text

application/pdf

1985-12-01

dissertation

Doctor of Philosophy (PhD)

Atlanta University

Department of Biology

LeFlore, William B.

Clark Atlanta University

Georgia--Atlanta

http://hdl.handle.net/20.500.12322/cau.td:1985_moore_revelyn_m