Fine Structure of Gametogony and Oocyst Formation in Sarcocystis sp. in Cell Culture

Abstract

SYNOPSIS Fine structure of gametocytes and oocyst formation of Sarcocystis sp. from Quiscalus quiscula Linnaeus grown in cultured embryonic bovine kidney cells was studied. Microgametocytes measured up to ∼5 μm diameter. During nuclear division of the microgametocyte, dense plaques were found adjacent to the nucleus just beneath the pellicle; occasionally microtubules were present within these plaques. These microtubules subsequently formed 2 basal bodies with a bundle of 4 microtubules between them. Microgametocytes also contained numerous mitochondria, micropores, granules, vacuoles, and free ribosomes. Each microgamete was covered by a single membrane and consisted of 2 basal bodies, 2 flagella, a bundle of 4 microtubules, a perforatorium, a mitochondrion, and a long dense nucleus which extended anteriorly and posteriorly beyond the mitochondrion. The bundle of 4 microtubules is thought to be the rudiment of a 3rd flagellum. Macrogametes were covered by a double membrane pellicle, and contained a large nucleus (∼2.5 μm), vacuoles, and a dilated nuclear envelope connected with the rough endoplasmic reticulum (ER). In young macrogametes (∼4 μm), the ER was arranged in concentric rows in the cortical region, and several sizes of dense granules were found in the cytoplasm. However, in later stages (∼8 μm) the ER was irregularly arranged and was dilated with numerous cisternae; only large dark granules remained and a few scattered polysaccharide granules were found. No Golgi apparatus or micropores were observed. After the disappearance of dark granules 5 concentric membranes appeared. Four of these fused to form an oocyst wall composed of a dense outer layer (∼66 nm thick) and a thin inner layer (∼7 nm). The 5th or innermost membrane surrounded the cytoplasmic mass which was covered by a 2‐layered pellicle and contained a nucleus, small amounts of ER, large vacuoles, and mitochondria. The sexual stages described greatly resemble those of Eimeria and Toxoplasma.

Ultrastructural changes during in vitro encystment ofBlastocystis hominis

“…In their ultrastructural study on Giardia lamblia, Reiner et al (1990) showed that a regulated pathway of transport and secretion of cyst wall antigens via a novel class of large, osmiophilic secretory vesicles, the encystation-specific vesicles, was assembled during encystation. Vetterling et al (1973) and Zaman and Colley (1975) observed that the wall-forming bodies in some species of Sarcocystis gave rise to the outer layer of the oocyst wall. The inclusion-like bodies (SAI) lining the rim of the cytoplasm in our study could be similar to the encystation secretory vesicle in Giardia and to the wall-forming bodies in coccidians previously mentioned by other workers and may perform similar functions.…”

Cytoskeleton of Apicomplexan Parasites

“…The male gamete (microgamete) is flagellated and swims to the female gamete (macrogamete) to carry out fertilization. The anterior end of apicomplexan microgametes is pointed and contains three basal bodies in close proximity to the apical pole (116,137,158,181). These basal bodies nucleate two or three flagella that extend past the nucleus and away from the apical end.…”

“…In some species this third flagellum is present only in rudimentary form as a band of microtubules that extends along the length of the gamete. In contrast to the atypical centrioles observed in other stages, the basal body of male gametes has a typical triplet microtubule structure with ninefold symmetry and the flagellar axoneme contains a conventional 9ϩ2 arrangement of doublet microtubules surrounding the central pair of microtubules (137,(158)(159)(160)181). In Plasmodium, genesis of the basal bodies involves an intermediate 9ϩ1 singlet form similar to the centrioles in other apicomplexans (157).…”

Fine structure of the development ofSarcocystis singaporensisinPython reticulatusfrom macrogamont to sporulated oocyst stage

“…including S. singaporensis only a single type of wallforming-like body present, also referred to as "dense granules" or "bodies" (Vetterling et al, 1973;Entzeroth et al, 1985). Viewing the fine structural evidences available to date, the species-specificity of their configuration is certain.…”

“…Viewing the fine structural evidences available to date, the species-specificity of their configuration is certain. Less certain (see Entzeroth et al, 1985) is their claimed role in wall formation (Vetterling et al, 1973;Zaman & Colly, 1975). A seemingly anlagen of wall-forming-like bodies within the perimeter of a Golgi-like organelle recalls the suggested role of the Golgi system in the formation of type 1 wall-forming bodies in eimerians (Scholtyseck et al, 1971).…”