Electron Microscopic and Histochemical Studies of Sporozoite Formation in Plasmodium berghei*

Abstract

SYNOPSIS. Observations were made on the differentiation of fine structure during sporogonic development of Plasmodium berghei. The oocyst in the process of sporozoite formation is an encapsulated structure 30‐40 μ in diameter. It typically develops while in an extracellular position, attached to the basement membrane of the mosquito midgut and projecting into the mosquito hemocoel. Occasionally, however, ookinetes passing thru the midgut epithelial cells may become impacted within a cell so that the resulting oocyst develops intracellularly. Each oocyst has a large differentiating region, the sporoblastoid body. This body contains large dividing nuclei which are Feulgenpositive, and a cytoplasm which includes mitochondria, dense rodlike structures, cytoplasmic membranes, cisternae and vacuolar structures, Golgi material, and ribosomes which are both free and membrane‐associated. Sporozoite budding takes place along the surface of the sporoblastoid body. Bits of a new membrane condense under the plasma membrane which bounds the sporoblastoid body. These 2‐membraned sites then bulge out, continue to elongate, and eventually become sporozoites. The various nuclear and cytoplasmic components of the sporoblastoid body are passed into the sporozoites during their elongation. In addition, the sporozoite develops a system of elogate, subpellicular microtubules, possibly contractile in function. The pellicle of the sporozoite is broken by an opening, the cytostome (micropyle). The anterior end is truncate.

The biology of malarial parasite in the mosquito: a review

“…stephensi and An. quadrimaculatus (Vanderberg et al 1967). The same localization was described in P. vinckei by Bafort (1971) who concluded that both mechanical pressure and physiological mechanisms play a role in the movement of oocysts to the hemocoelomic surface.…”

“…Oocyst development is predominantly extracellular (Duncan et al 1960, Garnham et al 1969, Howells & Davies 1971), but occasionally occurs within the midgut epithelial cell (Vanderberg et al 1967, Bafort 1971, Beaudoin et al 1974. The ookinete usually comes to rest beneath the basal lamina 18-24 hr after the infective blood meal (Sinden 1978).…”

“…The young oocyst is enveloped by a thick plasmalemma that is covered on the hemocoelomic surface by a fibrous basal lamina. Oocysts from the second day onwards are also covered by an amorphous capsule which becomes reduced in thickness at maturity (Vanderberg et al 1967, Aikawa 1971, Strome & Beaudoin 1974.…”

“…Autoradiographic studies with P. gallinaceum in Ae. aegypti mosquitoes indicated that 3 H-leucine is uniformly incorporated throught the oocyst within 15 min of injection into hemocoele (Vanderberg et al 1967).…”

Cytoskeleton of Apicomplexan Parasites

“…The number of subpellicular microtubules ranges from a band of 3 or 4 in the tiny Plasmodium falciparum merozoites to ϳ60 in the considerably larger Plasmodium ookinetes (2,3,12,26,136,156,157). In coccidian parasites (Toxoplasma and Eimeria), the subpellicular microtubules are evenly spaced beneath the periphery of the pellicle; however, in Plasmodium species, most of the microtubules occupy twothirds of the circumference and one microtubule is centered within the latter one-third of the pellicle (3,157,180). P. falciparum merozoites are an exception to this spacing generalization; they have a reduced number (three or four) of subpellicular microtubules termed f-MAST (falciparum merozoite-associated assemblage of subellicular microtubules) that extend down one side of the merozoite membrane from the apex toward the posterior (12,59).…”