THE TRANSFORMATION OF THE PLASMODIUM GALLINACEUM OOCYST IN AEDES AEGYPTI MOSQUITOES

Abstract

Sporoblast and sporozoite formation from oocysts of the avian malarial parasite, Plasmodium gallinaceum, after the seventh day of infection in Aedes aegypti mosquitoes offers an interesting example of differentiation involving the appearance and modification of several cellular components. Sporoblast formation is preceded by (a) invaginations of the oocyst capsule into the oocyst cytoplasm, (b) subcapsular vacuolization and cleft formation, (c) the appearance of small tufts of capsule material on the previously noted invaginations, and (d) linear dense areas located just below the oocyst plasma membrane which predetermine the site of emerging sporozoites from the sporoblast. The subcapsular clefts subdivide the once-solid oocyst into sporoblast peninsula. Within the sporoblast, nuclei migrate from the random distribution seen in the solid oocyst and come to lie at the periphery of the sporoblast just below the linear dense areas noted in the earlier stage. A typical nuclear fiber apparatus occurs in most of the nuclei seen in random sections at this stage although such a fiber apparatus may occasionally be seen in the solid oocyst stage. The nucleus, its associated fiber apparatus, and the overlying dense area appear to induce the onset of sporozoite budding from the sporoblast as well as the formation of the sporozoite pellicular complex and the paired organelle precursor. Several mitochondria are present in each sporozoite, in contrast to the single mitochondrion seen in the merozoites of the erythrocytic and exoerythrocytic stages of avian malaria infection. The paired organelles and associated dense inclusion bodies are formed by condensation of an irregular meshwork of membranebound, coarse, dense material. The nature of small, particulate cytoplasmic inclusions is described.

Arrested Oocyst Maturation in Plasmodium Parasites Lacking Type II NADH:Ubiquinone Dehydrogenase

“…For P. berghei, cristae have been reported for pre-erythrocytic stages (50), gametocytes, sporogonic stages (51), and oocysts (52,53), whereas trophozoites were termed acristate (51). Similarly, few cristae were found in asexual stages of P. falciparum and more in gametocytes (54,55).…”

Structures and Functions of the Nuclear Envelope

“…Plaquelike differentiations within the nuclear envelope resembling those of the Ascomycetes have been described in some protozoa such as the malarial parasites (Aikawa et al, 1967;Terzakis et al, 1967;Aikawa and Beaudoin, 1968;Scalzi and Bahr, 1968), hypermastigid flagellates (Hollande and Valentin, 1968), and radiolarians (Hollande et al, 1969). Some authors have suggested that such polar plaques might represent a specialized pore complex (Robinow and Marak, 1966;Scalzi and Bahr, 1968;Unger et al, 1971;Peters on et al, 1972.…”

The fine structure of Leucocytozoon simondi. V. The oocyst

“…Early light microscope studies on the development of Plasmodium oocysts have indicated a similar location in the midgut of the mosquito vector (12). In their recent ultrastructural studies of oocyst transformation in P. gallinacezm and P. cynomolgi, Terzakis et al (18,19,20) have suggested that the oocysts come to lie on "the external surface of the epithelial basal lamina." This indicates that the ookinete must penetrate through the basal lamina before transforming into an oocyst.…”

“…When ookinetes of Leucocytozoon round up beneath the basal lamina of the midgut epithelium to form oocysts, they undergo no further growth, and in most species less than 100 sporozoites are formed around a single sporoblast center (7). Oocysts of Plasmodium, on the other hand, may undergo a 5000-fold increase in volume during their development, and thousands of sporozoites are formed around multiple sporoblast centers (13,18,19,20,22). The latter are produced by subcapsular vacuolization and cleft formation, processes which were not observed during the development of the smaller oocysts of L. simondi.…”

“…There have been several ultrastructural studies on the transformation of oocysts of Plasmodium species (18,19,20,21,22). This phase of development has been largely neglected in the other Haemosporidia.…”