Morphogenesis of the polaroplast in Enterocytozoon bieneusi Desportes et al., 1985, a microsporidan parasite of HIV infected patients

The development of the microsporidan Enterocytozoon bieneusi is characterized by the formation of the extrusion apparatus of the spore before the division of the sporogonial plasmodium into sporoblasts. The extrusion apparatus consists of the classical polar tube, polaroplast and anchoring disc reported in the other Microsporida. It is shown that the precursors of the polaroplast are already present in early developmental stages i.e. uninucleate meronts. Each consists of an aggregate of vesicles which originates from the endoplasmic reticulum and develops into stacks of saccules. The saccules, which display the morphologic polarity of a Golgi apparatus, correspond to the future polaroplasts. The nuclear divisions and concomitant production of new aggregates of vesicles result in the formation of plasmodia containing several nuclei, each of them closely associated with a polaroplast. Elongated cisternae of the endoplasmic reticulum, characteristic of the plasmodial cytoplasm, contribute to the differentiation of the polar tubes. The extrusion apparatus is achieved after the association of the polar tubes with the preformed polaroplasts. In most Microsporida the formation of the extrusion apparatus occurs in the sporoblasts, in which the polar tube emerges from a reticular structure. Thus the differentiation of the extrusion apparatus observed in E. bieneusi may be considered as another characteristic of this microsporidan species.