Dynamic organization of microtubules and microtubule-organizing centers during the sexual phase of a parasitic protozoan, Lecudina tuzetae (Gregarine, Apicomplexa).

Lecudina tuzetae is a parasitic protozoan (Gregarine, Apicomplexa) living in the intestine of a marine polychaete annelid, Nereis diversicolor. Using electron and fluorescence microscopy, we have characterized the dynamic changes in microtubule organization during the sexual phase of the life cycle. The gametocyst excreted from the host worm into seawater consists of two (one male and one female) gamonts in which cortical microtubule arrays are discernible. Each gamont undergoes multiple nuclear divisions without cytokinesis, resulting in the formation of large multinucleate haploid cells. After cellularization, approximately 1000 individual gametes are produced from each gamont within 24 h. Female gametes are spherical and contain interphase cytoplasmic microtubule arrays emanating from a gamma-tubulin-containing site. In male gametes, both interphase microtubules and a flagellum with "6 + 0" axonemal microtubules extend from the same microtubule-organizing site. At the beginning of spore formation, each zygote secretes a wall to form a sporocyst. Following meiotic and mitotic divisions, each sporocyst gives rise to eight haploid cells that ultimately differentiate into sporozoites. The ovoid shaped sporocyst is asymmetric and forms at least two distinctive microtubule arrays: spindle microtubules and microtubule bundles originating from the protruding apical end corresponding to the dehiscence pole of the sporocyst. Because antibodies raised against mammalian centrosome components, such as gamma-tubulin, pericentrin, Cep135, and mitosis-specific phosphoproteins, react strongly with the microtubule-nucleating sites of Lecudina, this protozoan is likely to share common centrosomal antigens with higher eukaryotes.

Organ of Bellonci of an Antarctic crustacean, the marine isopod Glyptonotus antarcticus.

The paired organ of Bellonci protrudes from the optic lobe of the giant Antarctic isopod, Glyptonotus antarcticus. It is linked to the cortex by a broad peduncle. No connection to the cuticle or "sensory pore organ" was found. A cluster of sensory-like cells forms two outer ciliary segments branching into numerous microvilli with microtubules. The putative sensory somata are irregular in shape and contain a very high density of glycogen granules. The two outer segments sprout from two pits of the soma in different directions, forming a right angle. Glial cells wrap around the sensory cells and also delimit lacunae into which bundles of microvilli project. These lacunae contain electron-dense granules of small size and with species-specific patterns. Lacunae and dense granules show features typical of a degeneration process in the sensory cells. This general morphology corresponds to the unilobular type of organ of Bellonci, known in other isopods; it differs from the plurilobular type with onion bodies found in other Crustacea.