Malaria is caused by intraerythrocytic protozoan parasites belonging to Plasmodium spp. (phylum Apicomplexa) that produce significant morbidity and mortality, mostly in developing countries. Plasmodium parasites have a complex life cycle that includes multiple stages in anopheline mosquito vectors and vertebrate hosts. During the life cycle, the parasites undergo several cycles of extreme population growth within a brief span, and this is critical for their continued transmission and a contributing factor for their pathogenesis in the host. As with other eukaryotes, successful mitosis is an essential requirement for Plasmodium reproduction; however, some aspects of Plasmodium mitosis are quite distinct and not fully understood. In this review, we will discuss the current understanding of the architecture and key events of mitosis in Plasmodium falciparum and related parasites and compare them with the traditional mitotic events described for other eukaryotes. SERIAL MITOSIS IS A COMMON THEME IN MALARIA PARASITE REPRODUCTIONThere are four critical points in the life cycle of Plasmodium parasites in which a small number of parasites rapidly multiply to generate much larger populations (60). These life cycle stages are male gamete development (72), sporozoite formation (5, 13), liver-stage development (68), and blood-stage asexual reproduction (9, 60). The first two of these processes occur within the mosquito vector, and the second two processes take place in the vertebrate host. During each of these Plasmodium life cycle stages, the parasites increase their numbers by using serial rounds of mitosis to create multinuclear cells and then orchestrating mass cytokinesis events to release their progeny (71). Mitosis is the process by which eukaryotic cells segregate their chromosomes in preparation for cell division (33,47,51).To create male gametes in preparation for sexual reproduction, the parasite begins with a haploid (1n) cell called a microgametocyte which is ingested by the mosquito during a blood meal (34,72). Within 12 min, this microgametocyte undergoes three rapid rounds of DNA synthesis and mitosis to generate a cell with an 8n genomic complement (35,36,73). Over the next 3 min, these genomes separate from one another and eight new haploid (1n) male gametes begin to assemble from the surface of the original cell (4, 69, 71).Within the mosquito midgut, a small number of the male gametes will fuse with female gametes that have also developed in this compartment, and this fusion will create diploid (2n) zygotes (15). These zygotes develop into motile ookinetes (4n) (36) that ultimately become embedded in the basal lamina beneath the midgut epithelial wall as oocysts (14). Over the course of several days, a single oocyst undergoes 10 to 11 rounds of DNA synthesis and mitosis to create a syncytial cell (sporoblast) with thousands of nuclei (61,70,82). In a massive cytokinesis event, thousands of haploid (1n) daughter sporozoites assemble from the surface of the mother cell (61, 67), and these infective sporozo...
The small GTPase racE is essential for cytokinesis in Dictyostelium. We found that this requirement is restricted to cells grown in suspension. When attached to a substrate, racE null cells form an actomyosin contractile ring and complete cytokinesis normally. Nonetheless, racE null cells fail completely in cytokinesis when in suspension. To understand this conditional requirement for racE, we developed a method to observe cytokinesis in suspension. Using this approach, we found that racE null cells attempt cytokinesis in suspension by forming a contractile ring and cleavage furrow. However, the cells form multiple blebs and fail in cytokinesis by regression of the cleavage furrow. We believe this phenotype is caused by the extremely low level of cortical tension found in racE null cells compared to wild-type cells. The reduced cortical tension of racE null cells is not caused by a decrease in their content of F-actin. Instead, mitotic racE null cells contain abnormal F-actin aggregates. These results suggest that racE is essential for the organization of the cortical cytoskeleton to maintain proper cortical integrity. This function of racE is independent of attachment to a substrate, but can be bypassed by other signaling pathways induced by adhesion to a substrate.
The cause of Lyme disease, Borrelia burgdorferi, was discovered in 1983. A 2-tiered testing protocol was established for serodiagnosis in 1994, involving an enzyme immunoassay (EIA) or indirect fluorescence antibody, followed (if reactive) by immunoglobulin M and immunoglobulin G Western immunoblots. These assays were prepared from whole-cell cultured B. burgdorferi, lacking key in vivo expressed antigens and expressing antigens that can bind non-Borrelia antibodies. Additional drawbacks, particular to the Western immunoblot component, include low sensitivity in early infection, technical complexity, and subjective interpretation when scored by visual examination. Nevertheless, 2-tiered testing with immunoblotting remains the benchmark for evaluation of new methods or approaches. Next-generation serologic assays, prepared with recombinant proteins or synthetic peptides, and alternative testing protocols, can now overcome or circumvent many of these past drawbacks. This article describes next-generation serodiagnostic testing for Lyme disease, focusing on methods that are currently available or near-at-hand.
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