Apical complex

Abstract: Cryptosporidium species cause acute gastroenteritis and diarrhoea worldwide. They are members of the Apicomplexa--protozoan pathogens that invade host cells by using a specialized apical complex and are usually transmitted by an invertebrate vector or intermediate host. In contrast to other Apicomplexans, Cryptosporidium is transmitted by ingestion of oocysts and completes its life cycle in a single host. No therapy is available, and control focuses on eliminating oocysts in water supplies. Two species, C. hominis and C. parvum, which differ in host range, genotype and pathogenicity, are most relevant to humans. C. hominis is restricted to humans, whereas C. parvum also infects other mammals. Here we describe the eight-chromosome approximately 9.2-million-base genome of C. hominis. The complement of C. hominis protein-coding genes shows a striking concordance with the requirements imposed by the environmental niches the parasite inhabits. Energy metabolism is largely from glycolysis. Both aerobic and anaerobic metabolisms are available, the former requiring an alternative electron transport system in a simplified mitochondrion. Biosynthesis capabilities are limited, explaining an extensive array of transporters. Evidence of an apicoplast is absent, but genes associated with apical complex organelles are present. C. hominis and C. parvum exhibit very similar gene complements, and phenotypic differences between these parasites must be due to subtle sequence divergence.

Abstract: Drosophila neuroblasts are a model system for studying asymmetric cell division: they divide unequally to produce an apical neuroblast and a basal ganglion mother cell that differ in size, mitotic activity and developmental potential During neuroblast mitosis, an apical protein complex orients the mitotic spindle and targets determinants of cell fate to the basal cortex1, but the mechanism of each process is unknown Here we show that the tumour-suppressor genes lethal giant larvae (lgl) and discs large (dlg) regulate basal protein targeting, but not apical complex formation or spindle orientation, in both embryonic and larval neuroblasts Dlg protein is apically enriched and is required for maintaining cortical localization of Lgl protein Basal protein targeting requires microfilament and myosin function, yet the lgl phenotype is strongly suppressed by reducing levels of myosin II We conclude that Dlg and Lgl promote, and myosin II inhibits, actomyosin-dependent basal protein targeting in neuroblasts

Abstract: About the turn of the century the Apicomplexa plus some other groups were called Sporozoa. With the advent of the electron microscope, it was realized that most "Sporozoa" have an apical complex; those which do not (the Microspora, Myxozoa, and Ascetospora) were removed and the name Apicomplexa was put forward by Dr. Levine in 1970. Most of the important Apicomplexa fall into five main groups: the gregarines, haemogregarines (about which there is relatively little known), coccidia, haemosporids, and piroplasms. These two volumes classify, list (with synonyms and hosts) and give references to descriptions of the approximately 4600 species of Apicomplexa that have been named so far. Volume I contains an 8-page introduction and covers the gregarines and coccidia (including the haemogregarines). In volume II are the Sarcocystidae (the predator-prey coccidia) the haemosporids (the malaria and related parasites), the piroplasms, and some parasites of uncertain affinities. The Apicomplexa are divided into over 300 genera and more than 60 families, but this division is deceiving. Most of these groups contain only one or a few species. There are fewer than 50 genera with 10 or more named species, and only 8 with 100 or more. These 8 genera (Eimeria, Haemogregarina, Gregarina, Isospora, Haemoproteus, Plasmodium, Sarcocystis, and Babesia) comprise more than half of the species.

Abstract: The apical complex of Toxoplasma gondii is widely believed to serve essential functions in both invasion of its host cells (including human cells), and in replication of the parasite. The understanding of apical complex function, the basis for its novel structure, and the mechanism for its motility are greatly impeded by lack of knowledge of its molecular composition. We have partially purified the conoid/apical complex, identified ~200 proteins that represent 70% of its cytoskeletal protein components, characterized seven novel proteins, and determined the sequence of recruitment of five of these proteins into the cytoskeleton during cell division. Our results provide new markers for the different subcompartments within the apical complex, and revealed previously unknown cellular compartments, which facilitate our understanding of how the invasion machinery is built. Surprisingly, the extreme apical and extreme basal structures of this highly polarized cell originate in the same location and at the same time very early during parasite replication.