Geographic distribution and frequency of a taurine Bos taurus and an indicine Bos indicus Y specific allele amongst sub-saharan African cattle breeds.

We report for the first time, and for the whole of sub-Saharan Africa, the geographical distribution and the frequency of an indicine and a taurine Y specific allele amongst African cattle breeds. A total of 984 males from 69 indigenous African populations from 22 countries were analysed at the microsatellite locus INRA 124. The taurine allele is probably the oldest one on the continent. However, the taurine and the indicine alleles were present in 291 males (30%), and 693 males (70%), respectively. More particularly, 96% of zebu males (n = 470), 50% of taurine males (n = 263), 29% of sanga males (crossbreed Bos taurus x Bos indicus, n = 263) and 95% of zebu x sanga crossbred males (n = 56) had the indicine allele. The Borgou, a breed classified as zebu x taurine cross showed only the zebu allele (n = 12). The indicine allele dominates today in the Abyssinian region, a large part of the Lake Victoria region and the sahelian belt of West Africa. All the sanga males (n = 64) but only one from the Abyssinian region had the indicine allele. The taurine allele is the commonest only among the sanga breeds of the southern African region and the trypanotolerant taurine breeds of West Africa. In West Africa and in the southern Africa regions, zones of introgression were detected with breeds showing both Y chromosome alleles. Our data also reveal a pattern of male zebu introgression in Mozambique and Zimbabwe, probably originating from the Mozambique coast. The sanga cattle from the Lake Victoria region and the Kuri cattle of Lake Chad, cattle populations surrounded by zebu breeds were, surprisingly, completely devoid of the indicine allele. Human migration, phenotypic preferences by the pastoralists, adaptation to specific habitats and to specific diseases are the main factors explaining the present-day distribution of the alleles in sub-Saharan Africa.

The transferrin receptor in African trypanosomes: identification, partial characterization and subcellular localization.

All eukaryotic cells, including African trypanosomes, require iron for growth and division, and this iron is acquired by the receptor-mediated endocytosis of iron-loaded transferrin (diFe(3+)-transferrin). In trypanosomes transferrin (Tf) has been shown to be delivered into lysosomes and may not recycle back to the cell surface as it does in mammalian cells (Grab, D. J., et al., Eur. J. Cell Biol. 59, 398-404 (1992)). Here, we describe for the first time, the characteristics of a Tf-binding protein with receptor-like properties in Trypanosoma brucei brucei. Bloodstream forms of rodent-adapted T. brucei were incubated with [35S]methionine and detergent lysates chromatographed on a Sephacryl S-300 column. Fractions were incubated with anti-Tf serum to immunoprecipitate Tf/Tf-binding protein complexes. On sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) the molecular mass of the major protein in the immunoprecipitate was 88 to 92 kDa. Tf-binding proteins could also be isolated using diferric Tf-Sepharose. The molecular mass of the major Tf-binding protein, as estimated from Sephacryl S-300 column chromatography, in the presence of detergent, was approximately 90 to 100 kDa and 90 kDa with SDS-PAGE. Each 90 kDa Tf-binding protein was able to bind one molecule of diferric Tf. Since monoclonal antibodies to human and bovine Tf receptors failed to react with any trypanosome proteins, antisera were raised against the T. brucei Tf-binding proteins eluted from Tf-Sepharose at low pH. These antibodies recognized a 90 kDa protein on Western blots of a T. brucei lysate and inhibited the growth of T. brucei in vitro. Immunolocalization studies, using this antiserum showed that the Tf-binding protein was localized in the flagellar pocket and within the early endosomal compartments. In the presence of protease inhibitors there was additional localization in lysosome-like organelles. The Tf-binding characteristics and localization of this 90 kDa protein suggest that this molecule is a strong candidate as a physiological receptor for Tf in these parasites.

Immune CD4+ T cells specific for Theileria parva-infected lymphocytes recognize a 24-kilodalton protein.

Theileria parva is a protozoan parasite that infects and transforms bovine lymphocytes. Here we report the partial purification of a T. parva-specific protein from infected lymphocytes that is recognized by CD4+ parasite-specific T-cell clones derived from immune cattle. T. parva-infected lymphocytes were homogenized in Dulbecco's phosphate-buffered saline in the presence of protease inhibitors. The antigen was purified from a postmicrosomal supernatant by using a combination of DEAE-cellulose chromatography and hydroxylapatite column chromatography. After labelling with 125I, the antigen preparation was subjected to sodium dodecyl sulfate-polyacrylamide gel electrophoresis and found to contain 8 to 10 proteins. This preparation was subjected to chromatography in phosphate-buffered saline on HPLC TSK-250/125 columns coupled in tandem. A radiolabelled protein of M(r) 24,000 correlated with antigenic activity.

Subcellular localization of a variable surface glycoprotein phosphatidylinositol-specific phospholipase-C in African trypanosomes.

African trypanosomes contain a membrane-bound enzyme capable of removing dimyristylglycerol from the membrane-attached form of the variable surface glycoprotein (mfVSG; Ferguson, M. A. J., K. Halder, and G. A. M. Cross, 1985, J. Biol Chem., 260:4963-4968). Although mfVSG phospholipase-C has been implicated in the removal of the VSG from the trypanosome surface (Cardoso de Almeida, M. L., and M. J. Turner, 1983, Nature (Lond.)., 302:349-352; Ferguson, M. A. J., K. Halder, and G. A. M. Cross, 1985, J. Biol Chem., 260:4963-4968), its precise function and subcellular location have not been determined. We have developed a procedure for the separation of the cell fractions and organelles of Trypanosoma brucei brucei (and other trypanosome species) by differential sucrose and isopycnic PercollR centrifugation. These fractions were tested for mfVSG phospholipase activity using Trypanosoma brucei mfVSG labeled with 3H-myristic acid as substrate. The highest enzyme-specific activity was associated with the flagella and evidence is presented to suggest that it is localized in the flagellar pocket. Some activity was also associated with the Golgi complex. These results suggest that the mfVSG phospholipase is localized primarily in the membrane of the flagella pocket and possibly other membrane organelles derived from and associated with this structure, and may be part of the VSG-membrane recycling system in African trypanosomes. The activity of mfVSG phospholipase amongst various trypanosome species was determined. We show that, in contrast to the bloodstream forms of Trypanosoma brucei, cultured procyclic Trypanosoma brucei and bloodstream Trypanosoma vivax had little or no mfVSG phospholipase activity. The activity found in bloodstream forms of Trypanosoma congolense was intermediate between Trypanosoma vivax and Trypanosoma brucei.

The intracellular pathway and assembly of newly formed variable surface glycoprotein of Trypanosoma brucei.

Pulse-chase experiments using L-[35S]methionine suggest that Trypanosoma brucei MITat 1.2 variable surface glycoprotein (VSG) synthesized in the rough endoplasmic reticulum, a process that takes 6-8 min, is shuttled to the Golgi complex 8 min later. Labeling of ultrathin frozen sections with affinity-purified anti-cross-reacting determinant (CRD) IgG followed by protein A-colloidal gold shows that the CRD is localized in the trans-Golgi region. cis-Golgi is not labeled. VSG, when solubilized by treatment with the detergent Nonidet P-40, behaves on sucrose density gradients as a non-membrane protein with a sedimentation value of 5 S. In contrast, VSG solubilized in the presence of Zwittergent TM 3-14 yielded several VSG-containing fractions greater than 5 S, and only the 5S fraction contained the CRD. Lack of the CRD in VSG complexes with sedimentation values greater than 5 S suggests that this determinant is either masked from antibody, perhaps by involvement in polymer formation, or represents the membrane form of VSG recently described by Cardoso de Almeida and Turner [Cardoso de Almeida, M. L. & Turner, M. J. (1983) Nature (London) 302, 349-352].