title: Metacyclic variant surface glycoprotein genes of Trypanosoma brucei subsp. rhodesiense are activated in situ, and their expression is transcriptionally regulated.
abstract: During the metacyclic stage in the life cycle of Trypanosoma brucei subsp. rhodesiense, the expression of variant surface glycoproteins (VSGs) is restricted to a small subset of antigenic types. Previously we identified cDNAs for the VSGs expressed in metacyclic variant antigen types (MVATs) 4 and 7 and found that these VSG genes do not rearrange when expressed at the metacyclic stage (M. J. Lenardo, A. C. Rice-Ficht, G. Kelly, K. Esser, and J. E. Donelson, Proc. Nathl. Acad Sci. USA 81:6642-6646, 1984). We now provide further evidence that these genes do not rearrange and demonstrate that their 5' upstream regions lack the 72 to 76-base-pair repeats which are considered the substrate for duplication and transposition events. Pulsed field gradient electrophoresis showed that the MVAT VSG genes were located on the largest chromosome-sized DNA molecules, and the lack of the MVAT 4 gene in one of two different serodemes suggested that one mechanism for the evolution of MVAT repertoires is gene deletion. When MVATs were inoculated into the bloodstream of a mammalian host by a bite from the insect vector, they rapidly switched into nonmetacyclic VSG types. We found that this switch was accomplished by a loss of MVAT RNA concomitant with the loss of metacyclic VSGs. Transcription studies with isolated metacyclic nuclei showed that the MVAT genes were expressed in situ from a single locus and were regulated at the level of transcription.
mesh_terms: D000818:Animals; D000953:Antigens, Protozoan / Q000235:genetics*; D002874:Chromosome Mapping; D005786:Gene Expression Regulation; D005796:Genes; D006023:Glycoproteins / Q000235:genetics*; D012333:RNA, Messenger / Q000235:genetics; D011995:Recombination, Genetic; D014158:Transcription, Genetic; D014346:Trypanosoma brucei brucei / Q000235:genetics* / Q000254:growth & development / Q000276:immunology; D014643:Variant Surface Glycoproteins, Trypanosoma
chemical_list: D000953:Antigens, Protozoan; D006023:Glycoproteins; D012333:RNA, Messenger; D014643:Variant Surface Glycoproteins, Trypanosoma