Cornelissen A W, Bakkeren G A, Barry J D, Michels P A, Borst P
Nucleic Acids Res. 1985 Jul 11;13(13):4661-76. doi: 10.1093/nar/13.13.4661.
Trypanosoma brucei contains a repertoire of more than 100 different genes for Variant Surface Glycoproteins (VSGs). A small and strain-specific fraction of these genes is expressed in the salivary glands of the tsetse fly (M-genes), giving rise to metacyclic Variable Antigen Types (M-VATs). Antibodies produced in a chronic trypanosome infection initiated by syringe inoculation of bloodstream forms into mammals (i.e. against B-VATs), will react with most of the M-VATs suggesting that these B-VATs express VSG genes that are similar or identical to M-genes. We have cloned DNA complementary to the VSG mRNA of four of such B-VATs and used this to characterize the corresponding VSG genes. In three of the four VATs we find a single VSG gene hybridizing with the cDNA probe and we provide supporting evidence that this gene is expressed as an M-gene. In the bloodstream repertoire these genes appear to be activated by duplicative translocation to another telomere. In all four variants the putative M-genes are telomeric and in the three cases where the location of the genes on chromosome-sized DNA molecules could be determined, the genes were located in large DNA, whereas the majority of the telomeric VSG genes are in chromosomes less than 1000 kb. Our results are best explained by models for M-gene activation involving telomeric expression sites for these genes which are separate from those used by bloodstream forms. The implications of these results for vaccination are discussed.
布氏锥虫含有100多种不同的可变表面糖蛋白（VSG）基因。这些基因中的一小部分且具有菌株特异性的基因在采采蝇的唾液腺中表达（M基因），产生循环后期可变抗原类型（M-VATs）。通过将血流形式的锥虫经注射器接种到哺乳动物体内引发慢性锥虫感染所产生的抗体（即针对B-VATs的抗体），将与大多数M-VATs发生反应，这表明这些B-VATs表达的VSG基因与M基因相似或相同。我们克隆了与四种此类B-VATs的VSG mRNA互补的DNA，并以此来表征相应的VSG基因。在这四种VATs中的三种中，我们发现有一个单一的VSG基因与cDNA探针杂交，并且我们提供了支持性证据表明该基因作为M基因表达。在血流基因库中，这些基因似乎通过复制易位到另一个端粒而被激活。在所有四个变体中，推定的M基因都是端粒基因，在其中三种能够确定基因在染色体大小的DNA分子上位置的情况下，这些基因位于大的DNA中，而大多数端粒VSG基因位于小于1000 kb的染色体中。我们的结果最好用涉及这些基因的端粒表达位点的M基因激活模型来解释，这些位点与血流形式所使用的位点是分开的。讨论了这些结果对疫苗接种的影响。
