Trypanosomes of subgenus Trypanozoon are diploid for housekeeping genes

Abstract

The ploidy of trypanosomes has until now remained undetermined, although isoenzyme studies and direct measurements of DNA content and complexity suggest diploidy. Direct cytogenetic analysis is not possible, because the chromosomes do not condense at any stage of the cell cycle. We now present evidence from analysis of restriction site polymorphisms in and around three glycolytic enzyme genes (phosphoglycerate kinase, triosephosphate isomerase, glyceraldehyde phosphate dehydrogenase) and the tubulin gene cluster, that trypanosomes of subgenus Trypanozoon are diploid for these housekeeping genes. This result is still compatible with the single copy nature of variant surface glycoprotein (VSG) genes in Trypanozoon, if different VSG genes are present in corresponding positions on paired chromosomes. Using pulse field gradient gel electrophoresis, we show that the genes for the three glycolytic enzymes are all located in very large DNA molecules, but the gene for triosephosphate isomerase is in another fraction from the genes for the other two enzymes. Since all three enzymes are located in glycosomes, which are trypanosome microbodies, the genes for glycosomal enzymes are not all clustered in one chromosomal segment of the trypanosome genome.