Analysis of expressed sequence tags from the four main developmental stages of Trypanosoma congolense

Abstract

Trypanosoma congolense is one of the most economically important pathogens of livestock in Africa. Culture-derived parasites of each of the three main insect stages of the T. congolense life cycle, i.e., the procyclic, epimastigote and metacyclic stages, and bloodstream stage parasites isolated from infected mice, were used to construct stage-specific cDNA libraries and expressed sequence tags (ESTs or cDNA clones) in each library were sequenced. Thirteen EST clusters encoding different variant surface glycoproteins (VSGs) were detected in the metacyclic library and twenty-six VSG EST clusters were found in the bloodstream library, six of which are shared by the metacyclic library. Rare VSG ESTs are present in the epimastigote library, and none were detected in the procyclic library. ESTs encoding enzymes that catalyze oxidative phosphorylation and amino acid metabolism are about twice as abundant in the procyclic and epimastigote stages as in the metacyclic and bloodstream stages. In contrast, ESTs encoding enzymes involved in glycolysis, the citric acid cycle and nucleotide metabolism are about the same in all four developmental stages. Cysteine proteases, kinases and phosphatases are the most abundant enzyme groups represented by the ESTs. All four libraries contain T. congolense-specific expressed sequences not present in the T. brucei and T. cruzi genomes. Normalized cDNA libraries were constructed from the metacyclic and bloodstream stages, and found to be further enriched for T. congolense-specific ESTs. Given that cultured T. congolense offers an experimental advantage over other African trypanosome species, these ESTs provide a basis for further investigation of the molecular properties of these four developmental stages, especially the epimastigote and metacyclic stages for which it is difficult to obtain large quantities of organisms. The T. congolense EST databases are available at: http://www.sanger.ac.uk/Projects/T_congolense/EST_index.shtml.

Mapping of VSG similarities in Trypanosoma brucei

“…We also examined whether functional expressed VSGs of another African trypanosome species, Trypanosoma congolense , [29–31] fall into similar N-terminal types. Using an E < 1e-03 threshold of similarity, 17 available T. congolense VSGs (as determined from cDNAs) occurred in the N4 N-terminal type (Fig.…”

“…Panels A – E contain 767 VSGs for which all annotation information is available, including N- and C-terminal sequences, chromosomal gene location and predicted functional annotations (functional, atypical, or pseudogene) [7, 8]. Panel F contains 17 additional expressed (cDNA) N-terminal VSG sequences from other T. brucei isolates [25–28], and 17 expressed (cDNA) N-terminal VSG sequences from T. congolense [29–31], for a total of 801 sequences. All panels were clustered according to similarity between the N-terminal VSG amino acid sequences determined by a BLAST hit of E < 1e-03.…”

Antigenic diversity is generated by distinct evolutionary mechanisms in African trypanosome species

“…Functional variant antigens in T. brucei consist of a-and b-type VSG (hereafter a-VSG and b-VSG), which share the cysteine-rich C-terminal domain (CTD) but are otherwise distantly related (9)(10)(11). Although VSG are known to occur in T. congolense and T. vivax (12)(13)(14)(15)(16), the repertoire of variant antigens in these species is uncharacterized. Consequently, the evolutionary diversification of the VSG gene family has not been examined, although it has been suggested that VSG are a source of novel genes.…”

“…Hence, T. congolense b-VSG are more structurally heterogeneous than T. brucei b-VSG are. We know that both Fam13 and Fam16 contain functional variant antigens because each family encompasses both published T. congolense VSG (12)(13)(14) and VSG expressed sequence tags (15). Although there is no a-VSG variant antigen, there are homologs of the a-VSG-like TFR genes of T. brucei, i.e., ESAG6/7 (Fam15; n = 43), as well as the procyclin-associated genes (PAG) (Fam14, n = 22), which also have an a-VSG-like structure (20).…”

The epimastigote stage-specific gene expression of CESP is tightly regulated by its 3′ UTR

“…T. congolense EMF parasites tightly adhere via their flagella to the lining of the labrum located in the mouthparts of tsetse fly by hemidesmosome-like structures [3]. Our previous studies reported that congolense epimastigote-specific protein (CESP) (accession number: AB300788) was exclusively translated in the EMF stage [4,5]. Eventually, EMF trypanosomes develop into the non-adherent animal-infective metacyclic form (MCF) and differentiate into the proliferating BSF in the new vertebrate host.…”