Expression profiles of tsetse (glossina spp) glossina proteolytic lectin (gpl) gene

Abstract

Tsetse flies are important agricultural and medical vectors of African trypanosomes, the causative agents of trypanosomosis in humans and animals. The life cycle of the protozoan parasite Trypanosoma, in its invertebrate vector begins when the tsetse fly feeds on an infected mammalian host. An important step in the establishment of tsetse midgut infection involves transformation of bloodstream-form trypanosomes into procyclic forms. This process is mediated by a wide variety of factors, all of which are intrinsic to the tsetse, trypanosome and the host blood. Tsetse midgut factors involved include lectins, trypsin-like molecules, lysins and lectin-trypsin complex. Recently Glossina proteolytic lectin gene (Gp!) that encodes for a protein with both lectin and trypsin activities in Glossina fuscipes fuscipes was discovered. Glossina proteolytic lectin induces transformation of bloodstream-forms trypanosomes to procyclic forms in vitro.The gene is ~loodmeal induced and is expressed in members of Glossina species but not in other haematophagous insects., This suggests that it may be playing an important role in the interactions between tsetse and the trypanosomes and hence the vectorial capacity. The present study was undertaken to gain insight into the effect of trypanosome parasites on the expression of Gpl gene and how its expression compares in different G!ossina _'S."pec.Ies. Quantitative competitive reverse transcriptase polymerase chain reaction (QCRT- PCR) was used to assess the expression levels of Gpl gene in infected and uninfected G·fjilscipes~24, 48 and 72 h post feeding. Expression levels were also compared in G. pallidipes and G. f fuscipes at 0, 24, 48 and 72 h post feeding. Expression levels of Gpl gene remained high throughout th~ digestion cycle following both infective and uninfective bloodmeal. However, the expression was parasite responsive, with the expression being lower in trypanosome infected G j fuscipes (p<0.05). At 24, 48, and 72 h, infected G. f fuscipes expressed 6.02 x 105; 6.73 X 105 and 7.92 x 105 Gpl gene transcripts respectively, while uninfected G.ffuscipes expressed 7.29 x 105; 7.45 X 105; 8.89 X 105 transcripts respectively. Down regulation of Gpl gene expression by trypanosomes might be a possible mechanism used by the parasites to survive and establish themselves in the hostile midgut environment.Expression of Gpl gene varied significantly in G. pallidipes and G j fuscipes with G. pallidipes expressing lower levels of the transcripts (p<0.05). In both species a linear increase in the gene expression was observed with teneral flies expressing low transcript levels. Teneral G. pallidipes expressed 4.82 x 105 and G. f fuscipes expressed 6.22 X 105. At 24, 48 and 72 h, G. pallidipes expressed 5.25 x 105; 6.39 X 105 and 7.19 x 105 Gpl ger;e transcripts respectively as compared to 7.29 x 105; 7.45 X 105; and 8.89 x 105 in G. f fuscipes. This trend suggests regulation at transcription level. Higher Gpl Igene transcript levels in G. f fuscipes may be among the factors contributing to their refractoriness to trypanosome infection as opposed to the susceptible G. pallidipes. Although several factors have been implicated in the successful transformation and t!stablishment of trypanosomes in tsetse, down regulation of expression of Gpl gene in refractory G. f fuscipes and the variation of its expression in susceptible (G. pallidipes) and refractory (G. f fuscipesy tsetse flies suggest that there is an optimal concentration of Gpl requised for ~the establishment of midgut infection. Trypanosomes could be playing a key role in the modulation .