Expression of the Glossina Proteolytic Lectin (Gpl) Gene in Tsetse Flies and other Haematophagous Arthropods

Abstract

African animal trypanosomosis, transmitted by the tsetse fly (Glossina spp.) remains a major constraint to food security in areas of Africa that hold the continent's greatest potential for expanded agriculture production. The flies also transmit the parasite responsible for human sleeping sickness. Other haematophagous arthropods like stable flies also transmit trypanosomes mechanically. Mechanical transmission only accounts for a small percentage (-16 % ) of the trypanosomes transmission since the haematophagous arthropods do not provide an environment for tr)-panosome development within their tissues unlike in tsetse flies. The life cycle of the parasitic African trypanosome in its invertebrate vector begins when the tsetse fly feeds from an infected mammalian host. Within the fly, the parasites are transformed from the bloodstream forms to procyclic forms and an infection is established. Many midgut enzymes have been shown to play a role in the establishment phase of the infection. Lectin-trypsin complex is one of the molecules that have been shown to play a role in the transformation of trypanosomes from bloodstream forms to procyclic forms in vitro, the first crucial step in the establishment of primary midgut infections in the fly. Glossina proteolytic lectin (Gp/) gene encodes the a subunit of the lectin-trypsin protein. A study was undertaken to evaluate the expression profile of Gp/ in Glossina fuscipesfuscipes using RT- PCR based techniques. In teneral flies, very low levels of transcript could be detected, but the expression was rapidly induced as early as 1 h post bloodmeal acquisition. Transcript levels decreased slightly after 6 h and stabilized, then increased after 24 h and peaked between 48 and 72 b of starvation. A further decrease of transcript levels was observed. The transcript abundance after 120 h of starvation was higher than in teneral guts. This non-constitutive mode of expression suggests that the gene is regulated at the transcription level. Analysis for the expression of Gpl was also carried out in Anopheles gamhiae, Phlel>otomus dubosci, Rhipicephal/us appendiculatus and Stomoxys ca/cirans besides the k:nmm cyclic vectors of trypanosomes using RT-PCR technique. The evaluation of Glossina proteolytic lectin gene in these haematophagous arthropods by PCR revealed that this gene is only expressed in G/ossina species. The conservation of this gene in Glossina species only may be the reason for the cyclic mode of transmission of trypanosomes exhibited by tsetse flies.