| Summary: | <p>Abstract</p> <p>Background</p> <p>In the life cycle of Leishmania within the alimentary canal of sand flies the parasites have to survive the hostile environment of blood meal digestion, escape the blood bolus and attach to the midgut epithelium before differentiating into the infective metacyclic stages. The molecular interactions between the Leishmania parasites and the gut of the sand fly are poorly understood. In the present work we sequenced five cDNA libraries constructed from midgut tissue from the sand fly <it>Lutzomyia longipalpis </it>and analyzed the transcripts present following sugar feeding, blood feeding and after the blood meal has been processed and excreted, both in the presence and absence of <it>Leishmania infantum chagasi</it>.</p> <p>Results</p> <p>Comparative analysis of the transcripts from sugar-fed and blood-fed cDNA libraries resulted in the identification of transcripts differentially expressed during blood feeding. This included upregulated transcripts such as four distinct microvillar-like proteins (LuloMVP1, 2, 4 and 5), two peritrophin like proteins, a trypsin like protein (Lltryp1), two chymotrypsin like proteins (LuloChym1A and 2) and an unknown protein. Downregulated transcripts by blood feeding were a microvillar-like protein (LuloMVP3), a trypsin like protein (Lltryp2) and an astacin-like metalloprotease (LuloAstacin). Furthermore, a comparative analysis between blood-fed and <it>Leishmania </it>infected midgut cDNA libraries resulted in the identification of the transcripts that were differentially expressed due to the presence of Leishmania in the gut of the sand fly. This included down regulated transcripts such as four microvillar-like proteins (LuloMVP1,2, 4 and 5), a Chymotrypsin (LuloChym1A) and a carboxypeptidase (LuloCpepA1), among others. Upregulated midgut transcripts in the presence of Leishmania were a peritrophin like protein (LuloPer1), a trypsin-like protein (Lltryp2) and an unknown protein.</p> <p>Conclusion</p> <p>This transcriptome analysis represents the largest set of sequence data reported from a specific sand fly tissue and provides further information of the transcripts present in the sand fly <it>Lutzomyia longipalpis</it>. This analysis provides the detailed information of molecules present in the midgut of this sand fly and the transcripts potentially modulated by blood feeding and by the presence of the Leishmania parasite. More importantly, this analysis suggests that <it>Leishmania infantum chagasi </it>alters the expression profile of certain midgut transcripts in the sand fly during blood meal digestion and that this modulation may be relevant for the survival and establishment of the parasite in the gut of the fly. Moreover, this analysis suggests that these changes may be occurring during the digestion of the blood meal and not afterwards.</p>
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