Leishmania infection induces a limited differential gene expression in the sand fly midgut

Abstract

22Background: Phlebotomine sand flies are the vectors of Leishmania worldwide. To develop in 23 the sand fly midgut, Leishmania multiplies and undergoes multiple stage differentiations leading 24 to the infective form, the metacyclic promastigotes. To gain a better understanding of the 25 influence of Leishmania infection in midgut gene expression, we performed RNA-Seq 26 comparing uninfected Lutzomyia longipalpis midguts and Leishmania infantum-infected 27 Lutzomyia longipalpis midguts at seven time points which cover the various developmental 28Leishmania stages including early time points when blood digestion is taking place and late time 29 points when the parasites are undergoing metacyclogenesis. 30Results: Out of over 13,841 transcripts assembled de novo, only 113 sand fly transcripts, about 31 1%, were differentially expressed. Further, we observed a low overlap of differentially expressed 32 sand fly transcripts across different time points suggesting a specific influence of each 33Leishmania stage on midgut gene expression. Two main patterns of sand fly gene expression 34 modulation were noticed. At early time points (days 1-4), more transcripts were down-regulated 35by Leishmania infection at large fold changes (> -32 fold). Among the down-regulated genes, the 36 transcription factor Forkhead/HNF-3 and hormone degradation enzymes were differentially 37 regulated on day 4 and appear to be the upstream regulators of nutrient transport, digestive 38 enzymes, and peritrophic matrix proteins. Conversely, at later time points (days 6 onwards), 39 most of the differentially expressed transcripts were up-regulated by small fold changes (< 32 40 fold), and the molecular function of such genes are associated with the metabolism of lipids and 41 detoxification of xenobiotics (P450). 42 Conclusion:Overall, it appears that Leishmania modulates sand fly gene expression early on in 43 order to overcome the barriers imposed by the midgut, yet it behaves like a commensal at later 44 time points, when modest midgut gene expression changes correlate with a massive amount of 45 parasites in the anterior midgut. 46

Leishmaniasis: the act of transmission

“…On day 6 after infection and onwards, multiple genes related to the metabolism of lipids and detoxification of xenobiotics were upregulated [15]. Overall, Leishmania seems to manipulate midgut genes from day 2 to day 4 after infection in order to survive midgut barriers related to structure and metabolism, whereas it behaves as a commensal at day 12 to 14 after infection when the midgut imposes little difficulty for parasite development [14][15][16]. The presence of blood upregulates transcripts from the Toll (Spätzle and GNBP3) and IMD pathways in sand flies [16].…”

“…Surprisingly, only 113 differentially expressed midgut genes were observed upon Leishmania infection when compared with blood-fed sand flies [15]. Importantly, immune genes from the insect gut were not significantly upregulated in the presence of Leishmania [14][15][16]. On day 6 after infection and onwards, multiple genes related to the metabolism of lipids and detoxification of xenobiotics were upregulated [15].…”

“…The presence of blood upregulates transcripts from the Toll (Spätzle and GNBP3) and IMD pathways in sand flies [16]. However, these immune genes are not significantly modulated by the presence of Leishmania [14][15][16] and are most likely reacting to the observed increase in sand fly gut bacteria in the presence of blood [6]. Interestingly, knockdown of the negative regulator of the IMD pathway, caspar, reduced Leishmania mexicana survival in Lu.…”

“…However, ookinetes traverse the mosquito midgut epithelium, damaging it in the process, while Leishmania parasites remain extracellular in the lumen of the sand fly midgut [1]. Despite the presence of a large number of Leishmania parasites, the sand fly midgut is not immunologically responsive to Leishmania infection when compared with blood-fed sand flies [14][15][16]. The differential expression of sand fly midgut genes in Leishmania-infected sand flies was assessed by RNA-Seq [14][15][16].…”

“…Despite the presence of a large number of Leishmania parasites, the sand fly midgut is not immunologically responsive to Leishmania infection when compared with blood-fed sand flies [14][15][16]. The differential expression of sand fly midgut genes in Leishmania-infected sand flies was assessed by RNA-Seq [14][15][16]. Surprisingly, only 113 differentially expressed midgut genes were observed upon Leishmania infection when compared with blood-fed sand flies [15].…”