An Alba-domain protein contributes to the stage-regulated stability of amastin transcripts in Leishmania.

Leishmania infantum promastigotes differentiate into amastigote forms within the phagolysosome of mammalian macrophages causing visceral leishmaniasis. Delta-amastins belong to a multigenic surface protein family of potential virulence factors that are specifically expressed in the amastigote life cycle stage through distinct regulatory elements in the 3' UTR controlling either mRNA stability or translation. Here, we provide novel insights on trans-acting factors regulating amastin developmental gene expression. Using RNA affinity chromatography with a 300 nt regulatory region within the amastin 3' UTR as bait, we identified an Alba-domain protein of 25 kDa (LiAlba20) as a specific amastin mRNA-binding partner. Genomic depletion of LiAlba20 results in amastin mRNA destabilization specifically in amastigotes, supporting a role of LiAlba20 in amastin gene regulation. As shown by comparative DNA microarray analysis, several delta-amastin transcripts but also other known developmentally regulated transcripts were downregulated in LiAlba20-/- knockout parasites. Inactivation of the second Alba-domain gene, LiAlba13, does not seem to affect amastin mRNA stability in either life stage of the parasite. These data indicate an important role of Alba-domain proteins in the regulation of Leishmania differentially expressed transcripts and open a new field of investigation for better understanding mechanisms contributing to post-transcriptional control in these parasites.