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Eukaryotic Cell doi:10.1128/EC.00147-06
Copyright (c) 2006, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

A NOVEL CLASS OF DEVELOPMENTALLY REGULATED NON-CODING RNAs IN LEISHMANIA

Infectious Diseases Research Center, CHUL Research Center of Laval University and Department of Medical Biology, Faculty of Medicine, Laval University, Quebec, Canada

^* To whom correspondence should be addressed. Email: barbara.papadopoulou{at}crchul.ulaval.ca.

	Abstract

Leishmania is a protozoan parasite which causes serious morbidity and mortality in humans, worldwide. The ability of these parasites to survive within the phagolysosomes of mammalian macrophages is dependent on the developmental regulation of a variety of genes. Identifying genomic sequences that are preferentially expressed during the parasite's intracellular growth would provide new insights about the mechanisms controlling stage-specific gene regulation for intracellular development of the parasite. Using a genomic library which was differentially hybridised to probes made from total RNA of Leishmania infantum amastigote or promastigote life-cycle stages, we identified a new class of non-coding RNAs (ncRNAs) ranging from 300-600 nt in size which are expressed specifically in the intracellular amastigote stage. These ncRNAs are transcribed by RNA polymerase II from genomic clusters of tandem head-to-tail repeats, which are mainly located within subtelomeric regions. Remarkably, both the sense and antisense orientations of these ncRNAs are transcribed and are processed by trans splicing and polyadenylation. Antisense transcript levels are at least 10-fold lower than that of the sense and are tightly regulated. The sense and antisense ncRNAs are cytosolic as shown by fluorescence in situ hybridisation studies and co-sediment with a small RNP complex. Amastigote-specific regulation of these ncRNAs occurs possibly at the level of RNA stability. Interestingly, overexpression of these ncRNAs in promastigotes, as part of an episomal expression vector, failed to produce any transcript, which further highlights the instability of these RNAs in the promastigote stage. This is the first report describing developmentally regulated ncRNAs in protozoan parasites.