Lights and shadows on gene organization and regulation of gene expression in Leishmania.

Regulation of gene expression is one of the most intriguing aspects of Leishmania biology. This review deals with current knowledge concerning gene organization and regulation of gene expression in this protozoan parasite, which cause serious illness and death in humans living in tropical and subtropical regions. Post-transcriptional regulation is especially important for Leishmania, and other trypanosomatids, due to the unusual features related to transcription and mRNA maturation. In these organisms, genes are organized into polycistronic transcription units, whereby many genes are cotranscribed by RNA polymerase II from not well characterized, upstream promoters. These organisms represent an extreme in which the expression of their genome is almost exclusively controlled post-transcriptionally. Because the regulatory needs of these parasites are considerable as they undergo complex developmental transitions, post-transcriptional mechanisms that involve RNA and protein regulatory processes are of paramount importance for these protozoa. This review summarizes recent results on the post-transcriptional mechanisms in Leishmania that regulate protein abundance through influencing RNA splicing, nuclear-cytoplasmic mRNA stability, translation, or post-translational events such as protein stability and modification.