ALBERT

Description: Background: Alpha tubulin is a fundamental component of the cytoskeleton which is responsible for cell shape and is involved in cell division, ciliary and flagellar motility and intracellular transport. Alpha tubulin gene expression varies according to the morphological changes suffered by Leishmania in its life cycle. However, the objective of studying the mechanisms responsible for the differential expression has resulted to be a difficult task due to the complex genome organization of tubulin genes and to the non-conventional mechanisms of gene regulation operating in Leishmania. Results: We started this work by analyzing the genomic organization of alpha-tubulin genes in the Leishmania braziliensis genome database. The genomic organization of L. braziliensis alpha-tubulin genes differs from that existing in the L. major and L. infantum genomes. Two loci containing alpha-tubulin genes were found in the chromosomes 13 and 29, even though the existence of sequence gaps does not allow knowing the exact number of genes at each locus. Southern blot assays showed that alpha-tubulin locus at chromosome 13 contains at least 8 gene copies, which are tandemly organized with a 2.08-kb repetition unit; the locus at chromosome 29 seems to contain a sole alpha-tubulin gene. In addition, it was found that L. braziliensis alpha-tubulin locus at chromosome 13 contains two types of alpha-tubulin genes differing in their 3[prime] UTR, each one presumably containing different regulatory motifs. It was also determined that the mRNA expression levels of these genes are controlled by post-transcriptional mechanisms tightly linked to the growth temperature. Moreover, the decrease in the alpha-tubulin mRNA abundance observed when promastigotes were cultured at 35[degree sign]C, was accompanied by parasite morphology alterations, similar to that occurring during the promastigote to amastigote differentiation. Conclusions: Information found in the genome databases indicates that alpha-tubulin genes have been reorganized in a drastic manner along Leishmania speciation. In the L. braziliensis genome database, two loci containing alpha-tubulin sequences were found, but only the locus at chromosome 13 contains the prototypic alpha-tubulin genes, which are repeated in a head-to-tail manner. Also, we determined that the levels of alpha-tubulin mRNAs are down-regulated drastically in response to heat shock by a post-transcriptional mechanism which is dependent upon active protein synthesis.