Protozoan parasites of the genus Leishmania are found as promastigotes in the sandfly vector and as amastigotes in mammalian macrophages. Mechanisms controlling stage-regulated gene expression in these organisms are poorly understood. Here, we applied a comprehensive approach consisting of protein prefractionation, global proteomics and targeted DNA microarray analysis to the study of stage differentiation in Leishmania. By excluding some abundant structural proteins and reducing complexity, we detected and identified numerous novel differentially expressed protein isoforms in L. infantum. Using 2-D gels, over 2200 protein isoforms were visualized in each developmental stage. Of these, 6.1% were strongly increased or appeared unique in the promastigote stage, while the relative amounts of 12.4% were increased in amastigotes. Amastigote-specific protein isoform and mRNA expression trends correlated modestly (53%), while no correlation was found for promastigote-specific spots. Even where direction of regulation was similar, fold-changes were more modest at the RNA than protein level. Many proteins were present in multiple spots, suggesting that PTM is extensive in this organism. In several cases, different isoforms appeared to be specific to different life stages. Our results suggest that post-transcriptional controls at translational and post-translational levels could play major roles in differentiation in Leishmania parasites.

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The cohesin complex is essential for mitosis and meiosis. The specific meiotic roles of individual cohesin proteins are incompletely understood. We report in vivo functions of the only meiosisspecific STAG component of cohesin, STAG3. Newly generated STAG3-deficient mice of both sexes are sterile with meiotic arrest. In these mice, meiotic chromosome architecture is severely disrupted as no bona fide axial elements (AE) form and homologous chromosomes do not synapse. Axial element protein SYCP3 forms dot-like structures, many partially overlapping with centromeres. Asynapsis marker HORMAD1 is diffusely distributed throughout the chromatin, and SYCP1, which normally marks synapsed axes, is largely absent. Centromeric and telomeric sister chromatid cohesion are impaired. Centromere and telomere clustering occurs in the absence of STAG3, and telomere structure is not severely affected. Other cohesin proteins are present, localize throughout the STAG3-devoid chromatin, and form complexes with cohesin SMC1b. No other deficiency in a single meiosisspecific cohesin causes a phenotype as drastic as STAG3 deficiency. STAG3 emerges as the key STAG cohesin involved in major functions of meiotic cohesin.