Translation regulation

Translational Regulation in Plasmodium

Early work in our lab identified the translation initiation sites in Plasmodium falciparum, a parasite with one of the most AT-rich genomes sequenced to date. As start codons are also AT-rich (ATG), there is a high probability of finding start codons and upstream open reading frames (ORFs) in the parasite genome. Indeed, we showed that mRNAs of P. falciparum contain an average of 3-4 uORFs, a number significantly higher than that seen in the human genome. As uORFs are well-established repressors of the translation of their downstream genes, we studied their role in the regulation of a family of virulence genes called var genes. Despite repression mediated by uORFs, we showed that parasites can translate the coding sequences of the genome using mechanisms of re-initiation and leaky scanning. These are governed by multiple parameters such as the Kozak sequence, uORF length and inter-cistronic length. To better understand translational regulation in Plasmodium, we collaborate with Sandip Kaledhonkar to determine the structure of the Plasmodium Translation Enhancing Factor (PTEF) using cryoEM.

Stage Conversion in Toxoplasma gondii

Our lab has now expanded its focus to Toxoplasma gondii, an apicomplexan parasite which infects one-third of the global population and causes Toxoplasmosis. (Montoya & Liesenfeld, 2004). The infective asexual stages are the fast-replicating tachyzoite stage which converts to a slow-replicating, latent cyst-forming stage called bradyzoites leading to recrudescence. We aim at understanding this conversion process within the parasite.

This stage conversion is accompanied by distinct morphological and phenotypic changes, including transcriptional and translational rewiring that lead to slower replication rates and metabolic changes, making this process highly complex and regulated at multiple levels. The stress response leading to bradyzoite formation begins with the initiation of the integrated stress response involving phosphorylation of eIF2α, leading to suppression of cap-dependent translation while selectively upregulating stress-responsive transcripts. This also initiates a parallel pathway that leads to the transcription and translation of many bradyzoite-specific regulators, such as Bradyzoite Formation Deficient-1 and Bradyzoite Formation Deficient-2 (BFD1 and BFD-2). BFD1 is under translational control due the presence of large uORFs in the mRNA. We are trying to understand the role of these uORFs in stress-induced translation of BFD-1 by leveraging differences in the cyst-forming abilities of different strains of T. gondii.

Furthermore, this project aims to understand and identify novel regulators of tachyzoite to bradyzoite conversion process using in-silico and experimental approaches. We have used a phylogeny-based approach to identify conserved proteins among other bradyzoite-cyst-forming members of the Sarcocystidae family (to which Toxoplasma belongs). We have a comprehensive list of potential candidates that we are validating experimentally to add novel regulators to this complex pathway.

Funded by: Board for Research in Nuclear Sciences, Department of Atomic Energy, Government of India (2007/37/64/BRNS), International Center for Genetic Engineering & Biotechnology (Grant No. CRP/22/005) and Department of Biotechnology, Govt. of India. (Grant No: RD/0213-DBT0000-003).

Translation initiation team