Biology subjects

Licon, M. H.

Publications and source records attributed to Licon, M. H..

4 recordsLinked to original sources

bioRxiv2023

Translation initiation factor eIF1.2 promotes Toxoplasma stage conversion by regulating levels of key differentiation factors

AbstractsThe parasite Toxoplasma gondii persists in its hosts by converting from replicating tachyzoites to latent bradyzoites housed in tissue cysts. The molecular mechanisms that mediate T. gondii differentiation remain poorly understood. Through a mutagenesis screen, we identified translation initiation factor eIF1.2 as a critical factor for T. gondii differentiation. A F97L mutation in eIF1.2 or the genetic ablation of eIF1.2 ({Delta}eif1.2) markedly impeded bradyzoite cyst formation in vitro and in vivo. We demonstrated, at single-molecule level, that the eIF1.2 F97L mutation impacts the scanning process of the ribosome preinitiation complex on a model mRNA. RNA sequencing and ribosome profiling experiments unveiled that {Delta}eif1.2 parasites are defective in upregulating bradyzoite induction factors BFD1 and BFD2 during stress-induced differentiation. Forced expression of BFD1 or BFD2 significantly restored differentiation in {Delta}eif1.2 parasites. Together, our findings suggest that eIF1.2 functions by regulating the translation of key differentiation factors necessary to establish chronic toxoplasmosis.

microbiology↗

bioRxiv2022

A positive feedback loop controls Toxoplasma chronic differentiation

Successful infection strategies must balance pathogen amplification and persistence. In Toxoplasma gondii, this is accomplished through differentiation into dedicated cyst-forming chronic stages that avoid clearance by the host immune system. The transcription factor BFD1 is both necessary and sufficient for stage conversion; however, its regulation is not understood. We examine five factors transcriptionally activated by BFD1. One of these is a cytosolic RNA-binding protein of the CCCH-type zinc finger family, which we name BFD2. Parasites lacking BFD2 fail to induce BFD1 and are consequently unable to fully differentiate in culture or in mice. BFD2 interacts with the BFD1 transcript in a stress-dependent manner. Deletion of BFD2 reduces BFD1 protein levels, but not mRNA abundance. The reciprocal effects on BFD2 transcription and BFD1 translation outline a positive feedback loop that enforces commitment to differentiation. BFD2 helps explain how parasites commit to the chronic gene-expression program and elucidates how the balance between proliferation and persistence is achieved over the course of infection.

microbiology↗

bioRxiv2020

Distinct cis-acting elements govern purine-responsive regulation of the Leishmania donovani nucleoside transporters, LdNT1 and LdNT2

Purine salvage from the host is an obligatory process for all protozoan parasites. In Leishmania donovani, this is accomplished by four membrane nucleoside and nucleobase transporters, or LdNTs. Previously, we demonstrated that purine starvation invokes a robust stress response in Leishmania and characterized the proteomic changes involved. However, because Leishmania do not control the transcription of individual genes, the underlying mechanisms responsible for these changes were ill-defined. LdNT1 and LdNT2 are among the most rapidly and significantly upregulated genes in purine-starved L. donovani parasites. Thus, to better understand post-transcriptional mechanisms of purine-responsive gene expression, we have examined regulation of these genes in molecular detail. Here we report that LdNT1 and LdNT2 are controlled by distinct cis-acting elements. In the case of LdNT2, mRNA abundance and translational enhancement under purine stress depend on a 76 nt-long polypyrimidine tract encoded in the LdNT2 mRNA 3-UTR. Transcripts containing the LdNT2 polypyrimidine tract were found to localize to discrete cytoplasmic foci in purine-replete cells, suggesting that the LdNT2 message may be stored in RNA granules at steady-state. In the case of LdNT1, we found that purine-responsiveness is conferred by a 48 nt-long polypyrimidine tract and additional upstream element, termed UE1. Both features are independently required for regulation, with the polypyrimidine tract and UE1 controlling mRNA abundance and translation, respectively. Together, these results highlight a remarkable degree of complexity in the regulation of the Leishmania purine stress response and set the stage for future investigations to identify the larger network of RNA-protein and protein-protein interactions involved.

genetics↗

bioRxiv2020

Purine-responsive expression of the Leishmania donovani NT3 purine nucleobase transporter is mediated by a conserved RNA stem-loop

The ability to modulate gene expression in response to changes in the host environment is essential for survival of the kinetoplastid parasite Leishmania. Unlike most eukaryotes, gene expression in kinetoplastids is predominately regulated post-transcriptionally. Consequently, RNA-binding proteins (RBPs) and mRNA-encoded sequence elements serve as primary determinants of gene regulation in these organisms; however, few have been ascribed roles in specific stress-response pathways. Leishmania lack the capacity for de novo purine synthesis and must scavenge these essential nutrients from the host. Leishmania have evolved a robust stress response to withstand sustained periods of purine scarcity during their lifecycle. The purine nucleobase transporter, LdNT3, is among the most substantially upregulated proteins in purine-starved L. donovani. Here we report that the post-translational stability of the LdNT3 protein is unchanged in response to purine starvation. Instead, LdNT3 upregulation is primarily mediated by a 33 nucleotide (nt) sequence in the LdNT3 mRNA 3-untranslated region that is predicted to adopt a stem-loop structure. While this sequence is highly conserved within the mRNAs of orthologous transporters in multiple kinetoplastid species, putative stem-loops from L. donovani and Trypanosoma brucei nucleobase transporter mRNAs are not functionally interchangeable for purine-responsive regulation. Through mutational analysis of the element, we demonstrate that species specificity is attributable to just three variant bases within the predicted loop. Finally, we provide evidence that the abundance of the trans-acting factor that binds the LdNT3 stem-loop in vivo is substantially higher than required for regulation of LdNT3 alone, implying a potential role in regulating other purine-responsive genes.

molecular biology↗