Biology subjects

Simard, M. J.

Publications and source records attributed to Simard, M. J..

4 recordsLinked to original sources

bioRxiv2025

DAF-18/PTEN prevents oocyte wastage in spermless C. elegans hermaphrodites by blocking spermatheca neck dilation through RHO-1/RhoA disinhibition

Loss of the Phosphatase and TENsin homolog PTEN drives cancer in humans. In C. elegans hermaphrodites that lack sperm, the PTEN ortholog DAF-18 is required for oocyte quiescence and their proximal accumulation, along with the concomitant homeostatic downregulation of germline stem cell proliferation. As such, spermless daf-18(o) mutants undergo full-scale oogenesis and ovulation in a futile manner, wasting all produced oocytes. When oocyte laying is prevented in these mutants, oocytes hyperaccumulate to form differentiated benign tumors. Here, we show that daf-18 expression in the spermatheca neck myoepithelium is sufficient to induce oocyte arrest and homeostatic downregulation of germline stem cell proliferation in spermless hermaphrodites, altogether prohibiting tumorigenesis. We demonstrate that DAF-18 promotes spermatheca neck contractility through limiting PIP3 levels and AKT activity, preventing the latter from inactivating RHO-1/RhoA by direct phosphorylation at a conserved site. Loss of PTEN may therefore promote benign tumorigenesis in humans through similar cell non-autonomous effects.

genetics↗

bioRxiv2025

CSDE1 promotes passenger strand cleavage of miR-486

Strand separation of the RNA duplex is a critical step in miRNA biogenesis, in which only the guide strand is retained to form the mature miRISC. The erythroid miRNA miR-486-5p uniquely requires AGO2 catalytic slicing of its passenger strand miR-486-3p, yet the factors regulating this process remain poorly understood. Here, we identify the RNA-binding protein CSDE1 as a key cofactor that promotes AGO2-dependent passenger-strand removal and miR-486-5p maturation. CSDE1 interacts with the N-terminal domain of AGO2, essential for strand release. Loss of CSDE1 increased the miR-486-3p/5p ratio, reduced cleavage efficiency, and derepressed miR-486 targets such as FOXO1 and PTEN. Restoring full-length CSDE1 expression restored AGO2-dependent passenger strand cleavage and this function requires the N-terminal cold-shock domain CSD1, which mediates CSDE1 interaction with AGO2. Together, these results demonstrate CSDE1 as a critical regulator of AGO2-mediated strand separation, potentiating miR-486-5p function in target gene silencing associated with in hematological malignancies.

molecular biology↗

bioRxiv2024

Interaction between a J-domain co-chaperone and a specific Argonaute protein contributes to microRNA function in animals

MicroRNAs (miRNAs) are essential regulators of several biological processes. They are loaded onto Argonaute (AGO) proteins to achieve their repressive function, forming the microRNA-Induced Silencing Complex (miRISC). While several AGO proteins are expressed in plants and animals, it is still unclear why specific AGOs are strictly binding miRNAs. Here, we identified the co-chaperone DNJ-12 as a new interactor of ALG-1, one of the two major miRNA-specific AGOs in Caenorhabditis elegans. DNJ-12 does not interact with ALG-2, the other major miRNA-specific AGO, and PRG-1 and RDE-1, two AGOs involved in other small RNA pathways, making it a specific actor in ALG-1-dependent miRNA-mediated gene silencing. The loss of DNJ-12 causes developmental defects associated with defective miRNA function. Using the Auxin Inducible Degron (AID) system, a powerful tool to acutely degrade proteins in specific tissues, we show that DNJ-12 depletion hampers ALG-1 interaction with HSP70, a chaperone required for miRISC loading in vitro. Moreover, DNJ-12 depletion leads to the decrease of several miRNAs and prevents their loading onto ALG-1. This study uncovers the importance of a co-chaperone for the miRNA function in vivo and provides insights to explain how different small RNAs associate with specific AGO in animals.

molecular biology↗

bioRxiv2023

Defining the contribution of microRNA-specific slicing Argonautes in animals

microRNAs regulate gene expression through interaction with an Argonaute protein family member. While some members of this protein family retain an enzymatic activity capable of cleaving RNA molecules complementary to Argonaute-bound small RNAs, the role of the slicing activity in the canonical microRNA pathway is still unclear in animals. To address the importance of slicing Argonautes in animals, we created Caenorhabditis elegans strains, carrying catalytically dead endogenous ALG-1 and ALG-2, the only two slicing Argonautes essential for the miRNA pathway in this animal model. We observe that the loss of ALG-1 and ALG-2 slicing activity affects overall animal fitness and causes phenotypes, reminiscent of miRNA defects, only when grown and maintained at restrictive temperature. Furthermore, the analysis of global miRNA expression shows that the catalytic activity of ALG-1 and ALG-2 differentially regulate the level of specific subsets of miRNAs in young adults. We also demonstrate that altering the slicing activity of those miRNA-specific Argonautes does not result in any defect in the production of canonical miRNAs. Together, these data support that the slicing activity of miRNA- specific Argonautes function to maintain the levels of a set of miRNAs for optimal viability and fitness in animals particularly exposed to specific growing conditions.

molecular biology↗