A link between c. Elegans morphogenesis and mrna export

Abstract

Multiple studies have explored the mechanisms governing development of the Caenorhabditis elegans pharynx. In this study we used whole genome sequencing (WGS) and CloudMap/Hawaiian Variant Mapping to specifically map a mutation that produced a Pun pharynx (unattached pharynx) phenotype. We discovered a thermo-sensitive t2160 mutant allele of nuclear export 1, nxf-1. nxf-1/TAP encodes a protein that is required for mRNA export from the nucleus to the cytoplasm. To better understand the role of NXF-1 in C. elegans embryonic morphogenesis, we analysed the expression of several apical junction markers in nxf-1(t2160) homozygous embryos and we showed misregulation of these markers, especially DLG-1/Disk large, AJM-1 and HMR-1/E-cadherin. We demonstrated that nxf-1(t2160) arcade cells failed to generate adherens junctions. Furthermore, we visualised pharyngeal morphogenesis using membrane and nuclear PHA-4::GFP reporters. Our analysis suggests that nxf-1 plays a role in pharynx attachment by affecting arcade cell-cell membrane contacts and the actin filament network in the arcade cells. Additionally, depletion of the mRNA export machinery, NXF-1, NXT-1 and HEL-1, leads to embryonic lethality. These export factors regulate the export of the majority of mRNAs in all cells. However, we mainly observed epidermal and pharyngeal morphogenesis defects (Pun phenotype). Therefore, we suggest that some tissues are more sensitive during the developmental process, especially epithelial tissues such as the C. elegans pharynx and epidermis, which seem to need tight regulation of mRNA export. We co-immunoprecipitated (co-IP) the NXF-1 binding partner NXT-1/p15, nucleoporin NPP-9/RanBP2 and P granule protein GLH-1. We suggest that NPP-9/RanBP2 probably mediates the translocation step across nuclear pore complex (NPC) and that GLH-1 probably mediates the release into the cytoplasm. Furthermore, co-IP of P-body proteins allude to the possible involvement of NXF-1 in the mRNA life cycle after it is exported. We propose that C. elegans NXF-1 uses IMB-3, RAN-1 GTPase and RAN-2/RanGAP to be recycled back to the nucleus from the cytoplasm. In addition, our transcriptomic analysis reveals a probable feedback loop by which the mutation of nxf-1(t2160) affects the export of mRNA, causing the overexpression of genes involved in this process and mRNA surveillance pathway. Moreover, our transcriptomic and co-IP analysis uncovered a possible involvement of NXF-1 in regulating the heat shock response, immune response, and other transport pathways. Furthermore, we speculate a novel function of the C. elegans NXF-1 in the rRNA life cycle. Finally, we propose a possible function of NXF-1 in mitosis, independently of mRNA transport.