Clathrin regulates centrosome positioning by promoting acto-myosin cortical tension in C. elegans embryos

Abstract

Regulation of centrosome and spindle positioning is crucial for spatial cell division control. The one-cell Caenorhabditis elegans embryo has proven attractive for dissecting the mechanisms underlying centrosome and spindle positioning in a metazoan organism. Previous work revealed that these processes rely on an evolutionarily conserved force generator complex located at the cell cortex. This complex anchors the motor protein dynein, thus allowing cortical pulling forces to be exerted on astral microtubules emanating from microtubule organizing centers (MTOCs). Here, we report that the clathrin heavy chain CHC-1 negatively regulates pulling forces acting on centrosomes during interphase and on spindle poles during mitosis in one-cell C. elegans embryos. We establish a similar role for the cytokinesis/apoptosis/ RNA-binding protein CAR-1 and uncover that CAR-1 is needed to maintain proper levels of CHC-1. We demonstrate that CHC-1 is necessary for normal organization of the cortical acto-myosin network and for full cortical tension. Furthermore, we establish that the centrosome positioning phenotype of embryos depleted of CHC-1 is alleviated by stabilizing the acto-myosin network. Conversely, we demonstrate that slight perturbations of the acto-myosin network in otherwise wild-type embryos results in excess centrosome movements resembling those in chc-1(RNAi) embryos. We developed a 2D computational model to simulate cortical rigidity-dependent pulling forces, which recapitulates the experimental data and further demonstrates that excess centrosome movements are produced at medium cortical rigidity values. Overall, our findings lead us to propose that clathrin plays a critical role in centrosome positioning by promoting acto-myosin cortical tension.

Mechanical stress combines with planar polarised patterning during metaphase to orient embryonic epithelial cell divisions

“…We show that AP-patterning across the whole tissue, through the planar polarisation of Myosin II, biases the metaphase spindle towards AP for all mitotic cells. This generalises our previous finding that strongly Myosin II-enriched PSBs attract and stabilise spindle ends suggesting that Myosin II could be directly involved in attracting the spindle, possibly through increased cortex stiffness (Spiro et al, 2014). AP-patterning straddles the whole DV circumference of the embryo (Irvine and Wieschaus, 1994) so that even the ME domain has polarised Myosin II, driving AP-oriented division in these isotropic cells.…”

Suppressor of clathrin deficiency (Scd6)—An emerging RGG‐motif translation repressor

“…A transcriptome‐wide binding study identified few such mRNAs (for example, SEC6 [Secretory 6; a subunit of the exocyst complex], SEC13, SMY2 [Suppressor of Myo2‐66 2; involved in COPII vesicle formation], and SWA2 [Synthetic lethal With Arf1 2; involved in the uncoating of clathrin‐coated vesicles] binding to Scd6 (Tsvetanova, Klass, Salzman, & Brown, ). Strikingly, it was reported in worms that CAR‐1 depletion causes a decrease in CHC‐1 protein levels and knockdown of CAR‐1 leads to similar phenotypes as CHC‐1 knockdown (Spiro et al, ). The mechanism by which CAR‐1 affects CHC‐1 levels is unknown.…”

Regulation and Assembly of Actomyosin Contractile Rings in Cytokinesis and Cell Repair

“…In C. elegans embryos, it has been shown that a direct interaction between the conserved MT bundler protein regulator of cytokinesis 1 (PRC1) and centralspindlin is important for the mechanical robustness of the central spindle, which experiences considerable tensile forces (Lee et al, ). In C. elegans embryo cytokinesis, it has been shown that clathrin heavy chain 1 (CHC‐1) promotes actomyosin cortical tension, thus stabilizing CR position (Spiro et al, ).…”