Dofher, K. | bioRxiv Science

bioRxiv2026

Combinatorial regulation of cellular rotation by CUL-3-actomyosin-dependent oriented division, eggshell geometry, and Ras–MAPK signaling during dorsal–ventral axis establishment in Caenorhabditis elegans

Cellular rotation is an understudied mechanism that regulates animal morphogenesis. In C. elegans, the dorsal-ventral axis is established when the two-cell-stage AB cell rotates within the eggshell as it divides, generating the diamond-shaped blastomere arrangement at the four-cell stage that enables distinct cell fate specification. Multiple mechanisms, including actomyosin-dependent oriented division, chiral cortical flow, and eggshell shape, have been proposed to regulate this arrangement, but whether these represent conflicting hypotheses or co-acting mechanisms remains unclear. Here, we show that CUL-3-actomyosin-dependent oriented division, eggshell geometry, and the Ras-MAPK signaling pathway regulate distinct steps of cellular rotation. AB cell rotation occurred in two distinct phases: Phase I during AB cytokinesis and Phase II during cytokinesis of the neighboring P1 cell. Quantitative analysis revealed that CUL-3-actomyosin-dependent oriented division is the only one of these three pathways that regulates the AB division axis before anaphase. Actomyosin-dependent oriented division and eggshell geometry were both required for Phase I rotation, whereas Phase II rotation was independent of eggshell geometry. We further identified the Ras-MAPK signaling pathway as a regulator of AB cell rotation that acts independently of eggshell geometry. Strikingly, the CUL-3-actomyosin-dependent pathway may have two distinct roles: first, specifying the AB division axis, and second, correcting the division axis in all cell types during cytokinesis. Together, these functions contribute significantly to cellular rotation and dorsal-ventral axis establishment.

Cell Biology↗

bioRxiv2025

Identification of Genes Required for Spatial Control and Mechanical Resilience of Cytokinesis during Caenorhabditis elegans Embryogenesis

Cytokinesis is the final step of cell division, in which the dividing cell is physically separated into two daughter cells by the contractile ring. The contractile ring is a highly resilient molecular machine that can function properly under mechanical stress. Additionally, its function, position, and orientation are spatially modulated in developing animals to regulate morphogenesis. Although essential regulators of cytokinesis have been identified through previous genetic screens, the molecular mechanisms underlying these spatial controls and the mechanical resilience of cytokinesis remain elusive. To identify cytokinesis regulators involved in these processes, we performed a high-throughput RNAi screen using a gain-of-function mutant of actin that exhibits ectopic cortical contraction and abnormal spatial control of cytokinesis in Caenorhabditis elegans embryos. We obtained a list of early embryonic genes that suppress embryonic lethality in an act-2 mutant background. Two parallel secondary screens of candidate genes were conducted. The first secondary screen in a wild-type background identified 69 candidate genes regulating spatial cytokinesis control--asymmetric ring closure, positioning, and rotation--during early embryogenesis. The second secondary screen in the act-2(or295) background identified four genes required for cytokinesis in this background, including microtubule regulators, evl-20/ARL2, and lpin-1/Lipin1. This study will serve as a useful resource for the development of future hypotheses and provide insights into the precise regulation of cytokinesis in tissues.

cell biology↗