The MAPK phosphatase VHP-1 buffers pharynx-to-body proportions against tissue-specific growth imbalance in C. elegans

Maintaining appropriate organ size ratios in the face of growth fluctuations is critical for the development of a reproducible body plan. Yet the mechanisms involved remain poorly understood. Here, we investigated how pharynx-to-body proportions are maintained in Caenorhabditis elegans , combining tissue-specific perturbations, genetic screening, and longitudinal live imaging. A genome-wide RNAi screen revealed that knock-down of the dual-specificity MAPK phosphatase VHP-1 turns animals hypersensitive to inter-tissue growth imbalance caused by pharyngeal or epidermal depletion of the mTORC1 activator RAGA-1 or the ribosomal protein RPL-22. In contrast, vhp-1 mutants tolerated global raga-1 loss, indicating a specific requirement for vhp-1 under tissue growth imbalance. Knock-down of the p38 pathway suppressed the imbalance-specific defects of vhp-1 mutants. In contrast, JNK knock-down effectively rescued the pleiotropic phenotypes of vhp-1 mutants but only weakly reduced their sensitivity to RAGA-1 imbalance, indicating that these two stress-MAPK pathways make distinct contributions to the response to growth imbalance. Finally, whole-animal VHP-1 levels increased upon epidermal RAGA-1 depletion, and epidermal VHP-1 depletion did not reproduce the sensitivity caused by global vhp-1 loss, consistent with a contribution from VHP-1 outside the growth-perturbed epidermis in buffering against local growth imbalance.