A RAP2>CNH-MAP4K Signaling Pathway Promotes Non-Specialized Epithelial Cell Fate in So-Called Ground/Passive/Uninduced Cells

Abstract

During C. elegans development, EGF signal from the anchor cell (AC) induces the roughly six equipotent vulval precursor cells (VPCs) to assume the pattern 3˚-3˚-2˚-1˚-2˚-3˚ of cell fates. The VPC closest to the AC is induced via the Ras-Raf-MEK-ERK MAP kinase cascade to assume 1˚ fate. Presumptive 1˚ cells express DSL ligands to induce the two neighboring cells via the Notch receptor to assume 2˚ fate. In contrast, 3˚ fate is typically referred to as the “ground” or “uninduced” cell fate; 3˚ cells divide once and fuse with the surrounding epithelium. We observed that MIG-15, a MAP4 kinase, plays a role in VPC patterning. Upon genetic perturbation of MIG-15 function, we observed an increase in ectopic 1˚ as well as ectopic 2˚ cells. This is also true for RAP-2, a protein shown in various systems to activate MIG-15. Both RAP-2 and MIG-15 are necessary for full expression of a marker expressed in 3° cells. Endogenous CRISPR tags of MIG-15 and RAP-2 revealed ubiquitous expression with cytosolic and cell-membrane localization of both genes respectively. Our work positions us to explore signals that promote “ground” developmental state and perhaps informs the relationship between cancers and stromal cells.