Nuclear translocation of tagged endogenous ERK/MPK-1 MAP Kinase denotes a subset of activation events in C. elegans development

Abstract

The extracellular signal-regulated kinase (ERK) MAP kinase is utilized downstream of Ras>Raf>MEK signaling to control activation of a wide array of targets. Activation of ERK is elevated in Ras-driven tumors and RASopathies, and is thus a target for pharmacological inhibition. Regulatory mechanisms of ERK activation has been studied extensively in vitro and in cultured cells but little in living animals. We used CRISPR to tag the 3 end of the C. elegans ERK-encoding gene, mpk-1. Endogenous MPK-1 protein is ubiquitously expressed with elevated expression in certain tissues. We detected cytosol-to-nuclear translocation of MPK-1 in maturing oocytes and hence validated nuclear translocation as a reporter of some activation events. During developmental patterning of the six vulval precursor cells, MPK-1 is necessary and sufficient for the central cell, P6.p, to assume 1{degrees} fate. We observed MPK-1 to be recruited to the nuclei of all six VPCs in a temporal and concentration gradient centered on P6.p. This observation contrasts with previous results using the ERK-nKTR reporter of substrate activation, raising questions about mechanisms and indicators of MPK-1 activation. This system and reagent promise to provide critical insights into regulation of MPK-1 activation within a complex intercellular signaling network.