Nuclear translocation of tagged endogenous ERK/MPK-1 MAP Kinase denotes a subset of activation events inC. elegansdevelopment

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° 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.