The coordination of signals from different pathways is important for cell fate specification during animal development. Here, we define a novel mode of crosstalk between the epidermal growth factor receptor/Ras/mitogen-activated protein kinase cascade and the LIN-12/Notch pathway during Caenorhabditis elegans vulval development. Six vulval precursor cells (VPCs) are initially equivalent but adopt different fates as a result of an inductive signal mediated by the Ras pathway and a lateral signal mediated by the LIN-12/Notch pathway1. One consequence of activating Ras is a reduction of LIN-12 protein in P6.p (ref. 2), the VPC believed to be the source of the lateral signal. Here we identify a ‘downregulation targeting signal’ (DTS) in the LIN-12 intracellular domain, which encompasses a di-leucine-containing endocytic sorting motif. The DTS seems to be required for internalization of LIN-12, and on Ras activation it might mediate altered endocytic routing of LIN-12, leading to downregulation. We also show that if LIN-12 is stabilized in P6.p, lateral signalling is compromised, indicating that LIN-12 downregulation is important in the appropriate specification of cell fates in vivo.
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We thank M. Stern for the egl-17p::LacZ plasmid and helpful advice on making the modified egl-17 promoter; R. Waterston for anti-MH27 antibody; M. Han for the sur-2(ku9) strain; H. Fares for reagents and much helpful advice; K. Simpson for help with backcrossing integrated arrays; B. Grant for anti-sera against endocytic markers; D. Levitan for advice on immunostaining; R. Ruiz for technical assistance; and B. Grant, O. Hobert, S. Jarriault, X. Karp, G. Struhl and A. Tomlinson for discussion and critical reading of the manuscript. D.S. was supported by a National Science Foundation predoctoral fellowship and an NIH National Institute on Aging training grant, coordinated by R. Liem. I.G. is an Investigator of the Howard Hughes Medical Institute.
The authors declare that they have no competing financial interests.
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Journal of Developmental Biology (2018)
Cell Reports (2018)
Cellular Signalling (2018)