A new class B synthetic multivulva gene, ccar-1 works through the Ras pathway to regulate vulva development

Conserved Ras and Notch cell-signaling pathways promote Caenorhabditis elegans vulval cell fates. Ras pathway activity promotes the 1º vulval fate and inhibits the 2º vulval fate, and Notch pathway activity promotes the 2º vulval fate and inhibits the 1º vulval fate. Vulval cell fates are inhibited by the parallel-acting synthetic multivulva (synMuv) genes, which are grouped into either class A or B genes. We identified a new synMuv class B gene ccar-1, that works redundantly with class A genes to regulate vulva development. ccar-1 is activated by the Notch pathway to inhibit the Ras pathway in presumptive 2º vulval cells to ensure low levels of Ras pathway activity and proper 2º vulval fate specification. Our findings indicate that ccar-1 might inhibit the Ras pathway by repressing the transcription of the Ras pathway ligand lin-3 EGF. By analogy, we suggest that CCAR-1 might act as a tumor suppressor by inhibiting the expression of growth factor signals. Our study also highlights the identification of a first gain-of-function mutation that suppresses the synMuv phenotype. RNA-seq profiling of C. elegans wild strain N2, mutant Cel-ccar-1(gk433), and mutant Cel-ccar-1(n2070) at mixed stage.