The C. elegans postembryonic mesoderm, the M lineage, exhibits distinct dorsoventral asymmetry: the dorsal side produces two non-muscle coelomocytes (CCs), while the ventral side produces two sex myoblasts (SMs). We have previously shown that LIN-12/Notch signaling and the antagonism of BMP signaling by the Schnurri protein SMA-9 function independently to promote ventral and dorsal M lineage fates, respectively (Foehr and Liu, 2008). How these distinct signaling inputs are integrated is not known. We have found that the forkhead transcription factor UNC-130 is one of the key factors that function to integrate these distinct signaling inputs, and that this function of UNC-130 is independent of UNC-129, a TGF-beta factor whose expression in ventral bodywall muscles is known to be regulated by UNC-130 (Nash et al., 2000). A functional UNC-130::GFP is exclusively expressed in the ventral M lineage starting at the 8-M stage. We have found that the ventral M lineage expression of UNC-130::GFP requires LIN-12/Notch signaling, while the lack of UNC-130::GFP expression in the early M lineage and the dorsal M lineage is due to the antagonism of BMP signaling by SMA-9. We further showed that unc-130(0), but not unc-129(0), mutation can suppress the M lineage dorsal-to-ventral fate transformation defect of sma-9(0) mutants. These findings provide critical molecular evidence for the role of SMA-9/Schnurri in antagonizing BMP signaling in C. elegans. unc-130(0) mutants have low penetrance of dorsoventral patterning defects in the M lineage, suggesting that additional factors function together with UNC-130 to integrate the two signaling inputs. Current work focuses on identifying these additional factors.
References:
1) Foehr ML, Liu J. (2008) Dorsoventral patterning of the C. elegans postembryonic mesoderm requires both LIN-12/Notch and TGFbeta signaling. Dev Biol. 313(1):256-66.
2) Nash B, Colavita A, Zheng H, Roy PJ, Culotti JG. (2000) The forkhead transcription factor UNC-130 is required for the graded spatial expression of the UNC-129 TGF-beta guidance factor in C. elegans. Genes Dev. 14(19):2486-500.