Evidence that the WNT-inducible growth arrest-specific gene 1 encodes an antagonist of sonic hedgehog signaling in the somite

The dorsal-ventral polarity of the somite is controlled by antagonistic sig nals from the dorsal neural tube/surface ectoderm, mediated by WNTs, and fr om the ventral notochord, mediated by sonic hedgehog (SHH). Each factor can act over a distance greater than a somite diameter in vitro, suggesting th ey must limit each other's actions within their own patterning domains in v ivo. We show here that the growth-arrest specific gene 1 (Gas1), which is e xpressed in the dorsal somite, is induced by WNTs and encodes a protein tha t can bind to SHH. Furthermore, ectopic expression of Gas1 in presomitic ce lls attenuates the response of these cells to SHH in vitro. Taken together, these data suggest that GAS1 functions to reduce the availability of activ e SHH within the dorsal somite.