FGF signaling enhances a Shh negative feedback loop to control initiation of spinal cord ventral patterning

Spanish government; contract grant numbers: BFU2014-57494-R, BFU2011-29490, BFU2010-15665, BFU2005-02972 (to A. M. and R. D.) and BFU2007-61774, BFU2010-16031-P (to P. B.).