A 2.7-kb region upstream of the Gdf6 gene drives neural tube expression but not limb joint expression in transgenic mouse embryos. Top: diagram of the p2.7βgeo construct. The LacZ* denotes the LacZ/neo fusion gene plus polyA signal. Bottom: Side (left) and dorsal (right) views of a 14.5-dpc mouse embryo transgenic for p2.7βgeo. Arrowheads indicate staining in the dorsal neural tube. Arrow indicates forebrain expression.