Temporal control of BMP signalling determines neuronal subtype identity in the dorsal neural tube.

The conventional explanation for how a morphogen patterns a tissue holds that cells interpret different concentrations of an extrinsic ligand by producing corresponding levels of intracellular signalling activity, which in turn regulate differential gene expression. However, this view has been challenged, raising the possibility that distinct mechanisms are used to interpret different morphogens. Here, we investigate graded BMP signalling in the vertebrate neural tube. We show that defined exposure times to Bmp4 generate distinct levels of signalling and induce specific dorsal identities. Moreover, we provide evidence that a dynamic gradient of BMP activity confers progressively more dorsal neural identities in vivo. These results highlight a strategy for morphogen interpretation in which the tight temporal control of signalling is important for the spatial pattern of cellular differentiation.