ArRAnging the hindbrain.

The retinoic acid (RA)-dependent mechanisms that orchestrate the development of the hindbrain have been the focus of intense studies over the last decade. A wide range of model systems and experimental approaches have been used to provide important insights into hindbrain patterning. A recent paper could help to unify seemingly disparate observations across species and experimental approaches. Specification of the entire caudal hindbrain is fully dependent on retinoic acid, and specification of individual rhombomeres (r) follows a strict rostrocaudal sequence at precise developmental time windows. Progressively higher RA signalling is necessary for assigning more posterior territories. Complete RA deficiency results in the caudal hindbrain assuming an r4-like identity, which is postulated to be the hindbrain ground state.