Roof plate mediated morphogenesis of the forebrain: New players join the game.

The roof plate is a crucial signaling center located at the dorsal midline of the developing central nervous system (CNS) along its rostro-caudal axis. By virtue of secreting multiple signaling molecules, it regulates diverse processes such as specification of dorsal fate, proliferation and axon guidance. In the forebrain, the roof plate is not only involved in patterning but is also involved in the division of the single forebrain vesicle into the two cerebral hemispheres, the failure of which leads to certain forms of holoprosencephaly. Although several molecular players such as Fgfs, BMPs, Wnts and Shh have been identified as crucial regulators of development of the forebrain, little is known about how they interact to bring about the morphological changes associated with the division of the forebrain vesicle into the cerebral hemispheres. Recent studies have now identified the dorsal mesenchyme as an additional source of signaling cues, which is likely to influence the division of the forebrain vesicle into cerebral hemispheres. In this review, we discuss the current understanding about the molecular mechanisms of roof plate mediated patterning and morphogenesis of the forebrain including some recently identified factors that influence this process and also highlight the gaps in our knowledge that remain.