BMP/Smad signaling and embryonic cerebellum development: stem cell specification and heterogeneity of anterior rhombic lip.

The canonical bone morphogenetic proteins (BMPs) signaling have been shown to mediate many embryonic developmental processes. Due to its complexity, there are still many unknowns about this signal pathway including the Smad usage and requirement. Cerebellum, one of the most studied neural organs in development biology, requires canonical BMP signaling for stem cell specification. Here we review the role of canonical BMP signaling during the embryonic cerebellum development. Also, we raise several unsolved issues concerning the BMP signaling including the co-Smad independency of this signaling pathway. Besides, we also propose two models for explaining the cerebellar anterior rhombic lip (ARL) specification mechanisms. In addition, we review the heterogeneity of the ARL stem cells, which may provide new insight into understanding the neural stem cell specification process of the embryonic cerebellum.