In the developing central nervous system, neural specification is often controlled by signals secreted from local signalling centres. The cerebellar territory, for example, is initially established by the isthmus (a signalling centre at the mid-hindbrain junction), but what specifies the neural cell types within this territory is unclear. Chizhikov and co-workers now report that the roof plate of dorsal rhombomere 1 (r1; the neural tube region that becomes cerebellum) is a signalling centre for multiple aspects of cerebellar patterning (see ). The researchers define several cell populations in the cerebellar anlage using gene expression and fate mapping studies. They then show that secreted signals from the r1 roof plate are necessary and sufficient for the specification of the adjacent cerebellar rhombic lip. These signals are not, however, absolutely needed to specify more distal cerebellar regions but instead regulate progenitor proliferation and cell position throughout the anlage. Thus, the researchers conclude, the r1 roof plate is a second,important signalling centre during cerebellar development.
