Peri- and postnatal development of cerebellar compartments in the mouse.

The adult cerebellar cortex is compartmentalized into longitudinal stripes, in which Purkinje cells (PCs) have compartment-specific molecular expression profiles. Since the striped compartments have specific afferent and efferent projection patterns, they underlie the functional localization of the cerebellum. How these compartments form during development is generally not understood. Our recent study focuses on development of the cerebellar compartmentalization from embryonic day 17.5 (E17.5), when embryonic clustered compartmentalization is evidently observed, to postnatal day 6 (P6), when adult-type striped compartmentalization begins to be established, in mouse. FoxP2, one of the marker molecules for immature PCs, has been used to identify E17.5 PCs. PC subsets or clusters have been distinguished from each other by using different expression profiles of several marker molecules (PLCβ4, EphA4, Pcdh10, and a reporter molecule of the 1NM13 transgenic mouse strain). Analysis of spatial organization of PC clusters by three-dimensional reconstruction from multiple-stained serial sections has indicated 54 PC clusters in the E17.5 cerebellum. Individual clusters are spatially rearranged into stripes in the period from E17.5 to P6. In summary, the clustered compartments in the E17.5 cerebellum are basically direct origin of the adult-type striped compartments in the cerebellar cortex.