Development of cerebellar modules: extrinsic control of late-phase zebrin II pattern and the exploration of rat/mouse...

The vertebrate cerebellum is divided into a characteristic set of 13 parasagittal "bands" or modules that are revealed in many different domains-ranging from patterns of gene and protein expression to the organization of afferent input. We have used the expression of Zebrin II/aldolase C in Purkinje cells as a marker of these bands and have discovered several new features of their regulation. We find that appearance of the banded expression of aldolase C during development differs between rat and mouse. In agreement with previous reports there is, in rat, a transient period during which all Purkinje cells are positive for aldolase C expression. By contrast, in mouse, the pattern emerges in its adult (banded) form from the earliest postnatal times. This species difference is found in both mRNA and protein expression. There also appears to be a transition that occurs in vivo between postnatal days 8 and 10. Slice cultures established from cerebella at the younger age do not develop a complete banding pattern, even after 6 days in culture. Slice cultures established from postnatal day 10 mice develop the full pattern within 2 days. This difference cannot be overcome by manipulating the levels of neuronal activity in the cultures. Thus some event must occur in vivo that "releases" the adult pattern and allows it to be realized in the more artificial situation of the slice culture. Taken together the results offer a more complete picture of the regulation of the aldolase C gene in cerebellar Purkinje cells and suggest important species differences in its developmental expression pattern.