Granule cell raphes in the developing mouse cerebellum

T(h)e cerebellar cortex of many vertebrates shows a striking parasagittal c ompartmentation that is thought to play a role in the establishment and mai ntenance of functional cerebellar connectivity. Here, we demonstrate the ex istence of multiple parasagittal raphes of cells in the molecular layer of the developing cerebellar cortex of postnatal mouse. The histological appea rance and immunostaining profile of the raphe cells suggest that they are m igrating granule cells. We therefore conclude that the granule cell raphes previously described in birds also exist in a mammalian species. The raphes in mouse are visible on nuclear stains from around birth to postnatal day 6 and are frequently found at the boundaries of Purkinje cell segments that differentially express cadherins ("early-onset" parasagittal banding patte rn). A similar relation between the raphe pattern and various markers for t he early-onset banding pattern has been found in the chicken cerebellum. On e of the cadherins mapped in the present study (OL-protocadherin) continues to be expressed in specific Purkinje cell segments until at least postnata l day 14. At this stage of development, the borders of the OL-protocadherin -positive Purkinje cell segments coincide with the borders of Purkinje cell segments that express zebrin II, a marker for the "late-onset" parasagitta l banding pattern which persists in the adult cerebellum. These findings de monstrate that the early-onset banding pattern, as reflected in the complem entary arrangement of raphes/Purkinje cell segments, and the late-onset pat tern of zebrin II expression share at least some positional cues during dev elopment.