Compartmental organization of Purkinje cells in the mature and developing mouse cerebellum as revealed by an olfactory marker protein-lacZ transgene

In a line of transgenic mice (HpY-1), the pattern of expression of an olfac tory marker protein (OMP)-lacZ fusion gene was analyzed in the cerebellum, where, in adult mice, OMP-lacZ was expressed primarily in Purkinje cells (P Cs) of the posterior lobe. The transgene-expressing PCs were organized in p arasagittal bands, with a boundary of expression roughly corresponding to t he primary fissure that separates the cerebellum into anterior and posterio r compartments. The regional expression of the lacZ gene was also analyzed during embryonic and postnatal development of the cerebellum. Within the ce rebellum-isthmus region, transgene expression first was detected at embryon ic day 13.5 (E13.5) in a cluster of postmitotic cells. By E14.5, lacZ was a lso expressed by a subpopulation of migrating PCs in the postisthmal and la teral cerebellar primordium, and, by E16.5, transgene-positive PCs formed c audally four sagittal bands symmetric to the medial embryonic fissure. The caudal pattern was retained in postnatal cerebella, where, by postnatal day 0 (P0), transgene-positive PCs in vermal lobules VIII and IX appeared to b e organized in two prominent parasagittal compartments on either side of a negative midline band. In early postnatal animals, the transgene was expres sed transiently in the anterior lobe vermis. Hence, from P5 onward, transge ne expression appeared mostly restricted to the posterior lobe, where it fo llowed a caudal-to-rostral gradient. In the paraflocculus, transgene-expres sing PCs were confined to the rostrodorsal portion. The results indicate th at the anterior and posterior cerebellar lobes are regulated by distinct on togenetic programs, and PCs of functionally distinct cerebellar regions exp ress the transgene differentially. Furthermore, the data suggest that ectop ic expression of OMP-lacZ in the cerebellum is under the control of regulat ory elements that provide positional information for the regional specifica tion of PC subsets. J. Comp. Neurol. 404:97-113, 1999. (C) 1999 Wiley-Liss, Inc.