Young-Gil Jeong

The cyclin-dependent kinase 5 activator, p39, is expressed in stripes in the mouse cerebellum

Cyclin-dependent kinase 5 (Cdk5) activity is required for CNS development. The Cdk5 activator, p35, is well characterized but its isoform, p39, has been less studied. Previously, p39 mRNA expression in rat brain was shown to peak at 3 weeks postnatal, and the level remains high in the adult cerebellum [Neurosci Res 28 (1997) 355]. However, p39 protein expression and specific localization in the cerebellum, where p39 mRNA level significantly exceeds that of p35, have not been examined. Here, we explored the specific cerebellar localization of the p39 protein in the developing and adult mice. Adult cerebellar Purkinje cell somata and dendritic arbors were strongly positive for p39 but only rare and barely detectable p39 was observed in Purkinje cell axons. Cdk5 also localized in Purkinje cell somata and dendrites of the adult cerebellum, but p35 localized only in Purkinje cell somata, further suggesting a functional difference between p35 and p39. During development, cerebellar p39 was first noted at P10. Primary cultures of a developing cerebellum also showed strong p39 immunoreactivity in Purkinje cell somata and dendrites, but weak p39 immunoreactivity in Purkinje cell axons. Starting from P10, p39 was observed in a subset of Purkinje cells that form parasagittal bands throughout the vermis and hemispheres. These bands were bilaterally symmetrical and continuous from one lobule to another. Conversely, Cdk5 and p35 showed a uniform staining pattern. The pattern of p39 closely resembled that of zebrin II/aldolase C, suggesting that p39 may play a role in the adult cerebellum rather than in pattern development. This premise is consistent with the normal pattern of zebrin II/aldolase C zones and stripes in mutant p39-/- mice. The alternating p39 parasagittal band pattern may reflect a role for p39 or Cdk5/p39 in the functional compartmentation of the cerebellum.

Ectopic expression of tyrosine hydroxylase in Zebrin II immunoreactive Purkinje cells in the cerebellum of the ataxic mutant mouse, pogo

The pogo mouse is a new ataxic autosomal recessive mutant that arose in an inbred strain (KJR/MsKist) derived from a Korean wild mouse. The phenotype includes difficulty in maintaining normal posture and the inability to walk straight. Several previous studies have associated inherited ataxia with the ectopic expression of tyrosine hydroxylase (TH) in Purkinje cells. Therefore, in the present study, the distribution of TH expression was compared with that of zebrin II in Purkinje cells of adult pogo/pogo mutant mice. In normal control littermates, tyrosine hydroxylase immunoreactivity is confined to a delicate axonal plexus ramifying through the molecular layer. In pogo/pogo, in addition to the axonal plexus, TH-immunoreactive Purkinje cells were present in all lobules of the cerebellar vermis and hemispheres, distributed as series parasagittal bands. The general pattern of expression is reproducible between individuals and symmetrical about the midline. Alternating stripes of TH expression are also seen in the hemispheres, and most Purkinje cells in the paraflocculi and flocculi are immunoreactive. In pogo/+ mice, TH-immunoreactive Purkinje cells are rare. The pattern of zebrin II expression was used to map TH immunoreactive Purkinje cells in pogo/pogo mutant mice. Double immunofluorescence labeling combining anti-zebrin II fand anti-TH showed that all TH-immunoreactive Purkinje cells are zebrin II+, but that many zebrin II+ Purkinje cells within a band do not stain with anti-TH. Taken together with the morphological changes observed in the Purkinje cell axons, this suggests that abnormal Purkinje cell function may contribute to the ataxic phenotype in pogo/pogo mice.

Tyrosine hydroxylase expression and Cdk5 kinase activity in ataxic cerebellum

Ataxia has been associated with abnormalities in neuronal differentiation and migration, which are regulated by Cyclin-dependent kinase 5 (Cdk5). The cerebellum of mice lacking Cdk5 or its activator, p35, resembles those of ataxic reeler and scrambler mice, suggesting that Cdk5 may contribute to ataxic pathology. As with other ataxic mice, the pogo/pogo mouse shows aberrant cerebellar tyrosine hydroxylase (TH) expression. Since Cdk5 phosphorylates and upregulates TH expression, we sought to analyze (i) Cdk5 activity in the pogo cerebellum, which exhibits abnormal TH expression, and (ii) TH expression in the cerebellum of p35−/− and p39−/− mice, which display reduced Cdk5 activity. Interestingly, we found that increased TH expression in the pogo cerebellum coincided with reduced Cdk5 activity. However, reduced Cdk5 activity in both p35−/− and p39−/− cerebellum did not correspond to defects in TH expression. Together, these suggest that abnormal TH expression in the cerebellum might be regulated by mechanisms other than Cdk5 activity.