THE LURCHER GENE INDUCES APOPTOTIC DEATH IN CEREBELLAR PURKINJE-CELLS

In the neurologically mutant mouse strain lurcher (Lc), heterozygous a nimals display cell autonomous degeneration of cerebellar Purkinje cel ls beginning in the second postnatal week. During the course of our st udies to identify the genetic lesion responsible for this disease (Nor man et al., 1991), we have formulated an hypothesis suggesting that in Lc Purkinje cells homeostasis is sufficiently perturbed to lead to th e activation of programmed cell death, thus resulting in neuronal loss and the consequent neurologic disease (Heintz, 1993). To address this possibility, we have examined the properties of Lc Purkinje cells as they die during the second postnatal week, Our light and electron micr oscopic studies demonstrate that dying Lc Purkinje cells exhibit the c haracteristic morphologic features of apoptosis, including nuclear con densation, axon beading and membrane blebbing, Using an in situ end-la beling method, we have also detected nicked nuclear DNA in these cells . Furthermore, we have examined the expression of the sulfated glycopr otein 2 (SGP2), whose mRNA is induced in both T-cells and prostate epi thelial cells undergoing apoptotic death. We show by in situ hybridiza tion that SGP2 is not expressed at detectable levels in normal Purkinj e cells, but that its mRNA is present in Lc Purkinje cells prior to th eir death. Also expression of the Kv3.3b potassium channel, which mark s the terminal phase of Purkinje cell differentiation, is evident in L c Purkinje cells prior to their death. These data demonstrate that the Lc mutation induces apoptosis in cerebellar Purkinje cells following their maturation in postnatal cerebellum. Isolation of the Lc mutation and further analysis of its action in eliciting apoptosis can provide an important opportunity for understanding the etiology of neurodegen erative disease.