Regulation of Purkinje cell (PC) number is critical for proper assembly and function of the cerebellum. Murine cerebellar neurogenesis yields supernumerary populations of cells that are subject to programmed cell death during development and aging. This study focuses on the control of mouse PC number during development and the consequences of interrupting normal cell death. Purkinje cell-specific regulatory elements from the pcp2 gene were employed to target expression of two anti-apoptotic proteins, human BCL-2 and adenovirus E1B 19k to the PCs of transgenic mice. Comparative morphometric analyses indicated no significant difference in PC numbers in the strongest BCL-2 expressing line, while a 14.2% increase was noted in the pcp2/E1B 19k transgenic line. The temporal transgene expression patterns of several mouse lines indicated that PC numbers are normally adjusted during the first postnatal week. Crossbreeding studies demonstrated that both Bcl-2 and E1B 19k transgenes provided Purkinje cell protection from SV40 Tag-induced cell death. Interestingly, RotaRod behavioral analysis demonstrated that 'rescued' Purkinje cells degrade cerebellar function. Furthermore, aged E1B 19k and Bcl-2 mice exhibited decreased RotaRod performance despite increased PC numbers. These findings have implications regarding neuronal death during development and aging as well as cellular and genetic strategies to circumvent neuronal degeneration.
Bibliographical noteFunding Information:
The authors thank Dr. Harry T. Orr for his support throughout this project. Maria Athanasiou derived and assisted with the initial characterization of the E1B 19k mice. We thank Bob Ehlenfeldt and Sandra Horn for generating the transgenic mice. Lu Ann Anderson, James Stallock, Matthew Price, and Wael Yunis assisted with the tissue collection, sectioning, and Purkinje cell counting studies. This work was supported by NIH Grant NS32320 to R.M.F., an American Cancer Society RPG #99-330-01-CGG to R.M.F., and NIH PO1 NS31318 to A.J.B.