Bitoun E., Oliver PL., Davies KE.
© Springer Science+Business Media Dordrecht 2013. Gene targeting is a very powerful approach for the generation of clinically relevant mouse models to elucidate the underlying molecular basis of cerebellar disorders. However, with the etiology of the vast majority of these conditions still unknown, a complementary approach based on large-scale random mutagenesis is now being employed to identify new genes and downstream signaling pathways that control neuronal cell death and survival in the cerebellum. This chapter presents the characterization of the robotic mouse, a novel model of autosomal dominant cerebellar Ataxia isolated from an N-ethyl-N-nitrosourea (ENU) mutagenesis screen, which shows general growth retardation, adult-onset region-specific Purkinje cell (PC) loss, cataracts, and defects in early T-cell maturation. The mutated protein ALL1-fused gene from chromosome 4 (AF4), which functions as a cofactor of RNA polymerase II (Pol II) elongation and disruptor of telomeric silencing-1 (DOT1)-mediated chromatin remodeling during transcription, abnormally accumulates in PCs of the cerebellum due to a slower turnover by the ubiquitin-proteasome pathway. This results in the sustained transcriptional repression of the PC survival factor insulin-like growth factor 1 (IGF-1) and deficits in downstream signaling activation, leading to degeneration and eventually death of PCs. The identification of AF4 and DOT1 as the first transcriptional negative regulators of IGF-1 expression in the cerebellum opens new avenues of research into the manipulation of this pathway for the treatment of cerebellar Ataxia. In addition, the functional conservation among the AF4-related proteins implies that deregulation of transcriptional elongation and chromatin remodeling may also underlie the pathogenesis of other disorders of the central nervous system (CNS), in particular mental retardation. The robotic mouse has revealed a critical novel function for AF4 in the cerebellum which could not have been predicted otherwise, and has been instrumental in the elucidation of the relevant transcriptional regulatory mechanisms.