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ly expressed in neural and extra-neural tissues, and plays a role in DNA synthesis at the G1/S cell-cycle checkpoint. The role of Ciz1 in the nervous system and relative contributions of gain- or loss- of function to the pathogenesis of Ciz1-associated dystonia remain indefinite. Using relative quantitative reverse transcriptase-PCR, cerebellum showed the highest expression levels of Ciz1 in adult mouse brain, over two fold higher than liver, and higher than striatum, midbrain and cerebral cortex. Overall, neural expression of Ciz1 increased with postnatal age. A Ciz1 gene-trap knock-out (KO) mouse model (Ciz1-/-) was generated to examine the functional role(s) of Ciz1 in the sensorimotor nervous system and contributions of Ciz1 to cell-cycle control in the mammalian brain. Ciz1 transcripts were absent in Ciz1-/- mice and reduced by approximately 50% in Ciz1+/- mice. Ciz1-/- mice were fertile but smaller than wild-type (WT) littermates. Ciz1-/- mice did not manifest dystonia, but exhibited mild motoric abnormalities on balance, open-field activity, and gait. To determine the effects of germline KO of Ciz1 on whole-genome gene expression in adult brain, total RNA from mouse cerebellum was harvested from 6 10-month old Ciz1-/- mice and 6 age- and gender- matched WT littermates for whole-genome gene expression analysis. Based on whole-genome gene-expression analyses, genes involved in cellular movement, cell development, cellular growth, cellular morphology and cell-to-cell signaling and interaction were up-regulated in Ciz1-/- mice. The top up-regulated pathways were metabolic and cytokine-cytokine receptor interactions. Down-regulated genes were involved in cell cycle, cellular development, cell death and survival, gene expression and cell morphology. Down-regulated networks included those related to metabolism, focal adhesion, neuroactive ligand-receptor interaction, and MAPK signaling. Based on pathway analyses, transcription factor 7-like 2 (TCF7L2), a member of the Wnt/beta-catenin signaling pathway, was a major hub for down-regulated genes, whereas NF-kappaB was a major hub for up-regulated genes. In aggregate, these data suggest that Ciz1 may be involved in the post-mitotic differentiation of neurons in response to external signals and changes in gene expression may compensate, in part, for Ciz1 deficiency in our Ciz1-/- mouse model. Although Ciz1 deficiency was associated with mild motor abnormalities, germline loss of Ciz1 was not associated with dystonia on the C57BL/6J background.