Rora Sg Research Articles

A promoter element with enhancer properties, and the orphan nuclear receptor RORα, are required for Purkinje cell-specific expression of a G i/o modulator

The promoter and structural portion of the gene, Pcp-2(L7), has frequently been used to target expression of proteins to cerebellar Purkinje cells. In our continuing analysis of the transcription of this gene and how it relates to the G-protein and Ca 2+ channel modulatory functions of the encoded protein, we have dissociated the promoter and structural gene and identified cooperative functions. A 0.9 kb fragment of the proximal promoter has positional properties of a classical enhancer, yet its function requires the presence of the structural gene. We demonstrate that RORα, the gene product of the mutant mouse locus called staggerer ( Rora sg ), binds to and activates expression through this promoter element using functional assays in vitro and in vivo. The structural gene has a repressive effect on gene expression outside Purkinje cells, and likely participates in the suppression of Pcp-2(L7) gene expression in the many other brain and non-neuronal cell types, besides Purkinje cells, known to express RORα. Additional studies in vivo show that while Pcp-2(L7) expression is dependent on RORα throughout the cerebellum, this dependence is greatest in the intermediate region between the vermis and far lateral hemispheres. Thus, in addition to its recently indicated role in Ca 2+-mediated reciprocal cell–cell signaling in Purkinje cells, RORα may also contribute to functional differences in cerebellar subregions.

Regional Variations of 5HT Concentrations in Rora sg (staggerer) Mutants

Ataxic Rora(sg) (staggerer) mouse mutants, containing a deletion of the Rora gene which encodes a retinoid-like nuclear receptor, were compared to non-ataxic controls for concentrations of 5-hydroxytryptamine (HT), its main metabolite (5-hydroxy-indole acetic acid, 5HIAA), and its precursor (tryptophan) in cerebellum, brainstem, and forebrain. In Rora(sg) cerebellum, 5HT concentrations increased relative to controls, while tryptophan concentrations decreased. 5HIAA concentrations increased in mutant cerebellum and brainstem, but the 5HIAA/5HT ratio declined only in cerebellum. These results indicate that 5HT turnover decreased in cerebellum of an ataxic mutant, perhaps indicative of presynaptic accumulation and compromised neurotransmission and susceptible to be modified by 5HT pharmacotherapy.

Effect of training on motor abilities of heterozygous staggerer mutant (Rora +/Rora sg) mice during aging

Heterozygous cerebellar mutant (Rora +/Rora sg) mice and control (Rora +/Rora +) mice of the same C57Bl6/J strain, 3–24 months old, were subjected to motor training on a rotorod for 10 days. Falling latency and percentage of time spent walking were measured. A good correlation was found between falling latency and walking time: the mice which maintained equilibrium for a long time were those which were walking, and the mice which fell early were those which were gripping suggesting that walking is obviously the most adapted strategy to keep balance on the rotorod. In Rora +/Rora + mice, scores before training were altered very precociously (from 6 months of age). Moreover, scores of Rora +/Rora sg mice were lower than those of Rora +/Rora + mice from the age of 3 months, while neuronal number in the cerebellar cortex of these mutants was quite normal and similar to that of Rora +/Rora + mice. This suggests that the motor skill disability would be due to fine structural and/or biochemical changes preceding neuronal death. Such subtle changes would begin several months earlier in Rora +/Rora sg than in Rora +/Rora + mice. Training on the rotorod resulted in increased scores in both genotypes at all ages. Motor learning abilities were therefore preserved in animals with a moderate neuronal loss in the cerebellum. It may be that motor learning is partly compensated by the striatum, which is known to play a major role in learning of motor skills.

Age-related phenotypes in the staggerer mouse expand the RORα nuclear receptor's role beyond the cerebellum

The homozygous mutant mouse staggerer (RORa sg /RORa sg ), was initially described as ataxic, due to the presence of massive neurodegeneration in the cerebellum [Science 136 (1962) 610]. The identification of the widely expressed Retinoic acid receptor-related Orphan Receptor, NR1F1 (RORα) gene as the site of mutation in the staggerer mouse has led to great progress in understanding the molecular basis of its phenotype in recent years [Nature 379 (1996) 736]. RORα is a transcription factor, belonging to the nuclear receptor superfamily, for which no natural ligand has yet been identified. Mice engineered for the disruption of the gene encoding RORα display the same cerebellar atrophic phenotype as the staggerer mouse [Proc. Natl. Acad. Sci. USA 95 (1998) 3960]. More recently, it has been shown that the mutation is semi-dominant, as heterozygous animals display an increased loss of Purkinje cells with age. Furthermore, a number of additional phenotypes outside the nervous system have recently been identified. These include a greater susceptibility to atherosclerosis [Circulation 15 (1998) 2738], immunodeficiencies linked to the overexpression of inflammatory cytokines [J. Neurochem. 58 (1992) 192], abnormalities in the formation and maintenance of bone tissue [Proc. Natl. Acad. Sci. USA 97 (2000) 9197] and changes in muscle differentiation [Nucleic Acids Res. 27 (1999) 411]. Thus, RORα has been directly linked to a number of age-related pathologies of great medical interest.