Mature Purkinje Cells Require the Retinoic Acid-Related Orphan Receptor-α (RORα) to Maintain Climbing Fiber Mono-Innervation and Other Adult Characteristics

Abstract

Neuronal maturation during development is a multistep process regulated by transcription factors. The transcription factor ROR␣ (retinoic acid-related orphan receptor ␣) is necessary for early Purkinje cell (PC) maturation but is also expressed throughout adulthood. To identify the role of ROR␣ in mature PCs, we used Cre-lox mouse genetic tools in vivo that delete it specifically from PCs between postnatal days 10 -21. Up to 14 d of age, differences between mutant and control PCs were not detectable: both were mono-innervated by climbing fibers (CFs) extending along their well-developed dendrites with spiny branchlets. By week 4, mutant mice were ataxic, some PCs had died, and remaining PC soma and dendrites were atrophic, with almost complete disappearance of spiny branchlets. The innervation pattern of surviving ROR␣-deleted PCs was abnormal with several immature characteristics. Notably, multiple functional CF innervation was reestablished on these mature PCs, simultaneously with the relocation of CF contacts to the PC soma and their stem dendrite. This morphological modification of CF contacts could be induced even later, using lentivirus-mediated depletion of rora from adult PCs. These data show that the late postnatal expression of ROR␣ cell-autonomously regulates the maintenance of PC dendritic complexity, and the CF innervation status of the PC (dendritic vs somatic contacts, and mono-innervation vs multi-innervation). Thus, the differentiation state of adult neurons is under the control of transcription factors; and in their absence, adult neurons lose their mature characteristics and acquire some characteristics of an earlier developmental stage.

Maintenance of postmitotic neuronal cell identity

“…A progressive dendritic and axonal dystrophy also resulted from loss of Nurr1 in adult DA neurons 26 . These findings provide intriguing examples of the requirement for transcriptional maintenance of adult neural connectivity by the very TFs that initially setup the neural circuitry 58 .…”

“…Postnatal Rorα deficiency in Purkinje cells caused a progressive impairment of various sensorimotor functions including deficits in motor coordination, muscle strength, and balance mimicking the severe ataxic phenotype of spontaneous ( staggerer ) or germ line targeted Rorα mutant mice 58 . Rorα is required for expression of several Purkinje cell genes involved in establishing normal motor learning and coordination 85 .…”

“…As Rorα expression continues across the life span conditional targeting approaches were used to determine whether it is also required for maintenance of PCs 58 . Conditional disruption of ongoing Rorα expression between postnatal days 10–21, when PC maturation is nearly complete, led to dendritic atrophy and distal spine loss 58 . Furthermore, substantially decreased numbers of PCs were detected several weeks later.…”

Conserved and Exapted Functions of Nuclear Receptors in Animal Development

“…Mutations in RORα were found to be the cause of the staggerer mutation in mice [50]. These mice present with severe cerebellar dysfunction and altered gait, due to an underlying defect in proliferation and differentiation of Purkinje cells [50, 51]. Like its invertebrate orthologs, RORα is a critical regulator of multiple developmental events [52-54].…”

What Does Low-Intensity rTMS Do to the Cerebellum?

“…Sham-treated animals underwent the same handling but the stimulator was not turned on. We then evaluated gait on a CatWalk XT (Noldus Information Technology, Wageningen, The Netherlands), motor coordination on an accelerating rotarod (TSE Systems, Bad Homburg Germany) and spatial learning in a Morris water maze according to our established protocols [9,12]. All our experiments followed guidelines established by le Comité National d'Ethique pour les Sciences de la Vie et de la Santé, in accordance with the European Communities Council Directive 2010/63/EU.…”