Thyroid hormone receptor β mutation causes severe impairment of cerebellar development Aline Cristina Portella a , Fernando Carvalho a , Larissa Faustino b , Fredric E. Wondisford c , Tânia Maria Ortiga-Carvalho b , Flávia Carvalho Alcantara Gomes a, ⁎ a Instituto de Ciências Biomédicas, Universidade Federal do Rio de Janeiro, 21941-590, Rio de Janeiro, RJ, Brazil b Instituto de Biofísica Carlos Chagas Filho, Universidade Federal do Rio de Janeiro, 21941-590, Rio de Janeiro, RJ, Brazil c Department of Pediatrics, Division of Metabolism, Johns Hopkins University Medical School, Baltimore, Maryland 21287, USA abstract article info Article history: Received 25 September 2009 Revised 28 December 2009 Accepted 19 February 2010 Available online 1 March 2010 Keywords: Cerebellum Thyroid hormone TRβ Nuclear receptors Foliation Bergmann glia Cerebellar development on the postnatal period is mainly characterized by cellular proliferation in the external granular layer (EGL) followed by migration of granular cells in the molecular layer through the Bergmann glia (BG) fibers in order to form the granular layer in the adult. All these events are drastically affected by thyroid hormones (TH), which actions are mainly mediated by alpha (TRα) and beta (TRβ) nuclear receptor isoforms. Here, we analyzed the effects of a natural human mutation (337T) in the TRβ locus, which impairs T3 binding to its receptor, on the mouse cerebellum ontogenesis. We report that target inactivation of TRβ-TH binding leads to a smaller cerebellum area characterized by impaired lamination and foliation. Further, TRβ mutant mice presented severe deficits in proliferation of granular precursors, arborization of Purkinje cells and organization of BG fibers. Together, our data suggest that the action of TH via TRβ regulates important events of cerebellar ontogenesis contributing to a better understanding of some neuroendocrine disorders. Further, our data correlate TRβ with cerebellar foliation, and provide, for the first time, evidence of a receptor-mediated mechanism underlying TH actions on this event. © 2010 Elsevier Inc. All rights reserved. Introduction The cerebellum is an excellent model to study mechanisms that control central nervous system (CNS) morphogenesis. Besides few cell types, the cerebellar cells undergo sequential steps of development in spatially well-defined regions, leading to a relatively simple and well- known laminar organization (Altman and Bayer, 1997; Corrales et al., 2006; Sillitoe and Joyner, 2007). The cerebellum is located on the back of the brain stem at the midbrain–hindbrain junction, traditionally associated to coordinating proprioceptive–motor functions. Emerging evidences from experi- mental animal models and cerebellar disorders in humans have recently implicated this structure in higher activities such as cognition, emotion, memory and language processing (Baillieux et al., 2008; Callu et al., 2007; Tavano et al., 2007). The mammalian cerebellum consists of a central vermis and two lateral hemispheres, each with its own set of fissures and folia. The noticeable morphological feature of the mammalian cerebellum is characterized by a coordinated three-dimensional complexity of medial–lateral and antero-posterior domains generated by a multi- factorial phenomenon known as foliation (Sillitoe and Joyner, 2007). In mice, cerebellar foliation is characterized by transition from the smoothed cerebellar surface to the X lobule cerebellum, a pattern mostly achieved 2–3 weeks after birth (Altman and Bayer, 1997). Mapping and physiological studies implied a correlation between specific folia and sensory-motor tasks (Sillitoe and Joyner, 2007; Sotelo, 2004). The conservation of the foliation pattern suggests that this event might be tightly genetically regulated, although it remains unknown how position of fissures, folia size and complexity are determined. Cerebellar granule precursors arise from the neuroepithelium at the rhombic lip that forms the posterior boundary to the cerebellar primordium. In rodents, granular cell precursors (GCPs) migrate rostrally over the surface of the cerebellum during the second half of embryogenesis, forming a second and transient germinal zone, the external granular layer (EGL). During the two postnatal weeks, the EGL precursors proliferate extensively and generate postmitotic granular cells, which migrate inward through Bergmann glia (BG) fibers, bypass the Purkinje cell layer (PCL), and finally generate the internal granular layer (IGL) (Miale and Sidman, 1961; Sotelo, 2004). Cerebellar ontogenesis undergoes dramatic modulation by thyroid hormones (THs) (Clos and Legrand, 1973; Clos et al., 1980; Gomes et al., 2001; Martinez and Gomes, 2002, 2005). Hypothyroidism is associated with several abnormalities in the cerebellar cortex such as persistence of the EGL, increased neuronal death in the IGL, impaired Molecular and Cellular Neuroscience 44 (2010) 68–77 ⁎ Corresponding author. Instituto de Ciências Biomédicas, Universidade Federal do Rio de Janeiro, Centro de Ciências da Saúde, Bloco F, Ilha do Fundão, 21941-590, Rio de Janeiro, RJ, Brazil. E-mail address: fgomes@anato.ufrj.br (F.C.A. Gomes). 1044-7431/$ – see front matter © 2010 Elsevier Inc. All rights reserved. doi:10.1016/j.mcn.2010.02.004 Contents lists available at ScienceDirect Molecular and Cellular Neuroscience journal homepage: www.elsevier.com/locate/ymcne