From laboratory tests to functional characterisation of Cockayne syndrome Manuela Lanzafame, Bruno Vaz 1 , Tiziana Nardo, Elena Botta, Donata Orioli *, Miria Stefanini * Istituto di Genetica Molecolare, Consiglio Nazionale delle Ricerche, Via Abbiategrasso 207, 27100 Pavia, Italy 1. Introduction Cockayne syndrome (CS) is a multi-system disorder charac- terised by pre- or post-natal growth failure and progressive neurological dysfunction. Associated clinical features are gait defects, progressive pigmentary retinopathy and other ocular anomalies such as cataracts and optic disk atrophy, skeletal abnormalities, impaired sexual development, sensorineural hear- ing loss, dental caries, signs of premature ageing and cutaneous photosensitivity (reviewed by Weidenheim et al., 2009). CS patients display a wide range in type and severity of symptoms and their clinical diagnosis usually refers to the criteria proposed by Nance and Berry (1992). These authors also suggested a classification of the disease into three clinically different subtypes. The clinical subtype I, which corresponds to the classical form of CS, accounts for the majority of cases in which the symptoms appear within the first few years of life. The clinical subtype II or severe form of CS includes severely affected patients in which the pathological hallmarks are already manifest at birth, with low birth-weight and poor or absent physical and neurological development. The clinical subtype III or mild form of CS, characterised by late onset and slow progression of symptoms, is limited to few patients who present with atypical phenotypes because of normal or slightly impaired intelligence, linear growth, or reproductive capacity. It is worthwhile mentioning that some of the major clinical symptoms of CS have been also reported in relatively rare patients who show in combination the cutaneous alterations of xeroderma pigmentosum (XP) and define a distinct clinical entity designated XP/CS (reviewed in Stefanini and Kraemer, 2008). The skin photosensitivity reported in many CS patients prompted investigations on their cellular response to ultraviolet (UV) light. Hypersensitivity to killing by UV-induced DNA damage, inability to recover DNA and RNA synthesis at late times after irradiation and increased mutability were clearly shown in a number of CS cells (reviewed in Stefanini and Ruggieri, 2008). In the early 90s, it was demonstrated that these alterations are a consequence of defects in two gene, designated CSA and CSB, which are both involved in transcription-coupled repair (TC-NER), the sub-pathway of nucleotide excision repair (NER) that rapidly removes damage blocking the progression of the transcription machinery in actively transcribed regions of DNA (reviewed in Lagerwerf et al., 2011; Nouspikel, 2011). The failure to recover normal RNA synthesis after UV exposure is a cellular parameter for diagnosing CS both pre- and post-natally by relatively simple and Mechanisms of Ageing and Development 134 (2013) 171–179 A R T I C L E I N F O Article history: Available online 6 April 2013 Keywords: UV damage Oxidative stress Neurodegeneration Ageing Cancer A B S T R A C T The significant progress made over the last few years on the pathogenesis of Cockayne syndrome (CS) greatly improved our knowledge on several aspects crucial for development and ageing, demonstrating that this disorder, even if rare, represents a valuable tool to clarify key aspects of human health. Primary cells from patients have been instrumental to elucidate the multiple roles of CS proteins and to approach the dissection of the complex interplay between repair and transcription that is central to the CS clinical phenotype. Here we discuss the results of the cellular assays applied for confirmation of the clinical diagnosis as well as the results of genetic and molecular studies in DNA repair defective patients. Furthermore, we provide a general overview of recent in vivo and in vitro studies indicating that both CSA and CSB proteins are involved in distinct aspects of the cellular responses to UV and oxidative stress, transcription and regulation of gene expression, chromatin remodelling, redox balance and cellular bioenergetics. In light of the literature data, we will finally discuss how inactivation of specific functional roles of CS proteins may differentially affect the phenotype, thus explaining the wide range in type and severity of symptoms reported in CS patients. ß 2013 Elsevier Ireland Ltd. All rights reserved. Abbreviations: BER, base excision repair; CPD, cyclobutane pyrimidine dimers; CS, Cockayne syndrome; GGR, global genome repair; mtDNA, mitochondrial DNA; NER, nucleotide excision repair; 8-OH-Gua, 8-hydroxyguanine; RNApol, RNA polymer- ase; ROS, reactive oxygen species; RRS, RNA synthesis recovery; TC-NER, transcription-coupled repair; UDS, UV-induced DNA repair synthesis; UV, ultraviolet; UV S S, UV-sensitive syndrome; XP, xeroderma pigmentosum. * Corresponding authors. Tel.: +39 0382 546330; fax: +39 0382 422286. E-mail addresses: orioli@igm.cnr.it (D. Orioli), stefanini@igm.cnr.it (M. Stefanini). 1 Present address: Institute of Pharmacology and Toxicology, University of Zurich-Vetsuisse, Winterthurerstrasse 260, CH-8057 Zu ¨ rich, Switzerland. Contents lists available at SciVerse ScienceDirect Mechanisms of Ageing and Development jo ur n al ho mep ag e: www .elsevier .c om /lo cate/m ec hag ed ev 0047-6374/$ – see front matter ß 2013 Elsevier Ireland Ltd. All rights reserved. http://dx.doi.org/10.1016/j.mad.2013.03.007