Defects in the ATR-dependent DNA damage response pathway and human syndromes

A multitude of clinically distinct human disorders exist whose underlying cause is a defect in the response to or repair of DNA damage. The clinical spectrum of these conditions provides evidence for the role of the DNA damage response (DDR) in mediating diverse processes such as genomic stability, immune system function and normal human development. Cell lines from these disorders provide a valuable resource to help dissect the consequences of compromised DDR at the molecular level. Ataxia telangiectasia and Rad3-related (ATR) and Ataxia telangiectasia Mutated (ATM) are apical protein kinases that play central roles in coordinating the cells response to DNA damage. Whilst ATM is activated by DNA double strand breaks (DSB's), ATR is activated by single stranded regions of DNA (ssDNA) which can occur, for example, during DNA replication fork stalling. There is significant functional overlap between these two kinases. In fact, they phosphorylate many of the same substrates, including p53 and Brca1. Nevertheless, ATR appears to be essential for embryonic development, unlike ATM. Mutations in ATM result in Ataxia telangiectasia (A-T) a progressive neurological disorder. Interestingly, a hypomorphic mutation in ATR is associated with Seckel syndrome, a clinically distinct disorder to that of A-T. Seckel syndrome is characterised by profound proportionate growth retardation with severe microcephaly. Why defects in these two related kinases should result in such distinct human disorders is unclear. Recently, mutations in Pericentrin/Kendrin (PCNT) have also been demonstrated in Seckel syndrome. PCNT encodes a core structural centrosomal protein. Interestingly, defective PCNT results in impaired ATR-dependent, but not ATM-dependent G2-M cell cycle checkpoint arrest. Using evidence from murine knockout studies and human cell-based work I will discuss the biological impact of compromised ATR-pathway function with the aim of trying to understand the link between genotype-phenotype in this context

Haploinsufficiency of DNA damage response genes and their potential influence in human genomic disorders

Genomic disorders are a clinically diverse group of conditions caused by gain, loss or re-orientation of a genomic region containing dosage-sensitive genes. One class of genomic disorder is caused by hemizygous deletions resulting in haploinsufficiency of a single or, more usually, several genes. For example, the heterozygous contiguous gene deletion on chromosome 22q11.2 causing DiGeorge syndrome involves at least 20-30 genes. Determining how the copy number variation (CNV) affects human variation and contributes to the aetiology and progression of various genomic disorders represents important questions for the future. Here, I will discuss the functional significance of one form of CNV, haploinsufficiency (i.e. loss of a gene copy), of DNA damage response components and its association with certain genomic disorders. There is increasing evidence that haploinsufficiency for certain genes encoding key players in the cells response to DNA damage, particularly those of the Ataxia Telangiectasia and Rad3-related (ATR)-pathway, has a functional impact. I will review this evidence and present examples of some well known clinically similar genomic disorders that have recently been shown to be defective in the ATR-dependent DNA damage response. Finally, I will discuss the potential implications of a haploinsufficiency-induced defective DNA damage response for the clinical management of certain human genomic disorders

Meier–Gorlin syndrome and Wolf–Hirschhorn syndrome: two developmental disorders highlighting the importance of efficient DNA replication for normal development and neurogenesis

Microcephaly represents one of the most obvious clinical manifestations of impaired neurogenesis. Defects in the DNA damage response, in DNA repair, and structural abnormalities in centrosomes, centrioles and the spindle microtubule network have all been demonstrated to cause microcephaly in humans. Work describing novel functional defects in cell lines from individuals with either Meier–Gorlin syndrome or Wolf–Hirschhorn syndrome highlight the significance of optimal DNA replication and S phase progression for normal human development, including neurogenesis. These findings illustrate how different primary defects in processes impacting upon DNA replication potentially influence similar phenotypic outcomes, including growth retardation and microcephaly. Herein, we will describe the nature of the S phase defects uncovered for each of these conditions and highlight some of the overlapping cellular features

Structure variation and evolution in microphase-separated grafted diblock copolymer films

The phase behavior of grafted d-polystyrene-block-poly(methyl methacrylate) diblock copolymer films is examined, with particular focus on the effect of solvent and annealing time. It was observed that the films undergo a two-step transformation from an initially disordered state, through an ordered metastable state, to the final equilibrium configuration. It was also found that altering the solvent used to wash the films, or complete removal of the solvent prior to thermal annealing using supercritical CO2, could influence the structure of the films in the metastable state, though the final equilibrium state was unaffected. To aid in the understanding to these experimental results, a series of self-consistent field theory calculations were done on a model diblock copolymer brush containing solvent. Of the different models examined, those which contained a solvent selective for the grafted polymer block most accurately matched the observed experimental behavior. We hypothesize that the structure of the films in the metastable state results from solvent enrichment of the film near the film/substrate interface in the case of films washed with solvent or faster relaxation of the nongrafted block for supercritical CO2 treated (solvent free) films. The persistence of the metastable structures was attributed to the slow reorganization of the polymer chains in the absence of solvent

Warrior ideologies in first millennium AD Europe : New light on monumental warrior stelae from Scotland

Thanks to the finders of the Tulloch stone, Brice Prentice and Alex Campbell, for their prompt reporting of the stone and Balfour Beatty for their support in transporting it. Also thanks to the colleagues who attended two workshops held at Perth Museum to discuss the discovery. Simon Gilmour gave access to radiocarbon information on Loch na Beirgh. Aberdeenshire Council and Historic Environment Scotland gave permission to excavate around the base of Rhynie No.3. Excavations at Rhynie have been supported by the University of Aberdeen Development Trust and Historic Environment Scotland. The writing of this article was supported by a Leverhulme Trust Research Leadership Award (RL-2016-069).Peer reviewedPublisher PD

ATR promotes cilia signalling: links to developmental impacts

Mutations in ATR (ataxia telangiectasia and RAD3-related) cause Seckel syndrome (ATR-SS), a microcephalic primordial dwarfism disorder. Hitherto, the clinical manifestation of ATR deficiency has been attributed to its canonical role in DNA damage response signalling following replication fork stalling/collapse. Here, we show that ATR regulates cilia-dependent signalling in a manner that can be uncoupled from its function during replication. ATR-depleted or patient-derived ATR-SS cells form cilia of slightly reduced length but are dramatically impaired in cilia-dependent signalling functions, including growth factor and Sonic hedgehog signalling. To better understand the developmental impact of ATR loss of function, we also used zebrafish as a model. Zebrafish embryos depleted of Atr resembled ATR-SS morphology, showed a modest but statistically significant reduction in cilia length and other morphological features indicative of cilia dysfunction. Additionally, they displayed defects in left-right asymmetry including ambiguous expression of southpaw, incorrectly looped hearts and randomized localization of internal organs including the pancreas, features typically conferred by cilia dysfunction. Our findings reveal a novel role for ATR in cilia signalling distinct from its canonical function during replication and strengthen emerging links between cilia function and development