CSB cooperates with SMARCAL1 to maintain telomere stability in ALT cells.

Elevated replication stress is evident at telomeres of about 10-15% of cancer cells, which maintain their telomeres via a homologous recombination (HR)-based mechanism, referred to as alternative lengthening of telomeres (ALT). How ALT cells resolve replication stress to support their growth remains incompletely characterized. Here, we report that CSB (also known as ERCC6) promotes recruitment of HR repair proteins (MRN, BRCA1, BLM and RPA32) and POLD3 to ALT telomeres, a process that requires the ATPase activity of CSB and is controlled by ATM- and CDK2-dependent phosphorylation. Loss of CSB stimulates telomeric recruitment of MUS81 and SLX4, components of the structure-specific MUS81-EME1-SLX1-SLX4 (MUS-SLX) endonuclease complex, suggesting that CSB restricts MUS-SLX-mediated processing of stalled forks at ALT telomeres. Loss of CSB coupled with depletion of SMARCAL1, a chromatin remodeler implicated in catalyzing regression of stalled forks, synergistically promotes not only telomeric recruitment of MUS81 but also the formation of fragile telomeres, the latter of which is reported to arise from fork stalling. These results altogether suggest that CSB-mediated HR repair and SMARCAL1-mediated fork regression cooperate to prevent stalled forks from being processed into fragile telomeres in ALT cells.

3-Dimensional simulations and student learning in orthodontic education.

INTRODUCTION: The electronic dental model (e-model) is an example of a digital 3-dimensional technology to support inquiry-based learning in undergraduate dental education. As student perceptions of and engagement with e-models vary, it is uncertain whether these perceptions have implications for their learning processes and outcomes. MATERIALS AND METHODS: Third-year dental students (N = 40) completed a questionnaire to identify their perceptions of and preferences for model modalities. They were divided into three groups based on their preference: Preferring plaster models (Group 1); Preferring e-models (Group 2); No preference (Group 3). Students from three groups (N = 9) attended a hands-on digital occlusion evaluation workshop, and then completed a case-based diagnostic evaluation test using digital occlusion evaluation software. Camtasia Studio™ recorded real-time and on-screen data of the number of mouse-clicks and time spent. RESULTS: Students reported positive feedbacks on the use of e-models, and 72.5% of the students preferred combination use of e-models and plaster models. After attending the hands-on digital dental occlusion evaluation workshop, Group 2 scored higher on the diagnostic evaluation test (p < .05) and registered more mouse-clicks than Group 1 when evaluating the arch symmetry (p < .05). Group 2 registered fewer mouse-clicks than Group 3 during tooth size measurement (p < .05). There was no significant difference regarding the time used to answer the knowledge questions amongst the three groups. CONCLUSION: Undergraduate dental students indicated a generally high acceptance of e-models for their learning in orthodontics, and more prefer a blended approach. Students preferring e-models presented higher performance outcomes, which supports cognitive load theory regarding prior exposure to simulation-based environments.

Orthodontic plate for management of obstructive sleep apnoea in infants with Pierre Robin sequence: experience and protocol in Hong Kong.

OBJECTIVE: To present the application of the pre-epiglottic baton plate (PEBP) in infants with Pierre Robin sequence (PRS) in the Southern Chinese population (Hong Kong) and to present the diagnosis and management protocol of these infants in our centre. DESIGN: Retrospective case series of three patients with PRS. SETTING: Neonatal Intensive Care Unit in Kwong Wah Hospital and Craniofacial Orthodontic Centre in United Christian Hospital, Hong Kong. PARTICIPANTS: Three new-born infants (two girls, one boy) with PRS and upper airway obstruction due to glossoptosis. METHODS: A protocol for the diagnosis and management of these infants in the Southern Chinese population (Hong Kong) was presented. The three patients received nasal high-flow oxygen and/or continuous positive airway pressure (CPAP) as first-line respiratory support, followed by PEBP for 3-5 months. A two-stage approach was undertaken to ensure accurate positioning of the PEBP. RESULTS: All three infants had improvement in clinical signs, symptoms and polysomnography upon discharge. PEBP and other respiratory aids were weaned off at 3-6 months. CONCLUSIONS: The PEBP, combined with other respiratory support, is a useful modality in the treatment of obstructive sleep apnoea in infants with PRS.

Cdk-dependent phosphorylation regulates TRF1 recruitment to PML bodies and promotes C-circle production in ALT cells.

TRF1, a duplex telomeric DNA binding protein, is implicated in homologous-recombination-based alternative lengthening of telomeres, known as ALT. However, how TRF1 promotes ALT activity has yet to be fully characterized. Here we report that Cdk-dependent TRF1 phosphorylation on T371 acts as a switch to create a pool of TRF1, referred to as (pT371)TRF1, which is recruited to ALT-associated PML bodies (APBs) in S and G2 phases independently of its binding to telomeric DNA. We find that phosphorylation of T371 is essential for APB formation and C-circle production, both of which are hallmarks of ALT. We show that the interaction of (pT371)TRF1 with APBs is dependent upon ATM and homologous-recombination-promoting factors Mre11 and BRCA1. In addition, (pT371)TRF1 interaction with APBs is sensitive to transcription inhibition, which also reduces DNA damage at telomeres. Furthermore, overexpression of RNaseH1 impairs (pT371)TRF1 recruitment to APBs in the presence of campothecin, an inhibitor that prevents topoisomerase I from resolving RNA-DNA hybrids. These results suggest that transcription-associated DNA damage, perhaps arising from processing RNA-DNA hybrids at telomeres, triggers (pT371)TRF1 recruitment to APBs to facilitate ALT activity.

TRF1 phosphorylation on T271 modulates telomerase-dependent telomere length maintenance as well as the formation of ALT-associated PML bodies.

TRF1, a component of the shelterin complex, plays a key role in both telomerase-dependent telomere maintenance and alternative lengthening of telomeres, the latter also known as ALT. Characteristics of ALT cells include C-circles and ALT-associated PML bodies, referred to as APBs. The function of TRF1 is tightly regulated by post-translational modification including phosphorylation, however TRF1 phosphorylation sites have yet to be fully characterized. Here we report a novel TRF1 phosphorylation site threonine 271. We show that a nonphosphorylatable mutation of T271A impairs TRF1 binding to telomeric DNA in vivo and renders TRF1 defective in inhibiting telomerase-dependent telomere elongation. On the other hand, TRF1 carrying a phosphomimic mutation of T271D is competent in not only binding to telomeric DNA but also inhibiting telomerase-mediated telomere lengthening. These results suggest that TRF1 phosphorylation on T271 negatively regulates telomerase-mediated telomere maintenance. We find that in telomerase-negative ALT cells, TRF1 carrying either a T271A or T271D mutation is able to promote C-circle production but fails to support APB formation. These results suggest that TRF1 phosphorylation on T271 is necessary for APB formation but dispensable for C-circle production. These results further imply that APB formation can be mechanistically separated from C-circle production.

Craniofacial characteristics related to daytime sleepiness screened by the paediatric daytime sleepiness scale.

The present cross-sectional study aimed to assess daytime sleepiness in Chinese adolescents using the Paediatric Daytime Sleepiness Scale (PDSS) and to identify associations between PDSS answers and craniofacial characteristics. A group of 265 Chinese adolescents aged 11-17 years self-completed the PDSS, and their extra- and intra-oral craniofacial characteristics were recorded. Among the participants, 59.7% (157) experienced one or more daytime sleepiness events. No significant associations were found between total PDSS scores and the craniofacial parameters, but when PDSS answers were assessed at the item level, several craniofacial characteristics were found to be positively associated with daytime sleepiness, such as hypertrophic tonsils (P = 0.05), a relatively large tongue (P < 0.01), a bilateral Class II molar relationship (P < 0.05) and increased overjet (P < 0.05). A short lower face (P < 0.01) and a convex profile (P < 0.01) were found to be negatively associated with daytime sleepiness. Daytime sleepiness is commonly reported among Chinese adolescents seeking orthodontic treatment and there are potential associations between the condition and craniofacial characteristics. An assessment of daytime sleepiness is recommended to orthodontists in young patients presenting with hypertrophic tonsils, relative large tongues and Class II tendency malocclusions, and appropriate medical referrals should also be considered.