A single double-strand break system reveals repair dynamics and mechanisms in heterochromatin and euchromatin.

Repair of DNA double-strand breaks (DSBs) must be properly orchestrated in diverse chromatin regions to maintain genome stability. The choice between two main DSB repair pathways, nonhomologous end-joining (NHEJ) and homologous recombination (HR), is regulated by the cell cycle as well as chromatin context.Pericentromeric heterochromatin forms a distinct nuclear domain that is enriched for repetitive DNA sequences that pose significant challenges for genome stability. Heterochromatic DSBs display specialized temporal and spatial dynamics that differ from euchromatic DSBs. Although HR is thought to be the main pathway used to repair heterochromatic DSBs, direct tests of this hypothesis are lacking. Here, we developed an in vivo single DSB system for both heterochromatic and euchromatic loci in Drosophila melanogaster Live imaging of single DSBs in larval imaginal discs recapitulates the spatio-temporal dynamics observed for irradiation (IR)-induced breaks in cell culture. Importantly, live imaging and sequence analysis of repair products reveal that DSBs in euchromatin and heterochromatin are repaired with similar kinetics, employ both NHEJ and HR, and can use homologous chromosomes as an HR template. This direct analysis reveals important insights into heterochromatin DSB repair in animal tissues and provides a foundation for further explorations of repair mechanisms in different chromatin domains.

Dry mouth in patients with a life-limiting condition or frailty: a study protocol for two intervention studies and a nested qualitative sub-study (the Dry mOuth Project, DROP).

BACKGROUND: Despite its prevalent and impactful nature, dry mouth remains an underexposed and undertreated symptom in patients with a life-limiting condition or frailty. The main contributing factors are a lack of awareness and knowledge amongst both healthcare professionals and patients, and a scarcity of effective, evidence-based interventions. In the DRy mOuth Project (DROP), we address these factors by investigating both a non-pharmacological and a pharmacological intervention: a nurse-led patient education program and locally applied pilocarpine. METHODS: This intervention-based research project consists of two parallel studies. The non-pharmacological study is a cluster non-randomized controlled trial in 228 palliative nursing home and hospital patients, investigating the effect of structured use of guidelines and of patient education on dry mouth symptoms. This intervention, a nurse-led patient education program (the Mouth Education Program, MEP), will be compared to care as usual, the control. The pharmacological study is a double-blind placebo-controlled randomized trial that examines the effect of locally applied pilocarpine drops in 120 patients with dry mouth symptoms. Both studies use the same mixed-methods study design, in which the primary outcome is the clinical response to the intervention at 4 weeks, as measured by a dry mouth severity score (numeric rating scale from 0 to 10). Other outcomes, as measured by questionnaires over a 12-week follow-up period, include durability of the effect, impact on quality of life and, adherence and acceptability of the intervention. In addition, the feasibility and cost-effectiveness are evaluated by means of questionnaires and focus groups with healthcare professionals, and interviews with patients. DISCUSSION: This study investigates the effectiveness and feasibility of two interventions for dry mouth symptoms in patients with life-limiting conditions or frailty. Due to the large-scale and mixed-method nature of the study, this study will also improve our understanding of dry mouth and its relating factors and of the patients' and healthcare professionals' experiences with symptoms, care and guidelines of dry mouth, including any perceived barriers and facilitators. TRIAL REGISTRATION: NCT05964959 & NCT05506137.