Heterochromatin mainly comprises repeated DNA sequences that are prone to ectopic recombination. In Drosophila cells, 'safe' repair of heterochromatic double-strand breaks by homologous recombination relies on the relocalization of repair sites to the nuclear periphery before strand invasion. The mechanisms responsible for this movement were unknown. Here we show that relocalization occurs by directed motion along nuclear actin filaments assembled at repair sites by the Arp2/3 complex. Relocalization requires nuclear myosins associated with the heterochromatin repair complex Smc5/6 and the myosin activator Unc45, which is recruited to repair sites by Smc5/6. ARP2/3, actin nucleation and myosins also relocalize heterochromatic double-strand breaks in mouse cells. Defects in this pathway result in impaired heterochromatin repair and chromosome rearrangements. These findings identify de novo nuclear actin filaments and myosins as effectors of chromatin dynamics for heterochromatin repair and stability in multicellular eukaryotes.

ImportanceRandomized clinical trials examining the effectiveness of neoadjuvant chemotherapy (NACT) for advanced ovarian cancer predominantly included patients with high-grade serous carcinomas. The use and outcomes of NACT in less common epithelial carcinomas are understudied.ObjectiveTo investigate the uptake and survival outcomes in treatment with NACT for less common histologic subtypes of epithelial ovarian cancer.Design, Setting, and ParticipantsA retrospective cohort study and systematic literature review with meta-analysis was conducted using the National Cancer Database from 2006 to 2017 and the National Cancer Institute’s Surveillance, Epidemiology, and End Results Program from 2006 to 2019. Data analysis was performed from July 2022 to April 2023. The evaluation included patients with stage III to IV ovarian cancer with clear cell, mucinous, or low-grade serous histologic subtypes who received multimodal treatment with surgery and chemotherapy.ExposuresExposure assignment per the sequence of treatment: primary debulking surgery (PDS) followed by chemotherapy (PDS group) or NACT followed by interval surgery (NACT group).Main Outcomes and MeasuresTemporal trends and characteristics of NACT use were assessed using multivariable analysis, and overall survival (OS) was assessed with the inverse probability of treatment weighting propensity score.ResultsA total of 3880 patients were examined in the National Cancer Database including 1829 women (median age, 56 [IQR, 49-63] years) with clear cell, 1156 women (median age, 53 [IQR, 42-64] years) with low-grade serous, and 895 women (median age, 57 [IQR, 48-66] years) with mucinous carcinomas. NACT use increased in patients with clear cell (from 10.2% to 16.2%, 58.8% relative increase; P < .001 for trend) or low-grade serous (from 7.7% to 14.2%, 84.4% relative increase; P = .007 for trend) carcinoma during the study period. This association remained consistent in multivariable analysis. NACT use also increased, but nonsignificantly, in mucinous carcinomas (from 8.6% to 13.9%, 61.6% relative increase; P = .07 for trend). Across the 3 histologic subtypes, older age and stage IV disease were independently associated with NACT use. In a propensity score–weighted model, the NACT and PDS groups had comparable OS for clear cell (4-year rates, 31.4% vs 37.7%; hazard ratio [HR], 1.12; 95% CI, 0.95-1.33) and mucinous (27.0% vs 26.7%; HR, 0.90; 95% CI, 0.68-1.19) carcinomas. For patients with low-grade serous carcinoma, NACT was associated with decreased OS compared with PDS (4-year rates, 56.4% vs 81.0%; HR, 2.12; 95% CI, 1.55-2.90). Increasing NACT use and histologic subtype–specific survival association were also found in the Surveillance, Epidemiology, and End Results Program cohort (n = 1447). A meta-analysis of 4 studies, including the current study, observed similar OS associations for clear cell (HR, 1.13; 95% CI, 0.96-1.34; 2 studies), mucinous (HR, 0.93; 95% CI, 0.71-1.21; 2 studies), and low-grade serous (HR, 2.11; 95% CI, 1.63-2.74; 3 studies) carcinomas.Conclusions and RelevanceDespite the lack of data on outcomes of NACT among patients with less common carcinomas, this study noted that NACT use for advanced disease has gradually increased in the US. Primary chemotherapy for advanced-stage, low-grade serous ovarian cancer may be associated with worse survival compared with PDS.

ObjectiveSurgery for placenta accreta spectrum is associated with significant maternal morbidity and mortality. The role of gynecologic oncologists in the surgical management of placenta accreta spectrum is currently under investigation. This study examined the practices, experiences, and interests of gynecologic oncologists in placenta accreta spectrum surgeries.MethodsThe intervention was an anonymous, cross-sectional, 20-question survey sent to 1084 members of the Society of Gynecologic Oncology in the USA.ResultsA total of 184 gynecologic oncologists responded to the survey (response rate 17.0%). Most participating gynecologic oncologists have been practicing for >10 years after fellowship (53.2%), practice in urban-teaching hospitals (84.8%) with delivery volumes ≥3000/year (54.3%), and have a multidisciplinary approach (82.5%). Three-quarters (78.7%) feel that the rate of placenta accreta spectrum is increasing over time. One-third (35.5%) perform ≥6 hysterectomies for placenta accreta spectrum yearly. Less than half (45.5%) practice conservative management. Approximately half are involved from the beginning of the case (49.7%) and perform the surgery in the main operating room (59.4%). Almost three-quarters (71.6%) have experienced surgical blood loss >5 L and one-third (36.6%) have experienced cases with blood loss >10 L. About half (50.3%) of participants are interested in placenta accreta spectrum surgery for future practice. Gynecologic oncologists engaging in a multidisciplinary approach are more likely to practice in an urban-teaching hospital, have higher surgical volume, be involved from the beginning of the case, and be interested in placenta accreta spectrum surgery. Those >10 years post-training and in the Southern US region are more likely to practice conservative management or delayed hysterectomy.ConclusionThis society-based cross-sectional survey suggests that gynecologic oncologists are actively involved in the surgical management of placenta accreta spectrum in the USA. Nearly half of gynecologic oncologists who responded to the survey expressed interest in surgery for placenta accreta spectrum.

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Pericentromeric heterochromatin is highly enriched for repetitive sequences prone to aberrant recombination. Previous studies showed that homologous recombination (HR) repair is uniquely regulated in this domain to enable ‘safe’ repair while preventing aberrant recombination. InDrosophilacells, DNA double-strand breaks (DSBs) relocalize to the nuclear periphery through nuclear actin-driven directed motions before recruiting the strand invasion protein Rad51 and completing HR. End-joining (EJ) repair also occurs with high frequency in heterochromatin of fly tissues, but how different EJ pathways operate in heterochromatin remains uncharacterized. Here, we induce DSBs in single euchromatic and heterochromatic sites using the DR-whitereporter and I-SceI expression in spermatogonia. We detect higher frequency of HR repair in heterochromatic insertions, relative to euchromatin. Sequencing of repair outcomes reveals the use of distinct EJ pathways across different euchromatic and heterochromatic sites. Interestingly, synthesis-dependent michrohomology-mediated end joining (SD-MMEJ) appears differentially regulated in the two domains, with a preferential use of motifs close to the cut site in heterochromatin relative to euchromatin, resulting in smaller deletions. Together, these studies establish a new approach to study repair outcomes in fly tissues, and support the conclusion that heterochromatin uses more HR and less mutagenic EJ repair relative to euchromatin.