PCAF promotes R-loop resolution via histone acetylation.

R-loops cause genome instability, disrupting normal cellular functions. Histone acetylation, particularly by p300/CBP-associated factor (PCAF), is essential for maintaining genome stability and regulating cellular processes. Understanding how R-loop formation and resolution are regulated is important because dysregulation of these processes can lead to multiple diseases, including cancer. This study explores the role of PCAF in maintaining genome stability, specifically for R-loop resolution. We found that PCAF depletion promotes the generation of R-loop structures, especially during ongoing transcription, thereby compromising genome stability. Mechanistically, we found that PCAF facilitates histone H4K8 acetylation, leading to recruitment of the a double-strand break repair protein (MRE11) and exonuclease 1 (EXO1) to R-loop sites. These in turn recruit Fanconi anemia (FA) proteins, including FANCM and BLM, to resolve the R-loop structure. Our findings suggest that PCAF, histone acetylation, and FA proteins collaborate to resolve R-loops and ensure genome stability. This study therefore provides novel mechanistic insights into the dynamics of R-loops as well as the role of PCAF in preserving genome stability. These results may help develop therapeutic strategies to target diseases associated with genome instability.

R-loops are harmful DNA-RNA hybrid structures that cause genome instability, disrupting normal cell functions. This study explored the role of the protein PCAF in resolving R-loops to maintain genome stability. The researchers found that depleting PCAF leads to increased R-loop formation, especially during transcription, compromising the genome. Mechanistically, PCAF facilitates histone acetylation, recruiting proteins like MRE11, EXO1, FANCM and BLM to R-loop sites. These proteins collaborate to resolve R-loop structures. The findings suggest that PCAF, histone acetylation, and these repair proteins work together to untangle R-loops and preserve genome integrity. Understanding this process provides insights into R-loop dynamics and PCAF's role in genome maintenance, potentially leading to therapeutic strategies for diseases associated with genome instability, such as cancer.

A simple active fluid model unites cytokinesis, cell crawling, and axonal outgrowth.

Axonal outgrowth, cell crawling, and cytokinesis utilize actomyosin, microtubule-based motors, cytoskeletal dynamics, and substrate adhesions to produce traction forces and bulk cellular motion. While it has long been appreciated that growth cones resemble crawling cells and that the mechanisms that drive cytokinesis help power cell crawling, they are typically viewed as unique processes. To better understand the relationship between these modes of motility, here, we developed a unified active fluid model of cytokinesis, amoeboid migration, mesenchymal migration, neuronal migration, and axonal outgrowth in terms of cytoskeletal flow, adhesions, viscosity, and force generation. Using numerical modeling, we fit subcellular velocity profiles of the motions of cytoskeletal structures and docked organelles from previously published studies to infer underlying patterns of force generation and adhesion. Our results indicate that, during cytokinesis, there is a primary converge zone at the cleavage furrow that drives flow towards it; adhesions are symmetric across the cell, and as a result, cells are stationary. In mesenchymal, amoeboid, and neuronal migration, the site of the converge zone shifts, and differences in adhesion between the front and back of the cell drive crawling. During neuronal migration and axonal outgrowth, the primary convergence zone lies within the growth cone, which drives actin retrograde flow in the P-domain and bulk anterograde flow of the axonal shaft. They differ in that during neuronal migration, the cell body is weakly attached to the substrate and thus moves forward at the same velocity as the axon. In contrast, during axonal outgrowth, the cell body strongly adheres to the substrate and remains stationary, resulting in a decrease in flow velocity away from the growth cone. The simplicity with which cytokinesis, cell crawling, and axonal outgrowth can be modeled by varying coefficients in a simple model suggests a deep connection between them.

How will early onset scoliosis surgery affect my child's future as a young adult? A follow-up study using patient-reported outcome measures.

PURPOSE: Using patient-reported outcome measures (PROMs), this study was undertaken to determine how well patients with early onset scoliosis (EOS) fare in adulthood. METHODS: Among eight healthcare centers, 272 patients (≥ 18 years) surgically managed for EOS (≥ 5 years) completed the Scoliosis Research Society (SRS)-22r, Functional Assessment of Chronic Illness Therapy-10 (FACIT-Dyspnea-10), and Short Form (SF)-12. Functional and demographic data were collected. RESULTS: The response rate was 40% (108/272). EOS etiologies were congenital (45%), neuromuscular (20%), idiopathic (20%) syndromic (11%), and unknown (4%). All patients scored within normal limits on the FACIT-Dyspnea-10 pulmonary (no breathing aids, 78%; no oxygen, 92%). SF-12 physical health scores and most SRS-22r domains were significantly decreased (p < 0.05 and p < 0.001, respectively) compared with normative values. SF-12 and SRS-22r mental health scores (MHS) were lower than normative values (p < 0.05 and p < 0.02, respectively). Physical health PROMs varied between etiologies. Treatment varied by etiology. Patients with congenital EOS were half as likely to undergo definitive fusion. There was no difference between EOS etiologies in SF-12 MHS, with t scores being slightly lower than normative peers. CONCLUSION: Good long-term physical and social function and patient-reported quality of life were noted in surgically managed patients. Patients with idiopathic EOS physically outperformed those with other etiologies in objective and PROM categories but had similar MHS PROMs. Compared to normative values, EOS patients demonstrated decreased long-term physical capacity, slightly lower MHS, and preserved cardiopulmonary function. LEVEL OF EVIDENCE: Level IV Case Series.

PARticular MARks: Histone ADP-ribosylation and the DNA damage response.

Cellular and molecular responses to DNA damage are highly orchestrated and dynamic, acting to preserve the maintenance and integrity of the genome. Histone proteins bind DNA and organize the genome into chromatin. Post-translational modifications of histones have been shown to play an essential role in orchestrating the chromatin response to DNA damage by regulating the DNA damage response pathway. Among the histone modifications that contribute to this intricate network, histone ADP-ribosylation (ADPr) is emerging as a pivotal component of chromatin-based DNA damage response (DDR) pathways. In this review, we survey how histone ADPr is regulated to promote the DDR and how it impacts chromatin and other histone marks. Recent advancements have revealed histone ADPr effects on chromatin structure and the regulation of DNA repair factor recruitment to DNA lesions. Additionally, we highlight advancements in technology that have enabled the identification and functional validation of histone ADPr in cells and in response to DNA damage. Given the involvement of DNA damage and epigenetic regulation in human diseases including cancer, these findings have clinical implications for histone ADPr, which are also discussed. Overall, this review covers the involvement of histone ADPr in the DDR and highlights potential future investigations aimed at identifying mechanisms governed by histone ADPr that participate in the DDR, human diseases, and their treatments.

Microwave Ablation of the Pig Growth Plate: Proof of Concept for Minimally Invasive Epiphysiodesis.

BACKGROUND: Different surgical methods for epiphysiodesis of limb length discrepancy (LLD) have been described. Although these methods are variably effective, they are associated with morbidity (pain and limp) and potential complications. Microwave ablation is a less-invasive opportunity to halt growth by selectively destroying the growth plate via thermal energy to treat LLD in children. QUESTIONS/PURPOSES: In this proof-of-concept study using an in vivo pig model, we asked: (1) What is the durability of response 2 to 4 months after microwave ablation of the tibial growth plate as measured by length and angulation of the tibia via a CT scan? (2) Was articular cartilage maintained as measured by standard histologic staining for articular cartilage viability? METHODS: To develop an in vivo protocol for microwave ablation, we placed microwave antennas adjacent to the proximal tibia growth plate in the cadaveric hindlimbs of 18 3-month-old pigs. To determine the suitable time, we varied ablation from 90 to 270 seconds at 65-W power settings. After sectioning the tibia, we visually assessed for discoloration (implying growth plate destruction) that included the central growth plate but did not encroach into the epiphysis in a manner that could disrupt the articular surface. Using this information, we then performed microwave ablation on three live female pigs (3.5 to 4 months old) to evaluate physiologic changes and durability of response. A postprocedure MRI was performed to ensure the intervention led to spatial growth plate alterations similar to that seen in cadavers. This was followed by serial CT, which was used to assess the potential effect on local bone and growth until the animals were euthanized 2 to 4 months after the procedure. We analyzed LLD, angular deformity, and bony deformity using CT scans of both tibias. The visibility of articular cartilage was compared with that of the contralateral tibia via standard histologic staining, and growth rates of the proximal tibial growth plate were compared via fluorochrome labeling. RESULTS: Eighteen cadaveric specimens showed ablation zones across the growth plate without visual damage to the articular surface. The three live pigs did not exhibit changes in gait or require notable pain medication after the procedure. Each animal demonstrated growth plate destruction, expected limb shortening (0.8, 1.2, and 1.5 cm), and bony cavitation around the growth plate. Slight valgus bone angulation (4º, 5º, and 12º) compared with the control tibia was noted. No qualitatively observable articular cartilage damage was encountered from the histologic comparison with the contralateral tibia for articular cartilage thickness and cellular morphology. CONCLUSION: A microwave antenna placed into a pig's proximal tibia growth plate can slow the growth of the tibia without apparent pain and alteration of gait and function. CLINICAL RELEVANCE: Further investigation and refinement of our animal model is ongoing and includes shorter ablation times and comparison of dynamic ablation (moving the antennae during the ablation) as well as static ablation of the tibia from a medial and lateral portal. These refinements and planned comparison with standard mechanical growth arrest in our pig model may lead to a similar approach to ablate growth plates in children with LLD.

Healthcare Experiences and Health Outcomes Among Rural LGBTQ+ Individuals.

PURPOSE: To describe healthcare experiences and health outcomes among rural LGBTQ + individuals. DESIGN: 2022 cross-sectional survey. SETTING: Southern Illinois. SAMPLE: 85 individuals. MEASURES: Demographics, sexual orientation and gender identity, healthcare experiences, health outcomes. ANALYSIS: Experiences and outcomes were assessed vs orientation and identity. Distribution comparison was by t-test and chi-square, risk prediction by logistic regression, and significance assumed at P < .050. RESULTS: By orientation, participants were: 35.3% gay, 16.5% lesbian, and 45.8% bisexual plus; and by identity they were: 49.4% cisgender, 25.9% transgender, and 24.8% other identity. Survey item responses ranged from 95%-99%. Compared to gay men, lesbians and bisexual plus individuals more frequently reported medical bill payment difficulty (58.3% and 57.9% vs 25.0%; P = .020) and more past month days of poor mental health (19.4 and 15.8 vs 10.6; P = .018). Compared to heterosexual and other identity, transgender individuals less frequently reported having a routine medical provider (72.7% vs 92.7% and 95.0%; P = .037) and more frequently reported past healthcare denial (45.5% vs 17.5% and 18.8%; P = .042). Current health was associated with medical bill payment ability (OR = .33, 95% CI = .13-.86) and respectful treatment by healthcare administrators (OR = 3.90, 95% CI = 1.34-11.35) and clinicians (OR = 3.82, 95% CI = 1.39-10.47). Significance of some findings likely limited due to sample size. CONCLUSIONS: Our data describes healthcare experience and health outcome disparities among rural lesbian, gay, bisexual, transgender, queer and other sexual and gender minority individuals, and indicate that clinical experiences directly influence health outcomes.

The Risk of Sympathetic Ophthalmia Associated with Open-Globe Injury Management Strategies: A Meta-analysis.

TOPIC: Sympathetic ophthalmia (SO) is a sight-threatening granulomatous panuveitis caused by a sensitizing event. Primary enucleation or primary evisceration, versus primary repair, as a risk management strategy after open-globe injury (OGI) remains controversial. CLINICAL RELEVANCE: This systematic review was conducted to report the incidence of SO after primary repair compared with that of after primary enucleation or primary evisceration. This enabled the reporting of an estimated number needed to treat. METHODS: Five journal databases were searched. This review was registered with International Prospective Register of Systematic Reviews (identifier, CRD42021262616). Searches were carried out on June 29, 2021, and were updated on December 10, 2022. Prospective or retrospective studies that reported outcomes (including SO or lack of SO) in a patient population who underwent either primary repair and primary enucleation or primary evisceration were included. A systematic review and meta-analysis were carried out in accordance with Preferred Reporting Items for Systematic Reviews and Meta-analyses guidelines. Random effects modelling was used to estimate pooled SO rates and absolute risk reduction (ARR). RESULTS: Eight studies reporting SO as an outcome were included in total. The included studies contained 7500 patients and 7635 OGIs. In total, 7620 OGIs met the criteria for inclusion in this analysis; SO developed in 21 patients with OGI. When all included studies were pooled, the estimated SO rate was 0.12% (95% confidence interval [CI], 0.00%-0.25%) after OGI. Of 779 patients who underwent primary enucleation or primary evisceration, no SO cases were reported, resulting in a pooled SO estimate of 0.05% (95% CI, 0.00%-0.21%). For primary repair, the pooled estimate of SO rate was 0.15% (95% CI, 0.00%-0.33%). The ARR using a random effects model was -0.0010 (in favour of eye removal; 95% CI, -0.0031 [in favor of eye removal] to 0.0011 [in favor of primary repair]). Grading of Recommendations, Assessment, Development, and Evaluations analysis highlighted a low certainty of evidence because the included studies were observational, and a risk of bias resulted from missing data. DISCUSSION: Based on the available data, no evidence exists that primary enucleation or primary evisceration reduce the risk of secondary SO. FINANCIAL DISCLOSURE(S): Proprietary or commercial disclosure may be found in the Footnotes and Disclosures at the end of this article.

Dephasingless laser wakefield acceleration in the bubble regime.

Laser wakefield accelerators (LWFAs) have electric fields that are orders of magnitude larger than those of conventional accelerators, promising an attractive, small-scale alternative for next-generation light sources and lepton colliders. The maximum energy gain in a single-stage LWFA is limited by dephasing, which occurs when the trapped particles outrun the accelerating phase of the wakefield. Here, we demonstrate that a single space-time structured laser pulse can be used for ionization injection and electron acceleration over many dephasing lengths in the bubble regime. Simulations of a dephasingless laser wakefield accelerator driven by a 6.2-J laser pulse show 25 pC of injected charge accelerated over 20 dephasing lengths (1.3 cm) to a maximum energy of 2.1 GeV. The space-time structured laser pulse features an ultrashort, programmable-trajectory focus. Accelerating the focus, reducing the focused spot-size variation, and mitigating unwanted self-focusing stabilize the electron acceleration, which improves beam quality and leads to projected energy gains of 125 GeV in a single, sub-meter stage driven by a 500-J pulse.

APOBEC3B regulates R-loops and promotes transcription-associated mutagenesis in cancer.

The single-stranded DNA cytosine-to-uracil deaminase APOBEC3B is an antiviral protein implicated in cancer. However, its substrates in cells are not fully delineated. Here APOBEC3B proteomics reveal interactions with a surprising number of R-loop factors. Biochemical experiments show APOBEC3B binding to R-loops in cells and in vitro. Genetic experiments demonstrate R-loop increases in cells lacking APOBEC3B and decreases in cells overexpressing APOBEC3B. Genome-wide analyses show major changes in the overall landscape of physiological and stimulus-induced R-loops with thousands of differentially altered regions, as well as binding of APOBEC3B to many of these sites. APOBEC3 mutagenesis impacts genes overexpressed in tumors and splice factor mutant tumors preferentially, and APOBEC3-attributed kataegis are enriched in RTCW motifs consistent with APOBEC3B deamination. Taken together with the fact that APOBEC3B binds single-stranded DNA and RNA and preferentially deaminates DNA, these results support a mechanism in which APOBEC3B regulates R-loops and contributes to R-loop mutagenesis in cancer.

High Fat High Sugar Diet Reduces Small Intestinal Secretion by Sex-Dependent Mechanisms.

BACKGROUND/AIMS: The goal of this study was to determine the influence of high-fat high-sugar diet (Western diet) on intestinal function and subsequently to determine if there were any beneficial effects of exercise, genistein (a naturally occurring phytoestrogen) or both, on the intestine. METHODS: We measured transepithelial short circuit current (Isc), across freshly isolated segments of jejunum from male and female C57Bl/6J mice randomly assigned to one of the following groups for the 12-week study duration: high-fat high-sugar diet (HFS), HFS with genistein (Gen), HFS with exercise (Ex), or HFS with both genistein and exercise (Gen+Ex) and compared them to lean controls. Genistein concentration was 600 mg genistein/kg diet. Exercise comprised of moderate intensity treadmill running (150 min per week). At the completion of the study, segments of jejunum were frozen for western blot determination of key proteins involved in secretory and absorptive functions, as well as senescence. Intestinal morphology was assessed. Serum cytokine assays were performed. RESULTS: Basal Isc was significantly decreased (by 70%, P<0.05) in HFS females and males versus leans. This decrease was partially mitigated by exercise in both sexes. In females, the HFS-induced decrease in Isc was attributed to a significant loss of CLC2, NKCC1 and CFTR expression whereas in males this was due to a significant loss of Na/K-ATPase, KCa and NKCC1 expression (indicating sex-dependent mechanisms). Exercise mitigated most of the loss of Isc in both sexes. Our data suggested that A2BR levels were dysregulated in HFS fed mice and that concomitant treatment with Gen or Gen+Ex prevented this disruption in females only. Inflammatory state was associated with body weight changes. CONCLUSION: Our data suggests that the reduced basal jejunal Isc in HFS mice is attributed to sex-dependent mechanisms and while exercise partially mitigated this, it's mechanism of action was unclear. Improved understanding of Western diet induced intestinal dysfunctions may allow for the development of novel drug targets to treat gastrointestinal disturbances in diabetic obesity.

The Use of Preoperative Prophylactic Systemic Antibiotics for the Prevention of Endopthalmitis in Open Globe Injuries: A Meta-Analysis.

TOPIC: This study reports the effect of systemic prophylactic antibiotics (and their route) on the risk of endophthalmitis after open globe injury (OGI). CLINICAL RELEVANCE: Endophthalmitis is a major complication of OGI; it can lead to rapid sight loss in the affected eye. The administration of systemic antibiotic prophylaxis is common practice in some health care systems, although there is no consensus on their use. METHODS: PubMed, CENTRAL, Web of Science, CINAHL, and Embase were searched. This was completed July 6, 2021 and updated December 10, 2022. We included randomized and nonrandomized prospective studies which reported the rate of post-OGI endophthalmitis when systemic preoperative antibiotic prophylaxis (via the oral or IV route) was given. The Cochrane Risk of Bias tool and ROBINS-I tool were used for assessing the risk of bias. Where meta-analysis was performed, results were reported as an odds ratio. PROSPERO registration: CRD42021271271. RESULTS: Three studies were included. One prospective observational study compared outcomes of patients who had received systemic or no systemic preoperative antibiotics. The endophthalmitis rates reported were 3.75% and 4.91% in the systemic and no systemic preoperative antibiotics groups, a nonsignificant difference (P = 0.68). Two randomized controlled trials were included (1555 patients). The rates of endophthalmitis were 17 events in 751 patients (2.26%) and 17 events in 804 patients (2.11%) in the oral antibiotics and IV (± oral) antibiotics groups, respectively. Meta-analysis demonstrated no significant differences between groups (odds ratio, 1.07; 95% confidence interval, 0.54-2.12). CONCLUSIONS: The incidences of endophthalmitis after OGI were low with and without systemic antibiotic prophylaxis, although high-risk cases were excluded in the included studies. When antibiotic prophylaxis is considered, there is moderate evidence that oral antibiotic administration is noninferior to IV. FINANCIAL DISCLOSURE(S): The author(s) have no proprietary or commercial interest in any materials discussed in this article.

A novel role of TRIM28 B box domain in L1 retrotransposition and ORF2p-mediated cDNA synthesis.

The long interspersed element 1 (LINE-1 or L1) integration is affected by many cellular factors through various mechanisms. Some of these factors are required for L1 amplification, while others either suppress or enhance specific steps during L1 propagation. Previously, TRIM28 has been identified to suppress transposable elements, including L1 expression via its canonical role in chromatin remodeling. Here, we report that TRIM28 through its B box domain increases L1 retrotransposition and facilitates shorter cDNA and L1 insert generation in cultured cells. Consistent with the latter, we observe that tumor specific L1 inserts are shorter in endometrial, ovarian, and prostate tumors with higher TRIM28 mRNA expression than in those with lower TRIM28 expression. We determine that three amino acids in the B box domain that are involved in TRIM28 multimerization are critical for its effect on both L1 retrotransposition and cDNA synthesis. We provide evidence that B boxes from the other two members in the Class VI TRIM proteins, TRIM24 and TRIM33, also increase L1 retrotransposition. Our findings could lead to a better understanding of the host/L1 evolutionary arms race in the germline and their interplay during tumorigenesis.

Clinical and Mechanistic Implications of R-Loops in Human Leukemias.

Genetic mutations or environmental agents are major contributors to leukemia and are associated with genomic instability. R-loops are three-stranded nucleic acid structures consisting of an RNA-DNA hybrid and a non-template single-stranded DNA. These structures regulate various cellular processes, including transcription, replication, and DSB repair. However, unregulated R-loop formation can cause DNA damage and genomic instability, which are potential drivers of cancer including leukemia. In this review, we discuss the current understanding of aberrant R-loop formation and how it influences genomic instability and leukemia development. We also consider the possibility of R-loops as therapeutic targets for cancer treatment.

Histone H2A variants: Diversifying chromatin to ensure genome integrity.

Histone variants represent chromatin components that diversify the structure and function of the genome. The variants of H2A, primarily H2A.X, H2A.Z and macroH2A, are well-established participants in DNA damage response (DDR) pathways, which function to protect the integrity of the genome. Through their deposition, post-translational modifications and unique protein interaction networks, these variants guard DNA from endogenous threats including replication stress and genome fragility as well as from DNA lesions inflicted by exogenous sources. A growing body of work is now providing a clearer picture on the involvement and mechanistic basis of H2A variant contribution to genome integrity. Beyond their well-documented role in gene regulation, we review here how histone H2A variants promote genome stability and how alterations in these pathways contribute to human diseases including cancer.

Applying a Military Teleophthalmology Mobile App in a Noncombat Emergent Care Setting.

INTRODUCTION: Teleophthalmology has a natural role in the military due to the inherent organization of its medical system, which provides care to patients in remote locations around the world. Improving access to ophthalmic care enhances force readiness because ocular trauma and disease can cause vision impairment or blindness and can occur anywhere service members are located. Recently, a secure, Health Insurance Portability and Accountability Act-compliant mobile phone application (app) for teleophthalmology called Forward Operating Base Expert Telemedicine Resource Utilizing Mobile Application for Trauma (FOXTROT) was beta tested in Afghanistan and demonstrated that this solution can improve and extend ophthalmic care in a deployed environment. There are few civilian or military teleophthalmology solutions for ocular trauma and disease in an urgent or emergent ophthalmic care setting. Civilian teleophthalmology solutions have largely been developed for disease-specific models of care. In this work, we address this gap by testing the FOXTROT app in a non-deployed, emergent care setting. MATERIALS AND METHODS: We evaluated the use of the teleophthalmology mobile phone app (FOXTROT) in a non-deployed military setting at the Malcolm Grow Medical Clinics and Surgery Center at Joint Base Andrews in Maryland. Consults from the emergent care center were placed by providers using the app, and the on-call ophthalmologist responded with treatment and management recommendations. The primary outcomes were response within the requested time, visual acuity tested in both eyes, agreement between the teleophthalmology and the final diagnosis, and the number of communication or technical errors that prevented the completion of consults. The secondary outcomes were average response time and the number of consults uploaded to the medical record. RESULTS: From October 2020 to January 2022, 109 consults were received. Ten consults had communication or technical errors that prevented the completion of consults within the app and were excluded from the analysis of completed consults. Of the 99 completed consults, responses were given within the requested time in 95 (96.0%), with the average response time in 11 minutes 48 seconds (95% confidence interval, 8 minutes 57 seconds to 14 minutes 41 seconds). Visual acuity was tested in both eyes in 56 (56.6%). There was agreement between the teleophthalmology diagnosis and the final diagnosisin 40 of 50 (80.0%) consults with both a teleophthalmology and final diagnosis. Ninety-eight (99.0%) consults were uploaded to the patient's medical record. CONCLUSIONS: Beta testing of a teleophthalmology mobile phone app (FOXTROT) in a noncombat emergent care setting demonstrated that this solution can extend ophthalmic care in this environment at a military treatment facility. However, improvements in the reliability of the platform are needed in future developments to reduce communication and technical errors.

Single-Cell Analysis of Histone Acetylation Dynamics at Replication Forks Using PLA and SIRF.

Genome integrity is constantly challenged by various processes including DNA damage, structured DNA, transcription, and DNA-protein crosslinks. During DNA replication, active replication forks that encounter these obstacles can result in their stalling and collapse. Accurate DNA replication requires the ability of forks to navigate these threats, which is aided by DNA repair proteins. Histone acetylation participates in this process through an ability to signal and recruit proteins to regions of replicating DNA. For example, the histone acetyltransferase PCAF promotes the recruitment of the DNA repair factors MRE11 and EXO1 to stalled forks by acetylating histone H4 at lysine 8 (H4K8ac). These highly dynamic processes can be detected and analyzed using a modified proximity ligation assay (PLA) method, known as SIRF (in situ protein interactions with nascent DNA replication forks). This single-cell assay combines PLA with EdU-coupled Click-iT chemistry reactions and fluorescence microscopy to detect these interactions at sites of replicating DNA. Here we provide a detailed protocol utilizing SIRF that detects the HAT PCAF and histone acetylation at replication forks. This technique provides a robust methodology to determine protein recruitment and modifications at the replication fork with single-cell resolution.

Looking on the horizon; potential and unique approaches to developing radiation countermeasures for deep space travel.

Future lunar missions and beyond will require new and innovative approaches to radiation countermeasures. The Translational Research Institute for Space Health (TRISH) is focused on identifying and supporting unique approaches to reduce risks to human health and performance on future missions beyond low Earth orbit. This paper will describe three funded and complementary avenues for reducing the risk to humans from radiation exposure experienced in deep space. The first focus is on identifying new therapeutic targets to reduce the damaging effects of radiation by focusing on high throughput genetic screens in accessible, sometimes called lower, organism models. The second focus is to design innovative approaches for countermeasure development with special attention to nucleotide-based methodologies that may constitute a more agile way to design therapeutics. The final focus is to develop new and innovative ways to test radiation countermeasures in a human model system. While animal studies continue to be beneficial in the study of space radiation, they can have imperfect translation to humans. The use of three-dimensional (3D) complex in vitro models is a promising approach to aid the development of new countermeasures and personalized assessments of radiation risks. These three distinct and unique approaches complement traditional space radiation efforts and should provide future space explorers with more options to safeguard their short and long-term health.

RAD51AP1 regulates ALT-HDR through chromatin-directed homeostasis of TERRA.

Alternative lengthening of telomeres (ALT) is a homology-directed repair (HDR) mechanism of telomere elongation that controls proliferation in subsets of aggressive cancer. Recent studies have revealed that telomere repeat-containing RNA (TERRA) promotes ALT-associated HDR (ALT-HDR). Here, we report that RAD51AP1, a crucial ALT factor, interacts with TERRA and utilizes it to generate D- and R-loop HR intermediates. We also show that RAD51AP1 binds to and might stabilize TERRA-containing R-loops as RAD51AP1 depletion reduces R-loop formation at telomere DNA breaks. Proteomic analyses uncover a role for RAD51AP1-mediated TERRA R-loop homeostasis in a mechanism of chromatin-directed suppression of TERRA and prevention of transcription-replication collisions (TRCs) during ALT-HDR. Intriguingly, we find that both TERRA binding and this non-canonical function of RAD51AP1 require its intrinsic SUMO-SIM regulatory axis. These findings provide insights into the multi-contextual functions of RAD51AP1 within the ALT mechanism and regulation of TERRA.