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Although health promotion is not the primary function of public libraries, it is well documented that many libraries engage in health promotion activities, even when resources are constrained. Less understood is the readiness of the public library workforce, particularly in rural communities, to implement evidence-based health promotion programs. This study uses a modified version of the Competency Assessment for Tier 2 Public Health Professionals to assess the readiness of a small sample (n = 21) of Oregon rural library managers to implement evidence-based health initiatives. Results show that outside of communication skills, most rural library workers do not consider themselves to have proficiency in core health promotion competencies. Although some slight differences were found among librarians based on socio-demographic factors, those differences were not statistically significant. Implications include the need for strengthened support to build the capacity for rural public library workers who are interested in delivering evidence-based health promotion programs., (© 2024. The Author(s).)

Objective: To examine the effect of Medicaid immediate postpartum long-acting reversible contraception (IPP LARC) reforms on self-reported mental health among low-income mothers aged 18-44 years., Data Sources and Study Setting: We used national secondary data on self-reported mental health status in the past 30 days from the core component (2014-2019) of the Behavioral Risk Factor Surveillance System (BRFSS)., Study Design: We estimated linear probability models for reporting any days of not good mental health in the past 30 days. We adjusted for individual-level factors, state-level factors, and state and year fixed effects. Our primary independent variable was an indicator for IPP LARC payment reform. We examined the effect of the Medicaid payment reforms on self-reported mental health status in the past 30 days using difference-in-differences and event-study designs., Data Collection/extraction Methods: Not applicable., Principal Findings: State adoption of Medicaid IPP LARC reforms was associated with significant reductions (between 5.7% and 11.5%) in the predicted probability of reporting any days of not good mental health among low-income mothers. Treatment effects appeared to be driven by respondents reporting two or more children (less than 18 years of age) in the household (ATT = -0.028, p = 0.04). Results are robust to a series of sensitivity tests and alternative estimation strategies., Conclusions: Our findings suggest that contemporary efforts to improve access to contraceptive methods may have important benefits beyond reproductive autonomy. These findings have implications for policymakers as the landscape related to family planning services continues to shift., (© 2024 The Authors. Health Services Research published by Wiley Periodicals LLC on behalf of Health Research and Educational Trust.)

Introduction: Type 2 diabetes impacts millions and poor maintenance of diabetes can lead to preventable complications, which is why achieving and maintaining target A1C levels is critical. Thus, we aimed to examine inequities in A1C over time, place, and individual characteristics, given known inequities across these indicators and the need to provide continued surveillance., Methods: Secondary de-identified data from medical claims from a single payer in Texas was merged with population health data. Generalized Estimating Equations were utilized to assess multiple years of data examining the likelihood of having non-target (>7% and ≥7%, two slightly different cut points based on different sources) and separately uncontrolled (>9%) A1C. Adults in Texas, with a Type 2 Diabetes (T2D) flag and with A1C reported in first quarter of the year using data from 2016 and 2019 were included in analyses., Results: Approximately 50% had A1Cs within target ranges (<7% and ≤7%), with 50% considered having non-target (>7% and ≥7%) A1Cs; with 83% within the controlled ranges (≤9%) as compared to approximately 17% having uncontrolled (>9%) A1Cs. The likelihood of non-target A1C was higher among those individuals residing in rural (vs urban) areas ( P  < .0001); similar for the likelihood of reporting uncontrolled A1C, where those in rural areas were more likely to report uncontrolled A1C ( P  < .0001). In adjusted analysis, ACA enrollees in 2016 were approx. 5% more likely (OR = 1.049, 95% CI = 1.002-1.099) to have non-target A1C (≥7%) compared to 2019; in contrast non-ACA enrollees were approx. 4% more likely to have non-target A1C (≥7%) in 2019 compared to 2016 (OR = 1.039, 95% CI = 1.001-1.079). In adjusted analysis, ACA enrollees in 2016 were 9% more likely (OR = 1.093, 95% CI = 1.025-1.164) to have uncontrolled A1C compared to 2019; whereas there was no significant change among non-ACA enrollees., Conclusions: This study can inform health care interactions in diabetes care settings and help health policy makers explore strategies to reduce health inequities among patients with diabetes. Key partners should consider interventions to aid those enrolled in ACA plans, those in rural and border areas, and who may have coexisting health inequities., Competing Interests: Declaration of Conflicting InterestsThe author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Rural consumers often face a limited choice of carriers and plans and high premiums. To mitigate this issue, Texas recently adjusted its Affordable Care Act Marketplace rating areas to integrate rural areas into nearby urban markets for rating purposes. We found that rural consumers subsequently saw increases in carrier and plan choices, as well as decreases in overall plan premiums.

Background: The trend of Type 2 diabetes-related costs over 4 years could be classified into different groups. Patient demographics, clinical factors (e.g., A1C, short- and long-term complications), and rurality could be associated with different trends of cost. Study objectives are to: (1) understand the trajectories of cost in different groups; (2) investigate the relationship between cost and key factors in each cost trajectory group; and (3) assess significant factors associated with different cost trajectories., Methods: Commercial claims data in Texas from 2016 to 2019 were provided by a large commercial insurer and were analyzed using group-based trajectory analysis, longitudinal analysis of cost, and logistic regression analyses of different trends of cost., Results: Five groups of distinct trends of Type 2 diabetes-related cost were identified. Close to 20% of patients had an increasing cost trend over the 4 years. High A1C values, diabetes complications, and other comorbidities were significantly associated with higher Type 2 diabetes costs and higher chances of increasing trend over time. Rurality was significantly associated with higher chances of increasing trend over time., Conclusions: Group-based trajectory analysis revealed distinct patient groups with increased cost and stable cost at low, medium, and high levels in the 4-year period. The significant associations found between the trend of cost and A1C, complications, and rurality have important policy and program implications for potentially improving health outcomes and constraining healthcare costs., (© 2023. BioMed Central Ltd., part of Springer Nature.)

Background: Rural residents generally lack adequate physical activity to benefit health and reduce disparities in chronic diseases, such as cardiovascular disease and certain cancers. The Socioecological Model describes physical activity as involving a dynamic and reciprocal interaction between individual, social, and community factors. Community group-based walking programs and civic engagement interventions aimed at enhancing physical activity have been successful in rural communities but have not targeted all three socioecological levels. Public libraries can act as innovative public health partners in rural communities. However, challenges remain because rural libraries often lack the capacity to implement evidence-based health promotion programming. The goals of this study are (1) build the capacity for rural libraries to implement evidence-based health promotion programs, (2) compare changes in physical activity between a group-based walking program and a combined group-based walking and civic engagement program with rural residents, and (3) conduct an implementation evaluation., Methods: We will conduct a comparative effectiveness study of a group-based walking (standard approach) versus a group-based walking plus civic engagement program (combined approach) aimed at enhancing walkability to increase physical activity among rural adults. Key mediators between the program effects and change in outcomes will also be identified. Finally, we will evaluate program implementation, conduct a cost effectiveness evaluation, and use a positive deviance analysis to understand experiences of high and low changers on key outcomes. Twenty towns will be matched and randomized to one of the two conditions and our aim is to enroll a total of 350-400 rural residents (15-20 per town). Study outcomes will be assessed at baseline, and 6, 12, and 24 months., Discussion: This study will build the capacity of rural libraries to implement evidence-based walking programs as well as other health promotion programs in their communities. The study results will answer questions regarding the relative effectiveness and cost effectiveness of two multilevel physical activity interventions targeting rural communities. We will learn what works and how these multilevel interventions can be implemented in rural populations., Trial Registration: ClinicalTrials.gov Identifier: NCT05677906., (© 2023. BioMed Central Ltd., part of Springer Nature.)

Objective: This study will identify factors associated with higher hemoglobin A1c (A1c) values and diabetes-related costs among commercially insured adults in Texas diagnosed with type 2 diabetes., Research Design and Methods: This secondary data analysis was based on claims data from commercially insured individuals 18-64 years of age residing in Texas with diagnosed type 2 diabetes during the 2018-2019 study period. The final analysis sample after all the exclusions consisted of 34,992 individuals. Measures included hemoglobin A1c, diabetes-related costs, Charlson Comorbidity Index, diabetes-related complications, rurality and other socioeconomic characteristics. Longitudinal A1c measurements were modeled using age, sex, rurality, comorbidity, and diabetes-related complications in generalized linear longitudinal regression models adjusting the observation time, which was one of the 8 quarters in 2018 and 2019. The diabetes-related costs were similarly modeled in both univariable and multivariable generalized linear longitudinal regression models adjusting the observation time by calendar quarters and covariates., Results: The median A1c value was 7, and the median quarterly diabetes-related cost was $120. A positive statistically significant relationship (p = < .0001) was found between A1c levels and diabetes-related costs, although this trend slowed down as A1c levels exceeded 8.0%. Higher A1c values were associated with being male, having diabetes-related complications, and living in rural areas. Higher costs were associated with higher A1c values, older age, and higher Charlson Comorbidity Index scores., Conclusion: The study adds updated analyses of the interrelationships among demographic and geographic factors, clinical indicators, and health-related costs, reinforcing the role of higher A1c values and complications as diabetes-related cost drivers., Competing Interests: The commercial affiliation for Dr. Preston was declared as she was employed by a commercial company at the time this manuscript was prepared., (Copyright: © 2023 Ory et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.)

Objectives: To assess the impact of adding neighborhood social determinants of health (SDOH) data to demographic and clinical characteristics for predicting high-cost utilizers and to examine variations across age groups., Study Design: Using US Census data and 2017-2018 commercial claims from a large national insurer, we estimated association between neighborhood-level SDOH and the probability of being a high-cost utilizer., Methods: Observational study using administrative claims from a national insurer and US Census data. Data included a 50% random sample of commercially insured individuals who were younger than 89 years and had 1 year of continuous eligibility in 2017 and at least 30 days in 2018. Probit models assessed impact of SDOH and neighborhood conditions on predicting cost status., Results: SDOH did not improve predictive power of evaluated models. However, disadvantaged neighborhood residence was still associated with being a high-cost utilizer. Adults 65 years and older in disadvantaged neighborhoods had increased likelihood of high-cost utilization. Children and younger adults in disadvantaged neighborhoods had lower risk of becoming high-cost utilizers., Conclusions: Policy makers and industry stakeholders should be aware of the mechanisms behind the relationship between neighborhood social conditions and health outcomes and how the relationship differs across age groups.

Background: Laparoscopic cyst enucleation has its advantages and limitations in treatment of gastrointestinal tract (GIT) duplications. It allows to avoid bowel resection in such locations as ileocecal valve. We introduced laparoscopic cyst enucleation with further bowel plasty using cyst muscle layer and without monopolar coagulation, for cyst dissection we used straight scissors., Materials and Methods: Our study included 20 children with GIT duplications, who underwent cyst enucleation from 2018 to 2021. Laparoscopy was performed in all cases with various cyst locations (stomach - 2, duodenum - 3, small bowel - 14, ileocecal area - 1). Mean age of surgery was 40 ± 35,3 days (min 6 days, max 150 days)., Results: Mean operation time was 84,4 ± 27,35 min (min - 40 min, max - 160 min). We had no intraoperative complications. All patients received parenteral feeding for 3-5 days after the operation. Postoperative complications occurred in 3 cases: bowel perforation which required enterostomy (10%) and bowel volvulus required resection (5%). To our opinion, perforations occurred due to monopolar coagulation used for cyst enucleation in these children. No complications were observed in patients who underwent enucleation by straight scissors. Mean postoperative hospital stay was 15.6 ± 10.48 days (min - 4 days, max - 58 days). We observed neither stenosis nor any other complications in the long-term follow-up., Conclusions: Laparoscopic cyst enucleation is a feasible and safe approach for GIT duplications. It allows to avoid bowel resection, and the use of straight scissors instead of monopolar coagulation provides less postoperative complications such as perforation., The Level of Evidence: III., (Copyright © 2022 Elsevier Inc. All rights reserved.)

Purpose: Nursing turnover is a leading cause of inefficiency in health care delivery. Few studies have examined turnover among nurses who work in rural areas., Methods: We accessed human resources data that tracked hiring and terminations from a large health system operating in South Dakota, North Dakota, and Minnesota between January 2016 and December 2017. Our study sample included 7,634 registered nurses, 1,765 of whom worked in a rural community. Within the health system, there were 27 affiliated hospitals, 17 of which were designated critical access hospitals. We estimated nursing turnover rates overall and stratified turnover rates by available demographic and occupational characteristics, including whether the nurse worked in a community with an affiliated acute care hospital or critical access hospital., Findings: Overall, 19% of nurses left their position between January 2016 and December 2017. Turnover rates were associated with state, nurse gender and age, and occupational tenure, but were similar in urban and rural areas. Of note, turnover rates were significantly higher in communities without an affiliated acute care hospital or critical access hospital., Conclusion: Between 2016 and 2017, nearly 1 in 5 nurses working in this health system left their position. Turnover rates differed based on nurse demographics and selected occupational characteristics, including tenure. We also found higher turnover rates among nurses who worked in communities without an affiliated hospital, which points to a potential but unexplored benefit of hospitals in rural areas., (© 2022 National Rural Health Association.)

Background: Access to health care continues to be a challenge, especially in remote areas. Since 2013, 70 rural hospitals have closed in the United States further exacerbating barriers to health care access in rural areas., Objective: The objective of this study is to identify the impact of rural hospital closures on total medical spending and utilization among the commercially insured rural population., Research Design: We use a pre-post study design with a comparison group. Individual-level Texas commercial claims data in 2014-2019 were linked to the Centers for Medicare & Medicaid Services (CMS) Provider of Services Current Files, Area Health Resource File, and Census American Community Survey. We performed an event study to test for pre-trends., Subjects: Analysis sample included commercially insured individuals 19-64 years of age residing in Texas., Measures: Total medical spending and counts of health care encounters., Results: Individuals residing in rural Texas areas affected by a hospital closure experienced decreases in outpatient and emergency department (ED) utilization and no statistically significant changes in total medical spending relative to the unaffected individuals. Outpatient and ED utilization decreased by 0.133 (<0.1) and 0.015 (7<0.05) visits, respectively. Heterogeneity analysis showed that individuals residing in urban Texas experienced increases in total medical spending by $12.2 per month (<0.01) as well as individual spending subcategories., Conclusions: Rural hospital closures led to significant decreases in outpatient and ED utilization while having no effect on health care spending. Close attention must be paid to rural hospital closures to ensure equitable health care access, especially for underserved populations., (Copyright © 2022 Wolters Kluwer Health, Inc. All rights reserved.)

Position effect variegation (PEV) is a phenomenon wherein the expression level of a gene strongly depends on its genomic position. PEV can be observed when a gene is moved via a chromosome rearrangement or identical genetic constructs are inserted into different regions of the genome. The eukaryotic genome has a domain organization, and gene activity within a domain depends not only on the nucleotide sequence of a gene, but also on the state of surrounding chromatin, thus being regulated epigenetically. Chromatin is a complex of DNA, RNA, and associated structural and regulatory proteins. The epigenetic status of chromatin depends on the replication time of a given genomic region, particular regulatory DNA motifs, and contacts with the inner nuclear envelope (lamina) and other chromosome regions (topologically associated domains). PEV results from the changes in the epigenetic state of a gene and provides a unique tool to study the molecular and biochemical processes that underlie the establishment and switching of epigenetic states. Understanding the molecular mechanisms of PEV in human is of clinical importance, in particular, for the detection and treatment of retroviral infections because the local chromatin state may determine the latent/active state transition of an infection, such as HIV. In addition, a large number of human neurodegenerative diseases are caused by epigenetic gene inactivation due to expansion of short repeats. Finally, to apply gene therapy methods, it is important to develop approaches that ensure a necessary level of transgene expression with sufficient accuracy.

Objectives: To estimate the frequency and factors associated with foregone and delayed medical care attributed to the COVID-19 pandemic among nonelderly adults from August to December 2020 in the United States., Methods: We used three survey waves from the Urban Institute's Household Pulse Survey (HPS) collected between August 19-31, October 14-26 and December 9-21. The final sample included 155,825 nonelderly (18-64) respondents representing 135,835,598 million individuals in the United States. We used two multivariable logistic regressions to estimate the association between respondents' characteristics and foregone and delayed care., Results: The frequency of foregone and delayed medical care was 26.9% and 35.9%, respectively. Around 60% of respondents reported difficulties in paying for usual household expenses in the last 7 days. More than half reported several days of mental health issues. The regression results indicated that foregone or delayed care were significantly associated with difficulties in paying usual household expenses (p < 0.001), worse self-reported health status (p < 0.001), increased mental health problems (p < 0.001), Veterans Affairs (p <0.001) or Medicaid (p = 0.003) coverage compared to private healthcare coverage, and older age groups. Individuals who participated in the latter two waves of the survey (October, December) were less likely to report foregone and delayed care compared to those who participated in Wave 1 (August)., Conclusion: Overall, the frequency of foregone and delayed medical care remained high from August to December 2020 among nonelderly US adults. Our findings highlight that pandemic-induced access barriers are major drivers of reduced healthcare provision during the second half of the pandemic and highlight the need for policies to support patients in seeking timely care., (© 2021 John Wiley & Sons Ltd.)

This study was conducted to assess if neighborhood-level social determinants of health improve model performance of predicting preventable hospitalization. Using medical and pharmacy claims and neighborhood-level social determinants and the split sample method (67% training with balanced sample and 33% validation), the authors developed prospective modeling for preventable hospital use, defined as hospitalization for ambulatory care sensitive conditions (Agency for Healthcare Research and Quality Prevention Quality Indicators 90 and 92) and preventable emergency department (ED) use (based on Billing's algorithm). Performance of age-gender only or age-gender with administrative claims models were compared to models with the addition of social determinants. Adding social determinants to age-gender only models and claim history models improves model performance as measured by Brier score, C statistics, and area under the precision-recall curve for preventable ED use measures while it leads to similar performance for predicting preventable hospital use compared to models without social determinants. Adding neighborhood-level social determinants improved prediction for preventable ED use in the absence of individual-level social determinants, regardless of the availability of full administrative claims history.

Background: The coronavirus disease 2019 (COVID-19) pandemic has critically affected healthcare delivery in the United States. Little is known on its impact on the utilization of emergency department (ED) services, particularly for conditions that might be medically urgent. The objective of this study was to explore trends in the number of outpatient (treat and release) ED visits during the COVID-19 pandemic., Methods: We conducted a cross-sectional, retrospective study of outpatient emergency department visits from January 1, 2019 to August 31, 2020 using data from a large, urban, academic hospital system in Utah. Using weekly counts and trend analyses, we explored changes in overall ED visits, by patients' area of residence, by medical urgency, and by specific medical conditions., Results: While outpatient ED visits were higher (+6.0%) in the first trimester of 2020 relative to the same period in 2019, the overall volume between January and August of 2020 was lower (-8.1%) than in 2019. The largest decrease occurred in April 2020 (-30.4%), followed by the May to August period (-12.8%). The largest declines were observed for visits by out-of-state residents, visits classified as non-emergent, primary care treatable or preventable, and for patients diagnosed with hypertension, diabetes, headaches and migraines, mood and personality disorders, fluid and electrolyte disorders, and abdominal pain. Outpatient ED visits for emergent conditions, such as palpitations and tachycardia, open wounds, syncope and collapse remained relatively unchanged, while lower respiratory disease-related visits were 67.5% higher in 2020 relative to 2019, particularly from March to April 2020. However, almost all types of outpatient ED visits bounced back after May 2020., Conclusions: Overall outpatient ED visits declined from mid-March to August 2020, particularly for non-medically urgent conditions which can be treated in other more appropriate care settings. Our findings also have implications for insurers, policymakers, and other stakeholders seeking to assist patients in choosing more appropriate setting for their care during and after the pandemic., Competing Interests: Declaration of Competing Interest All authors report not conflict of interest., (Copyright © 2020 Elsevier Inc. All rights reserved.)

Growing evidence suggests that medical marijuana laws have harm reduction effects across a variety of outcomes related to risky health behaviors. This study investigates the impact of medical marijuana laws on self-reported health using data from the Behavioral Risk Factor Surveillance System from 1993 to 2013. In our analyses we separately identify the effect of a medical marijuana law and the impact of subsequent active and legally protected dispensaries. Our main results show surprisingly limited improvements in self-reported health after the legalization of medical marijuana and legally protected dispensaries. Subsample analyses reveal strong improvements in health among non-white individuals, those reporting chronic pain, and those with a high school degree, driven predominately by whether or not the state had active and legally protected dispensaries. We also complement the analysis by evaluating the impact on risky health behaviors and find that the aforementioned demographic groups experience large reductions in alcohol consumption after the implementation of a medical marijuana law.

Objective: To assess the availability and price of naloxone as well as pharmacy staff knowledge of the standing order for naloxone in Pennsylvania pharmacies., Methods: We conducted a telephone audit study from December 2016 to April 2017 in which staff from Pennsylvania pharmacies were surveyed to evaluate naloxone availability, staff understanding of the naloxone standing order, and out-of-pocket cost of naloxone., Results: Responses were obtained from 682 of 758 contacted pharmacies (90% response rate). Naloxone was stocked (ie, available for dispensing) in 306 (45%) pharmacies surveyed. Of the 376 (55%) pharmacies that did not stock naloxone, 118 (31%) stated that they could place an order for naloxone for pickup within 1 business day. Responses by pharmacy staff to questions about key components of the standing order for naloxone were collected from 581 of the 682 pharmacies who participated in the survey (85%). Of the 581 pharmacy staff members who stated that they either stocked or could order naloxone, 64% correctly answered all questions pertaining to understanding of the naloxone standing order. The respective median out-of-pocket prices stated in the audit varied by formulation and ranged from $50 to $4000. Staff from national pharmacies were significantly more likely than staff from regional/local chain and non-chain pharmacies to correctly answer that a prescription was not required to obtain naloxone (68.5%, 57.7%, and 52.4% respectively, (P = 0.0045)., Conclusions: Multiple barriers to naloxone access exist in pharmacies across a large, diverse state, despite the presence of a standing order to facilitate such access. Limited availability of naloxone in pharmacies, lack of knowledge or understanding by pharmacy staff of the standing order, and variability in out-of-pocket cost for this drug are among these potential barriers. Regulatory or legal incentives for pharmacies or drug manufacturers, education efforts directed toward pharmacy staff members, or other interventions may be needed to increase naloxone availability in pharmacies.

This study evaluates the effect of minimum wage on risky health behaviors, healthcare access, and self-reported health. We use data from the 1993-2015 Behavioral Risk Factor Surveillance System, and employ a difference-in-differences strategy that utilizes time variation in new minimum wage laws across U.S. states. Results suggest that the minimum wage increases the probability of being obese and decreases daily fruit and vegetable intake, but also decreases days with functional limitations while having no impact on healthcare access. Subsample analyses reveal that the increase in weight and decrease in fruit and vegetable intake are driven by the older population, married, and whites. The improvement in self-reported health is especially strong among non-whites, females, and married.

Violence is a widespread problem that affects the physical, mental, and social health of individuals and communities. Violence comes with an immense economic cost to its victims and society at large. Although violence interventions have traditionally targeted individuals, changes to the built environment in places where violence occurs show promise as practical, sustainable, and high-impact preventive measures. This review examines studies that use quasi-experimental or experimental designs to compare violence outcomes for treatment and control groups before and after a change is implemented in the built environment. The most consistent evidence exists in the realm of housing and blight remediation of buildings and land. Some evidence suggests that reducing alcohol availability, improving street connectivity, and providing green housing environments can reduce violent crimes. Finally, studies suggest that neither transit changes nor school openings affect community violence.

Spindle assembly relies on three main classes of microtubules (MTs): MTs nucleated by the centrosomes, MTs nucleated near the chromosomes/kinetochores and MTs nucleated from preexisting MTs through the augmin-based pathway. Here, we review the roles of these microtubule generation pathways in Drosophila spindle assembly. The extant results indicate that female meiotic cells, male meiotic cells, larval brain cells and S2 tissue culture cells exploit specific pathway combinations for generating the MTs necessary for spindle formation. Thus, different Drosophila cell types have specific modes of spindle assembly, which might be related to specific functional and developmental requirements.

Intercalary heterochromatin consists of extended chromosomal domains which are interspersed throughout the euchromatin and contain silent genetic material. These domains comprise either clusters of functionally unrelated genes or tandem gene duplications and possibly stretches of noncoding sequences. Strong repression of genetic activity means that intercalary heterochromatin displays properties that are normally attributable to classic pericentric heterochromatin: high compaction, late replication and underreplication in polytene chromosomes, and the presence of heterochromatin-specific proteins. Late replication and underreplication occurs when the suppressor of underreplication protein is present in intercalary heterochromatic regions. Intercalary heterochromatin underreplication in polytene chromosomes results in free double-stranded ends of DNA molecules; ligation of these free ends is the most likely mechanism for ectopic pairing between intercalary heterochromatic and pericentric heterochromatic regions. No support has been found for the view that the frequency of chromosome aberrations is elevated in intercalary heterochromatin.

DNA in Drosophila melanogaster polytene chromosomes is known to be locally underreplicated in both pericentric and intercalary heterochromatin. When the SuUR gene is mutant, complete and partial suppression of underreplication are observed in intercalary and pericentric heterochromatin, respectively; in contrast, overexpression of SuUR results in stronger underreplication. Using antibodies against phosphorylated histone H2Av and flies with different levels of SuUR expression, we demonstrated a clear correlation between the extent of underreplication in specific chromosome regions and the accumulation of H2Av phosphorylated at S137 (gamma-H2AX) at the same sites. Phosphorylated H2Av is a well-established marker of DNA double-stranded breaks (DSB). Our data thus argue that DNA underreplication leads to DSBs and that DSBs accumulate as salivary gland cells progress throughout repeated endocycles. We speculate that ligation of free double-stranded DNA termini causes the formation of ectopic contacts between the underreplicated regions in heterochromatin.

Polytene chromosomes were described in 1881 and since 1934 they have served as an outstanding model for a variety of genetic experiments. Using the polytene chromosomes, numerous biological phenomena were discovered. First the polytene chromosomes served as a model of the interphase chromosomes in general. In polytene chromosomes, condensed (bands), decondensed (interbands), genetically active (puffs), and silent (pericentric and intercalary heterochromatin as well as regions subject to position effect variegation) regions were found and their features were described in detail. Analysis of the general organization of replication and transcription at the cytological level has become possible using polytene chromosomes. In studies of sequential puff formation it was found for the first time that the steroid hormone (ecdysone) exerts its action through gene activation, and that the process of gene activation upon ecdysone proceeds as a cascade. Namely on the polytene chromosomes a new phenomenon of cellular stress response (heat shock) was discovered. Subsequently chromatin boundaries (insulators) were discovered to flank the heat shock puffs. Major progress in solving the problems of dosage compensation and position effect variegation phenomena was mainly related to studies on polytene chromosomes. This review summarizes the current status of studies of polytene chromosomes and of various phenomena described using this successful model.

Salivary gland polytene chromosomes of Drosophila melanogaster have a reproducible set of intercalary heterochromatin (IH) sites, characterized by late DNA replication, underreplicated DNA, breaks and frequent ectopic contacts. The SuUR mutation has been shown to suppress underreplication, and wild-type SuUR protein is found at late-replicating IH sites and in pericentric heterochromatin. Here we show that the SuUR gene influences all four IH features. The SuUR mutation leads to earlier completion of DNA replication. Using transgenic strains with two, four or six additional SuUR(+) doses (4-8xSuUR(+)) we show that wild-type SuUR is an enhancer of DNA underreplication, causing many late-replicating sites to become underreplicated. We map the underreplication sites and show that their number increases from 58 in normal strains (2xSuUR(+)) to 161 in 4-8xSuUR(+) strains. In one of these new sites (1AB) DNA polytenization decreases from 100% in the wild type to 51%-85% in the 4xSuUR (+) strain. In the 4xSuUR(+) strain, 60% of the weak points coincide with the localization of Polycomb group (PcG) proteins. At the IH region 89E1-4 (the Bithorax complex), a typical underreplication site, the degree of underreplication increases with four doses of SuUR(+) but the extent of the underreplicated region is the same as in wild type and corresponds to the region containing PcG binding sites. We conclude that the polytene chromosome regions known as IH are binding sites for SuUR protein and in many cases PcG silencing proteins. We propose that these stable silenced regions are late replicated and, in the presence of SuUR protein, become underreplicated.