Colorimetric and Electrochemical Dual-Mode Detection of Thioredoxin 1 Based on the Efficient Peroxidase-Mimicking and Electrocatalytic Property of Prussian Blue Nanoparticles.

As a potent detection method for cancer biomarkers in physiological fluid, a colorimetric and electrochemical dual-mode sensing platform for breast cancer biomarker thioredoxin 1 (TRX1) was developed based on the excellent peroxidase-mimicking and electrocatalytic property of Prussian blue nanoparticles (PBNPs). PBNPs were hydrothermally synthesized using K3[Fe(CN)6] as a precursor and polyvinylpyrrolidone (PVP) as a capping agent. The synthesized spherical PBNPs showed a significant peroxidase-like activity, having approximately 20 and 60% lower Km values for 3,3',5,5'-tetramethylbenzidine (TMB) and H2O2, respectively, compared to those of horseradish peroxidase (HRP). The PBNPs also enhanced the electron transfer on the electrode surface. Based on the beneficial features, PBNPs were used to detect target TRX1 via sandwich-type immunoassay procedures. Using the strategies, TRX1 was selectively and sensitively detected, yielding limit of detection (LOD) values as low as 9.0 and 6.5 ng mL-1 via colorimetric and electrochemical approaches, respectively, with a linear range of 10-50 ng mL-1 in both strategies. The PBNP-based TRX1 immunoassays also exhibited a high degree of precision when applied to real human serum samples, demonstrating significant potentials to replace conventional HRP-based immunoassay systems into rapid, robust, reliable, and convenient dual-mode assay systems which can be widely utilized for the identification of important target molecules including cancer biomarkers.

Dynamic 1D search and processive nucleosome translocations by RSC and ISW2 chromatin remodelers.

Eukaryotic gene expression is linked to chromatin structure and nucleosome positioning by ATP-dependent chromatin remodelers that establish and maintain nucleosome-depleted regions (NDRs) near transcription start sites. Conserved yeast RSC and ISW2 remodelers exert antagonistic effects on nucleosomes flanking NDRs, but the temporal dynamics of remodeler search, engagement, and directional nucleosome mobilization for promoter accessibility are unknown. Using optical tweezers and two-color single-particle imaging, we investigated the Brownian diffusion of RSC and ISW2 on free DNA and sparse nucleosome arrays. RSC and ISW2 rapidly scan DNA by one-dimensional hopping and sliding, respectively, with dynamic collisions between remodelers followed by recoil or apparent co-diffusion. Static nucleosomes block remodeler diffusion resulting in remodeler recoil or sequestration. Remarkably, both RSC and ISW2 use ATP hydrolysis to translocate mono-nucleosomes processively at ~30 bp/s on extended linear DNA under tension. Processivity and opposing push-pull directionalities of nucleosome translocation shown by RSC and ISW2 shape the distinctive landscape of promoter chromatin.

Dynamic 1D Search and Processive Nucleosome Translocations by RSC and ISW2 Chromatin Remodelers.

Eukaryotic gene expression is linked to chromatin structure and nucleosome positioning by ATP-dependent chromatin remodelers that establish and maintain nucleosome-depleted regions (NDRs) near transcription start-sites. Conserved yeast RSC and ISW2 remodelers exert antagonistic effects on nucleosomes flanking NDRs, but the temporal dynamics of remodeler search, engagement and directional nucleosome mobilization for promoter accessibility are unknown. Using optical tweezers and 2-color single-particle imaging, we investigated the Brownian diffusion of RSC and ISW2 on free DNA and sparse nucleosome arrays. RSC and ISW2 rapidly scan DNA by one-dimensional hopping and sliding respectively, with dynamic collisions between remodelers followed by recoil or apparent co-diffusion. Static nucleosomes block remodeler diffusion resulting in remodeler recoil or sequestration. Remarkably, both RSC and ISW2 use ATP hydrolysis to translocate mono-nucleosomes processively at ~30 bp/sec on extended linear DNA under tension. Processivity and opposing push-pull directionalities of nucleosome translocation shown by RSC and ISW2 shape the distinctive landscape of promoter chromatin.

Ficin-copper hybrid nanoflowers with enhanced peroxidase-like activity for colorimetric detection of biothiols.

The proteolytic enzyme ficin exhibits peroxidase-like activity but it is low and insufficient for real applications. Herein, we developed ficin-copper hybrid nanoflowers and demonstrated that they have significantly enhanced peroxidase-like activity of over 6-fold higher than that of free ficin, with one of the lowest Km and highest kcat values among all reported ficin-based peroxidase-like nanozymes. This was most likely caused by the synergistic catalysis of co-existing ficin and crystalline copper phosphate within nanoflower matrices having a large surface area. The nanoflowers were easily prepared by incubating ficin and copper sulfate at ambient temperature, causing coordination interactions between ficin's amine/amide moieties and copper ions, followed by concomitant anisotropic growth of petals composed of copper phosphate crystals with ficin. When compared to free ficin and natural horseradish peroxidase, the resulting nanoflowers' affinity toward H2O2 was greatly increased, yielding Km values of half and one-tenth, respectively, as well as noticeably improved stability. The nanoflowers were then applied to colorimetric determination of biological thiols (biothiols), such as cysteine (Cys), glutathione (GSH), and homocysteine (Hcy), based on their inhibition of nanoflowers' peroxidase-like activity, producing reduced color intensities as the concentration of biothiols increased. This strategy achieved highly sensitive colorimetric determinations of Cys, GSH, and Hcy after only 25-min incubation. Additionally, using this technique, biothiols in human serum were successfully determined with excellent precision, suggesting the potential application of this technology in clinical settings, particularly in point-of-care testing environments.

Acute COVID-19 in unvaccinated children without a history of previous infection during the delta and omicron periods.

BACKGROUND: The Omicron variant has been the predominant severe acute respiratory syndrome coronavirus 2 variant circulating in Korea since January 2022. This study evaluated and compared the clinical characteristics of children with coronavirus disease 2019 (COVID-19) between the Delta and Omicron periods. METHODS: The medical records of children aged < 12 years diagnosed with acute COVID-19 (<2 weeks of symptom onset) at seven university-affiliated hospitals were retrospectively reviewed. Children with a previous history of COVID-19 or vaccination were excluded. The clinical characteristics of the included children during the Delta (1 August 2021 to 15 January 2022) and Omicron (16 January to 30 June 2022) periods were compared. RESULTS: Among the 515 children included in the study, 36 (7.0%) and 479 (93.0%) were diagnosed with COVID-19 during the Delta and Omicron periods, respectively. A total of 142 (27.6%) were hospitalized, and the hospitalization rate was higher during the Delta period than the Omicron period (91.7% vs. 22.8%, p < 0.001). The incidence of fever (p = 0.009), vomiting (p = 0.031), and seizures (p = 0.007) was higher during the Omicron period, whereas the incidence of rhinorrhea (p = 0.027) was higher during the Delta period. Clinical severity and outcomes were comparable between the two periods. During the Omicron period, 6.4% of the hospitalized children received oxygen therapy and 1.8% received intensive care. CONCLUSION: The incidence of fever and seizures was higher during the Omicron period in pediatric patients without a history of vaccination or previous COVID-19. However, the clinical severity was similar during both periods.

Characteristics of febrile seizures with SARS-CoV-2 infection in the Omicron era.

Background: While the pandemic of coronavirus disease 2019 (COVID-19) is ongoing, the Omicron variant of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has been dominant recently. The Omicron variant causes more seizures in pediatric patients compared with previously circulated variants. This study aimed to investigate the incidence and clinical features of febrile seizure (FS) in pediatric patients with COVID-19 during the Omicron era. Methods: The medical records of pediatric patients (≤18 years of age) diagnosed with COVID-19, who presented with FS between February 2020 and June 2022, were reviewed retrospectively to analyze clinical characteristics of FS in seven university-affiliated hospitals of Korea. Results: Of 664 pediatric patients with COVID-19 during the study period, 46 during the pre-Omicron period and 589 during the Omicron period were included in the study analysis; 29 patients during the transition period were excluded. Among the included patients, 81 (12.8%) had concomitant FS, and most (76.5%) experienced simple FS. All FS episodes occurred during the Omicron period and none of them during pre-Omicron period (P=0.016). Sixty-five (80.2%) and 16 (19.8%) patients were categorized as FS (patient age ≤60 months) and late-onset FS (patient age >60 months), respectively. Underlying neurologic disease (P=0.013) and focal onset seizure (P=0.012) were more common in the late-onset FS group than in the FS group; however, overall clinical manifestations and outcomes including seizures consistent with characteristics of complex FS and subsequent epilepsy were similar between the two groups. Conclusions: As the COVID-19 pandemic persists, the incidence of FS has increased with the emergence of the Omicron variant. About one-fifth of the patients experiencing FS due to infection by the Omicron variant of SARS-CoV-2 were aged >60 months; however, clinical characteristics and outcomes were favorable. More information and long-term prognoses in patients with FS due to COVID-19 should be acquired.

Impact of COVID-19 on the incidence of respiratory viral infections and clinical characteristics of associated febrile seizures.

Background: Viral infections of the upper respiratory tract are one of the most common causes of febrile seizures (FSs). During the coronavirus disease-2019 (COVID-19) pandemic, mitigation measures have contributed to changes in the incidence of respiratory viral infections. Therefore, we aimed to evaluate the impact of the COVID-19 pandemic on the incidence of respiratory viral infections and clinical characteristics of FSs. Methods: We retrospectively reviewed the medical records of 988 episodes of FS (865 before the pandemic and 123 during the pandemic) between March 2016 and February 2022. Seizure characteristics and their outcomes, along with the distribution of identified respiratory viruses were compared before and during the pandemic. Results: The occurrence of FSs decreased during the COVID-19 pandemic compared to that before the pandemic. A substantial reduction in the incidence of influenza virus infections was observed (P<0.001) during the pandemic, while the incidence of rhinovirus infection was not significantly changed (P=0.811). Interestingly, a significantly high incidence of parainfluenza virus (P=0.001) infections was observed during the pandemic. No statistically significant between-group differences were observed in the clinical presentation and outcomes of FSs before and during the pandemic. Conclusions: Despite epidemiological changes in respiratory viral infections, the clinical characteristics and outcomes of FSs before and during the COVID-19 pandemic were comparable.

The impact of the Well-Dying Law in Korea: comparing clinical characteristics and ICU admissions.

BACKGROUND: Since Korea implemented the Well-Dying Law in 2018, intensive, and end-of-life care have greatly changed. This study sought to determine whether there were any changes in the clinical aspects or appropriateness of intensive care unit admissions before and after the law was implemented. METHODS: We performed a single-center retrospective study for 3 months with patients admitted to a medical intensive care unit before and after the law was implemented. We studied a total of 178 patients, divided pre-legislative group (83 patients) and a post-legislative group (95 patients). RESULTS: There were no significant differences in baseline characteristics, including age, sex, educational level, religion, economic status, and the Eastern Cooperative Oncology Group performance scale at the time of admission to the intensive care unit. There were no changes in the proportion of patients with terminal comorbidities, including malignancy and chronic lung diseases, with the exception of a decrease in patients with liver cirrhosis (12.1% in pre vs. 3.2% in post-legislative group, P=0.040). There were no differences in the APACHE II score at the time of admission, or in prognosis, including in-unit mortality (33.7 vs. 33.6%, P=0.53), in-hospital mortality (38.6% vs. 42.1%, P=0.73), and length of stay in the intensive care unit (IQR, 4.0-11.0 vs. 3.0-11.0 days, P=0.493). Last, no differences were observed in the appropriateness of admission, which was assessed by two separate intensivists, before and after implementing the law (P=0.646, and P=0.315, respectively). CONCLUSIONS: After the Well-Dying Law was implemented, there was a significant decrease in the number of liver cirrhosis patients admitted to the intensive care unit. No changes in other clinical characteristics, prognosis, and the appropriateness of admission were evident with the implementation of the law.

ATP binding facilitates target search of SWR1 chromatin remodeler by promoting one-dimensional diffusion on DNA.

One-dimensional (1D) target search is a well-characterized phenomenon for many DNA-binding proteins but is poorly understood for chromatin remodelers. Herein, we characterize the 1D scanning properties of SWR1, a conserved yeast chromatin remodeler that performs histone exchange on +1 nucleosomes adjacent to a nucleosome-depleted region (NDR) at gene promoters. We demonstrate that SWR1 has a kinetic binding preference for DNA of NDR length as opposed to gene-body linker length DNA. Using single and dual color single-particle tracking on DNA stretched with optical tweezers, we directly observe SWR1 diffusion on DNA. We found that various factors impact SWR1 scanning, including ATP which promotes diffusion through nucleotide binding rather than ATP hydrolysis. A DNA-binding subunit, Swc2, plays an important role in the overall diffusive behavior of the complex, as the subunit in isolation retains similar, although faster, scanning properties as the whole remodeler. ATP-bound SWR1 slides until it encounters a protein roadblock, of which we tested dCas9 and nucleosomes. The median diffusion coefficient, 0.024 µm2/s, in the regime of helical sliding, would mediate rapid encounter of NDR-flanking nucleosomes at length scales found in cellular chromatin.

Change in perception of the quality of death in the intensive care unit by healthcare workers associated with the implementation of the "well-dying law".

PURPOSE: The importance of dying with dignity in the intensive care unit (ICU) has been emphasized. The South Korean government implemented the "well-dying law" in 2018, which enables patients to refuse futile life-sustaining treatment (LST) after being determined as terminally ill. We aimed to study whether the well-dying law is associated with a significant change in the quality of death in the ICU. METHODS: The Quality of Dying and Death (QODD) questionnaires were prospectively collected from the doctors and nurses of deceased patients of four South Korean medical ICUs after the law was passed (January 2019 to May 2020). Results were compared with those of our previous study, which used the same metric before the law was passed (June 2016 to May 2017). We compared baseline characteristics of the deceased patients, enrolled staff, QODD scores, and staff opinions about withdrawing LST from before to after the law was passed. RESULTS: After the well-dying law was passed, deceased patients (N = 252) were slightly older (68.6 vs. 66.6, p = 0.03) and fewer patients were admitted to the ICU for post-resuscitation care (10.3% vs. 20%, p = 0.003). The mean total QODD score significantly increased after the law was passed (36.9 vs. 31.3, p = 0.001). The law had a positive independent association with the increased QODD score in a multiple regression analysis. CONCLUSION: Our study is the first to show that implementing the well-dying law is associated with quality of death in the ICU, although the quality of death in South Korea remains relatively low and should be further improved.

FACT is recruited to the +1 nucleosome of transcribed genes and spreads in a Chd1-dependent manner.

The histone chaperone FACT occupies transcribed regions where it plays prominent roles in maintaining chromatin integrity and preserving epigenetic information. How it is targeted to transcribed regions, however, remains unclear. Proposed models include docking on the RNA polymerase II (RNAPII) C-terminal domain (CTD), recruitment by elongation factors, recognition of modified histone tails, and binding partially disassembled nucleosomes. Here, we systematically test these and other scenarios in Saccharomyces cerevisiae and find that FACT binds transcribed chromatin, not RNAPII. Through a combination of high-resolution genome-wide mapping, single-molecule tracking, and mathematical modeling, we propose that FACT recognizes the +1 nucleosome, as it is partially unwrapped by the engaging RNAPII, and spreads to downstream nucleosomes aided by the chromatin remodeler Chd1. Our work clarifies how FACT interacts with genes, suggests a processive mechanism for FACT function, and provides a framework to further dissect the molecular mechanisms of transcription-coupled histone chaperoning.

Transient Hyperinsulinemic Hypoglycemia Linked to PAX6 Mutation.

Prolonged hyperinsulinemic hypoglycemia in infancy can result in developmental sequelae. A mutation in the paired box-6 gene (PAX6) has been reported to cause disorders in oculogenesis and neurogenesis. A limited number of cases of diabetes mellitus in adults with a PAX6 mutation suggest that the gene also plays a role in glucose homeostasis. The present case report describes a boy with a PAX6 mutation, born with anophthalmia, who underwent hypoglycemic seizures starting at 5 months old, and showed a prediabetic condition at 60 months. This patient provides novel evidence that connects PAX6 to glucose homeostasis and highlights that life-threatening hypoglycemia or early onset glucose intolerance may be encountered. The role of PAX6 in glucose metabolism and insulin regulation should be further investigated.

Single-molecule imaging of chromatin remodelers reveals role of ATPase in promoting fast kinetics of target search and dissociation from chromatin.

Conserved ATP-dependent chromatin remodelers establish and maintain genome-wide chromatin architectures of regulatory DNA during cellular lifespan, but the temporal interactions between remodelers and chromatin targets have been obscure. We performed live-cell single-molecule tracking for RSC, SWI/SNF, CHD1, ISW1, ISW2, and INO80 remodeling complexes in budding yeast and detected hyperkinetic behaviors for chromatin-bound molecules that frequently transition to the free state for all complexes. Chromatin-bound remodelers display notably higher diffusion than nucleosomal histones, and strikingly fast dissociation kinetics with 4-7 s mean residence times. These enhanced dynamics require ATP binding or hydrolysis by the catalytic ATPase, uncovering an additional function to its established role in nucleosome remodeling. Kinetic simulations show that multiple remodelers can repeatedly occupy the same promoter region on a timescale of minutes, implicating an unending 'tug-of-war' that controls a temporally shifting window of accessibility for the transcription initiation machinery.

Usefulness of the IgA and IgG Responses to Macrophage Migration Inhibitory Factor for the Diagnosis of Tuberculosis.

Serological tests offer the potential in order to improve the diagnosis of tuberculosis (TB). Macrophage migration inhibitory factor (MIF) plays a protective role in infection control in TB; however, to date, no studies on antibody responses to MIF have been reported. We measured immunoglobulin (Ig)A and IgG responses to MIF in individuals with either active tuberculosis (ATB; n = 65), latent tuberculosis (LTBI; n = 53), or in non-infected individuals (NI; n = 62). The QuantiFERON-TB Gold In-Tube (QFT-GIT) assay was used in order to screen for LTBI. The level of IgA against MIF was significantly lower in LTBI and ATB patients than in NI individuals, was significantly related to LTBI and ATB diagnosis, and it could discriminate between LTBI and ATB. In contrast, the level of IgG against MIF was significantly lower in LTBI patients than in NI individuals and was significantly related to LTBI diagnosis. Anti-MIF IgG levels were significantly lower in AFB-negative TB, minimal TB, and new ATB patients, than in the NI group. IgA and IgG levels against MIF both showed significant negative correlations with IFN-γ levels, as assessed using the QFT-GIT test. Although none of the antibodies could achieve high diagnostic predictive power individually, our results suggest the possibility of using IgA antibody responses to MIF in the diagnosis of LTBI and ATB.

Diagnostic Potential of IgG and IgA Responses to Mycobacterium tuberculosis Antigens for Discrimination among Active Tuberculosis, Latent Tuberculosis Infection, and Non-Infected Individuals.

Tuberculosis remains a major public health problem. Conventional tests are inadequate to distinguish between active tuberculosis (ATB) and latent tuberculosis infection (LTBI). We measured antibody responses to Mycobacterium tuberculosis antigens (Mycobacterium tuberculosis chorismate mutase (TBCM), antigen 85B (Ag85B), early secreted antigen-6 (ESAT-6), and culture filtrate protein-10 (CFP-10) in ATB, LTBI, and non-infected (NI) individuals. Serum immunoglobulin G (IgG) and immunoglobulin A (IgA) levels were measured and the QuantiFERON-TB Gold In-Tube assay was used to diagnose LTBI. IgG levels against TBCM were significantly higher in LTBI than NI subjects. IgG and IgA levels against Ag85B and IgG levels against CFP-10 were significantly higher in ATB, followed by LTBI, and then NI. When the ATB group was subdivided, IgG levels against Ag85B and CFP-10 were significantly higher in each subgroup compared with those in LTBI and NI groups. Positive correlation trends between interferon-gamma and IgG levels against Ag85B, TBCM, and CFP-10 and IgA levels against Ag85B in LTBI and NI subjects were observed. Age- and sex-adjusted models showed that IgG against TBCM and CFP-10 was independently related to LTBI diagnosis, and IgG against Ag85B was independently related to the diagnosis of ATB and could distinguish between LTBI and ATB. Overall, IgG antibody responses to TBCM, Ag85B, and CFP-10 can discriminate among ATB, LTBI, and NI groups.

Live-cell single particle imaging reveals the role of RNA polymerase II in histone H2A.Z eviction.

The H2A.Z histone variant, a genome-wide hallmark of permissive chromatin, is enriched near transcription start sites in all eukaryotes. H2A.Z is deposited by the SWR1 chromatin remodeler and evicted by unclear mechanisms. We tracked H2A.Z in living yeast at single-molecule resolution, and found that H2A.Z eviction is dependent on RNA Polymerase II (Pol II) and the Kin28/Cdk7 kinase, which phosphorylates Serine 5 of heptapeptide repeats on the carboxy-terminal domain of the largest Pol II subunit Rpb1. These findings link H2A.Z eviction to transcription initiation, promoter escape and early elongation activities of Pol II. Because passage of Pol II through +1 nucleosomes genome-wide would obligate H2A.Z turnover, we propose that global transcription at yeast promoters is responsible for eviction of H2A.Z. Such usage of yeast Pol II suggests a general mechanism coupling eukaryotic transcription to erasure of the H2A.Z epigenetic signal.

Lung injury associated with inhalation of effective microorganism blends.

Since 2009, effective microorganisms (EMs) have been supplied by the local government to the citizens of Seongnam, Korea, for various environment-protective uses including manufacturing detergents, cosmetics and humidifier disinfectants. A 68-year-old man who had placed an EM blends into a humidifier for inhalation visited the emergency room with complaints of fever and dyspnea. He was in a shock state with hypoxia. Chest computed tomography revealed diffuse ground-glass opacities that were dominant in the bilateral upper lobes. Fiberoptic bronchoscopy with bronchoalveolar lavage and transbronchial lung biopsy was performed. Bronchoalveolar lavage fluid analysis and biopsy findings were consistent with alveolar hemorrhage. All microbiological and virological test results were negative. His symptoms and radiographic opacities had improved markedly after several days of conservative care, and he was discharged healthy after 1 week of hospital stay.

Mortality risk and causes of death in patients with non-cystic fibrosis bronchiectasis.

BACKGROUND: All-cause mortality risk and causes of death in bronchiectasis patients have not been fully investigated. The aim of this study was to compare the mortality risk and causes of death between individuals with bronchiectasis and those without bronchiectasis. METHODS: Patients with or without bronchiectasis determined based on chest computed tomography (CT) at one centre between 2005 and 2016 were enrolled. Among the patients without bronchiectasis, a control group was selected after applying additional exclusion criteria. We compared the mortality risk and causes of death between the bronchiectasis and control groups without lung disease. Subgroup analyses were also performed according to identification of Pseudomonas or non-tuberculous mycobacteria, airflow limitation, and smoking status. RESULTS: Of the total 217,702 patients who underwent chest CT, 18,134 bronchiectasis patients and 90,313 non-bronchiectasis patients were included. The all-cause mortality rate in the bronchiectasis group was 1608.8 per 100,000 person-years (95% confidence interval (CI), 1531.5-1690.0), which was higher than that in the control group (133.5 per 100,000 person-years; 95% CI, 124.1-143.8; P < 0.001). The bronchiectasis group had higher all-cause (adjusted hazard ratio (aHR), 1.26; 95% CI, 1.09-1.47), respiratory (aHR, 3.49; 95% CI, 2.21-5.51), and lung cancer-related (aHR, 3.48; 95% CI, 2.33-5.22) mortality risks than the control group. In subgroup analysis, patients with airflow limitation and ever smokers showed higher all-cause mortality risk among bronchiectasis patients. Therefore, we observed significant interrelation between bronchiectasis and smoking, concerning the risks of all-cause mortality (P for multiplicative interaction, 0.030, RERI, 0.432; 95% CI, 0.097-0.769) and lung cancer-related mortality (RERI, 8.68; 95% CI, 1.631-15.736). CONCLUSION: Individuals with bronchiectasis had a higher risk of all-cause, respiratory, and lung cancer-related mortality compared to control group. The risk of all-cause mortality was more prominent in those with airflow limitation and in ever smokers.

Asymmetric histone inheritance via strand-specific incorporation and biased replication fork movement.

Many stem cells undergo asymmetric division to produce a self-renewing stem cell and a differentiating daughter cell. Here we show that, similarly to H3, histone H4 is inherited asymmetrically in Drosophila melanogaster male germline stem cells undergoing asymmetric division. In contrast, both H2A and H2B are inherited symmetrically. By combining super-resolution microscopy and chromatin fiber analyses with proximity ligation assays on intact nuclei, we find that old H3 is preferentially incorporated by the leading strand, whereas newly synthesized H3 is enriched on the lagging strand. Using a sequential nucleoside analog incorporation assay, we detect a high incidence of unidirectional replication fork movement in testes-derived chromatin and DNA fibers. Biased fork movement coupled with a strand preference in histone incorporation would explain how asymmetric old and new H3 and H4 are established during replication. These results suggest a role for DNA replication in patterning epigenetic information in asymmetrically dividing cells in multicellular organisms.