Matter-wave interferometry in a double well on an atom chip

Matter-wave interference experiments enable us to study matter at its most basic, quantum level and form the basis of high-precision sensors for applications such as inertial and gravitational field sensing. Success in both of these pursuits requires the development of atom-optical elements that can manipulate matter waves at the same time as preserving their coherence and phase. Here, we present an integrated interferometer based on a simple, coherent matter-wave beam splitter constructed on an atom chip. Through the use of radio-frequency-induced adiabatic double-well potentials, we demonstrate the splitting of Bose-Einstein condensates into two clouds separated by distances ranging from 3 to 80 microns, enabling access to both tunnelling and isolated regimes. Moreover, by analysing the interference patterns formed by combining two clouds of ultracold atoms originating from a single condensate, we measure the deterministic phase evolution throughout the splitting process. We show that we can control the relative phase between the two fully separated samples and that our beam splitter is phase-preserving

Association of metabolic equivalent of task (MET) score in length of stay in hospital following radical cystectomy with urinary diversion:a multi-institutional study

PURPOSE: The Metabolic equivalent of task (MET) score is used in patients’ preoperative functional capacity assessment. It is commonly thought that patients with a higher MET score will have better postoperative outcomes than patients with a lower MET score. However, such a link remains the subject of debate and is yet unvalidated in major urological surgery. This study aimed to explore the association of patients’ MET score with their postoperative outcomes following radical cystectomy. METHODS: We used records-linkage methodology with unique identifiers (Community Health Index/hospital number) and electronic databases to assess postoperative outcomes of patients who had underwent radical cystectomies between 2015 and 2020. The outcome measure was patients’ length of hospital stay. This was compared with multiple basic characteristics such as age, sex, MET score and comorbid conditions. A MET score of less than four (< 4) is taken as the threshold for a poor functional capacity. We conducted unadjusted and adjusted Cox regression analyses for time to discharge against MET score. RESULTS: A total of 126 patients were included in the analysis. Mean age on date of operation was 66.2 (SD 12.2) years and 49 (38.9%) were female. A lower MET score was associated with a statistically significant lower time-dependent risk of hospital discharge (i.e. longer hospital stay) when adjusted for covariates (HR 0.224; 95% CI 0.077–0.652; p = 0.006). Older age (adjusted HR 0.531; 95% CI 0.332–0.848; p = 0.008) and postoperative complications (adjusted HR 0.503; 95% CI 0.323–0.848; p = 0.002) were also found to be associated with longer hospital stay. Other comorbid conditions, BMI, disease staging and 30-day all-cause mortality were statistically insignificant. CONCLUSION: A lower MET score in this cohort of patients was associated with a longer hospital stay length following radical cystectomy with urinary diversion. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s11255-021-02813-x

Direct observation of topoisomerase IA gate dynamics

Type IA topoisomerases cleave single-stranded DNA and relieve negative supercoils in discrete steps corresponding to the passage of the intact DNA strand through the cleaved strand. Although type IA topoisomerases are assumed to accomplish this strand passage via a protein-mediated DNA gate, opening of this gate has never been observed. We developed a single-molecule assay to directly measure gate opening of the Escherichia coli type IA topoisomerases I and III. We found that after cleavage of single-stranded DNA, the protein gate opens by as much as 6.6 nm and can close against forces in excess of 16 pN. Key differences in the cleavage, ligation, and gate dynamics of these two enzymes provide insights into their different cellular functions. The single-molecule results are broadly consistent with conformational changes obtained from molecular dynamics simulations. These results allowed us to develop a mechanistic model of interactions between type IA topoisomerases and single-stranded DNA

Chromosome-level assembly of the water buffalo genome surpasses human and goat genomes in sequence contiguity

Rapid innovation in sequencing technologies and improvement in assembly algorithms have enabled the creation of highly contiguous mammalian genomes. Here we report a chromosome-level assembly of the water buffalo (Bubalus bubalis) genome using single-molecule sequencing and chromatin conformation capture data. PacBio Sequel reads, with a mean length of 11.5 kb, helped to resolve repetitive elements and generate sequence contiguity. All five B. bubalis sub-metacentric chromosomes were correctly scaffolded with centromeres spanned. Although the index animal was partly inbred, 58% of the genome was haplotype-phased by FALCON-Unzip. This new reference genome improves the contig N50 of the previous short-read based buffalo assembly more than a thousand-fold and contains only 383 gaps. It surpasses the human and goat references in sequence contiguity and facilitates the annotation of hard to assemble gene clusters such as the major histocompatibility complex (MHC)

Polycomb repressive complex PRC1 spatially constrains the mouse embryonic stem cell genome.

The Polycomb repressive complexes PRC1 and PRC2 maintain embryonic stem cell (ESC) pluripotency by silencing lineage-specifying developmental regulator genes. Emerging evidence suggests that Polycomb complexes act through controlling spatial genome organization. We show that PRC1 functions as a master regulator of mouse ESC genome architecture by organizing genes in three-dimensional interaction networks. The strongest spatial network is composed of the four Hox gene clusters and early developmental transcription factor genes, the majority of which contact poised enhancers. Removal of Polycomb repression leads to disruption of promoter-promoter contacts in the Hox gene network. In contrast, promoter-enhancer contacts are maintained in the absence of Polycomb repression, with accompanying widespread acquisition of active chromatin signatures at network enhancers and pronounced transcriptional upregulation of network genes. Thus, PRC1 physically constrains developmental transcription factor genes and their enhancers in a silenced but poised spatial network. We propose that the selective release of genes from this spatial network underlies cell fate specification during early embryonic development

The progression of replication forks at natural replication barriers in live bacteria

Protein–DNA complexes are one of the principal barriers the replisome encounters during replication. One such barrier is the Tus–ter complex, which is a direction dependent barrier for replication fork progression. The details concerning the dynamics of the replisome when encountering these Tus–ter barriers in the cell are poorly understood. By performing quantitative fluorescence microscopy with microfuidics, we investigate the effect on the replisome when encountering these barriers in live Escherichia coli cells. We make use of an E. coli variant that includes only an ectopic origin of replication that is positioned such that one of the two replisomes encounters a Tus–ter barrier before the other replisome. This enables us to single out the effect of encountering a Tus–ter roadblock on an individual replisome. We demonstrate that the replisome remains stably bound after encountering a Tus–ter complex from the non-permissive direction. Furthermore, the replisome is only transiently blocked, and continues replication beyond the barrier. Additionally, we demonstrate that these barriers affect sister chromosome segregation by visualizing specific chromosomal loci in the presence and absence of the Tus protein. These observations demonstrate the resilience of the replication fork to natural barriers and the sensitivity of chromosome alignment to fork progression. </p