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Epithelial cells spontaneously form acini (also known as cysts or spheroids) with a single, fluid-filled central lumen when grown in 3D matrices. The size of the lumen is dependent on apical secretion of chloride ions, most notably by the CFTR channel, which has been suggested to establish pressure in the lumen due to water influx. To study the cellular biomechanics of acini morphogenesis and homeostasis, we used MDCK-2 cells. Using FRET-force biosensors for E-cadherin, we observed significant increases in the average tension per molecule for each protein in mature 3D acini as compared to 2D monolayers. Increases in CFTR activity resulted in increased E-cadherin forces, indicating that ionic gradients affect cellular tension. Direct measurements of pressure revealed that mature acini experience significant internal hydrostatic pressure (37 ± 10.9 Pa). Changes in CFTR activity resulted in pressure and/or volume changes, both of which affect E-cadherin tension. Increases in CFTR chloride secretion also induced YAP signaling and cellular proliferation. In order to recapitulate disruption of acinar homeostasis, we induced epithelial-to-mesenchymal transition (EMT). During the initial stages of EMT, there was a gradual decrease in E-cadherin force and lumen pressure that correlated with lumen infilling. Strikingly, increasing CFTR activity was sufficient to block EMT. Our results show that ion secretion is an important regulator of morphogenesis and homeostasis in epithelial acini. Furthermore, this work demonstrates that, for closed 3D cellular systems, ion gradients can generate osmotic pressure or volume changes, both of which result in increased cellular tension.

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Interactions between the genome and the nuclear pore complex (NPC) have been implicated in multiple gene regulatory processes, but the underlying logic of these interactions remains poorly defined. Here, we report high-resolution chromatin binding maps of two core components of the NPC, Nup107 and Nup93, in Drosophila cells. Our investigation uncovered differential binding of these NPC subunits, where Nup107 preferentially targets active genes while Nup93 associates primarily with Polycomb-silenced regions. Comparison to Lamin-associated domains (LADs) revealed that NPC binding sites can be found within LADs, demonstrating a linear binding of the genome along the nuclear envelope. Importantly, we identified a functional role of Nup93 in silencing of Polycomb target genes and in spatial folding of Polycomb domains. Our findings lend to a model where different nuclear pores bind different types of chromatin via interactions with specific NPC sub-complexes, and a subset of Polycomb domains is stabilized by interactions with Nup93.

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Cell proliferation and contact inhibition play a major role in maintaining epithelial cell homeostasis. Prior experiments have shown that externally applied forces, such as stretch, result in increased proliferation in an E-cadherin force-dependent manner. In this study, the spatial regulation of cell proliferation in large epithelial colonies was examined. Surprisingly, cells at the center of the colony still had increased proliferation as compared to cells in confluent monolayers. E-cadherin forces were found to be elevated for both cells at the edge and center of these larger colonies when compared to confluent monolayers. To determine if high levels of E-cadherin force were necessary to induce proliferation at the center of the colony, a lower-force mutant of E-cadherin was developed. Cells with lower E-cadherin force had significantly reduced proliferation for cells at the center of the colony but minimal differences for cells at the edges of the colony. Similarly, increasing substrate stiffness was found to increase E-cadherin force and increase the proliferation rate across the colony. Taken together, these results show that forces through cell-cell junctions regulate proliferation across large groups of epithelial cells. In addition, an important finding of this study is that junction forces are dynamic and modulate cellular function even in the absence of externally applied loads.

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OBJECTIVE: There has been little research to examine the association of post-discharge adverse events (AEs) with timely follow-up visits after hospital discharge. We aimed to examine whether having a timely follow-up outpatient visit would reduce the risk for post-discharge AEs. METHODS: This was a methods study of patients at risk for post-discharge AEs from December 2011 through October 2012. Five hundred and forty-five patients who were under the care of hospitalist physicians and were discharged home from a community hospital, spoke English, and could be contacted after discharge were evaluated. The aim of the study was to examine the association of post-discharge AEs with timely follow-up visits after hospital discharge based on structured telephone interviews, health record review, and adjudication by two blinded, trained physicians using a previously established methodology. RESULTS: We observed a higher incidence of AEs with patients that had their first follow-up visit within 7 days after hospital discharge (33.5% vs. 23.0%, p = 0.007). This effect was attenuated somewhat but remained significant when adjusted for several patient factors (adjusted OR 1.33, 95% confidence interval 1.16-2.71). CONCLUSION: This observational study paradoxically showed an increase in post-discharge AEs with early follow-up, likely a result of confounding by indication and/or information bias that could not be completely adjusted for. This study illustrates the potential hazards with conducting observational studies to determine the efficacy of various transitional care interventions, such as early follow-up, where risk for confounding by indication is high.

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BACKGROUND: There has been little research to examine post-discharge adverse events (AEs) in rural patients discharged from community hospitals. OBJECTIVE: We aimed to determine the rate of post-discharge AEs, classify the types of post-discharge AEs, and identify risk factors for post-discharge AEs in urban and rural patients. DESIGN: This was a prospective cohort study of patients at risk for post-discharge adverse events from December 2011 through October 2012. PATIENTS: Six hundred and eighty-four patients who were under the care of hospitalist physicians and were being discharged home, spoke English, and could be contacted after discharge, were admitted to the medical service. Patients were stratified as urban/rural using zip code of residence. Rural patients were oversampled to ensure equal enrollment of urban and rural patients. MAIN MEASURES: The main outcome of the study was post-discharge AEs based on structured telephone interviews, health record review, and adjudication by two blinded, trained physicians using a previously established methodology. RESULTS: Over 28% of 684 patients experienced post-discharge AEs, most of which were either preventable or ameliorable. There was no difference in the incidence of post-discharge AEs in urban versus rural patients (ARR 1.04 95% CI 0.82-1.32 ), but post-discharge AEs were associated with hypertension, type 2 diabetes mellitus, and number of secondary discharge diagnoses only in urban patients. CONCLUSIONS: Post-discharge AEs were common in both urban and rural patients and many were preventable or ameliorable. Potentially different risk factors for AEs in urban versus rural patients suggests the need for further research into the underlying causes. Different interventions may be required in urban versus rural patients to improve patient safety during transitions in care.

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