Transcription factor antagonism regulates heterogeneity in embryonic stem cell states.

Gene expression heterogeneity underlies cell states and contributes to developmental robustness. While heterogeneity can arise from stochastic transcriptional processes, the extent to which it is regulated is unclear. Here, we characterize the regulatory program underlying heterogeneity in murine embryonic stem cell (mESC) states. We identify differentially active and transcribed enhancers (DATEs) across states. DATEs regulate differentially expressed genes and are distinguished by co-binding of transcription factors Klf4 and Zfp281. In contrast to other factors that interact in a positive feedback network stabilizing mESC cell-type identity, Klf4 and Zfp281 drive opposing transcriptional and chromatin programs. Abrogation of factor binding to DATEs dampens variation in gene expression, and factor loss alters kinetics of switching between states. These results show antagonism between factors at enhancers results in gene expression heterogeneity and formation of cell states, with implications for the generation of diverse cell types during development.

Modern disposable hydrogel contact lens removal has a minimal effect on intraocular pressure.

PURPOSE: To determine whether the removal of modern disposable hydrogel contact lenses may influence intraocular pressure (IOP) measurement, and if so, how long the effect may last. METHODS: Twenty-five healthy experienced contact lens wearers aged 19-25 inserted their lenses at least 30 min prior to the study. Each participant was asked to remove a contact lens from one eye (control eye, selected at random) upon commencement of the study, and then to remove the lens in the other eye (lens-wearing eye) after a 30 min washout period. IOP was measured immediately in both eyes using non-contact tonometry, then repeated every 3 min for 12 min. To determine the change in IOP due to lens removal, the IOP in the lens-wearing eye was compared to the control eye using paired t-tests at each time point. RESULTS: The IOP was significantly higher in the lens-wearing eye immediately following lens removal (0.7 ± 1.0 mmHg, t(24) = 3.46, p < 0.01), but was within baseline values at 3 min (0.2 ± 1.0 mmHg, t(24) = 0.84, p = 0.41), 6 min (0.3 ± 1.1 mmHg, t(24) = 1.39, p = 0.18), 9 min (0.3 ± 1.2 mmHg, t(24) = 1.14, p = 0.27) and 12 min (-0.1 ± 0.9 mmHg, t(24) = -0.49, p = 0.63, paired t-test). CONCLUSIONS: There was a slight statistically significant increase in IOP following contact lens removal, with a maximum duration of 3 min. Given the small magnitude of the change in IOP, and its transient nature, there appears to be no clinical reason to delay IOP measurements following the removal of modern disposable hydrogel contact lenses.

Walking for a short distance at a brisk pace reduces intraocular pressure by a clinically significant amount.

PURPOSE: To determine if walking for a short distance in a natural outdoor setting will have a clinically significant effect on intraocular pressure (IOP). METHODS: Twenty-five healthy participants (25 eyes) aged 20.8±1.3 years had their IOP measured using noncontact tonometry at baseline, after completing a 1046 m outdoor walking course at a brisk pace and after a 20-minute resting period in a seated position. Repeated-measures analysis of variance was used to compare the average IOP at each time point and Pearson correlation was used to assess relationships between the difference in IOP, baseline IOP, and walking pace. RESULTS: IOP decreased from 16.0±2.6 mm Hg at baseline to 14.6±3.2 mm Hg (-1.4±1.1 mm Hg, P<0.001, 95% confidence interval: +0.7--3.3 mm Hg) after the walk. The IOP remained -0.7 mm Hg below the baseline level (P=0.028, paired t test with Bonferroni correction) after the 20-minute resting period. The decrease in IOP was larger in eyes with a lower baseline IOP (partial Pearson r=0.433, P=0.035, controlled for pace). The average walking pace was 4.7±0.5 km/h and was negatively correlated to the decrease in IOP (partial Pearson r=-0.432, P=0.035, controlled for baseline IOP). The postrest recovery of IOP was greater for participants who demonstrated a greater decrease in IOP during the walking period (Pearson r=-0.427, P=0.033). CONCLUSIONS: A short brisk walk caused a clinically significant reduction in IOP by an amount that was related to the relative intensity of the exertion, and it did not recover within a 20-minute period. Clinicians are advised to seek information regarding recent physical activity (including walking) and the subsequent resting period, when highly accurate measurements of IOP are required.

Effect of a proparacaine 0.50%-sodium fluorescein 0.25% mix and contact ultrasound pachymetry on central and midperipheral corneal thickness measured by noncontact optical pachymetry.

PURPOSE: To assess the effect of a combination of proparacaine 0.50%-sodium fluorescein 0.25% and ultrasound (US) pachymetry on central and midperipheral corneal thickness. SETTING: School of Optometry and Vision Sciences, Cardiff University, Cardiff, Wales, United Kingdom. DESIGN: Case series. METHOD: Topographic measurements of corneal thickness in healthy right eyes were obtained using a scanning-slit device (Orbscan IIz) and a Scheimpflug device (Pentacam) before and after application of proparacaine 0.50%-sodium fluorescein 0.25% and US pachymetry. Changes in corneal thickness in the center and 2.5 mm from the center in the temporal, nasal, inferior, and superior locations were assessed. RESULTS: The study evaluated 35 eyes. The scanning-slit and Scheimpflug devices recorded a small but statistically significant increase in corneal thickness at all locations (mean 4.9 ± 14.3 [SD] to 9.1 ± 11.7 µm; P<.05, paired t test). The cornea swelled uniformly across its diameter (scanning slit, P=.934; Scheimpflug, P=.654; analysis of variance); there was no statistically significant difference in the amount of swelling between the 2 devices (P>.05, t test). The 95% limits of agreement were broad (-10 to +30 µm), suggesting a large degree of interindividual variability. CONCLUSIONS: Ultrasound pachymetry combined with proparacaine 0.50%-sodium fluorescein 0.25% caused a small (<10 µm) but significant amount of corneal swelling on average. Because the effect on corneal thickness may be greater than -10 to +30 µm in individual cases, clinicians should avoid contact procedures before obtaining topographic maps of corneal thickness using scanning-slit and Scheimpflug devices.