Endothelial Cyp26b1 restrains murine heart valve growth during development.

Endothelial cells (ECs) are critical to proper heart valve development, directly contributing to the mesenchyme of the cardiac cushions, which progressively transform into mature valves. To date, investigators have lacked sufficient markers of valve ECs to evaluate their contributions during valve morphogenesis fully. As a result, it has been unclear whether the well-characterized regional differentiation of valves correlates with any endothelial domains in the heart. Furthermore, it has been difficult to ascertain whether endothelial heterogeneity in the heart influences underlying mesenchymal zones in an angiocrine manner. To identify regionally expressed EC genes in the heart valves, we screened publicly available databases and assembled a toolkit of endothelial-enriched genes. We identified Cyp26b1 as one of many endothelial enriched genes found to be expressed in the endocardium of the developing cushions and valves. Here, we show that Cyp26b1 is required for normal heart valve development. Genetic ablation of Cyp26b1 in mouse embryos leads to abnormally thickened aortic valve leaflets, which is due in part to increased endothelial and mesenchymal cell proliferation in the remodeling valves. In addition, Cyp26b1 mutant hearts display ventricular septal defects (VSDs) in a portion of null embryos. We show that loss of Cyp26b1 results in upregulation of retinoic acid (RA) target genes, supporting the observation that Cyp26b1 has RA-dependent roles. Together, this work identifies a novel role for Cyp26b1 in heart valve morphogenesis and points to a role of RA in this process. Understanding the spatiotemporal expression dynamics of cardiac EC genes will pave the way for investigation of both normal and dysfunctional heart valve development.

Enhancing CRISPR/Cas systems with nanotechnology.

CRISPR/Cas systems have revolutionized biology and medicine, and have led to new paradigms in disease diagnostics and therapeutics. However, these complexes suffer from key limitations regarding barriers to cellular entry, stability in biological environments, and off-target effects. Integrating nanotechnology with CRISPR/Cas systems has emerged as a promising strategy to overcome these challenges and has further unlocked structures that accumulate preferentially in tissues of interest, have tunable pharmacological properties, and are activated in response to desired stimuli. Nanomaterials can also enhance CRISPR/Cas-mediated detection platforms by enabling faster, more sensitive, and convenient readouts. We highlight recent advances in this rapidly growing field. We also outline areas that need further development to fully realize the potential of CRISPR technologies.

14-3-3gamma binds to MDMX that is phosphorylated by UV-activated Chk1, resulting in p53 activation.

It has been shown that MDMX inhibits the activity of the tumor suppressor p53 by primarily cooperating with the p53 feedback regulator MDM2. Here, our study shows that this inhibition can be overcome by 14-3-3gamma and Chk1. 14-3-3gamma was identified as an MDMX-associated protein via an immuno-affinity purification-coupled mass spectrometry. Consistently, 14-3-3gamma directly interacted with MDMX in vitro, and this interaction was stimulated by MDMX phosphorylation in vitro and in cells. Interestingly, in response to UV irradiation, the wild-type, but not the kinase-dead mutant, Chk1 phosphorylated MDMX at serine 367, enhanced the 14-3-3gamma-MDMX binding and the cytoplasmic retaining of MDMX. The Chk1 specific inhibitor UCN-01 repressed all of these effects. Moreover, overexpression of 14-3-3gamma, but not its mutant K50E, which did not bind to MDMX, suppressed MDMX-enhanced p53 ubiquitination, leading to p53 stabilization and activation. Finally, ablation of 14-3-3gamma by siRNA reduced UV-induced p53 level and G1 arrest. Thus, these results demonstrate 14-3-3gamma and Chk1 as two novel regulators of MDMX in response to UV irradiation.