Non-histone methylation of SET7/9 and its biological functions

Background: (su(var)-3-9,enhancer-of-zeste,trithorax) domain-containing protein 7/9 (SET7/9) is a member of the protein lysine methyltransferases (PLMTs or PKMTs) family. It contains a SET domain. Recent studies demonstrate that SET7/9 methylates both lysine 4 of histone 3 (H3-K4) and lysine(s) of non-histone proteins, including transcription factors, tumor suppressors, and membrane-associated receptors. Objective: This article mainly reviews the non-histone methylation effects of SET7/9 and its functions in tumorigenesis and development. Methods: PubMed was screened for this information. Results: SET7/9 plays a key regulatory role in various biological processes such as cell proliferation, transcription regulation, cell cycle, protein stability, cardiac morphogenesis, and development. In addition, SET7/9 is involved in the pathogenesis of hair loss, breast cancer progression, human carotid plaque atherosclerosis, chronic kidney disease, diabetes, obesity, ovarian cancer, prostate cancer, hepatocellular carcinoma, and pulmonary fibrosis. Conclusion: SET7/9 is an important methyltransferase, which can catalyze the methylation of a variety of proteins. Its substrates are closely related to the occurrence and development of tumors.

The Spatiotemporal Expression of Notch1 and Numb and Their Functional Interaction during Cardiac Morphogenesis

Numb family proteins (NFPs), including Numb and Numblike (Numbl), are commonly known for their role as cell fate determinants for multiple types of progenitor cells, mainly due to their function as Notch inhibitors. Previous studies have shown that myocardial NFP double knockout (MDKO) hearts display an up-regulated Notch activation and various defects in cardiac progenitor cell differentiation and cardiac morphogenesis. Whether enhanced Notch activation causes these defects in MDKO is not fully clear. To answer the question, we examined the spatiotemporal patterns of Notch1 expression, Notch activation, and Numb expression in the murine embryonic hearts using multiple approaches including RNAScope, and Numb and Notch reporter mouse lines. To further interrogate the interaction between NFPs and Notch signaling activation, we deleted both Notch1 or RBPJk alleles in the MDKO. We examined and compared the phenotypes of Notch1 knockout, NFPs double knockout, Notch1; Numb; Numbl and RBPJk; Numb; Numbl triple knockouts. Our study showed that Notch1 is expressed and activated in the myocardium at several stages, and Numb is enriched in the epicardium and did not show the asymmetric distribution in the myocardium. Cardiac-specific Notch1 deletion causes multiple structural defects and embryonic lethality. Notch1 or RBPJk deletion in MDKO did not rescue the structural defects in the MDKO but partially rescued the defects of cardiac progenitor cell differentiation, cardiomyocyte proliferation, and trabecular morphogenesis. Our study concludes that NFPs regulate progenitor cell differentiation, cardiomyocyte proliferation, and trabecular morphogenesis partially through Notch1 and play more roles than inhibiting Notch1 signaling during cardiac morphogenesis.

The developing epicardium regulates cardiac chamber morphogenesis by promoting cardiomyocyte growth

The epicardium, the outermost layer of the heart, is an important regulator of cardiac regeneration. However, a detailed understanding of the crosstalk between the epicardium and myocardium during development requires further investigation. Here, we generated three models of epicardial impairment in zebrafish by mutating the transcription factor genes tcf21 and wt1a, and by ablating tcf21+ epicardial cells. Notably, all three epicardial-impairment models exhibit smaller ventricles. We identified the initial cause of this phenotype as defective cardiomyocyte growth, resulting in reduced cell surface and volume. This failure of cardiomyocytes to grow is followed by decreased proliferation and increased abluminal extrusion. By temporally manipulating its ablation, we show that the epicardium is required to support ventricular growth during early cardiac morphogenesis. By transcriptomic profiling of sorted epicardial cells, we identified reduced expression of FGF and VEGF ligand genes in tcf21-/- hearts, and pharmacological inhibition of these signaling pathways partially recapitulated the ventricular growth defects. Thus, the analysis of these epicardial-impairment models further elucidates the distinct roles of the epicardium during cardiac morphogenesis and the signaling pathways underlying epicardial-myocardial crosstalk.

Cardiovascular Development and Congenital Heart Disease Modeling in the Pig

Background Modeling cardiovascular diseases in mice has provided invaluable insights into the cause of congenital heart disease. However, the small size of the mouse heart has precluded translational studies. Given current high‐efficiency gene editing, congenital heart disease modeling in other species is possible. The pig is advantageous given its cardiac anatomy, physiology, and size are similar to human infants. We profiled pig cardiovascular development and generated genetically edited pigs with congenital heart defects. Methods and Results Pig conceptuses and fetuses were collected spanning 7 stages (day 20 to birth at day 115), with at least 3 embryos analyzed per stage. A combination of magnetic resonance imaging and 3‐dimensional histological reconstructions with episcopic confocal microscopy were conducted. Gross dissections were performed in late‐stage or term fetuses by using sequential segmental analysis of the atrial, ventricular, and arterial segments. At day 20, the heart has looped, forming a common atria and ventricle and an undivided outflow tract. Cardiac morphogenesis progressed rapidly, with atrial and outflow septation evident by day 26 and ventricular septation completed by day 30. The outflow and atrioventricular cushions seen at day 20 undergo remodeling to form mature valves, a process continuing beyond day 42. Genetically edited pigs generated with mutation in chromatin modifier SAP130 exhibited tricuspid dysplasia, with tricuspid atresia associated with early embryonic lethality. Conclusions The major events in pig cardiac morphogenesis are largely complete by day 30. The developmental profile is similar to human and mouse, indicating gene edited pigs may provide new opportunities for preclinical studies focused on outcome improvements for congenital heart disease.

The EMT transcription factor Snai1 maintains myocardial wall integrity by repressing intermediate filament gene expression

The transcription factor Snai1, a well-known regulator of epithelial-to-mesenchymal transition, has been implicated in early cardiac morphogenesis as well as in cardiac valve formation. However, a role for Snai1 in regulating other aspects of cardiac morphogenesis has not been reported. Using genetic, transcriptomic, and chimeric analyses in zebrafish, we find that Snai1b is required in cardiomyocytes for myocardial wall integrity. Loss of snai1b increases the frequency of cardiomyocyte extrusion away from the cardiac lumen. Extruding cardiomyocytes exhibit increased actomyosin contractility basally as revealed by enrichment of p-myosin and α-catenin epitope α-18, as well as disrupted intercellular junctions. Transcriptomic analysis of wild-type and snai1b mutant hearts revealed the dysregulation of intermediate filament genes, including desmin b (desmb) upregulation. Cardiomyocyte-specific desmb overexpression caused increased cardiomyocyte extrusion, recapitulating the snai1b mutant phenotype. Altogether, these results indicate that Snai1 maintains the integrity of the myocardial epithelium, at least in part by repressing desmb expression.

Evolution of Cardiac Tissue and Flow Mechanics in Developing Japanese Medaka

The effects of pressure drop across cardiac valve cushion regions and endocardial wall strain triggering cardiac morphogenesis in a teleost species heart are poorly understood. In the presented work, we utilize microscale particle image velocimetry (µPIV) flow measurements of developing medaka hearts from 3 to 14 dpf (n = 4–5 at each dpf) to quantify the pressure field and endocardial wall strain. Peak pressure drop at the atrioventricular canal (ΔPAVC) and outflow tract (ΔPOFT) show a steady increase with fish age progression. Pressure drops when non-dimensionalized with blood viscosity and heart rate at each dpf are comparable with measurements in zebrafish hearts. Retrograde flows captured at these regions display a negative pressure drop. A novel metric, Endocardial Work (EW), is introduced by analyzing the ΔPAVC-strain curves, which is a non-invasive measure of work required for ventricle filling. EW is a metric that can differentiate between the linear heart stage (< 100 Pa-%), cardiac looped chamber stage (< 300 Pa-%), and the fully formed chamber stage (> 300 Pa-%).

Lamb1a regulates atrial growth by limiting excessive, contractility-dependent second heart field addition during zebrafish heart development

During early vertebrate heart development, the heart transitions from a linear tube to a complex asymmetric structure. This process includes looping of the tube and ballooning of the emerging cardiac chambers, which occur simultaneously with growth of the heart. A key driver of cardiac growth is deployment of cells from the Second Heart Field (SHF) into both poles of the heart, with cardiac morphogenesis and growth intimately linked in heart development. Laminin is a core component of extracellular matrix (ECM) basement membranes, and although mutations in specific laminin subunits are linked with a variety of cardiac abnormalities, including congenital heart disease and dilated cardiomyopathy, no role for laminin has been identified in early vertebrate heart morphogenesis. We identified dynamic, tissue-specific expression of laminin subunit genes in the developing zebrafish heart, supporting a role for laminins in heart morphogenesis.lamb1amutants exhibit cardiomegaly from 2dpf onwards, with subsequent progressive defects in cardiac morphogenesis characterised by a failure of the chambers to compact around the developing atrioventricular canal. We show that loss oflamb1aresults in excess addition of SHF cells to the atrium, revealing that Lamb1a functions to limit heart size during cardiac development by restricting SHF addition to the venous pole.lamb1amutants exhibit hallmarks of altered haemodynamics, and specifically blocking cardiac contractility inlamb1amutants rescues heart size and atrial SHF addition. Furthermore, we identify that FGF and RA signalling, two conserved pathways promoting SHF addition, are regulated by heart contractility and are dysregulated inlamb1amutants, suggesting that laminin mediates interactions between SHF deployment, heart biomechanics, and biochemical signalling during heart development. Together, this describes the first requirement for laminins in early vertebrate heart morphogenesis, reinforcing the importance of specialised ECM composition in cardiac development.

Dlc1 controls cardio-vascular development downstream of Vegfa/Kdrl/Nrp1 signaling in the zebrafish embryo

ABSTRACTThe family of deleted-in-liver-cancer (dlc) genes encodes RhoGTPases and plays pivotal roles in cardiovascular development, but animal models for studying their functions are sparse due to early embryonic lethality. Gain and loss of function of dlc1 and dlc3 severely altered the growth of intersegmental vessels in the trunk of zebrafish embryos. Additionally, overexpression of dlc1 affected the growth of the common cardinal veins, but could rescue the arrest of angiogenesis induced by Vegfr2 inhibition, placing dlc1 downstream of kdrl signaling. Loss of dlc1 negatively affected the lumenization of the first aortic arch arteries and the lateral dorsal aortae. dlc1 mutants displayed a full obstruction in the early outflow tract during cardiac morphogenesis, which models to alterations in DLC1 detected in congenital heart defects in human patients. This study provides a functional in vivo characterization of dlc1 and dlc3 during vertebrate embryogenesis and places dlc1 as a key gene to control vascular development.