Isolation of a ventricle-specific promoter for the zebrafish ventricular myosin heavy chain (vmhc) gene and its regulation by GATA factors during embryonic heart development

Developmental and cardiac toxicity assessment of Ethyl 3-(N-butylacetamido) propanoate (EBAAP) in zebrafish embryos

Ethyl 3-(N-butylacetamido) propanoate (EBAAP) is one of the most widely used mosquito repellents worldwide, and is also commonly used to produce cosmetics. Residues have recently been detected in surface and groundwater in many countries, and their potential to harm the environment is unknown. Therefore, more studies are needed to fully assess the toxicity of EBAAP. This is the first investigation into the developmental toxicity and cardiotoxicity of EBAAP on zebrafish embryos. EBAAP was toxic to zebrafish, with a lethal concentration 50 (LC50) of 140 mg/L at 72 hours post fertilization (hpf). EBAAP exposure also reduced body length, slowed the yolk absorption rate, induced spinal curvature and pericardial edema, decreased heart rate, promoted linear lengthening of the heart, and diminished cardiac pumping ability. The expression of heart developmental-related genes (nkx2.5, myh6, tbx5a, vmhc, gata4, tbx2b) was dysregulated, intracellular oxidative stress increased significantly, the activities of catalase (CAT) and superoxide dismutase (SOD) decreased, and malondialdehyde (MDA) content increased significantly. The expression of apoptosis-related genes (bax/bcl2, p53, caspase9, caspase3) was significantly upregulated. In conclusion, EBAAP induced abnormal morphology and heart defects during the early stages of zebrafish embryo development by potentially inducing the generation and accumulation of reactive oxygen species (ROS) in vivo and activating the oxidative stress response. These events dysregulate the expression of several genes and activate endogenous apoptosis pathways, eventually leading to developmental disorders and heart defects.

Lenvatinib induces cardiac developmental toxicity in zebrafish embryos through regulation of Notch mediated-oxidative stress generation

Due to an increasing number of abused drugs dumped into the wastewater, more and more drugs are detected in the water environment, which may affect the survival of aquatic organisms. Lenvatinib is a multi-targeted tyrosine kinase inhibitor, and is clinically used to treat differentiated thyroid cancer, renal epithelial cell carcinoma and liver cancer. However, there are few reports on the effects of lenvatinib in embryos development. In this study, zebrafish embryos were used to evaluate the effect of lenvatinib on cardiovascular development. Well-developed zebrafish embryos were selected at 6 h post fertilization (hpf) and exposed to 0.05 mg/L, 0.1 mg/L and 0.2 mg/L lenvatinib up to 72 hpf. The processed embryos demonstrated cardiac edema, decreased heart rate, prolonged SV-BA distance, inhibited angiogenesis, and blocked blood circulation. Lenvatinib caused cardiac defects in the whole stage of cardiac development and increased the apoptosis of cardiomyocyte. Oxidative stress in the processed embryos was accumulated and inhibiting oxidative stress could rescue cardiac defects induced by lenvatinib. Additionally, we found that lenvatinib downregulated Notch signaling, and the activation of Notch signaling could rescue cardiac developmental defects and downregulate oxidative stress level induced by lenvatinib. Our results suggested that lenvatinib might induce cardiac developmental toxicity through inducing Notch mediated-oxidative stress generation, raising concerns about the harm of exposure to lenvatinib in aquatic organisms.

Exposure to Oxadiazon-Butachlor causes cardiac toxicity in zebrafish embryos

Oxadiazon-Butachlor (OB) is a widely used herbicide for controlling most annual weeds in rice fields. However, its potential toxicity in aquatic organisms has not been evaluated so far. We used the zebrafish embryo model to assess the toxicity of OB, and found that it affected early cardiac development and caused extensive cardiac damage. Mechanistically, OB significantly increased oxidative stress in the embryos by inhibiting antioxidant enzymes that resulted in excessive production of reactive oxygen species (ROS), eventually leading to cardiomyocyte apoptosis. In addition, OB also inhibited the WNT signaling pathway and downregulated its target genes includinglef1, axin2 and β-catenin. Reactivation of this pathway by the Wnt activator BML-284 and the antioxidant astaxanthin rescued the embryos form the cardiotoxic effects of OB, indicating that oxidative stress, and inhibition of WNT target genes are the mechanistic basis of OB-induced damage in zebrafish. Our study shows that OB exposure causes cardiotoxicity in zebrafish embryos and may be potentially toxic to other aquatic life and even humans.

Multiple transcription factors mediating the expressional regulation of myosin heavy chain gene involved in the indeterminate muscle growth of fish

Torafugu myosin heavy chain gene, MYH_M2528-1, is specifically expressed in neonatal slow and fast muscle fibers, suggesting its functional role in indeterminate muscle growth in fish. However, the transcriptional regulatory mechanisms of MYH_M2528-1 involved in indeterminate muscle growth in fish remained unknown. We previously isolated a 2100 bp 5'- flanking sequence of torafugu MYH_M2528-1 that showed sufficient promoter activity to allow specific gene expression in neonatal muscle fibers of zebrafish. Here, we examined the cis-regulatory mechanism of 2100 bp 5'-flanking region of torafugu MYH_M2528-1 using deletion-mutation analysis in zebrafish embryo. We discovered that myoblast determining factor (MyoD) binding elements play a key role and participate in the transcriptional regulation of MYH_M2528-1 expression in zebrafish embryos. We further discovered that paired box protein (Pax3) are required for promoting MYH_M2528-1 expression and myocyte enhancer factor-2 (MEF2) binding sites participate in the transcriptional regulation of MYH_M2528-1 expression in slow/fast skeletal muscles. Our study also confirmed that the nuclear factor of activated T-cell (NFAT) binding sites take part in the transcriptional regulation of MYH_M2528-1 expression in slow and fast muscles fiber in relation to indeterminate muscle growth. These results obviously confirmed that multiple cis-elements in the 5'-flanking region of MYH_M2528-1 function in the transcriptional regulation of its expression.

Investigation of Pathogenic Genes in Chinese sporadic Hypertrophic Cardiomyopathy Patients by Whole Exome Sequencing

Hypertrophic cardiomyopathy (HCM) is a cardiovascular disease with high heterogeneity. Limited knowledge concerning the genetic background of nearly 40% HCM cases indicates there is a clear need for further investigation to explore the genetic pathogenesis of the disease. In this study, we undertook a whole exome sequencing (WES) approach to identify novel candidate genes and mutations associated with HCM. The cohort consisted of 74 unrelated patients with sporadic HCM (sHCM) previously determined to be negative for mutations in eight sarcomere genes. The results showed that 7 of 74 patients (9.5%) had damaging mutations in 43 known HCM disease genes. Furthermore, after analysis combining the Transmission and De novo Association (TADA) program and the ToppGene program, 10 putative genes gained priority. A thorough review of public databases and related literature revealed that there is strong supporting evidence for most of the genes playing roles in various aspects of heart development. Findings from recent studies suggest that the putative and known disease genes converge on three functional pathways: sarcomere function, calcium signaling and metabolism pathway. This study illustrates the benefit of WES, in combination with rare variant analysis tools, in providing valuable insight into the genetic etiology of a heterogeneous sporadic disease.

Epicardial GATA factors regulate early coronary vascular plexus formation

During early development, GATA factors have been shown to be important for key events of coronary vasculogenesis, including formation of the epicardium. Myocardial GATA factors are required for coronary vascular (CV) formation; however, the role of epicardial localized GATAs in this process has not been addressed. The current study was conducted to investigate the molecular mechanisms by which the epicardium controls coronary vasculogenesis, focusing on the role of epicardial GATAs in establishing the endothelial plexus during early coronary vasculogenesis. To address the role of epicardial GATAs, we ablated GATA4 and GATA6 transcription factors specifically from the mouse epicardium and found that the number of endothelial cells in the sub-epicardium was drastically reduced, and concomitant coronary vascular plexus formation was significantly compromised. Here we present evidence for a novel role for epicardial GATA factors in controlling plexus formation by recruiting endothelial cells to the sub-epicardium.

Lrrc10 is a novel cardiac-specific target gene of Nkx2-5 and GATA4

Cardiac gene expression is precisely regulated and its perturbation causes developmental defects and heart disease. Leucine-rich repeat containing 10 (Lrrc10) is a cardiac-specific factor that is crucial for proper cardiac development and deletion of Lrrc10 in mice results in dilated cardiomyopathy. However, the mechanisms regulating Lrrc10 expression in cardiomyocytes remain unknown. Therefore, we set out to determine trans-acting factors and cis-elements critical for mediating Lrrc10 expression. We identify Lrrc10 as a transcriptional target of Nkx2-5 and GATA4. The Lrrc10 promoter region contains two highly conserved cardiac regulatory elements, which are functional in cardiomyocytes but not in fibroblasts. In vivo, Nkx2-5 and GATA4 endogenously occupy the proximal and distal cardiac regulatory elements of Lrrc10 in the heart. Moreover, embryonic hearts of Nkx2-5 knockout mice have dramatically reduced expression of Lrrc10. These data demonstrate the importance of Nkx2-5 and GATA4 in regulation of Lrrc10 expression in vivo. The proximal cardiac regulatory element located at around -200bp is synergistically activated by Nkx2-5 and GATA4 while the distal cardiac regulatory element present around -3kb requires SRF in addition to Nkx2-5 and GATA4 for synergistic activation. Mutational analyses identify a pair of adjacent Nkx2-5 and GATA binding sites within the proximal cardiac regulatory element that are necessary to induce expression of Lrrc10. In contrast, only the GATA site is functional in the distal regulatory element. Taken together, our data demonstrate that the transcription factors Nkx2-5 and GATA4 cooperatively regulate cardiac-specific expression of Lrrc10.

Heavy and light roles: myosin in the morphogenesis of the heart

Myosin is an essential component of cardiac muscle, from the onset of cardiogenesis through to the adult heart. Although traditionally known for its role in energy transduction and force development, recent studies suggest that both myosin heavy-chain and myosin light-chain proteins are required for a correctly formed heart. Myosins are structural proteins that are not only expressed from early stages of heart development, but when mutated in humans they may give rise to congenital heart defects. This review will discuss the roles of myosin, specifically with regards to the developing heart. The expression of each myosin protein will be described, and the effects that altering expression has on the heart in embryogenesis in different animal models will be discussed. The human molecular genetics of the myosins will also be reviewed.

Multiple cis-elements in the 5'-flanking region of embryonic/larval fast-type of the myosin heavy chain gene of torafugu, MYH(M743-2), function in the transcriptional regulation of its expression

The myosin heavy chain gene, MYH(M743-2), is highly expressed in fast muscle fibers of torafugu embryos and larvae, suggesting its functional roles for embryonic and larval muscle development. However, the transcriptional regulatory mechanism involved in its expression remained unknown. Here, we analyzed the 2075bp 5'-flanking region of torafugu MYH(M743-2) to examine the spatial and temporal regulation by using transgenic and transient expression techniques in zebrafish embryos. Combining both transient and transgenic analyses, we demonstrated that the 2075bp 5'-flanking sequences was sufficient for its expression in skeletal, craniofacial and pectoral fin muscles. The immunohistochemical observation revealed that the zebrafish larvae from the stable transgenic line consistently expressed enhanced green fluorescent protein (EGFP) in fast muscle fibers. Promoter deletion analyses demonstrated that the minimum 468bp promoter region could direct MYH(M743-2) expression in zebrafish larvae. We discovered that the serum response factor (SRF)-like binding sites are required for promoting MYH(M743-2) expression and myoblast determining factor (MyoD) and myocyte enhancer factor-2 (MEF2) binding sites participate in the transcriptional control of MYH(M743-2) expression in fast skeletal muscles. We further discovered that MyoD binding sites, but not MEF2, participate in the transcriptional regulation of MYH(M743-2) expression in pectoral fin and craniofacial muscles. These results clearly demonstrated that multiple cis-elements in the 5'-flanking region of MYH(M743-2) function in the transcriptional control of its expression.