Plakoglobin has both structural and signalling roles in zebrafish development

AbstractPlakoglobin, or gamma-catenin, is found in both desmosomes and adherens junctions and participates in Wnt signalling. Mutations in the human gene are implicated in the congenital heart disorder, arrhythmogenic right ventricular cardiomyopathy (ARVC), but the signalling effects of plakoglobin loss in ARVC have not been established. Here we report that knockdown of plakoglobin in zebrafish results in decreased heart size, reduced heartbeat, cardiac oedema, reflux of blood between heart chambers and a twisted tail. Wholemount in situ hybridisation shows reduced expression of the heart markers nkx2.5 at 24 hours post fertilisation (hpf), and cmlc2 and vmhc at 48 hpf, while there is lack of restriction of the valve markers notch1b and bmp4 at 48 hpf. Wnt target gene expression was examined by semi-quantitative RT-PCR and found to be increased in morphant embryos indicating that plakoglobin is antagonistic to Wnt signalling. Co-expression of the Wnt inhibitor, Dkk1, rescues the cardiac phenotype of the plakoglobin morphant. β-catenin protein expression is increased in morphant embryos as is its colocalisation with E-cadherin in adherens junctions. Endothelial cells at the atrioventricular boundary of morphant hearts have an aberrant morphology, indicating problems with valvulogenesis. Morphants also have decreased numbers of desmosomes and adherens junctions in the intercalated discs. These results establish the zebrafish as a model for ARVC caused by loss of plakoglobin function and indicate that there are signalling as well as structural consequences of this loss

Insulin-like growth factor-2 regulates early neural and cardiovascular system development in zebrafish embryos

The insulin-like growth factor (IGF) family is essential for normal embryonic growth and development and it is highly conserved through vertebrate evolution. However, the roles that the individual members of the IGF family play in embryonic development have not been fully elucidated. This study focuses on the role of IGF-2 in zebrafish embryonic development. Two igf-2 genes, igf-2a and igf-2b, are present in the zebrafish genome. Antisense morpholinos were designed to knock down both igf-2 genes. The neural and cardiovascular defects in IGF-2 morphant embryos were then examined further using wholemount in situ hybridisation, TUNEL analysis and O-dianisidine staining. Knockdown of igf-2a or igf-2b resulted in ventralised embryos with reduced growth, reduced eyes, disrupted brain structures and a disrupted cardiovascular system, with igf-2b playing a more significant role in development. During gastrulation, igf-2a and igf-2b are required for development of anterior neural structures and for regulation of genes critical to dorsal-ventral patterning. As development proceeds, igf-2a and igf-2b play antiapoptotic roles. Gene expression analysis demonstrates that igf-2a and igf-2b play overlapping roles in angiogenesis and cardiac outflow tract development. igf-2b is specifically required for cardiac valve development and cardiac looping. Injection of a dominant negative IGF-1 receptor led to similar defects in angiogenesis and cardiac valve development, indicating IGF-2 signals through this receptor to regulate cardiovascular development. This is the first study describing two functional igf-2 genes in zebrafish. This work demonstrates that igf-2a and igf-2b are critical to neural and cardiovascular development in zebrafish embryos. The finding that igf-2a and igf-2b do not act exclusively in a redundant manner may explain why both genes have been stably maintained in the genome

Insulin-like growth factor-2 regulates early neural and cardiovascular system development in zebrafish embryos

The insulin-like growth factor (IGF) family is essential for normal embryonic growth and development and it is highly conserved through vertebrate evolution. However, the roles that the individual members of the IGF family play in embryonic development have not been fully elucidated. This study focuses on the role of IGF-2 in zebrafish embryonic development. Two igf-2 genes, igf-2a and igf-2b, are present in the zebrafish genome. Antisense morpholinos were designed to knock down both igf-2 genes. The neural and cardiovascular defects in IGF-2 morphant embryos were then examined further using wholemount in situ hybridisation, TUNEL analysis and O-dianisidine staining. Knockdown of igf-2a or igf-2b resulted in ventralised embryos with reduced growth, reduced eyes, disrupted brain structures and a disrupted cardiovascular system, with igf-2b playing a more significant role in development. During gastrulation, igf-2a and igf-2b are required for development of anterior neural structures and for regulation of genes critical to dorsal-ventral patterning. As development proceeds, igf-2a and igf-2b play antiapoptotic roles. Gene expression analysis demonstrates that igf-2a and igf-2b play overlapping roles in angiogenesis and cardiac outflow tract development. igf-2b is specifically required for cardiac valve development and cardiac looping. Injection of a dominant negative IGF-1 receptor led to similar defects in angiogenesis and cardiac valve development, indicating IGF-2 signals through this receptor to regulate cardiovascular development. This is the first study describing two functional igf-2 genes in zebrafish. This work demonstrates that igf-2a and igf-2b are critical to neural and cardiovascular development in zebrafish embryos. The finding that igf-2a and igf-2b do not act exclusively in a redundant manner may explain why both genes have been stably maintained in the genome

Insulin-like growth factor-2 regulates early neural and cardiovascular system development in zebrafish embryos

The insulin-like growth factor (IGF) family is essential for normal embryonic growth and development and it is highly conserved through vertebrate evolution. However, the roles that the individual members of the IGF family play in embryonic development have not been fully elucidated. This study focuses on the role of IGF-2 in zebrafish embryonic development. Two igf-2 genes, igf-2a and igf-2b, are present in the zebrafish genome. Antisense morpholinos were designed to knock down both igf-2 genes. The neural and cardiovascular defects in IGF-2 morphant embryos were then examined further using wholemount in situ hybridisation, TUNEL analysis and O-dianisidine staining. Knockdown of igf-2a or igf-2b resulted in ventralised embryos with reduced growth, reduced eyes, disrupted brain structures and a disrupted cardiovascular system, with igf-2b playing a more significant role in development. During gastrulation, igf-2a and igf-2b are required for development of anterior neural structures and for regulation of genes critical to dorsal-ventral patterning. As development proceeds, igf-2a and igf-2b play antiapoptotic roles. Gene expression analysis demonstrates that igf-2a and igf-2b play overlapping roles in angiogenesis and cardiac outflow tract development. igf-2b is specifically required for cardiac valve development and cardiac looping. Injection of a dominant negative IGF-1 receptor led to similar defects in angiogenesis and cardiac valve development, indicating IGF-2 signals through this receptor to regulate cardiovascular development. This is the first study describing two functional igf-2 genes in zebrafish. This work demonstrates that igf-2a and igf-2b are critical to neural and cardiovascular development in zebrafish embryos. The finding that igf-2a and igf-2b do not act exclusively in a redundant manner may explain why both genes have been stably maintained in the genome

Loss of plakophilin 2 disrupts heart development in zebrafish

The desmosomal armadillo protein plakophilin 2 is the only plakophilin expressed in the heart, and mutations in the human plakophilin 2 gene result in arrhythmogenic right ventricular cardiomyopathy. To investigate loss of function, we knocked down plakophilin 2 by morpholino microinjection in zebrafish.This resulted in decreased heart rate, cardiac oedema, blood pooling, a failure of the heart to pattern correctly and a twisted tail. Co-injection of plakophilin 2 mRNA rescued the morphant phenotype, indicating the specificity of the knockdown. Desmosome numbers were decreased in morphant hearts and the plaque and midline structures of the desmosomes in the intercalated discs were disrupted when examined by electron microscopy. cmlc2 and vmhc expression at 48 hours post-fertilization (hpf) showed incomplete looping of the heart in morphant embryos by whole mount in situ hybridization, and bmp4 expression was expanded into the ventricle. The domain of expression of the heart marker nkx2.5 at 24 hpf was expanded. At the 18 somite stage, expression of the cardiogenic gene lefty2 was abolished in the left cardiac field, with concomitant increases in bmp4, spaw and lefty1 expression, likely resulting in the looping defects.These results indicate that plakophilin 2 has both structural and signalling roles in zebrafish heart development

Loss of plakophilin 2 disrupts heart development in zebrafish

The desmosomal armadillo protein plakophilin 2 is the only plakophilin expressed in the heart, and mutations in the human plakophilin 2 gene result in arrhythmogenic right ventricular cardiomyopathy. To investigate loss of function, we knocked down plakophilin 2 by morpholino microinjection in zebrafish.This resulted in decreased heart rate, cardiac oedema, blood pooling, a failure of the heart to pattern correctly and a twisted tail. Co-injection of plakophilin 2 mRNA rescued the morphant phenotype, indicating the specificity of the knockdown. Desmosome numbers were decreased in morphant hearts and the plaque and midline structures of the desmosomes in the intercalated discs were disrupted when examined by electron microscopy. cmlc2 and vmhc expression at 48 hours post-fertilization (hpf) showed incomplete looping of the heart in morphant embryos by whole mount in situ hybridization, and bmp4 expression was expanded into the ventricle. The domain of expression of the heart marker nkx2.5 at 24 hpf was expanded. At the 18 somite stage, expression of the cardiogenic gene lefty2 was abolished in the left cardiac field, with concomitant increases in bmp4, spaw and lefty1 expression, likely resulting in the looping defects.These results indicate that plakophilin 2 has both structural and signalling roles in zebrafish heart development

Metabolic reprogramming and membrane glycan remodeling as potential drivers of zebrafish heart regeneration

The ability of the zebrafish heart to regenerate following injury makes it a valuable model to deduce why this capability in mammals is limited to early neonatal stages. Although metabolic reprogramming and glycosylation remodeling have emerged as key aspects in many biological processes, how they may trigger a cardiac regenerative response in zebrafish is still a crucial question. Here, by using an up-to-date panel of transcriptomic, proteomic and glycomic approaches, we identify a metabolic switch from mitochondrial oxidative phosphorylation to glycolysis associated with membrane glycosylation remodeling during heart regeneration. Importantly, we establish the N- and O-linked glycan structural repertoire of the regenerating zebrafish heart, and link alterations in both sialylation and high mannose structures across the phases of regeneration. Our results show that metabolic reprogramming and glycan structural remodeling are potential drivers of tissue regeneration after cardiac injury, providing the biological rationale to develop novel therapeutics to elicit heart regeneration in mammals