RESUMO
Establishment of the hemochorial uterine-placental interface requires exodus of trophoblast cells from the placenta and their transformative actions on the uterus, which represent processes critical for a successful pregnancy, but are poorly understood. We examined the involvement of CBP/p300-interacting transactivator with glutamic acid/aspartic acid-rich carboxyl-terminal domain 2 (CITED2) in rat and human trophoblast cell development. The rat and human exhibit deep hemochorial placentation. CITED2 was distinctively expressed in the junctional zone (JZ) and invasive trophoblast cells of the rat. Homozygous Cited2 gene deletion resulted in placental and fetal growth restriction. Small Cited2 null placentas were characterized by disruptions in the JZ, delays in intrauterine trophoblast cell invasion, and compromised plasticity. In the human placentation site, CITED2 was uniquely expressed in the extravillous trophoblast (EVT) cell column and importantly contributed to the development of the EVT cell lineage. We conclude that CITED2 is a conserved regulator of deep hemochorial placentation.
Assuntos
Placenta , Placentação , Proteínas Repressoras , Transativadores , Animais , Feminino , Humanos , Gravidez , Ratos , Placentação/genética , Proteínas Repressoras/genética , Transativadores/genética , Trofoblastos , ÚteroRESUMO
In mammals, most cardiomyocytes (CMs) become polyploid (they have more than two complete sets of chromosomes). The purpose of this review is to evaluate assumptions about CM ploidy that are commonly discussed, even if not experimentally demonstrated, and to highlight key issues that are still to be resolved. Topics discussed here include (a) technical and conceptual difficulties in defining a polyploid CM, (b) the candidate role of reactive oxygen as a proximal trigger for the onset of polyploidy, (c) the relationship between polyploidization and other aspects of CM maturation, (d) recent insights related to the regenerative role of the subpopulation of CMs that are not polyploid, and (e) speculations as to why CMs become polyploid at all. New approaches to experimentally manipulate CM ploidy may resolve some of these long-standing and fundamental questions.
Assuntos
Miócitos Cardíacos/fisiologia , Poliploidia , Regeneração/fisiologia , Proliferação de Células , Humanos , Miocárdio/citologiaRESUMO
Cardiomyocyte proliferation is a difficult phenomenon to capture and prove. Here we employ a retrospective analysis of single cell ventricular suspensions to definitively identify cardiomyocytes that have completed cell division. Through this analysis we determined that the capacity of cardiomyocytes to re-enter the cell cycle and complete cell division after injury are separate and variable traits. Further, we provide evidence that Tnni3k definitively influences both early and final stages of the cell cycle.
Assuntos
Coração , Miócitos Cardíacos , Ciclo Celular , Divisão Celular , Proliferação de Células , Ventrículos do Coração , Miócitos Cardíacos/metabolismo , Estudos Retrospectivos , Animais , CamundongosRESUMO
TNNI3K expression worsens disease progression in several mouse heart pathology models. TNNI3K expression also reduces the number of diploid cardiomyocytes, which may be detrimental to adult heart regeneration. However, the gene is evolutionarily conserved, suggesting a beneficial function that has remained obscure. Here, we show that C57BL/6J-inbred Tnni3k mutant mice develop concentric remodeling, characterized by ventricular wall thickening and substantial reduction of cardiomyocyte aspect ratio. This pathology occurs in mice carrying a Tnni3k null allele, a K489R point mutation rendering the protein kinase-dead, or an allele corresponding to human I686T, the most common human non-synonymous TNNI3K variant, which is hypomorphic for kinase activity. Mutant mice develop these conditions in the absence of fibrosis or hypertension, implying a primary cardiomyocyte etiology. In culture, mutant cardiomyocytes were impaired in contractility and calcium dynamics and in protein kinase A signaling in response to isoproterenol, indicating diminished contractile reserve. These results demonstrate a beneficial function of TNNI3K in the adult heart that might explain its evolutionary conservation and imply that human TNNI3K variants, in particular the widespread I686T allele, may convey elevated risk for altered heart geometry and hypertrophy.
Assuntos
Cardiopatias/patologia , Contração Muscular , Mutação , Miócitos Cardíacos/patologia , Proteínas Serina-Treonina Quinases/genética , Remodelação Vascular , Animais , Cardiopatias/etiologia , Cardiopatias/metabolismo , Humanos , Camundongos , Camundongos Endogâmicos C57BL , Miócitos Cardíacos/metabolismoRESUMO
The role played by the Notch pathway in cardiac progenitor cell biology remains to be elucidated. Delta-like ligand 4 (Dll4), the arterial-specific Notch ligand, is expressed by second heart field (SHF) progenitors at time-points that are crucial in SHF biology. Dll4-mediated Notch signaling is required for maintaining an adequate pool of SHF progenitors, such that Dll4 knockout results in a reduction in proliferation and an increase in apoptosis. A reduced SHF progenitor pool leads to an underdeveloped right ventricle (RV) and outflow tract (OFT). In its most severe form, there is severe RV hypoplasia and poorly developed OFT resulting in early embryonic lethality. In its milder form, the OFT is foreshortened and misaligned, resulting in a double outlet right ventricle. Dll4-mediated Notch signaling maintains Fgf8 expression by transcriptional regulation at the promoter level. Combined heterozygous knockout of Dll4 and Fgf8 demonstrates genetic synergy in OFT alignment. Exogenous supplemental Fgf8 rescues proliferation in Dll4 mutants in ex-vivo culture. Our results establish a novel role for Dll4-mediated Notch signaling in SHF biology. More broadly, our model provides a platform for understanding oligogenic inheritance that results in clinically relevant OFT malformations.
Assuntos
Proteínas Adaptadoras de Transdução de Sinal/metabolismo , Proteínas de Ligação ao Cálcio/metabolismo , Proliferação de Células , Fator 8 de Crescimento de Fibroblasto/biossíntese , Regulação da Expressão Gênica no Desenvolvimento , Ventrículos do Coração/embriologia , Receptores Notch/metabolismo , Transdução de Sinais , Células-Tronco/metabolismo , Proteínas Adaptadoras de Transdução de Sinal/genética , Animais , Proteínas de Ligação ao Cálcio/genética , Fator 8 de Crescimento de Fibroblasto/genética , Camundongos , Camundongos Knockout , Receptores Notch/genéticaRESUMO
Mesodermal progenitors in the second heart field (SHF) express Delta-like-ligand 4 (Dll4) that regulates Notch-mediated proliferation. As cells of SHF lineage mature to assume endocardial and myocardial cell fates, we have shown that Dll4 expression is lost, and the subsequent expression of another Notch ligand Jagged1 regulates Notch-mediated maturation events in the developing heart. A subset of SHF progenitors also matures to form the pharyngeal arch artery (PAA) endothelium. Dll4 was originally identified as an arterial endothelial-specific Notch ligand that plays an important role in blood vessel maturation, but its role in aortic arch maturation has not been studied to date secondary to the early lethality observed in Dll4 knockout mice. We show that, unlike in SHF-derived endocardium and myocardium, Dll4 expression persists in SHF-derived arterial endothelial cells. Using SHF-specific conditional deletion of Dll4, we demonstrate that as SHF cells transition from their progenitor state to an endothelial fate, Dll4-mediated Notch signalling switches from providing proliferative to maturation cues. Dll4 expression maintains arterial identity in the PAAs and plays a critical role in the maturation and re-organization of the 4th pharyngeal arch artery, in particular. Haploinsufficiency of Dll4 in SHF leads to highly penetrant aortic arch artery abnormalities, similar to those observed in the clinic, primarily resulting from aberrant reorganization of bilateral 4th pharyngeal arch arteries. Hence, we show that cells of SHF lineage that assume an arterial endothelial fate continue to express Dll4 and the resulting Dll4-mediated Notch signalling transitions from an early proliferative to a later maturation role during aortic arch development.
Assuntos
Proteínas Adaptadoras de Transdução de Sinal , Proteínas de Ligação ao Cálcio , Células Endoteliais , Receptores Notch , Proteínas Adaptadoras de Transdução de Sinal/genética , Proteínas Adaptadoras de Transdução de Sinal/metabolismo , Animais , Artérias/metabolismo , Proteínas de Ligação ao Cálcio/genética , Proteínas de Ligação ao Cálcio/metabolismo , Células Endoteliais/metabolismo , Endotélio Vascular/metabolismo , Ligantes , Camundongos , Camundongos Knockout , Receptores Notch/genética , Receptores Notch/metabolismoRESUMO
During the past two decades, the field of mammalian myocardial regeneration has grown dramatically, and with this expanded interest comes increasing claims of experimental manipulations that mediate bona fide proliferation of cardiomyocytes. Too often, however, insufficient evidence or improper controls are provided to support claims that cardiomyocytes have definitively proliferated, a process that should be strictly defined as the generation of two de novo functional cardiomyocytes from one original cardiomyocyte. Throughout the literature, one finds inconsistent levels of experimental rigor applied, and frequently the specific data supplied as evidence of cardiomyocyte proliferation simply indicate cell-cycle activation or DNA synthesis, which do not necessarily lead to the generation of new cardiomyocytes. In this review, we highlight potential problems and limitations faced when characterizing cardiomyocyte proliferation in the mammalian heart, and summarize tools and experimental standards, which should be used to support claims of proliferation-based remuscularization. In the end, definitive establishment of de novo cardiomyogenesis can be difficult to prove; therefore, rigorous experimental strategies should be used for such claims.
Assuntos
Miócitos Cardíacos , Regeneração , Animais , Ciclo Celular , Proliferação de Células , Coração/fisiologia , Mamíferos , Miócitos Cardíacos/fisiologiaRESUMO
Recent evidence implicates mononuclear diploid cardiomyocytes as a proliferative and regenerative subpopulation of the postnatal heart. The number of these cardiomyocytes is a complex trait showing substantial natural variation among inbred mouse strains based on the combined influences of multiple polymorphic genes. One gene confirmed to influence this parameter is the cardiomyocyte-specific kinase Tnni3k. Here, we have studied Tnni3k alleles across a number of species. Using a newly-generated kinase-dead allele in mice, we show that Tnni3k function is dependent on its kinase activity. In an in vitro kinase assay, we show that several common human TNNI3K kinase domain variants substantially compromise kinase activity, suggesting that TNNI3K may influence human heart regenerative capacity and potentially also other aspects of human heart disease. We show that two kinase domain frameshift mutations in mice cause loss-of-function consequences by nonsense-mediated decay. We further show that the Tnni3k gene in two species of mole-rat has independently devolved into a pseudogene, presumably associated with the transition of these species to a low metabolism and hypoxic subterranean life. This may be explained by the observation that Tnni3k function in mice converges with oxidative stress to regulate mononuclear diploid cardiomyocyte frequency. Unlike other studied rodents, naked mole-rats have a surprisingly high (30%) mononuclear cardiomyocyte level but most of their mononuclear cardiomyocytes are polyploid; their mononuclear diploid cardiomyocyte level (7%) is within the known range (2-10%) of inbred mouse strains. Naked mole-rats provide further insight on a recent proposal that cardiomyocyte polyploidy is associated with evolutionary acquisition of endothermy.
Assuntos
Evolução Molecular , Cardiopatias/genética , Proteínas Serina-Treonina Quinases/genética , Alelos , Animais , Diferenciação Celular/genética , Linhagem da Célula/genética , Proliferação de Células/genética , Cardiopatias/metabolismo , Ventrículos do Coração/crescimento & desenvolvimento , Ventrículos do Coração/metabolismo , Humanos , Mutação com Perda de Função/genética , Camundongos , Ratos-Toupeira/genética , Miocárdio/metabolismo , Miócitos Cardíacos/metabolismo , Estresse Oxidativo/genética , Poliploidia , Regeneração/genéticaRESUMO
The original version of this article unfortunately contained a mistake. In reviewing the phenotype associated with Mapk14 (p38alpha MAPK) mutation as evaluated by Adams et al. (2000) using tetraploid aggregation chimeric embryos, the authors mistakenly stated that rescue of embryo lethality was short-lived and that embryos died two days later of non-placenta-related causes. In fact, as reported by Adams et al. (2000), when the placental defect of global null embryos was rescued, p38alpha(-/-) embryos developed to term and were normal in appearance. The authors apologize for the error.
RESUMO
BACKGROUND: The embryonic day E10-13 period of mouse heart development is characterized by robust cardiomyocyte proliferation that creates the compact zone of thickened ventricular wall myocardium. This process is initiated by the formation of the epicardium on the outer heart surface, which releases insulin-like growth factor 2 (IGF2) as the primary cardiomyocyte mitogen. Two receptors mediate IGF2 signaling, the IGF1R and the insulin receptor (INSR). RESULTS: In this study, we addressed the relative roles of the two IGF2 receptors in mouse heart development. We find that both receptors are expressed in the mouse heart during the E10-13 period, although IGF1R is much more prominently activated by IGF2 than INSR. Genetic manipulation indicates that only Igf1r is required for embryonic ventricular wall morphogenesis. INSR is not hyperactivated in the absence of IGF1R, and INSR does not compensate functionally for IGF1R in the absence of the latter. CONCLUSIONS: These results define the molecular components that are responsible for a major burst of cardiomyocyte proliferation during heart development. These results may also be relevant to understanding the efficiency of regeneration of the mammalian heart after neonatal and adult injury.
Assuntos
Coração/embriologia , Fator de Crescimento Insulin-Like II/metabolismo , Pericárdio/metabolismo , Receptor IGF Tipo 1/metabolismo , Receptor de Insulina/metabolismo , Animais , Proliferação de Células/fisiologia , Camundongos , Camundongos Knockout , Miócitos Cardíacos/citologia , Organogênese , Pericárdio/crescimento & desenvolvimentoRESUMO
If viewed as a movie, heart morphogenesis appears to unfold in a continuous and seamless manner. At the mechanistic level, however, a series of discreet and separable processes sequentially underlie heart development. This is evident in examining the expansion of the ventricular wall, which accounts for most of the contractile force of each heartbeat. Ventricular wall expansion is driven by cardiomyocyte proliferation coupled with a morphogenetic program that causes wall thickening rather than lengthening. Although most studies of these processes have focused on heart-intrinsic processes, it is increasingly clear that extracardiac events influence or even direct heart morphogenesis. In this review, we specifically consider mechanisms responsible for coordinating cardiomyocyte proliferation and ventricular wall expansion in mammalian development, relying primarily on studies from mouse development where a wealth of molecular and genetic data have been accumulated.
Assuntos
Proliferação de Células , Ventrículos do Coração/embriologia , Morfogênese/fisiologia , Miócitos Cardíacos/metabolismo , Animais , Ventrículos do Coração/metabolismo , Proteína 2 de Ligação a Fator de Crescimento Semelhante à Insulina/metabolismo , CamundongosRESUMO
RATIONALE: There is persistent uncertainty regarding the developmental origins of coronary vessels, with 2 principal sources suggested as ventricular endocardium or sinus venosus (SV). These 2 proposed origins implicate fundamentally distinct mechanisms of vessel formation. Resolution of this controversy is critical for deciphering the programs that result in the formation of coronary vessels and has implications for research on therapeutic angiogenesis. OBJECTIVE: To resolve the controversy over the developmental origin of coronary vessels. METHODS AND RESULTS: We first generated nuclear factor of activated T cells (Nfatc1)-Cre and Nfatc1-Dre lineage tracers for endocardium labeling. We found that Nfatc1 recombinases also label a significant portion of SV endothelial cells in addition to endocardium. Therefore, restricted endocardial lineage tracing requires a specific marker that distinguishes endocardium from SV. By single-cell gene expression analysis, we identified a novel endocardial gene natriuretic peptide receptor 3 (Npr3). Npr3 is expressed in the entirety of the endocardium but not in the SV. Genetic lineage tracing based on Npr3-CreER showed that endocardium contributes to a minority of coronary vessels in the free walls of embryonic heart. Intersectional genetic lineage tracing experiments demonstrated that endocardium minimally contributes to coronary endothelium in the embryonic ventricular free walls. CONCLUSIONS: Our study suggested that SV, but not endocardium, is the major origin for coronary endothelium in the embryonic ventricular free walls. This work thus resolves the recent controversy over the developmental origin of coronary endothelium, providing the basis for studying coronary vessel formation and regeneration after injury.
Assuntos
Linhagem da Célula , Vasos Coronários/embriologia , Endocárdio/embriologia , Endotélio Vascular/metabolismo , Ventrículos do Coração/embriologia , Animais , Vasos Coronários/citologia , Vasos Coronários/metabolismo , Endocárdio/citologia , Endocárdio/metabolismo , Endotélio Vascular/citologia , Ventrículos do Coração/citologia , Ventrículos do Coração/metabolismo , Camundongos , Fatores de Transcrição NFATC/genética , Fatores de Transcrição NFATC/metabolismo , Receptores do Fator Natriurético Atrial/genética , Receptores do Fator Natriurético Atrial/metabolismoRESUMO
The hearts of many mammalian species are surrounded by an extensive layer of fat called epicardial adipose tissue (EAT). The lineage origins and determinative mechanisms of EAT development are unclear, in part because mice and other experimentally tractable model organisms are thought to not have this tissue. In this study, we show that mouse hearts have EAT, localized to a specific region in the atrial-ventricular groove. Lineage analysis indicates that this adipose tissue originates from the epicardium, a multipotent epithelium that until now is only established to normally generate cardiac fibroblasts and coronary smooth muscle cells. We show that adoption of the adipocyte fate in vivo requires activation of the peroxisome proliferator activated receptor gamma (PPARγ) pathway, and that this fate can be ectopically induced in mouse ventricular epicardium, either in embryonic or adult stages, by expression and activation of PPARγ at times of epicardium-mesenchymal transformation. Human embryonic ventricular epicardial cells natively express PPARγ, which explains the abundant presence of fat seen in human hearts at birth and throughout life.
Assuntos
Adipogenia , Mesoderma/citologia , PPAR gama/agonistas , Pericárdio/citologia , Animais , Linhagem Celular Transformada , Linhagem da Célula , Humanos , CamundongosRESUMO
Heart outflow tract septation in mouse embryos carrying mutations in retinoic acid receptor genes fails with complete penetrance. In this mutant background, ectopic TGFß signaling in the distal outflow tract is responsible for septation failure, but it was uncertain what tissue was responsive to ectopic TGFß and why this response interfered with septation. By combining RAR gene mutation with tissue-specific Cre drivers and a conditional type II TGFß receptor (Tgfbr2) allele, we determined that ectopic activation of TGFß signaling in the endocardium is responsible for septation defects. Ectopic TGFß signaling results in ectopic mesenchymal transformation of the endocardium and thereby in improperly constituted distal OFT cushions. Our analysis highlights the interactions between myocardium, endocardium, and neural crest cells in outflow tract morphogenesis, and demonstrates the requirement for proper TGFß signaling in outflow tract cushion organization and septation.
Assuntos
Endocárdio/patologia , Insuficiência Cardíaca/patologia , Defeitos dos Septos Cardíacos/patologia , Mesoderma/patologia , Transdução de Sinais , Fator de Crescimento Transformador beta/metabolismo , Animais , Endocárdio/embriologia , Endocárdio/metabolismo , Insuficiência Cardíaca/embriologia , Insuficiência Cardíaca/metabolismo , Defeitos dos Septos Cardíacos/embriologia , Defeitos dos Septos Cardíacos/metabolismo , Mesoderma/embriologia , Camundongos , Mutação/genética , Especificidade de Órgãos , Fenótipo , Receptores do Ácido Retinoico/metabolismoRESUMO
A complex regulatory network of morphogens and transcription factors is essential for normal cardiac development. Nkx2-5 is among the earliest known markers of cardiac mesoderm that is central to the regulatory pathways mediating second heart field (SHF) development. Here, we have examined the specific requirements for Nkx2-5 in the SHF progenitors. We show that Nkx2-5 potentiates Wnt signaling by regulating the expression of the R-spondin3 (Rspo3) gene during cardiogenesis. R-spondins are secreted factors and potent Wnt agonists that in part regulate stem cell proliferation. Our data show that Rspo3 is markedly downregulated in Nkx2-5 mutants and that Rspo3 expression is regulated by Nkx2-5. Conditional inactivation of Rspo3 in the Isl1 lineage resulted in embryonic lethality secondary to impaired development of SHF. More importantly, we find that Wnt signaling is significantly attenuated in Nkx2-5 mutants and that enhancing Wnt/ß-catenin signaling by pharmacological treatment or by transgenic expression of Rspo3 rescues the SHF defects in the conditional Nkx2-5(+/-) mutants. We have identified a previously unrecognized genetic link between Nkx2-5 and Wnt signaling that supports continued cardiac growth and proliferation during development. Identification of Rspo3 in cardiac development provides a new paradigm in temporal regulation of Wnt signaling by cardiac-specific transcription factors.
Assuntos
Coração/embriologia , Proteínas de Homeodomínio/fisiologia , Trombospondinas/fisiologia , Fatores de Transcrição/fisiologia , Via de Sinalização Wnt , Animais , Sequência de Bases , Linhagem da Célula , Proliferação de Células , Endocárdio/embriologia , Feminino , Regulação da Expressão Gênica no Desenvolvimento , Proteína Homeobox Nkx-2.5 , Proteínas de Homeodomínio/genética , Masculino , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Transgênicos , Dados de Sequência Molecular , Mutação , Regiões Promotoras Genéticas , Homologia de Sequência do Ácido Nucleico , Células-Tronco/citologia , Trombospondinas/genética , Fatores de Transcrição/genética , Proteínas Wnt/metabolismo , beta Catenina/metabolismoRESUMO
Secreted factors from the epicardium are believed to be important in directing heart ventricular cardiomyocyte proliferation and morphogenesis, although the specific factors involved have not been identified or characterized adequately. We found that IGF2 is the most prominent mitogen made by primary mouse embryonic epicardial cells and by a newly derived immortalized mouse embryonic epicardial cell line called MEC1. In vivo, Igf2 is expressed in the embryonic mouse epicardium during midgestation heart development. Using a whole embryo culture assay in the presence of inhibitors, we confirmed that IGF signaling is required to activate the ERK proliferation pathway in the developing heart, and that the epicardium is required for this response. Global disruption of the Igf2 gene, or conditional disruption of the two IGF receptor genes Igf1r and Insr together in the myocardium, each resulted in a significant decrease in ventricular wall proliferation and in ventricular wall hypoplasia. Ventricular cardiomyocyte proliferation in mutant embryos was restored to normal at E14.5, concurrent with the establishment of coronary circulation. Our results define IGF2 as a previously unexplored epicardial mitogen that is required for normal ventricular chamber development.
Assuntos
Proliferação de Células , Coração/embriologia , Fator de Crescimento Insulin-Like II/fisiologia , Miócitos Cardíacos/fisiologia , Animais , Proliferação de Células/efeitos dos fármacos , Células Cultivadas , Embrião de Mamíferos , Regulação da Expressão Gênica no Desenvolvimento/efeitos dos fármacos , Coração/efeitos dos fármacos , Ventrículos do Coração/citologia , Ventrículos do Coração/metabolismo , Fator de Crescimento Insulin-Like II/genética , Fator de Crescimento Insulin-Like II/metabolismo , Fator de Crescimento Insulin-Like II/farmacologia , Camundongos , Camundongos Endogâmicos ICR , Camundongos Transgênicos , Miocárdio/metabolismo , Miócitos Cardíacos/efeitos dos fármacos , Miócitos Cardíacos/metabolismo , RNA Interferente Pequeno/farmacologia , Receptor IGF Tipo 2/genética , Receptor IGF Tipo 2/metabolismo , Receptor IGF Tipo 2/fisiologia , Transdução de Sinais/efeitos dos fármacos , Transdução de Sinais/genética , Transdução de Sinais/fisiologiaRESUMO
Epicardial signaling and Rxra are required for expansion of the ventricular myocardial compact zone. Here, we examine Raldh2(-/-) and Rxra(-/-) mouse embryos to investigate the role of retinoic acid (RA) signaling in this developmental process. The heart phenotypes of Raldh2 and Rxra mutants are very similar and are characterized by a prominent defect in ventricular compact zone growth. Although RA activity is completely lost in Raldh2(-/-) epicardium and the adjacent myocardium, RA activity is not lost in Rxra(-/-) hearts, suggesting that RA signaling in the epicardium/myocardium is not required for myocardial compact zone formation. We explored the possibility that RA-mediated target gene transcription in non-cardiac tissues is required for this process. We found that hepatic expression of erythropoietin (EPO), a secreted factor implicated in myocardial expansion, is dependent on both Raldh2 and Rxra. Chromatin immunoprecipitation studies support Epo as a direct target of RA signaling in embryonic liver. Treatment of an epicardial cell line with EPO, but not RA, upregulates Igf2. Furthermore, both Raldh2(-/-) and Rxra(-/-) hearts exhibit downregulation of Igf2 mRNA in the epicardium. EPO treatment of cultured Raldh2(-/-) hearts restores epicardial Igf2 expression and rescues ventricular cardiomyocyte proliferation. We propose a new model for the mechanism of RA-mediated myocardial expansion in which RA directly induces hepatic Epo resulting in activation of epicardial Igf2 that stimulates compact zone growth. This RA-EPO-IGF2 signaling axis coordinates liver hematopoiesis with heart development.
Assuntos
Eritropoetina/metabolismo , Fator de Crescimento Insulin-Like II/metabolismo , Miocárdio/metabolismo , Pericárdio/metabolismo , Tretinoína/farmacologia , Aldeído Oxirredutases/genética , Aldeído Oxirredutases/metabolismo , Animais , Células Cultivadas , Imunoprecipitação da Cromatina , Eritropoetina/genética , Coração/efeitos dos fármacos , Coração/embriologia , Imuno-Histoquímica , Hibridização In Situ , Fator de Crescimento Insulin-Like II/genética , Ceratolíticos/farmacologia , Fígado/efeitos dos fármacos , Fígado/metabolismo , Camundongos , Camundongos Transgênicos , Técnicas de Cultura de Órgãos , Pericárdio/efeitos dos fármacos , Receptor X Retinoide alfa/genética , Receptor X Retinoide alfa/metabolismo , Reação em Cadeia da Polimerase Via Transcriptase ReversaRESUMO
During development, sympathetic neurons extend axons along a myriad of distinct trajectories, often consisting of arteries, to innervate one of a large variety of distinct final target tissues. Whether or not subsets of neurons within complex sympathetic ganglia are predetermined to innervate select end-organs is unknown. Here we demonstrate in mouse embryos that the endothelin family member Edn3 (ref. 1), acting through the endothelin receptor EdnrA (refs 2, 3), directs extension of axons of a subset of sympathetic neurons from the superior cervical ganglion to a preferred intermediate target, the external carotid artery, which serves as the gateway to select targets, including the salivary glands. These findings establish a previously unknown mechanism of axonal pathfinding involving vascular-derived endothelins, and have broad implications for endothelins as general mediators of axonal growth and guidance in the developing nervous system. Moreover, they suggest a model in which newborn sympathetic neurons distinguish and choose between distinct vascular trajectories to innervate their appropriate end organs.
Assuntos
Axônios/fisiologia , Artérias Carótidas/metabolismo , Endotelinas/metabolismo , Transdução de Sinais , Gânglio Cervical Superior/citologia , Animais , Artérias Carótidas/citologia , Sinais (Psicologia) , Embrião de Mamíferos/irrigação sanguínea , Embrião de Mamíferos/citologia , Endotelina-3/metabolismo , Camundongos , Neuritos/fisiologia , Receptores de Endotelina/metabolismo , Glândulas Salivares/inervação , Gânglio Cervical Superior/metabolismoRESUMO
Most mammalian cardiomyocytes become polyploid in the neonatal period, concurrent with their loss of proliferative capacity. In mice, natural or engineered mutation of the cardiomyocyte-specific kinase gene Tnni3k causes a higher level of diploid CMs and a higher capacity to support proliferation after adult injury. Here, we identified a polymorphism in the canine Tnni3k gene that is particularly common in the West Highland White Terrier breed, and show that this variant eliminates Tnni3k kinase activity. Thus, in several species, natural Tnni3k polymorphisms exist that are predicted to contribute to variation in diploid CM level and heart regenerative ability.
RESUMO
Mammalian cardiomyocytes (CMs) mostly become polyploid shortly after birth. Because this feature may relate to several aspects of heart biology, including regeneration after injury, the mechanisms that cause polyploidy are of interest. BALB/cJ and BALB/cByJ mice are highly related sister strains that diverge substantially in CM ploidy. We identified a large deletion in the Cyth1 gene that arose uniquely in BALB/cByJ mice that creates a null allele. The deletion also results in ectopic transcription of the downstream gene Dnah17, although this transcript is unlikely to encode a protein. By evaluating the natural null allele from BALB/cByJ and an engineered knockout allele in the C57BL/6J background, we determined that absence of Cyth1 does not by itself influence CM ploidy. The ready availability of BALB/cByJ mice may be helpful to other investigations of Cyth1 in other biological processes.