RESUMEN
In metazoans, transition from fetal to adult heart is accompanied by a switch in energy metabolism-glycolysis to fatty acid oxidation. The molecular factors regulating this metabolic switch remain largely unexplored. We first demonstrate that the molecular signatures in 1-year (y) matured human embryonic stem cell-derived cardiomyocytes (hESC-CMs) are similar to those seen in in vivo-derived mature cardiac tissues, thus making them an excellent model to study human cardiac maturation. We further show that let-7 is the most highly up-regulated microRNA (miRNA) family during in vitro human cardiac maturation. Gain- and loss-of-function analyses of let-7g in hESC-CMs demonstrate it is both required and sufficient for maturation, but not for early differentiation of CMs. Overexpression of let-7 family members in hESC-CMs enhances cell size, sarcomere length, force of contraction, and respiratory capacity. Interestingly, large-scale expression data, target analysis, and metabolic flux assays suggest this let-7-driven CM maturation could be a result of down-regulation of the phosphoinositide 3 kinase (PI3K)/AKT protein kinase/insulin pathway and an up-regulation of fatty acid metabolism. These results indicate let-7 is an important mediator in augmenting metabolic energetics in maturing CMs. Promoting maturation of hESC-CMs with let-7 overexpression will be highly significant for basic and applied research.
Asunto(s)
MicroARNs/genética , MicroARNs/metabolismo , Miocitos Cardíacos/citología , Miocitos Cardíacos/metabolismo , Adulto , Diferenciación Celular/genética , Línea Celular , Células Madre Embrionarias/citología , Células Madre Embrionarias/metabolismo , Metabolismo Energético , Regulación del Desarrollo de la Expresión Génica , Humanos , Modelos Cardiovasculares , Contracción Miocárdica , Miocitos Cardíacos/fisiología , Transducción de Señal , Ingeniería de Tejidos , Regulación hacia ArribaRESUMEN
The simple structure of Arabidopsis roots provides an excellent model system to study epidermal cell fate specification. Epidermal cells in contact with 2 underlying cortical cells differentiate into hair cells (H cells; trichoblasts), whereas cells that contact only a single cortical cell differentiate into mature hairless cells (N cells; atrichoblasts). This position-dependent patterning, in combination with the constrained orientation of cell divisions, results in hair and nonhair cell files running longitudinally along the root epidermis. Here, we present strong evidence that steroid hormones called brassinosteroids (BRs) are required to maintain position-dependent fate specification in roots. We show that BRs are required for normal expression levels and patterns of WEREWOLF (WER) and GLABRA2 (GL2), master regulators of epidermal patterning. Loss of BR signaling results in loss of hair cells in H positions, likely as a consequence of reduced expression of CAPRICE (CPC), a direct downstream target of WER. Our observations demonstrate that in addition to their well-known role in cell expansion, BRs play an essential role in directing cell fate.
Asunto(s)
Arabidopsis/citología , Arabidopsis/metabolismo , Raíces de Plantas/metabolismo , Esteroides/metabolismo , Proteínas de Arabidopsis/metabolismo , Diferenciación Celular , División Celular , Linaje de la Célula , Cicloheximida/farmacología , Regulación de la Expresión Génica de las Plantas , Modelos Biológicos , Fenotipo , Proteínas de Plantas/metabolismo , Reacción en Cadena de la Polimerasa de Transcriptasa Inversa , Transducción de SeñalRESUMEN
The postembryonic development of lateral roots and nodules is a highly regulated process. Recent studies suggest the existence of cross talk and interdependency in the growth of these two organs. Although plant hormones, including auxin and cytokinin, appear to be key players in coordinating this cross talk, very few genes that cross-regulate root and nodule development have been uncovered so far. This study reports that a homolog of CELL DIVISION CYCLE16 (CDC16), a core component of the Anaphase Promoting Complex, is one of the key mediators in controlling the overall number of lateral roots and nodules. A partial suppression of this gene in Medicago truncatula leads to a decrease in number of lateral roots and a 4-fold increase in number of nodules. The roots showing lowered expression of MtCDC16 also show reduced sensitivity to phytohormone auxin, thus providing a potential function of CDC16 in auxin signaling.
Asunto(s)
Proteínas de Ciclo Celular/metabolismo , Ácidos Indolacéticos/metabolismo , Medicago truncatula/genética , Proteínas de Plantas/metabolismo , Nodulación de la Raíz de la Planta/genética , Nódulos de las Raíces de las Plantas/crecimiento & desarrollo , Secuencia de Aminoácidos , Proteínas de Ciclo Celular/genética , ADN de Plantas/genética , Regulación de la Expresión Génica de las Plantas , Técnicas de Silenciamiento del Gen , Medicago truncatula/citología , Medicago truncatula/crecimiento & desarrollo , Datos de Secuencia Molecular , Análisis de Secuencia por Matrices de Oligonucleótidos , Reguladores del Crecimiento de las Plantas/metabolismo , Proteínas de Plantas/genética , Plantas Modificadas Genéticamente/citología , Plantas Modificadas Genéticamente/genética , Plantas Modificadas Genéticamente/crecimiento & desarrollo , Interferencia de ARN , Análisis de Secuencia de ADNRESUMEN
Pluripotent stem cells have distinct metabolic requirements, and reprogramming cells to pluripotency requires a shift from oxidative to glycolytic metabolism. Here, we show that this shift occurs early during reprogramming of human cells and requires hypoxia-inducible factors (HIFs) in a stage-specific manner. HIF1α and HIF2α are both necessary to initiate this metabolic switch and for the acquisition of pluripotency, and the stabilization of either protein during early phases of reprogramming is sufficient to induce the switch to glycolytic metabolism. In contrast, stabilization of HIF2α during later stages represses reprogramming, partly because of the upregulation of TNF-related apoptosis-inducing ligand (TRAIL). TRAIL inhibits induced pluripotent stem cell (iPSC) generation by repressing apoptotic caspase 3 activity specifically in cells undergoing reprogramming but not human embryonic stem cells (hESCs), and inhibiting TRAIL activity enhances human iPSC generation. These results shed light on the mechanisms underlying the metabolic shifts associated with the acquisition of a pluripotent identity during reprogramming.
Asunto(s)
Factores de Transcripción con Motivo Hélice-Asa-Hélice Básico/metabolismo , Reprogramación Celular/fisiología , Factores de Transcripción con Motivo Hélice-Asa-Hélice Básico/genética , Caspasa 3/genética , Caspasa 3/metabolismo , Células Cultivadas , Reprogramación Celular/genética , Células Madre Embrionarias/citología , Células Madre Embrionarias/metabolismo , Fibroblastos , Humanos , Subunidad alfa del Factor 1 Inducible por Hipoxia/genética , Subunidad alfa del Factor 1 Inducible por Hipoxia/metabolismo , Células Madre Pluripotentes Inducidas/citología , Células Madre Pluripotentes Inducidas/metabolismo , ARN Interferente Pequeño , Ligando Inductor de Apoptosis Relacionado con TNF/genética , Ligando Inductor de Apoptosis Relacionado con TNF/metabolismo , Factores de TiempoRESUMEN
Recent studies suggest that hormones act through a web of interacting responses rather than through isolated linear pathways. This signal integration architecture may be one mechanism for increasing the specificity of outcomes in different cellular contexts. Several common themes for cross-regulation between pathways can be observed. Here, we propose a classification scheme for different levels of signaling pathway cross-regulation. This scheme is based on which parts of the individual pathways are acting as information conduits between pathways. Examples from the recent plant hormone biology literature are used to illustrate the different modes of interaction.
Asunto(s)
Reguladores del Crecimiento de las Plantas/fisiología , Fenómenos Fisiológicos de las Plantas , Ácido Abscísico/fisiología , Ciclopentanos/metabolismo , Giberelinas/metabolismo , Homeostasis , Ácidos Indolacéticos/metabolismo , Medicago/fisiología , Oxilipinas/metabolismo , Transducción de SeñalRESUMEN
Ethyl methanesulfonate mutagenesis of the model legume Medicago truncatula has previously identified several genes required for early steps in nodulation. Here, we describe a new mutant that is defective in intermediate steps of nodule differentiation. The lin (lumpy infections) mutant is characterized by a 4-fold reduction in the number of infections, all of which arrest in the root epidermis, and by nodule primordia that initiate normally but fail to mature. Genetic analyses indicate that the symbiotic phenotype is conferred by a single gene that maps to the lower arm of linkage group 1. Transcriptional markers for early Nod factor responses (RIP1 and ENOD40) are induced in lin, as is another early nodulin, ENOD20, a gene expressed during the differentiation of nodule primordia. By contrast, other markers correlated with primordium differentiation (CCS52A), infection progression (MtN6), or nodule morphogenesis (ENOD2 and ENOD8) show reduced or no induction in homozygous lin individuals. Taken together, these results suggest that LIN functions in maintenance of rhizobial infections and differentiation of nodules from nodule primordia.