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In humans and in mice the formation of nephrons during embryonic development reaches completion near the end of gestation, after which no new nephrons are formed. The final nephron complement can vary 10-fold, with reduced nephron number predisposing individuals to hypertension, renal, and cardiovascular diseases in later life. While the heterochronic genes lin28 and let-7 are well-established regulators of developmental timing in invertebrates, their role in mammalian organogenesis is not fully understood. Here we report that the Lin28b/let-7 axis controls the duration of kidney development in mice. Suppression of let-7 miRNAs, directly or via the transient overexpression of LIN28B, can prolong nephrogenesis and enhance kidney function potentially via upregulation of the Igf2/H19 locus. In contrast, kidney-specific loss of Lin28b impairs renal development. Our study reveals mechanisms regulating persistence of nephrogenic mesenchyme and provides a rationale for therapies aimed at increasing nephron mass.
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Proteínas de Unión al ADN/metabolismo , Riñón/embriología , MicroARNs/metabolismo , Proteínas de Unión al ARN/metabolismo , Animales , Femenino , Factor II del Crecimiento Similar a la Insulina/metabolismo , Riñón/metabolismo , Pruebas de Función Renal , Masculino , Ratones Transgénicos , ARN Largo no Codificante/metabolismoRESUMEN
The heterochronic genes Lin28a/b and let-7 regulate invertebrate development, but their functions in patterning the mammalian body plan remain unexplored. Here, we describe how Lin28/let-7 influence caudal vertebrae number during body axis formation. We found that FoxD1-driven overexpression of Lin28a strikingly increased caudal vertebrae number and tail bud cell proliferation, whereas its knockout did the opposite. Lin28a overexpression downregulated the neural marker Sox2, causing a pro-mesodermal phenotype with a decreased proportion of neural tissue relative to nascent mesoderm. Manipulating Lin28a and let-7 led to opposite effects, and manipulating Lin28a's paralog, LIN28B caused similar yet distinct phenotypes. These findings suggest that Lin28/let-7 play a role in the regulation of tail length through heterochrony of the body plan. We propose that the Lin28/let-7 pathway controls the pool of caudal progenitors during tail development, promoting their self-renewal and balancing neural versus mesodermal cell fate decisions.
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MicroARNs/metabolismo , Morfogénesis/fisiología , Proteínas de Unión al ARN/metabolismo , Animales , Diferenciación Celular/genética , Diferenciación Celular/fisiología , Proliferación Celular/fisiología , Mamíferos/metabolismo , Ratones Transgénicos , MicroARNs/genética , Proteínas de Unión al ARN/genéticaRESUMEN
An explosion of findings driven by powerful new technologies has expanded our understanding of microglia, the resident immune cells of the central nervous system (CNS). This wave of discoveries has fueled a growing interest in the roles that these cells play in the development of the CNS and in the neuropathology of a diverse array of disorders. In this review, we discuss the crucial roles that microglia play in shaping the brain-from their influence on neurons and glia within the developing CNS to their roles in synaptic maturation and brain wiring-as well as some of the obstacles to overcome when assessing their contributions to normal brain development. Furthermore, we examine how normal developmental functions of microglia are perturbed or remerge in neurodevelopmental and neurodegenerative disease.
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Encéfalo/crecimiento & desarrollo , Sistema Nervioso Central/crecimiento & desarrollo , Microglía/metabolismo , Neuronas/metabolismo , Animales , Encéfalo/metabolismo , Encéfalo/patología , Sistema Nervioso Central/metabolismo , Sistema Nervioso Central/patología , Humanos , Microglía/patología , Enfermedades Neurodegenerativas , Neuroglía/metabolismo , Neuroglía/patología , Neuronas/patología , Transducción de Señal/genéticaRESUMEN
Extracellular proTGF-ß is covalently linked to "milieu" molecules in the matrix or on cell surfaces and is latent until TGF-ß is released by integrins. Here, we show that LRRC33 on the surface of microglia functions as a milieu molecule and enables highly localized, integrin-αVß8-dependent TGF-ß activation. Lrrc33-/- mice lack CNS vascular abnormalities associated with deficiency in TGF-ß-activating integrins but have microglia with a reactive phenotype and after 2 months develop ascending paraparesis with loss of myelinated axons and death by 5 months. Whole bone marrow transplantation results in selective repopulation of Lrrc33-/- brains with WT microglia and halts disease progression. The phenotypes of WT and Lrrc33-/- microglia in the same brain suggest that there is little spreading of TGF-ß activated from one microglial cell to neighboring microglia. Our results suggest that interactions between integrin-bearing cells and cells bearing milieu molecule-associated TGF-ß provide localized and selective activation of TGF-ß.
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Proteínas Portadoras/metabolismo , Microglía/metabolismo , Sistema Nervioso/metabolismo , Factor de Crecimiento Transformador beta/metabolismo , Animales , Axones/metabolismo , Trasplante de Médula Ósea , Encéfalo/metabolismo , Proteínas Portadoras/clasificación , Proteínas Portadoras/genética , Células Cultivadas , Integrinas/metabolismo , Estimación de Kaplan-Meier , Macrófagos/citología , Macrófagos/inmunología , Macrófagos/metabolismo , Ratones , Ratones Endogámicos C57BL , Ratones Noqueados , Microglía/citología , Mutagénesis Sitio-Dirigida , Enfermedades Neurodegenerativas/mortalidad , Enfermedades Neurodegenerativas/patología , Enfermedades Neurodegenerativas/terapia , Filogenia , Unión Proteica , Precursores de Proteínas/genética , Precursores de Proteínas/metabolismo , Factor de Crecimiento Transformador beta/genéticaRESUMEN
Lin28a/b are RNA-binding proteins that influence stem cell maintenance, metabolism, and oncogenesis. Poorly differentiated, aggressive cancers often overexpress Lin28, but its role in tumor initiation or maintenance has not been definitively addressed. We report that LIN28B overexpression is sufficient to initiate hepatoblastoma and hepatocellular carcinoma in murine models. We also detected Lin28b overexpression in MYC-driven hepatoblastomas, and liver-specific deletion of Lin28a/b reduced tumor burden, extended latency, and prolonged survival. Both intravenous siRNA against Lin28b and conditional Lin28b deletion reduced tumor burden and prolonged survival. Igf2bp proteins are upregulated, and Igf2bp3 is required in the context of LIN28B overexpression to promote growth. Therefore, multiple murine models demonstrate that Lin28b is both sufficient to initiate liver cancer and necessary for its maintenance.
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Carcinogénesis/metabolismo , Hepatoblastoma/metabolismo , Neoplasias Hepáticas Experimentales/metabolismo , Proteínas de Unión al ARN/fisiología , Animales , Hepatoblastoma/patología , Humanos , Neoplasias Hepáticas Experimentales/patología , Ratones , Ratones Transgénicos , Oncogenes , Proteínas Proto-Oncogénicas c-myc/metabolismo , Proteínas de Unión al ARN/metabolismo , Carga TumoralRESUMEN
Factor-induced reprogramming of somatic cells into induced pluripotent stem cells (iPSCs) is inefficient, complicating mechanistic studies. Here, we examined defined intermediate cell populations poised to becoming iPSCs by genome-wide analyses. We show that induced pluripotency elicits two transcriptional waves, which are driven by c-Myc/Klf4 (first wave) and Oct4/Sox2/Klf4 (second wave). Cells that become refractory to reprogramming activate the first but fail to initiate the second transcriptional wave and can be rescued by elevated expression of all four factors. The establishment of bivalent domains occurs gradually after the first wave, whereas changes in DNA methylation take place after the second wave when cells acquire stable pluripotency. This integrative analysis allowed us to identify genes that act as roadblocks during reprogramming and surface markers that further enrich for cells prone to forming iPSCs. Collectively, our data offer new mechanistic insights into the nature and sequence of molecular events inherent to cellular reprogramming.
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Reprogramación Celular , Técnicas Citológicas/métodos , Células Madre Pluripotentes Inducidas/citología , Animales , Estudio de Asociación del Genoma Completo , Humanos , Células Madre Pluripotentes Inducidas/metabolismo , Factor 4 Similar a Kruppel , Ratones , Factores de Transcripción/metabolismoRESUMEN
The field of stem-cell biology has been catapulted forward by the startling development of reprogramming technology. The ability to restore pluripotency to somatic cells through the ectopic co-expression of reprogramming factors has created powerful new opportunities for modelling human diseases and offers hope for personalized regenerative cell therapies. While the field is racing ahead, some researchers are pausing to evaluate whether induced pluripotent stem cells are indeed the true equivalents of embryonic stem cells and whether subtle differences between these types of cell might affect their research applications and therapeutic potential.