RESUMEN
Thousands of small proteins, called microproteins, are encoded in small open reading frames (smORFs) throughout the genome. Despite assumptions that these proteins would be too small to properly fold and function, a recent study by Chen et al. identifies the surprisingly complex roles of one such microprotein.
Asunto(s)
Genoma , Proteínas , Proteínas/genética , Sistemas de Lectura Abierta/genéticaRESUMEN
Regeneration is a complex chain of events that restores a tissue to its original size and shape. The tissue-wide coordination of cellular dynamics that is needed for proper morphogenesis is challenged by the large dimensions of regenerating body parts. Feedback mechanisms in biochemical pathways can provide effective communication across great distances1-5, but how they might regulate growth during tissue regeneration is unresolved6,7. Here we report that rhythmic travelling waves of Erk activity control the growth of bone in time and space in regenerating zebrafish scales, millimetre-sized discs of protective body armour. We find that waves of Erk activity travel across the osteoblast population as expanding concentric rings that are broadcast from a central source, inducing ring-like patterns of tissue growth. Using a combination of theoretical and experimental analyses, we show that Erk activity propagates as excitable trigger waves that are able to traverse the entire scale in approximately two days and that the frequency of wave generation controls the rate of scale regeneration. Furthermore, the periodic induction of synchronous, tissue-wide activation of Erk in place of travelling waves impairs tissue growth, which indicates that wave-distributed Erk activation is key to regeneration. Our findings reveal trigger waves as a regulatory strategy to coordinate cell behaviour and instruct tissue form during regeneration.
Asunto(s)
Quinasas MAP Reguladas por Señal Extracelular/metabolismo , Sistema de Señalización de MAP Quinasas , Osteoblastos/citología , Osteoblastos/metabolismo , Regeneración , Pez Cebra/fisiología , Escamas de Animales/citología , Escamas de Animales/enzimología , Escamas de Animales/crecimiento & desarrollo , Escamas de Animales/fisiología , Animales , Difusión , Femenino , Masculino , Pez Cebra/crecimiento & desarrolloRESUMEN
How tissue regeneration programs are triggered by injury has received limited research attention. Here we investigate the existence of enhancer regulatory elements that are activated in regenerating tissue. Transcriptomic analyses reveal that leptin b (lepb) is highly induced in regenerating hearts and fins of zebrafish. Epigenetic profiling identified a short DNA sequence element upstream and distal to lepb that acquires open chromatin marks during regeneration and enables injury-dependent expression from minimal promoters. This element could activate expression in injured neonatal mouse tissues and was divisible into tissue-specific modules sufficient for expression in regenerating zebrafish fins or hearts. Simple enhancer-effector transgenes employing lepb-linked sequences upstream of pro- or anti-regenerative factors controlled the efficacy of regeneration in zebrafish. Our findings provide evidence for 'tissue regeneration enhancer elements' (TREEs) that trigger gene expression in injury sites and can be engineered to modulate the regenerative potential of vertebrate organs.
Asunto(s)
Elementos de Facilitación Genéticos/genética , Especificidad de Órganos/genética , Regeneración/genética , Regeneración/fisiología , Cicatrización de Heridas/genética , Pez Cebra/genética , Pez Cebra/fisiología , Acetilación , Aletas de Animales/lesiones , Aletas de Animales/metabolismo , Animales , Animales Recién Nacidos , Proliferación Celular , Ensamble y Desensamble de Cromatina/genética , Epigénesis Genética/genética , Femenino , Perfilación de la Expresión Génica , Regulación de la Expresión Génica/genética , Corazón , Histonas/química , Histonas/metabolismo , Leptina/biosíntesis , Leptina/genética , Lisina/metabolismo , Masculino , Ratones , Miocitos Cardíacos/citología , Regiones Promotoras Genéticas/genética , Transgenes/genética , Proteínas de Pez Cebra/genéticaRESUMEN
The blastema is a mass of progenitor cells responsible for regeneration of amputated salamander limbs and fish fins. Previous studies have indicated that resident cell sources producing the blastema contribute lineage-restricted progeny to regenerating tissue. However, these studies have labeled general cell types rather than granular cell subpopulations, and they do not explain the developmental transitions that must occur for distal structures to arise from cells with proximal identities in the appendage stump. Here, we find that regulatory sequences of tph1b, which encodes an enzyme that synthesizes serotonin, mark a subpopulation of fibroblast-like cells restricted to the joints of uninjured adult zebrafish fins. Amputation stimulates serotonin production in regenerating fin fibroblasts, yet targeted tph1b mutations abrogating this response do not disrupt fin regeneration. In uninjured animals, tph1b-expressing cells contribute fibroblast progeny that remain restricted to joints throughout life. By contrast, upon amputation, tph1b+ joint cells give rise to fibroblasts that distribute across the entire lengths of regenerating fin rays. Our experiments visualize and quantify how incorporation into an appendage blastema broadens the progeny contributions of a cellular subpopulation that normally has proximodistal restrictions.
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Fibroblastos/citología , Regeneración/fisiología , Aletas de Animales/citología , Aletas de Animales/metabolismo , Animales , Fibroblastos/metabolismo , Articulaciones/metabolismo , Articulaciones/fisiología , Regeneración/genética , Pez CebraRESUMEN
The orchestrated division of cardiomyocytes assembles heart chambers of distinct morphology. To understand the structural divergence of the cardiac chambers, we determined the contributions of individual embryonic cardiomyocytes to the atrium in zebrafish by multicolor fate-mapping and we compare our analysis to the established proliferation dynamics of ventricular cardiomyocytes. We find that most atrial cardiomyocytes become rod-shaped in the second week of life, generating a single-muscle-cell-thick myocardial wall with a striking webbed morphology. Inner pectinate myofibers form mainly by direct branching, unlike delamination events that create ventricular trabeculae. Thus, muscle clones assembling the atrial chamber can extend from wall to lumen. As zebrafish mature, atrial wall cardiomyocytes proliferate laterally to generate cohesive patches of diverse shapes and sizes, frequently with dominant clones that comprise 20-30% of the wall area. A subpopulation of cardiomyocytes that transiently express atrial myosin heavy chain (amhc) contributes substantially to specific regions of the ventricle, suggesting an unappreciated level of plasticity during chamber formation. Our findings reveal proliferation dynamics and fate decisions of cardiomyocytes that produce the distinct architecture of the atrium.
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Atrios Cardíacos/citología , Atrios Cardíacos/crecimiento & desarrollo , Imagenología Tridimensional , Miocitos Cardíacos/citología , Pez Cebra/crecimiento & desarrollo , Animales , Animales Modificados Genéticamente , Proliferación Celular , Células Clonales , Femenino , Ventrículos Cardíacos/crecimiento & desarrollo , Larva/metabolismo , Masculino , Músculos/metabolismo , Miocardio/metabolismo , Coloración y EtiquetadoRESUMEN
Many fish and salamander species regenerate amputated fins or limbs, restoring the size and shape of the original appendage. Regeneration requires that spared cells retain or recall information encoding pattern, a phenomenon termed positional memory. Few factors have been implicated in positional memory during vertebrate appendage regeneration. Here, we investigated potential regulators of anteroposterior (AP) pattern during fin regeneration in adult zebrafish. Sequence-based profiling from tissues along the AP axis of uninjured pectoral fins identified many genes with region-specific expression, several of which encoded transcription factors with known AP-specific expression or function in developing embryonic pectoral appendages. Transgenic reporter strains revealed that regulatory sequences of the transcription factor gene alx4a activated expression in fibroblasts and osteoblasts within anterior fin rays, whereas hand2 regulatory sequences activated expression in these same cell types within posterior rays. Transgenic overexpression of hand2 in all pectoral fin rays did not affect formation of the proliferative regeneration blastema, yet modified the lengths and widths of regenerating bones. Hand2 influenced the character of regenerated rays in part by elevation of the vitamin D-inactivating enzyme encoded by cyp24a1, contributing to region-specific regulation of bone metabolism. Systemic administration of vitamin D during regeneration partially rescued bone defects resulting from hand2 overexpression. Thus, bone-forming cells in a regenerating appendage maintain expression throughout life of transcription factor genes that can influence AP pattern, and differ across the AP axis in their expression signatures of these and other genes. These findings have implications for mechanisms of positional memory in vertebrate tissues.
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Aletas de Animales/crecimiento & desarrollo , Tipificación del Cuerpo/genética , Regeneración/genética , Transcripción Genética , Pez Cebra/crecimiento & desarrollo , Pez Cebra/genética , Animales , Factores de Transcripción con Motivo Hélice-Asa-Hélice Básico/genética , Factores de Transcripción con Motivo Hélice-Asa-Hélice Básico/metabolismo , Huesos/anatomía & histología , Fibroblastos/metabolismo , Regulación del Desarrollo de la Expresión Génica , Masculino , Modelos Biológicos , Especificidad de Órganos/genética , Osteoblastos/metabolismo , Transducción de Señal/genética , Vitamina D/metabolismo , Proteínas de Pez Cebra/genética , Proteínas de Pez Cebra/metabolismoRESUMEN
The capacity for embryonic cells to differentiate relies on a large-scale reprogramming of the oocyte and sperm nucleus into a transient totipotent state. In zebrafish, this reprogramming step is achieved by the pioneer factors Nanog, Pou5f3, and Sox19b (NPS). Yet, it remains unclear whether cells lacking this reprogramming step are directed towards wild type states or towards novel developmental canals in the Waddington landscape of embryonic development. Here we investigate the developmental fate of embryonic cells mutant for NPS by analyzing their single-cell gene expression profiles. We find that cells lacking the first developmental reprogramming steps can acquire distinct cell states. These states are manifested by gene expression modules that result from a failure of nuclear reprogramming, the persistence of the maternal program, and the activation of somatic compensatory programs. As a result, most mutant cells follow new developmental canals and acquire new mixed cell states in development. In contrast, a group of mutant cells acquire primordial germ cell-like states, suggesting that NPS-dependent reprogramming is dispensable for these cell states. Together, these results demonstrate that developmental reprogramming after fertilization is required to differentiate most canonical developmental programs, and loss of the transient totipotent state canalizes embryonic cells into new developmental states in vivo.
RESUMEN
Bioethics is the formal study of ethical judgments concerning the advances and applications of biology, medicine and related technologies. In a time of unprecedented biomedical advances, it is critical to integrate bioethical frameworks more fully into biomedical research to align these scientific advances with their intended societal needs. In this Perspective, we describe some motivations and frameworks for cross-disciplinary bioethical training for biomedical researchers, and discuss how actively considering bioethics in research and study design could maximize biomedical researchers' intended impacts in society.
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Bioética , Investigación Biomédica , Humanos , Proyectos de Investigación , InvestigadoresRESUMEN
Thousands of long intergenic non-coding RNAs (lincRNAs) are transcribed throughout the vertebrate genome. A subset of lincRNAs enriched in developing brains have recently been found to contain cryptic open-reading frames and are speculated to encode micropeptides. However, systematic identification and functional assessment of these transcripts have been hindered by technical challenges caused by their small size. Here, we show that two putative lincRNAs (linc-mipep, also called lnc-rps25, and linc-wrb) encode micropeptides with homology to the vertebrate-specific chromatin architectural protein, Hmgn1, and demonstrate that they are required for development of vertebrate-specific brain cell types. Specifically, we show that NMDA receptor-mediated pathways are dysregulated in zebrafish lacking these micropeptides and that their loss preferentially alters the gene regulatory networks that establish cerebellar cells and oligodendrocytes - evolutionarily newer cell types that develop postnatally in humans. These findings reveal a key missing link in the evolution of vertebrate brain cell development and illustrate a genetic basis for how some neural cell types are more susceptible to chromatin disruptions, with implications for neurodevelopmental disorders and disease.
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ARN Largo no Codificante , Animales , Humanos , ARN Largo no Codificante/genética , Cromatina , Pez Cebra/genética , Pez Cebra/metabolismo , Diferenciación Celular/genética , MicropéptidosRESUMEN
A cell's identity is commonly regarded as its transcriptomic profile. In this issue of Developmental Cell, Fujii et al. (2021) show that a global translation factor subunit acts differentially on transcripts to modulate morphogen signaling levels, revealing a global mechanism of transcript-specific translational control in development.
RESUMEN
Attaining proper organ size during development and regeneration hinges on the activity of mitogenic factors. Here, we performed a large-scale chemical screen in embryonic zebrafish to identify cardiomyocyte mitogens. Although commonly considered anti-proliferative, vitamin D analogs like alfacalcidol had rapid, potent mitogenic effects on embryonic and adult cardiomyocytes in vivo. Moreover, pharmacologic or genetic manipulation of vitamin D signaling controlled proliferation in multiple adult cell types and dictated growth rates in embryonic and juvenile zebrafish. Tissue-specific modulation of vitamin D receptor (VDR) signaling had organ-restricted effects, with cardiac VDR activation causing cardiomegaly. Alfacalcidol enhanced the regenerative response of injured zebrafish hearts, whereas VDR blockade inhibited regeneration. Alfacalcidol activated cardiac expression of genes associated with ErbB2 signaling, while ErbB2 inhibition blunted its effects on cell proliferation. Our findings identify vitamin D as mitogenic for cardiomyocytes and other cell types in zebrafish and indicate a mechanism to regulate organ size and regeneration.
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Corazón/anatomía & histología , Corazón/fisiología , Miocitos Cardíacos/citología , Regeneración/efectos de los fármacos , Vitamina D/farmacología , Pez Cebra/anatomía & histología , Pez Cebra/fisiología , Animales , Ciclo Celular/efectos de los fármacos , Proliferación Celular/efectos de los fármacos , Embrión no Mamífero/citología , Embrión no Mamífero/efectos de los fármacos , Corazón/efectos de los fármacos , Mitógenos/farmacología , Miocitos Cardíacos/efectos de los fármacos , Miocitos Cardíacos/metabolismo , Tamaño de los Órganos/efectos de los fármacos , Especificidad de Órganos , Transducción de Señal/efectos de los fármacos , Pez Cebra/embriología , Proteínas de Pez Cebra/metabolismoRESUMEN
Osteoblasts are matrix-depositing cells that can divide and heal bone injuries. Their deep-tissue location and the slow progression of bone regeneration challenge attempts to capture osteoblast behaviors in live tissue at high spatiotemporal resolution. Here, we have developed an imaging platform to monitor and quantify individual and collective behaviors of osteoblasts in adult zebrafish scales, skeletal body armor discs that regenerate rapidly after loss. Using a panel of transgenic lines that visualize and manipulate osteoblasts, we find that a founder pool of osteoblasts emerges through de novo differentiation within one day of scale plucking. These osteoblasts undergo division events that are largely uniform in frequency and orientation to establish a primordium. Osteoblast proliferation dynamics diversify across the primordium by two days after injury, with cell divisions focused near, and with orientations parallel to, the scale periphery, occurring coincident with dynamic localization of fgf20a gene expression. In posterior scale regions, cell elongation events initiate in areas soon occupied by mineralized grooves called radii, beginning approximately 2 days post injury, with patterned osteoblast death events accompanying maturation of these radii. By imaging at single-cell resolution, we detail acquisition of spatiotemporally distinct cell division, motility, and death dynamics within a founder osteoblast pool as bone regenerates.
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Regeneración Ósea/fisiología , Imagen Óptica/métodos , Osteoblastos/fisiología , Análisis de la Célula Individual/métodos , Pez Cebra/fisiología , Animales , Animales Modificados Genéticamente , Diferenciación Celular , División CelularRESUMEN
The blastema is a mass of progenitor cells that enables regeneration of amputated salamander limbs or fish fins. Methodology to label and track blastemal cell progeny has been deficient, restricting our understanding of appendage regeneration. Here, we created a system for clonal analysis and quantitative imaging of hundreds of blastemal cells and their respective progeny in living adult zebrafish undergoing fin regeneration. Amputation stimulates resident cells within a limited recruitment zone to reset proximodistal (PD) positional information and assemble the blastema. Within the newly formed blastema, the spatial coordinates of connective tissue progenitors are predictive of their ultimate contributions to regenerated skeletal structures, indicating early development of an approximate PD pre-pattern. Calcineurin regulates size recovery by controlling the average number of progeny divisions without disrupting this pre-pattern. Our longitudinal clonal analyses of regenerating zebrafish fins provide evidence that connective tissue progenitors are rapidly organized into a scalable blueprint of lost structures.
Asunto(s)
Aletas de Animales/fisiología , Regeneración , Pez Cebra/fisiología , Animales , Calcineurina/metabolismo , Femenino , Masculino , Células Madre , Proteínas de Pez Cebra/metabolismoRESUMEN
Regeneration of a lost appendage in adult amphibians and fish is a remarkable feat of developmental patterning. Although the limb or fin may be years removed from its initial creation by an embryonic primordium, the blastema that emerges at the injury site fashions a close mimic of adult form. Central to understanding these events are revealing the cellular origins of new structures, how positional identity is maintained, and the determinants for completion. Each of these topics has been advanced recently, strengthening models for how complex tissue pattern is recalled in the adult context.