SEARCH · Search bioRxiv

Results for “Developmental Biology”

Search indexed bioRxiv preprints in genomics, neuroscience, cell biology and bioinformatics. Read source abstracts and check manuscript versions; preprints are not peer reviewed.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 829 records · Page 46Linked to original sources

bioRxiv2018

Nucleoporin 133 deficiency leads to glomerular damage in zebrafish

Although structural nuclear pore proteins (nucleoporins) are seemingly required in every cell type to assemble a functional nuclear transport machinery, mutations or deregulation of a subset of them have been associated with specific human hereditary diseases. In particular, previous genetic studies of patients with nephrotic syndrome identified mutations in Nup107 that impaired the expression or the localization of its direct partner at nuclear pores, Nup133. In the present study, we characterized the zebrafish nup133 orthologous gene and its expression pattern during larval development. Morpholino-mediated gene knockdown revealed that Nup133 depletion in zebrafish larvae leads to the formation of kidney cysts, a phenotype that can be rescued by co-injection of wild type mRNA. Analysis of different markers for tubular and glomerular development shows that the overall kidney development is not affected by nup133 knockdown. On the other hand, we demonstrate that nup133 is essential for the organization and functional integrity of the pronephric glomerular filtration barrier, as its downregulation results in proteinuria and moderate foot process effacement, mimicking some of the abnormalities typically featured by patients with nephrotic syndrome. These data indicate that nup133 is a new gene required for proper glomerular structure and function in zebrafish.

developmental biology↗

bioRxiv2018

Hair Follicle Epidermal Stem Cells Define a Niche for Tactile Sensation

The heterogeneity and compartmentalization of stem cells is a common principle in many epithelia, and is known to function in epithelial maintenance, but its other physiological roles remain elusive. Here we show transcriptional and anatomical contributions of compartmentalized epidermal stem cells (EpSCs) in tactile sensory unit formation in the hair follicle (HF). EpSCs in the follicle upper-bulge, where mechanosensory lanceolate complexes (LCs) innervate, express a unique set of extracellular matrix (ECM) and neurogenesis-related genes. These EpSCs deposit an ECM protein EGFL6 into the collar matrix, a novel ECM that tightly ensheathes LCs. EGFL6 is required for the proper patterning, touch responses, and v integrin-enrichment of LCs. By maintaining a quiescent original EpSC niche, the old bulge, EpSCs provide anatomically stable HF-LC interfaces, irrespective of the stage of follicle regeneration cycle. Thus, compartmentalized EpSCs provide a niche linking the HF and the nervous system throughout the hair cycle.

developmental biology↗

bioRxiv2018

Cooption of antagonistic RNA-binding proteins establishes cell hierarchy in Drosophila neuro-developmental tumors

The mechanisms that govern the hierarchical organization of tumors are still poorly understood, especially in highly heterogeneous neural cancers. Previously, we had shown that aggressive neural tumors can be induced upon dedifferentiation of susceptible intermediate progenitors produced during early development (Narbonne-Reveau et al., 2016). Using clonal analysis, stochastic modelling and single-cell transcriptomics, we now find that such tumors rapidly become heterogeneous, containing progenitors with different proliferative potentials. We demonstrate that tumor heterogeneity emerges from the deregulated transition between two antagonistic RNA-binding proteins, Imp and Syncrip, that switch neural progenitors from a default self-renewing to a differentiation-prone state during development. Consequently, aberrant maintenance of Imp confers a cancer stem cell-like identity as Imp+ progenitors sustain tumor growth while being able to continuously generate Syncrip+ progenitors. The latter exhibit limited self-renewal likely due to Syncrip-mediated metabolic exhaustion. This study provides an example of how a subverted developmental transition establishes a hierarchical tumor.

developmental biology↗

bioRxiv2018

A novel mechanism of gland formation in zebrafish involving transdifferentiation of renal epithelial cells and live cell extrusion

Transdifferentiation is the poorly understood phenomenon whereby a terminally differentiated cell acquires a completely new identity. Here, we describe a rare example of a naturally occurring transdifferentiation in zebrafish in which kidney distal tubule epithelial cells are converted into an endocrine gland known as the Corpuscles of Stannius (CS). We find that this process requires Notch signalling and is associated with the cytoplasmic sequestration of the Hnf1b transcription factor, a master-regulator of renal tubule fate. A deficiency in the Irx3b transcription factor results in ectopic transdifferentiation of distal tubule cells to a CS identity but in a Notch-dependent fashion. Using live-cell imaging we show that CS cells undergo apical constriction en masse and are then extruded from the tubule to form a distinct organ. This system provides a valuable new model to understand the molecular and morphological basis of transdifferentiation and will advance efforts to exploit this rare phenomenon therapeutically.

developmental biology↗

bioRxiv2018

The mirtron miR-1010 functions in concert with its host gene SKIP to maintain synaptic homeostasis

Mirtrons are non-canonical miRNAs arising by splicing and debranching from short introns. A plethora of introns have been inferred by computational analyses as potential mirtrons. Yet, few have been experimentally validated and their functions, particularly in relation to their host genes, remain poorly understood. Here, we found that larvae lacking the mirtron miR-1010 are unable to grow properly and pupariate. We show that miR-1010 downregulates nAcR{beta}2. Increase of cortical nAcR{beta}2 mediated by neural activity elevates the level of intracellular Ca2+, which in turn activates CaMKII and, further downstream, the transcription factor Adf-1. We reveal that Adf-1 initiates the expression of SKIP, the host gene of miR-1010. Preventing synaptic potentials from overshooting their optimal range requires both SKIP to temper synaptic potentials (incoherent feedforward loop) and miR-1010 to reduce nAcR{beta}2 mRNA levels (negative feedback loop). Our results demonstrate how a mirtron, in coordination with its host gene, contributes to maintaining homeostasis.

developmental biology↗

bioRxiv2018

Drosophila small ovary encodes a zinc-finger repressor required for ovarian differentiation

Repression is essential for coordinated cell type-specific gene regulation and controlling the expression of transposons. In the Drosophila ovary, stem cell regeneration and differentiation requires controlled gene expression, with derepression leading to tissue degeneration and ovarian tumors. Likewise, the ovary is acutely sensitive to deleterious consequences of transposon derepression. The small ovary (sov) locus was identified in a female sterile screen, and mutants show dramatic ovarian morphogenesis defects. We mapped the locus to the uncharacterized gene CG14438, which encodes a zinc-finger protein that colocalizes with the essential Heterochromatin Protein 1 (HP1a). We demonstrate that Sov functions to repress inappropriate cell signaling, silence transposons, and suppress position-effect variegation in the eye, suggesting a central role in heterochromatin stabilization.

developmental biology↗

bioRxiv2018

Regulatory T-cells are required for neonatal heart regeneration

Previous work has elegantly demonstrated that, unlike adult mammalian heart, the neonatal heart is able to regenerate after injury from postnatal day (P) 1 to 7. Recently, macrophages are found to be required in the repair process as depletion of which abolishes endogenous regenerative capability of the neonatal heart. Nevertheless, whether innate immunity alone is sufficient for neonatal heart regeneration is obscure. Here, we investigate a hitherto novel role of FOXP3+ regulatory T-cells (Treg) in neonatal heart regeneration. Unlike their wild type counterparts, NOD/SCID mice that are deficient for T-cells but innate immune cells including macrophages fail to regenerate their injured heart as early as P3. In wild type mice, both conventional CD4+ T-cells and Treg are recruited to cardiac muscle within the first week after injury. Treatment with the lytic anti-CD4 antibody that specifically depletes conventional CD4+ T-cells leads to reduced cardiac fibrosis; while treatment with the lytic anti-CD25 antibody that specifically depletes CD4+CD25hiFOXP3+ Treg contributes to increased fibrosis of the neonatal heart after injury. Moreover, adoptive transfer of Treg to NOD/SCID mice results in mitigated fibrosis and increased proliferation and function of cardiac muscle of the neonatal heart after injury. Mechanistically, single cell transcriptomic profiling reveals that Treg are a source of chemokines and cytokines that attract monocytes and macrophages previously known to drive neonatal heart regeneration. Furthermore, Treg directly promote proliferation of both mouse and human cardiomyocytes in a paracrine manner. Our findings uncover an unappreciated mechanism in neonatal heart regeneration; and offer new avenues for developing novel therapeutics targeting Treg-mediated heart regeneration.

developmental biology↗

bioRxiv2018

Canonical Wnt signaling regulates patterning, differentiation and nucleogenesis in mouse hypothalamus and prethalamus.

The hypothalamus is a small, but anatomically and functionally complex, region of the brain whose development is poorly understood. In this study, we have explored its development by studying the canonical Wntsignalling pathway, generating gain and loss of function mutations of betacaten in(Ctnnb1) in both hypothalamic and prethalamic neuroepithelium. Deletion of Ctnnb1 resulted in an anteriorized and hypoplastic hypothalamus. Posterior structures were lost or reduced, and anterior structures were expanded. In contrast, over expression of a constitutively active mutant form of Ctnnb1 resulted in severe hyperplasia of prethalamus and hypothalamus, and expanded expression of a subset of posterior and premamillary hypothalamic markers. Moderate defects in differentiation of Arx-positive GABAergic neural precursors were observed in both prethalamus and hypothalamus of Ctnnb1 loss of function mutants, while in gain of function mutants, their differentiation was completely suppressed, although markers of prethalamic progenitors were preserved. Multiple other region-specific markers, including several specific posterior hypothalamic structures, were also suppressed in Ctnnb1 gain of function mutations. Severe, region-specific defects in hypothalamic nucleogenesis were also observed in both gain and loss of function mutations of Ctnnb1. Finally, both gain and loss of function of Ctnnb1 also produced severe, cell nonautonomous disruptions of pituitary development. These findings demonstrate acentral and multifaceted role for canonical Wnt signalling in regulating growth, patterning, differentiation and nucleogenesis in multiple diencephalic regions.\n\nHighlightsO_LICanonical Wnt signalling regulates anteroposterior patterning in the hypothalamus.\nC_LIO_LICanonical Wnt signalling regulates differentiation of GABAergic neurons in both prethalamus and hypothalamus.\nC_LIO_LICanonical Wnt signalling regulates differentiation and nucleogenesis of multiple hypothalamic neuronal subtypes.\nC_LIO_LICanonical Wnt signalling in hypothalamic neuroepithelium regulates pituitary morphogenesis and differentiation.\nC_LI

developmental biology↗

bioRxiv2018

Myc is dispensable for cardiac development in the mouse but can rescue Mycn-deficient hearts through functional replacement and cell competition

Myc is considered an essential transcription factor for heart development, but cardiac defects have only been studied in global Myc loss of function models. Here, we eliminated Myc by recombining a Myc floxed allele with the Nkx2.5Cre driver. We observed no anatomical, cellular or functional alterations in either fetuses or adult cardiac Myc-deficient mice. We re-examined Myc expression during development and found no expression in developing cardiomyocytes. In contrast, we confirmed that Mycn is essential for cardiomyocyte proliferation and cardiogenesis. Mosaic Myc overexpression in a Mycn-deficient background, shows that Myc can replace Mycn function, recovering heart development. We further show that this recovery involves the elimination of Mycn-deficient cells by Cell Competition. Our results indicate that Myc is dispensable during cardiogenesis and adult heart homeostasis and Mycn is exclusively responsible for cardiomyocyte proliferation during heart development. Nonetheless, our results show that Myc can functionally replace Mycn. We also show that cardiomyocytes compete according to their overall Myc+Mycn levels and that Cell Competition eliminates flawed cardiomyocytes, suggesting its relevance as a quality control mechanism in cardiac development.

developmental biology↗

bioRxiv2018

N-Cadherin Provides a Cis and Trans Ligand for Astrotactin that Functions in Glial-Guided Neuronal Migration

Prior studies demonstrate that Astrotactin (ASTN1) provides a neuronal receptor for glial-guided CNS migration. Here we report that ASTN1 binds N-cadherin (CDH2) and that the ASTN1:CDH2 interaction supports cell-cell adhesion. To test the function of ASTN1:CDH2 binding in glial-guided neuronal migration, we generated a conditional loss of Cdh2 in cerebellar granule cells and in glia. Granule cell migration was slowed in cerebellar slice cultures after a conditional loss of neuronal Cdh2, and more severe migration defects occurred after a conditional loss of glial Cdh2. Expression of a mutant form of ASTN1 that does not bind CDH2, in granule cells, also slowed migration. Moreover, in vitro chimeras of granule cells and glia showed impaired neuron-glia attachment in the absence of glial, but not neuronal, Cdh2. Thus, cis and trans bindings of ASTN1 to neuronal and glial CDH2 form an asymmetric neuron-glial bridge complex that promotes glial-guided neuronal migration.

developmental biology↗

bioRxiv2018

Development and analytical validation of an enzyme-linked immunosorbent assay based on baculovirus recombinant LipL32 protein antigen for the accurate detection of canine leptospirosis

Leptospira infects a wide range of companion, domestic and wild animal species, shedding the spirochetes into the environment via urine. Dogs become infected by direct or indirect contact with wild or domestic infected animal reservoirs increasing the risk of zoonotic transmission of the disease. The microscopic agglutination test has been used as the gold standard for the diagnosis of leptospirosis but has low sensitivity and is technically complex. Several ELISA tests have been developed based on recombinant proteins of Leptospira for the diagnosis of leptospirosis with similar or higher specificity and sensitivity levels than the microscopic agglutination test. Here, we developed and analytically validated an ELISA test based on recombinant LipL32 protein of Leptospira expressed in baculovirus. The LipL32 protein was successfully adapted in an indirect ELISA using dog plasma samples. Optimization of the ELISA resulted in a P/N ratio of 7.18 using only 5 ng of rLipL32 per well. Inter-assay and intra-assay variation showed a CV of 3.96% and 6.98% respectively, suggesting that the ELISA-LipL32 is highly reproducible. When tested with field samples, concordance of the ELISA-LipL32 with a real-time PCR, positive concordance was 100%. Our results indicate that the ELISA-LipL32 has the potential to be used by veterinarians and public health investigators as a safe, rapid, inexpensive and reliable method for the early diagnosis of Leptospira infection in dogs. Additional studies are still required for clinical validation on field samples under different epidemiological scenarios.

developmental biology↗

bioRxiv2018

Hydra Bcl-2 and TMBIMP family proteins display anti-apoptotic functions

BackgroundMechanisms of programmed cell death differ considerably between animals, plants and fungi. In animals they depend on caspases and Bcl-2 family proteins and this kind of cell death is called apoptosis. Most gene families encoding proteins involved in apoptosis are found in multicellular animals already in the eldest phyla but their functional conservation is still being studied. Much older protein families have cytoprotective functions across all kingdoms of life. This includes the TMBIMP-family, the presence and function of which in early metazoans has not been investigated yet.\n\nMethodsWe quantified apoptosis in transgenic Hydra overexpressing HyBcl-2-like 4. Moreover, we investigated putative TMBIMP-family members in Hydra by sequence comparison. By overexpression of TMBIMP-family members in Hydra and human HEK cells we analysed their subcellular localisation and in one case their capacity to protect cells from camptothecin induced apoptosis.\n\nResultsHyBcl-2-like 4, as previously shown in a heterologous system, was localised to mitochondria and able to protect Hydra epithelial cells from apoptosis. The TMBIMP-family in Hydra includes HyBax-Inhibitor-1, HyLifeguard-1a and -1b and HyLifeguard 4 proteins. HyBax-inhibitor-1 protein was found localised to ER-membranes, HyLifeguard-family members were found at the plasma membrane and in Golgi-vesicles. Moreover, HyBax-inhibitor-1 protected human cells from apoptosis.\n\nConclusionThis work provides the first functional study to support an anti-apoptotic function of Bcl-2 like proteins in pre-bilaterians within a physiological context. Furthermore it illustrates that genes that were \"inherited\" from non-animal ancestors, like the TMBIMP-family, were recruited to carry out cell protective anti-apoptotic functions already in early metazoans.

developmental biology↗

bioRxiv2018

DNMT1 in Six2 progenitor cells is essential for transposable element silencing and kidney development

Cytosine methylation (5mC) plays a key role in maintaining progenitor cell self-renewal and differentiation. Here, we analyzed the role of 5mC in kidney development by genome-wide methylation, expression profiling, and by systematic genetic targeting of DNA methyltransferases (Dnmt) and Ten-eleven translocation methylcytosine hydroxylases (Tet).\n\nIn mice, nephrons differentiate from Six2+ progenitor cells, therefore we created animals with genetic deletion of Dnmt1, 3a, 3b, Tet1, and Tet2 in the Six2+ population (Six2Cre/Dnmt1flox/flox, Six2Cre/Dnmt3aflox/flox, Six2Cre/Dnmt3bflox/flox, Six2Cre/Tet2flox/flox and Tet1-/-). Animals with conditional deletion of Dnmt3a, 3b, Tet1 and Tet2 showed no significant structural or functional renal abnormalities. On the other hand, Six2Cre/Dnmt1flox/flox mice died within 24hrs of birth. Dnmt1 knock-out animals had small kidneys and significantly reduced nephron number. Genome-wide methylation analysis indicated marked loss of methylation mostly on transposable elements. RNA sequencing detected endogenous retroviral (ERV) gene transcripts and early embryonic genes. Increase in levels of interferon (and RIG-I signaling) and apoptosis (Trp53) in response to ERV activity likely contributed to the phenotype development. Once epithelial differentiation was established, loss of Dnmt1, 3a, 3b, Tet1 or Tet2 in glomerular epithelial cells did not lead to functional or structural differences at baseline or following toxic glomerular injury.\n\nGenome-wide cytosine methylation and gene expression profiling showed that Dnmt1-mediated DNA methylation is essential for kidney development by preventing regression of progenitor cells into a primitive undifferentiated state and demethylation of transposable elements.\n\nSignificanceCytosine methylation of regulatory regions (promoters and enhancers) has been proposed to play a key role in establishing gene expression and thereby cellular phenotype. DNMT1 is the key enzyme responsible for maintaining methylation patterns during DNA replication. While the role of Dnmt1 has been described in multiple organs, here we identified a novel, critically important mechanism how Dnmt1 controls tissue progenitors. The greatest methylation difference in Dnmt1 knock-out mice was observed on transposable elements (TE), which resulted in increase of endogenous retroviruses and cell death. We believe that release of TE was a critically overlooked component of phenotype development in previous studies that our comprehensive genome wide methylation analysis allowed us to identify.\n\nCompeting interestsThe Susztak lab receives research support from Biogen, Boehringer Ingelheim, Celgene, GSK, Merck, Regeneron and ONO Pharma for work not related to this manuscript.

developmental biology↗

bioRxiv2018

Novel exc Genes Involved in Formation of the Tubular Excretory Canals of C. elegans

Regulation of luminal diameter is critical to the function of small single-celled tubes, of which the seamless tubular excretory canals of C. elegans provide a tractable genetic model. Mutations in several sets of genes exhibit the Exc phenotype, in which canal luminal growth is visibly altered. Here, a focused reverse genomic screen of genes highly expressed in the canals found 24 genes that significantly affect luminal outgrowth or diameter. These genes encode novel proteins as well as highly conserved proteins involved in processes including gene expression, cytoskeletal regulation, vesicular movement, and transmembrane transport. In addition, two genes act as suppressors on a pathway of conserved genes whose products mediate vesicle movement from early to recycling endosomes. The results provide new tools for understanding the integration of cytoplasmic structure and physiology in forming and maintaining the narrow diameter of single-cell tubules.

developmental biology↗

bioRxiv2018

A transition from SoxB1 to SoxE transcription factors is essential for progression from pluripotent blastula cells to neural crest cells

The neural crest is a stem cell population unique to vertebrate embryos that gives rise to derivatives from multiple embryonic germ layers. The molecular underpinnings of potency that govern neural crest potential is highly conserved with that of pluripotent blastula stem cells, suggesting that neural crest cells may have evolved through retention of aspects of the pluripotency gene regulatory network (GRN). A striking difference in the regulatory factors utilized in pluripotent blastula cells and neural crest cells is the deployment of different subfamilies of Sox transcription factors; SoxB1 factors play central roles in the pluripotency of naive blastula and ES cells, whereas neural crest cells require SoxE function. Here we explore the shared and distinct activities of these factors to shed light on the role that this molecular hand-off of Sox factor activity plays in the genesis of neural crest and the lineages derived from it. Our findings provide evidence that SoxB1 and SoxE factors have both overlapping and distinct activities in regulating pluripotency and lineage restriction in the embryo. We hypothesize that SoxE factors may transiently replace SoxB1 factors to control pluripotency in neural crest cells, and then poise these cells to contribute to glial, chondrogenic and melanocyte lineages at stages when SoxB1 factors promote neuronal progenitor formation.

developmental biology↗

bioRxiv2018

Thyroid hormone signaling specifies cone subtypes in human retinal organoids

The mechanisms underlying the specification of diverse neuronal subtypes within the human nervous system are largely unknown. The blue (shortwavelength/S), green (medium-wavelength/M) and red (long-wavelength/L) cone photoreceptors of the human retina enable high-acuity daytime vision and trichromatic color perception. Cone subtypes are specified in a poorly understood two-step process, with a first decision between S and L/M fates, followed by a decision between L and M fates. To determine the mechanism controlling S vs. L/M fates, we studied the differentiation of human retinal organoids. We found that human organoids and retinas have similar distributions, gene expression profiles, and morphologies of cone subtypes. We found that S cones are specified first, followed by L/M cones, and that thyroid hormone signaling is necessary and sufficient for this temporal switch. Temporally dynamic expression of thyroid hormone degrading and activating proteins supports a model in which the retina itself controls thyroid hormone levels, ensuring low signaling early to specify S cones and high signaling late to produce L/M cones. This work establishes organoids as a model for determining the mechanisms of cell fate specification during human development.\n\nOne sentence summaryCone specification in human organoids

developmental biology↗

bioRxiv2018

The Mediator CDK8-Cyclin C complex modulates vein patterning in Drosophila by stimulating Mad-dependent transcription

Dysregulations of CDK8 and its regulatory partner CycC, two subunits of the conserved Mediator complex, have been linked to diverse human diseases such as cancer, thus it is essential to understand the regulatory network mobilizing the CDK8-CycC complex in both normal development and tumorigenesis. To identify upstream regulators or downstream effectors of CDK8, we performed a dominant modifier genetic screen in Drosophila based on the defects in vein patterning caused by specific depletion or overexpression of CDK8 or CycC in wing imaginal discs. We identified 26 genomic loci whose haploinsufficiency can modify these CDK8-specific phenotypes. Further analysis of two deficiency lines and mutant alleles led us to identify interactions between CDK8-CycC and the components of the Decapentaplegic (Dpp, the Drosophila homolog of TGF{beta}) signaling pathway. We observed that CDK8-CycC positively regulates transcription activated by Mad (Mothers against dpp), the primary transcription factor downstream of the Dpp/TGF{beta} signaling pathway. CDK8 can directly interact with Mad in vitro through the linker region between the DNA-binding MH1 (Mad homology 1) domain and the carboxy terminal MH2 transactivation domain. Besides CDK8 and CycC, further analyses of other subunits of the Mediator complex have revealed six additional Mediator subunits that are required for Mad-dependent transcription in the wing discs, including Med12, Med13, Med15, Med23, Med24, and Med31. Furthermore, CDK9 and Yorkie also positively regulate Mad-dependent gene expression in vivo. These results suggest that the Mediator complex may coordinate with other transcription cofactors in regulating Mad-dependent transcription during the wing vein patterning in Drosophila.\n\nSignificanceCDK8 is a conserved subunit of the transcription cofactor Mediator complex that bridges transcription factors with RNA Polymerase II in eukaryotes. Here we explore the role of CDK8 in Drosophila by performing a dominant modifier genetic screen based on vein patterning defects caused by alteration of CDK8-specific activities. We show that components of the Dpp/TGF{beta} signaling pathway genetically interact with CDK8; CDK8 positively regulates gene expression activated by Mad, the key transcription factor downstream of Dpp/TGF{beta} signaling, by directly interacting with the linker region of Mad protein. Given the fundamental roles of Dpp/TGF{beta} signaling in regulating development and its misregulation in various diseases, understanding how Mad/Smad interacts the Mediator complex may have broad implications in understanding and treating these diseases.

developmental biology↗

bioRxiv2018

Mitogen-Activated Protein Kinase-Dependent Fiber-Type Regulation in Skeletal Muscle

Mitogen-activated protein kinases (MAPK) are conserved protein kinases that regulate a diverse array of cellular activities. Stress or mitogenic signals activate three primary branches of the greater MAPK cascade, each of which consists of a phosphorylation-dependent array of successively acting kinases. The extracellular signal-regulated kinase 1/2 (ERK1/2) branch is regulated by growth factory signaling at the cell membrane, leading to phosphorylation of the dual-specificity kinase MEK1, which is dedicated to ERK1/2 phosphorylation. Previous studies have established a link between MAPK activation and endurance exercise, but whether a single MAPK is responsible for establishing muscle metabolic fate is unclear. Using mouse genetics we observed that muscle-specific expression of a constitutively active MEK1 promotes greater ERK1/2 signaling that mediates fiber-type switching in mouse skeletal muscle to a slow, oxidative phenotype with type I myosin heavy chain expression. Induced expression of the activated MEK1 mutant using either a MyoD-Cre or myosin light chain-Cre strategy equally increased the number of type I fibers in skeletal muscle with significantly reduced size compared to controls. Moreover, activation of MEK1 in mature myofibers of an adult mouse using a transgene containing a tamoxifen inducible MerCreMer cDNA under the control of a skeletal -actin promoter produced a similar phenotype of switching towards a slow-oxidative program. Physiologic assessment of mice with greater skeletal muscle slow-oxidative fibers showed enhanced metabolic activity and oxygen consumption with greater fatigue resistance of individual muscles. In summary, these results show that sustained MEK1-ERK1/2 activity in skeletal muscle produces a fast-to-slow fiber-type switch, suggesting that modulation of this signaling pathway may represent a therapeutic approach to enhance the long-term metabolic effectiveness of muscle in vivo.

developmental biology↗