miRNAs are small RNAs directing many developmental processes by posttranscriptional regulation of protein-coding genes. We uncovered a new role for miR-1-1/133a-2 and miR-1-2/133a-1 clusters in the specification of embryonic cardiomyocytes allowing transition from an immature state characterized by expression of smooth muscle (SM) genes to a more mature fetal phenotype. Concomitant knockout of miR-1-1/133a-2 and miR-1-2/133a-1 released suppression of the transcriptional co-activator myocardin, a major regulator of SM gene expression, but not of its binding partner SRF. Overexpression of myocardin in the embryonic heart essentially recapitulated the miR-1/133a mutant phenotype at the molecular level, arresting embryonic cardiomyocytes in an immature state. Interestingly, the majority of postulated miR-1/133a targets was not altered in double mutant mice, indicating that the ability of miR-1/133a to suppress target molecules strongly depends on the cellular context. Finally, we show that myocardin positively regulates expression of miR-1/133a, thus constituting a negative feedback loop that is essential for early cardiac development.
miRNAs are small non-coding RNAs involved in posttranscriptional regulation of protein-coding genes. In the mammalian genome, two distinct gene clusters code for miR-1 and miR-133a. Primary sequences of mature miR-1 or miR-133a are identical and both gene clusters show similar expression in the heart and skeletal muscle. We have generated compound mutant mice of both miR-1/133a gene clusters resulting in early arrest of heart development while single cluster mutants showed normal morphology but reacted differently to pressure overload. Compound mutant cardiomyocytes were characterized by an immature, mixed smooth muscle-heart muscle phenotype, indicating that miR1-/133a are responsible for specification of the cardiomyogenic lineage. Our search for miR1-/133a targets identified myocardin, which was strongly up-regulated in mutant hearts, while several other putative miR-1/133a targets that have been described before were not altered, indicating that miR-1/133a target control strongly depends on the cellular context. Overexpression of myocardin in embryonic hearts recapitulated major aspects of the miR-1/133a mutant phenotype, suggesting that loss of myocardin suppression is the primary reason for incorrect heart muscle specification in the mutants. In addition, we found that myocardin overexpression stimulated expression of miR-1/133a, which argues for a negative feedback loop required for adjustment of myocardin concentrations in the heart.
Nephronophthisis (NPHP), an autosomal recessive cystic kidney disease, leads to chronic renal failure in children. The genes mutated in NPHP1 and NPHP4 have been identified, and a gene locus associated with infantile nephronophthisis (NPHP2) was mapped. The kidney phenotype of NPHP2 combines clinical features of NPHP and polycystic kidney disease (PKD). Here, we identify inversin (INVS) as the gene mutated in NPHP2 with and without situs inversus. We show molecular interaction of inversin with nephrocystin, the product of the gene mutated in NPHP1 and interaction of nephrocystin with β-tubulin, a main component of primary cilia. We show that nephrocystin, inversin and β-tubulin colocalize to primary cilia of renal tubular cells. Furthermore, we produce a PKD-like renal cystic phenotype and randomization of heart looping by knockdown of invs expression in zebrafish. The interaction and colocalization in cilia of inversin, nephrocystin and β-tubulin connect pathogenetic aspects of NPHP to PKD, to primary cilia function and to left-right axis determination.
The atypical protein kinases C (PKC) isoforms ι/λ and ζ play crucial roles in many cellular processes including development, cell proliferation, differentiation and cell survival. Possible redundancy between the two isoforms has always been an issue since most biochemical tools do not differentiate between the two proteins. Thus, much effort has been made during the last decades to characterize the functions of aPKCs using gene targeting approaches and depletion studies. However, little is known about the specific roles of each isoform in mouse development.
To evaluate the importance of PKCι in mouse development we designed PKCι deletion mutants using the gene targeting approach. We show that the deletion of PKCι, results in a reduced size of the amniotic cavity at E7.5 and impaired growth of the embryo at E8.5 with subsequent absorption of the embryo. Our data also indicate an impaired localization of ZO-1 and disorganized structure of the epithelial tissue in the embryo. Importantly, using electron microscopy, embryoid body formation and immunofluorescence analysis, we found, that in the absence of PKCι, tight junctions and apico-basal polarity were still established. Finally, our study points to a non-redundant PKCι function at E9.5, since expression of PKCζ is able to rescue the E7.5 phenotype, but could not prevent embryonic lethality at a later time-point (E9.5).
Our data show that PKCι is crucial for mouse embryogenesis but is dispensable for the establishment of polarity and tight junction formation. We present a compensatory function of PKCζ at E7.5, rescuing the phenotype. Furthermore, this study indicates at least one specific, yet unknown, PKCι function that cannot be compensated by the overexpression of PKCζ at E9.5.
Smooth muscle cells are of key importance for the proper functioning of different visceral organs including those of the urogenital system. In the mouse ureter, the two transcriptional regulators TSHZ3 and SOX9 are independently required for initiation of smooth muscle differentiation from uncommitted mesenchymal precursor cells. However, it has remained unclear whether TSHZ3 and SOX9 act independently or as part of a larger regulatory network. Here, we set out to characterize the molecular function of TSHZ3 in the differentiation of the ureteric mesenchyme. Using a yeast-two-hybrid screen, we identified SOX9 as an interacting protein. We show that TSHZ3 also binds to the master regulator of the smooth muscle program, MYOCD, and displaces it from the coregulator SRF, thereby disrupting the activation of smooth muscle specific genes. We found that the initiation of the expression of smooth muscle specific genes in MYOCD-positive ureteric mesenchyme coincides with the down regulation of Sox9 expression, identifying SOX9 as a possible negative regulator of smooth muscle cell differentiation. To test this hypothesis, we prolonged the expression of Sox9 in the ureteric mesenchyme in vivo. We found that Sox9 does not affect Myocd expression but significantly reduces the expression of MYOCD/SRF-dependent smooth muscle genes, suggesting that down-regulation of Sox9 is a prerequisite for MYOCD activity. We propose that the dynamic expression of Sox9 and the interaction between TSHZ3, SOX9 and MYOCD provide a mechanism that regulates the pace of progression of the myogenic program in the ureter.
Vertebrate organ development relies on the precise spatiotemporal orchestration of proliferation rates and differentiation patterns in adjacent tissue compartments. The underlying integration of patterning and cell cycle control during organogenesis is insufficiently understood. Here, we have investigated the function of the patterning T-box transcription factor gene Tbx2 in lung development. We show that lungs of Tbx2-deficient mice are markedly hypoplastic and exhibit reduced branching morphogenesis. Mesenchymal proliferation was severely decreased, while mesenchymal differentiation into fibrocytes was prematurely induced. In the epithelial compartment, proliferation was reduced and differentiation of alveolar epithelial cells type 1 was compromised. Prior to the observed cellular changes, canonical Wnt signaling was downregulated, and Cdkn1a (p21) and Cdkn1b (p27) (two members of the Cip/Kip family of cell cycle inhibitors) were strongly induced in the Tbx2-deficient lung mesenchyme. Deletion of both Cdkn1a and Cdkn1b rescued, to a large degree, the growth deficits of Tbx2-deficient lungs. Prolongation of Tbx2 expression into adulthood led to hyperproliferation and maintenance of mesenchymal progenitor cells, with branching morphogenesis remaining unaffected. Expression of Cdkn1a and Cdkn1b was ablated from the lung mesenchyme in this gain-of-function setting. We further show by ChIP experiments that Tbx2 directly binds to Cdkn1a and Cdkn1b loci in vivo, defining these two genes as direct targets of Tbx2 repressive activity in the lung mesenchyme. We conclude that Tbx2-mediated regulation of Cdkn1a and Cdkn1b represents a crucial node in the network integrating patterning information and cell cycle regulation that underlies growth, differentiation, and branching morphogenesis of this organ.
During organ formation, proliferation rates and differentiation patterns vary widely between different stages and tissue compartments. It is poorly understood how cell cycle progression is locally controlled and integrated with patterning processes in these developmental programs. Here, we used the mouse lung as a model to study how growth and differentiation are controlled on a transcriptional level. Combining genetic loss- and gain-of-function approaches, we show that the T-box transcription factor gene Tbx2 is required and sufficient to direct appropriate lung growth by maintaining proliferation and inhibiting differentiation in the mesenchymal compartment of the lung. We found that expression of the cell cycle inhibitor genes Cdkn1a (p21) and Cdkn1b (p27) inversely correlates with expression of Tbx2 and that deletion of both genes rescues, to a large degree, the growth deficits of Tbx2-mutant lungs. We further show by biochemical assays that Tbx2 directly binds to Cdkn1a and Cdkn1b loci in vivo, defining these two genes as direct targets of Tbx2 repressive activity in the lung mesenchyme. We conclude that Tbx2-mediated regulation of Cdkn1a and Cdkn1b represents a crucial module for the tissue-specific control of cell cycle progression that underlies growth, differentiation, and branching morphogenesis of this organ.
The homeobox containing transcription factor Uncx4.1 is, amongst others, expressed in the mouse midbrain. The early expression of this transcription factor in the mouse, as well as in the chick midbrain, points to a conserved function of Uncx4.1, but so far a functional analysis in this brain territory is missing. The goal of the current study was to analyze in which midbrain neuronal subgroups Uncx4.1 is expressed and to examine whether this factor plays a role in the early development of these neuronal subgroups.
We have shown that Uncx4.1 is expressed in GABAergic, glutamatergic and dopaminergic neurons in the mouse midbrain. In midbrain dopaminergic (mDA) neurons Uncx4.1 expression is particularly high around E11.5 and strongly diminished already at E17.5. The analysis of knockout mice revealed that the loss of Uncx4.1 is accompanied with a 25% decrease in the population of mDA neurons, as marked by tyrosine hydroxylase (TH), dopamine transporter (DAT), Pitx3 and Ngn2. In contrast, the number of glutamatergic Pax6-positive cells was augmented, while the GABAergic neuron population appears not affected in Uncx4.1-deficient embryos.
We conclude that Uncx4.1 is implicated in the development of mDA neurons where it displays a unique temporal expression profile in the early postmitotic stage. Our data indicate that the mechanism underlying the role of Uncx4.1 in mDA development is likely related to differentiation processes in postmitotic stages, and where Ngn2 is engaged. Moreover, Uncx4.1 might play an important role during glutamatergic neuronal differentiation in the mouse midbrain.
Uncx4.1; Midbrain; mDA neurons; Ngn2; Pax6; Differentiation; Expression
Primary ciliary dyskinesia (PCD) is an inherited disorder characterized by recurrent infections of the upper and lower respiratory tract, reduced fertility in males and situs inversus in about 50% of affected individuals (Kartagener syndrome). It is caused by motility defects in the respiratory cilia that are responsible for airway clearance, the flagella that propel sperm cells and the nodal monocilia that determine left-right asymmetry1. Recessive mutations that cause PCD have been identified in genes encoding components of the outer dynein arms, radial spokes and cytoplasmic pre-assembly factors of axonemal dyneins, but these mutations account for only about 50% of cases of PCD. We exploited the unique properties of dog populations to positionally clone a new PCD gene, CCDC39. We found that loss-of-function mutations in the human ortholog underlie a substantial fraction of PCD cases with axonemal disorganization and abnormal ciliary beating. Functional analyses indicated that CCDC39 localizes to ciliary axonemes and is essential for assembly of inner dynein arms and the dynein regulatory complex.
The pleuropericardial membranes are fibro-serous walls that separate the pericardial and pleural cavities and anchor the heart inside the mediastinum. Partial or complete absence of pleuropericardial membranes is a rare human disease, the etiology of which is poorly understood. As an attempt to better understand these defects, we wished to analyze the cellular and molecular mechanisms directing the separation of pericardial and pleural cavities by pleuropericardial membranes in the mouse. We found by histological analyses that both in Tbx18- and Wt1-deficient mice the pleural and pericardial cavities communicate due to a partial absence of the pleuropericardial membranes in the hilus region. We trace these defects to a persisting embryonic connection between these cavities, the pericardioperitoneal canals. Furthermore, we identify mesenchymal ridges in the sinus venosus region that tether the growing pleuropericardial membranes to the hilus of the lung, and thus, close the pericardioperitoneal canals. In Tbx18-deficient embryos these mesenchymal ridges are not established, whereas in Wt1-deficient embryos the final fusion process between these tissues and the body wall does not occur. We suggest that this fusion is an active rather than a passive process, and discuss the interrelation between closure of the pericardioperitoneal canals, lateral release of the pleuropericardial membranes from the lateral body wall, and sinus horn development.
Neph proteins are evolutionarily conserved members of the immunoglobulin superfamily of adhesion proteins and regulate morphogenesis and patterning of different tissues. They share a common protein structure consisting of extracellular immunoglobulin-like domains, a transmembrane region, and a carboxyl terminal cytoplasmic tail required for signaling. Neph orthologs have been widely characterized in invertebrates where they mediate such diverse processes as neural development, synaptogenesis, or myoblast fusion. Vertebrate Neph proteins have been described first at the glomerular filtration barrier of the kidney. Recently, there has been accumulating evidence suggesting a function of Neph proteins also outside the kidney. Here we demonstrate that Neph1, Neph2, and Neph3 are expressed differentially in various tissues during ontogenesis in mouse and chicken. Neph1 and Neph2 were found to be amply expressed in the central nervous system while Neph3 expression remained localized to the cerebellum anlage and the spinal cord. Outside the nervous system, Neph mRNAs were also differentially expressed in branchial arches, somites, heart, lung bud, and apical ectodermal ridge. Our findings support the concept that vertebrate Neph proteins, similarly to their Drosophila and C. elegans orthologs, provide guidance cues for cell recognition and tissue patterning in various organs which may open interesting perspectives for future research on Neph1-3 controlled morphogenesis.
Neph1; Neph2; Neph3; SYG-1; SYG-2; Kirre-like; IrreC/Rst
A key step in heart development is the coordinated development of the atrioventricular canal (AVC), the constriction between the atria and ventricles that electrically and physically separates the chambers, and the development of the atrioventricular valves that ensure unidirectional blood flow. Using knock-out and inducible overexpression mouse models, we provide evidence that the developmentally important T-box factors Tbx2 and Tbx3, in a functionally redundant manner, maintain the AVC myocardium phenotype during the process of chamber differentiation. Expression profiling and ChIP-sequencing analysis of Tbx3 revealed that it directly interacts with and represses chamber myocardial genes, and induces the atrioventricular pacemaker-like phenotype by activating relevant genes. Moreover, mutant mice lacking 3 or 4 functional alleles of Tbx2 and Tbx3 failed to form atrioventricular cushions, precursors of the valves and septa. Tbx2 and Tbx3 trigger development of the cushions through a regulatory feed-forward loop with Bmp2, thus providing a mechanism for the co-localization and coordination of these important processes in heart development.
Electronic supplementary material
The online version of this article (doi:10.1007/s00018-011-0884-2) contains supplementary material, which is available to authorized users.
Endocardial cushion; Mesenchyme; Atrioventricular; T-box factors; Tbx3; BMP; Differentiation; Interaction; Repression
The eyes absent 1 protein (Eya1) plays an essential role in the development of various organs in both invertebrates and vertebrates. Mutations in the human EYA1 gene are linked to BOR (branchio-oto-renal) syndrome, characterized by kidney defects, hearing loss, and branchial arch anomalies. For a better understanding of Eya1's function, we have set out to identify new Eya1-interacting proteins. Here we report the identification of the related proteins Sipl1 (Shank-interacting protein-like 1) and Rbck1 (RBCC protein interacting with PKC1) as novel interaction partners of Eya1. We confirmed the interactions by glutathione S-transferase (GST) pulldown analysis and coimmunoprecipitation. A first mechanistic insight is provided by the demonstration that Sipl1 and Rbck1 enhance the function of Eya proteins to act as coactivators for the Six transcription factors. Using reverse transcriptase PCR (RT-PCR) and in situ hybridization, we show that Sipl1 and Rbck1 are coexpressed with Eya1 in several organs during embryogenesis of both the mouse and zebrafish. By morpholino-mediated knockdown, we demonstrate that the Sipl1 and Rbck1 orthologs are involved in different aspects of zebrafish development. In particular, knockdown of one Sipl1 ortholog as well as one Rbck1 ortholog led to a BOR syndrome-like phenotype, with characteristic defects in ear and branchial arch formation.
The cardiac venous pole is a common focus of congenital malformations and atrial arrhythmias, yet little is known about the cellular and molecular mechanisms that regulate its development. The systemic venous return myocardium (sinus node and sinus horns) forms only late in cardiogenesis from a pool of pericardial mesenchymal precursor cells.
To analyze the cellular and molecular mechanisms directing the formation of the fetal sinus horns.
Methods and Results
We analyzed embryos deficient for the Wilms tumor 1 gene (Wt1) and observed a failure to form myocardialized sinus horns. Instead, the cardinal veins become embedded laterally in the pleuropericardial membranes (PPMs) that remain tethered to the lateral body wall by the persisting subcoelomic mesenchyme, a finding that correlates with decreased apoptosis in this region. We show by expression analysis and lineage tracing studies that Wt1 is expressed in the subcoelomic mesenchyme surrounding the cardinal veins, but that this Wt1-positive mesenchyme does not contribute cells to the sinus horn myocardium. Expression of the aldehyde dehydrogenase family 1, subfamily A2 gene (Raldh2) was lost from this mesenchyme in Wt1−/− embryos. Phenotypic analysis of Raldh2-mutant mice rescued from early cardiac defects by retinoic acid (RA) food supply revealed defects of the venous pole and pericardium highly similar to those of Wt1−/− mice.
Pericardium and sinus horn formation are coupled and depend on the expansion and correct temporal release of PPMs from the underlying subcoelomic mesenchyme. Wt1 and downstream Raldh2/RA-signaling are crucial regulators of this process. Thus, our results provide novel insight into the genetic and cellular pathways regulating the posterior extension of the mammalian heart and the formation of its coelomic lining.
sinus horn; venous pole; sinoatrial node; Tbx18; Raldh2; retinoic acid
Photoreceptor degeneration is a common feature of ciliopathies, owing to the importance of the highly specialized ciliary structure of these cells. Absence of AHI1, which encodes a cilium-localized protein, has been shown to cause a form of Joubert syndrome highly penetrant for retinal degeneration1,2. We show that Ahi1 knockout mice fail to form outer segments (OS), and show abnormal distribution of opsin throughout photoreceptors. Apoptotic cell death occurs rapidly between 2-4 weeks of age and is significantly delayed by reduced dosage of opsin. This phenotype also displays dosage-sensitive genetic interactions with Nphp1, another ciliopathy gene. Although not a primary cause of retinal blindness in humans, an allele of AHI1 modifies the relative risk of retinal degeneration greater than 7 fold within a nephronophthisis cohort. Our data support context-specific roles for AHI1 as a contributor to retinopathy and may explain a proportion of the variability of retinal phenotypes observed in nephronophthisis.
We examined the role of WNT signaling in pituitary development by characterizing the pituitary phenotype of three WNT knockout mice and assessing the expression of WNT pathway components. Wnt5a mutants have expanded domains of Fgf10 and BMP expression in the ventral diencephalon and a reduced domain of LHX3 expression in Rathke's pouch. Wnt4 mutants have mildly reduced cell differentiation, reduced POU1F1 expression, and mild anterior lobe hypoplasia. Wnt4, Wnt5a double mutants exhibit an additive pituitary phenotype of dysmorphology and mild hypoplasia. Wnt6 mutants have no obvious pituitary phenotype. We surveyed WNT expression and identified transcripts for numerous Wnts, Frizzleds and downstream pathway members in the pituitary and ventral diencephalon. These findings support the emerging model that WNT signaling affects the pituitary gland via effects on ventral diencephalon signaling, and suggest additional Wnt genes that are worthy of functional studies.
Wnt5a; Wnt4; Wnt6; Wnt11; Wnt16; mouse knockout; development
Secreted frizzled related proteins (sFRPs) have emerged as key regulators of a wide range of developmental and disease processes, with virtually all known functions of mammalian sFRPs attributed to their ability to antagonize Wnt signaling. Recently however, the Xenopus and zebrafish sFRP, Sizzled, was shown to function as an antagonist of Chordin processing by Tolloid-like metalloproteinases, leading to the proposal that sFRPs may function as evolutionarily-conserved antagonists of the chordinase activities of this class of proteinases. Herein, in contrast to this proposal, we show that the mammalian sFRP, sFRP2, does not affect Chordin processing, but instead can serve as a direct enhancer of the procollagen C-proteinase activity of Tolloid-like metalloproteinases. We further show that the level of fibrosis, in which procollagen processing by Tolloid-like proteinases plays a rate-limiting role, is markedly reduced in sFRP2-null mice subjected to myocardial infarction. Importantly, this reduced level of fibrosis is accompanied by significantly improved cardiac function. This study thus uncovers a novel function for sFRP2 and a potential therapeutic application for sFRP2 antagonism in controlling fibrosis in the infarcted heart.
Neurotrophins regulate survival, axonal growth, and target innervation of sensory and other neurons. Neurotrophin-3 (NT-3) is expressed specifically in cells adjacent to extending axons of dorsal root ganglia neurons, and its absence results in loss of most of these neurons before their axons reach their targets. However, axons are not required for NT-3 expression in limbs; instead, local signals from ectoderm induce NT-3 expression in adjacent mesenchyme. Wnt factors expressed in limb ectoderm induce NT-3 in the underlying mesenchyme. Thus, epithelial-mesenchymal interactions mediated by Wnt factors control NT-3 expression and may regulate axonal growth and guidance.
Congenital malformations of the urinary tract are a major cause of renal failure in children and young adults. They are often caused by physical obstruction or by functional impairment of the peristaltic machinery of the ureter. The underlying molecular and cellular defects are, however, poorly understood. Here we present the phenotypic characterization of a new mouse model for congenital ureter malformation that revealed the molecular pathway important for the formation of the functional mesenchymal coating of the ureter. The gene encoding the T-box transcription factor Tbx18 was expressed in undifferentiated mesenchymal cells surrounding the distal ureter stalk. In Tbx18–/– mice, prospective ureteral mesenchymal cells largely dislocalized to the surface of the kidneys. The remaining ureteral mesenchymal cells showed reduced proliferation and failed to differentiate into smooth muscles, but instead became fibrous and ligamentous tissue. Absence of ureteral smooth muscles resulted in a short hydroureter and hydronephrosis at birth. Our analysis also showed that the ureteral mesenchyme derives from a distinct cell population that is separated early in kidney development from that of other mesenchymal cells of the renal system.