Establishment of left-right asymmetry in vertebrate development: the node in mouse embryos

Asymmetries of Left and Right Adrenal Glands in Neural Innervation and Glucocorticoids Production

The adrenal gland is paired peripheral end organs of the neuroendocrine system and is responsible for producing crucial stress hormones from its two functional compartments, the adrenal cortex, and the adrenal medulla under stimuli. Left-right asymmetry in vertebrates exists from the central nervous system to peripheral paired endocrine glands. The sided difference in the cerebral cortex is extensively investigated, while the knowledge of asymmetry of paired endocrine glands is still poor. The present study aims to investigate the asymmetries of bilateral adrenal glands, which play important roles in stress adaptation and energy homeostasis via steroid hormones produced from the distinct functional zones. Left and right adrenal glands from male C57BL/6J mice were initially histologically analyzed, and high-throughput RNA sequencing was then used to detect the gene transcriptional difference between left and right adrenal glands. Subsequently, the enrichment of functional pathways and ceRNA regulatory work was validated. The results demonstrated that the left adrenal gland had higher tissue mass and levels of energy expenditure, whereas the right adrenal gland appeared to be more potent in glucocorticoid secretion. Further analysis of adrenal stem/progenitor cell markers predicted that Shh signaling might play an important role in the left-right asymmetry of adrenal glands. Of the hub miRNAs, miRNA-466i-5p was identified in the left-right differential innervation of the adrenal glands. Therefore, the present study provides evidence that there are asymmetries between the left and right adrenal glands in glucocorticoid production and neural innervation, in which Shh signaling and miRNA-466i-5p play an important role.

Self-organized collective cell behaviors as design principles for synthetic developmental biology

Over the past two decades, molecular cell biology has graduated from a mostly analytic science to one with substantial synthetic capability. This success is built on a deep understanding of the structure and function of biomolecules and molecular mechanisms. For synthetic biology to achieve similar success at the scale of tissues and organs, an equally deep understanding of the principles of development is required. Here, we review some of the central concepts and recent progress in tissue patterning, morphogenesis and collective cell migration and discuss their value for synthetic developmental biology, emphasizing in particular the power of (guided) self-organization and the role of theoretical advances in making developmental insights applicable in synthesis.

Knockdown of Ift88 in fibroblasts causes extracellular matrix remodeling and decreases conduction velocity in cardiomyocyte monolayers

Background: Atrial fibrosis plays an important role in the development and persistence of atrial fibrillation by promoting reentry. Primary cilia have been identified as a regulator of fibroblasts (FB) activation and extracellular matrix (ECM) deposition. We hypothesized that selective reduction of primary cilia causes increased fibrosis and facilitates reentry.

Aim: The aim of this study was to disrupt the formation of primary cilia in FB and examine its consequences on ECM and conduction in a co-culture system of cardiomyocytes (CM) and FB.

Materials: Using short interfering RNA (siRNA), we removed primary cilia in neonatal rat ventricular FB by reducing the expression of Ift88 gene required for ciliary assembly. We co-cultured neonatal rat ventricular cardiomyocytes (CM) with FB previously transfected with Ift88 siRNA (siIft88) or negative control siRNA (siNC) for 48 h. We examined the consequences of ciliated fibroblasts reduction on conduction and tissue remodeling by performing electrical mapping, microelectrode, and gene expression measurements.

Results: Transfection of FB with siIft88 resulted in a significant 60% and 30% reduction of relative Ift88 expression in FB and CM-FB co-cultures, respectively, compared to siNC. Knockdown of Ift88 significantly increased the expression of ECM genes Fn1, Col1a1 and Ctgf by 38%, 30% and 18%, respectively, in comparison to transfection with siNC. Conduction velocity (CV) was significantly decreased in the siIft88 group in comparison to siNC [11.12 ± 4.27 cm/s (n = 10) vs. 17.00 ± 6.20 (n = 10) respectively, p < 0.05]. The fraction of sites with interelectrode activation block was larger in the siIft88 group than in the siNC group (6.59 × 10−2 ± 8.01 × 10−2 vs. 1.18 × 10−2 ± 3.72 × 10−2 respectively, p < 0.05). We documented spontaneous reentrant arrhythmias in two cultures in the siIft88 group and in none of the siNC group. Action potentials were not significantly different between siNC and siIft88 groups.

Conclusion: Disruption of cilia formation by siIft88 causes ECM remodeling and conduction abnormalities. Prevention of cilia loss could be a target for prevention of arrhythmias.

HMCES modulates the transcriptional regulation of nodal/activin and BMP signaling in mESCs

Despite the fundamental roles of TGF-β family signaling in cell fate determination in all metazoans, the mechanism by which these signals are spatially and temporally interpreted remains elusive. The cell-context-dependent function of TGF-β signaling largely relies on transcriptional regulation by SMAD proteins. Here, we discover that the DNA repair-related protein, HMCES, contributes to early development by maintaining nodal/activin- or BMP-signaling-regulated transcriptional network. HMCES binds with R-SMAD proteins, co-localizing at active histone marks. However, HMCES chromatin occupancy is independent on nodal/activin or BMP signaling. Mechanistically, HMCES competitively binds chromatin to limit binding by R-SMAD proteins, thereby forcing their dissociation and resulting in repression of their regulatory effects. In Xenopus laevis embryo, hmces KD causes dramatic development defects with abnormal left-right axis asymmetry along with increasing expression of lefty1. These findings reveal HMCES transcriptional regulatory function in the context of TGF-β family signaling.

Atypical Brain Asymmetry in Human Situs Inversus: Gut Feeling or Real Evidence?

The alignment of visceral and brain asymmetry observed in some vertebrate species raises the question of whether this association also exists in humans. While the visceral and brain systems may have developed asymmetry for different reasons, basic visceral left–right differentiation mechanisms could have been duplicated to establish brain asymmetry. We describe the main phenotypical anomalies and the general mechanism of left–right differentiation of vertebrate visceral and brain laterality. Next, we systematically review the available human studies that explored the prevalence of atypical behavioral and brain asymmetry in visceral situs anomalies, which almost exclusively involved participants with the mirrored visceral organization (situs inversus). The data show no direct link between human visceral and brain functional laterality as most participants with situs inversus show the typical population bias for handedness and brain functional asymmetry, although an increased prevalence of functional crowding may be present. At the same time, several independent studies present evidence for a possible relation between situs inversus and the gross morphological asymmetry of the brain torque with potential differences between subtypes of situs inversus with ciliary and non-ciliary etiologies.

Clinical diagnosis of presumed SOX2 gonadosomatic mosaicism

Purpose:

To describe a family with presumed SOX2 gonadosomatic mosaicism diagnosed upon ophthalmic examination of the proband’s mother.

Methods:

The family underwent comprehensive ophthalmic and physical examination. Variant detection was performed using trio exome analysis on peripheral leukocyte DNA from blood and saliva samples. Variant segregation analysis was performed using a custom panel NGS sequencing. An identified variant in the SOX2 gene was confirmed in the proband by Sanger sequencing.

Results:

We report an individual with bilateral microphthalmia, developmental delay, hearing loss, and dysmorphic features. Her mother was found to have asymptomatic forme fruste uveal coloboma affecting her anterior segment. Her father, aunt, and sisters were unaffected. Trio exome sequence analysis showed an apparent de novo heterozygous deletion in the proband, NM_003106.3:c.70_89del, NP_003097.1:p. (Asn24Argfs*65), classified as pathogenic. Testing of the other family members’ peripheral blood and saliva was negative for this variant. The iris transillumination abnormalities in the proband’s mother supports a gonadosomatic mosaicism scenario.

Conclusions:

The results from this family underscore the importance of performing detailed evaluations of the parents of apparently sporadically affected individuals with heritable ophthalmic disorders. The identification of mildly affected individuals could substantially alter recurrence risks.

Mouse gastrulation: Coordination of tissue patterning, specification and diversification of cell fate

During mouse embryonic development a mass of pluripotent epiblast tissue is transformed during gastrulation to generate the three definitive germ layers: endoderm, mesoderm, and ectoderm. During gastrulation, a spatiotemporally controlled sequence of events results in the generation of organ progenitors and positions them in a stereotypical fashion throughout the embryo. Key to the correct specification and differentiation of these cell fates is the establishment of an axial coordinate system along with the integration of multiple signals by individual epiblast cells to produce distinct outcomes. These signaling domains evolve as the anterior-posterior axis is established and the embryo grows in size. Gastrulation is initiated at the posteriorly positioned primitive streak, from which nascent mesoderm and endoderm progenitors ingress and begin to diversify. Advances in technology have facilitated the elaboration of landmark findings that originally described the epiblast fate map and signaling pathways required to execute those fates. Here we will discuss the current state of the field and reflect on how our understanding has shifted in recent years.

Long-Pentraxin 3 Affects Primary Cilium in Zebrafish Embryo and Cancer Cells via the FGF System

Primary cilium drives the left-right asymmetry process during embryonic development. Moreover, its dysregulation contributes to cancer progression by affecting various signaling pathways. The fibroblast growth factor (FGF)/FGF receptor (FGFR) system modulates primary cilium length and plays a pivotal role in embryogenesis and tumor growth. Here, we investigated the impact of the natural FGF trap long-pentraxin 3 (PTX3) on the determination of primary cilium extension in zebrafish embryo and cancer cells. The results demonstrate that down modulation of the PTX3 orthologue ptx3b causes the shortening of primary cilium in zebrafish embryo in a FGF-dependent manner, leading to defects in the left-right asymmetry determination. Conversely, PTX3 upregulation causes the elongation of primary cilium in FGF-dependent cancer cells. Previous observations have identified the PTX3-derived small molecule NSC12 as an orally available FGF trap with anticancer effects on FGF-dependent tumors. In keeping with the non-redundant role of the FGF/FGR system in primary cilium length determination, NSC12 induces the elongation of primary cilium in FGF-dependent tumor cells, thus acting as a ciliogenic anticancer molecule in vitro and in vivo. Together, these findings demonstrate the ability of the natural FGF trap PTX3 to exert a modulatory effect on primary cilium in embryonic development and cancer. Moreover, they set the basis for the design of novel ciliogenic drugs with potential implications for the therapy of FGF-dependent tumors.

Spatial and temporal deletion reveals a latent effect of Megf8 on the left-right patterning and heart development

Laterality disease is frequently associated with congenital heart disease (CHD). However, it is unclear what is behind this association, a pleiotropic effect of common genetic causes of laterality diseases or the impact of abnormal left-right patterning on the downstream cardiovascular development. MEGF8 is a disease gene of Carpenter syndrome characterized by defective lateralization and CHD. Here we performed spatial and temporal deletion to dissect the tissue and time requirements of Megf8 on cardiovascular development. None of conditional deletions in cardiomyocytes, endothelium/endocardium, epicardium, cardiac mesoderm or neural crest cells led to cardiovascular defects. More surprisingly, temporal deletion with a ubiquitous Cre driver at embryonic day 7.5 (E7.5), a time point before symmetry break and cardiogenesis, causes preaxial polydactyly (PPD) and exencephaly, but not laterality and cardiovascular defects. These data suggested that Megf8 was dispensable for cardiac organogenesis. Only with E6.5 deletion, we observed aortic arch artery defects including right aortic arch, an indicator of reversed left-right patterning. The concurrence of laterality and cardiovascular defects in pre-streak stage deletion rather than cardiac organogenesis stage deletion indicates that the laterality defect may directly impact heart development. Interestingly, the latent effect of Megf8 on the left-right patterning suggests that the regulation of laterality may be much earlier than we previously thought.

The Roles of Primary Cilia in Cardiovascular Diseases

Primary cilia are microtubule-based organelles found in most mammalian cell types. Cilia act as sensory organelles that transmit extracellular clues into intracellular signals for molecular and cellular responses. Biochemical and molecular defects in primary cilia are associated with a wide range of diseases, termed ciliopathies, with phenotypes ranging from polycystic kidney disease, liver disorders, mental retardation, and obesity to cardiovascular diseases. Primary cilia in vascular endothelia protrude into the lumen of blood vessels and function as molecular switches for calcium (Ca²⁺) and nitric oxide (NO) signaling. As mechanosensory organelles, endothelial cilia are involved in blood flow sensing. Dysfunction in endothelial cilia contributes to aberrant fluid-sensing and thus results in vascular disorders, including hypertension, aneurysm, and atherosclerosis. This review focuses on the most recent findings on the roles of endothelial primary cilia within vascular biology and alludes to the possibility of primary cilium as a therapeutic target for cardiovascular disorders.

Phylogenetic evidence for independent origins of GDF1 and GDF3 genes in anurans and mammals

Growth differentiation factors 1 (GDF1) and 3 (GDF3) are members of the transforming growth factor superfamily (TGF-β) that is involved in fundamental early-developmental processes that are conserved across vertebrates. The evolutionary history of these genes is still under debate due to ambiguous definitions of homologous relationships among vertebrates. Thus, the goal of this study was to unravel the evolution of the GDF1 and GDF3 genes of vertebrates, emphasizing the understanding of homologous relationships and their evolutionary origin. Our results revealed that the GDF1 and GDF3 genes found in anurans and mammals are the products of independent duplication events of an ancestral gene in the ancestor of each of these lineages. The main implication of this result is that the GDF1 and GDF3 genes of anurans and mammals are not 1:1 orthologs. In other words, genes that participate in fundamental processes during early development have been reinvented two independent times during the evolutionary history of tetrapods.

Symmetry Breaking in the Mammalian Embryo

We present an overview of symmetry breaking in early mammalian development as a continuous process from compaction to specification of the body axes. While earlier studies have focused on individual symmetry-breaking events, recent advances enable us to explore progressive symmetry breaking during early mammalian development. Although we primarily discuss embryonic development of the mouse, as it is the best-studied mammalian model system to date, we also highlight the shared and distinct aspects between different mammalian species. Finally, we discuss how insights gained from studying mammalian development can be generalized in light of self-organization principles. With this review, we hope to highlight new perspectives in studying symmetry breaking and self-organization in multicellular systems.

The Role of Hedgehog Signalling in the Formation of the Ventricular Septum

An incomplete septation of the ventricles in the vertebrate heart that disturbes the strict separation between the contents of the two ventricles is termed a ventricular septal defect (VSD). Together with bicuspid aortic valves, it is the most frequent congenital heart disease in humans. Until now, life-threatening VSDs are usually treated surgically. To avoid surgery and to develop an alternative therapy (e.g., a small molecule therapy), it is necessary to understand the molecular mechanisms underlying ventricular septum (VS) development. Consequently, various studies focus on the investigation of signalling pathways, which play essential roles in the formation of the VS. In the past decade, several reports found evidence for an involvement of Hedgehog (HH) signalling in VS development. In this review article, we will summarise the current knowledge about the association between HH signalling and VS formation and discuss the use of such knowledge to design treatment strategies against the development of VSDs.

From cytoskeletal dynamics to organ asymmetry: a nonlinear, regulative pathway underlies left-right patterning

Consistent left-right (LR) asymmetry is a fundamental aspect of the bodyplan across phyla, and errors of laterality form an important class of human birth defects. Its molecular underpinning was first discovered as a sequential pathway of left- and right-sided gene expression that controlled positioning of the heart and visceral organs. Recent data have revised this picture in two important ways. First, the physical origin of chirality has been identified; cytoskeletal dynamics underlie the asymmetry of single-cell behaviour and patterning of the LR axis. Second, the pathway is not linear: early disruptions that alter the normal sidedness of upstream asymmetric genes do not necessarily induce defects in the laterality of the downstream genes or in organ situs Thus, the LR pathway is a unique example of two fascinating aspects of biology: the interplay of physics and genetics in establishing large-scale anatomy, and regulative (shape-homeostatic) pathways that correct molecular and anatomical errors over time. Here, we review aspects of asymmetry from its intracellular, cytoplasmic origins to the recently uncovered ability of the LR control circuitry to achieve correct gene expression and morphology despite reversals of key 'determinant' genes. We provide novel functional data, in Xenopus laevis, on conserved elements of the cytoskeleton that drive asymmetry, and comparatively analyse it together with previously published results in the field. Our new observations and meta-analysis demonstrate that despite aberrant expression of upstream regulatory genes, embryos can progressively normalize transcriptional cascades and anatomical outcomes. LR patterning can thus serve as a paradigm of how subcellular physics and gene expression cooperate to achieve developmental robustness of a body axis.This article is part of the themed issue 'Provocative questions in left-right asymmetry'.

Mutations in the Katnb1 gene cause left-right asymmetry and heart defects

BACKGROUND

The microtubule-severing protein complex katanin is composed two subunits, the ATPase subunit, KATNA1, and the noncatalytic regulatory subunit, KATNB1. Recently, the Katnb1 gene has been linked to infertility, regulation of centriole and cilia formation in fish and mammals, as well as neocortical brain development. KATNB1 protein is expressed in germ cells in humans and mouse, mitotic/meiotic spindles and cilia, although the full expression pattern of the Katnb1 gene has not been described.

RESULTS

Using a knockin-knockout mouse model of Katnb1 dysfunction we demonstrate that Katnb1 is ubiquitously expressed during embryonic development, although a stronger expression is seen in the crown cells of the gastrulation organizer, the murine node. Furthermore, null and hypomorphic Katnb1 gene mutations show a novel correlation between Katnb1 dysregulation and the development of impaired left-right signaling, including cardiac malformations.

CONCLUSIONS

Katanin function is a critical regulator of heart development in mice. These findings are potentially relevant to human cardiac development. Developmental Dynamics 246:1027-1035, 2017. © 2017 Wiley Periodicals, Inc.

Genetic specification of left-right asymmetry in the diaphragm muscles and their motor innervation

The diaphragm muscle is essential for breathing in mammals. Its asymmetric elevation during contraction correlates with morphological features suggestive of inherent left–right (L/R) asymmetry. Whether this asymmetry is due to L versus R differences in the muscle or in the phrenic nerve activity is unknown. Here, we have combined the analysis of genetically modified mouse models with transcriptomic analysis to show that both the diaphragm muscle and phrenic nerves have asymmetries, which can be established independently of each other during early embryogenesis in pathway instructed by Nodal, a morphogen that also conveys asymmetry in other organs. We further found that phrenic motoneurons receive an early L/R genetic imprint, with L versus R differences both in Slit/Robo signaling and MMP2 activity and in the contribution of both pathways to establish phrenic nerve asymmetry. Our study therefore demonstrates L–R imprinting of spinal motoneurons and describes how L/R modulation of axon guidance signaling helps to match neural circuit formation to organ asymmetry.

DOI:http://dx.doi.org/10.7554/eLife.18481.001

The diaphragm is a dome-shaped muscle that forms the floor of the rib cage, separating the lungs from the abdomen. As we breathe in, the diaphragm contracts. This causes the chest cavity to expand, drawing air into the lungs. A pair of nerves called the phrenic nerves carry signals from the spinal cord to the diaphragm to tell it when to contract. These nerves project from the left and right sides of the spinal cord to the left and right sides of the diaphragm respectively.

The left and right sides of the diaphragm are not entirely level, but it was not known why. To investigate, Charoy et al. studied how the diaphragm develops in mouse embryos. This revealed that the left and right phrenic nerves are not symmetrical. Neither are the muscles on each side of the diaphragm. Further investigation revealed that a genetic program that establishes other differences between the left and right sides of the embryo also gives rise to the differences between the left and right sides of the diaphragm. This program switches on different genes in the left and right phrenic nerves, which activate different molecular pathways in the left and right sides of the diaphragm muscle.

The differences between the nerves and muscles on the left and right sides of the diaphragm could explain why some muscle disorders affect only one side of the diaphragm. Similarly, they could explain why congenital hernias caused by abdominal organs pushing through the diaphragm into the chest cavity mostly affect the left side of the diaphragm. Further studies are now needed to investigate these possibilities. The techniques used by Charoy et al. to map the molecular diversity of spinal cord neurons could also lead to new strategies for repairing damage to the spinal cord following injury or disease.

DOI:http://dx.doi.org/10.7554/eLife.18481.002

Modelling asymmetric somitogenesis: Deciphering the mechanisms behind species differences

Somitogenesis is one of the major hallmarks of bilateral symmetry in vertebrates. This symmetry is lost when retinoic acid (RA) signalling is inhibited, allowing the left-right determination pathway to influence somitogenesis. In all three studied vertebrate model species, zebrafish, chicken and mouse, the frequency of somite formation becomes asymmetric, with slower gene expression oscillations driving somitogenesis on the right side. Still, intriguingly, the resulting left-right asymmetric phenotypes differ significantly between these model species. While somitogenesis is generally considered as functionally equivalent among different vertebrates, substantial differences exist in the subset of oscillating genes between different vertebrate species. Variation also appears to exist in the way oscillations cease and somite boundaries become patterned. In addition, in absence of RA, the FGF8 gradient thought to constitute the determination wavefront becomes asymmetric in zebrafish and mouse, extending more anteriorly to the right, while remaining symmetric in chicken. Here we use a computational modelling approach to decipher the causes underlying species differences in asymmetric somitogenesis. Specifically, we investigate to what extent differences can be explained from observed differences in FGF asymmetry and whether differences in somite determination dynamics may also be involved. We demonstrate that a simple clock-and-wavefront model incorporating the observed left-right differences in somitogenesis frequency readily reproduces asymmetric somitogenesis in chicken. However, incorporating asymmetry in FGF signalling was insufficient to robustly reproduce mouse or zebrafish asymmetry phenotypes. In order to explain these phenoptypes we needed to extend the basic model, incorporating species-specific details of the somitogenesis determination mechanism. Our results thus demonstrate that a combination of differences in FGF dynamics and somite determination cause species differences in asymmetric somitogenesis. In addition,they highlight the power of using computational models as well as studying left-right asymmetry to obtain more insight in somitogenesis.

H+/K+-ATPase-Inhibition Causes Left-Right Aortic Arch Inversion in Mouse Development

An organ known as a "node" forms during embryogenesis and plays a vital role in determining laterality in vertebrates. However, according to some reports in vertebrates, left-right patterning may be determined long before the node has developed. In this study, we analyzed left-right asymmetry formation in mammals based on ion-signaling factors, which has never been attempted before. First, a proton pump inhibitor was injected into pregnant mice to investigate whether H⁺/K⁺-ATPase is involved in the differentiation of pharyngeal arch arteries during embryonic development. Injection of 30 mg/kg of lansoprazole early in the organogenesis period increased the penetrance of right aortic arch formation by 34% compared to a saline injection. Furthermore, administration of a proton pump inhibitor resulted in strong expression of PI3K/phosphor-AKT, which led to potent inhibition of apoptosis induction factors such as BAD. This could relate to why the right pharyngeal arch arteries, which should have disappeared during differentiation, remained intact. The other important point is that proton pump inhibitors suppressed calcineurin signaling, and Wnt5a expression was significantly higher than in the controls. This research is particularly notable for demonstrating that administration of an H⁺/K⁺-ATPase inhibitor could cause dextroposition of the fetal vasculature. Moreover, since previous publications have reported that H⁺/K⁺-ATPase plays a role in asymmetry in other species, this article adds important information for developmental biology in that the role of H⁺/K⁺-ATPase in asymmetry is conserved in the mouse model, suggesting that rodents are not unique and that a common mechanism may function across vertebrates.

Plasticity underlies tumor progression: role of Nodal signaling

The transforming growth factor beta (TGFβ) superfamily member Nodal is an established regulator of early embryonic development, with primary roles in endoderm induction, left-right asymmetry, and primitive streak formation. Nodal signals through TGFβ family receptors at the plasma membrane and induces signaling cascades leading to diverse transcriptional regulation. While conceptually simple, the regulation of Nodal and its molecular effects are profoundly complex and context dependent. Pioneering work by developmental biologists has characterized the signaling pathways, regulatory components, and provided detailed insight into the mechanisms by which Nodal mediates changes at the cellular and organismal levels. Nodal is also an important factor in maintaining pluripotency of embryonic stem cells through regulation of core transcriptional programs. Collectively, this work has led to an appreciation for Nodal as a powerful morphogen capable of orchestrating multiple cellular phenotypes. Although Nodal is not active in most adult tissues, its reexpression and signaling have been linked to multiple types of human cancer, and Nodal has emerged as a driver of tumor growth and cellular plasticity. In vitro and in vivo experimental evidence has demonstrated that inhibition of Nodal signaling reduces cancer cell aggressive characteristics, while clinical data have established associations with Nodal expression and patient outcomes. As a result, there is great interest in the potential targeting of Nodal activity in a therapeutic setting for cancer patients that may provide new avenues for suppressing tumor growth and metastasis. In this review, we evaluate our current understanding of the complexities of Nodal function in cancer and highlight recent experimental evidence that sheds light on the therapeutic potential of its inhibition.

Copy-number variant analysis of classic heterotaxy highlights the importance of body patterning pathways

Classic heterotaxy consists of congenital heart defects with abnormally positioned thoracic and abdominal organs. We aimed to uncover novel, genomic copy-number variants (CNVs) in classic heterotaxy cases. A microarray containing 2.5 million single-nucleotide polymorphisms (SNPs) was used to genotype 69 infants (cases) with classic heterotaxy identified from California live births from 1998 to 2009. CNVs were identified using the PennCNV software. We identified 56 rare CNVs encompassing genes in the NODAL (NIPBL, TBX6), BMP (PPP4C), and WNT (FZD3) signaling pathways, not previously linked to classic heterotaxy. We also identified a CNV involving FGF12, a gene previously noted in a classic heterotaxy case. CNVs involving RBFOX1 and near MIR302F were detected in multiple cases. Our findings illustrate the importance of body patterning pathways for cardiac development and left/right axes determination. FGF12, RBFOX1, and MIR302F could be important in human heterotaxy, because they were noted in multiple cases. Further investigation into genes involved in the NODAL, BMP, and WNT body patterning pathways and into the dosage effects of FGF12, RBFOX1, and MIR302F is warranted.

Left-right axis asymmetry determining human Cryptic gene is transcriptionally repressed by Snail

BACKGROUND

Establishment of the left-right axis is important for positioning organs asymmetrically in the developing vertebrate-embryo. A number of factors like maternally deposited molecules have emerged essential in initiating the specification of the axis; the downstream events, however, are regulated by signal-transduction and gene-expression changes identifying which remains a crucial challenge. The EGF-CFC family member Cryptic, that functions as a co-receptor for some TGF-beta ligands, is developmentally expressed in higher mammals and mutations in the gene cause loss or change in left-right axis asymmetry. Despite the strong phenotype, no transcriptional-regulator of this gene is known till date.

RESULTS

Using promoter-analyses tools, we found strong evidence that the developmentally essential transcription factor Snail binds to the human Cryptic-promoter. We cloned the promoter-region of human Cryptic in a reporter gene and observed decreased Cryptic-promoter activation upon increasing Snail expression. Further, the expression of Cryptic is down-regulated upon exogenous Snail expression, validating the reporter assays and the previously identified role of Snail as a transcriptional repressor. Finally, we demonstrate using gel-shift assay that Snail in nuclear extract of PANC1 cells interacts with the promoter-construct bearing putative Snail binding sites and confirm this finding using chromatin immunoprecipitation assay.

CONCLUSIONS

Snail represses the expression of human Cryptic and therefore, might affect the signaling via Nodal that has previously been demonstrated to specify the left-right axis using the EGF-CFC co-receptors.

Extracellular matrix motion and early morphogenesis

For over a century, embryologists who studied cellular motion in early amniotes generally assumed that morphogenetic movement reflected migration relative to a static extracellular matrix (ECM) scaffold. However, as we discuss in this Review, recent investigations reveal that the ECM is also moving during morphogenesis. Time-lapse studies show how convective tissue displacement patterns, as visualized by ECM markers, contribute to morphogenesis and organogenesis. Computational image analysis distinguishes between cell-autonomous (active) displacements and convection caused by large-scale (composite) tissue movements. Modern quantification of large-scale 'total' cellular motion and the accompanying ECM motion in the embryo demonstrates that a dynamic ECM is required for generation of the emergent motion patterns that drive amniote morphogenesis.

Left-Right Axis Differentiation and Functional Lateralization: a Haplotype in the Methyltransferase Encoding Gene SETDB2 Might Mediate Handedness in Healthy Adults

Handedness is a multifactorial trait, and genes contributing to the differentiation of the left-right axis during embryogenesis have been identified as a major gene group associated with this trait. The methyltransferase SETDB2 (SET domain, bifurcated 2) has been shown to regulate structural left-right asymmetry in the vertebrate central nervous system by suppressing fgf8 expression. Here, we investigated the relation of genetic variation in SETDB2-and its paralogue SETDB1-with different handedness phenotypes in 950 healthy adult participants. We identified a haplotype on SETDB2 for which homozygous individuals showed a significantly lower lateralization quotient for handedness than the rest of the cohort after correction for multiple comparisons. Moreover, direction of handedness was significantly associated with genetic variation in this haplotype. This effect was mainly, but not exclusively, driven by the sequence variation rs4942830, as individuals homozygous for the A allele of this single nucleotide polymorphism had a significantly lower lateralization quotient than individuals with at least one T allele. These findings further confirm a role of genetic pathways relevant for structural left-right axis differentiation for functional lateralization. Moreover, as the protein encoded by SETDB2 regulates gene expression epigenetically by histone H3 methylation, our findings highlight the importance of investigating the role of epigenetic modulations of gene expression in relation to handedness.

Situs inversus and ciliary abnormalities: 20 years later, what is the connection?

Heterotaxy (also known as situs ambiguous) and situs inversus totalis describe disorders of laterality in which internal organs do not display their typical pattern of asymmetry. First described around 1600 by Girolamo Fabrizio, numerous case reports about laterality disorders in humans were published without any idea about the underlying cause. Then, in 1976, immotile cilia were described as the cause of a human syndrome that was previously clinically described, both in 1904 by AK Siewert and in 1933 by Manes Kartagener, as an association of situs inversus with chronic sinusitis and bronchiectasis, now commonly known as Kartagener’s syndrome. Despite intense research, the underlying defect of laterality disorders remained unclear. Nearly 20 years later in 1995, Björn Afzelius discussed five hypotheses to explain the connection between ciliary defects and loss of laterality control in a paper published in the International Journal of Developmental Biology asking: ‘Situs inversus and ciliary abnormalities: What is the connection?’. Here, nearly 20 research years later, we revisit some of the key findings that led to the current knowledge about the connection between situs inversus and ciliary abnormalities.

Essential roles of epithelial bone morphogenetic protein signaling during prostatic development

Prostate is a male sex-accessory organ. The prostatic epithelia consist primarily of basal and luminal cells that differentiate from embryonic urogenital sinus epithelia. Prostate tumors are believed to originate in the basal and luminal cells. However, factors that promote normal epithelial differentiation have not been well elucidated, particularly for bone morphogenetic protein (Bmp) signaling. This study shows that Bmp signaling prominently increases during prostatic differentiation in the luminal epithelia, which is monitored by the expression of phosphorylated Smad1/5/8. To elucidate the mechanism of epithelial differentiation and the function of Bmp signaling during prostatic development, conditional male mutant mouse analysis for the epithelial-specific Bmp receptor 1a (Bmpr1a) was performed. We demonstrate that Bmp signaling is indispensable for luminal cell maturation, which regulates basal cell proliferation. Expression of the prostatic epithelial regulatory gene Nkx3.1 was significantly reduced in the Bmpr1a mutants. These results indicate that Bmp signaling is a key factor for prostatic epithelial differentiation, possibly by controlling the prostatic regulatory gene Nkx3.1.

Developmental signaling: does it bridge the gap between cilia dysfunction and renal cystogenesis?

For more than a decade, evidence has accumulated linking dysfunction of primary cilia to renal cystogenesis, yet molecular mechanisms remain undefined. The pathogenesis of renal cysts is complex, involving multiple cellular aberrations and signaling pathways. Adding to this complexity, primary cilia exhibit multiple roles in a context-dependent manner. On renal epithelial cells, primary cilia act as mechanosensors and trigger extracellular Ca(2+) influx in response to laminar fluid flow. During mammalian development, primary cilia mediate the Hedgehog (Hh), Wnt, and Notch pathways, which control cell proliferation and differentiation, and tissue morphogenesis. Further, experimental evidence suggests the developmental state of the kidney strongly influences renal cystic disease. Thus, we review evidence for regulation of Ca(2+) and cAMP, key molecules in renal cystogenesis, at the primary cilium, the role of Hh, Wnt, and Notch signaling in renal cystic disease, and the interplay between these developmental pathways and Ca(2+) signaling. Indeed if these developmental pathways influence renal cystogenesis, these may represent novel therapeutic targets that can be integrated into a combination therapy for renal cystic disease.

Primary cilia in stem cells and neural progenitors are regulated by neutral sphingomyelinase 2 and ceramide

Human embryonic stem and induced pluripotent stem cell–derived neuroprogenitors (NPs) develop primary cilia. Ciliogenesis depends on the sphingolipid ceramide and its interaction with atypical PKC, both of which distribute to the primary cilium and the apicolateral cell membrane in NP rosettes.

We show here that human embryonic stem (ES) and induced pluripotent stem cell–derived neuroprogenitors (NPs) develop primary cilia. Ciliogenesis depends on the sphingolipid ceramide and its interaction with atypical PKC (aPKC), both of which distribute to the primary cilium and the apicolateral cell membrane in NP rosettes. Neural differentiation of human ES cells to NPs is concurrent with a threefold elevation of ceramide—in particular, saturated, long-chain C_16:0 ceramide (N-palmitoyl sphingosine) and nonsaturated, very long chain C_24:1 ceramide (N-nervonoyl sphingosine). Decreasing ceramide levels by inhibiting ceramide synthase or neutral sphingomyelinase 2 leads to translocation of membrane-bound aPKC to the cytosol, concurrent with its activation and the phosphorylation of its substrate Aurora kinase A (AurA). Inhibition of aPKC, AurA, or a downstream target of AurA, HDAC6, restores ciliogenesis in ceramide-depleted cells. Of importance, addition of exogenous C_24:1 ceramide reestablishes membrane association of aPKC, restores primary cilia, and accelerates neural process formation. Taken together, these results suggest that ceramide prevents activation of HDAC6 by cytosolic aPKC and AurA, which promotes acetylation of tubulin in primary cilia and, potentially, neural processes. This is the first report on the critical role of ceramide generated by nSMase2 in stem cell ciliogenesis and differentiation.

Cilia and coordination of signaling networks during heart development

Primary cilia are unique sensory organelles that coordinate a wide variety of different signaling pathways to control cellular processes during development and in tissue homeostasis. Defects in function or assembly of these antenna-like structures are therefore associated with a broad range of developmental disorders and diseases called ciliopathies. Recent studies have indicated a major role of different populations of cilia, including nodal and cardiac primary cilia, in coordinating heart development, and defects in these cilia are associated with congenital heart disease. Here, we present an overview of the role of nodal and cardiac primary cilia in heart development.