S1pr2/Gα13 signaling controls myocardial migration by regulating endoderm convergence

Cardiac construction-Recent advances in morphological and transcriptional modeling of early heart development

During human embryonic development the early establishment of a functional heart is vital to support the growing fetus. However, forming the embryonic heart is an extremely complex process, requiring spatiotemporally controlled cell specification and differentiation, tissue organization, and coordination of cardiac function. These complexities, in concert with the early and rapid development of the embryonic heart, mean that understanding the intricate interplay between these processes that help shape the early heart remains highly challenging. In this review I focus on recent insights from animal models that have shed new light on the earliest stages of heart development. This includes specification and organization of cardiac progenitors, cell and tissue movements that make and shape the early heart tube, and the initiation of the first beat in the developing heart. In addition I highlight relevant in vitro models that could support translation of findings from animal models to human heart development. Finally I discuss challenges that are being addressed in the field, along with future considerations that together may help move us towards a deeper understanding of how our hearts are made.

The myocardium utilizes a platelet-derived growth factor receptor alpha (Pdgfra)-phosphoinositide 3-kinase (PI3K) signaling cascade to steer toward the midline during zebrafish heart tube formation

Coordinated cell movement is a fundamental process in organ formation. During heart development, bilateral myocardial precursors collectively move toward the midline (cardiac fusion) to form the primitive heart tube. Extrinsic influences such as the adjacent anterior endoderm are known to be required for cardiac fusion. We previously showed however, that the platelet-derived growth factor receptor alpha (Pdgfra) is also required for cardiac fusion (Bloomekatz et al., 2017). Nevertheless, an intrinsic mechanism that regulates myocardial movement has not been elucidated. Here, we show that the phosphoinositide 3-kinase (PI3K) intracellular signaling pathway has an essential intrinsic role in the myocardium directing movement toward the midline. In vivo imaging further reveals midline-oriented dynamic myocardial membrane protrusions that become unpolarized in PI3K-inhibited zebrafish embryos where myocardial movements are misdirected and slower. Moreover, we find that PI3K activity is dependent on and interacts with Pdgfra to regulate myocardial movement. Together our findings reveal an intrinsic myocardial steering mechanism that responds to extrinsic cues during the initiation of cardiac development.

Flat mount preparation for whole-mount fluorescent imaging of zebrafish embryos

The zebrafish is a widely used model organism for biomedical research due to its ease of maintenance, external fertilization of embryos, rapid embryonic development, and availability of established genetic tools. One notable advantage of using zebrafish is the transparency of the embryos, which enables high-resolution imaging of specific cells, tissues, and structures through the use of transgenic and knock-in lines. However, as the embryo develops, multiple layers of tissue wrap around the lipid-enriched yolk, which can create a challenge to image tissues located deep within the embryo. While various methods are available, such as two-photon imaging, cryosectioning, vibratome sectioning, and micro-surgery, each of these has limitations. In this study, we present a novel deyolking method that allows for high-quality imaging of tissues that are obscured by other tissues and the yolk. Embryos are lightly fixed in 1% PFA to remove the yolk without damaging embryonic tissues and are then refixed in 4% PFA and mounted on custom-made bridged slides. This method offers a simple way to prepare imaging samples that can be subjected to further preparation, such as immunostaining. Furthermore, the bridged slides described in this study can be used for imaging tissue and organ preparations from various model organisms.

Quantifying endodermal strains during heart tube formation in the developing chicken embryo

In the early avian embryo, the developing heart forms when bilateral fields of cardiac progenitor cells, which reside in the lateral plate mesoderm, move toward the embryonic midline, and fuse above the anterior intestinal portal (AIP) to form a straight, muscle-wrapped tube. During this process, the precardiac mesoderm remains in close contact with the underlying endoderm. Previous work has shown that the endoderm around the AIP actively contracts to pull the cardiac progenitors toward the midline. The morphogenetic deformations associated with this endodermal convergence, however, remain unclear, as do the signaling pathways that might regulate this process. Here, we fluorescently labeled populations of endodermal cells in early chicken embryos and tracked their motion during heart tube formation to compute time-varying strains along the anterior endoderm. We then determined how the computed endodermal strain distributions are affected by the pharmacological inhibition of either myosin II or fibroblast growth factor (FGF) signaling. Our data indicate that a mediolateral gradient in endodermal shortening is present around the AIP, as well as substantial convergence and extension movements both anterior and lateral to the AIP. These active endodermal deformations are disrupted if either actomyosin contractility or FGF signaling are inhibited pharmacologically. Taken together, these results demonstrate how active deformations along the anterior endoderm contribute to heart tube formation within the developing embryo.

Plpp3, a novel regulator of pluripotency exit and endodermal differentiation of mouse embryonic stem cells

In recent decades, study of the actions of bioactive lipids such as lysophosphatidic acid (LPA) and sphingosine-1-phosphate (S1P) has increased since they are involved in regulating many processes, including self-renewal of embryonic stem cells, embryo development and cancer. Phospholipid phosphatase type 3 (PLPP3) has been shown to be a key player in regulating the balance of these lipids and, in consequence, their signaling. Different lines of evidence suggest that PLPP3 could play a role in endoderm development. To approach this hypothesis, we used mouse embryonic stem cells (ESC) as a model to study Plpp3 function in self-renewal and the transition towards differentiation. We found that lack of PLPP3 mainly affects endoderm formation during differentiation of suspension-formed embryoid bodies. PLPP3-deficient ESC strongly decrease the amount of FOXA2-expressing cells and fail to properly downregulate the expression of pluripotency factors when subjected to an endoderm-directed differentiation protocol. Impaired endoderm differentiation correlated with a transient reduction in nuclear localization of YAP1. These phenotypes were rescued by transiently restoring the expression of catalytically active hPLPP3. In conclusion, PLPP3 plays a role in downregulating pluripotency-associated factors and in endodermal differentiation. PLPP3 regulates proper lipid/YAP1 signaling required for endodermal differentiation.

The myocardium utilizes Pdgfra-PI3K signaling to steer towards the midline during heart tube formation

Coordinated cell movement is a fundamental process in organ formation. During heart development, bilateral myocardial precursors collectively move towards the midline (cardiac fusion) to form the primitive heart tube. Along with extrinsic influences such as the adjacent anterior endoderm which are known to be required for cardiac fusion, we previously showed that the platelet-derived growth factor receptor alpha (Pdgfra) is also required. However, an intrinsic mechanism that regulates myocardial movement remains to be elucidated. Here, we uncover an essential intrinsic role in the myocardium for the phosphoinositide 3-kinase (PI3K) intracellular signaling pathway in directing myocardial movement towards the midline. In vivo imaging reveals that in PI3K-inhibited zebrafish embryos myocardial movements are misdirected and slower, while midline-oriented dynamic myocardial membrane protrusions become unpolarized. Moreover, PI3K activity is dependent on and genetically interacts with Pdgfra to regulate myocardial movement. Together our findings reveal an intrinsic myocardial steering mechanism that responds to extrinsic cues during the initiation of cardiac development.

Nodal signaling regulates asymmetric cellular behaviors, driving clockwise rotation of the heart tube in zebrafish

Clockwise rotation of the primitive heart tube, a process regulated by restricted left-sided Nodal signaling, is the first morphological manifestation of left-right asymmetry. How Nodal regulates cell behaviors to drive asymmetric morphogenesis remains poorly understood. Here, using high-resolution live imaging of zebrafish embryos, we simultaneously visualized cellular dynamics underlying early heart morphogenesis and resulting changes in tissue shape, to identify two key cell behaviors: cell rearrangement and cell shape change, which convert initially flat heart primordia into a tube through convergent extension. Interestingly, left cells were more active in these behaviors than right cells, driving more rapid convergence of the left primordium, and thereby rotating the heart tube. Loss of Nodal signaling abolished the asymmetric cell behaviors as well as the asymmetric convergence of the left and right heart primordia. Collectively, our results demonstrate that Nodal signaling regulates the magnitude of morphological changes by acting on basic cellular behaviors underlying heart tube formation, driving asymmetric deformation and rotation of the heart tube.

Fibronectin and Integrin α5 play overlapping and independent roles in regulating the development of pharyngeal endoderm and cartilage

Craniofacial skeletal elements are derived from cranial neural crest cells (CNCCs), which migrate along discrete paths and populate distinct pharyngeal arches, structures that are separated by the neighboring endodermal pouches (EPs). Interactions between the CNCCs and the endoderm are critical for proper craniofacial development. In zebrafish, integrin α5 (Itga5) functions in the endoderm to regulate formation of specifically the first EP (EP1) and the development of the hyoid cartilage. Here we show that fibronectin (Fn), a major component of the extracellular matrix (ECM), is also required for these developmental processes, and that the penetrance of defects in mutants is temperature-dependent. fn1a^-/- embryos exhibited defects that are similar to, but much more severe than, those of itga5^-/- embryos, and a loss of integrin av (itgav) function enhanced both endoderm and cartilage defects in itga5^-/- embryos, suggesting that Itga5 and Itgav cooperate to transmit signals from Fn to regulate the development of endoderm and cartilage. Whereas the endodermal defects in itga5; itga5v^-/- double mutant embryos were comparable to those of fn1a^-/- mutants, the cartilage defects were much milder. Furthermore, Fn assembly was detected in migrating CNCCs, and the epithelial organization and differentiation of CNCC-derived arches were impaired in fn1a^-/- embryos, indicating that Fn1 exerts functions in arch development that are independent of Itga5 and Itgav. Additionally, reduction of itga5 function in fn1a^-/- embryos led to profound defects in body axis elongation, as well as in endoderm and cartilage formation, suggesting that other ECM proteins signal through Itga5 to regulate development of the endoderm and cartilage. Thus, our studies reveal that Fn1a and Itga5 have both overlapping and independent functions in regulating development of the pharyngeal endoderm and cartilage.

Gα12 and Gα13: Versatility in Physiology and Pathology

G protein-coupled receptors (GPCRs), as the largest family of receptors in the human body, are involved in the pathological mechanisms of many diseases. Heterotrimeric G proteins represent the main molecular switch and receive cell surface signals from activated GPCRs. Growing evidence suggests that Gα₁₂ subfamily (Gα_12/13)-mediated signaling plays a crucial role in cellular function and various pathological processes. The current research on the physiological and pathological function of Gα_12/13 is constantly expanding, Changes in the expression levels of Gα_12/13 have been found in a wide range of human diseases. However, the mechanistic research on Gα_12/13 is scattered. This review briefly describes the structural sequences of the Gα_12/13 isoforms and introduces the coupling of GPCRs and non-GPCRs to Gα_12/13. The effects of Gα_12/13 on RhoA and other signaling pathways and their roles in cell proliferation, migration, and immune cell function, are discussed. Finally, we focus on the pathological impacts of Gα_12/13 in cancer, inflammation, metabolic diseases, fibrotic diseases, and circulatory disorders are brought to focus.

Mcm5 Represses Endodermal Migration through Cxcr4a-itgb1b Cascade Instead of Cell Cycle Control

Minichromosome maintenance protein 5 (MCM5) is a critical cell cycle regulator; its role in DNA replication is well known, but whether it is involved in the regulation of organogenesis in a cell cycle-independent way, is far from clear. In this study, we found that a loss of mcm5 function resulted in a mildly smaller liver, but that mcm5 overexpression led to liver bifida. Further, the data showed that mcm5 overexpression delayed endodermal migration in the ventral–dorsal axis and induced the liver bifida. Cell cycle analysis showed that a loss of mcm5 function, but not overexpression, resulted in cell cycle delay and increased cell apoptosis during gastrulation, implying that liver bifida was not the result of a cell cycle defect. In terms of its mechanism, our data proves that mcm5 represses the expression of cxcr4a, which sequentially causes a decrease in the expression of itgb1b during gastrulation. The downregulation of the cxcr4a-itgb1b cascade leads to an endodermal migration delay during gastrulation, as well as to the subsequent liver bifida during liver morphogenesis. In conclusion, our results suggest that in a cell cycle-independent way, mcm5 works as a gene expression regulator, either partially and directly, or indirectly repressing the expression of cxcr4a and the downstream gene itgb1b, to coordinate endodermal migration during gastrulation and liver location during liver organogenesis.

CARMIL3 is important for cell migration and morphogenesis during early development in zebrafish

Cell migration is important during early animal embryogenesis. Cell migration and cell shape are controlled by actin assembly and dynamics, which depend on capping proteins, including the barbed-end heterodimeric actin capping protein (CP). CP activity can be regulated by capping-protein-interacting (CPI) motif proteins, including CARMIL (capping protein Arp2/3 myosin-I linker) family proteins. Previous studies of CARMIL3, one of the three highly conserved CARMIL genes in vertebrates, have largely been limited to cells in culture. Towards understanding CARMIL function during embryogenesis in vivo, we analyzed zebrafish lines carrying mutations of carmil3. Maternal-zygotic mutants showed impaired endodermal migration during gastrulation, along with defects in dorsal forerunner cell (DFC) cluster formation, which affected the morphogenesis of Kupffer's vesicle (KV). Mutant KVs were smaller, contained fewer cells and displayed decreased numbers of cilia, leading to defects in left/right (L/R) patterning with variable penetrance and expressivity. The penetrance and expressivity of the KV phenotype in carmil3 mutants correlated well with the L/R heart positioning defect at the end of embryogenesis. This in vivo animal study of CARMIL3 reveals its new role during morphogenesis of the vertebrate embryo. This role involves migration of endodermal cells and DFCs, along with subsequent morphogenesis of the KV and L/R asymmetry.

Uncovering the 'sphinx' of sphingosine 1-phosphate signalling: from cellular events to organ morphogenesis

Sphingosine 1-phosphate (S1P) is a bioactive sphingolipid metabolite, functioning as a signalling molecule in diverse cellular processes. Over the past few decades, studies of S1P signalling have revealed that the physiological activity of S1P largely depends on S1P metabolizing enzymes, transporters and receptors on the plasma membrane, as well as on the intracellular proteins that S1P binds directly to. In addition to its roles in cancer signalling, immunity and inflammation, a large body of evidence has identified a close link of S1P signalling with organ morphogenesis. Here we discuss the vital role of S1P signalling in orchestrating various cellular events during organ morphogenesis through analysing each component along the extracellular and intracellular S1P signalling axes. For each component, we review advances in our understanding of S1P signalling and function from the upstream regulators to the downstream effectors and from cellular behaviours to tissue organization, primarily in the context of morphogenetic mechanisms. S1P-mediated vesicular trafficking is also discussed as a function independent of its signalling function. A picture emerges that reveals a multifaceted role of S1P-dependent pathways in the development and maintenance of organ structure and function.

Glypican 4 regulates planar cell polarity of endoderm cells by controlling the localization of Cadherin 2

Noncanonical Wnt/planar cell polarity (Wnt/PCP) signaling has been implicated in endoderm morphogenesis. However, the underlying cellular and molecular mechanisms of this process are unclear. We found that, during convergence and extension (C&E) in zebrafish, gut endodermal cells are polarized mediolaterally, with GFP-Vangl2 enriched at the anterior edges. Endoderm cell polarity is lost and intercalation is impaired in the absence of glypican 4 (gpc4), a heparan-sulfate proteoglycan that promotes Wnt/PCP signaling, suggesting that this signaling is required for endodermal cell polarity. Live imaging revealed that endoderm C&E is accomplished by polarized cell protrusions and junction remodeling, which are impaired in gpc4-deficient endodermal cells. Furthermore, in the absence of gpc4, Cadherin 2 expression on the endodermal cell surface is increased as a result of impaired Rab5c-mediated endocytosis, which partially accounts for the endodermal defects in these mutants. These findings indicate that Gpc4 regulates endodermal planar cell polarity during endoderm C&E by influencing the localization of Cadherin 2. Thus, our study uncovers a new mechanism by which Gpc4 regulates planar cell polarity and reveals the role of Wnt/PCP signaling in endoderm morphogenesis.

Sphingosine-1-Phosphate Metabolism and Signaling in Kidney Diseases

In the past few decades, sphingolipids and sphingolipid metabolites have gained attention because of their essential role in the pathogenesis and progression of kidney diseases. Studies in models of experimental and clinical nephropathies have described accumulation of sphingolipids and sphingolipid metabolites, and it has become clear that the intracellular sphingolipid composition of renal cells is an important determinant of renal function. Proper function of the glomerular filtration barrier depends heavily on the integrity of lipid rafts, which include sphingolipids as key components. In addition to contributing to the structural integrity of membranes, sphingolipid metabolites, such as sphingosine-1-phosphate (S1P), play important roles as second messengers regulating biologic processes, such as cell growth, differentiation, migration, and apoptosis. This review will focus on the role of S1P in renal cells and how aberrant extracellular and intracellular S1P signaling contributes to the pathogenesis and progression of kidney diseases.

Post-translational modifications of S1PR1 and endothelial barrier regulation

Sphingosine-1-phosphate receptor-1 (S1PR1), a G-protein coupled receptor that is expressed in endothelium and activated upon ligation by the bioactive lipid sphingosine-1-phosphate (S1P), is an important vascular-barrier protective mechanism at the level of adherens junctions (AJ). Loss of endothelial barrier function is a central factor in the pathogenesis of various inflammatory conditions characterized by protein-rich lung edema formation, such as acute respiratory distress syndrome (ARDS). While several S1PR1 agonists are available, the challenge of arresting the progression of protein-rich edema formation remains to be met. In this review, we discuss the role of S1PRs, especially S1PR1, in regulating endothelial barrier function. We review recent findings showing that replenishment of the pool of cell-surface S1PR1 may be crucial to the effectiveness of S1P in repairing the endothelial barrier. In this context, we discuss the S1P generating machinery and mechanisms that regulate S1PR1 at the cell surface and their impact on endothelial barrier function.

Genetic Deletion of miR-430 Disrupts Maternal-Zygotic Transition and Embryonic Body Plan

MiR-430 is considered an important regulator during embryonic development, but genetic loss-of-function study is still lacking. Here we demonstrated that genetic deletion of the miR-430 cluster resulted in developmental defects in cell movement, germ layer specification, axis patterning and organ progenitor formation in zebrafish. Transcriptome analysis indicated that the maternally provided transcripts were not properly degraded whereas the zygotic genome expressed genes were not fully activated in the miR-430 mutants. We further found that a reciprocal regulatory loop exists between miR-430 and maternally provided transcripts: the maternally provided transcripts (Nanog, Dicer1, Dgcr8, and AGOs) are required for miR-430 biogenesis and function, whereas miR-430 is required for the clearance of these maternally provided transcripts. These data provide the first genetic evidence that miR-430 is required for maternal-zygotic transition and subsequent establishment of embryonic body plan.

Divergent C-terminal motifs in Gα12 and Gα13 provide distinct mechanisms of effector binding and SRF activation

The G12/13 subfamily of heterotrimeric guanine nucleotide binding proteins comprises the α subunits Gα12 and Gα13, which transduce signals for cell growth, cytoskeletal rearrangements, and oncogenic transformation. In an increasing range of cancers, overexpressed Gα12 or Gα13 are implicated in aberrant cell proliferation and/or metastatic invasion. Although Gα12 and Gα13 bind non-redundant sets of effector proteins and participate in unique signalling pathways, the structural features responsible for functional differences between these α subunits are largely unknown. Invertebrates encode a single G12/13 homolog that participates in cytoskeletal changes yet appears to lack signalling to SRF (serum response factor), a transcriptional activator stimulated by mammalian Gα12 and Gα13 to promote growth and tumorigenesis. Our previous studies identified an evolutionarily divergent region in Gα12 for which replacement by homologous sequence from Drosophila melanogaster abolished SRF signalling, whereas the same invertebrate substitution was fully tolerated in Gα13 [Montgomery et al. (2014) Mol. Pharmacol. 85: 586]. These findings prompted our current approach of evolution-guided mutagenesis to identify fine structural features of Gα12 and Gα13 that underlie their respective SRF activation mechanisms. Our results identified two motifs flanking the α4 helix that play a key role in Gα12 signalling to SRF. We found the region encompassing these motifs to provide an interacting surface for multiple Gα12-specific target proteins that fail to bind Gα13. Adjacent to this divergent region, a highly-conserved domain was vital for SRF activation by both Gα12 and Gα13. However, dissection of this domain using invertebrate substitutions revealed different signalling mechanisms in these α subunits and identified Gα13-specific determinants of binding Rho-specific guanine nucleotide exchange factors. Furthermore, invertebrate substitutions in the C-terminal, α5 helical region were selectively disruptive to Gα12 signalling. Taken together, our results identify key structural features near the C-terminus that evolved after the divergence of Gα12 and Gα13, and should aid the development of agents to selectively manipulate signalling by individual α subunits of the G12/13 subfamily.

Marcksb plays a key role in the secretory pathway of zebrafish Bmp2b

During vertebrate early embryogenesis, the ventral development is directed by the ventral-to-dorsal activity gradient of the bone morphogenetic protein (BMP) signaling. As secreted ligands, the extracellular traffic of BMP has been extensively studied. However, it remains poorly understood that how BMP ligands are secreted from BMP-producing cells. In this work, we show the dominant role of Marcksb controlling the secretory process of Bmp2b via interaction with Hsp70 in vivo. We firstly carefully characterized the role of Marcksb in promoting BMP signaling during dorsoventral axis formation through knockdown approach. We then showed that Marcksb cell autonomously regulates the trafficking of Bmp2b from producing cell to the extracellular space and both the total and the extracellular Bmp2b was decreased in Marcksb-deficient embryos. However, neither the zygotic mutant of marcksb (Zmarcksb) nor the maternal zygotic mutant of marcksb (MZmarcksb) showed any defects of dorsalization. In contrast, the MZmarcksb embryos even showed increased BMP signaling activity as measured by expression of BMP targets, phosphorylated Smad1/5/9 levels and imaging of Bmp2b, suggesting that a phenomenon of “genetic over-compensation” arose. Finally, we revealed that the over-compensation effects of BMP signaling in MZmarcksb was achieved through a sequential up-regulation of MARCKS-family members Marcksa, Marcksl1a and Marcksl1b, and MARCKS-interacting protein Hsp70.3. We concluded that the Marcksb modulates BMP signaling through regulating the secretory pathway of Bmp2b.

Bone morphogenetic proteins (BMPs) are extracellular proteins which belong to the transforming growth factor-β (TGF-β) superfamily. BMP signaling is essential for embryonic development, organogenesis, and tissue regeneration and homeostasis, and tightly linked to various diseases and tumorigenesis. However, as secreted proteins, how BMPs are transported and secreted from BMP-producing cells remains poorly understood. In this study, we showed that Marcksb interacts with a molecular chaperon–Hsp70.3 to mediate the secretory pathway of BMP ligands during early development of zebrafish. Moreover, we discovered a novel phenomenon of “genetic over-compensation” in the genetic knock-out mutants of marcksb. To our knowledge, this is the first report that reveals the molecules and their related trafficking system mediating the secretion of BMPs. Considering the wide distribution of BMP and MARCKS within the human body, our work may shed light on the studies of BMPs secretion in organogenesis and adult tissue homeostasis. The finding of MARCKS in controlling BMP secretion may provide potential therapeutic targets for modulating the activity of BMP signaling and thus will be of interest to clinical research.

S1PR2 antagonist ameliorate high glucose-induced fission and dysfunction of mitochondria in HRGECs via regulating ROCK1

Aims

Sphingosine-1-phosphate receptor 2 (S1PR2) is a G-protein-coupled receptor that regulates sphingosine-1-phosphate-triggered cellular response. However, the role of S1PR2 in diabetes-induced glomerular endothelial cell dysfunction remains unclear. This study aims to investigate the effect of S1PR2 blockade on the morphology and function of mitochondria in human renal glomerular endothelial cells (HRGECs).

Methods

HRGECs were pretreated with a S1PR2 antagonist (JTE-013) or a Rho-associated coiled coil-containing protein kinase 1 (ROCK1) inhibitor (Y27632) for 30 min and then cultured with normal glucose (5.5 mM) or high glucose (30 mM) for 72 h. The protein expression levels of RhoA, ROCK1, and Dynmin-related protein-1(Drp1) were evaluated by immunoblotting; mitochondrial morphology was observed by electron microscopy; intracellular levels of ATP, ROS, and Ca²⁺ were measured by ATPlite, DCF-DA, and Rhod-2 AM assays, respectively. Additionally, the permeability, apoptosis, and migration of cells were determined to evaluate the effects of S1PR2 and ROCK1 inhibition on high glucose-induced endothelial dysfunction.

Results

High glucose induced mitochondrial fission and dysfunction, indicated by increased mitochondrial fragmentation, ROS generation, and calcium overload but decreased ATP production. High glucose also induced endothelial cell dysfunction, indicated by increased permeability and apoptosis but decreased migration. However, inhibition of either S1PR2 or ROCK1 almost completely blocked these high glucose-mediated cellular responses. Furthermore, inhibiting S1PR2 resulted in the deceased expression of RhoA, ROCK1, and Drp1 while inhibiting ROCK1 led to the downregulated expression of Drp1.

Conclusions

S1PR2 antagonist modulates the morphology and function of mitochondria in HRGECs via the positive regulation of the RhoA/ROCK1/Drp1 signaling pathway, suggesting that the S1PR2/ROCK1 pathway may play a crucial role in high glucose milieu.

Electronic supplementary material

The online version of this article (10.1186/s12882-019-1323-0) contains supplementary material, which is available to authorized users.

Abundance of Early Embryonic Primordial Germ Cells Promotes Zebrafish Female Differentiation as Revealed by Lifetime Labeling of Germline

Teleost sex differentiation largely depends on the number of undifferentiated germ cells. Here, we describe the generation and characterization of a novel transgenic zebrafish line, Tg(piwil1:egfp-UTRnanos3)^ihb327Tg, which specifically labels the whole lifetime of germ cells, i.e., from primordial germ cells (PGCs) at shield stage to the oogonia and early stage of oocytes in the ovary and to the early stage of spermatogonia, spermatocyte, and spermatid in the testis. By using this transgenic line, we carefully observed the numbers of PGCs from early embryonic stage to juvenile stage and the differentiation process of ovary and testis. The numbers of PGCs became variable at as early as 1 day post-fertilization (dpf). Interestingly, the embryos with a high amount of PGCs mainly developed into females and the ones with a low amount of PGCs mainly developed into males. By using transient overexpression and transgenic induction of PGC-specific bucky ball (buc), we further proved that induction of abundant PGCs at embryonic stage promoted later ovary differentiation and female development. Taken together, we generate an ideal transgenic line Tg(piwil1:egfp-UTRnanos3)^ihb327Tg which can visualize zebrafish germline for a lifetime, and we have utilized this line to study germ cell development and gonad differentiation of teleost and to demonstrate that the increase of PGC number at embryonic stage promotes female differentiation.

Glypican 4 and Mmp14 interact in regulating the migration of anterior endodermal cells by limiting extracellular matrix deposition

During embryogenesis, the germ layers, including the endoderm, undergo convergence and extension movements to narrow and elongate the body plan. In zebrafish, the dorsal migration of endodermal cells during gastrulation is controlled by chemokine signaling, but little is known about how they migrate during segmentation. Here, we show that glypican 4 (Gpc4), a member of the heparin sulfate proteoglycan family, is required for efficient migration of anterior endodermal cells during early segmentation, regulating Rac activation to maintain polarized actin-rich lamellipodia. An endoderm transplantation assay showed that Gpc4 regulates endoderm migration in a non-cell-autonomous fashion. Further analyses revealed that the impaired endoderm migration in gpc4 mutants results from increases in the expression and assembly of fibronectin and laminin, major components of the extracellular matrix (ECM). Notably, we found that matrix metalloproteinase 14 (Mmp14a/b) is required for the control of ECM expression during endoderm migration, with Gpc4 acting through Mmp14a/b to limit ECM expression. Our results suggest that Gpc4 is crucial for generating the environment required for efficient migration of endodermal cells, uncovering a novel function of Gpc4 during development.

Overlap in signaling between Smoothened and the α subunit of the heterotrimeric G protein G13

The Hedgehog family of morphogens has long been known to utilize, through the 7-transmembrane protein Smoothened (Smo), the heterotrimeric G protein Gi in both canonical and noncanonical forms of signaling. Other G proteins, while not specifically utilized by Smo, may nonetheless provide access to some of the events controlled by it. We reported several years ago that the G protein G13 activates one or more forms of the Gli family of transcription factors. While the Gli transcription factors are well known targets for Smo, the uncertain mechanism of activation by G13 and the identity of the targeted Gli(s) limited predictions as to the extent to which G13 might mimic Smo's actions. We evaluate here the potential for overlap in G13 and Smo signaling using C3H10T1/2 and 3T3-L1 cells as models of osteogenesis and adipogenesis, respectively. We find in C3H10T1/2 cells that a constitutively active form of Gα13 (Gα13QL) increases Gli1 mRNA, as does a constitutively active form of Smo (SmoA1). We find as well that Gα13QL induces alkaline phosphatase activity, a marker of osteogenesis, albeit the induction is far less substantial than that achieved by SmoA1. In 3T3-L1 cells both Gα13QL and SmoA1 markedly suppress adipogenic differentiation as determined by triglyceride accumulation. RNA sequencing reveals that Gα13QL and SmoA1 regulate many of the same genes but that quantitative and qualitative differences exist. Differences also exist, we find, between SmoA1 and purmorphamine, an agonist for Smo. Therefore, while comparisons of constitutively active proteins are informative, extrapolations to the setting of agonists require care.

The ceramide synthase 2b gene mediates genomic sensing and regulation of sphingosine levels during zebrafish embryogenesis

Sphingosine-1-phosphate (S1P) is generated through phosphorylation of sphingosine by sphingosine kinases (Sphk1 and Sphk2). We show that sphk2 maternal-zygotic mutant zebrafish embryos (sphk2^MZ) display early developmental phenotypes, including a delay in epiboly, depleted S1P levels, elevated levels of sphingosine, and resistance to sphingosine toxicity. The sphk2^MZ embryos also have strikingly increased levels of maternal transcripts encoding ceramide synthase 2b (Cers2b), and loss of Cers2b in sphk2^MZ embryos phenocopies sphingosine toxicity. An upstream region of the cers2b promoter supports enhanced expression of a reporter gene in sphk2^MZ embryos compared to wildtype embryos. Furthermore, ectopic expression of Cers2b protein itself reduces activity of the promoter, and this repression is relieved by exogenous sphingosine. Therefore, the sphk2^MZ genome recognizes the lack of sphingosine kinase activity and up-regulates cers2b as a salvage pathway for sphingosine turnover. Cers2b can also function as a sphingolipid-responsive factor to mediate at least part of a feedback regulatory mechanism.

Platelet-derived growth factor (PDGF) signaling directs cardiomyocyte movement toward the midline during heart tube assembly

Communication between neighboring tissues plays a central role in guiding organ morphogenesis. During heart tube assembly, interactions with the adjacent endoderm control the medial movement of cardiomyocytes, a process referred to as cardiac fusion. However, the molecular underpinnings of this endodermal-myocardial relationship remain unclear. Here, we show an essential role for platelet-derived growth factor receptor alpha (Pdgfra) in directing cardiac fusion. Mutation of pdgfra disrupts heart tube assembly in both zebrafish and mouse. Timelapse analysis of individual cardiomyocyte trajectories reveals misdirected cells in zebrafish pdgfra mutants, suggesting that PDGF signaling steers cardiomyocytes toward the midline during cardiac fusion. Intriguingly, the ligand pdgfaa is expressed in the endoderm medial to the pdgfra-expressing myocardial precursors. Ectopic expression of pdgfaa interferes with cardiac fusion, consistent with an instructive role for PDGF signaling. Together, these data uncover a novel mechanism through which endodermal-myocardial communication can guide the cell movements that initiate cardiac morphogenesis.

DOI:http://dx.doi.org/10.7554/eLife.21172.001

In the growing embryo, the heart initially develops in the form of a simple tube. Its outer layer is made up of muscular cells, called myocardial cells, that pump blood through the tube. Before the heart tube develops, two groups of myocardial cells exist – one on each side of the embryo. To assemble the heart, these two populations of cells must move as a group to the middle of the embryo, where they meet and merge through a process called cardiac fusion. This movement of myocardial cells toward the middle of the embryo depends upon interactions with a neighboring tissue called the endoderm. How the endoderm directs the movement of the myocardial cells was not well understood.

The PDGF signaling pathway guides the movement of several different types of cells in the body, but it had not been previously linked to the early stages of heart tube assembly. In this pathway, a molecule called platelet-derived growth factor (PDGF) binds to PDGF receptors that sit on the surface of cells. Using microscopy and genetic analysis to study zebrafish and mouse embryos, Bloomekatz et al. now show that embryos that carry mutations in a gene that encodes a PDGF receptor suffer from defects in heart tube assembly. Further examination of the mutant zebrafish embryos revealed that the myocardial cells were not properly directed toward the middle of the embryo. In fact, many of these cells appeared to move away from the midline.

Bloomekatz et al. also observed that, in normal embryos, the endoderm cells that lie adjacent to the myocardial cells produce PDGF. Therefore, it appears that PDGF produced by the endoderm could interact with PDGF receptors on the myocardial cells to direct these cells toward the middle of the embryo. The next step will be to figure out how this signaling influences the machinery inside the myocardial cells that controls their movement. Ultimately, this knowledge could lead to new ways to identify and treat congenital heart diseases.

DOI:http://dx.doi.org/10.7554/eLife.21172.002

Role of ectonucleotide pyrophosphatase/phosphodiesterase 2 in the midline axis formation of zebrafish

Lysophosphatidic acid (LPA) is a unique bioactive lysophospholipid that induces pleiotropic effects in various cell types and organisms by acting on its specific receptors. LPA is mainly synthetised extracellularly by the ectonucleotide pyrophosphatase/phosphodiesterase 2/autotaxin (enpp2). Altered LPA signalling is associated with embryonic abnormalities, suggesting critical roles for LPA during development. However, the role of LPA signalling during early embryogenesis is not well established. We demonstrate that enpp2/LPA signalling in the early zebrafish embryo results in altered axis and midline formation, defects in left right (L-R) patterning, ciliogenesis of the Kupffer’s vesicle (KV), through the modulation of cell migration during gastrulation in a lpar_1–3 Rho/ROCK-dependant manner. Overall, this study demonstrates an essential role of enpp2/LPA signalling during early embryogenesis.

Sphingosine 1-phosphate in metabolic syndrome (Review)

Metabolic syndrome (MetS), a clustering of components, is closely associated with the development and prognosis of cardiovascular disease and diabetes. Sphingosine 1-phosphate (S1P) is a lysophospholipid with paracrine and autocrine effects, which is associated with obesity, insulin resistance, hyperglycemia, dyslipidemia and hypertension through extracellular and intracellular signals to achieve a variety of biological functions. However, there is controversy regarding the role of S1P in MetS; the specific role played by S1P remains unclear. It ameliorates abnormal energy metabolism and deviant adipogenesis and mediates inflammation in obesity. Despite the fact that sphingosine kinase (SphK)2/S1P increases the glucose‑stimulated insulin secretion of β-cells, more evidence showed that activation of the SphK1/S1P/S1P2R pathway inhibited the feedback loop of insulin secretion and sensitivity. The majority of S1P1R activation improves diabetes whereas S1P2R activation worsens the condition. In hyperlipidemia, S1P binds to high-density lipoprotein, low‑density lipoprotein and very low-density lipoprotein exerting different effects. Moreover, low concentrations of S1P lead to vasodilation whereas high concentrations of S1P result in vasocontraction of isolated arterioles. This review discusses the means by which different SphKs, S1P concentrations or S1P receptor subtypes results to diverse result in MetS, and then examines the role of S1P in MetS.

The force within: endocardial development, mechanotransduction and signalling during cardiac morphogenesis

Endocardial cells are cardiac endothelial cells that line the interior of the heart tube. Historically, their contribution to cardiac development has mainly been considered from a morphological perspective. However, recent studies have begun to define novel instructive roles of the endocardium, as a sensor and signal transducer of biophysical forces induced by blood flow, and as an angiocrine signalling centre that is involved in myocardial cellular morphogenesis, regeneration and reprogramming. In this Review, we discuss how the endocardium develops, how endocardial-myocardial interactions influence the developing embryonic heart, and how the dysregulation of blood flow-responsive endocardial signalling can result in pathophysiological changes.

Mutations in zebrafish pitx2 model congenital malformations in Axenfeld-Rieger syndrome but do not disrupt left-right placement of visceral organs

Pitx2 is a conserved homeodomain transcription factor that has multiple functions during embryonic development. Mutations in human PITX2 cause autosomal dominant Axenfeld-Rieger syndrome (ARS), characterized by congenital eye and tooth malformations. Pitx2(-/-) knockout mouse models recapitulate aspects of ARS, but are embryonic lethal. To date, ARS treatments remain limited to managing individual symptoms due to an incomplete understanding of PITX2 function. In addition to regulating eye and tooth development, Pitx2 is a target of a conserved Nodal (TGFβ) signaling pathway that mediates left-right (LR) asymmetry of visceral organs. Based on its highly conserved asymmetric expression domain, the Nodal-Pitx2 axis has long been considered a common denominator of LR development in vertebrate embryos. However, functions of Pitx2 during asymmetric organ morphogenesis are not well understood. To gain new insight into Pitx2 function we used genome editing to create mutations in the zebrafish pitx2 gene. Mutations in the pitx2 homeodomain caused phenotypes reminiscent of ARS, including aberrant development of the cornea and anterior chamber of the eye and reduced or absent teeth. Intriguingly, LR asymmetric looping of the heart and gut was normal in pitx2 mutants. These results suggest conserved roles for Pitx2 in eye and tooth development and indicate Pitx2 is not required for asymmetric looping of zebrafish visceral organs. This work establishes zebrafish pitx2 mutants as a new animal model for investigating mechanisms underlying congenital malformations in ARS and high-throughput drug screening for ARS therapeutics. Additionally, pitx2 mutants present a unique opportunity to identify new genes involved in vertebrate LR patterning. We show Nodal signaling-independent of Pitx2-controls asymmetric expression of the fatty acid elongase elovl6 in zebrafish, pointing to a potential novel pathway during LR organogenesis.

On the role of mechanics in driving mesenchymal-to-epithelial transitions

The mesenchymal-to-epithelial transition (MET) is an intrinsically mechanical process describing a multi-step progression where autonomous mesenchymal cells gradually become tightly linked, polarized epithelial cells. METs are fundamental to a wide range of biological processes, including the evolution of multicellular organisms, generation of primary and secondary epithelia during development and organogenesis, and the progression of diseases including cancer. In these cases, there is an interplay between the establishment of cell polarity and the mechanics of neighboring cells and microenvironment. In this review, we highlight a spectrum of METs found in normal development as well as in pathological lesions, and provide insight into the critical role mechanics play at each step. We define MET as an independent process, distinct from a reverse-EMT, and propose questions to further explore the cellular and physical mechanisms of MET.

S1pr2/Gα13 signaling regulates the migration of endocardial precursors by controlling endoderm convergence

Formation of the heart tube requires synchronized migration of endocardial and myocardial precursors. Our previous studies indicated that in S1pr2/Gα13-deficient embryos, impaired endoderm convergence disrupted the medial migration of myocardial precursors, resulting in the formation of two myocardial populations. Here we show that endoderm convergence also regulates endocardial migration. In embryos defective for S1pr2/Gα13 signaling, endocardial precursors failed to migrate towards the midline, and the presumptive endocardium surrounded the bilaterally-located myocardial cells rather than being encompassed by them. In vivo imaging of control embryos revealed that, like their myocardial counterparts, endocardial precursors migrated with the converging endoderm, though from a more anterior point, then moved from the dorsal to the ventral side of the endoderm (subduction), and finally migrated posteriorly towards myocardial precursors, ultimately forming the inner layer of the heart tube. In embryos defective for endoderm convergence due to an S1pr2/Gα13 deficiency, both the medial migration and the subduction of endocardial precursors were impaired, and their posterior migration towards the myocardial precursors was premature. This placed them medial to the myocardial populations, physically blocking the medial migration of the myocardial precursors. Furthermore, contact between the endocardial and myocardial precursor populations disrupted the epithelial architecture of the myocardial precursors, and thus their medial migration; in embryos depleted of endocardial cells, the myocardial migration defect was partially rescued. Our data indicate that endoderm convergence regulates the medial migration of endocardial precursors, and that premature association of the endocardial and myocardial populations contributes to myocardial migration defects observed in S1pr2/Gα13-deficient embryos. The demonstration that endoderm convergence regulates the synchronized migration of endocardial and myocardial precursors reveals a new role of the endoderm in heart development.

Strategies for analyzing cardiac phenotypes in the zebrafish embryo

The molecular mechanisms underlying cardiogenesis are of critical biomedical importance due to the high prevalence of cardiac birth defects. Over the past two decades, the zebrafish has served as a powerful model organism for investigating heart development, facilitated by its powerful combination of optical access to the embryonic heart and plentiful opportunities for genetic analysis. Work in zebrafish has identified numerous factors that are required for various aspects of heart formation, including the specification and differentiation of cardiac progenitor cells, the morphogenesis of the heart tube, cardiac chambers, and atrioventricular canal, and the establishment of proper cardiac function. However, our current roster of regulators of cardiogenesis is by no means complete. It is therefore valuable for ongoing studies to continue pursuit of additional genes and pathways that control the size, shape, and function of the zebrafish heart. An extensive arsenal of techniques is available to distinguish whether particular mutations, morpholinos, or small molecules disrupt specific processes during heart development. In this chapter, we provide a guide to the experimental strategies that are especially effective for the characterization of cardiac phenotypes in the zebrafish embryo.

Endoderm convergence controls subduction of the myocardial precursors during heart-tube formation

Coordination between the endoderm and adjacent cardiac mesoderm is crucial for heart development. We previously showed that myocardial migration is promoted by convergent movement of the endoderm, which itself is controlled by the S1pr2/Gα13 signaling pathway, but it remains unclear how the movements of the two tissues is coordinated. Here, we image live and fixed embryos to follow these movements, revealing previously unappreciated details of strikingly complex and dynamic associations between the endoderm and myocardial precursors. We found that during segmentation the endoderm underwent three distinct phases of movement relative to the midline: rapid convergence, little convergence and slight expansion. During these periods, the myocardial cells exhibited different stage-dependent migratory modes: co-migration with the endoderm, movement from the dorsal to the ventral side of the endoderm (subduction) and migration independent of endoderm convergence. We also found that defects in S1pr2/Gα13-mediated endodermal convergence affected all three modes of myocardial cell migration, probably due to the disruption of fibronectin assembly around the myocardial cells and consequent disorganization of the myocardial epithelium. Moreover, we found that additional cell types within the anterior lateral plate mesoderm (ALPM) also underwent subduction, and that this movement likewise depended on endoderm convergence. Our study delineates for the first time the details of the intricate interplay between the endoderm and ALPM during embryogenesis, highlighting why endoderm movement is essential for heart development, and thus potential underpinnings of congenital heart disease.

Maternal or zygotic sphingosine kinase is required to regulate zebrafish cardiogenesis

BACKGROUND

The sphingosine 1-phosphate (S1P) signaling pathway regulates zebrafish cardiogenesis, and provides a paradigm for how signaling gradients coordinate collective cell migration across tissue layers. It is known that the S1P transporter (Spns2) functions in extra-embryonic YSL to activate G protein-coupled receptor (S1pr2) signaling in endoderm for deposition of positional cues (integrin, fibronectin, etc.). Such cues are recognized by overlying lateral precardiac mesoderm that migrates to the midline and fuses to form the primordial heart tube. However, the source of bio-active S1P is not known. There are multiple receptors and it is not known if there are earlier or even receptor-independent functions for S1P.

RESULTS

Because S1P can only be generated by sphingosine kinases, we targeted a mutation to the single kinase gene expressed during early embryogenesis (sphk2). Zygotic mutants survive to adulthood and appear normal, but maternal-zygotic mutant embryos phenocopy null zygotic mutants of spns2 or s1pr2.

CONCLUSIONS

The data show that maternally derived sphk2 RNA is fully sufficient to generate an S1P signaling gradient in the YSL that ultimately controls precardiac mesoderm migration during embryogenesis. Furthermore, despite maternal expression of sphk2, there are no obvious developmental functions requiring its activity prior to stimulation of S1pr2 in endoderm.

The endoderm and myocardium join forces to drive early heart tube assembly

Formation of the muscular layer of the heart, the myocardium, involves the medial movement of bilateral progenitor fields; driven primarily by shortening of the endoderm during foregut formation. Using a combination of time-lapse imaging, microsurgical perturbations and computational modeling, we show that the speed of the medial-ward movement of the myocardial progenitors is similar, but not identical to that of the adjacent endoderm. Further, the extracellular matrix microenvironment separating the two germ layers also moves with the myocardium, indicating that collective tissue motion and not cell migration drives tubular heart assembly. Importantly, as myocardial cells approach the midline, they perform distinct anterior-directed movements relative to the endoderm. Based on the analysis of microincision experiments and computational models, we propose two characteristic, autonomous morphogenetic activities within the early myocardium: 1) an active contraction of the medial portion of the heart field and 2) curling- the tendency of the unconstrained myocardial tissue to form a spherical surface with a concave ventral side. In the intact embryo, these deformations are constrained by the endoderm and the adjacent mesoderm, nevertheless the corresponding mechanical stresses contribute to the proper positioning of myocardial primordia.

Maternal and Zygotic Sphingosine Kinase 2 Are Indispensable for Cardiac Development in Zebrafish

Sphingosine 1-phosphate (S1P) is synthesized from sphingosine by sphingosine kinases (SPHK1 and SPHK2) in invertebrates and vertebrates, whereas specific receptors for S1P (S1PRs) selectively appear in vertebrates, suggesting that S1P acquires novel functions in vertebrates. Because the developmental functions of SPHK1 and SPHK2 remain obscure in vertebrates, we generated sphk1 or sphk2 gene-disrupted zebrafish by introducing premature stop codons in their coding regions using transcription activator-like effector nucleases. Both zygotic sphk1 and sphk2 zebrafish mutants exhibited no obvious developmental defects and grew to adults. The maternal-zygotic sphk2 mutant (MZsphk2), but not the maternal-zygotic sphk1 mutant and maternal sphk2 mutant, had a defect in the cardiac progenitor migration and a concomitant decrease in S1P level, leading to a two-heart phenotype (cardia bifida). Cardia bifida in MZsphk2, which was rescued by injecting sphk2 mRNA, was a phenotype identical to that of zygotic mutants of the S1P transporter spns2 and S1P receptor s1pr2, indicating that the Sphk2-Spns2-S1pr2 axis regulates the cardiac progenitor migration in zebrafish. The contribution of maternally supplied lipid mediators during vertebrate organogenesis presents as a requirement for maternal-zygotic Sphk2.

Phenotypic regulation of the sphingosine 1-phosphate receptor miles apart by G protein-coupled receptor kinase 2

The evolutionarily conserved DRY motif at the end of the third helix of rhodopsin-like, class-A G protein-coupled receptors (GPCRs) is a major regulator of receptor stability, signaling activity, and β-arrestin-mediated internalization. Substitution of the DRY arginine with histidine in the human vasopressin receptor results in a loss-of-function phenotype associated with diabetes insipidus. The analogous R150H substitution of the DRY motif in zebrafish sphingosine-1 phosphate receptor 2 (S1p2) produces a mutation, miles apart m⁹³ (mil^m93), that not only disrupts signaling but also impairs heart field migration. We hypothesized that constitutive S1p2 desensitization is the underlying cause of this strong zebrafish developmental defect. We observed in cell assays that the wild-type S1p2 receptor is at the cell surface whereas in distinct contrast the S1p2 R150H receptor is found in intracellular vesicles, blocking G protein but not arrestin signaling activity. Surface S1p2 R150H expression could be restored by inhibition of G protein-coupled receptor kinase 2 (GRK2). Moreover, we observed that β-arrestin 2 and GRK2 colocalize with S1p2 in developing zebrafish embryos and depletion of GRK2 in the S1p2 R150H miles apart zebrafish partially rescued cardia bifida. The ability of reduced GRK2 activity to reverse a developmental phenotype associated with constitutive desensitization supports efforts to genetically or pharmacologically target this kinase in diseases involving biased GPCR signaling.

S1P-Yap1 signaling regulates endoderm formation required for cardiac precursor cell migration in zebrafish

To form the primary heart tube in zebrafish, bilateral cardiac precursor cells (CPCs) migrate toward the midline beneath the endoderm. Mutants lacking endoderm and fish with defective sphingosine 1-phosphate (S1P) signaling exhibit cardia bifida. Endoderm defects lead to the lack of foothold for the CPCs, whereas the cause of cardia bifida in S1P signaling mutants remains unclear. Here we show that S1P signaling regulates CPC migration through Yes-associated protein 1 (Yap1)-dependent endoderm survival. Cardia bifida seen in spns2 (S1P transporter) morphants and s1pr2 (S1P receptor-2) morphants could be rescued by endodermal expression of nuclear localized form of yap1. yap1 morphants had decreased expression of the Yap1/Tead target connective tissue growth factor a (Ctgfa) and consequently increased endodermal cell apoptosis. Consistently, ctgfa morphants showed defects of the endodermal sheet and cardia bifida. Collectively, we show that S1pr2/Yap1-regulated ctgfa expression is essential for the proper endoderm formation required for CPC migration.

Lysophospholipid receptor nomenclature review: IUPHAR Review 8

Lysophospholipids encompass a diverse range of small, membrane-derived phospholipids that act as extracellular signals. The signalling properties are mediated by 7-transmembrane GPCRs, constituent members of which have continued to be identified after their initial discovery in the mid-1990s. Here we briefly review this class of receptors, with a particular emphasis on their protein and gene nomenclatures that reflect their cognate ligands. There are six lysophospholipid receptors that interact with lysophosphatidic acid (LPA): protein names LPA1 - LPA6 and italicized gene names LPAR1-LPAR6 (human) and Lpar1-Lpar6 (non-human). There are five sphingosine 1-phosphate (S1P) receptors: protein names S1P1 -S1P5 and italicized gene names S1PR1-S1PR5 (human) and S1pr1-S1pr5 (non-human). Recent additions to the lysophospholipid receptor family have resulted in the proposed names for a lysophosphatidyl inositol (LPI) receptor - protein name LPI1 and gene name LPIR1 (human) and Lpir1 (non-human) - and three lysophosphatidyl serine receptors - protein names LyPS1 , LyPS2 , LyPS3 and gene names LYPSR1-LYPSR3 (human) and Lypsr1-Lypsr3 (non-human) along with a variant form that does not appear to exist in humans that is provisionally named LyPS2L . This nomenclature incorporates previous recommendations from the International Union of Basic and Clinical Pharmacology, the Human Genome Organization, the Gene Nomenclature Committee, and the Mouse Genome Informatix.

Sphingosine 1-phosphate signalling

Sphingosine 1-phosphate (S1P) is a lipid mediator formed by the metabolism of sphingomyelin. In vertebrates, S1P is secreted into the extracellular environment and signals via G protein-coupled S1P receptors to regulate cell-cell and cell-matrix adhesion, and thereby influence cell migration, differentiation and survival. The expression and localization of S1P receptors is dynamically regulated and controls vascular development, vessel stability and immune cell trafficking. In addition, crucial events during embryogenesis, such as angiogenesis, cardiogenesis, limb development and neurogenesis, are regulated by S1P signalling. Here, and in the accompanying poster, we provide an overview of S1P signalling in development and in disease.

Zebrafish as a model of cardiac disease

The zebrafish has been rapidly adopted as a model for cardiac development and disease. The transparency of the embryo, its limited requirement for active oxygen delivery, and ease of use in genetic manipulations and chemical exposure have made it a powerful alternative to rodents. Novel technologies like TALEN/CRISPR-mediated genome engineering and advanced imaging methods will only accelerate its use. Here, we give an overview of heart development and function in the fish and highlight a number of areas where it is most actively contributing to the understanding of cardiac development and disease. We also review the current state of research on a feature that we only could wish to be conserved between fish and human; cardiac regeneration.