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PubMed2003

Whole-embryo culture of E5.5 mouse embryos: development to the gastrulation stage.

This study reports establishment of an in vitro culture system for E5.5 mouse embryos that supports development to the gastrulation stage and allows the use of experimental approaches to study gastrulation during mouse embryogenesis. Recent experiments suggest that the extraembryonic tissues may play a critical role for gastrulation from as early as E5.5. To apply whole embryo culture to E5.5 embryos and analyze gastrulation, it is essential to optimize the conditions so that most of the embryos develop to the gastrulation stage in culture. For this purpose, we established a protocol in which embryos were isolated using micromanipulator and cultured with 50-75% rat serum. Although cultured embryos tended to grow a larger extraembryonic portion, more than 80% of them developed the primitive streak and induce mesoderm, which corresponds to the mid-streak stage.

Animals↗
PubMed1993

Mechanisms of gastrulation and tail formation in ascidians.

Ascidian embryos are useful for examining how events that occur during fertilization and cleavage affect gastrulation because they gastrulate early in development, during the seventh cleavage. In ascidians, both dorsal-ventral and anterior-posterior axes are determined before first cleavage. The dorsal-ventral axis is fixed along the animal-vegetal axis of the fertilized egg following the first phase of ooplasmic segregation, perhaps due to determinants moved to the vegetal pole in concert with the myoplasm and plasma membrane components. The first ooplasmic movements appear to be driven by the actin network in the cortical myoplasm. The anterior-posterior axis becomes apparent after the second phase of ooplasmic segregation, when the cortical myoplasm becomes detached from the egg membrane, and moves to the posterior pole of the embryo. This movement is dependent on microtubules and has been attributed to the formation and movement of the sperm aster. A major component of the cortical myoplasm, p58, is co-localized along the microtubules emanating from the sperm aster. Gastrulation begins during the seventh cleavage with the invagination of the large endodermal cells at the vegetal pole of the embryo. The neural plate appears as a thickening of the epidermis on the dorsal side of the larva during the ninth cleavage; then the neural folds are formed, join, and close, elaborating the neural tube. Following neurulation, the tail is elongated as the neural tube and notochord cells intercalate at the midline of the embryo. Investigations using anural (tailless) ascidian larvae suggest that some of the processes underlying elongation can be restored by the zygotic genome. Although ascidian larvae contain fewer cells and cell types than vertebrate embryos, ascidian gastrulation and morphogenesis appear to employ similar mechanisms to those in vertebrate embryos. The extent of our current knowledge about the mechanisms involved in gastrulation and tail formation is summarized, and further experiments are suggested to explore the molecular mechanisms underlying these processes.

Animals↗
PubMed1981

An experimental analysis of the role of bottle cells and the deep marginal zone in gastrulation of Xenopus laevis.

Earlier work suggested that the change in shape or the active migration of the bottle cells in the amphibian blastoporal region results in an invagination that comprises a major part of gastrulation. In the present study of gastrulation in Xenopus laevis, microsurgical extirpation and rearrangement experiments, analyzed with time-lapse cinemicrography and scanning electron microscopy, show that the bottle cells have a lesser role in gastrulation. Gastrulation is not a process of invagination but of involution of the deep and superficial layers of the marginal zone. Involution is dependent on unique properties of the cells in the deep marginal zone. In contrast, the superficial layer, including the bottle cells, does not have properties essential for involution but is passively moved inside to form the lining of the archenteron by what is probably an active migration of the underlying cells of the deep marginal zone. Bottle cells form by the shrinking and thickening of the superficial layer in the late blastula and early gastrula. They are moved inside, largely because of their attachment to the underlying deep cells, and then they spread and flatten in the latter half of gastrulation to form a large area of the lining of the periphery of the archenteron. The formation of the initial blastoporal groove by bending of the superficial cells sheet during bottle cell formation and the extension of the periphery of the archenteron during spreading of the bottle cells is the extent of the active contribution of bottle cells to the depth of the archenteron. The bulk of the depth is generated by the vegetal extension of the marginal zone and the movement of the involuted deep cells toward the animal pole.

Animals↗
PubMed1993

Gastrulation and mesoderm morphogenesis in the white sturgeon.

This study presents a detailed description of gastrulation in the white sturgeon, Acipenser transmontanus, using scanning electron microscopy, histology, and time-lapse filming and video microscopy. This morphological analysis describes the similarity of gastrula structure in the sturgeon and the amphibian Xenopus laevis, and suggests that the species share many developmental mechanisms. It also identifies important differences, such as the equatorial dorsal lip in sturgeon, and provides a basis for interpreting experiments that test the effect of these differences on gastrulation. The onset of gastrulation in the sturgeon is marked by the appearance of a blastoporal equatorial pigment line that forms as the apices of bottle cells contract and concentrate surface pigment granules. Bottle cell formation at the blastopore lip and involution of surface material through the blastopore are strikingly similar to the equivalent processes in amphibian embryos. As gastrulation continues, a distinct cleft of Brachet forms between pre-involution and post-involution material. Following involution, the prospective axial mesoderm located on the dorsal surface of the late blastula (Ballard and Ginsburg: J. Exp. Zool., 213:69-103, 1980) ingresses from a central zone in the posterior archenteron roof surface in a process that is unlike any in Xenopus, but resembles events in other amphibians (Purcell, 1992; Smith: Dev. Biol., 98:250-254, 1983; King: Biol. Bull., 4:287-300, 1903). The detailed comparison of similarities and differences in gastrulation in different vertebrate lineages yields insights into the function and versatility of common developmental mechanisms.

Animals↗
PubMed1994

The sea urchin profilin gene is specifically expressed in mesenchyme cells during gastrulation.

Eggs and embryos of the purple sea urchin (Strongylocentrotus purpuratus) contain profilin that is partly supplied from maternal sources and partly produced by the gastrula. The maternal profilin protein content is about 13 microM and it persists in the embryo at least through gastrulation. Transcript quantitation from probe excess titrations show that very few profilin gene transcripts are present in the embryo during cleavage, but that they increase at the onset of gastrulation. By in situ hybridization, the newly synthesized profilin transcripts are localized in mesenchyme cells. Profilin gene expression increases when mesenchyme cells initiate migration and filopodial extension and retraction. We show that there are three isoforms of maternal profilin protein produced from the single copy gene during oogenesis. However, the blastula stage embryo only produces the major isoform, whereas the acidic isoform is produced in the early stages of gastrulation and the basic isoform appears by the end of gastrulation. Based on transcript prevalence and protein production rates, our calculations indicate that the amount of new protein produced in the mesenchyme cells in 12 hr is at maximum < 2% of that supplied from maternal sources. Because of the large amount of maternally supplied profilin present in the egg and embryo, we suggest that it may be used in the cytokinetic processes of cleavage. Alternatively, because of the small amount of embryonically produced profilin, we suggest that it may function in the cytoskeletal shape changes required for filopodial extension and motility in the mesenchyme cells during gastrulation.

Animals↗
PubMed1995

Disruption of gastrulation movements in Xenopus by a dominant-negative mutant for C-cadherin.

Gastrulation in Xenopus laevis transforms a ball of undifferentiated cells into a well-organized elongated embryo with a distinct body axis, as a result of extensive cell rearrangements and movements. Since cell adhesion is thought to play an important role during tissue morphogenesis, we investigated the potential role for C-cadherin, a primary cell-cell adhesion molecule in Xenopus, in gastrulation movements. A deletion mutant consisting of the extracellular and transmembrane domains but lacking the cytoplasmic tail (Ctrunc) was constructed to act as a dominant-negative inhibitor of the endogenous protein. Injection of in vitro transcribed Ctrunc mRNA into the prospective dorsal involuting marginal zone, the region that undergoes the most extensive movements, caused a reproducible defect in gastrulation. The defect, an inability to complete involution and close the blastopore, was cadherin-specific, because it could be rescued by expressing full length C-cadherin. Ctrune also seems to inhibit morphogenetic movements of animal cap explants isolated from injected embryos. Expression of Ctrunc did not appear to interfere with inductive processes in the embryos that developed gastrulation defects, because they formed complete axial structures, including a complete head and notochord. These results demonstrate that C-cadherin plays a critical role in Xenopus laevis gastrulation movements, and they support the hypothesis that cadherins can mediate cellular rearrangements during tissue morphogenesis.

Animals↗
PubMed2001

Overexpression of camello, a member of a novel protein family, reduces blastomere adhesion and inhibits gastrulation in Xenopus laevis.

Vertebrate gastrulation involves complex coordinated movements of cells and cell layers to establish the axial structures and the general body plan. Adhesion molecules and the components of extracellular matrix were shown to be involved in this process. However, other participating molecules and detailed mechanisms of the control of gastrulation movements remain largely unknown. Here, we describe a novel Xenopus gene camello (Xcml) which is expressed in the suprablastoporal zone of gastrulating embryos. Injection of Xcml RNA into dorsovegetal blastomeres retards or inhibits gastrulation movements. Database searches revealed a family of mammalian mRNAs encoding polypeptides highly similar to Xcml protein. Characteristic features of the camello family include the presence of the central hydrophobic domain and the N-acetyltransferase consensus motifs in the C-terminal part, as well as functional similarity to Xcml revealed by overexpression studies in Xenopus embryos. Xcml expression results in the decrease of cell adhesion as demonstrated by the microscopic analysis and the blastomere aggregation assay. Cell fractionation and confocal microscopy data suggest that Xcml protein is localized in the secretory pathway. We propose that Xcml may fine tune the gastrulation movements by modifying the cell surface and possibly extracellular matrix proteins passing through the secretory pathway.

Acetyltransferases↗
PubMed2001

The role of Brachyury (T) during gastrulation movements in the sea urchin Lytechinus variegatus.

The studies described here sought to identify and characterize genes involved in the gastrulation and morphogenetic movements that occur during sea urchin embryogenesis. An orthologue of the T-box family transcription factor, Brachyury, was cloned through a candidate gene approach. Brachyury (T) is the founding member of this T-box transcription factor family and has been implicated in gastrulation movements in Xenopus, zebrafish, and mouse embryogenesis. Polyclonal serum was generated to LvBrac in order to characterize protein expression. LvBrac initially appears at mesenchyme blastula stage in two distinct regions with embryonic expression perduring until pluteus stage. Vegetally, LvBrac expression is in endoderm and lies circumferentially around the blastopore. This torus-shaped area of LvBrac expression remains constant in size as endoderm cells express LvBrac upon moving into that circumference and cease LvBrac expression as they leave the circumference. Vegetal expression remains around the anus through pluteus stage. The second domain of LvBrac expression first appears broadly in the oral ectoderm at mesenchyme blastula stage and at later embryonic stages is refined to just the stomodael opening. Vegetal LvBrac expression depends on autonomous beta-catenin signaling in macromeres and does not require micromere or veg2-inductive signals. It was then determined that LvBrac is necessary for the morphogenetic movements occurring in both expression regions. A dominant-interfering construct was generated by fusing the DNA binding domain of LvBrac to the transcriptional repression module of the Drosophila Engrailed gene in order to perturb gene function. Microinjection of mRNA encoding this LvBrac-EN construct resulted in a block in gastrulation movements but not expression of endoderm and mesoderm marker genes. Furthermore, injection of LvBrac-EN into one of two blastomeres resulted in normal gastrulation movements of tissues derived from the injected blastomere, indicating that LvBrac downstream function may be nonautonomous during sea urchin gastrulation.

Africa, Western↗
PubMed1993

The involvement of TGF beta 1 in early avian development: gastrulation and chondrogenesis.

We examined the effects of transforming growth factor-beta 1 (TGF beta 1) and a neutralizing monoclonal antibody on two phases of early chick embryo development: gastrulation and chondrogenesis. We carried out experiments in vivo and in vitro on mesoderm cells from the gastrulating embryo at day 1, and on sclerotome cells from day 3 embryos, having previously shown that this factor is present among these cells at these stages of development. Addition of the antibody to cultures of these cells produced a dose-dependent decrease in cell out-growth and spreading and concomitantly reduced fibronectin deposition. In vivo studies of the effects of TGF beta 1 on mesoderm during gastrulation were carried out by grafting beads carrying this agent into gastrulating embryos. We used beads of ion-exchange resin as well as hydrolysed polyacrylamide, and found that the grafts produced an accumulation of mesoderm cells around the implant and, at later stages, the formation of enlarged somites. There was no effect on embryonic axis formation. Studies of bromodeoxyuridine (BrdU) incorporation indicated that the mesoderm accumulation was due, at least in part, to an increase in cell proliferation. However, examination of the effect of TGF beta 1 on BrdU incorporation by mesoderm during gastrulation and sclerotome cells in vitro indicated in inhibition of cell proliferation, an inconsistency explained in terms of the variation between the in vivo and in vitro conditions. We conclude that TGF beta 1 is both appropriately located, and is able, to influence cell proliferation among the mesodermal cell populations during early development, and that this effect contributes to the overall control of mesodermal morphogenesis.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1985

Alteration of the anterior-posterior embryonic axis: the pattern of gastrulation in macrocephalic frog embryos.

The production of an enlarged head or macrocephaly in frog embryos can be achieved by interspecific hybridization or by injection of the contents of the germinal vesicle (GV), the large nucleus of immature oocytes, into the blastocoels of embryos before they gastrulate. The macrocephalic embryos have large suckers and their neural tubes are larger anteriorly but smaller posteriorly as compared to controls. This abnormal syndrome has previously been thought to arise as a result of an axial structure determinant present in the germinal vesicle. When examined during gastrulation, however, Xenopus laevis and Rana pipiens macrocephalic embryos produced by GV injection as well as macrocephalic embryos produced by the hybrid cross, Rana septentrionalis female X Rana catesbeiana male, all exhibit alterations in the pattern of gastrulation. The most striking of these alterations is the persistence throughout gastrulation of a thick blastocoel roof composed of many cell layers, suggesting that there is an inhibition of posterior spreading of the roof normally associated with epiboly. In R. pipiens, the dorsal mesodermal mantle of GV-injected gastrulae is thicker as compared to controls, accounting for a neural plate which is wide at the anterior end. Vital dye mapping experiments on Xenopus laevis embryos show that dye marks placed on regions normally fated to become trunk epidermis become localized anteriorly when the embryos are GV injected, consistent with the idea that ectodermal cells are inhibited from moving posteriorly. These results indicate that the macrocephalic syndrome can be attributed to a localized inhibition of cell rearrangements during gastrulation as opposed to the effects of altered inducers or to axial determinants.

Animals↗
PubMed1987

Gastrulation in the sea urchin embryo requires the deposition of crosslinked collagen within the extracellular matrix.

This study demonstrates that a collagenous extracellular matrix (ECM) is necessary for gastrulation in the sea urchin embryo. The approach taken was to disrupt collagen processing with two types of agents (a lathyritic agent, beta-aminopropionitrile (BAPN), and three types of proline analogs: dehydroproline, cis-OH-proline, and azetidine carboxylic acid) and to assess the effect on embryogenesis by morphological, immunological, and biochemical criteria. Embryos chronically exposed to either of the agents following fertilization displayed no detectable developmental abnormalities before the mesenchyme blastula stage. These embryos, however, did not gastrulate nor differentiate any further and remained at the mesenchyme blastula stage for at least 36 hr. Upon removal of the agents, the embryos resumed a normal developmental schedule and formed pluteus larvae that were indistinguishable from control embryos. By immunofluorescence studies with monospecific antibodies to type I and type IV collagens it is seen that the lathyritic agent BAPN reduces the accumulation of collagens within the ECM. This effect is confirmed and quantitated by use of an ELISA and by a biochemical determination of OH-proline. When the agents are removed from the inhibited embryos, collagen deposition returns to normal, coincident with gastrulation. Western-blot analysis, using monospecific antibodies to collagen, demonstrates that the effect of the lathyritic agent is to reduce the stability of the extracellular collagen by inhibiting the intra- and intermolecular crosslinking of collagen molecules. BAPN exhibits a dose-dependent effect on morphogenesis, but has no effect on respiration nor on protein synthesis of the embryos throughout development. Although the lathyritic agent affects collagen deposition, it is shown to not affect the expression of other molecules of the ECM, nor that of several cell surface molecules. However, a cell surface molecule that is expressed specifically in the endoderm, termed Endo 1, is not expressed in the inhibited embryos. Endo 1 is expressed after removal of the lathyritic agent and its appearance is coincident with gastrulation in the recovered embryos. These results suggest that a collagenous ECM is important for gastrulation and subsequent differentiation in the sea urchin, but not for earlier developmental processes. In addition, the dependence of Endo 1 expression on the collagenous ECM raises the possibility that this cell surface molecule is in some way regulated by interactions of the presumptive endodermal cells with the ECM.

Aminopropionitrile↗
PubMed2006

p38 and a p38-interacting protein are critical for downregulation of E-cadherin during mouse gastrulation.

During vertebrate gastrulation, an epithelial to mesenchymal transition (EMT) is necessary for migration of mesoderm from the primitive streak. We demonstrate that p38 MAP kinase and a p38-interacting protein (p38IP) are critically required for downregulation of E-cadherin during gastrulation. In an ENU-mutagenesis screen we identified the droopy eye (drey) mutation, which affects splicing of p38IP. p38IP(drey) mutant embryos display incompletely penetrant defects in neural tube closure, eye development, and gastrulation. A stronger allele (p38IP(RRK)) exhibits gastrulation defects in which mesoderm migration is defective due to deficiency in E-cadherin protein downregulation in the primitive streak. We show that p38IP binds directly to p38 and is required for p38 activation in vivo. Moreover, both p38 and p38IP are required for E-cadherin downregulation during gastrulation. Finally, p38 regulates E-cadherin protein expression downstream from NCK-interacting kinase (NIK) and independently of the regulation of transcription by Fibroblast Growth Factor (Fgf) signaling and Snail.

Alternative Splicing↗
PubMed2003

Characterization of Brachyury genes in the dogfish S. canicula and the lamprey L. fluviatilis. Insights into gastrulation in a chondrichthyan.

In order to gain insights into the evolution of gastrulation mechanisms among vertebrates, we have characterized a Brachyury-related gene in a lamprey, Lampetra fluviatilis, and in a chondrichthyan, Scyliorhinus canicula. These two genes, respectively termed LfT and ScT, share with their osteichthyan counterparts prominent expression sites in the developing notochord, the tailbud, but also a transient expression in the prechordal plate, which is likely to be ancestral among vertebrates. In addition, the lamprey LfT gene is transcribed in the endoderm of the pharyngeal arches and the epiphysis, two expression sites that have not been reported thus far in gnathostomes, and, as in the chick, in the differentiating nephrotomes. Since Brachyury expression in nascent mesoderm and endoderm is highly conserved among vertebrates as well as cephalochordates, we have used this marker to identify these cell populations during gastrulation in the dogfish. The results suggest that these cells are initially present over the whole margin of the blastoderm and are displaced during gastrulation to its posterior part, which may correspond to the site of mesoderm and endoderm internalization. These data provide the first molecular characterization of gastrulation in a chondrichthyan. They indicate that gastrulation in the dogfish and in some amniotes shares striking similarities despite the phylogenetic distance between these species. This supports the hypothesis that the extensively divergent morphologies of gastrulae among vertebrates largely result from adaptations to the presence of yolk.

Animals↗
PubMed2003

The zebrafish band 4.1 member Mir is involved in cell movements associated with gastrulation.

Cellular processes rely on dynamic events occurring between the cortical cytoskeleton and plasma membrane. Members of the Band 4.1 superfamily, which are best known for their ability to tether the cytoskeleton to the plasma membrane, play prominent structural and regulatory roles that influence cell-cell and cell-substrate interactions, endo- and exocytosis, cell polarity, migration, proliferation, and differentiation. We have identified a new member of the zebrafish Band 4.1 superfamily, which is the homolog of human myosin regulatory light chain interacting protein (MIR), and have examined its role in embryonic development. Zebrafish Mir contains the conserved amino-terminal plasma membrane-binding FERM (Band 4.1/ezrin/radixin/moesin) domain as well as other putative protein-protein interacting domains, including a RING finger. Overall, zebrafish Mir is 71% identical to human MIR located at chromosome 6p23-p22.3, and maps on linkage group 19 to a region of synteny with human chromosome 6. In situ hybridization and RT-PCR revealed that mir is expressed maternally and ubiquitously throughout development. Blocking Mir translation using a mir-specific, morpholino-based, knock-down strategy or expressing Mir constructs lacking the RING finger domain disrupts gastrulation and leads to subsequent trunk and tail defects. In severe cases, morphants exogastrulate. The synergistic effect seen when two mir-specific morpholinos are used in conjunction reflects the specific knock-down of mir. In addition, morphant phenotypes induced by mir-specific morpholinos are rescued by overexpression of the full-length Mir. In situ hybridization analysis with mesodermal- and neural-specific markers shows that morphants exhibit a delay in cell movements associated with gastrulation, epiboly, convergence, and extension. A yeast two-hybrid analysis was performed to identify binding partners that may participate with Mir during gastrulation, and Annexin V, a calcium channel protein, was isolated. At early developmental stages, annexin V transcripts colocalize with mir, but after gastrulation, annexin V mRNA becomes localized to the distal tail region and an area in the olfactory placode. At the protein level, Mir colocalizes with Annexin V when expressed in COS cells. Together, these results indicate that Mir is essential for embryonic development and that its role in early embryonic development likely involves calcium-dependent mechanisms essential during the extensive cell movements associated with gastrulation.

Amino Acid Sequence↗
PubMed2004

The mitochondrial-apoptotic pathway is triggered in Xenopus mesoderm cells deprived of PDGF receptor signaling during gastrulation.

Platelet-derived growth factor receptor (PDGFR) signaling is required for normal gastrulation in Xenopus laevis. Embryos deprived of PDGFR signaling develop with a range of gastrulation-specific defects including spina bifida, shortened anteroposterior axis, and reduced anterior structures. These defects arise because the involuting mesoderm fails to move appropriately. In this study, we determine that inhibition of PDGFR signaling causes prospective head mesoderm cells to appear in the blastocoel cavity at the onset of gastrulation, stage 10. These aberrant cells undergo apoptosis via the caspase 3 pathway at an embryonic checkpoint called the early gastrula transition (EGT). They are TUNEL-positive and have increased levels of caspase 3 activity compared to control embryos. Apoptotic death of these mesoderm cells can be prevented by co-injection of mRNA encoding Bcl-2 or by injection of either a general caspase inhibitor or a caspase 3-specific inhibitor. Prevention of cell death, however, is not sufficient to rescue gastrulation defects in these embryos. Based on these data, we propose that PDGFR signaling is necessary for survival of prospective head mesoderm cells, and also plays an essential role in the control of their cell movement during gastrulation.

Animals↗
PubMed2003

The role of Ppt/Wnt5 in regulating cell shape and movement during zebrafish gastrulation.

Wnt genes play important roles in regulating patterning and morphogenesis during vertebrate gastrulation. In zebrafish, slb/wnt11 is required for convergence and extension movements, but not cell fate specification during gastrulation. To determine if other Wnt genes functionally interact with slb/wnt11, we analysed the role of ppt/wnt5 during zebrafish gastrulation. ppt/wnt5 is maternally provided and zygotically expressed at all stages during gastrulation. The analysis of ppt mutant embryos reveals that Ppt/Wnt5 regulates cell elongation and convergent extension movements in posterior regions of the gastrula, while its function in more anterior regions is largely redundant to that of Slb/Wnt11. Frizzled-2 functions downstream of ppt/wnt5, indicating that it might act as a receptor for Ppt/Wnt5 in this process. The characterisation of the role of Ppt/Wnt5 provides insight into the functional diversity of Wnt genes in regulating vertebrate gastrulation movements.

Animals↗
PubMed2003

Phosphoinositide 3-kinase is required for process outgrowth and cell polarization of gastrulating mesendodermal cells.

BACKGROUND: During vertebrate gastrulation, cell polarization and migration are core components in the cellular rearrangements that lead to the formation of the three germ layers, ectoderm, mesoderm, and endoderm. Previous studies have implicated the Wnt/planar cell polarity (PCP) signaling pathway in controlling cell morphology and movement during gastrulation. However, cell polarization and directed cell migration are reduced but not completely abolished in the absence of Wnt/PCP signals; this observation indicates that other signaling pathways must be involved. RESULTS: We show that Phosphoinositide 3-Kinases (PI3Ks) are required at the onset of zebrafish gastrulation in mesendodermal cells for process formation and cell polarization. Platelet Derived Growth Factor (PDGF) functions upstream of PI3K, while Protein Kinase B (PKB), a downstream effector of PI3K activity, localizes to the leading edge of migrating mesendodermal cells. In the absence of PI3K activity, PKB localization and cell polarization are strongly reduced in mesendodermal cells and are followed by slower but still highly coordinated and directed movements of these cells. CONCLUSIONS: We have identified a novel role of a signaling pathway comprised of PDGF, PI3K, and PKB in the control of morphogenetic cell movements during gastrulation. Furthermore, our findings provide insight into the relationship between cell polarization and directed cell migration at the onset of zebrafish gastrulation.

Animals↗
PubMed2004

The polarity-inducing kinase Par-1 controls Xenopus gastrulation in cooperation with 14-3-3 and aPKC.

Par (partitioning-defective) genes were originally identified in Caenorhabditis elegans as determinants of anterior/posterior polarity. However, neither their function in vertebrate development nor their action mechanism has been fully addressed. Here we show that two members of Par proteins, 14-3-3 (Par-5) and atypical PKC (aPKC), regulate the serine/threonine kinase Par-1 to control Xenopus gastrulation. We find first that Xenopus Par-1 (xPar-1) is essential for gastrulation but not for cell fate specification during early embryonic development. We then find that xPar-1 binds to 14-3-3 in an aPKC-dependent manner. Our analyses identify two aPKC phosphorylation sites in xPar-1, which are essential for 14-3-3 binding and for proper gastrulation movements. The aPKC phosphorylation-dependent binding of xPar-1 to 14-3-3 does not markedly affect the kinase activity of xPar-1, but induces relocation of xPar-1 from the plasma membranes to the cytoplasm. Finally, we show that Xenopus aPKC and its binding partner Xenopus Par-6 are also essential for gastrulation. Thus, our results identify a requirement of Par proteins for Xenopus gastrulation and reveal a novel interrelationship within Par proteins that may provide a general mechanism for spatial control of Par-1.

14-3-3 Proteins↗