Top PDF A major role for zygotic hunchback in patterning the Nasonia embryo

A major role for zygotic hunchback in patterning the
Nasonia embryo

A major role for zygotic hunchback in patterning the Nasonia embryo

Why does a lack of zygotic hunchback result in more severe consequences in Nasonia than in Drosophila, despite graded maternal Hunchback expression in both species? We hypothesized that because of the longer period of early development in Nasonia (Fig. 1) maternal Hunchback does not overlap temporally with zygotic Hunchback to the same extent that it does in Drosophila. To test this hypothesis, we examined Hunchback in Nasonia hunchback hl mutant embryos, and compared them with Drosophila embryos lacking zygotic Hunchback, during the period when maternal Hunchback is decaying. Specifically, we examined whether residual maternal Hunchback is detected near the onset of cellularization, when both Nasonia and Drosophila embryos begin to express Hunchback zygotically in a posterior cap (in addition to the anterior domain). In a tightly staged collection of male Nasonia embryos from hunchback hl /+ virgins, we observed 34 embryos expressing Hunchback in the anterior and incipient posterior caps (Fig. 7A), while 31 sibling embryos had no detectable Hunchback expression (Fig. 7B). In a control experiment, all of 50 Nasonia wild-type embryos of a similar age clearly showed the zygotic Hunchback expression pattern. These results show that in Nasonia embryos, maternal Hunchback does not persist into the period of posterior cap expression, but our characterization of maternal Hunchback in earlier embryos (see the previous section above) indicates that it is weakly expressed just prior to that time.
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A Genetic Screen for Zygotic Embryonic Lethal Mutations Affecting Cuticular Morphology in the Wasp Nasonia vitripennis

A Genetic Screen for Zygotic Embryonic Lethal Mutations Affecting Cuticular Morphology in the Wasp Nasonia vitripennis

Drosophila genes may control a different spectrum of whether candidate gene hypotheses are plausible. patterning functions, or patterning functions may be An important consideration for comparative genetic carried out in Nasonia by genes that do not function investigations is the cost of genetic stock maintenance. as embryonic patterning genes in Drosophila. Specific In Nasonia, embryonic lethal lines can be maintained comparisons of the Nasonia genes to Drosophila genes for ⬎1 year as diapause larvae; however, the cost of are detailed in results. embryonic lethal stock maintenance for Nasonia (see The Nasonia axial patterning mutant phenotypes materials and methods) is currently similar to that have pointed toward a lesser role of maternal contribu- reported for Tribolium (Berghammer et al. 1999). This tions to embryonic patterning in Nasonia than in Dro- has made it necessary to choose a limited number of sophila (Pultz et al. 1999). The zygotic head only mutant mutant lines to maintain from this pilot study, and we phenotype is most similar to that of Drosophila embryos have focused on those for which candidate gene hypoth- lacking both maternal and zygotic caudal function, while eses may be useful in relating our understanding of the zygotic headless mutant phenotype is most similar to Nasonia development to that of Drosophila. If muta- that of Drosophila embryos lacking both maternal and tions of interest are relatively easy to isolate in Nasonia zygotic hunchback function (Macdonald and Struhl but relatively costly to maintain, what approaches should 1986; Lehmann and Nu ¨ sslein-Volhard 1987; Simp- be taken for further study of this organism? First, by son-Brose et al. 1994; Pultz et al. 1999). We are testing developing an array of molecular probes to assay expres- the hypotheses that head only is Nasonia caudal and that sion and linkage for Nasonia orthologs of key develop- headless is Nasonia hunchback, through linkage analysis, mental regulatory genes
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The role of Mixer in patterning the early Xenopus
embryo

The role of Mixer in patterning the early Xenopus embryo

To establish the roles of Mixer in endoderm and mesoderm specification in Xenopus, we used antisense morpholino oligos (MixerMO) to block the translation of Mixer protein throughout the entire period of Mixer expression during gastrulation. We find that Mixer-depleted embryos develop with severe abnormalities of the head and gut, which are partially rescued by the expression of a non-complementary Mixer mRNA. The pattern of early zygotic gene expression is reproducibly altered at the gastrula stage, and the effects of Mixer-depletion are gene specific rather than germ layer specific. We show that Mixer loss-of-function results in overexpression of the mesodermal markers eomesodermin, Bix3 and Fgf8 in their usual equatorial location, as well as the spread of their expression into deeper endodermal territory. We also show that Mixer acts cell autonomously, and represses some genes (Bix3, Xnr5, Xnr1 and Fgf8) while activating others (cerberus, Xsox17). In functional assays of Mixer-depleted vegetal cells, we show that a major biological role of Mixer is to control the degree to which cells induce the formation of mesoderm.
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Regulation of Gastrulation Through Dynamic Patterning in the Drosophila Embryo

Regulation of Gastrulation Through Dynamic Patterning in the Drosophila Embryo

There have been many studies on the exact inputs into these transitions. Previous models such as a fixed time after fertilization or counting cell cycles have been negated (Lu et al., 2009). One prevailing view is the change in nucleocytoplasmic (N/C) ratio, or the concentration of DNA, that prompts MBT/MZT and also perhaps the slowing down of nuclear cycles 10-13 (Edgar et al., 1986; Lu et al., 2010; Sibon et al., 1997). There are, however, exceptions of genes that do not depend on the N/C ratio and in fact support MBT/MZT (Lu et al., 2009; Sokac and Wieschaus, 2008; Sung et al., 2013). Maternal genes have a major role in supporting gene patterning and initiating MBT/MZT. With the consecutive nuclear divisions of the syncytium, there is a temporal limit to the extent that transcription factors can activate gene expression. It is therefore maternal mRNAs that contribute to the robustness of gene patterning in the early embryo. For example, many of the key transcription factors required for establishing the dorsal-ventral and anterior- posterior axes are deposited maternally (discussed below). These maternal genes are also important to initiate zygotic transcription when the short nuclear cycle intervals no longer inhibit completion of transcripts. However, expression of maternal products is often ubiquitous, which limits their spatial influence. Hence, the formation of cellular membranes often occurs in conjunction with zygotic transcription, which can be spatially regulated.
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The time to measure positional information: maternal Hunchback is required for the synchrony of the Bicoid transcriptional response at the onset of zygotic transcription

The time to measure positional information: maternal Hunchback is required for the synchrony of the Bicoid transcriptional response at the onset of zygotic transcription

limited number of loci being activated. After mitosis, each new locus emerging from the replication of an activated locus would maintain activation through a process not strictly dependent on Bcd. By cycle 11, a majority of loci in the anterior would have had a chance to be activated at least once and such a memorization process would allow maintaining expression. The shape of the territories of clonally related nuclei is compatible with the shape of the hb transcription border and such a memorization mechanism can also explain why the border is becoming more convoluted as the number of nuclei increases. Time-lapse observation of the Bcd- EGFP gradients did not show colocalization of the Bcd protein with DNA during mitosis (Gregor et al., 2007b) and we did not observe a significant change in hb synchrony when reducing Bcd amounts in the embryo. By contrast, hb synchrony was reduced at cycle 11 when the dose of maternal Hb was lowered by half. Thus, Hb but not Bcd, is probably involved in this memory mechanism. Such memory process could either involve directly proteins of the transcription machinery maintained on DNA during mitosis such as TFIID (Xing et al., 2008) or chromatin modifications transmitted epigenetically after each division, such as H3K4 methylation (Muramoto et al., 2010). A consequence of such a memory process is that hb transcription would be much more dependent on Bcd thresholds at early cycles than at later cycles. This could explain why patterning along the AP axis is highly sensitive at early cycles (cycle 9 and cycle 10) and much less sensitive at later cycles (cycle 11 to cycle 13) to environmental perturbations induced by micro- fluidics devices destroying the Bcd gradient (Lucchetta et al., 2005; Lucchetta et al., 2008).
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New roles for FoxH1 in patterning the early embryo

New roles for FoxH1 in patterning the early embryo

FoxH1 (Fast1) was first characterized as the transcriptional partner for Smad proteins forming the activin response factor (ARF) binding to the Mix.2 promoter in Xenopus embryos (Chen et al., 1996). Foxh1 family members have been described in many vertebrate groups (for a review, see Carlsson and Mahlapuu, 2002). They show high homology in the fork- head DNA binding and Smad interaction domains and very little conservation outside those domains. Mice lacking FoxH1 are embryonic lethal and show defects ranging from total lack of embryonic structures, lack of anterior structures, or less severe notochord and node defects (Hoodless et al., 2001; Yamamoto et al., 2001). Analyses of these phenotypes concluded that FoxH1 was the major transcriptional transducer of nodal signaling in early development (Yamamoto et al., 2001). In contrast, zebrafish maternal/zygotic mutants of Foxh1 (schmalspur) had less severe phenotypes consisting of cyclopia, loss of floorplate and posterior chordal plate and ventral body curvature (Pogoda et al., 2000; Sirotkin et al., 2000). Also schmalspur mutants were able to induce the expression of the organizer gene goosecoid in response to nodal signaling, suggesting that FoxH1 is not strictly required to transmit nodal signals in zebrafish (Pogoda et al., 2000). However, studies on double mutants of zebrafish Foxh1 and Mix-like gene (Bon/Sur mutants) also placed zFoxH1 in the nodal signaling pathway (Kunwar et al., 2003; Trinh et al., 2003).
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Lef1 plays a role in patterning the mesoderm and ectoderm in Xenopus tropicalis

Lef1 plays a role in patterning the mesoderm and ectoderm in Xenopus tropicalis

Our experiments reveal that knockdown of lef1 leads to early developmental defects in the derivatives of the mesoderm and ectoderm in Xenopus, as expected from the expression pattern of lef1. In the mouse, targeted inactivation of Lef1, or Tcf1, did not produce early phenotypes, only null mutations in both Lef1 and Tcf1 caused a severe defect in the differentiation of paraxial mesoderm at the same time leading to the formation of additional neural tubes (Galceran et al., 1999). A redundant role of Lef1 and Tcf1 in Wnt signaling during early mouse development explained these results (Galceran et al., 1999). Since tcf1 is also expressed during early development in Xenopus (Roël et al., 2003), redun- dancy between lef1 and tcf1 functions is less or absent during Xenopus development. This difference may relate to the differ- ences in the timing of paraxial mesoderm differentiation between mouse and Xenopus (Pownall et al., 2002). Also, differences in the expression of Lef1 iso-forms between mouse and Xenopus may be important. Human LEF1 exon VI is naturally differentially spliced (Arce et al., 2006). Furthermore, natural dominant nega- tive LEF1 is present in normal human and murine thymus tissue (Arce et al., 2006; Travis et al., 1991). We showed that the genomic sequences of Xenopus and Fugu lef1 do not contain exon VI. Only a LEF1 isoform containing exon VI (Arce et al., 2006) can efficiently induce formation of an ectopic axis and
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The torso like gene functions to maintain the structure of the vitelline membrane in Nasonia vitripennis, implying its co option into Drosophila axis formation

The torso like gene functions to maintain the structure of the vitelline membrane in Nasonia vitripennis, implying its co option into Drosophila axis formation

Axis specification is a fundamental developmental process. Despite this, the mechanisms by which it is controlled across insect taxa are strikingly different. An excellent example of this is terminal patterning, which in Diptera such as Drosophila melanogaster occurs via the localized activation of the receptor tyrosine kinase Torso. In Hymenoptera, however, the same process appears to be achieved via localized mRNA. How these mechanisms evolved and what they evolved from remains largely unexplored. Here, we show that torso- like, known for its role in Drosophila terminal patterning, is instead required for the integrity of the vitelline membrane in the hymenopteran wasp Nasonia vitripennis. We find that other genes known to be involved in Drosophila terminal patterning, such as torso and Ptth, also do not function in Nasonia embryonic development. These findings extended to orthologues of Drosophila vitelline membrane proteins known to play a role in localizing Torso-like in Drosophila; in Nasonia these are instead required for dorso – ventral patterning, gastrulation and potentially terminal patterning. Our data underscore the importance of the vitelline membrane in insect development, and implies phenotypes caused by knockdown of torso-like must be interpreted in light of its function in the vitelline membrane. In addition, our data imply that the signalling components of the Drosophila terminal patterning systems were co-opted from roles in regulating moulting, and co-option into terminal patterning involved the evolution of a novel interaction with the vitelline membrane protein Torso-like. This article has an associated First Person interview with the first author of the paper.
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Genetic and molecular studies of segmentation and axon guidance in Drosophila

Genetic and molecular studies of segmentation and axon guidance in Drosophila

Axon guidance is usually considered at two levels. First, in pathway selection, wherein the axons travel along a route that leads them to a particular region of the embryo. The model systems used for this study are the guidance of commissural axons at the midline in Drosophila and vertebrates, or of circumferential migrations in C.elegans. Aside from the instructive cues described above that delineate a pathway, there are also guidance signals from other axons that are involved in pathway selection. Once a pathway has been laid out by pioneer axons navigating over a territory, subsequent growth cones growing towards their targets recognise and selectively fasciculate with subsets of the existing axon tracts laid down by these pioneers, and grow along them (the ‘labelled pathway hypothesis’, reviewed in Harrelson and Goodman, 1988). Second, axon guidance is studied at the level o f target selection, wherein once axons arrive within the domain of the target they select specific cells and form stable connections with them. This also occurs by instructive cues to the growth cone. The models used to study target selection include the retinotectal projections in vertebrates and motoneuron innervations of muscles in Drosophila. These combined studies indicate that a combination of multiple, evolutionarily conserved, signals and receptors regulate axon guidance in the developing embryo.
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A Deficiency Screen for Zygotic Loci Required for Establishment and Patterning of the Epidermis in Caenorhabditis elegans

A Deficiency Screen for Zygotic Loci Required for Establishment and Patterning of the Epidermis in Caenorhabditis elegans

The epidermal phenotype of these deficiency homozygotes generally did not indicate grossly abnormal numbers of lateral epidermal cells, and it therefore seems more likely th[r]

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In Vitro Regeneration of Sugar Palm (Arenga pinnata Wurmb Merr.)

In Vitro Regeneration of Sugar Palm (Arenga pinnata Wurmb Merr.)

1) Immature Zygotic Embryo Explant: When evaluating the performance of immature zygotic embryo explant for direct organogenesis, the morphogenic response obtained from each culture medium was the formation of adventitious roots and shoots. Based on a few series of preliminary study conducted, a typical generation response of zygotic embryo culture in sugar palm occurred in four phases, i.e. (a) swollen of zygotic embryo, (b) development and elongation of cotyledonary petiole / sheath, (c) development of primary and adventitious roots from the cotyledonary petiole tips, and (d) the establishment of shoot from the sheath’s cleft. These phases are the general development process of immature zygotic embryo explant being cultured on basal MS medium. Upon addition of PGRs to the culture medium,
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Active cell migration drives the unilateral movements of the anterior visceral endoderm

Active cell migration drives the unilateral movements of the anterior visceral endoderm

embryo is a specialised extra-embryonic tissue that is essential for anterior patterning of the embryo. It is characterised by the expression of anterior markers such as Hex, Cerberus-like and Lhx1. At pre-gastrula stages, cells of the AVE are initially located at the distal tip of the embryo, but they then move unilaterally to the future anterior. This movement is essential for converting the existing proximodistal axis into an anteroposterior axis. To investigate this process, we developed a culture system capable of imaging embryos in real time with single cell resolution. Our results show that AVE cells continuously change shape and project filopodial processes in their direction of motion, suggesting that they are actively migrating. Their proximal movement stops abruptly at the
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The role of Otx2 in organizing the anterior patterning in mouse

The role of Otx2 in organizing the anterior patterning in mouse

ABSTRACT Understanding the molecular mechanism controlling induction and maintenance of signals required for specifying anterior territory (forebrain and midbrain) of the central nervous system is a major task of molecular embryology. The current view indicates that in mouse, early specification of the anterior patterning is established at the beginning of gastrulation by the anterior visceral endoderm, while maintenance and refinement of the early specification is under the control of epiblast-derived tissues corresponding to the axial mesendoderm and rostral neuroectoderm. In vertebrates a remarkable amount of data has been collected on the role of genes contributing to brain morphogenesis. Among these genes, the orthodenticle group is defined by the Drosophila orthodenticle and the vertebrate Otx1 and Otx2 genes, which contain a bicoid-like homeodomain. Mouse models and chimera experiments have provided strong evidence that Otx2 plays an important role in the specification and maintenance of the rostral neuroectoderm destined to become forebrain and midbrain. In evolutionary terms, some of these findings lead us to hypothesize a fascinating and crucial contribution of the Otx genes to the genetic program underlying the establishment of the mammalian brain.
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Global analysis of dorsoventral patterning in the wasp Nasonia reveals extensive incorporation of novelty in a regulatory network

Global analysis of dorsoventral patterning in the wasp Nasonia reveals extensive incorporation of novelty in a regulatory network

The quality of the resulting sequences was checked using fastQC and the sequences were then processed for entry into the Cufflinks package. The procedure outlined in [23] was followed with slight alterations, including updated software versions. Jobs sent to the CHEOPS cluster located at the University of Cologne contained the relevant parameters, and are presented in Additional file 1: Methods. We primarily relied on annotation 2.0 of the N. vitripennis genome, found at http://arthropods. eugenes.org/EvidentialGene/nasonia/genes/. This annota- tion was modified slightly to be compatible with the Cuf- flinks analyses. This altered file is available on request. Annotation 2.0 was mapped to version 1.0 of the Nasonia genome assembly (http://www.hymenopteragenome.org/ drupal/sites/hymenopteragenome.org.nasonia/files/data/ Nvit_1.0_scaffolds.fa.gz). Very similar but not identical re- sults were obtained using annotation 1.2 combined with as- sembly 2.0: (http://www.hymenopteragenome.org/nasonia/ ?q=sequencing_and_analysis_consortium_datasets). Dis- crepancies are discussed as appropriate in the main text. The raw cuffdiff results for both experiments are provided as Additional files 2 and 3. A compilation of all genes that showed significant differential expression (DE) in one or more comparisons (regardless of whether our additional criteria were met) is presented in Additional file 4. Additional file 5 contains the annotations of the 110 genes with confirmed expression in this analysis.
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microRNA 31 modulates skeletal patterning in the sea urchin embryo

microRNA 31 modulates skeletal patterning in the sea urchin embryo

To test the impact of miR-31 regulation of key genes within the PMC GRN in the dynamic environment of a developing embryo, we designed miR-31 target protector morpholino antisense oligonucleotides (miR-31 TPs) to competitively block endogenous miR-31 suppression of Alx1 or VegfR7 (Staton and Giraldez, 2011; Stepicheva et al., 2015). BLASTN of the miR-31 TP sequences indicated that they are uniquely complementary to the functional miR-31 sites identified by the luciferase assays. We microinjected Alx1 miR-31 TP, VegfR7 miR-31 TP or both into newly fertilized eggs and observed a significant decrease in the skeleton spicule length compared with control embryos (Fig. 6A,B). A small but significant decrease in skeleton spicule length persisted in Alx1, but not in VegfR7, miR-31 TP-injected larvae (72 hpf ) (Fig. S4). We found that 2%, 7.5% and 4.6% of Alx1, VegfR7 and Alx1+VegfR7 miR-31 TP-injected gastrulae developed extra tri-radiate rudiments, respectively (Fig. 6A). We also observed that some PMCs were mislocalized in the miR-31 TP-injected embryos compared with the control using the PMC-specific antibody 1D5 (McClay et al., 1983) (Fig. 6C,D). The decrease in skeleton spicule length, formation of the extra tri-radiate rudiments and the defects in PMC patterning (Fig. 6) in the Alx1 and VegfR7 miR-31 TP-injected embryos partially mimicked the miR-31 KD phenotypes (Figs 2 and 3), indicating that miR-31 KD phenotypes are in part caused by the lack of miR-31 regulation within PMCs.
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Influence of AGNO3 on zygotic embryo culture as an efficient tool for conservation of a vulnerable medicinally important forest tree Oroxylum indicum (l) kurz

Influence of AGNO3 on zygotic embryo culture as an efficient tool for conservation of a vulnerable medicinally important forest tree Oroxylum indicum (l) kurz

(32±0.02) of shoots per explant was developed at 3.0 mg/L TDZ followed by 4.0 mg/L TDZ. MS medium fortified with BAP alone showed superiority over KIN for the induction of maximum frequency number of multiple shoots. While MS medium with lower and higher concentrations of all the cytokinins showed a decreasing effect on percentage of germination, days for germination. These results are similar to Shahnaz Begum (2007) reported in Ophiorhiza prostrata. The absolute percentage of zygotic embryo germination (100%) and conversion into seedling was obtained on MS medium supplemented with 3-4.0 mg/L TDZ (32±0.02; 28±0.62) followed by 92 and 89% at 5.0 mg/L BAP and KIN (24±0.29; 18±0.07) respectively in combination with 0.1 mg/L AgNO 3 ;
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Testing of Algerian fir zygotic and somatic embryos on defence reactions in vitro

  Testing of Algerian fir zygotic and somatic embryos on defence reactions in vitro

diverge, depending on all or some of the sources of variation. Several variants of fixed models were, for this reason, prepared to prove magnitude of defence reactions in mycelium in response to embryo type and control and sides of measurement (towards or opposite to embryo). A general logistic model was fitted early to the combined data. In more complex models, the coefficients were allowed to vary de- pending on embryo types and sides of measurement. Competing nested models were compared by likeli- hood ratio chi-square test to establish significance of the added terms. Estimates of the coefficients α, β 0 and β 1 were obtained by iterative Gauss-Newton algorithm. The process of iteration to convergence was traced.
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Patterning of the embryo: the first spatial decisions in the life of a mouse

Patterning of the embryo: the first spatial decisions in the life of a mouse

A solution to this dilemma may become clear once we understand better the mechanisms by which polarity is established in normal development and learn what actually occurs when an embryo recovers from experimental manipulations. At present there are several possibilities that could account for regulative responses in the context of normal development. First, regulative ability might mean that when the initial polarity of the egg is perturbed, it becomes re- established. For this to occur, positional information would have to be preserved at least to some extent. There could be, for example, a morphogenetic gradient in the egg or embryo that relies on the relative and not the absolute concentration of a morphogen. In this case, even after one pole is removed, the gradient could persist and still be able to direct proper development. It is also possible that either remaining pole of the egg is able to define polarity because it contains information that identifies it as one end of an axis. Thus, in the experimental manipulations described above, polarity would have been disturbed but not really destroyed. Second, regulative development might indicate that when intrinsic polarity is disturbed or destroyed, other asymmetries in the embryo itself or its environment can be adopted as spatial cues to re-establish polarity. In such event, the axes of the regulating embryo might not have the original orientation as in the unperturbed embryo, but might nevertheless arise out of the tendency to polarise using whatever cues might be available in those altered circumstances. A third possibility is, of course, that polarity had not actually been disturbed in experiments that cut away poles of the egg or embryos (Zernicka-Goetz, 1998; Ciemerych et al., 2000). This would be the case if polarised components were sequestered not into the animal or vegetal poles, but resided in other regions, such as at the sides of the egg or embryo, or if they were spatially distributed according to some other positional cue. Alternatively, if the polarity of an embryo were defined through a polarised component such as the cytoskeleton, then it could persist even in a fragment of the embryo. Finally, even in normal development, mammalian embryonic axes could be established by a combination of intrinsic positional cues in the zygote and by the interactions of cells with each other or with their environment. Such a mechanism would also explain the great versatility of the early mammalian embryo. Overall, the regulative aspects of development might provide safeguards that, as in other biological processes, ensure a robust, failsafe system.
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Fgf signalling controls the dorsoventral patterning of the zebrafish embryo

Fgf signalling controls the dorsoventral patterning of the zebrafish embryo

In the zebrafish embryo, three genes encoding Bmps, bmp2b, bmp7 and bmp4, are expressed at blastula and gastrula stages (Kishimoto et al., 1997; Nikaido et al., 1997; Dick et al., 2000; Schmid et al., 2000). bmp2b and bmp7 are expressed first, at the sphere stage (4 hpf) soon after the beginning of expression of the zygotic genome, whereas bmp4 transcripts become detectable about 1 hour later (30% epiboly). At sphere stage, expression of bmp2b and bmp7 is detected throughout the blastoderm (Fig. 1A,D). Within the next 30 minutes, bmp2b transcripts disappear from the dorsalmost aspect of the blastula margin (not shown). This dorsal bmp2b-free zone then rapidly expands towards the ventral side and the animal pole (Fig. 1B) so that at the onset of gastrulation (shield stage, 6 hpf) bmp2b transcripts are excluded from the dorsal half of the non- marginal blastoderm (Fig. 1C). A similar dynamic disappearance from dorsal territories is observed for bmp7 (Fig. 1D-F). At shield stage, bmp2b expression becomes moreover detectable at the dorsal margin (Fig. 1C). This marginal expression domain is unaffected in mutants disrupting DV patterning (Schmid et al., 2000), strongly suggesting that it is unrelated to the establishment of the DV polarity.
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Patterning the early Xenopus embryo

Patterning the early Xenopus embryo

Over the past 5 years, the usefulness of the Xenopus model organism has grown considerably as a result of the Xenopus Genome Initiative (see www.xenbase.org/). This endeavor has provided a quantum increase in the amount of information available on Xenopus genes and the resources with which to study them. The development of loss- of-function technology has also increased our knowledge of individual gene function (Heasman et al., 2000). The result is that many more molecules have been shown to control early Xenopus development. The challenge for the modern developmental biologist is to stay abreast of this information. In this review, I summarize these new findings and incorporate them with the old. Inevitably, this survey will be incomplete. [For further information, see De Robertis and Kuroda (De Robertis and Kuroda, 2004), and for a comparison with zebrafish axis patterning, see Schier and Talbot (Schier and Talbot, 2005). For research into germ-line establishment, see also Zhou and King (Zhou and King, 2004).] For example, the nuts and bolts of development, including the cytoskeletal and adhesion machinery, many components of signaling pathways, transcriptional and cell cycle regulators are incompletely covered. The question that drives this review is, ‘What insight have recent functional studies given us on the mechanisms that pattern the early Xenopus embryo?’.
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