Dorsoventral axis

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Opposing gradients of Gli repressor and activators mediate Shh signaling along the dorsoventral axis of the inner ear

Opposing gradients of Gli repressor and activators mediate Shh signaling along the dorsoventral axis of the inner ear

Organization of the vertebrate inner ear is mainly dependent on localized signals from surrounding tissues. Previous studies demonstrated that sonic hedgehog (Shh) secreted from the floor plate and notochord is required for specification of ventral (auditory) and dorsal (vestibular) inner ear structures, yet it was not clear how this signaling activity is propagated. To elucidate the molecular mechanisms by which Shh regulates inner ear development, we examined embryos with various combinations of mutant alleles for Shh , Gli2 and Gli3 . Our study shows that Gli3 repressor (R) is required for patterning dorsal inner ear structures, whereas Gli activator (A) proteins are essential for ventral inner ear structures. A proper balance of Gli3R and Gli2/3A is required along the length of the dorsoventral axis of the inner ear to mediate graded levels of Shh signaling, emanating from ventral midline tissues. Formation of the ventral-most otic region, the distal cochlear duct, requires robust Gli2/3A function. By contrast, the formation of the proximal cochlear duct and saccule, which requires less Shh signaling, is achieved by antagonizing Gli3R. The dorsal vestibular region requires the least amount of Shh signaling in order to generate the correct dose of Gli3R required for the development of this otic region. Taken together, our data suggest that reciprocal gradients of GliA and GliR mediate the responses to Shh signaling along the dorsoventral axis of the inner ear.

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A β1,4 galactosyltransferase is required for Bmp2 dependent patterning of the dorsoventral axis during zebrafish embryogenesis

A β1,4 galactosyltransferase is required for Bmp2 dependent patterning of the dorsoventral axis during zebrafish embryogenesis

The results presented here represent the first functional characterization of a specific glycosyltransferase during early patterning of the zebrafish embryo. ␤ 4GalT5 was initially identified by an in silico search, and was subsequently cloned from a 48-hour RNA library. At the amino acid level, ␤ 4GalT5 is 69.9% identical to the human ␤ 4GalT5. ␤ 4GalT5 is not expressed in the oocyte, but is expressed by the early epiboly stage and reaches a steady state level of expression by mid-somitogenesis. Furthermore, ␤ 4GalT5 shows widespread expression throughout the embryo during the first 24 hours of development, with enhanced expression within several structures at the 20-somite stage. Insight into the biological function of ␤ 4GalT5 was addressed by the injection of three specific morpholino oligonucleotides, all of which resulted in a dorsalized embryo. Consistent with the hypothesis that ␤ 4GalT5 is essential for patterning of the dorsoventral axis, the expression of chordin was inappropriately expanded into the ventral hemisphere, similar to what is observed with well-studied dorsoventral patterning mutants

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Cell migration that orients the dorsoventral axis is coordinated with anteroposterior patterning mediated by Hedgehog signaling in the early spider embryo

Cell migration that orients the dorsoventral axis is coordinated with anteroposterior patterning mediated by Hedgehog signaling in the early spider embryo

At early stage 5, when the CM cells begin migration in the normal embryo, At-smo RNAi germ discs showed various degrees of expansion of the At-Delta expression domain (Fig. 8D-G). To investigate the relationship between the expansion phenotype and the cumulus-shift phenotype (Fig. 2B,C), we analyzed serial egg sacs derived from individual females injected with At-smo1 dsRNA or gfp dsRNA (Fig. 8H). Embryos from each egg sac were divided into two pools. One pool was examined for At-Delta expression at early stage 5 and the expansion levels categorized into four classes: class I, comparable to normal; class II, slightly expanded; class III, Fig. 8. Early patterning defects in At-smo RNAi germ discs and their relation to the cumulus-shift defects. (A-G)  Expression of At-Delta transcripts (purple) and 022_P10 (red) in At-smo RNAi germ discs at early stage 4 (A), late stage 4 (B) and early stage 5 (D-G) and in a gfp RNAi germ disc at early stage 5 (C). The germ discs in A and B are derived from the same egg sac produced by female #3 on day 25 (see H). Compare these with the wild-type germ discs in Fig. 1C. The degree of expansion of the At-Delta expression domain at early stage 5 was categorized as class I to IV (D-G; see text). Scale bar: 100  m. (H)  The percentage of embryos in each At-Delta expression phenotype category (above) and with each cumulus-shift phenotype (below) in serial egg sacs. The data in each pair of bar charts refer to individual females (#1-5) injected with gfp or At- smo1 dsRNA. Female #5 was given six injections, whereas the others were given four injections. Bars show data obtained from individual egg sacs produced on the day indicated on the horizontal axis (days after the first injection of dsRNA). At the top of each bar, the total number of examined embryos is indicated. Asterisks indicate egg sacs not examined. (I)  Spearman correlation matrix of the percentage of embryos in the At-Delta expression phenotype categories and the percentage of embryos with the cumulus-shift phenotypes. The correlation was analyzed with Prism version 4 (GraphPad). The Spearman rank correlation coefficients (r s ) are shown together with P-values (p). Blue boxes highlight the significant

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Asymmetric distribution of hypoxia inducible factor α regulates dorsoventral axis establishment in the early sea urchin embryo

Asymmetric distribution of hypoxia inducible factor α regulates dorsoventral axis establishment in the early sea urchin embryo

One of the crucial events during early embryogenesis in animals is the establishment of the body axes. For bilaterians, proper dorsoventral (DV) axial patterning results in their bilaterally symmetric bodies. In echinoderm embryos, a redox gradient is involved in DV patterning (Coffman and Denegre, 2007). Studies during the 1940s demonstrated that redox inhibitors were effective in orienting the bilateral plane of sand dollar embryos (Pease, 1941, 1942a,b). The most inhibited region becomes dorsal, and the least inhibited region ventral. At approximately the same time, C. M. Child monitored the intracellular indophenol oxidase activity and observed regional differences in echinoderm blastula embryos (Child, 1941). Czihak further demonstrated that an activity gradient of the mitochondrial enzyme cytochrome oxidase is present as early as the 8-cell stage (Czihak, 1963). Using a fluorescent probe, it has been shown that the distribution of the mitochondria is asymmetric in unfertilized sea urchin eggs and the embryo; the side inheriting more mitochondria has a strong bias toward becoming the ventral side. Embryos cultured under hypoxia are defective in ectoderm specification along the DV axis (Agca et al., 2009; Coffman et al., 2004). Results from these studies

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Modular development of the teleost trunk along the dorsoventral axis and zic1/zic4 as selector genes in the dorsal module

Modular development of the teleost trunk along the dorsoventral axis and zic1/zic4 as selector genes in the dorsal module

Teleost fish exhibit remarkable diversity in morphology, such as fins and coloration, particularly on the dorsal side. These structures are evolutionary adaptive because their back is highly visible to other individuals. However, owing to the late phenotypic appearance (from larva to adult) and lack of appropriate mutants, the genetic mechanisms that regulate these dorsoventrally asymmetric external patterns are largely unknown. To address this, we have analyzed the spontaneous medaka mutant Double anal fin ( Da ), which exhibits a mirror-image duplication of the ventral half across the lateral midline from larva to adult. Da is an enhancer mutant for zic1 and zic4 in which their expression in dorsal somites is lost. We show that the dorsoventral polarity in Da somites is lost and then demonstrate using transplantation techniques that somites and their derived tissues globally determine the multiple dorsal-specific characteristics of the body (fin morphology and pigmentation) from embryo to adult. Intriguingly, the zic1 / zic4 expression in the wild type persists throughout life in the dorsal parts of somite derivatives, i.e. the myotome, dermis and vertebrae, forming a broad dorsal domain in the trunk. Comparative analysis further implies a central role for zic1/zic4 in morphological diversification of the teleost body. Taken together, we propose that the teleost trunk consists of dorsal/ventral developmental modules and that zic1 / zic4 in somites function as selector genes in the dorsal module to regulate multiple dorsal morphologies.

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A prominent requirement for single minded and the ventral midline in patterning the dorsoventral axis of the crustacean Parhyale hawaiensis

A prominent requirement for single minded and the ventral midline in patterning the dorsoventral axis of the crustacean Parhyale hawaiensis

Although the Dorsal-dependent DV patterning system seen in Drosophila has been well characterized, it is thought to be evolutionarily derived (novel) with respect to other arthropod groups; even within insects, it has been suggested that some groups rely on Dorsal to lesser degrees to pattern the DV axis (Nunes da Fonseca et al., 2008). Meanwhile, other aspects of DV patterning, such as the role of BMP antagonists in specifying neurogenic ectoderm, appear to be well conserved throughout Bilateria (Holley et al., 1995). When considering the evolution of DV patterning, however, one significant omission has been the lack of functional characterization of sim and the ventral midline in non-insect arthropods. This is possibly owing to the relatively restricted role that they play in Drosophila. As the presence of ventral midline cells in Parhyale represents the first visible manifestation of DV differentiation in the ectodermal grid, we sought to characterize the function of sim and the ventral midline in the overall organization of the DV axis in this animal. We describe here the basic DV fates in the Parhyale embryo, and, through laser ablation of midline cells and knockdown of sim expression, we define the role of the midline in patterning the DV axis of the embryo.

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Apparent role of Tribolium orthodenticle in anteroposterior blastoderm patterning largely reflects novel functions in dorsoventral axis formation and cell survival

Apparent role of Tribolium orthodenticle in anteroposterior blastoderm patterning largely reflects novel functions in dorsoventral axis formation and cell survival

Drosophila AP axis formation depends on spatial gradients of the maternal transcription factors Bicoid (Bcd) and Hunchback (Hb) (St Johnston and Nusslein-Volhard, 1992). Bcd activates multiple target genes, including gap and pair-rule genes (Blankenship and Wieschaus, 2001; Driever and Nusslein-Volhard, 1988; Gao and Finkelstein, 1998; Hulskamp et al., 1990; Rivera- Pomar et al., 1995; Small et al., 1992). In the absence of Bcd, the head, thorax and a subset of abdominal segments fail to develop and anterior terminal structures are transformed to a posterior fate (Driever and Nusslein-Volhard, 1988). However, although Bcd is essential to anterior patterning in Drosophila, no bcd ortholog has been isolated in any organism apart from the higher dipterans (Brown et al., 2001; Stauber et al., 1999; Stauber et al., 2002; Richards et al., 2008). It has been alleged that bcd evolved through duplication of an ancestral Hox-3/zen homolog and that afterwards one copy, zen, retained its function in specifying extra-embryonic tissues (Stauber et al., 1999), whereas the other copy (bcd) acquired new features, resembling those of orthodenticle (otd; oc – FlyBase) (Finkelstein and Perrimon, 1990; Tahayato et al., 2003; Wimmer et al., 2000). In insects, Otd acts as a zygotic head gap gene (Cohen and Jurgens, 1990; Finkelstein and Perrimon, 1990; Finkelstein et al., 1990; Schinko et al., 2008; Schroder, 2003). Owing to this conserved function in head development and the Bcd-like DNA binding specificity, Otd has been proposed as an ancestral anterior patterning gene in insects (Lynch et al., 2006; Schroder, 2003; Wimmer et al., 2000).

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Mirror represses pipe expression in follicle cells to initiate dorsoventral axis formation in Drosophila

Mirror represses pipe expression in follicle cells to initiate dorsoventral axis formation in Drosophila

We thank A. Olza for Drosophila injections; L. Bardia for support with confocal analyses; Z. Paroush, J. Bernués, G. Pyrowolakis, J. Relat and S. Shvartsman for Fig. 4. Roles of Mirr and Cic in pipe regulation. (A)  Mirr-dependent regulation of pipe in follicle cells. The Mirr gradient peaks at the dorsal- anterior region (red). Lateral and dorsal-posterior follicle cells (pale red) contain very low levels of Mirr protein that are nevertheless sufficient to repress pipe, thereby restricting its expression to ventral cells (green). nc, nurse cells; fc, follicle cells. (B)  Model of regulatory networks involved in dorsoventral (DV) and anteroposterior (AP) embryonic patterning. Both processes require RTK signals that, together with other inputs, induce expression of repressor factors (Mirr and Tll). Note that Torso signaling induces tll expression simply by relieving Cic repression (Astigarraga et al., 2007; Cinnamon et al., 2008). In regions where RTK signaling is low or absent, Cic represses mirr and tll, thereby supporting the expression of key patterning genes such as pipe, Kr and kni.

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Genome wide identification of Tribolium dorsoventral patterning genes

Genome wide identification of Tribolium dorsoventral patterning genes

The gene regulatory network controlling dorsoventral axis formation in insects has undergone drastic evolutionary changes. In Drosophila, a stable long-range gradient of Toll signalling specifies ventral cell fates and restricts BMP signalling to the dorsal half of the embryo. In Tribolium, however, Toll signalling is transient and only indirectly controls BMP signalling. In order to gain unbiased insights into the Tribolium network, we performed comparative transcriptome analyses of embryos with various dorsoventral pattering defects produced by parental RNAi for Toll and BMP signalling components. We also included embryos lacking the mesoderm ( produced by Tc- twist RNAi) and characterized similarities and differences between Drosophila and Tribolium twist loss-of-function phenotypes. Using stringent conditions, we identified over 750 differentially expressed genes and analysed a subset with altered expression in more than one knockdown condition. We found new genes with localized expression and showed that conserved genes frequently possess earlier and stronger phenotypes than their Drosophila orthologues. For example, the leucine-rich repeat (LRR) protein Tartan, which has only a minor influence on nervous system development in Drosophila, is essential for early neurogenesis in Tribolium and the Tc-zinc-finger homeodomain protein 1 (Tc-zfh1), the orthologue of which plays a minor role in Drosophila muscle development, is essential for maintaining early Tc-twist expression, indicating an important function for mesoderm specification.

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Recombinase mediated cassette exchange reveals the selective use of
Gq/G11 dependent and  independent endothelin
1/endothelin type A receptor signaling in pharyngeal arch development

Recombinase mediated cassette exchange reveals the selective use of Gq/G11 dependent and independent endothelin 1/endothelin type A receptor signaling in pharyngeal arch development

The endothelin (Edn) system comprises three ligands (Edn1, Edn2 and Edn3) and their G-protein-coupled type A (Ednra) and type B (Ednrb) receptors. During embryogenesis, the Edn1/Ednra signaling is thought to regulate the dorsoventral axis patterning of pharyngeal arches via Dlx5/Dlx6 upregulation. To further clarify the underlying mechanism, we have established mice in which gene cassettes can be efficiently knocked-in into the Ednra locus using recombinase-mediated cassette exchange (RMCE) based on the Cre-lox system. The first homologous recombination introducing mutant lox -flanked Neo resulted in homeotic transformation of the lower jaw to an upper jaw, as expected. Subsequent RMCE-mediated knock-in of lacZ targeted its expression to the

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p38 MAPK is essential for secondary axis specification and patterning in sea urchin embryos

p38 MAPK is essential for secondary axis specification and patterning in sea urchin embryos

Most eggs in the animal kingdom establish a primary, animal-vegetal axis maternally, and specify the remaining two axes during development. In sea urchin embryos, the expression of Nodal on the oral (ventral) side of the embryo is the first known molecular determinant of the oral-aboral axis (the embryonic dorsoventral axis), and is crucial for specification of the oral territory. We show that p38 MAPK acts upstream of Nodal and is required for Nodal expression in the oral territory. p38 is uniformly activated early in development, but, for a short interval at late blastula stage, is asymmetrically inactivated in future aboral nuclei. Experiments show that this transient asymmetry of p38 activation corresponds temporally to both oral specification and the onset of oral Nodal expression. Uniform inhibition of p38 prevents Nodal expression and axis specification, resulting in aboralized embryos. Nodal and its target Gsc each rescue oral-aboral specification and patterning when expressed asymmetrically in p38-inhibited embryos. Thus, our results indicate that p38 is required for oral specification through its promotion of Nodal expression in the oral territory.

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Inverse dynamic modelling of jumping in the red-legged running frog Kassina maculata

Inverse dynamic modelling of jumping in the red-legged running frog Kassina maculata

One individual was scanned using micro-computed tomography (µCT) at the Cambridge Biotomography Centre (University of Cambridge, UK) on an X-Tek H 225 µCT scanner (Nikon Metrology, Tring, UK) at 65 kV and 340 µA producing 1158 TIFF images with a resolution of 0.0493 mm/voxel. Scans were processed in Avizo 8.0 (FEI, Oregon, USA) producing 3D models of the bones and soft-tissues of the left foot, tarsus, shank, thigh, and body (pelvis-abdominal-thoracic segment, head and fore limbs). The long-axis of each segment was aligned with the global Y axis and the proximal joint of each segment (vent of the body segment) directed towards the origin; the dorsal aspect of each segment was directed towards positive Z. A custom-written MATLAB script (Allen et al. 2013) was used to calculate mass, COM location and moments of inertia about all axes for each segment (the latter two measured from the proximal joint), assuming a density of 1.93 g cm -3 for

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The cortical hem regulates the size and patterning of neocortex

The cortical hem regulates the size and patterning of neocortex

and the areas of Pa or Oc, were outlined and measured using ImageJ software (series 1.48, NIH, public domain). The expansion of frontal neocortical (Fr) in hem-ablated mice, in particular, was determined as described in the text. To confirm dorsal expansion of piriform cortex in hem-ablated mice, the D/V length of piriform cortex was determined in coronal sections from six control and six hem-ablated E18.5 forebrains (six coronal sections per cerebral cortex, evenly spaced along the R/C axis). Sections were processed with in situ hybridization (ISH) for Nrp2 expression, which demarcates piriform cortex. The outer contour of piriform cortex was drawn on section images, matched for R/C level, and measured in ImageJ. To assess differences in cell proliferation along the R/C and medial to lateral (M/L, equivalent to D/V) axes of the neocortical primordium, E11.5-E17.5 brains were sectioned sagittally or coronally and processed with immunohistochemistry to show pHH3 immunoreactivity. Mitotic pHH3-IR cells were counted in rectangular fields of consistent size, positioned on section images, centered over the cortical VZ. Statistical comparisons of measurements of cell counts in mutant and control mice were made with a t-test ( paired or unpaired as appropriate), for example, when comparing cell proliferation in hem-ablated and control dorsomedial CP, or with two-way ANOVA (Prism 6, GraphPad Software), when determining whether cell proliferation varies differentially along the R/C axis between hem-ablated and control CP.

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Biochemical Defects of Mutant nudel Alleles Causing Early Developmental Arrest or Dorsalization of the Drosophila Embryo

Biochemical Defects of Mutant nudel Alleles Causing Early Developmental Arrest or Dorsalization of the Drosophila Embryo

The nudel gene of Drosophila is maternally required both for structural integrity of the egg and for dorsoventral patterning of the embryo. It encodes a structurally modular protein that is secreted by ovarian follicle cells. Genetic and molecular studies have suggested that the Nudel protein is also functionally modular, with a serine protease domain that is specifically required for ventral development. Here we describe biochemical and immunolocalization studies that provide insight into the molecular basis for the distinct phenotypes produced by nudel mutations and for the interactions between these alleles. Mutations causing loss of embryonic dorsoventral polarity result in a failure to activate the protease domain of Nudel. Our analyses support previous findings that catalytic activity of the protease domain is required for dorsoventral patterning and that the Nudel protease is auto-activated and reveal an important role for a region adjacent to the protease domain in Nudel protease function. Mutations causing egg fragility and early embryonic arrest result in a significant decrease in extracellular Nudel protein, due to defects in post-translational processing, stability, or secretion. On the basis of these and other studies of serine proteases, we suggest potential mechanisms for the complementary and antagonistic interactions between the nudel alleles.

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Anatomical Structure Study of Aerial Organs of Crataegus Ambigua C. A. Mey

Anatomical Structure Study of Aerial Organs of Crataegus Ambigua C. A. Mey

The purpose of the present research was to study the peculiarities of the anatomical structure of some vegetative and genesic organs of Crataegus ambigua C.A.Mey. growing in the territory of Mangistau region. The findings of investigation allowed determining that the annual sprouts and pedicel of this species have a primary anatomical structure with the transition to secondary growth. Leaf of the Crataegus ambigua is of a dorsoventral type of light mesophytic structure, hypostomatic in terms of stomata arrangement. The fetal epidermis is presented by polygonal cells of the epidermis without additional elements. The pulp consists of large and loosely-arranged parenchymal cells. The epidermis of the corolla is represented by oval thick-walled cells. The pericarp of the seed consists of three well-defined layers (exocarp, mesocarp and endocarp). The corcule occupies the entire internal cavity. In terms of the cover and pulp structure, Crataegus ambigua has a structure similar to other species. Characteristic features for this species are the shape and the arrangement of the main cells of the epidermis, stomata and simple unicellular trichomes.

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Role of the hindbrain in dorsoventral but not anteroposterior axial specification of the inner ear

Role of the hindbrain in dorsoventral but not anteroposterior axial specification of the inner ear

We further assessed the dorsal fates of these inner ears using the expression pattern of Gbx2, which is normally associated with the dorsomedial region of the otocyst (Fig. 7A,D) (Hidalgo-Sanchez et al., 2000). Consistent with the expression patterns of ventrally expressed genes, Gbx2 expression in the dorsal otic tissues is abolished in the operated embryos, indicating the loss of dorsal fates (Fig. 7B,E; n=14). However, Gbx2 expression is not induced in the ventral otocyst of embryos with dorsoventrally rotated neural tube. Presumably, this is due to a considerable increase in distance between the original dorsal neural tube tissue and the otic epithelium after rotation (Fig. 7D,E; vertical bar). Interestingly, in some specimens, ectopic otocysts are present ventrally due to the inadvertent translocation of a part of the otic epithelium during neural tube rotation and Gbx2 expression is induced in these ectopic ventrally positioned otocysts (Fig. 7C,F; arrows; n=9). This suggests that intrinsic signals in the dorsal neural tube are sufficient to confer dorsal otic fates, despite potential ventral signals from other surrounding tissues. Taken together, these experiments demonstrate the importance of the hindbrain in establishing the DV axis of the inner ear.

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Non-canonical dorsoventral patterning in the moth midge Clogmia albipunctata

Non-canonical dorsoventral patterning in the moth midge Clogmia albipunctata

The resulting free ligand dimers attach to their recep- tors [encoded by punt (put), saxophone (sax), and thick veins (tkv)], which form transmembrane complexes [9, 12] (Fig.  1c). This binding event triggers an intracellular signalling process: once the ligand–receptor complex has been established, SAX and TKV phosphorylate Moth- ers against dpp (MAD). Phosphorylated MAD (pMAD) (associated with the signal transducer Medea) trans- locates to the nucleus (Fig.  1d) to activate or repress a number of target genes (such as brinker, Dorsocross, tai- lup, twist, snail, pannier, among others), whose localised regulation induces different tissue fates along the DV axis. In the DV patterning system, initially triggered by the Toll signalling pathway [13, 14], dpp is a key factor for the determination of dorsal tissues and acts as a morpho- gen for the specification of the dorsal ectoderm and the amnioserosa [6, 15]; see [9, 10] for a review.

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Ems and Nkx6 are central regulators in dorsoventral patterning of the Drosophila brain

Ems and Nkx6 are central regulators in dorsoventral patterning of the Drosophila brain

It has been largely unclear how expression of Nkx6 is regulated in the brain NE, although Vnd has been suggested to act as a positive regulator (Uhler et al., 2002). At the blastodermal stage, coexpression of ems and vnd is only observed in the intermediate and ventral NE of the TC and DC, which might account for early Nkx6 expression being limited to the respective NE in the brain and absent from the trunk. Our data indicate that Ems and Vnd together facilitate the activation of Nkx6. Ems expression closely prefigures the domain of Nkx6 expression in the TC and DC (Fig. 7A), and together with the fact that Nkx6 is completely abolished in ems mutants, this suggests that Ems might act as a direct activator to regulate the extension of the Nkx6 domain along the AP axis. Vnd indirectly regulates the enlargement of the Nkx6 domain along the DV axis by repressing the Nkx6-repressor Msh. That DV patterning in the brain NE integrates AP signals is additionally supported by the fact that Ems is also necessary for activation of ind and msh, indicating that ems is a key regulator in DV patterning of the TC and DC. We also provide evidence for a negative-feedback control in the DV regulatory network, in which Ems is needed to activate its own later-stage repressors, Nkx6 and Ind (Fig. 7B). Together, our data suggest not only that Ems regulates the expression of all DV genes (activating Nkx6, ind, msh and repressing vnd), but also that DV factors (Nkx6, Ind and Vnd) control expression of ems, indicating that integration of DV and AP patterning signals takes place at different levels in the DV genetic network.

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Fgf signalling controls the dorsoventral patterning of the zebrafish embryo

Fgf signalling controls the dorsoventral patterning of the zebrafish embryo

Previous analysis has shown that Fgf signalling is involved in the establishment of the anteroposterior patterning of the neural plate (Kudoh et al., 2002). We therefore analysed the expression of markers of either the anterior or the posterior neurectoderm in Fgf-depleted embryos. The expression of Fig. 6. Fgf-mediated restriction of Bmp gene expression is essential for dorsoventral patterning. bmp2b expression in wild type (A), or following overexpression of spry2 (B), injection of RNA encoding a dn-fgfr (C) or treatment with SU5402 (D). (E,F) Following dn-fgfr injection, the expression of the Bmp target gene ved expands dorsally. (G-J) Inhibition of Fgf signalling reduces or abolishes the expression of dorsal mesodermal markers goosecoid (gsc, G,H) and sonic hedgehog (shh, I,J). (K,L) Conversely, the expression territory of draculin (drl), a marker of the ventral hypoblast, is expanded compared with wild type. (M-P) Compared with wild type (M,O) dn-ras injection causes a severe reduction of the expression domain of the pan-neural marker zic2 (N,P). (Q,R) Two-colour in situ hybridisation with bmp2b (blue) and the anterior neural marker otx2 (green) or (S,T) with ved (blue) and cyp26a (green). Arrowheads (Q-T) indicate the border between the gene expression domains. (A-H) Shield stage, (I-T) 70% epiboly.

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Anteroposterior and dorsoventral patterning are coordinated by an identical patterning clock

Anteroposterior and dorsoventral patterning are coordinated by an identical patterning clock

A study in Xenopus showed that in dorsal tissues the linker region of Smad1 is sequentially phosphorylated by MAPK and GSK3, causing it to be degraded (Fuentealba et al., 2007). The degradation of P-Smad1 and loss of BMP signaling dorsally then allows neural tissue development and AP patterning by FGF and Wnt signaling. In zebrafish, the ventral P-Smad1/5 gradient appears to be stable along the AP axis until 75% epiboly, when prospective caudal hindbrain tissue is patterned (Fig. 5M-O) (Tucker et al., 2008). These data suggest that a degradation mechanism in ventral vegetal regions does not regulate the temporal function of BMP signaling in zebrafish. We tested whether a modified mechanism might be acting in which P-Smad1/5 function is inhibited by FGF/MAPK and Wnt/GSK3 through a non-degradation mechanism to temporally coordinate DV and AP patterning during gastrulation. We investigated the localization of GSK3-phosphorylated Smad1/5 (P-Smad1/5 GSK3 ) and MAPK-phosphorylated Smad1/5 (P-

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