Top PDF Localization of Maternal RNAs in the Early Embryo of Drosophila

Localization of Maternal RNAs in the Early Embryo of Drosophila

Localization of Maternal RNAs in the Early Embryo of Drosophila

A comparison of the spatial distribution of bicoid and Adducin-like transcripts in the maternal effect RNA-localization mutants exuperantia, swallow and staufen indicates different genet[r]

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Posterior localization of the Drosophila Gi alpha protein during early embryogenesis requires a subset of the posterior group genes

Posterior localization of the Drosophila Gi alpha protein during early embryogenesis requires a subset of the posterior group genes

Int J De> BioI 39 581 586 (1995) Origilzal Article Posterior localization of the Drosophila Gio protein during early embryogenesis requires a subset of the posterior group genes WILLIAM J WOLFGANG' an[.]

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Time Course of Degradation and Deadenylation of Maternal c-mos and Cyclin A2 mRNA during Early Development of One-Cell Embryo in Mouse

Time Course of Degradation and Deadenylation of Maternal c-mos and Cyclin A2 mRNA during Early Development of One-Cell Embryo in Mouse

I n many species, transcription is effectively silent during the meiotic maturation and the early stage of embryo development. Maternally synthesized RNA and proteins that are loaded into the cytoplasm of developing oocyte program the completion of meiosis and develop- mental progression in the early embryo [1]. Therefore, the regulation of gene expression at post- transcriptional level (localization, translation and stability) probably plays a critical role in the control of early development [2]. Furthermore, changes in the stability of specific maternal mRNA are a way of removing transcripts that encode proteins harmful for embryonic development, as suggested for Cdc25 gene product in Drosophila [3].
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piRNAs and PIWI proteins: regulators of gene expression in development and stem cells

piRNAs and PIWI proteins: regulators of gene expression in development and stem cells

Fig. 1. Maternal mRNA regulation by Aub and piRNAs during Drosophila oogenesis and early embryogenesis. (A) mRNA scanning by piRNAs during oogenesis (stage 8). Egg chambers are composed of 15 nurse cells and one oocyte. The nuage (green), which is composed of ribonucleoprotein particles and in which the ‘ ping-pong ’ cycle takes place, assembles around nurse cell nuclei (blue). piRNAs loaded into Aub are proposed to perform transcriptome-wide scanning of transposable elements (TEs) and maternal mRNAs during their export to the cytoplasm through the nuage. Imperfect piRNA complementarity allows the recruitment of Aub to maternal mRNAs, which are then transported to the oocyte through ring canals (black arrows). (B) Maternal mRNA localization by Aub and piRNAs during oogenesis (stage 12). Nurse cell cytoplasm is poured into the oocyte through ring canals (black horizontal arrows). This contributes to a rotating flow in the cytoplasm of the oocyte (black circular arrow), allowing diffusion of maternal mRNAs and their localization to the germ plasm by anchoring. Polar granules that are ribonucleoprotein particles related to nuage assemble in the germ plasm and contain Aub, its interactor Tudor, as well as Vasa and Oskar. Aub binds maternal mRNAs through piRNA incomplete base pairing, which anchors them to the germ plasm. Wispy poly(A) polymerase colocalizes with Aub in the germ plasm. This mechanism of localization is inefficient and a large proportion of mRNA-protein complexes remains in the cytoplasm of the oocyte. (C) Dual role of piRNAs and Aub in maternal mRNA decay in the soma and stabilization in the germ plasm. Smaug (Smg) is expressed in early embryos and binds maternal mRNAs through Smg recognition elements (SRE). Aub is also bound to maternal mRNAs through piRNA base pairing (A,B). Smg and Aub recruit the CCR4-NOT complex, which induces mRNA deadenylation and decay. CCR4-NOT is also involved in translational repression independently of deadenylation (Go ̈ tze et al., 2017). In addition, Aub can induce mRNA decay by direct cleavage. In the germ plasm, Smg is sequestered by Oskar, preventing its binding to maternal mRNAs. Aub directly interacts with the Wispy poly(A) polymerase, inducing mRNA poly(A) tail elongation and stabilization. Polyadenylation also likely contributes to the translation of mRNAs localized to the germ
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Temporal and spacial control of RNA stability in the early embryo of Drosophila melanogaster

Temporal and spacial control of RNA stability in the early embryo of Drosophila melanogaster

In addition, oskar and Pgc transcripts move back to the posterior pole of the oocyte at stage 9, whereas the bicoid and Add-hts RNAs never show the early posterior localization but are e[r]

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Pgc suppresses the zygotically acting RNA decay pathway to protect germ plasm RNAs in the Drosophila embryo

Pgc suppresses the zygotically acting RNA decay pathway to protect germ plasm RNAs in the Drosophila embryo

To test whether the loss of Nos is sufficient to explain the death of pgc – pole cells, we examined whether increasing Nos levels in pole cells could suppress the pgc mutant phenotype. Expression of nos in the germ plasm depends on the nos 3 ′ untranslated region (3 ′ UTR), which contains regulatory elements for the localization and translation of nos mRNA (Gavis et al., 1996a,b; Dahanukar and Wharton, 1996; Bashirullah et al., 1999). As only 4% of maternal nos mRNA is localized in the germ plasm through a diffusion and entrapment mechanism (Bergsten and Gavis, 1999; Forrest and Gavis, 2003), the amount of nos mRNA in the embryo would not be a rate-limiting step for the expression of Nos in the germ plasm. To express Nos in pole cells independently of the mechanisms that regulate endogenous nos mRNA, we generated a transgene in which the nos-coding sequence was fused to the pgc 3 ′ UTR, which targets transcripts to the germ plasm (Rangan et al., 2009). Ectopic Nos expression can affect embryonic patterning (Gavis and Lehmann, 1992). Consistent with this, embryos exhibited severe patterning defects when the nos-pgc 3 ′ UTR transgene was expressed during oogenesis under the control of the germline- specific nos-GAL4-VP16 driver. The resulting somatic defects made it difficult to analyze the effect of nos overexpression on pole cell development. In contrast, when a weaker otu-GAL4-VP16 driver (Rørth, 1998) was used to express the nos-pgc 3 ′ UTR transgene, 75% of embryos were morphologically normal and could be analyzed for pole cell development. These embryos contained significantly more gonadal pole cells (3.3±2.6, n=100) than did the pgc – embryos (1.0±1.3, n=100) (Fig. 2A-D and Table S2). The rescued pole cells developed into functional germ cells, as indicated by the restored fertility of the adult progeny (Table S2). These
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The maternal to zygotic transition revisited

The maternal to zygotic transition revisited

In addition to specific repressors, histones have been identified as more general repressors of transcription in X. laevis and zebrafish (Almouzni and Wolffe, 1995; Amodeo et al., 2015; Joseph et al., 2017). Histones are present in large excess in early embryos (Adamson and Woodland, 1974; Anderson and Lengyel, 1980); they bind with high affinity and little sequence specificity to DNA (Campos and Reinberg, 2009), and, when bound in the form of nucleosomes, they block access of the transcriptional machinery to DNA (Lorch et al., 1987; Workman and Kingston, 1998). In zebrafish and Drosophila embryos, the concentration of soluble histones in the nucleus drops in the approach to genome activation (Joseph et al., 2017; Shindo and Amodeo, 2019). Moreover, experiments in zebrafish have revealed that the drop in the concentration of soluble histones in the nucleus provides an opportunity for the transcriptional machinery to successfully compete for DNA access and activate transcription (Joseph et al., 2017; Pálfy et al., 2017). Developmental changes in the early embryo provide at least two mechanisms by which the concentration of histones may be reduced during embryogenesis. First, the exponential increase in DNA during the rapid cleavage divisions might titrate out histones. A role for DNA content in regulating the onset of transcription is supported by experiments in which increasing DNA content results in premature onset of transcription in X. laevis, zebrafish and Drosophila (Dekens et al., 2003; Jevtic ́ and Levy, 2017; Lu et al., 2009; Newport and Kirschner, 1982; Prioleau et al., 1994). However, the quantification of both histones and DNA content has shown that, at least in zebrafish, the increase in DNA content is not sufficient to titrate the levels of soluble histones significantly (Joseph et al., 2017). Another possible explanation for the decrease in nuclear histone concentration involves a change in the nuclear import dynamics of histones. This could be a consequence of the dilution of import machinery caused by the increasing number of nuclei (Shindo and Amodeo, 2019) or of the marked increase in the ratio of nuclear over cytoplasmic volume during the cleavage stages (Joseph et al., 2017). The latter has been suggested to limit the capacity of the nucleus to concentrate proteins (Kim and Elbaum, 2013a,b; Kopito and Elbaum, 2007; Kopito and Elbaum, 2009), changing the distribution of histones between nucleus and cytoplasm. A role for import dynamics is supported by the observation that an experimentally induced increase in nuclear volume results in earlier genome activation in X. laevis (Jevtic ́ and Levy, 2015; Jevtic ́ and Levy, 2017). We conclude that both specific and general repressors play a role in changing the balance from transcriptional repression to transcriptional activation during ZGA.
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Co localization of neural cell adhesion molecule and fibroblast growth factor receptor 2 in early embryo development

Co localization of neural cell adhesion molecule and fibroblast growth factor receptor 2 in early embryo development

isoform (Fig. 5A). The same pattern was observed for the 2-cell embryos, with Fgfr2-1 showing significantly higher expression (Fig. 5A). This is in concordance with a previous study observing the presence of Fgfr2-1 and Fgfr2-2 during early zygotic transcrip- tion (Haffner-Krausz et al., 1999). This difference in relative expression of Fgfr2 isoforms seems to be more pronounced in oocytes compared to 2-cell embryos (Fig. 5A) indicating that Fgfr2-1 is a more abundant maternal FGFR2 transcript than Fgfr2-2. FGFR2-2 primarily binds FGF10 and FGF7, whereas FGFR2-1 binds FGF2 (Ohuchi et al., 2000, Yan et al., 1993, Yeh et al., 2003) thus enabling a differential embryo response accord- ing to the specific FGFR2 isoform expressed. In addition, studies show that Fgfr2 expression becomes asymmetrical along the animal-vegetal axis of the mature blastocyst (Haffner-Krausz et al., 1999) suggesting a role for the different FGFR2 isoforms in the orientation and polarity of the preimplantation embryo. The mouse Fgfr2 knockout produced a recessive embryonic lethal mutation with a normal development up until blastocyst stage (Arman et al., 1998). Homozygous embryos die a few hours after implantation indicating that FGFR2 is required for early postimplantation development.
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Dorsal Ventral Patterning and Gene Regulation in the Early Embryo of Drosophila melanogaster

Dorsal Ventral Patterning and Gene Regulation in the Early Embryo of Drosophila melanogaster

We generated grh germline clone females in order to deplete both maternal and zygotic grh expression from embryos. The conventional method of creating germline clones (Perrimon, 1998), which relies on flipase catalyzed mitotic recombination in the context of transheterozygous FRT ovoD (dominant female sterile mutation) and FRT grh chromosomes, for example, could not be used because ovoD within the commonly used FRT ovoD chromosome is most likely inserted at the grh locus. FRT ovoD in combination with all grh alleles tested are zygotically lethal, but no lethality was observed with ovoD insertions located on other chromosomes. Thus, it was necessary to make germline clones in females of the genetic background FRT grh/FRT GFP. Embryos obtained from these females were manually screened for absence of GFP (Luschnig et al., 2004), thus allowing isolation of embryos containing the mutant form of grh. To ensure that grh zygotic transcripts were absent, females containing germline clones were mated to males containing appropriate balancer chromosomes to allow detection in the early embryo (i.e., FRT grh/ Cyo ftz-lacZ; see Materials and Methods).
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Maternal RNAs encoding transcription factors for germline specific gene expression in Drosophila embryos

Maternal RNAs encoding transcription factors for germline specific gene expression in Drosophila embryos

and Stefanovsky, 2002; Grummt, 2003). TIF-IA acts as the key regulator for rRNA transcription by recruiting RNA polI into the rRNA promoter pre-initiation complex, and the interaction be- tween TIF-IA and RNA polI is regulated by various pathways linking biosynthetic activities (Moss and Stefanovsky, 2002; Grummt, 2003). In early pole cells, RNA polII-dependent tran- scription is globally inhibited by maternal Pgc (Martinho et al., 2004), but RNA polI-dependent transcription remains active (Seydoux and Dunn, 1997). Furthermore, the observed rate of protein synthesis is higher in pole cells than in the rest of somatic Fig. 3. vas and nos expression in dsRNA-in- jected embryos. (A,G) vas (A) and nos expression (G) in the stage-15/16 control embryos injected with dsRNAs for GFP. (B–F and H-L) Expression of vas (B-F) and nos (H-L) in the stage-15/16 embryos injected with dsRNAs for ovo (B,H), CG31716 (C,I), bip2 (D,J), Trf2 (E,L), l(2)NC136 (F) and Tif-IA (K). (A’-L’) Higher magnification images of the embry- onic gonads shown in (A-L). Anterior is to the left. Arrowheads in (A-L) point to the gonads. Scale bars, 20 µ m.
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A caudal mRNA gradient controls posterior development in the
wasp Nasonia

A caudal mRNA gradient controls posterior development in the wasp Nasonia

The mechanism that establishes the Cad gradient in Nasonia is of particular importance as bcd is a new addition to the developmental network and is found only in higher dipterans. Consequently, Bcd cannot be responsible for establishing the Cad gradient in more ancestral species (Lynch and Desplan, 2003). Nonetheless the Cad gradient is conserved among insects. In Tribolium, Cad protein is first expressed homogenously throughout the embryo. Later, however, a posterior to anterior protein gradient forms but nothing is known about the mechanisms leading to the formation of this gradient. Interestingly, however, when a transgene encoding the Tc cad mRNA is placed in Drosophila, it leads to the formation of a translational gradient that is dependent on bcd (Wolff et al., 1998). This argues that a common underlying mechanism may be responsible for establishing the protein gradient in Tribolium and in Drosophila. It is likely that bcd took over the function of a translational repressor present in ancestral insects, perhaps including Nasonia. The mRNA gradient might therefore be specific to the wasp. Interestingly, Nvit otd mRNA is also localized to both the anterior and posterior poles of the embryo, which has not been reported in any other species (Lynch et al., 2006a). This suggests that Nasonia may extensively use RNA localization mechanisms for setting up the anteroposterior axes in the embryo. Moreover, maternal mRNA localization may be a common feature of long germ development. Studies performed in other Hymenopterans, which undergo extremely diverse modes of embryogenesis, ranging from long-germ embryogenesis in Apis mellifera (Davis and Patel, 2002) to the polyembryonic development of Copidosoma floridanum (Grbic, 2003) will aid in identifying the conserved mechanisms among these diverse modes of embryogenesis. In Copidosoma, up to 2000 embryos may be produced clonally from a single egg, showing that maternal determinants cannot play similar axial patterning roles in this insect as seen in long and short germ insects (Zhurov et al., 2004). However, work in the long germ Apis mellifera might elucidate whether maternal mRNA localization is a common feature of long-germ embryogenesis.
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The Role of Maternal HP1a in Early Drosophila Embryogenesis via Regulation of Maternal Transcript Production

The Role of Maternal HP1a in Early Drosophila Embryogenesis via Regulation of Maternal Transcript Production

mRNA sequencing data were collected from a HiSeq2000 at the Yale Stem Cell Center Genomics Core for HP1a RNAi and EGFP RNAi lines, either from stage 14 eggs or ovaries. After the sequencing quality evaluation by FASTQC, sequences were mapped to D. melanogaster Berkeley Drosophila Genome Project (BDGP) release 6 by Tophat2.1.1 with the default mapping option (Supplemental Material, Table S1). The gene annotation used for the analysis was D. melanogaster BDGP6.84. The Rsubread package was used for the read count assignment (Liao et al. 2013). Reproducibility evalua- tion was measured by Pearson correlation between replicates and visualized in scatterplots (Figure S1, A–D). The sche- matic of the transcriptome analysis pipeline is displayed in Figure S2A. DEseq2 was applied to analyze the expression level changes of genes in HP1a RNAi samples compared to those of control RNAi samples (Anders and Huber 2010). For each RNAi line, genes with P-value # 0.05 were considered to be differentially expressed (DE) genes. To rule out the effect caused by the different insertion sites of RNAi, we sub- tracted the differentially expressed genes identified in the control RNAi in the corresponding HP1a RNAi. To account for shRNA off-target effects, we only kept the common differentially expressed genes of the two RNAi lines and regarded those with consistent changes in trend (up- or downregulated) as differentially expressed genes for further analysis. A volcano plot showing the fold change and P-value was used to display the mRNA level change for all genes in the HP1a RNAi samples (Figure S1, E and F).
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A novel function for the IκB inhibitor Cactus in promoting Dorsal nuclear localization and activity in the Drosophila embryo

A novel function for the IκB inhibitor Cactus in promoting Dorsal nuclear localization and activity in the Drosophila embryo

Fig. 1. Cact inhibits Toll in lateral regions and enhances Toll signals in ventral regions of the embryo. (A) Optical section showing a control Dl gradient. (B-D) Nuclear Dl was extracted, measured and plotted as half gradients for control embryos (black) or embryos from cact[A2]/+ (B), cact[A2]/cact[011] (C) or cact[A2]/Df(cact) (D) mothers (red). The y axis represents nDl fluorescence intensity along the ventral-to-dorsal embryonic axis (x axis). Data are mean±s.e.m. (E-L) In situ hybridization for sna (green) in the mesoderm and sog ( pink) in the lateral neuroectoderm of embryos with maternal cact loss-of-function alleles. In embryos from cact[011]/+ or cact [A2]/+, the ventral and lateral territories are similar to wild type (F,J). Stronger allelic combinations lead to dorsal expansion of lateral sog and ventral sna reduction in the prospective mesoderm (G,H,K,L). Anterior is leftwards and posterior is rightwards in E-L; dorsal is upwards in G-L. Plus signs in upper right corner indicate the severity of the allelic cact combination (+++>++>+), defined by loss of activity and protein levels (Fig. S1). (M,N) The sna domain width measured at 50% and 75% egg length. Data are mean±s.e.m. Statistically significant differences were determined using Student ’ s t-test (***P ≤ 0.001, *P ≤ 0.05).
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Regulation of cytoskeletal organization and junctional remodeling by the atypical cadherin Fat

Regulation of cytoskeletal organization and junctional remodeling by the atypical cadherin Fat

is associated with excessive growth and contraction at dorsal and ventral cell borders and a reduction in cell elongation and alignment. These results suggest a model in which Fat regulates planar polarized junctional localization and remodeling, which in turn influences cell shape. The atypical myosin Dachs is asymmetrically localized in denticle-forming cells and loss of dachs partially suppresses the denticle and junctional defects in fat mutants, suggesting that aberrant Dachs activity contributes to the defects in fat mutants. However, junctional and denticle planar polarity are correctly established in dachs mutants, indicating that Dachs is not essential for these processes. Defects in junctional planar polarity, but not denticle localization, are recapitulated in embryos that express activated Notch and embryos mutant for Expanded, Hippo or Warts. These results demonstrate an essential role for Fat and Hippo/Warts signaling in regulating planar polarized adherens junction localization in the Drosophila embryo. Although the Hippo/Warts pathway has generally been thought to be separate from the role of Fat in planar polarity, we demonstrate an unexpected role for Expanded, Hippo and Warts in junctional planar polarity in the Drosophila embryo. Hippo/Warts signaling could influence planar polarity by modulating the size of the apical epithelial domain or the levels of junctional and signaling Fig. 5. Junctional planar polarity requires Expanded, Hippo and Warts but is independent of Yorkie. (A-H) Stage 14 denticle belts stained for ZO-1 (green) in Drosophila wild type (WT) (A); embryos zygotically mutant for fat Grv (B), ex E1 (C), fat Grv ex E1 (D); embryos maternally and
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Wollknäuel is required for embryo patterning and encodes the
Drosophila ALG5 UDP glucose:dolichyl phosphate
glucosyltransferase

Wollknäuel is required for embryo patterning and encodes the Drosophila ALG5 UDP glucose:dolichyl phosphate glucosyltransferase

Taken together, these results confirm that the UPR is activated in wol mutants, and indicate that translation might be attenuated in wol embryos. We propose that this causes the observed patterning defects. According to this model, reduced maternal wol activity would lead to accumulation of unfolded proteins in the ER in early embryos, with a consequent transient increase in eIF2 α phosphorylation. Translation of selected maternal mRNAs, including cad and the activator of dpp expression, would be particularly sensitive to increased eIF2 α phosphorylation. Reduced amounts of these transcription factors result in disruption of posterior segmentation and of dorsal-ventral patterning. Although the UPR plays important developmental and physiological roles in C. elegans, Drosophila and mammals (Ryoo et al., 2007; Shen et al., 2001; Shen et al., 2005; Souid et al., 2007; Wu and Kaufman, 2006), this is the first report to indicate that inappropriate UPR activation may disrupt embryonic patterning.
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The embryonically active gene, unkempt, of Drosophila encodes a Cys3His finger protein.

The embryonically active gene, unkempt, of Drosophila encodes a Cys3His finger protein.

The unkempt gene of Drosophila encodes a set of embryonic RNAs, which are abundant during early stages of embryogenesis and are present ubiquitously in most somatic t[r]

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The role of homeotic genes in determining the segmental pattern of chordotonal organs in Drosophila

The role of homeotic genes in determining the segmental pattern of chordotonal organs in Drosophila

The relatively few studies of ch organ distribution outside of Drosophila indicate that sense organs considered here are strikingly conserved across distantly related insects suggesting that the chordotonal organs may be fundamental elements of a ground plan sensory system common to all insects. The grasshopper embryo has a set of ch organs in T2 and T3 that are highly likely to be homologs of Drosophila dch3, while the sternal and pleural ch organs of the grasshopper abdomen are likely homologs of the lch5 and vchA/B of Drosophila (Meier et al., 1991). In the late stage embryo of the moth Manduca sexta the distribution of ch organs in the abdominal segments shows a striking similarity to Drosophila, with a pair of ventral ch, a single lch and a parallel cluster of 4 ch in the lateral region (Grueber and Truman, 1999) which positionally correspond to Droso- phila vchA and B, v’ch1 and lch5, respectively. It is interesting that the lch is composed of four sensilla in M. sexta compared with the five of Drosophila. Adult moths preserve a three sensillum dch in the thoracic segments, except noctuoid moths, which have evolved a hearing organ around the sense organ and reduced the number of associated sensilla (Hasenfuss, 1997). As in M. sexta larvae, the lch5 homolog in the first abdominal segment is composed of four sensilla (Hasenfuss, 1997). The wealth of knowledge concerning the devel- opment of the Drosophila sensory nervous system and the role of homeotic genes in the regulation of segmental identity holds promise that a parallel investigation of sense organ development and homeotic genes in other arthropods could contribute greatly to a phylogenetic perspective on nervous system development.
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Seeing is believing: the Bicoid protein reveals its path

Seeing is believing: the Bicoid protein reveals its path

SSD model was its presumption that the Bcd protein dif- fused throughout the embryo (Fig. 1e). This was fueled by studies where fluorescently labeled dextrane particles injected at the anterior pole were used to simulate the diffusion of Bcd [12]. In retrospect, it was a daring pro- posal, however, the constraints of this approach were clear from the very beginning. Nevertheless, the ap- proach was too simplistic to assume that a protein would behave like a dextrane particle. Subsequently, other reports measured higher diffusion rates [13–15], calculated to be high enough to explain the SDD diffu- sion model, corroborated by a recent biophysical model analysis [16].
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Generating asymmetries in the early vertebrate embryo: the role of the Cerberus like family

Generating asymmetries in the early vertebrate embryo: the role of the Cerberus like family

Cerberus-related proteins have been identified in other verte- brate species (see Table 1): mouse cerberus-like gene (cerl-1; Belo et al., 1997; Biben et al., 1998; Shawlot et al., 1998), chick Cerberus (cCer; Rodriguez-Esteban et al., 1999; Yokouchi et al., 1999; Zhu et al., 1999), Xenopus Coco (Bell et al., 2003), zebrafish Charon (Hashimoto et al., 2004) and mouse Cerberus- like-2 (Cerl–2; Marques et al., 2004), and are now grouped in the Cerberus/Dan gene family. Xenopus XCer, chick cCer and mouse Cerl-1 genes are syntenic (www.metazome.net) and, at peri gastrulation stages, are expressed in topological equivalent embryonic structures, such as the anterior endomesoderm, hypo- blast and anterior visceral endoderm, respectively (Bouwmeester et al., 1996; Foley et al., 2000; Belo et al., 1997). In contrast, Xenopus coco was found to be expressed during pre-gastrula stages exclusively in the animal pole. At gastrula stages, coco transcripts can be detected in both the dorsal and ventral marginal zone as well as in the animal cap ectoderm (Bell et al., 2003). By early neurulation stages, mouse Cerl-1 and chick cCer transcripts are also detected in the anterior definitive mesendoderm (Belo et al., 1997; Rodriguez-Esteban et al., 1999). But at later stages, during somitogenesis, Cerberus-related genes display very dis- tinct expression patterns. XCer expression is no longer observed. Mouse Cerl-1 transcripts are found in the rostral half of the two newly formed somites and rostral presomitic mesoderm. Chick cCer is expressed in the left paraxial and lateral plate mesoderm. Zebrafish Charon and mouse Cerl-2 are both expressed around the node region but with a remarkable difference between their expression patterns: while Charon has a symmetric domain, Cerl- 2 becomes strongly expressed on the right side (Bouwmeester et al., 1996; Belo et al., 1997; Rodriguez-Esteban et al., 1999; Hashimoto et al., 2004; Marques et al., 2004). Very recently, Xcoco was shown to be expressed bilaterally in the posterior paraxial mesoderm during neurula stages (Vonica and Brivanlou, 2007).
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The role of the polarizing zone in the pattern of experimental chondrogenesis in the chick embryo interdigital space

The role of the polarizing zone in the pattern of experimental chondrogenesis in the chick embryo interdigital space

)"t J De\' BioI 35 63 67 (1991) 63 Shurl CUIII rilil/liull The role of the polarizing zone in the pattern of experimental chondrogenesis in the chick embryo interdigital space DOMINGO MACiAS' and YOLA[.]

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