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PubMed1997

The zebrafish homologue of the ret receptor and its pattern of expression during embryogenesis.

The c-ret proto-oncogene, a member of the receptor tyrosine kinase gene superfamily, plays a critical role in the development of the excretory system and the enteric and autonomic nervous systems of mammalian embryos. To study the potential function of the c-ret locus in lower vertebrates, we have isolated its zebrafish homologue, ret1 and established its expression pattern during embryogenesis. Ret1 mRNA first appears during early somitogenesis in the presumptive brain, spinal cord and excretory system. Within the CNS, expression of ret1 is detected in primary motor and sensory (Rohon-Beard) neurons. Ret1 transcripts are also expressed in subsets of neural crest cells and cranial ganglia as well as in the enteric nervous system. In the excretory system, expression is detected in the developing nephric duct and the pronephros. Our findings reveal a remarkable similarity in the expression pattern of c-ret between higher and lower vertebrates, suggesting that the function of this locus has been conserved throughout vertebrate evolution. Furthermore, the conservation of ret1 expression in cell types which remain unaffected by the mammalian c-ret mutations, such as motor and sensory neurons, suggests a function of this receptor in these cell lineages.

Amino Acid Sequence↗

PubMed1997

Mouse Neogenin, a DCC-like molecule, has four splice variants and is expressed widely in the adult mouse and during embryogenesis.

Neogenin is a member of the N-CAM family of cell adhesion molecules and is closely related to the DCC tumor suppressor gene product. Recently, it has been demonstrated that the DCC/Neogenin subfamily plays a key role in axonal guidance within the embryonic nervous system, however little is known about the function of DCC or Neogenin in non-neuronal tissues in vertebrates. To gain an understanding of Neogenin function outside of the nervous system we have cloned and sequenced the mouse homologue of Neogenin. We describe three alternatively spliced exons within the extracellular domain of Neogenin and a fourth alternatively spliced exon within the cytoplasmic domain. We further demonstrate that three of these alternatively spliced exons are developmentally regulated. Analysis of Neogenin mRNA expression showed that two distinct Neogenin transcripts are expressed at significant levels in a broad spectrum of adult mouse tissues and throughout the mid to late stages of embryogenesis. In situ hybridization studies on day 15.5 mouse embryos revealed that Neogenin is expressed widely throughout the developing mouse embryo, in both neuronal and non-neuronal tissues. These observations suggests that Neogenin may play an integral role in regulating differentiation programmes and/or cell migration events within many embryonic and adult tissues.

Alternative Splicing↗

PubMed2004

Involvement of cadherins 7 and 20 in mouse embryogenesis and melanocyte transformation.

We have determined the expression profiles of cdh7, and the related cdh20 during development. Both transcripts are found in the adult brain, but only cadherin-20 mRNA was detected during embryogenesis. In mouse embryos, cadherin-20 is synthesized by the forebrain, anterior neural ridge, developing visual system, primitive external granular layer of the cerebellum and a subset of neural crest cells likely to develop into melanoblasts. We found that the other embryonic tissues in which cadherin-20 was synthesized depended on genetic background. Melanoma cell lines contained transcripts for cadherin-7 but not for cadherin-20. The majority of the malignant melanoma cell lines produced N-cadherin (N-Cad) and/or cadherin-7 whereas melanocyte cell lines did not. The converse was observed for E-cadherin (E-Cad). Our data suggest that during development cadherin-20 is a key player in compartmentalization of the neural tube and establishment of neural circuitry. Finally, during oncogenesis, cadherin-7, N-cad and E-cad could be used as an efficient marker set for melanoma.

Amino Acid Sequence↗

PubMed1995

Expression of a Xenopus counterpart of mammalian syndecan 2 during embryogenesis.

We have identified a Xenopus cDNA, XS-2, by screening a Xenopus embryonic stage-22-24 cDNA library with a DNA probe encoding the transmembrane and cytoplasmic domains of mouse syndecan 1. The 1.4 kb cDNA consists of an open reading frame of 642 nucleotides encoding a protein of 191 amino acids. The predicted protein of 20869 Da contains a 25-amino acid putative transmembrane domain and a 32-amino acid putative cytoplasmic domain, both of which are highly similar to the corresponding regions of rat syndecan 2 (92% identity) and to a lesser degree those of rat syndecans 1, 3 and 4 (62, 64 and 78% respectively). The putative N-terminal ectodomain contains a possible attachment site for heparan sulphate, identical with the comparable glycosaminoglycan-attachment sequence of rat syndecan 2. Polyclonal antisera raised against recombinant ectodomain of XS-2, expressed as a fusion protein, recognized a heparan sulphate proteoglycan in XTC cell-culture medium. This proteoglycan bound to DEAE-Sephacel and was eluted with 1 M NaCl; digestion with heparitinase but not chondroitinase ABC resulted in the identification of a 46 kDa protein by these antisera. Northern-blot analysis indicated that XS-2 identifies two Xenopus mRNA species approx. 4 and 2 kb in size in embryos ranging in maturation from the 64-cell stage to stage 54. These results demonstrate that a heparan sulphate proteoglycan, similar to syndecan 2, is expressed during Xenopus embryogenesis.

Amino Acid Sequence↗

PubMed1996

Biotin carboxyl carrier protein and carboxyltransferase subunits of the multi-subunit form of acetyl-CoA carboxylase from Brassica napus: cloning and analysis of expression during oilseed rape embryogenesis.

In the oilseed rape Brassica napus there are two forms of acetyl-CoA carboxylase (ACCase). As in other dicotyledonous plants there is a type I ACCase, the single polypeptide 220 kDa form, and a type II multi-subunit complex analogous to that of Escherichia coli and Anabaena. This paper describes the cloning and characterization of a plant biotin carboxyl carrier protein (BCCP) from the type II ACCase complex that shows 61% identity/79% similarity with Anabaena BCCP at the amino acid level. Six classes of nuclear encoded oilseed rape BCCP cDNA were clones, two of which contained the entire coding region. The BCCP sequences allowed the assignment of function to two previously unassigned Arabidopsis expressed sequence tag (EST) sequences. We also report the cloning of a second type II ACCase component from oilseed rape, the beta-carboxyltransferase subunit (betaCT), which is chloroplast-encoded. Northern analysis showed that although the relative levels of BCCP and betaCT mRNA differed between different oilseed rape tissues, their temporal patterns of expression were identical during embryo development. At the protein level, expression of BCCP during embryo development was studied by Western blotting, using affinity-purified anti-biotin polyclonal sera. With this technique a 35 kDa protein thought to be BCCP was shown to reside within the chloroplast. This analysis also permitted us to view the differential expression of several unidentified biotinylated proteins during embryogenesis.

Acetyl-CoA Carboxylase↗

PubMed2000

Chimaeric mice with disruption of the gene coding for phosphatidylinositol glycan class A (Pig-a) were defective in embryogenesis and spermatogenesis.

Mutations in the gene encoding PIG-A (phosphatidylinositol glycan class A) are found in patients with paroxysmal nocturnal haemoglobinuria (PNH), an acquired haematopoietic stem cell disorder. Individuals with hereditary PIG-A mutations have never been identified, which is also manifested by the difficulties in generating Pig-a knockout (KO) mice. This study investigated the effect of Pig-a mutations on the development of visceral and genital organs in addition to the haematopoietic system by the generation of Pig-a KO chimaeric mice. Of a total of 54 live births out of 1684 blastocysts injected, chimaerism for Pig-a knockout was detected in 29 mice, suggesting the importance of Pig-a in embryogenesis and in live birth. Quantification of the degree of chimaerism in different organs of the surviving chimaeric mice revealed extremely low levels of Pig-a KO cells in the liver and spleen. In contrast, high levels of KO signals were usually detected in the brain, heart, lung and kidney. Haematopoiesis proceeded normally in these chimaeric mice (as measured by 'complete blood cell counting') and the Pig-a KO cells were present at low levels in red blood cells and B lymphocytes but at high levels in T lymphocytes, although these KO cells did not gain any growth advantage. The effect of Pig-a knockout was also prominent in the reproductive system, another organ with high mitotic activity. Breeding the male chimaeras revealed a high rate of infertility and abnormality in the male genital organs, including abnormally shaped testes, epididymis and seminal vesicles. Even in the absence of gross abnormalities of the genital organs, low counts of motile sperm were also discernible. Pig-a KO sperm was detected in these organs; however, no transmission of the KO allele was observed. The results suggest a possible mechanism underlying the non-transmission of the Pig-a KO gene in germlines.

Animals↗

PubMed1998

Smad6 functions as an intracellular antagonist of some TGF-beta family members during Xenopus embryogenesis.

BACKGROUND: Bone morphogenetic proteins (BMPs) transmit signals via the intracellular protein Smad1, which is phosphorylated by ligand bound receptors, translocates to the nucleus, and functions to activate BMP target genes. Recently, a subclass of Smad proteins has been shown to inhibit, rather than transduce, BMP signalling, either by binding to the intracellular domain of BMP receptors, thereby preventing phosphorylation-mediated activation of Smad1, or by binding directly to Smad1, thereby inhibiting its ability to activate gene transcription. RESULTS: We have identified a Xenopus Smad (Smad6) that is 52% identical to mammalian Smad6, an inhibitory Smad. The spatial pattern of expression of Smad6 changes dynamically during embryogenesis and is similar to that of BMP-4 at the tailbud stage. Overexpression of Smad6 in Xenopus embryos phenocopies the effect of blocking BMP-4 signalling, leading to dorsalization of mesoderm and neuralization of ectoderm. Xenopus Smad6 completely blocks the activity of exogenous BMP-4, and, unlike human Smad6, partially blocks the activity of activin, in a mesoderm induction assay. We also find that Smad6 protein accumulates at the membrane in some cells but is partially or completely restricted to nuclei of most overexpressing cells. CONCLUSIONS: We have identified an inhibitory Xenopus Smad, Smad6, that functions as an intracellular antagonist of activin and BMP-4 signalling. Our finding that Smad6 protein is partially or completely restricted to nuclei of most overexpressing cells suggests that it may employ a novel or additional mechanism of action to antagonize TGF-beta family signalling other than that reported for other inhibitory Smads.

Activins↗

PubMed2000

The conserved nuclear receptor Ftz-F1 is required for embryogenesis, moulting and reproduction in Caenorhabditis elegans.

BACKGROUND: Nuclear receptors are essential players in the development of all metazoans. The nematode Caenorhabditis elegans possesses more than 200 putative nuclear receptor genes, several times more than the number known in any other organism. Very few of these transcription factors are conserved with components of the steroid response pathways in vertebrates and arthropods. Ftz-F1, one of the evolutionarily oldest nuclear receptor types, is required for steroidogenesis and sexual differentiation in mice and for segmentation and metamorphosis in Drosophila. RESULTS: We employed two complementary approaches, direct mutagenesis and RNA interference, to explore the role of nhr-25, a C. elegans ortholog of Ftz-F1. Deletion mutants show that nhr-25 is essential for embryogenesis. RNA interference reveals additional requirements throughout the postembryonic life, namely in moulting and differentiation of the gonad and vulva. All these defects are consistent with the nhr-25 expression pattern, determined by in situ hybridization and GFP reporter activity. CONCLUSIONS: Our data link the C. elegans Ftz-F1 ortholog with a number of developmental processes. Significantly, its role in the periodical replacement of cuticle (moulting) appears to be evolutionarily shared with insects and thus supports the monophyletic origin of moulting.

Animals↗

PubMed2001

Sez4 gene encoding an elongation subunit of DNA polymerase zeta is required for normal embryogenesis.

BACKGROUND: Sez4 identified as a seizure-activated gene shows a similarity to the yeast REV3 that encodes a catalytic subunit of the nonessential DNA polymerase zeta which is involved in error-prone translesion synthesis. Although yeast REV3 homologues in mouse and human have recently been identified and characterized, their precise roles remain elusive. RESULTS: Here we investigated the role of mouse pol zeta by targeted inactivation of the Sez4 gene. The homozygous Sez4 mutants died around embryonic day (E) 10.5. This lethal effect was the result of developmental defects and apoptotic cell death within the embryo proper at the gastrulation stage, and it was partially rescued at E12.5 by the expression of a Sez4-transgene. In wild-type embryos, Sez4 transcripts were up-regulated within the embryo proper from E7.5, correlating well with the lethal stage of Sez4-inactivation. CONCLUSION: Our findings indicate that Sez4 is essential for epiblast lineage-specific development and suggests a requirement of mammalian DNA polymerase zeta in the survival of certain subcellular populations which are indispensable to normal embryogenesis.

Animals↗

PubMed1994

Identification of molecular markers of embryogenesis in Arabidopsis thaliana by promoter trapping.

The technique of promoter trapping has been exploited to identify markers of embryogenesis in Arabidopsis thaliana. A population of transgenic A. thaliana was generated containing the promoter trap vector pdeltagusBin19, following Agrobacterium tumefaciens-mediated transformation. This vector contains at the T-DNA left border, a promoterless gusA gene, which is activated following integration downstream of a native gene promoter that directs transgene transcription. Screening of a population of 430 independent transgenic lines revealed that 74 lines (17.2%) exhibited GUS activity in siliques, as determined by fluorimetric assay. Histochemical GUS analysis was used to identify lines that expressed GUS in embryos, and three lines that were demonstrated to contain single T-DNA inserts were analysed in detail. Each line showed a distinct pattern of GUS fusion activity. Fusion transcripts were identified, demonstrating that transcription was initiated in the genomic DNA flanking the T-DNA left border. Inverse PCR was used to clone the T-DNA flanking sequences, and for one line a corresponding cDNA was identified, demonstrating that the tagged sequences are transcribed. The markers represent the earliest embryonic genes known to be expressed in plants.

Arabidopsis↗

PubMed1999

Footprinting in vivo reveals changing profiles of multiple factor interactions with the beta-phaseolin promoter during embryogenesis

Whereas in vitro techniques are essentially limited to the analysis of interactions with a single or limited number of cis-elements, in vivo footprinting techniques can be used to assess the total profile of factor interactions with a promoter. By probing with dimethylsulphate and using sensitive ligation-mediated PCR analytical techniques, the in vivo status of the phas promoter was determined in transcriptionally active (embryo) and inactive (leaf) tissues. Changes in factor occupancy were detected during embryogenesis, and the greatest complexity seen (at mid-maturation) was in accordance with the many potential binding sites predicted on the basis of sequence comparison. Evidence was obtained that several cis-elements not previously shown to be used for factor binding in plant promoters are occupied. The great complexity of footprints may represent the need for multiple factor interaction to achieve high levels of transcription. Alternatively, it is possible that the differential levels of expression in individual regions of the embryo evident from histochemical analysis of the GUS reporter result from the interaction of relatively few factors, with the overall footprinting pattern representing a summation of patterns from various tissues.

Journal Article↗

PubMed2003

The GLOBULAR ARREST1 gene, which is involved in the biosynthesis of folates, is essential for embryogenesis in Arabidopsis thaliana.

We identified a mutation in Arabidopsis that resulted in defective embryos, and we designated this mutation globular arrest1 (gla1). The predicted amino acid sequence encoded by the GLA1 gene is homologous to the amino acid sequences of folylpolyglutamate synthetase (FPGS) and dihydrofolate synthetase (DHFS), which participate in folate biosynthesis. The defect of gla1 in the formation of calli was rescued by the supplement of 5-formyl tetrahydrofolate. These results indicated that GLA1 is involved in the biosynthesis of tetrahydrofolate. The gla1 embryos developed normally in the early stage of development but did not undergo the transition to the heart stage. Thus, the function of the GLA1 gene in embryogenesis appears to be required after the globular stage. However, when the levels of GLA1 transcripts in transgenic plants were increased by introduction of several copies of a GLA1 transgene (GLA6.8), the gla1 embryos that grew on gla1/gla1 GLA6.8/- plants developed as far as the heart to bent-cotyledon stage. This result suggests that the GLA1 function is provided to embryos by maternal tissues until embryos reach the globular stage.

Amino Acid Sequence↗

PubMed1994

Distribution of mRNA coding for alpha-2-macroglobulin, the murinoglobulins, the alpha-2-macroglobulin receptor and the alpha-2-macroglobulin receptor associated protein during mouse embryogenesis and in adult tissues.

The distribution of mRNA coding for the members of the wide-spectrum proteinase scavenging system of the alpha-2-macroglobulin family was examined in the mouse: Alpha-2-macroglobulin (MAM), the murinoglobulins (MUG), the alpha-2-macroglobulin receptor (alpha 2MR) and the receptor associated protein, the heparin binding protein-44 (alpha 2MRAP/HBP-44), a component of unknown function. The results demonstrate that MAM is expressed in the mouse embryo exclusively in the liver and not before day 13 of gestation. MUG mRNA was never detected during embryogenesis. On the other hand, both the alpha 2MR and the alpha 2MRAP/HBP-44 messages were present throughout all embryonal stages examined. The distribution of the alpha 2MR mRNA was widespread in most tissues, with stronger signals observed in developing mouse brain, in whisker follicles and in the perifollicular mesenchyme, in lung, liver, kidney, intestine and placenta. The alpha 2MRAP/HBP-44 mRNA was detected predominantly in brain, lung, liver, kidney and placenta. Interestingly, within each tissue the cellular distribution of the alpha 2MR and alpha 2MRAP/HBP-44 mRNA was quite different with the most remarkable extremes observed in kidney and in placenta. The implication of these observations for receptor expression and function are discussed. Northern analysis of adult tissues extended these observations: major signals for MAM and MUG were seen only in liver, while the expression of the alpha 2MR and the alpha 2MRAP/HBP-44 was widespread with highest levels of the 15-kb alpha 2MR mRNA in liver. Kidney was the most abundant source of alpha 2MRAP/HBP-44 mRNA with the 1.8- and 3.6-kb mRNAs, derived from the same gene by alternative mRNA splicing, present in nearly constant ratios in most tissues, except in testis. The notable absence of expression of MAM in the first half of gestation indicates that during this period the receptor is scavenging for proteinases complexed to MAM derived from the maternal circulation or is being used for endocytosis of the other documented ligands, such as plasminogen activator complexes or apolipoprotein E-containing lipoprotein particles.

Animals↗

PubMed1999

Overexpression of thyroid hormone receptor alpha 1 during zebrafish embryogenesis disrupts hindbrain patterning and implicates retinoic acid receptors in the control of hox gene expression.

Nuclear receptors play key roles in anterior/posterior (A/P) axis formation during vertebrate embryogenesis. Within this gene family, retinoic acid receptors and retinoic acid itself have profound influences on the establishment of the A/P axis. Thyroid hormone receptors are expressed during early periods of development, long before the establishment of the thyroid gland, and are able to interact with retinoic acid receptors. Here we examined the ability of the thyroid hormone receptor alpha 1 to affect early embryonic development by mRNA injection of either repressor or activator forms of the thyroid hormone receptor. Overexpression of either the thyroid hormone receptor alpha 1 or a constitutive repressor form, v-erbA, caused a swelling in the rostral hindbrain. These defects were associated with disorganization and loss of rhombomere borders as well as an increase in the number of acetylcholine esterase positive cells. This phenotype correlated with a reduction in hoxa1 expression during gastrulation. Furthermore, injection of either thyroid hormone receptor alpha 1 or v-erbA mRNA repressed a reporter gene that contained a retinoic acid response element, demonstrating the ability of the thyroid hormone receptor alpha 1 to repress retinoic acid signaling during gastrulation. In contrast, embryos treated with retinoic acid alone or embryos injected with thyroid hormone receptor alpha 1 and treated with the thyroid hormone analog TRIAC displayed a similar set of defects, including loss of the midbrain-hindbrain border and severe disruption of the rostral hindbrain. These studies support the involvement of retinoic acid and its receptors in the direct control of Hox gene expression and the early patterning of the zebrafish central nervous system.

Animals↗

PubMed2002

Notch signaling is involved in the regulation of Id3 gene transcription during Xenopus embryogenesis.

During Xenopus embryogenesis, XId3, a member of the Id helix-loop-helix protein family, is expressed in a large variety of differentiating tissues including epidermis, cement gland, brain, neural tube, neural crest cell derivatives, somites, and tailbud. Transcription of XId3 is mediated by several cis-regulatory elements including an enhancer of 440 bp located 870 bp upstream from the transcription initiation site. The enhancer activity in embryos was studied using transgenic methodology. A galactosidase reporter gene, driven by a regulatory element composed of the enhancer and a minimal promoter derived from the XId3 gene, was expressed in transgenic embryos with a profile that faithfully reproduced that of the endogenous XId3 gene. The pattern resulted from a synergistic effect between the enhancer and the promoter, and in vitro transactivation assays showed that transcription can be stimulated by Notch signaling. The presence of potential Su(H) binding sites, in both the enhancer and the promoter, suggests that these represent candidates for in vivo cis-regulatory elements. The data presented here suggest that Notch control of differentiation may involve activation of transcription of Id, a negative regulator of bHLH transcription factors.

Amino Acid Sequence↗

PubMed2002

Molecular characterization of a novel nuclear transglutaminase that is expressed during starfish embryogenesis.

We report the constitution and molecular characterization of a novel transglutaminase (EC 2.3.2.13) that starts to accumulate specifically in the nucleus in the starfish (Asterina pectinifera) embryo after progression through the early blastula stage. The cDNA for the nuclear transglutaminase was cloned and the cDNA-deduced sequence defines a single open reading frame encoding a protein with 737 amino acids and a predicted molecular mass of 83 kDa. A comparison of this transglutaminase with other members of the gene family revealed an overall sequence identity of 33-41%. A special sequence feature of this transglutaminase, which is not found in other transglutaminases, is the presence of nuclear localization signal-like sequences in the N-terminal region. Microinjection of hybrid constructs that encode the N-terminal segment fused to reporter proteins into the germinal vesicle of an oocyte produced chimeric proteins by transcription-coupled translation. It was found that the N-terminal segment alone was sufficient to effect nuclear accumulation of an otherwise cytoplasmic protein. These results suggest that the nuclear accumulation of the transglutaminase may play an important role in nuclear remodeling during early starfish embryogenesis.

Amino Acid Sequence↗

PubMed2000

Applications of microelectroporation for studies of chick embryogenesis.

A technique by which genes can be introduced into the cells and tissues of developing embryos has great potential for studying the roles of genes during vertebrate embryogenesis. The 'microelectroporation' technique, in which DNA is introduced into cells within a restricted area of developing chick embryos with high reproducibility, was developed by the authors. In this review, the advantages and applications of this microelectroporation technique for developmental studies and functional analysis of genes in chick embryos is discussed.

Animals↗

PubMed2001

Disappearance of an epithelial cell surface-specific glycoprotein (Epith-1) associated with epithelial-mesenchymal conversion in sea urchin embryogenesis.

Cell surface modification during mesenchyme ingression was examined using a monoclonal antibody (mAb), anti-Epith-1 mAb, raised against a protein (Epith-1) that was confined to the lateral surface of the epithelial cells in embryo of the sea urchin, Temnopleurus hardwicki. The mAb epitope was N-glycosylated oligosaccharides of 160 kDa monomeric Epith-1 protein. The glycoprotein was negatively charged, and its isoelectric point (IP) was 4.98. The mAb, however, is not immunologically cross-reactive with other sea urchin embryos including Hemicentrotus pulcherrimus, Strongylocentrotus nudus, and Scaphechinus mirabilis. Epith-1 is present initially in the cytoplasm of unfertilized eggs. Cytoplasmic Epith-1 shifted to the cell surface to be integrated in plasma membrane during the first cleavage, and remained there during early embryogenesis by retaining the same relative molecular mass (Mr). During primary and secondary mesenchyme ingression periods, however, Epith-1 disappears from the presumptive mesenchyme cell surface that was associated with internalization of the protein. In plutei, an additional anti-Epith-1 mAb-positive protein appears at the 142 kDa region, which was not associated with any visible alteration of the histologic localization of the protein in larvae. Anti-Epith-1 mAb IgG did not inhibit the reaggregation of epithelial cells in vitro, which suggests that either the protein is not involved in cell-cell adhesion or that the mAb is not recognizing the active site of the protein.

Amidohydrolases↗