pinecone/core-2020-05-10-deduplication huggingface dataset:
Lack of Regulation in the Heart Forming Region of Avian Embryos

AbstractThe ability to regenerate a heart after ablation of cardiogenic mesoderm has been demonstrated in early stage fish and amphibian embryos but this type of regulation of the heart field has not been seen in avians or mammals. The regulative potential of the cardiogenic mesoderm was examined in avian embryos and related to the spatial expression of genes implicated in early cardiogenesis. With the identification of early cardiac regulators such asbmp-2andnkx-2.5,it is now possible to reconcile classical embryological studies with molecular mechanisms of cardiac lineage determinationin vivo.The most anterior lateral embryonic cells were identified as the region that becomes the heart and removal of all or any subset of these cells resulted in the loss of corresponding cardiac structures. In addition, removal of the lateral heart forming mesoderm while leaving the lateral endoderm intact also results in loss of cardiac structures. Thus the medial anterior mesoderm cannot be recruited into the heart lineagein vivoeven in the presence of potentially cardiac inducing endoderm.In situanalysis demonstrated that genes involved in early events of cardiogenesis such as bone morphogenetic protein 2 (bmp-2) andnkx-2.5are expressed coincidentally with the mapped far lateral heart forming region. The activin type IIa receptor (actR-IIa) is a potential mediator of BMP signaling since it is expressed throughout the anterior mesoderm with the highest level of expression occurring in the lateral prospective heart cells. The posterior boundary ofactR-IIais consistent with the posterior boundary ofnkx-2.5expression, supporting a model whereby ActR-IIa is involved in restricting the heart forming region to an anterior subset of lateral cells exposed to BMP-2. Analysis of the cardiogenic potential of the lateral plate mesoderm posterior tonkx-2.5andactR-IIaexpression demonstrated that these cells are not cardiogenicin vitroand that removal of these cells from the embryo does not result in loss of heart tissuein vivo.Thus, the region of the avian embryo that will become the heart is defined medially, laterally, and posteriorly bynkx-2.5gene expression. Removal of all or part of thenkx-2.5expressing region results in the loss of corresponding heart structures, demonstrating the inability of the chick embryo to regenerate cardiac tissuein vivoat stages afternkx-2.5expression is initiated
Dominant-Negative Smad2 Mutants Inhibit Activin/Vg1 Signaling and Disrupt Axis Formation in Xenopus

AbstractSmads are central mediators of signal transduction for the TGFβ superfamily. However, the precise functions of Smad-mediated signaling pathways in early development are unclear. Here we demonstrate a requirement for Smad2 signaling in dorsoanterior axis formation during Xenopus development. Using two point mutations of Smad2 previously identified in colorectal carcinomas, we show that Smad2 ushers Smad4 to the nucleus to form a transcriptional activation complex with the nuclear DNA-binding protein FAST-1 and that the mutant proteins interact normally with FAST-1 but fail to recruit Smad4 into the nucleus. This mechanism of inhibition specifically restricts the dominant-negative activity of these mutants to the activin/Vg1 signaling pathway without inhibiting BMPs. Furthermore, expression of these mutants in Xenopus animal caps inhibits but does not abolish activin and Vg1 induction of mesoderm and in the embryo results in a truncated dorsoanterior axis. These studies define a mechanism through which mutations in Smad2 may block TGFβ-dependent signaling and suggest a critical role for inductive signaling mediated by the Smad2 pathway in Xenopus organizer function
Characterisation of a SecondpatchedGene in the ZebrafishDanio rerioand the Differential Response ofpatchedGenes to Hedgehog Signalling

AbstractHedgehog signalling has been implicated in a variety of processes in vertebrate development, and in each case, the activity of Hh proteins is thought to be mediated by their interaction with a large multipass transmembrane protein encoded by thepatched(ptc) gene. In this study we present the full-length coding sequence and describe the wild-type expression pattern of a secondptcgene in zebrafish,Zf-ptc2.We find that at the sequence level Zf-ptc2is more closely related thanZf-ptc1to theptcgenes initially characterised in other vertebrate species. We also show that transcription ofZf-ptc2,likeZf-ptc1,is dependent upon Hh signalling and present evidence that it is activated in response to lower levels of Hh activity than isZf-ptc1.In addition we find no evidence for any specificity in the regulatory interactions between the various Hh proteins and the twoptcgenes in the zebrafish
Isolation and Characterization ofdrosocrystallin,a Lens Crystallin Gene ofDrosophila melanogaster

AbstractWe have cloned thedrosocrystallingene (dcy) ofDrosophila melanogaster,which encodes a major protein of the corneal lens, previously described in part by Komoriet al.(1992,J. Cell Sci.102, 191–201). Synthesis of the DCY protein starts weakly in 2-day-old pupae, reaches a peak at day 3 and day 4 of pupal development, and decreases very fast in young adults. ThedcymRNA is detected in the compound eyes as well as in the ocelli. The presence of a putative signal peptide and the extracellular location of DCY suggest that DCY is a secreted protein. Interestingly, thedcygene shows sequence similarities to some insect cuticular proteins and is detected as well in two closely relatedDrosophilaspecies,D. sechelliaandD. simulans,and in one more distantly related species,D. virilis.This finding supports the hypothesis thatDrosophilaused the same strategy as vertebrates and mollusks, namely, recruiting a multifunctional protein for refraction in the lens, by a gene-sharing mechanism. Furthermore, it supports our intercalary evolution hypothesis, which suggests that the development of an elaborate structure (for example, a compound eye) from an original primitive form (an ancestral photoreceptor organ) can be achieved by recruiting novel genes into the original developmental pathway
Gap Junction Signalling Mediated through Connexin-43 Is Required for Chick Limb Development

AbstractDuring chick limb development the gap junction protein Connexin-43 (Cx43) is expressed in discrete spatially restricted domains in the apical ectodermal ridge (AER) and mesenchyme of the zone of polarising activity. Antisense oligonucleotides (ODNs) were used to investigate the role of Connexin-43 (Cx43) in the development of the chick limb bud. We have used unmodified ODNs in Pluronic F-127 gel, which is liquid at low temperature but sets at room temperature and so remains situated at the point of application. As a mild surfactant, the gel increases antisense ODN penetration and supplies ODNs to the embryo continually for 12–18 h. We have shown a strong decrease in Cx43 protein expression after application of specific antisense oligonucleotides but the abundance of a closely related protein, Connexin-32 (Cx32), was not affected. Application of antisense Cx43 ODNs at stages 8–15 HH before limb outgrowth resulted in dramatic limb phenotypes. About 40% of treated embryos exhibited defects such as truncation of the limb bud, fragmentation into two or more domains, or complete splitting of the limb bud into two or three branches. Molecular analysis of antisense treated embryos failed to detect Shh or Bmp-2 in anterior structures and suggested that extra lobes seen in nicked and split limbs were not a result of establishment of new signalling centres as found after the application of FGF to the flank. However, examination of markers for the AER showed a number of abnormalities. In severely truncated specimens we were unable to detect the expression of either Fgf-4 or Fgf-8. In both nicked and split limbs the expression of these genes was discontinuous. Down-regulation of Cx43 after the antisense application could be comparable to AER removal and results in distal truncation of the limb bud. Taken together these data suggest the existence of a feedback loop between the FGFs and signalling mediated by Cx43
Discrete Regional Distributions Suggest Diverse Functional Roles of Calcium Channel α1 Subunits in Sperm

AbstractThe Ca channels of male germ-line cells are partially characterized, but the molecular properties and subcellular localization of the Ca channels of mature sperm are unknown. Here, we probe rodent sperm with anti-peptide antibodies directed to cytosolic domains of cloned rat brain α1A, α1C, and α1E Ca channel subunits. Each recognizes a 200- to 245-kDa band on immunoblots of whole rat sperm extracts. A smaller (∼110-kDa) α1C band also is detected. Confocal fluorescence images of mouse sperm show characteristic patterns of punctate α1A-, α1C-, and α1E-immunoreactivity. For α1A, the puncta are larger, less numerous, and more variable in distribution than for α1C and α1E. They are absent from the acrosomal crescent, but are present elsewhere over the sperm head, often at the apical tip and equatorial segment. They also are found at irregular intervals along both the midpiece and the principal piece of the flagellum. For α1C and α1E, puncta are dense along dorsal and ventral aspects of the acrosomal cap. For α1E but not α1C, the remainder of the acrosomal region also is labeled. Neither is found in the postacrosomal region or on the midpiece. Puncta of α1C and α1E occur at regular intervals each in two parallel rows, at the dorsal and ventral aspects of the proximal segment of the flagellar principal piece. The puncta in these arrays become less abundant and intense in the distal flagellum. These results demonstrate that multiple Ca channel proteins are present in mature sperm and are regionally localized in ways that may give them different regulatory roles
Morphogenesis of theCaenorhabditis elegansMale Tail Tip

AbstractUsing electron microscopy and immunofluorescent labeling of adherens junctions, we have reconstructed the changes in cell architecture and intercellular associations that occur during morphogenesis of the nematode male tail tip. During late postembryonic development, theCaenorhabditis elegansmale tail is reshaped to form a copulatory structure. The most posterior hypodermal cells in the tail define a specialized, sexually dimorphic compartment in which cells fuse and retract in the male, changing their shape from a tapered cone to a blunt dome. Developmental profiles using electron microscopy and immunofluorescent staining suggest that cell fusions are initiated at or adjacent to adherens junctions. Anterior portions of the tail tip cells show the first evidence of retractions and fusions, consistent with our hypothesis that an anterior event triggers these morphogenetic events. Available mutations that interfere with morphogenesis implicate particular regulatory pathways and suggest loci at which evolutionary changes could have produced morphological diversity
Activin and TGFβ Limit Murine Primordial Germ Cell Proliferation

AbstractMammalian primordial germ cells (PGCs) proliferate as they migrate from their initial location in the extraembryonic mesoderm to the genital ridge, the gonadal anlage. Once in the genital ridge, PGCs cease dividing and differentiate according to their gender. To identify ligands that might limit PGC proliferation, we analyzed growth factor receptors encoded in RNA obtained from purified germ cells shortly after their arrival in the genital ridge. Receptors for two members of the TGFβ superfamily were found, TGFβ1 and activin. As the signal-transducing domains of both receptor systems are highly conserved, the effects of both TGFβ1 and activin on PGCs would be expected to be similar. We found that both ligands limited the accumulation of germ cells in primary PGC cultures. BrdU incorporation assays demonstrated that either ligand inhibits PGC proliferation. These results suggest that these signal transduction pathways are important elements of the mechanism that determines germ cell endowment
Development of Cephalic Neural Crest Cells in Embryos of Lampetra japonica, with Special Reference to the Evolution of the Jaw

AbstractNeural crest cells contribute extensively to vertebrate head morphogenesis and their origin is an important question to address in understanding the evolution of the craniate head. The distribution pattern of cephalic crest cells was examined in embryos of one of the living agnathan vertebrates, Lampetra japonica. The initial appearance of putative crest cells was observed on the dorsal aspect of the neural rod at stage 20.5 and ventral expansion of these cells was first seen at the level of rostral somites. As in gnathostomes, cephalic crest cells migrate beneath the surface ectoderm and form three major cell populations, each being separated at the levels of rhombomeres (r) 3 and r5. The neural crest seems initially to be produced at all neuraxial levels except for the rostral-most area, and cephalic crest cells are secondarily excluded from levels r3 and r5. Such a pattern of crest cell distribution prefigures the morphology of the cranial nerve anlage. The second or middle crest cell population passes medial to the otocyst, implying that the otocyst does not serve as a barrier to separate the crest cell populations. The three cephalic crest cell populations fill the pharyngeal arch ventrally, covering the pharyngeal mesoderm laterally with the rostral-most population covering the premandibular region and mandibular arch. The third cell population is equivalent to the circumpharyngeal crest cells in the chick, and its influx into the pharyngeal region precedes the formation of postotic pharyngeal arches. Focal injection of DiI revealed the existence of an anteroposterior organization in the neural crest at the neurular stage, destined for each pharyngeal region. The crest cells derived from the posterior midbrain that express the LjOtxA gene, the Otx2 cognate, were shown to migrate into the mandibular arch, a pattern which is identical to gnathostome embryos. It was concluded that the head region of the lamprey embryo shares a common set of morphological characters with gnathostome embryos and that the morphological deviation of the mandibular arch between the gnathostomes and the lamprey is not based on the early embryonic patterning
Essential Roles of Retinoic Acid Signaling in Interdigital Apoptosis and Control of BMP-7 Expression in Mouse Autopods

AbstractWe previously reported that mice lacking the RARγ gene and one or both alleles of the RARβ gene (i.e., RARβ+/−/RARγ−/−and RARβ−/−/RARγ−/−mutants) display a severe and fully penetrant interdigital webbing (soft tissue syndactyly), caused by the persistence of the fetal interdigital mesenchyme (Ghyselincket al.,1997,Int. J. Dev. Biol.41, 425–447). In the present study, these compound mutants were used to investigate the cellular and molecular mechanisms involved in retinoic acid (RA)-dependent formation of the interdigital necrotic zones (INZs). The mutant INZs show a marked decrease in the number of apoptotic cells accompanied by an increase of cell proliferation. This marked decrease was not paralleled by a reduction of the number of macrophages, indicating that the chemotactic cues which normally attract these cells into the INZs were not affected. The expression of a number of genes known to be involved in the establishment of the INZs, the patterning of the autopod, and/or the initiation of apoptosis was also unaffected. These genes includedBMP-2,BMP-4,Msx-1,Msx-2, 5′ members of Hox complexes,Bcl2, Bax,andp53.In contrast, the mutant INZs displayed a specific, graded, down-regulation of tissue transglutaminase (tTG) promoter activity and of stromelysin-3 expression upon the removal of one or both alleles of the RARβ gene from the RARγ null genetic background. As retinoic acid response elements are present in the promoter regions of both tTG and stromelysin-3 genes, we propose that RA might increase the amount of cell death in the INZs through a direct modulation of tTG expression and that it also contributes to the process of tissue remodeling, which accompanies cell death, through an up-regulation of stromelysin-3 expression in the INZs. Approximately 10% of the RARβ−/−/RARγ−/−mutants displayed a supernumerary preaxial digit on hindfeet, which is also a feature of theBMP-7null phenotype (Dudleyet al.,1995,Genes Dev.9, 2795–2807; Luoet al.,1995,Genes Dev.9, 2808–2820).BMP-7was globally down-regulated at an early stage in the autopods of these RAR double null mutants, prior to the appearance of the digital rays. Therefore, RA may exert some of its effects on anteroposterior autopod patterning through controllingBMP-7expression
Expression Pattern of Brachyury and Not in the Sea Urchin: Comparative Implications for the Origins of Mesoderm in the Basal Deuterostomes

AbstractThis work concerns the expression of two transcription factors during the development of the sea urchin Strongylocentrotus purpuratus: SpNot, the orthologue of the vertebrate Not gene, and SpBra, the orthologue of the vertebrate Brachyury gene. SpNot transcripts are detected by in situ hybridization in the vegetal plate at the mesenchyme–blastula stage. Later the gene is expressed in the secondary mesenchyme, but expression is no longer detectable after gastrulation. SpNot is upregulated during larval development, in the invaginating vestibule of the adult rudiment. Transcripts are also found in several larva-specific tissues, including the epaulets, blastocoelar cells, and pigment cells. SpBra also displays a discontinuous pattern of expression. Much like SpNot, this gene is expressed during embryogenesis in the embryonic vegetal plate and secondary mesenchyme founder cells, and expression is then extinguished. The gene is upregulated over a week later in the feeding larva, in the vestibule of the adult rudiment. In contrast to SpNot, SpBra is also expressed in the mesoderm of both left and right hydrocoels, and it is not expressed in any larva-specific tissues. We compare the spatial expression profile determined in this study with that of the orthologous Brachyury gene in an indirectly developing enteropneust hemichordate, a representative of the sister group to the echinoderms within the deuterostomes. These observations illuminate the genetic basis underlying the process of maximal indirect development in basal deuterostomes. Finally, Brachyury appears to be an excellent marker for the progeny of the set-aside cells of the sea urchin embryo
Involvement of Chk1 Kinase in Prophase I Arrest of Xenopus Oocytes

AbstractChk1 kinase, a DNA damage/replication G2 checkpoint kinase, has recently been shown to phosphorylate and inhibit Cdc25C, a Cdc2 Tyr-15 phosphatase, thereby directly linking the G2 checkpoint to negative regulation of Cdc2. Immature Xenopus oocytes are arrested naturally at the first meiotic prophase (prophase I) or the late G2 phase, with sustained Cdc2 Tyr-15 phosphorylation. Here we have cloned a Xenopus homolog of Chk1, determined its developmental expression, and examined its possible role in prophase I arrest of oocytes. Xenopus Chk1 protein is expressed at approximately constant levels throughout oocyte maturation and early embryogenesis. Overexpression of wild-type Chk1 in oocytes prevents the release from prophase I arrest by progesterone. Conversely, specific inhibition of endogenous Chk1 either by overexpression of a dominant-negative Chk1 mutant or by injection of a neutralizing anti-Chk1 antibody facilitates prophase I release by progesterone. Moreover, when ectopically expressed in oocytes, a Chk1-nonphosphorylatable Cdc25C mutant alone can induce prophase I release much more efficiently than wild-type Cdc25C; if endogenous Chk1 function is inhibited, however, even wild-type Cdc25C can induce the release very efficiently. These results suggest strongly that Chk1 is involved in physiological prophase I arrest of Xenopus oocytes via the direct phosphorylation and inhibition of Cdc25C. We discuss the possibility that Chk1 might function either as a G2 checkpoint kinase or as an ordinary cell cycle regulator in prophase-I-arrested oocytes
HoxGene Expression in Limbs: Colinearity by Opposite Regulatory Controls

AbstractGenes of theHoxDcomplex have a crucial role in the morphogenesis of vertebrate limbs. During development, their functional domains are colinear with their genomic positions within theHoxDcluster such thatHoxd13andHoxd12are necessary for digit development, whereasHoxd11andHoxd10are involved in making forearms. Mutational analyses of these genes have demonstrated their importance and illustrated the requirement for a precise control of their expression during early limb morphogenesis. To study the nature of this control, we have scanned the posterior part of theHoxDcomplex with a targeted reporter transgene and analyzed the response of this foreign promoter to limb regulatory influences. The results suggest that this regulation is achieved through the opposite effects of two enhancer elements which would compete with each other for interacting with nearby-located promoters. The physical position of a given gene within this genomic interval of opposite regulations might thus determine its final expression pattern. This model provides a conceptual link between the morphology of the future limb and the genetic organization of theHoxgene cluster, a translation of a genomic context into a morphogenetic topology
Identification of a Novel Cardiac Lineage-Associated Protein(cCLP-1): A Candidate Regulator of Cardiogenesis

AbstractWe describe the isolation and characterization of a cDNA clone, called cCLP-1, that is a candidate for the previously described early cardiac-specific transcription factor BBF-1. BBF-1 binds the MEF2 (or element B) binding site within the cardiac myosin light chain 2 (MLC2) gene promoter. We used the element B sequence as a probe to screen an expression library constructed from mRNA obtained from the presumptive heart-forming regions of stage 6 chicken embryos. This yielded the cCLP-1 cDNA clone. Gel-shift analysis of stage 6 embryonic chicken protein extracts suggests that a protein that is recognized by the anti-cCLP-1 antibody binds to the same element B binding site to which BBF-1 binds. cCLP-1 mRNA was detected early in chicken development, prior to cardiac fate assignment at stage 4. The expression pattern of cCLP-1, based on whole mountin situhybridization, coincides remarkably well with the established morphogenetic field of early heart formation. The nuclear localization of cCLP-1 is phosphorylation-dependent, suggesting that cCLP-1 may be a member of that class of transcription factors whose activity is regulated by cytoplasm to nucleus transport. Taken together, these data suggest that cCLP-1 may encode a novel transcription factor whose expression pattern is in agreement with that of the cardiogenic precursor cells of the early chicken embryo