pinecone/core-2020-05-10-deduplication huggingface dataset:
Developmental Potential of Rat L6 Myoblastsin VivoFollowing Injection into Regenerating Muscles

AbstractTo examine the relative importance of myoblast lineage and environmental influences on the development of muscle fiber typesin vivo,the phenotype of muscle fibers formed from rat L6 myoblasts was examined following their injection into different regenerating adult muscles. Myoblasts were infected with a retroviral vector carrying a LacZ reporter gene and their fatein vivowas examined using a panel of antibodies against various myosin heavy chain (MyHC) isoforms. Since L6 myoblasts express IIX MyHC following differentiationin vitro,we wanted to determine if they would form IIX muscle fibersin vivoand whether innervation would alter this fate. Following injection, L6 cells either fused with each other to form homotypic fibers or fused with host muscle cells to form heterotypic fibers. Initially, homotypic fibers expressed embryonic MyHC—similar to L6 myotubesin vitro.However, by 4 weeks postinjection IIX MyHC had replaced embryonic MyHC as the predominant isoform. Single fiber analysis using an antibody specific for NCAM indicated that this transition was independent of innervation. Analysis of heterotypic fibers resulting from the incorporation of donor L6 myoblasts into host fast IIA and IIB fibers revealed that L6-derived nuclei express embryonic and IIX MyHCs for up to 8 weeks postinjection, often as nuclear domains surrounding L6 nuclei. These results suggest that MyHC expression in muscle fibers derived from L6 myoblasts is regulated, in part, by intrinsic factors that limit the fiber type potential of these cellsin vivo
Dorsal-Ventral Patterning during Neural Induction inXenopus:Assessment of Spinal Cord Regionalization withxHB9,a Marker for the Motor Neuron Region

AbstractWhile the role of the notochord and floor plate in patterning the dorsal-ventral (D/V) axis of the neural tube is clearly established, relatively little is known about the earliest stages of D/V regionalization. In an effort to examine more closely the initial, preneural plate stages of regionalization along the prospective D/V neural axis, we have performed a series of explant experiments employingxHB9,a novel marker of the motor neuron region inXenopus.Using tissue recombinants and Keller explants we show that direct mesodermal contact is both necessary and sufficient for the initial induction ofxHB9in the motor neuron region. We also show that presumptive neural plate explants removed as early as midgastrulation and cultured in isolation are already specified to expressxHB9but do so in an inappropriate spatial pattern while identical explants are specified to express the floor plate markervhh-1with correct spatial patterning. Our data suggest that, in addition to floor plate signaling, continued interactions with the underlying mesoderm through neural tube stages are essential for proper spatial patterning of the motor neuron region
Retinoic Acid Changes the Proximodistal Developmental Competence and Affinity of Distal Cells in the Developing Chick Limb Bud

AbstractIn the developing chick limb bud, retinoic acid (RA) has a striking effect on anteroposterior axis formation, resulting in a duplicated pattern of digits. There is no evidence, however, that RA affects proximodistal axis formation in the developing chick limb bud, although RA induces proximodistal duplication in regenerating amphibian limbs. We describe a series of investigations on the effect of RA on the proximodistal axis in the chick limb bud. A RA-containing bead applied to the anterior margin of the chick limb bud at stage 20 induces the anteroposterior duplication of autopodial structures at the wrist level. We found that the RA-treated tissue has the ability to form more proximal structures. When a tissue graft from the RA-treated anterior region was implanted into a stage 17 wing bud (in which the stylopod is developing in the progress zone), the graft produced a humerus, radius–ulna, and digits. When the graft was implanted into a stage 19 wing bud (in which the zeugopod is developing in the progress zone), a zeugopod and digits were formed. These results were associated with changes in the expression of Hox-A genes in the RA-treated grafts, whose domains were reorganized to be similar to those in host tissues 24 h after grafting. When a small graft of RA-treated tissue was implanted into the apex of a stage 19 wing bud, the cells were found in the zeugopod and autopod, whereas cells of control fragments were found only in the autopod region.In vitro,distal cells from different stage limb buds are known to segregate from each other. However, RA-treated stage 24 distal cells did not sort out from stage 20 distal cells and mixed homogeneously. These results suggest that RA induces distal cells to adopt “younger” properties which render them susceptible to forming more proximal patterns under the direction of host signals. The effects of RA on proximodistal patterns in developing chick limb buds appear to differ from its effects on proximodistal patterns in regenerating urodele limbs because RA can induce the proximodistal duplicationin situin the regenerating limbs
Model Systems for the Study of Kidney Development: Use of the Pronephros in the Analysis of Organ Induction and Patterning

AbstractMost vertebrate organs, once formed, continue to perform the function for which they were generated until the death of the organism. The kidney is a notable exception to this rule. Vertebrates, even those that do not undergo metamorphosis, utilize a progression of more complex kidneys as they grow and develop. This is presumably due to the changing conditions to which the organism must respond to retain what Homer Smith referred to as our physiological freedom. To quote, “Recognizing that we have the kind of blood we have because we have the kind of kidneys we have, we must acknowledge that our kidneys constitute the major foundation of our physiological freedom. Only because they work the way they do has it become possible for us to have bones, muscles, glands, and brains. Superficially, it might be said that the function of the kidneys is to make urine; but in a more considered view one can say that the kidneys make the stuff of philosophy itself” (“From Fish to Philosopher,” Little, Brown and Co., Boston, 1953). Different kidneys are used to make the stuff of philosophy at different stages of development depending on the age and needs of the organism, rather than the usual approach of simply making embryonic organs larger as the animal grows. Although evolution has provided the higher vertebrates with complex adult kidneys, they continue to utilize simple kidneys in embryogenesis. In lower vertebrates with simple adult kidneys, even more simple versions are used during early developmental stages. In this review the anatomy, development, and gene expression patterns of the embryonic kidney, the pronephros, will be described and compared to the more complex kidney forms. Despite some differences in anatomy, similar developmental pathways seem to be responsible for the induction and the response to induction in both evanescent and permanent kidney forms. Gene expression patterns can, therefore, be added to the morphological and functional data indicating that all forms of the kidney are closely related structures. Given the similarities between the development of simple and complex kidneys, the embryonic kidneys may be an ideal model system in which to investigate the genesis of multicomponent organ systems
Comparative Effects of Insulin on the Activation of the Raf/Mos-Dependent MAP Kinase Cascade in Vitellogenic versus PostvitellogenicXenopusOocytes

AbstractXenopuspostvitellogenic oocytes resume meiosisin vitroupon exposure to insulin or insulin-like growth factor 1 (IGF-1) via a ras-dependent pathway, whereas stage IV (600 μm < diameter < 1000 μm) oocytes cannot. The aim of the present study was to determine which event(s) of the transduction pathway from IGF-1 receptor to maturation-promoting factor (MPF) activation is deficient in the small, vitellogenic, oocytes to explain their inability to undergo germinal vesicle breakdown (GVB) after insulin treatment. We thus analyzed the effect of insulin on the Ras/Raf-dependent mitogen-activated protein kinase cascade because of its crucial role prior to MPF activation. The effect of insulin on pp39mossynthesis in stage IV oocytes was also studied since this protein kinase participates in the mitogen-activated protein kinase (MAPK) pathway as a MAPKK kinase like Raf. Contrary to what is observed in postvitellogenic oocytes, MAPK was not activated in insulin-treated stage IV oocytes even 20 hr after the stimulation. This was not caused by the absence of MAPK activators like MEK (MAPKK), Raf, or Ras, but rather by the inability of insulin to activate Ras. Interestingly, injection of constitutively activerafmRNA as well as oncogenic Ras protein, Ha-Ras lys12, in stage IV oocytes resulted in MAPK activation, whereas neither Mos accumulation nor GVB occurred, suggesting that the Ras → Raf → MAPKK → MAPK cascade was functional but that MAPK activation alone was not sufficient for the mitogenic signal to proceed further down in the pathway leading to MPF activation. Treatment of stage IV oocytes with insulin did not stimulate Mos synthesis either, indicating a dysfunction in the “Mos synthesis machinery.” The present results show that incompetence ofXenopusstage IV oocytes to activate MPF in response to insulin is primarily due to the inability of the peptide to activate Ras and to stimulate pp39mossynthesis and secondarily to a deficiency in the mitogenic pathway that connects MAPK to MPF activation
Role of FGF andNogginin Neural Crest Induction

AbstractA study of the moleculesnogginand fibroblast growth factor (FGF) and its receptor in the induction of the prospective neural crest inXenopus laevisembryos has been carried out, using the expression of the geneXsluas a marker for the neural crest. We show that when a truncated FGF receptor (XFD) was expressed ectopically in order to block FGF signalingXsluexpression was inhibited. The effect of XFD onXsluwas specific and could be reversed by the coinjection of the wild-type FGF receptor (FGFR). Inhibition ofXsluexpression by XFD is not a consequence of neural plate inhibition, as was shown by analyzingXsox-2 expression. When ectoderm expressing XFD was transplanted into the prospective neural fold region of embryosXsluinduction was inhibited. The neural crest can also be induced by an interaction between neural plate and epidermis. As this induction is suppressed by the presence of XFD in the neural plate and not in the epidermis, it suggests that the neural crest is induced by FGF from the epidermis. However, treatment of neural plate with FGF was not able to induceXslugexpression, showing that in addition to FGF other non-FGF factors are also required. Previously we have suggested that the ectopic ventral expression ofXsluproduced by overexpression ofnogginmRNA resulted from an interaction ofnogginwith a ventral signal. Overexpression of XFD inhibits this effect, suggesting that FGF could be one component involved in this ventral signaling. Overexpression of FGFR produced a remarkable increase in the expression ofXsluin the posterior neural folds and around the blastopore. Injections in different blastomeres of the embryo suggest that the target cells of this effect are the ventral cells. Finally, we proposed a model in which the induction of the neural crests at the border of the neural plate requires functional FGF signaling, which possibly interacts with a neural inducer such asnoggin
Organizer Induction Determines Left–Right Asymmetry inXenopus

AbstractVertebrates appear bilaterally symmetrical but have considerable left–right (LR) asymmetry in the anatomy and placement of internal organs such as the heart. Although a number of asymmetrically expressed genes are known to affect LR patterning, both the initial source of asymmetry and the mechanism that correctly orients the LR axis remain controversial. In this study, we show that the induction of dorsal organizing centers in the embryo can orient LR asymmetry. Ectopic organizing centers were induced by microinjection of mRNA encoding a variety of body axis duplicating proteins, including members of the Wnt signal transduction pathway. The ectopic and primary body axes form side-by-side conjoined twins, with the secondary axis developing as either the left or right sibling. In all cases, correct LR asymmetry was observed in the left twin, regardless of whether it was derived from the primary axis or inducedde novoby injection ofXwnt-8, β-catenin,orSiamoismRNA. In contrast, the right twin was generally unbiased, regardless of the origin of the left body axis, as seen in many instances of experimentally induced and spontaneous conjoined twins. An unanticipated exception was that right twins induced by β-catenin and Siamois, two downstream effectors of Wnt signaling, exhibited predominately normal heart looping, even when they formed the right twin. Taken together, these results indicate that LR asymmetry is locally oriented as a consequence of Wnt signaling through β-catenin and Siamois. We discuss the possibility that signals upstream of β-catenin and Siamois might be required in order for a right sibling to be randomized
Rhodopsin Replacement Rescues Photoreceptor Structure during a Critical Developmental Window

AbstractRhodopsin is essential for normal photoreceptor development inDrosophila(O'Tousaet al.,1989; Leonardet al.,1992; Kumar and Ready, 1995) and in mice (Humphrieset al.,1997). Here we report studies in which a rhodopsin transgene is expressed at restricted stages during the development ofDrosophilaphotoreceptors otherwise lacking rhodopsin. Substantial rescue of normal photoreceptor structure and physiology is effected by rhodopsin expression during the time of the normal onset of rhodopsin synthesis. Expression shortly before or after this critical period does not rescue these deficits. There is a critical developmental period in which rhodopsin plays its key role in photoreceptor morphogenesis
Induction of Endocardial Cushion Tissue in the Avian Heart is Regulated, in Part, by TGFβ-3-Mediated Autocrine Signaling

AbstractValvuloseptal morphogenesis of the primitive heart tube into a four-chambered organ requires the formation of endocardial cushion tissue. The latter is the outcome of an inductive interaction in which endocardial (endothelial) cells are induced to transform into mesenchyme by paracrine signals secreted by the adjacent myocardium. In this study, we propose that transforming endothelial/mesenchymal cells themselves secrete a factor—TGFβ-3—that functions in an autocrine mode to promote/sustain mesenchyme formation and possibly in a paracrine manner to amplify the original (myocardial) inductive event. Cushion mesenchyme-conditioned medium, previously demonstrated to be an endogenous source of autocrine, migration-promoting factors, was found in the present study to contain TGFβ-3, as detected by immunoblot analysis. Immunoneutralization of TGFβ-3 in preparations of cushion mesenchyme-conditioned medium resulted in a failure of treated target endocardial cells to migrate as mesenchyme, whereas inclusion of a control antibody did not inhibit the migration-promoting activity of the conditioned medium. Similar to treatment with the conditioned medium, direct addition of TGFβ-3 to target endocardial cells also elicited invasive migration but only in cultures which had been activatedin vivoby inductive interaction with the myocardium prior to treatment. Selective inhibition of TGFβ-3-mediated autocrine signaling in continuous cocultures of endocardium plus myocardium resulted in endocardial cells which did not migrate, even though they had expressed early markers associated with endocardial cell activation (e.g., α-smooth muscle actin, ES/130, and TGFβ-3). Collectively, these results suggest that (i) two signaling pathways, myocardial and endocardial, are required to start and complete epithelial–mesenchymal transformation in cushion-forming regions of the heart and (ii) the endocardial pathway signals through iteration of TGFβ-3 and is not functionally redundant to the myocardial pathway
Novel Expression Gradients of Eph-like Receptor Tyrosine Kinases in the Developing Chick Retina

AbstractEph-like receptor tyrosine kinases have recently been identified as critical components in the development of the retinotectal system. Complementary gradients of receptors and ligands in the retina and tectum, and within the retina itself, have previously been described. Here, we present a novel centroperipheral gradient of expression for one member of this family of receptors, Cek9, suggesting that retinal patterning and axon guidance during the establishment of retinotectal projections may involve coordinate mapping along three axes. Furthermore, we show matching gradients of two cytoplasmic kinases, compatible with their putative involvement in the intracellular signaling pathways used by these receptors in the retina. We also demonstrate a dorsal to ventral expression gradient for Cek11, an Eck-like receptor, the Eph subclass previously suggested to specify positional information along the temporonasal axis
VEGF and VEGF-C: Specific Induction of Angiogenesis and Lymphangiogenesis in the Differentiated Avian Chorioallantoic Membrane

AbstractThe lymphangiogenic potency of endothelial growth factors has not been studied to date. This is partially due to the lack ofin vivolymphangiogenesis assays. We have studied the lymphatics of differentiated avian chorioallantoic membrane (CAM) using microinjection of Mercox resin, semi- and ultrathin sectioning, immunohistochemical detection of fibronectin and α-smooth muscle actin, andin situhybridization with VEGFR-2 and VEGFR-3 probes. CAM is drained by lymphatic vessels which are arranged in a regular pattern. Arterioles and arteries are accompanied by a pair of interconnected lymphatics and form a plexus around bigger arteries. Veins are also associated with lymphatics, particularly larger veins, which are surrounded by a lymphatic plexus. The lymphatics are characterized by an extremely thin endothelial lining, pores, and the absence of a basal lamina. Patches of the extracellular matrix can be stained with an antibody against fibronectin. Lymphatic endothelial cells of differentiated CAM show ultrastructural features of this cell type. CAM lymphatics do not possess mediae. In contrast, the lymphatic trunks of the umbilical stalk are invested by a single but discontinuous layer of smooth muscle cells. CAM lymphatics express VEGFR-2 and VEGFR-3. Both the regular pattern and the typical structure of these lymphatics suggest that CAM is a suitable site to study thein vivoeffects of potential lymphangiogenic factors. We have studied the effects of VEGF homo- and heterodimers, VEGF/PlGF heterodimers, and PlGF and VEGF-C homodimers on Day 13 CAM. All the growth factors containing at least one VEGF chain are angiogenic but do not induce lymphangiogenesis. PlGF-1 and PlGF-2 are neither angiogenic nor lymphangiogenic. VEGF-C is the first lymphangiogenic factor and seems to be highly chemoattractive for lymphatic endothelial cells. It induces proliferation of lymphatic endothelial cells and development of new lymphatic sinuses which are directed immediately beneath the chorionic epithelium. Our studies show that VEGF and VEGF-C are specific angiogenic and lymphangiogenic growth factors, respectively
Esx1,a Novel X Chromosome-Linked Homeobox Gene Expressed in Mouse Extraembryonic Tissues and Male Germ Cells

AbstractA novelpaired-like homeobox gene, designatedEsx1,was isolated in a screen for homeobox genes that regulate mouse embryogenesis. Analysis of a mouse interspecific backcross panel demonstrated thatEsx1mapped to the distal arm of the X chromosome. During embryogenesis,Esx1expression was restricted to extraembryonic tissues, including the endoderm of the visceral yolk sac, the ectoderm of the chorion, and subsequently the labyrinthine trophoblast of the chorioallantoic placenta. In adult tissues,Esx1expression was detected only in testes. However,Esx1transcripts were not detected in the testes of sterileW/Wvmice, suggesting thatEsx1expression is restricted to male germ cells.In situhybridization experiments of testes indicated thatEsx1transcripts were most abundant in pre- and postmeiotic germ cells. Hybridization experiments suggested thatEsx1was conserved among vertebrates, including amphibians, birds, and mammals. During mouse development, the paternally derived X chromosome is preferentially inactivated in extraembryonic tissues of XX embryos, including the trophoblast, visceral endoderm, and parietal endoderm. In addition, the X chromosome is transiently inactivated during the meiotic stages of spermatogenesis. Thus, the identification ofEsx1provides a molecular entry point into a genetic pathway to understand X chromosome-regulated fetal–maternal interactions and male germ cell development
Chicken Nkx-2.8: A Novel Homeobox Gene Expressed in Early Heart Progenitor Cells and Pharyngeal Pouch-2 and -3 Endoderm

AbstractMembers of the NK family of homeobox transcription factors regulate critical steps of organogenesis during vertebrate development. In the studies described in this report, we have isolated and functionally characterized the chickenNkx-2.8(cNkx-2.8) cDNA and protein and defined the temporal and spatial pattern ofcNkx-2.8gene expression during chicken development.cNkx-2.8transcripts are first detectable at HH stage 7 in the splanchnopleura. At stage 10+, thecNkx-2.8gene is expressed in the linear heart tube and the dorsal half of the vitelline vein. However, after looping, HH stage 13,cNkx-2.8is no longer expressed in the looped heart tube, but is expressed in the ventral pharyngeal endoderm. At stage 15, in addition to the pharyngeal expression pattern,cNkx-2.8is expressed in the ectoderm of the pharyngeal arches and the aortic sac. By HH Stage 17,cNkx-2.8expression is detectable in lateral endoderm of the second and third pharyngeal pouches, the posterior portion of the aortic sac, and the sinus venosus. cNkx-2.8 binds to previously characterized Nkx2-1 and Nkx2-5 DNA-binding sites and overexpression of cNkx-2.8 transactivates a minimal promoter which contains multimerized Nkx-2 DNA-binding sites. In addition, cNkx-2.8 and serum response factor can coactivate a minimal cardiac α-actin promoter. These data are consistent with a model in which cNkx-2.8 performs a unique temporally and spatially restricted function in the developing embryonic heart and pharyngeal region. Moreover, the coexpression ofcNkx-2.5and-2.8raises the possibility that cNkx-2.8 may have a redundant role with cNkx-2.5 in the coalescing heart tube and may play an important role in the transcriptional program(s) that underlies thymus formation. The existence of multiple NK-2 family members and their partially overlapping patterns of expression are discussed within the framework of a “Nkx code.