Signals from the Yolk Cell Induce Mesoderm, Neuroectoderm, the Trunk Organizer, and the Notochord in Zebrafish

AbstractWe have analyzed the role of the zebrafish yolk cell in the processes of mesoderm induction and establishment of the organizer. By recombining blastomere-free yolk cells and animal cap tissue we have shown that the yolk cell itself can induce mesoderm in neighboring blastomeres. We further demonstrate the competence of all blastomeres to form mesoderm, suggesting the endogenous mesoderm inducing signal to be locally restricted. Ablation of the vegetal third of the yolk cell during the first 20 min of development does not interfere with mesoderm formation in general, but results in completely ventralized embryos. These embryos lack the notochord, neuroectoderm, and the anterior-most 14–15 somites, demonstrating that the ablation affects the formation of the trunk-, but not the tail region of the embryo. This suggests the presence of a trunk organizer in fish. The dorsalized mutant swirl (zbmp-2b) shows expanded dorsal structures and missing ventral structures. In contrast to the phenotypes obtained upon the ablation treatment in wild-type embryos, removal of the vegetal-most yolk in swirl mutants results in embryos which do form neuroectoderm and anterior trunk somites. However, both wild-type and swirl mutants lack a notochord upon vegetal yolk removal. These ablation experiments in wild-type and swirl mutant embryos demonstrate that in zebrafish dorsal determining factors originate from the vegetal part of the yolk cell. These factors set up two independent activities: one induces the notochord and the other is involved in the formation of the neuroectoderm and the trunk region by counteracting the function of swirl. In addition, these experiments show that the establishment of the anteroposterior axis is independent of the dorsoventral axis

Early Endocardial Morphogenesis Requires Scl/Tal1

The primitive heart tube is composed of an outer myocardial and an inner endocardial layer that will give rise to the cardiac valves and septa. Specification and differentiation of these two cell layers are among the earliest events in heart development, but the embryonic origins and genetic regulation of early endocardial development remain largely undefined. We have analyzed early endocardial development in the zebrafish using time-lapse confocal microscopy and show that the endocardium seems to originate from a region in the lateral plate mesoderm that will give rise to hematopoietic cells of the primitive myeloid lineage. Endocardial precursors appear to rapidly migrate to the site of heart tube formation, where they arrive prior to the bilateral myocardial primordia. Analysis of a newly discovered zebrafish Scl/Tal1 mutant showed an additional and previously undescribed role of this transcription factor during the development of the endocardium. In Scl/Tal1 mutant embryos, endocardial precursors are specified, but migration is severely defective and endocardial cells aggregate at the ventricular pole of the heart. We further show that the initial fusion of the bilateral myocardial precursor populations occurs independently of the endocardium and tal1 function. Our results suggest early separation of the two components of the primitive heart tube and imply Scl/Tal1 as an indispensable component of the molecular hierarchy that controls endocardium morphogenesis

Оценка эффективности комбинированной терапии у больных артериальной гипертензией

Представлены результаты исследования воздействия комбинации антигипертензивного препарата аккупро и психотропного препарата золофта на клинические показатели больных артериальной гипертензией и их психологическое состояние и качество жизни. Показана высокая эффективность комбинированной терапии.The findings of the research of the effect of combination of an antihypertensive drug Accupro and a psychotropic drug Zoloft on clinical parameters in patients with arterial hypertension as well as their mental state and quality of life are presented. A high efficacy of the combined therapy is shown

Analysis of a Zebrafish VEGF Receptor Mutant Reveals Specific Disruption of Angiogenesis

AbstractBlood vessels form either by the assembly and differentiation of mesodermal precursor cells (vasculogenesis) or by sprouting from preexisting vessels (angiogenesis) [1–3]. Endothelial-specific receptor tyrosine kinases and their ligands are known to be essential for these processes. Targeted disruption of vascular endothelial growth factor (VEGF) or its receptor kdr (flk1, VEGFR2) in mouse embryos results in a severe reduction of all blood vessels [4–6], while the complete loss of flt1 (VEGFR1) leads to an increased number of hemangioblasts and a disorganized vasculature [7, 8]. In a large-scale forward genetic screen, we identified two allelic zebrafish mutants in which the sprouting of blood vessels is specifically disrupted without affecting the assembly and differentiation of angioblasts. Molecular cloning revealed nonsense mutations in flk1. Analysis of mRNA expression in flk1 mutant embryos showed that flk1 expression was severely downregulated, while the expression of other genes (scl, gata1, and fli1) involved in vasculogenesis or hematopoiesis was unchanged. Overexpression of vegf121+165 led to the formation of additional vessels only in sibling larvae, not in flk1 mutants. We demonstrate that flk1 is not required for proper vasculogenesis and hematopoiesis in zebrafish embryos. However, the disruption of flk1 impairs the formation or function of vessels generated by sprouting angiogenesis

Zebrafish VEGF Receptors: A Guideline to Nomenclature

Stem Cell and Regenerative Biolog

Reaction wavefront theory of notochord segment patterning

The vertebrate axis is segmented into repetitive structures, the vertebrae. In fish, these segmented structures are thought to form from the paraxial mesoderm and the adjacent notochord. Recent work revealed an autonomous patterning mechanism in the zebrafish notochord, with inputs from the segmented paraxial mesoderm. The notochord pattern is established in a sequential manner, progressing from anterior to posterior. Building on this previous work, here, we propose a reaction wavefront theory describing notochord patterning in zebrafish. The pattern is generated by an activator–inhibitor reaction–diffusion mechanism. Cues from the paraxial mesoderm are introduced as a profile of inhibitor sinks. Reactions are turned on by a wavefront that advances from anterior to posterior. We show that this reaction wavefront ensures that a pattern is formed sequentially, in register with the cues, despite the presence of fluctuations. We find that the velocity and shape of the reaction wavefront can modulate the prevalence of defective patterns. Normal patterning is supported in a wide range of sink profile wavelengths, while a minimum sink strength is required for the pattern to follow the cues. The theory predicts that distinct defect types occur for small or large wavelengths. Thus, the reaction wavefront theory provides a possible scenario for notochord patterning, with testable predictions that prompt future experiments.Fil: Fernández Arancibia, Sol Maria. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigación en Biomedicina de Buenos Aires - Instituto Partner de la Sociedad Max Planck; ArgentinaFil: Oates, Andrew C.. Ecole Polytechnique Fédérale de Lausanne; SuizaFil: Schulte Merker, Stefan. Westfälische Wilhelms Universität; AlemaniaFil: Morelli, Luis Guillermo. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigación en Biomedicina de Buenos Aires - Instituto Partner de la Sociedad Max Planck; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Física; Argentina. Institut Max Planck fur Molekulare Physiologie; Alemani

A mutation in the zebrafish maternal-effect gene nebel affects furrow formation and vasa RNA localization

AbstractBackground: In many animals, embryonic patterning depends on a careful interplay between cell division and the segregation of localized cellular components. Both of these processes in turn rely on cytoskeletal elements and motor proteins. A type of localized cellular component found in most animals is the germ plasm, a specialized region of cytoplasm that specifies the germ-cell fate. The gene vasa has been shown in Drosophila to encode an essential component of the germ plasm and is thought to have a similar function in other organisms. In the zebrafish embryo, the vasa RNA is localized to the furrows of the early cellular divisions.Results: We identified the gene nebel in a pilot screen for zebrafish maternal-effect mutations. Embryos from females homozygous for a mutation in nebel exhibit defects in cell adhesion. Our analysis provides genetic evidence for a function of the microtubule array that normally develops at the furrow in the deposition of adhesive membrane at the cleavage plane. In addition, nebel mutant embryos show defects in the early localization of vasa RNA. The vasa RNA localization phenotype could be mimicked with microtubule-inhibiting drugs, and confocal microscopy suggests an interaction between microtubules and vasa-RNA-containing aggregates.Conclusions:Our data support two functions for the microtubule reorganization at the furrow, one for the exocytosis of adhesive membrane, and another for the translocation of vasa RNA along the forming furrow

Endothelin receptor Aa regulates proliferation and differentiation of Erb-dependant pigment progenitors in zebrafish

<div><p>Skin pigment patterns are important, being under strong selection for multiple roles including camouflage and UV protection. Pigment cells underlying these patterns form from adult pigment stem cells (APSCs). In zebrafish, APSCs derive from embryonic neural crest cells, but sit dormant until activated to produce pigment cells during metamorphosis. The APSCs are set-aside in an ErbB signaling dependent manner, but the mechanism maintaining quiescence until metamorphosis remains unknown. Mutants for a pigment pattern gene, <i>parade</i>, exhibit ectopic pigment cells localised to the ventral trunk, but also supernumerary cells restricted to the Ventral Stripe. Contrary to expectations, these melanocytes and iridophores are discrete cells, but closely apposed. We show that <i>parade</i> encodes Endothelin receptor Aa, expressed in the blood vessels, most prominently in the medial blood vessels, consistent with the ventral trunk phenotype. We provide evidence that neuronal fates are not affected in <i>parade</i> mutants, arguing against transdifferentiation of sympathetic neurons to pigment cells. We show that inhibition of BMP signaling prevents specification of sympathetic neurons, indicating conservation of this molecular mechanism with chick and mouse. However, inhibition of sympathetic neuron differentiation does not enhance the <i>parade</i> phenotype. Instead, we pinpoint ventral trunk-restricted proliferation of neural crest cells as an early feature of the <i>parade</i> phenotype. Importantly, using a chemical genetic screen for rescue of the ectopic pigment cell phenotype of <i>parade</i> mutants (whilst leaving the embryonic pattern untouched), we identify ErbB inhibitors as a key hit. The time-window of sensitivity to these inhibitors mirrors precisely the window defined previously as crucial for the setting aside of APSCs in the embryo, strongly implicating adult pigment stem cells as the source of the ectopic pigment cells. We propose that a novel population of APSCs exists in association with medial blood vessels, and that their quiescence is dependent upon Endothelin-dependent factors expressed by the blood vessels.</p></div

A novel multistep mechanism for initial lymphangiogenesis in mouse embryos based on ultramicroscopy

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