pinecone/core-2020-05-10-deduplication huggingface dataset:
Cellular Processes Associated with Germ Band Retraction in Drosophila

AbstractLarge-scale movements of epithelial sheets are necessary for most embryonic and regenerative morphogenetic events. We have characterized the cellular processes associated with germ band retraction (GBR) in the Drosophila embryo. During GBR, the caudal end of the embryo retracts to its final posterior position. We show using time-lapse recordings that, in contrast to germ band extension, cells within the lateral germ band do not intercalate. In addition, the germ band and amnioserosa move as one coherent sheet, and the amnioserosa strongly shortens along its dorsal–ventral axis. Furthermore, during GBR, the amnioserosa adheres to and migrates over the caudal end of the germ band via lamellipodia. Expression of both dominant-negative and constitutively active RhoA in the amnioserosa disrupts GBR. As RhoA acts on both actomyosin contractility and cell–matrix adhesion, it suggests a role for such processes in the amnioserosa during GBR. The results establish the cellular movements and shape changes occurring during GBR and provide the basis for an analysis of the forces acting during GBR
Twist Function Is Required for the Morphogenesis of the Cephalic Neural Tube and the Differentiation of the Cranial Neural Crest Cells in the Mouse Embryo

AbstractLoss of Twist function in the cranial mesenchyme of the mouse embryo causes failure of closure of the cephalic neural tube and malformation of the branchial arches. In the Twist−/− embryo, the expression of molecular markers that signify dorsal forebrain tissues is either absent or reduced, but those associated with ventral tissues display expanded domains of expression. Dorsoventral organization of the mid- and hindbrain and the anterior–posterior pattern of the neural tube are not affected. In the Twist−/− embryo, neural crest cells stray from the subectodermal migratory path and the late-migrating subpopulation invades the cell-free zone separating streams of cells going to the first and second branchial arches. Cell transplantation studies reveal that Twist activity is required in the cranial mesenchyme for directing the migration of the neural crest cells, as well as in the neural crest cells within the first branchial arch to achieve correct localization. Twist is also required for the proper differentiation of the first arch tissues into bone, muscle, and teeth
Structure and Expression of Three Emx Genes in the Dogfish Scyliorhinus canicula: Functional and Evolutionary Implications

AbstractWe report the characterization of three Emx genes in a chondrichthyan, the dogfish Scyliorhinus canicula. Comparisons of these genes with their osteichthyan counterparts indicate that the gnathostome Emx genes belong to three distinct orthology classes, each containing one of the dogfish genes and either the tetrapod Emx1 genes (Emx1 class), the osteichthyan Emx2 genes (Emx2 class) or the zebrafish Emx1 gene (Emx3 class). While the three classes could be retrieved from the pufferfish genome data, no indication of an Emx3-related gene in tetrapods could be found in the databases, suggesting that this class may have been lost in this taxon. Expression pattern comparisons of the three dogfish Emx genes and their osteichthyan counterparts indicate that not only telencephalic, but also diencephalic Emx expression territories are highly conserved among gnathostomes. In particular, all gnathostomes share an early, dynamic phase of Emx expression, spanning presumptive dorsal diencephalic territories, which involves Emx3 in the dogfish, but another orthology class, Emx2, in tetrapods. In addition, the dogfish Emx2 gene shows a highly specific expression domain in the cephalic paraxial mesoderm from the end of gastrulation and throughout neurulation, which suggests a role in the segmentation of the cephalic mesoderm
Zebrafish Hox Paralogue Group 2 Genes Function Redundantly as Selector Genes to Pattern the Second Pharyngeal Arch

AbstractThe pharyngeal arches are one of the defining features of the vertebrates, with the first arch forming the mandibles of the jaw and the second forming jaw support structures. The cartilaginous elements of each arch are formed from separate migratory neural crest cell streams, which derive from the dorsal aspect of the neural tube. The second and more posterior crest streams are characterized by specific Hox gene expression. The zebrafish has a larger overall number of Hox genes than the tetrapod vertebrates, as the result of a duplication event in its lineage. However, in both zebrafish and mouse, there are just two members of Hox paralogue group 2 (PG2): Hoxa2 and Hoxb2. Here, we show that morpholino-mediated “knock-down” of both zebrafish Hox PG2 genes results in major defects in second pharyngeal arch cartilages, involving replacement of ventral elements with a mirror-image duplication of first arch structures, and accompanying changes to pharyngeal musculature. In the mouse, null mutants of Hoxa2 have revealed that this single Hox gene is required for normal second arch patterning. By contrast, loss-of-function of either zebrafish Hox PG2 gene individually has no phenotypic consequence, showing that these two genes function redundantly to confer proper pattern to the second pharyngeal arch. We have also used hoxb1a mis-expression to induce localized ectopic expression of zebrafish Hox PG2 genes in the first arch; using this strategy, we find that ectopic expression of either Hox PG2 gene can confer second arch identity onto first arch structures, suggesting that the zebrafish Hox PG2 genes act as “selector genes.
Genetic Manipulation of Single Neurons in Vivo Reveals Specific Roles of Flamingo in Neuronal Morphogenesis

AbstractTo study the roles of intracellular factors in neuronal morphogenesis, we used the mosaic analysis with a repressible cell marker (MARCM) technique to visualize identifiable single multiple dendritic (MD) neurons in living Drosophila larvae. We found that individual neurons in the peripheral nervous system (PNS) developed clear morphological polarity and diverse dendritic branching patterns in larval stages. Each MD neuron in the same dorsal cluster developed a unique dendritic field, suggesting that they have specific physiological functions. Single-neuron analysis revealed that Flamingo did not affect the general dendritic branching patterns in postmitotic neurons. Instead, Flamingo limited the extension of one or more dorsal dendrites without grossly affecting lateral branches. The dendritic overextension phenotype was partially conferred by the precocious initiation of dorsal dendrites in flamingo mutant embryos. In addition, Flamingo is required cell autonomously to promote axonal growth and to prevent premature axonal branching of PNS neurons. Our molecular analysis also indicated that the amino acid sequence near the first EGF motif is important for the proper localization and function of Flamingo. These results demonstrate that Flamingo plays a role in early neuronal differentiation and exerts specific effects on dendrites and axons
A Role for Phosphoinositide 3-Kinase in the Control of Cell Division and Survival during Retinal Development

AbstractNeurogenesis in the retina requires the concerted action of three different cellular processes: proliferation, differentiation, and apoptosis. Class IA phosphoinositide 3-kinase (PI3K) is a heterodimer composed of a p85 regulatory and a p110 catalytic subunit. p110α has been shown to regulate cell division and survival. Little is known of its function in development, however, as p110α knockout mice exhibit CNS defects, but death at early embryonic stages impairs further study. Here, we examine the role of PI3K in mouse retina development by expressing an activating form of PI3K regulatory subunit, p65PI3K, as a transgene in the retina. Mice expressing p65PI3K showed severely disrupted retina morphogenesis, with ectopic cell masses in the neuroepithelium that evolved into infoldings of adult retinal cell layers. These changes correlated with an altered cell proliferation/cell death balance at early developmental stages. Nonetheless, the most affected cell layer in adult retina was that of photoreceptors, which correlated with selectively increased survival of these cells at developmental stages at which cell division has ceased. These results demonstrate the relevance of accurate PI3K regulation for normal retinal development, supporting class IA PI3K involvement in induction of cell division at early stages of neurogenesis. These data also show that, even after cell division decline, PI3K activation mediates survival of differentiated neurons in vivo
Pattern Formation in a Pentameral Animal: Induction of Early Adult Rudiment Development in Sea Urchins

AbstractWe investigated adult rudiment induction in the direct-developing sea urchin Heliocidaris erythrogramma microsurgically. After removal of the archenteron (which includes presumptive coelomic mesoderm as well as presumptive endoderm) from late gastrulae, larval ectoderm develops properly but obvious rudiments (tube feet, nervous system, and adult skeleton) fail to form, indicating that coelomic mesoderm, endoderm, or both are required for induction of adult development. Recombination of ectoderm and archenteron rescues development. Implanted endoderm alone or left coelom alone each regenerate the full complement of archenteron derivatives; thus, they are uninformative as to the relative inductive potential of the two regions. However, in isolated ectoderm, more limited regeneration gives rise to larvae containing no archenteron derivatives at all, endoderm only, or both endoderm and left coelom. Adult nervous system begins to develop only in the latter, indicating that left coelom is required for the inductive signal. Isolated ectoderm develops a vestibule (the precursor of adult ectoderm) and correctly regulates vestibular expression of the ectodermal territory marker HeET-1, indicating that the early phase of vestibule development occurs autonomously; only later development requires the inductive signal. Another ectodermal marker, HeARS, is regulated properly in the larval ectoderm region, but not in the vestibule. HeARS regulation thus represents an early response to the inducing signal. We compare HeARS expression in H. erythrogramma with that in indirect developers and discuss its implications for modularity in the evolution of developmental mode
The Competence of Marginal Zone Cells to Become Spemann's Organizer Is Controlled by Xcad2

AbstractThe organizer in vertebrate embryos is responsible for the formation of the primary body axis. In amphibian embryos, the organizer forms in the dorsal marginal zone (prospective dorsal mesoderm) at a location determined by the point of sperm entry. Using inducible versions of axis-inducing proteins, it has been shown that, irrespective of the mode of secondary axis induction, organizer formation in the ventral marginal zone is temporally restricted from the midblastula transition to the onset of gastrulation. Here, we show that the competence of marginal zone cells to respond to organizer-inducing signals is under temporal control, one of the regulators being the homeobox transcription factor Xcad2. Overexpression of Xcad2 restricts the temporal competence for axis induction, whereas partial loss of function expands this competence, supporting our suggestion. We propose that Xcad2 competes with putative axis-inducing signals within the marginal zone to prevent expression of organizer-specific genes. Elimination of endogenous Xcad2 allows for the activation of organizer genes beyond the normal competence window during early/mid-gastrulation. We conclude that Xcad2, through its early expression in the ventrolateral marginal zone, terminates the competence of this embryonic region to respond to organizer-inducing signals by preventing the activation of organizer-specific genes
Experimental Studies on the Spatiotemporal Expression of WT1 and RALDH2 in the Embryonic Avian Heart: A Model for the Regulation of Myocardial and Valvuloseptal Development by Epicardially Derived Cells (EPDCs)

AbstractEpicardially derived cells (EPDCs) delaminate from the primitive epicardium through an epithelial-to-mesenchymal transformation (EMT). After this transformation, a subpopulation of cells progressively invades myocardial and valvuloseptal tissues. The first aim of the study was to determine the tissue-specific distribution of two molecules that are thought to play a crucial function in the interaction between EPDCs and other cardiac tissues, namely the Wilms' Tumor transcription factor (WT1) and retinaldehyde-dehydrogenase2 (RALDH2). This study was performed in normal avian and in quail-to-chick chimeric embryos. It was found that EPDCs that maintain the expression of WT1 and RALDH2 initially populate the subepicardial space and subsequently invade the ventricular myocardium. As EPDCs differentiate into the smooth muscle and endothelial cell lineage of the coronary vessels, the expression of WT1 and RALDH2 becomes downregulated. This process is accompanied by the upregulation of lineage-specific markers. We also observed EPDCs that continued to express WT1 (but very little RALDH2) which did not contribute to the formation of the coronary system. A subset of these cells eventually migrates into the atrioventricular (AV) cushions, at which point they no longer express WT1. The WT1/RALDH2-negative EPDCs in the AV cushions do, however, express the smooth muscle cell marker caldesmon. The second aim of this study was to determine the impact of abnormal epicardial growth on cardiac development. Experimental delay of epicardial growth distorted normal epicardial development, reduced the number of invasive WT1/RALDH2-positive EPDCs, and provoked anomalies in the coronary vessels, the ventricular myocardium, and the AV cushions. We suggest that the proper development of ventricular myocardium is dependent on the invasion of undifferentiated, WT1-positive, retinoic acid-synthesizing EPDCs. Furthermore, we propose that an interaction between EPDCs and endocardial (derived) cells is imperative for correct development of the AV cushions
Fgf4 Positively Regulates scleraxis and Tenascin Expression in Chick Limb Tendons

AbstractIn vertebrates, tendons connect muscles to skeletal elements. Surgical experiments in the chick have underlined developmental interactions between tendons and muscles. Initial formation of tendons occurs autonomously with respect to muscle. However, further tendon development requires the presence of muscle. The molecular signals involved in these interactions remain unknown. In the chick limb, Fgf4 transcripts are located at the extremities of muscles, where the future tendons will attach. In this paper, we analyse the putative role of muscle-Fgf4 on tendon development. We have used three general tendon markers, scleraxis, tenascin, and Fgf8 to analyse the regulation of these tendon-associated molecules by Fgf4 under different experimental conditions. In the absence of Fgf4, in muscleless and aneural limbs, the expression of the three tendon-associated molecules, scleraxis, tenascin, and Fgf8, is down-regulated. Exogenous implantation of Fgf4 in normal, aneural, and muscleless limbs induces scleraxis and tenascin expression but not that of Fgf8. These results indicate that Fgf4 expressed in muscle is required for the maintenance of scleraxis and tenascin but not Fgf8 expression in tendons
Meiotic Prophase Abnormalities and Metaphase Cell Death in MLH1-Deficient Mouse Spermatocytes: Insights into Regulation of Spermatogenic Progress

AbstractThe MLH1 protein is required for normal meiosis in mice and its absence leads to failure in maintenance of pairing between bivalent chromosomes, abnormal meiotic division, and ensuing sterility in both sexes. In this study, we investigated whether failure to develop foci of MLH1 protein on chromosomes in prophase would lead to elimination of prophase spermatocytes, and, if not, whether univalent chromosomes could align normally on the meiotic spindle and whether metaphase spermatocytes would be delayed and/or eliminated. In spite of the absence of MLH1 foci, no apoptosis of spermatocytes in prophase was detected. In fact, chromosomes of pachytene spermatocytes from Mlh1−/− mice were competent to condense metaphase chromosomes, both in vivo and in vitro. Most condensed chromosomes were univalents with spatially distinct FISH signals. Typical metaphase events, such as synaptonemal complex breakdown and the phosphorylation of Ser10 on histone H3, occurred in Mlh1−/− spermatocytes, suggesting that there is no inhibition of onset of meiotic metaphase in the face of massive chromosomal abnormalities. However, the condensed univalent chromosomes did not align correctly onto the spindle apparatus in the majority of Mlh1−/− spermatocytes. Most meiotic metaphase spermatocytes were characterized with bipolar spindles, but chromosomes radiated away from the microtubule-organizing centers in a prometaphase-like pattern rather than achieving a bipolar orientation. Apoptosis was not observed until after the onset of meiotic metaphase. Thus, spermatocytes are not eliminated in direct response to the initial meiotic defect, but are eliminated later. Taken together, these observations suggest that a spindle assembly checkpoint, rather than a recombination or chiasmata checkpoint, may be activated in response to meiotic errors, thereby ensuring elimination of chromosomally abnormal gamete precursors
The Homeobox Gene mbx Is Involved in Eye and Tectum Development

AbstractThe homeobox gene mbx is first activated at the end of gastrulation in zebrafish in the presumptive forebrain and midbrain region. During somitogenesis stages, the anterior expression of mbx, which partly overlaps the future eye field, gradually decreases, while midbrain expression intensifies and becomes restricted to the presumptive tectum. Knockdown of mbx expression by morpholino antisense oligonucleotides (mbx-MO) leads to a reduction in the size of the eyes and tectum. Expression domains of rx1 and pax6 in the eye field and of mab21l2 in the eye field and tectum anlage were reduced in size in mbx-MO-injected embryos by somitogenesis stages. Further, induction of islet1 and lim3 expression in the eye at 2 days postfertilization (dpf) was suppressed in mbx-MO-injected embryos. In mbx-MO-injected embryos at 2–5 dpf, the lamination of the eye was disorganized and the number of retinal axons was substantially reduced, but the few remaining axons navigated appropriately to the contralateral tectum. A chimeric protein composed of the Mbx DNA-binding domain and the VP16 activation domain affected eye and tectum development similarly to mbx-MO knockdown, suggesting that Mbx acts as a transcriptional repressor in the zebrafish embryo. Based on these data, we propose that the mbx homeobox gene is required for the development of the eyes and tectum
In Vivo Imaging of Embryonic Vascular Development Using Transgenic Zebrafish

AbstractIn this study we describe a model system that allows continuous in vivo observation of the vertebrate embryonic vasculature. We find that the zebrafish fli1 promoter is able to drive expression of enhanced green fluorescent protein (EGFP) in all blood vessels throughout embryogenesis. We demonstrate the utility of vascular-specific transgenic zebrafish in conjunction with time-lapse multiphoton laser scanning microscopy by directly observing angiogenesis within the brain of developing embryos. Our images reveal that blood vessels undergoing active angiogenic growth display extensive filopodial activity and pathfinding behavior similar to that of neuronal growth cones. We further show, using the zebrafish mindbomb mutant as an example, that the expression of EGFP within developing blood vessels permits detailed analysis of vascular defects associated with genetic mutations. Thus, these transgenic lines allow detailed analysis of both wild type and mutant embryonic vasculature and, together with the ability to perform large scale forward-genetic screens in zebrafish, will facilitate identification of new mutants affecting vascular development
Essential Function of Wnt-4 for Tubulogenesis in the Xenopus Pronephric Kidney

AbstractIn the vertebrate embryo, development of the excretory system is characterized by the successive formation of three distinct kidneys: the pronephros, mesonephros, and metanephros. While tubulogenesis in the metanephric kidney is critically dependent on the signaling molecule Wnt-4, it is unknown whether Wnt signaling is equally required for the formation of renal epithelia in the other embryonic kidney forms. We therefore investigated the expression of Wnt genes during the pronephric kidney development in Xenopus. Wnt4 was found to be associated with developing pronephric tubules, but was absent from the pronephric duct. Onset of pronephric Wnt-4 expression coincided with mesenchyme-to-epithelium transformation. To investigate Wnt-4 gene function, we performed gain- and loss-of-function experiments. Misexpression of Wnt4 in the intermediate and lateral mesoderm caused abnormal morphogenesis of the pronephric tubules, but was not sufficient to initiate ectopic tubule formation. We used a morpholino antisense oligonucleotide-based gene knockdown strategy to disrupt Wnt-4 gene function. Xenopus embryos injected with antisense Wnt-4 morpholinos developed normally, but marker gene and morphological analysis revealed a complete absence of pronephric tubules. Pronephric duct development was largely unaffected, indicating that ductogenesis may occur normally in the absence of pronephric tubules. Our results show that, as in the metanephric kidney, Wnt-4 is critically required for tubulogenesis in the pronephric kidney, indicating that a common, evolutionary conserved gene regulatory network may control tubulogenesis in different vertebrate excretory organs
The Dlx5 Homeobox Gene Is Essential for Vestibular Morphogenesis in the Mouse Embryo through a BMP4-Mediated Pathway

AbstractIn the mouse embryo, Dlx5 is expressed in the otic placode and vesicle, and later in the semicircular canals of the inner ear. In mice homozygous for a null Dlx5/LacZ allele, a severe dysmorphogenesis of the vestibular region is observed, characterized by the absence of semicircular canals and the shortening of the endolymphatic duct. Minor defects are observed in the cochlea, although Dlx5 is not expressed in this region. Cristae formation is severely impaired; however, sensory epithelial cells, recognized by calretinin immunostaining, are present in the vestibular epithelium of Dlx5−/− mice. The maculae of utricle and saccule are present but cells appear sparse and misplaced. The abnormal morphogenesis of the semicircular canals is accompanied by an altered distribution of proliferating and apoptotic cells. In the Dlx5−/− embryos, no changes in expression of Nkx5.1(Hmx3), Pax2, and Lfng have been seen, while expression of bone morphogenetic protein-4 (Bmp4) was drastically reduced. Notably, BMP4 has been shown to play a fundamental role in vestibular morphogenesis of the chick embryo. We propose that development of the semicircular canals and the vestibular inner ear requires the independent control of several homeobox genes, which appear to exert their function via tight regulation of BPM4 expression and the regional organization of cell differentiation, proliferation, and apoptosis