pinecone/core-2020-05-10-deduplication huggingface dataset:
A Widespread and Early Requirement for a Novel Notch Function during Drosophila Embryogenesis

AbstractThe Notch pathway plays a key role in the formation of many tissues and cell types in Metazoans. We recently showed that Notch acts in two pathways to determine muscle precursor fates. The first is the “standard” Notch pathway, in which Delta activates the Notch receptor, which then translocates into the nucleus in conjunction with Su(H) to reprogram transcription patterns and bring about changes in cell fates. The second pathway is poorly defined, but known to be independent of the ligands and downstream effectors of the standard pathway. The standard pathway is required in many different developmental contexts and we wondered if there was also a general requirement for the novel pathway. Here we show that the novel Notch pathway is required for the development of each of five examined cell types. These results indicate that the novel pathway is a widespread and fundamental component of Notch function. We further show that both Notch pathways operate in the differentiation of the same cell types. In such cases, the novel pathway acts first and appears to set up or limit the size of equivalence groups. The standard pathway then acts within the equivalence groups to limit individual cell fates
Regulation of Cell-Fate Determination in Dictyostelium

AbstractA key step in the development of all multicellular organisms is the differentiation of specialized cell types. The eukaryotic microorganism Dictyostelium discoideum provides a unique experimental system for studying cell-type determination and spatial patterning in a developing multicellular organism. Unlike metazoans, which become multicellular by undergoing many rounds of cell division after fertilization of an egg, the social amoeba Dictyostelium achieves multicellularity by the aggregation of ∼105 cells in response to nutrient depletion. Following aggregation, cell-type differentiation and morphogenesis result in a multicellular organism with only a few cell types that exhibit a defined patterning along the anterior–posterior axis of the organism. Analysis of the mechanisms that control these processes is facilitated by the relative simplicity of Dictyostelium development and the availability of molecular, genetic, and cell biological tools. Interestingly, analysis has shown that many molecules that play integral roles in the development of higher eukaryotes, such as PKA, STATs, and GSK-3, are also essential for cell-type differentiation and patterning in Dictyostelium. The role of these and other signaling pathways in the induction, maintenance, and patterning of cell types during Dictyostelium development is discussed
Developmental Change in TATA-Box Utilization during Preimplantation Mouse Development

AbstractActivation of the embryonic genome during preimplantation mouse development is characterized by a marked reprogramming of gene expression that is essential for further development. Expression of the protein translation initiation factor eIF-1A gene is driven by a proximal TATA-containing promoter and a distal TATA-less promoter. Using specific amplification of cDNA ends that resolves transcripts derived from the TATA-less and TATA-containing promoters, we find that 70% of the eIF-1A transcripts are derived from the TATA-containing promoter in the fully-grown oocyte. Activation of the embryonic genome during the two-cell stage is accompanied by a change in promoter utilization such that only 25% of the transcripts are now derived from the TATA-containing promoter, i.e., 75% are derived from the TATA-less promoter. When one-cell embryos are cultured to the two-cell stage in the presence of α-amanitin, this change in transcript abundance is not observed, i.e., the distribution of transcripts is similar to that observed in the oocyte. By the blastocyst stage only 5% of the transcripts are generated from the TATA-containing promoter. If the change in TATA-box utilization for the eIF-1A reflects an underlying global change in TATA-box utilization, a dramatic change in promoter utilization may occur during preimplantation development such that TATA-less promoters are more efficiently utilized. Such a change in promoter utilization could contribute significantly to the reprogramming of gene expression that occurs during the maternal-to-zygotic transition
Complementary Domains of Retinoic Acid Production and Degradation in the Early Chick Embryo

AbstractExcess retinoids as well as retinoid deprivation cause abnormal development, suggesting that retinoid homeostasis is critical for proper morphogenesis. RALDH-2 and CYP26, two key enzymes that carry out retinoic acid (RA) synthesis and degradation, respectively, were cloned from the chick and show significant homology with their orthologs in other vertebrates. Expression patterns of RALDH-2 and CYP26 genes were determined in the early chick embryo by in situ hybridization. During gastrulation and neurulation RALDH-2 and CYP26 were expressed in nonoverlapping regions, with RALDH-2 transcripts localized to the presumptive presomitic and lateral plate mesoderm and CYP26 mRNA to the presumptive mid- and forebrain. The two domains of expression were separated by an approximately 300-μm-wide gap, encompassing the presumptive hindbrain. In the limb region, a similar spatial segregation of RALDH-2 and CYP26 expression was found at stages 14 and 15. Limb region mesoderm expressed RALDH-2, whereas the overlying limb ectoderm expressed CYP26. RA-synthesizing and -degrading enzymatic activities were measured biochemically in regions expressing RALDH-2 or CYP26. Regions expressing RALDH-2 generated RA efficiently from precursor retinal but degraded RA only inefficiently. Conversely, tissue expressing CYP26 efficiently degraded but did not synthesize RA. Localized regions of RA synthesis and degradation mediated by these two enzymes may therefore provide a mechanism to regulate RA homeostasis spatially in vertebrate embryos
Spatial and Temporal Changes in Myosin Heavy Chain Gene Expression in Skeletal Muscle Development

AbstractSeven myosin heavy chains (MyHC) are expressed in mammalian skeletal muscle in spatially and temporally regulated patterns. The timing, distribution, and quantitation of MyHC expression during development and early postnatal life of the mouse are reported here. The three adult fast MyHC RNAs (IIa, IIb, and IId/x) are expressed in the mouse embryo and each mRNA has a distinct temporal and spatial distribution. In situ hybridization analysis demonstrates expression of IIb mRNA by 14.5 dpc, which proceeds developmentally in a rostral to caudal pattern. IId/x and IIa mRNAs are detectable 2 days later. Ribonuclease protection assays demonstrate that the three adult fast genes are expressed at approximately equal levels relative to each other in the embryo but at quite low levels relative to the two developmental isoforms, embryonic and perinatal. Just after birth major changes in the relative proportions of different MyHC RNAs and protein occur. In all cases, RNA expression and protein expression appear coincident. The changes in MyHC RNA and protein expression are distinct in different muscles and are restricted in some cases to particular regions of the muscle and do not always reflect their distribution in the adult
Topographic Targeting and Pathfinding Errors of Retinal Axons Following Overexpression of EphrinA Ligands on Retinal Ganglion Cell Axons

AbstractIn the retinotectal projection, the Eph receptor tyrosine kinase ligands ephrinA2 and ephrinA5 are differentially expressed not only in the tectum, but also in a high-nasal-to-low-temporal pattern in the retina. Recently, we have shown that retrovirally driven overexpression of ephrinA2 on retinal axons leads to topographic targeting errors of temporal axons in that they overshoot their normal termination zones in the rostral tectum and project onto the mid- and caudal tectum. The behavior of nasal axons, however, was only marginally affected. Here, we show that overexpression of ephrinA5 affects the topographic targeting behavior of both temporal and nasal axons. These data reinforce the idea that differential ligand expression on retinal axons contributes to topographic targeting in the retinotectal projection. Additionally, we found that ectopic expression of ephrinA2 and ephrinA5 frequently leads to pathfinding errors at the chiasm, resulting in an increased stable ipsilateral projection
The Spatial–Temporal Gradient of Naturally Occurring Motoneuron Death Reflects the Time of Prior Exit from the Cell Cycle and Position within the Lateral Motor Column

AbstractEmbryonic lumbar spinal motoneurons (MNs) are characterized by a period of programmed cell death (PCD) that spans several days and occurs in a rostrocaudal gradient. The generation of these MNs also takes place in a temporal–spatial gradient, such that MNs within rostral lumbar segments exit the cell cycle earlier and MNs within progressively caudal regions are born later. In vitro studies have shown that the latest born spinal MNs, presumably through the possession of endogenous “survival properties,” are also the last to acquire their trophic dependence. If the birth date and therefore spinal cord location of lumbar spinal MNs influence the spatial–temporal pattern of PCD, then earlier born MNs should die sooner and be located more rostrally than those generated later. Alternatively, if the time at which MNs die during development is unrelated to their prior exit from the cell cycle, those born at various phases should die throughout the period of PCD. We report here that lumbar MNs generated during the earliest part (embryonic day 2–3) of the proliferative period in the developing chick spinal cord tend to die during the earliest stages of the PCD period and that MNs born in successive 12-h intervals die at correspondingly later periods during PCD. Furthermore, the spatial progression of PCD of these subpopulations of MNs occurs in a rostrocaudal gradient. Finally, while MNs do appear to die in a mediolateral gradient during the period of MN PCD, this pattern is only partly accounted for by MNs born in consecutive intervals. These data support the notion that the timing and rostrocaudal location of MNs undergoing PCD reflect their time of exit from the cell cycle
The gon-1 Gene Is Required for Gonadal Morphogenesis in Caenorhabditis elegans

AbstractIn wild-type Caenorhabditis elegans, the gonad is a complex epithelial tube that consists of long arms composed predominantly of germline tissue as well as somatic structures specialized for particular reproductive functions. In gon-1 mutants, the adult gonad is severely disorganized with essentially no arm extension and no recognizable somatic structure. The developmental defects in gon-1 mutants are limited to the gonad; other cells, tissues, and organs appear to develop normally. Previous work defined the regulatory “leader” cells as crucial for extension of the gonadal arms (J. E. Kimble and J. G. White, 1981, Dev. Biol. 81, 208–219). In gon-1 mutants, the leader cells are specified correctly, but they fail to migrate and gonadal arms are not generated. In addition, gon-1 is required for morphogenesis of the gonadal somatic structures. This second role appears to be independent of that required for leader migration. Parallel studies have shown that gon-1 encodes a secreted metalloprotease (R. Blelloch and J. Kimble, 1999, Nature 399, 586–590). We discuss how a metalloprotease may control two aspects of gonadal morphogenesis
Nonchordate Classic Cadherins Have a Structurally and Functionally Unique Domain That Is Absent from Chordate Classic Cadherins

AbstractClassic cadherins, which are adhesion molecules in cell-cell adherens junctions, have a large contribution to the construction of the animal body. Their molecular structures show clear differences between chordate and nonchordate metazoans. Although nonchordate classic cadherins have cadherin superfamily-specific extracellular repeats (CRs) and a highly conserved cytoplasmic domain (CP), these cadherins have a unique extracellular domain that is absent from vertebrate and ascidian classic cadherins. We called this the primitive classic cadherin domain (PCCD). To understand the roles of the PCCD, we constructed and characterized a series of mutant forms of the Drosophila classic cadherin DE-cadherin. Biochemical analyses indicated that the last two CRs and PCCD form a special structure with proteolytic cleavage. Mutations in the PCCD did not eliminate the cell-cell-binding function of DE-cadherin in cultured cells, but prevented the cadherin from efficiently translocating to the plasma membrane in epithelial cells of the developing embryo. In addition, genetic rescue assays suggested that although CP-mediated control plays a central role in tracheal fusion, the role of the PCCD in efficient recruitment of DE-cadherin to apical areas of the plasma membranes is also important for dynamic epithelial morphogenesis. We propose that there is a fundamental difference in the mode of classic cadherin-mediated cell-cell adhesion between chordate and nonchordate metazoans
Ventral Cell Rearrangements Contribute to Anterior-Posterior Axis Lengthening between Neurula and Tailbud Stages in Xenopus laevis

AbstractStudies of morphogenesis in early Xenopus embryos have focused primarily on gastrulation and neurulation. Immediately following these stages is another period of intense morphogenetic activity, the neurula-to-tailbud transition. During this period the embryo is transformed from the spherical shape of the early stages into the long, thin shape of the tailbud stages. While gastrulation and neurulation depend largely on active cell rearrangement and cell shape changes in dorsal tissues, we find that the neurula-to-tailbud transition depends in part on activities of ventral cells. Ventral explants of neurulae lengthen automously as much as the ventral sides of intact embryos, while dorsal explants lengthen less than the dorsal sides of intact embryos. Analyses of cell division, cell shapes, and cell rearrangement by transplantation of labeled cells and by time lapse recordings in live intact embryos concur that cell rearrangements in ventral mesoderm and ectoderm contribute to the autonomous anterior-posterior axis lengthening of ventral explants between neurula and tailbud stages
In Xenopus Embryos, BMP Heterodimers Are Not Required for Mesoderm Induction, but BMP Activity Is Necessary for Dorsal/Ventral Patterning

AbstractThe activity of bone morphogenetic protein (BMP) heterodimers has been shown to be more potent than that of homodimers in a number of contexts, including mesoderm induction. Although BMP-2/7 and -4/7 heterodimers are potent inducers of ventral mesoderm in ectodermal explants, we show that they are not a necessary component of the primary mesoderm-inducing signal in intact Xenopus embryos. The secreted BMP antagonists noggin and gremlin both efficiently block mesoderm induction by BMP homo- and heterodimers in animal caps. When these antagonists are ectopically expressed in the ventral marginal zone of early embryos the initial formation of mesoderm as indicated by panmesodermal markers remains unaffected. Only the subsequent dorsal/ventral patterning of this mesoderm appears to be altered, with expression of a number of organizer-specific transcripts observed in the marginal zone where BMP signaling has been abolished. Thus, we conclude that BMPs do not contribute an essential signal to mesodermal induction or patterning until gastrulation. The activities of noggin and gremlin are strikingly different from that of the multifunctional antagonist cerberus, which completely abolishes mesoderm induction when misexpressed during early development
Chondroitin Sulphate-Binding Molecules May Pattern Central Projections of Sensory Axons within the Cranial Mesenchyme of the Developing Mouse

AbstractDuring mammalian hindbrain development, sensory axons grow along highly stereotyped routes within the cranial mesenchyme to reach their appropriate entry points into the neuroepithelium. Thus, trigeminal ganglion axons always project to rhombomere (r)2, whilst facial/acoustic ganglia axons always project to r4. Axons are never observed to enter the mesenchyme adjacent to r3, raising the possibility that r3 mesenchyme contains an axon growth-inhibitory activity. Conversely, in mice which lack the erbB4 receptor (normally expressed in r3), trigeminal and facial/acoustic ganglia axons misproject into r3 mesenchyme, suggesting that the putative axon barrier is absent. To investigate this hypothesis, we have developed an in vitro model in which dissociated wild-type embryonic trigeminal ganglion neurons are cultured on longitudinal cryosections of embryonic mouse head. We observed that on wild-type embryonic day 10 (E10) cryosections, neurites generally failed to grow into r3 mesenchyme from the adjacent r2 or r4 mesenchyme. This barrier was removed if cryosections were pretreated with chondroitinase or were washed with excess chondroitin 6-sulphate or hypertonic saline. By contrast, when trigeminal neurons were seeded onto cryosections of E10 erbB4 −/− embryo heads their neurites readily entered mutant r3 mesenchyme. Immunohistochemical analysis demonstrated chondroitin-sulphated proteoglycans throughout the cranial mesenchyme in both wild-type and erbB4 −/− embryos. We propose that trigeminal axons are excluded from wild-type r3 mesenchyme by a growth-inhibitory activity which associates with chondroitin-sulphated proteoglycans and that the synthesis of this activity may rely on signals transduced by erbB receptors
Neurogenesis and Neuronal Migration in the Neonatal Rat Forebrain Anterior Subventricular Zone Do Not Require GFAP-Positive Astrocytes

AbstractA prolific neuronal progenitor cell population in the anterior portion of the neonatal rat forebrain subventricular zone, the SVZa, is specialized for the production of olfactory bulb interneurons. At all ages, SVZa-derived cells traverse a tangential migratory pathway, the rostral migratory stream (RMS), while en route to the olfactory bulb. Unlike other neuronal progenitor cells of the forebrain, migrating progeny of SVZa progenitors express neuronal-specific proteins and continue to divide into adulthood. Recent studies indicate that in the adult, migrating SVZa-derived cells are ensheathed by astrocytes, although the function of these astrocytes has not been determined. To explore the possible role(s) of astrocytes in the rat SVZa and RMS, we examined the expression of astroglial-specific genes in the postnatal SVZa and RMS using RT-PCR, in situ hybridization, and immunohistochemistry during (Postnatal Days 1–10) and after the period of peak olfactory bulb interneuron generation. We also examined the expression of neuronal-specific genes throughout the rostral-caudal extent of the postnatal subventricular zone to determine if differential cell type-specific gene expression could distinguish the neurogenic SVZa as a region distinct from the remainder of the SVZ. We found little to no astrocyte-specific gene expression in the P0-P7 SVZa, although the neuron-specific isoforms of tubulin (Tα1 and β-III tubulin) were expressed abundantly in the SVZa and RMS. In contrast, astrocyte-specific genes were strongly expressed in the SVZ posterior to the SVZa. GFAP expressions begins to appear in some restricted areas of the rostral migratory stream after the first postnatal week. These data suggest that astroglia are not involved in the generation or migration of most olfactory bulb interneurons. Moreover, the scarcity of glial markers in the neonatal SVZa indicates that the forebrain subventricular zone includes a distinct neurogenic anterior region containing predominantly committed neuronal progenitor cells
Multiple Signalling Pathways Establish Cell Fate and Cell Number in Drosophila Malpighian Tubules

AbstractA unique cell, the tip mother cell, arises in the primordium of each Drosophila Malpighian tubule by lateral inhibition within a cluster of achaete-expressing cells. This cell maintains achaete expression and divides to produce daughters of equivalent potential, of which only one, the tip cell, adopts the primary fate and continues to express achaete, while in the other, the sibling cell, achaete expression is lost (M. Hoch et al., 1994, Development 120, 3439–3450). In this paper we chart the mechanisms by which achaete expression is differentially maintained in the tip cell lineage to stabilise cell fate. First, wingless is required to maintain the expression of achaete in the tubule primordium so that wingless mutants lack tip cells. Conversely, increasing wingless expression results in the persistence of achaete expression in the cell cluster. Second, Notch signalling is restricted by the asymmetric segregation of Numb, as the tip mother cell divides, so that achaete expression is maintained only in the tip cell. In embryos mutant for Notch tip cells segregate at the expense of sibling cells, whereas in numb neither daughter cell adopts the tip cell fate resulting in tubules with two sibling cells. Conversely, when numb is overexpressed two tip cells segregate and tubules have no sibling cells. Analysis of cell proliferation in the developing tubules of embryos lacking Wingless after the critical period for tip cell allocation reveals an additional requirement for wingless for the promotion of cell division. In contrast, alteration in the expression of numb has no effect on the final tubule cell number
A Three-Dimensional Model of the Mouse at Embryonic Day 9

AbstractThis paper describes a digital, three-dimensional model of the mouse embryo at E9. The model was made by reconstruction from images of serial histological sections digitally warped to remove distortions and has a resolution of approximately 9 μm. The model can be digitally resectioned in any plane to provide images which resemble conventional histological sections. The main tissues have been identified and delineated by digital painting so that the anatomical components can be visualized and manipulated in 3-D surface- and volume-rendered views. This provides a three-dimensional definition of anatomy that will provide a useful tool for interpreting and understanding spatial data in mouse embryos. The anatomy of the model is discussed where it provides landmarks for interpretation and navigation or where it is unexpected in light of existing descriptions of the E9 mouse embryo. The complete anatomy is not presented in this paper but will be available on CD-ROM. A detailed description of the technical aspects of the construction of the model is included in an appendix. The model is the first of a series that will form the basis for an atlas/database of mouse development. This reconstruction and its associated anatomy are available in a variety of data formats with some supporting software from http://genex.hgu.mrc.ac.uk/