bluuebunny/crossref_metadata_2025_split huggingface dataset:
Concentration-dependent patterning of the Xenopus ectoderm by BMP4 and its signal transducer Smad1
Authors: Wilson Paul A. , Lagna Giorgio , Suzuki Atsushi , Hemmati-Brivanlou Ali 
Published: April 2021

ABSTRACT
Morphogens are thought to establish pattern in early embryos by specifying several cell fates along a gradient of concentration; a well-studied example is the Drosophila protein decapentaplegic (DPP) acting in the wing disc. Recent work has established that bone morphogenetic protein 4 (BMP4), the vertebrate homologue of DPP, controls the fundamental choice between neural and epidermal fates in the vertebrate ectoderm, under the control of antagonists secreted by the organizer region of the mesoderm. We now show that BMP4 can act as a morphogen, evoking distinct responses in Xenopus ecto-dermal cells at high and low concentrations, in a pattern consistent with the positions of the corresponding cell types in the embryo. Moreover, this complex cellular response to extracellular BMP4 concentration does not require subsequent cell-cell communication and is thus direct, as required of a classical morphogen. We also show that the same series of cell types – epidermis, cement gland and neural tissue – can be produced by progressively inhibiting endogenous BMP signaling with specific antagonists, including the organizer factor noggin. Finally, expression of increasing doses of the signal transduction molecule Smad1 accurately reproduces the response to BMP4 protein. Since Smads have been shown to act in the nucleus, this finding implies a direct translation of extracellular morphogen concentration into transcription factor activity. We propose that a graded distribution of BMP activity controls the specification of several cell types in the gastrula ectoderm and that this extracellular gradient acts by establishing an intracellular and then nuclear gradient of Smad activity.
The RXR homolog Ultraspiracle is an essential component of the Drosophila ecdysone receptor
Authors: Hall Bonnie L. , Thummel Carl S. 
Published: April 2021

ABSTRACT
Pulses of the steroid hormone ecdysone function as key temporal signals during insect development, coordinating the major postembryonic developmental transitions, including molting and metamorphosis. In vitro studies have demonstrated that the EcR ecdysone receptor requires an RXR heterodimer partner for its activity, encoded by the ultraspiracle (usp) locus. We show here that usp exerts no apparent function in mid-third instar larvae, when a regulatory hierarchy prepares the animal for the onset of metamorphosis. Rather, usp is required in late third instar larvae for appropriate developmental and transcriptional responses to the ecdysone pulse that triggers puparium formation. The imaginal discs in usp mutants begin to evert but do not elongate or differentiate, the larval midgut and salivary glands fail to undergo programmed cell death and the adult midgut fails to form. Consistent with these developmental phenotypes, usp mutants show pleiotropic defects in ecdysone-regulated gene expression at the larvalprepupal transition. usp mutants also recapitulate aspects of a larval molt at puparium formation, forming a supernumerary cuticle. These observations indicate that usp is required for ecdysone receptor activity in vivo, demonstrate that the EcR/USP heterodimer functions in a stage-specific manner during the onset of metamorphosis and implicate a role for usp in the decision to molt or pupariate in response to ecdysone pulses during larval development.
Phosphorylation modulates direct interactions between the Toll receptor, Pelle kinase and Tube
Authors: Shen Baohe , Manley James L. 
Published: April 2021

ABSTRACT
Determination of dorsal/ventral polarity in Drosophila requires 12 genetically defined, maternally encoded proteins. These include Toll, a transmembrane receptor, Pelle, a ser/thr protein kinase and Tube, all of which function intracytoplasmically to initiate the cascade that ultimately activates Dorsal, an NF-KB family transcription factor. Here we describe biochemical interactions between recombinant Toll, Pelle and Tube that provide insights into early events in activation of the signaling cascade. We first show that Pelle binds directly to a region within the Toll intracytoplasmic domain, providing the first evidence that these two evolutionarily conserved molecules physically interact. We then demonstrate that Pelle can be autophosphorylated, and that this prevents binding to Toll as well as Tube. Autophosphorylation occurs in the N-terminal, death-domain-containing region of Pelle, which is dispensable for binding to Toll but required for enzymatic activity. We also show that Pelle phosphorylates Toll, within the region required for Pelle interaction, but this phosphorylation can be blocked by a previously characterized inhibitory domain at the Toll C terminus. These and other results allow us to propose a model by which multiple phosphorylation-regulated interactions between these three proteins lead to activation of the Dorsal signaling pathway.
Hoxa1 and Krox-20 synergize to control the development of rhombomere 3
Authors: Helmbacher Françoise , Pujades Cristina , Desmarquet Carole , Frain Monique , Rijli Filippo M. , Chambon Pierre , Charnay Patrick 
Published: April 2021

ABSTRACT
The transcription factor genes Hoxa1 and Krox-20 have been shown to play important roles in vertebrate hindbrain segmentation. In this report, we present evidence for novel functions of these genes which co-operate in specifying cellular identity in rhombomere (r) 3. Although Hoxa1 has not been observed to be expressed rostrally to the prospective r3/r4 boundary, its inactivation results in (i) the appearance of patches of cells presenting an r2-like molecular identity within r3, (ii) early neuronal differentiation in r3, normally characteristic of even- numbered rhombomeres, and (iii) abnormal navigation of r3 motor axons, similar to that observed in even-numbered rhombomeres. These phenotypic manifestations become more severe in the context of the additional inactivation of one allele of the Krox-20 gene, demonstrating that Hoxa1 and Krox-20 synergize in a dosage-dependent manner to specify r3 identity and odd- versus even-numbered rhombomere characters. In addition, these data suggest that the control of the development of r3 may not be autonomous but dependent on interactions with Hoxa1- expressing cells.
Functional and biochemical interactions of Wnts with FrzA, a secreted Wnt antagonist
Authors: Xu Qihong , D’Amore Patricia A. , Sokol Sergei Y. 
Published: April 2021

ABSTRACT
Wnts are highly conserved developmental regulators that mediate inductive signaling between neighboring cells and participate in the determination of embryonic axes. Frizzled proteins constitute a large family of putative transmembrane receptors for Wnt signals. FrzA is a novel protein that shares sequence similarity with the extracellular domain of Frizzled. The Xenopus homologue of FrzA is dynamically regulated during early development. At the neurula stages, XfrzA mRNA is abundant in the somitic mesoderm, but later becomes strongly expressed in developing heart, neural crest derivatives, endoderm, otic vesicle and other sites of organogenesis. To evaluate possible biological functions of FrzA, we analyzed its effect on early Xenopus development. Microinjection of bovine or Xenopus FrzA mRNA into dorsal blastomeres resulted in a shortened body axis, suggesting a block of convergent extension movements. Consistent with this possibility, FrzA blocked elongation of ectodermal explants in response to activin, a potent mesoderm-inducing factor. FrzA inhibited induction of secondary axes by Xwnt8 and human Wnt2, but not by Xdsh, supporting the idea that FrzA interferes with Wnt signaling. Furthermore, FrzA suppressed Wnt-dependent activation of the early response genes in ectodermal explants and in the marginal zone. Finally, immunoprecipitation experiments demonstrate that FrzA binds to the soluble Wingless protein in cell culture supernatants in vitro. Our results indicate that FrzA is a naturally occurring secreted antagonist of Wnt signaling.
Developmentally regulated nuclear transport of transcription factors in Drosophila embryos enable the heat shock response
Authors: Wang Zhaohui , Lindquist Susan 
Published: April 2021

ABSTRACT
Hsp70 is a broadly conserved thermotolerance factor, but inhibits growth at normal temperatures and cannot be induced in early embryos. We report that in Drosophila embryos the temporal and spatial patterns of Hsp70 inducibility were unexpectedly complex, with striking differences between the soma and the germline. In both, regulation occurred at the level of transcription. During the refractory period for Hsp70 induction, HSF (heat-shock transcription factor) exhibited specific DNA-binding activity characteristic of activation in extracts of heated embryos. Remarkably, however, HSF was restricted to the cytoplasm in intact embryos even after heat shock. HSF moved from the cytoplasm to the nucleus in the absence of heat precisely when the capacity to induce Hsp70 was acquired (cycle 12 of the germline, cycle 13 in the soma). During oogenesis, Hsp70 inducibility was lost in nurse cells around stage 10, in a posterior-to-anterior gradient and HSF redistributed from nucleus to cytoplasm in the same spatiotemporal pattern. In a highly inbred derivative of the Samarkind strain, HSF moved into embryonic nuclei earlier than in our standard wild-type strain. Correspondingly, Hsp70 was inducible earlier, confirming that nuclear transport of HSF controls the inducibility of Hsp70 in early embryos. We also report for the first time the nuclear import patterns of two general transcription factors, RNA polymerase subunit Ilc and TATA binding protein (TBP). Both enter nuclei in a highly synchronous manner, independently of each other and of HSF. The import of TBP coincides with the first reported appearance of transcripts in the embryo. We suggest that the potentiation of general and heat shock-specific transcription in Drosophila embryos is controlled by the developmentally programmed relocalization of general and heat shock-specific transcription factors. Restricted nuclear entry of HSF represents a newly described mechanism for regulating the heat-shock response.
small wing encodes a phospholipase C-γ that acts as a negative regulator of R7 development in Drosophila
Authors: Thackeray Justin R. , Gaines Peter C.W. , Ebert Paul , Carlson John R. 
Published: April 2021

ABSTRACT
Phospholipase C-γ (PLC-γ) is activated in many cell types following growth factor stimulation. Our understanding of the role of PLC-γ in cell growth and differentiation has been severely limited by the dearth of mutations in any organism. In this study, we show that the Drosophila gene small wing (sl), identified by Bridges in 1915, encodes a PLC-γ. Mutations of sl result in extra R7 photoreceptors in the compound eye, consistent with overactivation of the receptor tyrosine kinase pathways that control R7 development. The data presented here provide the first genetic evidence that PLC-γ is involved in Ras-mediated signaling and indicate that PLC-γ acts as a negative regulator in such pathways in Drosophila.
Semaphorins act as attractive and repulsive guidance signals during the development of cortical projections
Authors: Bagnard Dominique , Lohrum Marion , Uziel Daniela , Püschel Andreas W. , Bolz Jürgen 
Published: April 2021

ABSTRACT
Members of the semaphorin family have been implicated in mediating axonal guidance in the nervous system by their ability to collapse growth cones and to function as chemorepellents. The present findings show that recombinant Semaphorin D has similar effects on cortical axons and, in addition, inhibits axonal branching. In contrast, semaphorin E acts as an attractive guidance signal for cortical axons. Attractive effects were only observed when growth cones encountered increasing concentrations or a patterned distribution of Semaphorin E, but not when they are exposed to uniform concentrations of this molecule. Specific binding sites for Semaphorin D and Semaphorin E were present on cortical fibers both in vitro and in vivo at the time when corticofugal projections are established. In situ hybridization analysis revealed that the population of cortical neurons used in our experiments express neuropilin-1 and neuropilin-2, which are essential components of receptors for the class III semaphorins. Moreover, semD mRNA was detected in the ventricular zone of the neocortex whereas semE mRNA was restricted to the subventricular zone. Taken together, these results indicate that semaphorins are bifunctional molecules whose effects depend on their spatial distribution. The coordinated expression of different semaphorins, together with their specific activities on cortical axons, suggests that multiple guidance signals contribute to the formation of precise corticofugal pathways.
A role for rhoB in the delamination of neural crest cells from the dorsal neural tube
Authors: Liu Jeh-Ping , Jessell Thomas M. 
Published: April 2021

ABSTRACT
The differentiation of neural crest cells from progenitors located in the dorsal neural tube appears to involve three sequential steps: the specification of premigratory neural crest cell fate, the delamination of these cells from the neural epithelium and the migration of neural crest cells in the periphery. BMP signaling has been implicated in the specification of neural crest cell fate but the mechanisms that control the emergence of neural crest cells from the neural tube remain poorly understood. To identify molecules that might function at early steps of neural crest differentiation, we performed a PCR-based screen for genes induced by BMPs in chick neural plate cells. We describe the cloning and characterization of one gene obtained from this screen, rhoB, a member of the rho family GTP-binding proteins. rhoB is expressed in the dorsal neural tube and its expression persists transiently in migrating neural crest cells. BMPs induce the neural expression of rhoB but not the more widely expressed rho family member, rhoA. Inhibition of rho activity by C3 exotoxin prevents the delamination of neural crest cells from neural tube explants but has little effect on the initial specification of premigratory neural crest cell fate or on the later migration of neural crest cells. These results suggest that rhoB has a role in the delamination of neural crest cells from the dorsal neural tube.
Regionalization within the mammalian telencephalon is mediated by changes in responsiveness to Sonic Hedgehog
Authors: Kohtz Jhumku D. , Baker Darren P. , Corte Giorgio , Fishell Gord 
Published: April 2021

ABSTRACT
The cortex and basal ganglia are the major structures of the adult brain derived from the embryonic telencephalon. Two morphologically distinct regions of the basal ganglia are evident within the mature ventral telencephalon, the globus pallidus medially, and the striatum, which is positioned between the globus pallidus and the cortex. Deletion of the Sonic Hedgehog gene in mice indicates that this secreted signaling molecule is vital for the generation of both these ventral telencephalic regions. Previous experiments showed that Sonic Hedgehog induces differentiation of ventral neurons characteristic of the medial ganglionic eminence, the embryonic structure which gives rise to the globus pallidus. In this paper, we show that later in development, Sonic Hedgehog induces ventral neurons with patterns of gene expression characteristic of the lateral ganglionic eminence. This is the embryonic structure from which the striatum is derived. These results suggest that temporally regulated changes in Sonic Hedgehog responsiveness are integral in the sequential induction of basal telencephalic structures.
Visceral endoderm-restricted translation of Otx1 mediates recovery of Otx2 requirements for specification of anterior neural plate and normal gastrulation
Authors: Acampora Dario , Avantaggiato Virginia , Tuorto Francesca , Briata Paola , Corte Giorgio , Simeone Antonio 
Published: April 2021

ABSTRACT
Otx1 and Otx2, two murine homologs of the Drosophila orthodenticle (otd) gene, contribute to brain morphogenesis. In particular Otx1 null mice are viable and show spontaneous epileptic seizures and abnormalities affecting the dorsal telencephalic cortex. Otx2 null mice die early in development and fail in specification of the rostral neuroectoderm and proper gastrulation. In order to determine whether Otx1−/− and Otx2−/− highly divergent phenotypes reflect differences in temporal expression or biochemical activity of OTX1 and OTX2 proteins, the Otx2- coding sequence was replaced by a human Otx1 full-coding cDNA. Homozygous mutant embryos recovered anterior neural plate and proper gastrulation but failed to maintain forebrain-midbrain identities, displaying a headless phenotype from 9 days post coitum (d.p.c.) onwards. Unexpectedly, in spite of the RNA distribution in both visceral endoderm (VE) and epiblast, the hOTX1 protein was synthesized only in the VE. This VE-restricted translation was sufficient to recover Otx2 requirements for specification of the anterior neural plate and proper organization of the primitive streak, thus providing evidence that the difference between Otx1 and Otx2 null mice phenotypes originates from their divergent expression patterns.
Moreover, our data lead us to hypothesize that the differential post-transcriptional control existing between VE and epiblast cells may potentially contribute to fundamental regulatory mechanisms required for head specification.
Avian VEGF-C: cloning, embryonic expression pattern and stimulation of the differentiation of VEGFR2-expressing endothelial cell precursors
Authors: Eichmann Anne , Corbel Catherine , Jaffredo Thierry , Bréant Christiane , Joukov Vladimir , Kumar Vijay , Alitalo Kari , Douarin Nicole M. le 
Published: April 2021

ABSTRACT
VEGF-C is a recently discovered secreted polypeptide related to the angiogenic mitogen VEGF. We have isolated the quail VEGF-C cDNA and shown that its protein product is secreted from transfected cells and interacts with the avian VEGFR3 and VEGFR2. In situ hybridization shows that quail VEGF-C mRNA is strongly expressed in regions destined to be rich in lymphatic vessels, particularly the mesenteries, mesocardium and myotome, in the region surrounding the jugular veins, and in the kidney. These expression sites are similar to those observed in the mouse embryo (E. Kukk, A. Lymboussaki, S. Taira, A. Kaipainen, M. Jeltsch, V. Joukov and K. Alitalo, 1996, Development 122, 3829-3837). We have observed VEGFR3-positive endothelial cells in proximity to most of the VEGF-C-expressing sites, suggesting functional relationships between this receptor-ligand couple. The comparison of the VEGF and VEGFR2 knockout phenotypes had suggested the existence of another ligand for VEGFR2. We therefore investigated the effect of VEGF-C on VEGFR2-positive cells isolated from the posterior mesoderm of gastrulating embryos. We have recently shown that VEGF binding triggers endothelial differentiation of these cells, whereas hemopoietic differentiation appears to be mediated by binding of a so far unidentified VEGFR2 ligand. We show here that VEGF-C also triggers endothelial differentiation of these cells, presumably via VEGFR2. These results indicate that VEGF and VEGF-C can act in a redundant manner via VEGFR2. In conclusion, VEGF-C appears to act during two different developmental phases, one early in posterior mesodermal VEGFR2-positive endothelial cell precursors which are negative for VEGFR3 and one later in regions rich in lymphatic vessels at a time when endothelial cells express both VEGFR2 and VEGFR3.
Ganglion cells influence the fate of dividing retinal cells in culture
Authors: Waid David K. , McLoon Steven C. 
Published: April 2021

ABSTRACT
The different retinal cell types arise during vertebrate development from a common pool of progenitor cells. The mechanisms responsible for determining the fate of individual retinal cells are, as yet, poorly understood. Ganglion cells are one of the first cell types to be produced in the developing vertebrate retina and few ganglion cells are produced late in development. It is possible that, as the retina matures, the cellular environment changes such that it is not conducive to ganglion cell determination. The present study showed that older retinal cells secrete a factor that inhibits the production of ganglion cells. This was shown by culturing younger retinal cells, the test population, adjacent to various ages of older retinal cells. Increasingly older retinal cells, up to embryonic day 9, were more effective at inhibiting production of ganglion cells in the test cell population. Ganglion cell production was restored when ganglion cells were depleted from the older cell population. This suggests that ganglion cells secrete a factor that actively prevents cells from choosing the ganglion cell fate. This factor appeared to be active in medium conditioned by older retinal cells. Analysis of the conditioned medium established that the factor was heat stable and was present in the &lt;3 kDa and &gt;10 kDa fractions. Previous work showed that the neurogenic protein, Notch, might also be active in blocking production of ganglion cells. The present study showed that decreasing Notch expression with an antisense oligonucleotide increased the number of ganglion cells produced in a population of young retinal cells. Ganglion cell production, however, was still inhibited in cultures using antisense oligonucleotide to Notch in medium conditioned by older retinal cells. This suggests that the factor secreted by older retinal cells inhibits ganglion cell production through a different pathway than that mediated by Notch.
Regulation of growth region cartilage proliferation and differentiation by perichondrium
Authors: Long Fanxin , Linsenmayer Thomas F. 
Published: April 2021

ABSTRACT
Endochondral bone formation in vertebrates requires precise coordination between proliferation and differentiation of the participating chondrocytes. We examined the role of perichondrium in this process using an organ culture system of chicken embryonic tibiotarsi. A monoclonal antibody against chicken collagen type X, specifically expressed by hypertrophic chondrocytes, was utilized to monitor the terminal differentiation of chondrocytes. Proliferation of chondrocytes was examined by a BrdU-labeling procedure. The absence of perichondrium is correlated with an extended zone of cartilage expressing collagen type X, suggesting that the perichondrium regulates chondrocyte hypertrophy in a negative manner. Removal of perichondrium, in addition, resulted in an extended zone of chondrocytes incorporating BrdU, indicating that the perichondrium also negatively regulates the proliferation of chondrocytes. Partial removal of perichondrium from one side of the tibiotarsus led to expansion of both the collagen type X-positive domain and the BrdU-positive zone at the site of removal but not where the perichondrium remained intact. This suggests that both types of regulation by the perichondrium are local effects. Furthermore, addition of bovine parathyroid hormone (PTH) to perichondrium-free cultures reversed the expansion of the collagen type X-positive domain but not that of the proliferative zone. This suggests that the regulation of differentiation is dependent upon the PTH/PTHrP receptor and that the regulation of proliferation is likely independent of it. Taken together, these results are consistent with a model where perichondrium regulates both the exit of chondrocytes from the cell cycle, and their subsequent differentiation.