bluuebunny/crossref_metadata_2025_split huggingface dataset:
Antagonism of EGFR and Notch signalling in the reiterative recruitment of Drosophila adult chordotonal sense organ precursors
Authors: Lage Petra zur , Jarman Andrew P. 
Published: April 2021

ABSTRACT
The selection of Drosophila melanogaster sense organ precursors (SOPs) for sensory bristles is a progressive process: each neural equivalence group is transiently defined by the expression of proneural genes (proneural cluster), and neural fate is refined to single cells by Notch- Delta lateral inhibitory signalling between the cells. Unlike sensory bristles, SOPs of chordotonal (stretch receptor) sense organs are tightly clustered. Here we show that for one large adult chordotonal SOP array, clustering results from the progressive accumulation of a large number of SOPs from a persistent proneural cluster. This is achieved by a novel interplay of inductive epidermal growth factor-receptor (EGFR) and competitive Notch signals. EGFR acts in opposition to Notch signalling in two ways: it promotes continuous SOP recruitment despite lateral inhibition, and it attenuates the effect of lateral inhibition on the proneural cluster equivalence group, thus maintaining the persistent proneural cluster. SOP recruitment is reiterative because the inductive signal comes from previously recruited SOPs.
XCtBP is a XTcf-3 co-repressor with roles throughout Xenopus development
Authors: Brannon Mark , Brown Jeffrey D. , Bates Rebecca , Kimelman David , Moon Randall T. 
Published: April 2021

ABSTRACT
XTcf-3 is an HMG box transcription factor that mediates Xenopus dorsal-ventral axis formation. As a Wnt pathway effector, XTcf-3 interacts with β-catenin and activates the expression of the dorsal organizing gene siamois, while in the absence of β-catenin, XTcf-3 functions as a transcriptional repressor. We show that XTcf-3 contains amino- and carboxy-terminal repressor domains and have identified a Xenopus member of the C-terminal Binding Protein family of transcriptional co-repressors (XCtBP) as the C-terminal co-repressor. We show that two XCtBP binding sites near the XTcf-3 carboxy-terminus are required for the interaction of XTcf-3 and XCtBP and for the transcriptional repression mediated by the XTcf-3 carboxy-terminal domain. By fusing the GAL4 activation domain to XCtBP we have generated an antimorphic protein, XCtBP/G4A, that activates siamois transcription through an interaction with endogenous XTcf-3. Ectopic expression of XCtBP/G4A demonstrates that XCtBP functions in the regulation of head and notochord development. Our data support a role for XCtBP as a co-repressor throughout Xenopus development and indicate that XCtBP/G4A will be a useful tool in determining how XCtBP functions in various developmental processes.
Gli proteins encode context-dependent positive and negative functions: implications for development and disease
Authors: Altaba A. Ruiz i 
Published: April 2021

ABSTRACT
Several lines of evidence implicate zinc finger proteins of the Gli family in the final steps of Hedgehog signaling in normal development and disease. C-terminally truncated mutant GLI3 proteins are also associated with human syndromes, but it is not clear whether these C-terminally truncated Gli proteins fulfil the same function as full-length ones. Here, structure-function analyses of Gli proteins have been performed using floor plate and neuronal induction assays in frog embryos, as well as induction of alkaline phosphatase (AP) in SHH-responsive mouse C3H10T1/2 (10T1/2) cells. These assays show that C-terminal sequences are required for positive inducing activity and cytoplasmic localization, whereas N-terminal sequences determine dominant negative function and nuclear localization. Analyses of nuclear targeted Gli1 and Gli2 proteins suggest that both activator and dominant negative proteins are modified forms. In embryos and COS cells, tagged Gli cDNAs yield C-terminally deleted forms similar to that of Ci. These results thus provide a molecular basis for the human Polydactyly type A and Pallister-Hall Syndrome phenotypes, derived from the deregulated production of C-terminally truncated GLI3 proteins. Analyses of full-length Gli function in 10T1/2 cells suggest that nuclear localization of activating forms is a regulated event and show that only Gli1 mimics SHH in inducing AP activity. Moreover, full-length Gli3 and all C-terminally truncated forms act antagonistically whereas Gli2 is inactive in this assay. In 10T1/2 cells, protein kinase A (PKA), a known inhibitor of Hh signaling, promotes Gli3 repressor formation and inhibits Gli1 function. Together, these findings suggest a context-dependent functional divergence of Gli protein function, in which a cell represses Gli3 and activates Gli1/2 prevents the formation of repressor Gli forms to respond to Shh. Interpretation of Hh signals by Gli proteins therefore appears to involve a fine balance of divergent functions within each and among different Gli proteins, the misregulation of which has profound biological consequences.
The transcription factor dHAND is a downstream effector of BMPs in sympathetic neuron specification
Authors: Howard Marthe J. , Stanke Matthias , Schneider Carolin , Wu X. , Rohrer Hermann 
Published: April 2021

ABSTRACT
The dHAND basic helix-loop-helix transcription factor is expressed in neurons of sympathetic ganglia and has previously been shown to induce the differentiation of catecholaminergic neurons in avian neural crest cultures. We now demonstrate that dHAND expression is sufficient to elicit the generation of ectopic sympathetic neurons in vivo. The expression of the dHAND gene is controlled by bone morphogenetic proteins (BMPs), as suggested by BMP4 overexpression in vivo and in vitro, and by noggin-mediated inhibition of BMP function in vivo. The timing of dHAND expression in sympathetic ganglion primordia, together with the induction of dHAND expression in response to Phox2b implicate a role for dHAND as transcriptional regulator downstream of Phox2b in BMP-induced sympathetic neuron differentiation.
Homeotic transformation of branchial arch identity after Hoxa2 overexpression
Authors: Grammatopoulos George A. , Bell Esther , Toole Leah , Lumsden Andrew , Tucker Abigail S. 
Published: April 2021

ABSTRACT
Overexpression of Hoxa2 in the chick first branchial arch leads to a transformation of first arch cartilages, such as Meckel’s and the quadrate, into second arch elements, such as the tongue skeleton. These duplicated elements are fused to the original in a similar manner to that seen in the Hoxa2 knockout, where the reverse transformation of second to first arch morphology is observed. This confirms the role of Hoxa2 as a selector gene specifying second arch fate.
When first arch neural crest alone is targeted, first arch elements are lost, but the Hoxa2-expressing crest is unable to develop into second arch elements. This is not due to Hoxa2 preventing differentiation of cartilages. Upregulation of a second arch marker in the first arch, and homeotic transformation of cartilage elements is only produced after global Hoxa2 overexpression in the crest and the surrounding tissue. Thus, although the neural crest appears to contain some patterning information, it needs to read cues from the environment to form a coordinated pattern. Hoxa2 appears to exert its effect during differentiation of the cartilage elements in the branchial arches, rather than during crest migration, implying that pattern is determined quite late in development.
Signaling and transcriptional regulation in the neural crest-derived melanocyte lineage: interactions between KIT and MITF
Authors: Hou Ling , Panthier Jean-Jacques , Arnheiter Heinz 
Published: April 2021

ABSTRACT
Genetic and cell culture analyses have shown that the development of melanocytes from neural crest-derived precursor cells critically depends on the tyrosine kinase receptor KIT and the basic-helix-loop-helix-leucine zipper transcription factor MITF. KIT and MITF show complex interactions in that MITF is needed for the maintenance of Kit expression in melanoblasts and KIT signaling modulates MITF activity and stability in melanocyte cell lines. Using primary neural crest cell cultures from embryos homozygous for a Kit null allele marked by an inserted LacZ gene (KitW-LacZ), we show that the onset of Mitf expression in melanoblasts does not require KIT. In fact, provided that the melanocyte growth factor endothelin-3 is present, a small number of MITF/β-Gal-positive cells can be maintained for at least 2 weeks in KitW-LacZ/KitW-LacZ cultures. These cells express several pigment cell-specific genes that are thought or have been shown to be activated by MITF, including dautochrome tautomerase, pMel 17/Silver and tyrosinase-related protein-1, but lack expression of the MITF target gene tyrosinase, which encodes the rate-limiting enzyme in melanin synthesis. Consequently, the cells remain unpigmented. Addition of cholera toxin, which elevates cAMP levels and mimics part of the KIT signaling pathway, increases the number of MITF-positive cells in KitW-LacZ/KitW-LacZ cultures, leads to tyrosinase expression, and induces the differentiation of melanoblasts into mature, pigmented melanocytes. Even when added on day 5-6 of culture, cholera toxin still rescues tyrosinase expression and differentiation. The results thus demonstrate that the presence of MITF is not sufficient for tyrosinase expression in melanoblasts and that KIT signaling influences gene expression during melanocyte development in a gene-selective manner.
Taube nuss is a novel gene essential for the survival of pluripotent cells of early mouse embryos
Authors: Voss Anne K. , Thomas Tim , Petrou Petros , Anastassiadis Konstantinos , Schöler Hans , Gruss Peter 
Published: April 2021

ABSTRACT
The cells of the inner cell mass constitute the pluripotent cell population of the early embryo. They have the potential to form all of the tissues of the embryo proper and some extra-embryonic tissues. They can be considered a transient stem cell population for the whole of the embryo, and stem cells maintaining the same capacity can be isolated from these cells. We have isolated, characterised and mutated a novel gene, taube nuss (Tbn), that is essential for the survival of this important cell population. The taube nuss protein sequence (TBN) was highly conserved between human, mouse, Xenopus laevis, Drosophila melanogaster, Caenorhabditis elegans and Arabidopsis thaliana, particularly in a domain that is not present in any published proteins, showing that TBN is the founding member of a completely new class of proteins with an important function in development. The Tbn gene was expressed ubiquitously as early as E2.5 and throughout embryonic development. It was also expressed in adult brain with slightly higher levels in the hippocampus. The Tbn mutant embryos developed normally to the blastocyst stage and contained inner cell masses. They hatched from the zonae pellucidae, implanted and induced decidual reactions, but failed to develop beyond E4.0. At this time the trophoblast cells were viable, but inner cell masses were not detectable. At E3.75, massive TUNEL-positive DNA degradation and chromatin condensation were visible within the inner cell masses, whereas the cell membranes where intact. Caspase 3 was expressed in these cells. In vitro, the inner cell mass of mutant embryos failed to proliferate and died after a short period in culture. These results indicate that the novel protein, taube nuss, is necessary for the survival of the inner cell mass cells and that inner cell mass cells died of apoptosis in the absence of the taube nuss protein. As cell pruning by apoptosis is a recognised developmental process at this stage of development, the taube nuss protein may be one of the factors regulating the extent of programmed cell death at this time point.
Mechanisms that control knox gene expression in the Arabidopsis shoot
Authors: Ori Naomi , Eshed Yuval , Chuck George , Bowman John L. , Hake Sarah 
Published: April 2021

ABSTRACT
Knotted1-like homeobox (knox) genes are expressed in specific patterns within shoot meristems and play an important role in meristem maintenance. Misexpression of the knox genes, KNAT1 or KNAT2, in Arabidopsis produces a variety of phenotypes, including lobed leaves and ectopic stipules and meristems in the sinus, the region between lobes. We sought to determine the mechanisms that control knox gene expression in the shoot by examining recessive mutants that share phenotypic characteristics with 35S∷KNAT1 plants. Double mutants of serrate (se) with either asymmetric1 (as1) or asymmetric2 (as2) showed lobed leaves, ectopic stipules in the sinuses and defects in the timely elongation of sepals, petals and stamens, similar to 35S∷KNAT1 plants. Ectopic stipules and in rare cases, ectopic meristems, were detected in the sinuses on plants that were mutant for pickle and either as1 or as2. KNAT1 and KNAT2 were misexpressed in the leaves and flowers of single as1 and as2 mutants and in the sinuses of leaves of the different double mutants, but not in se or pickle single mutants. These results suggest that AS1 and AS2 promote leaf differentiation through repression of knox expression in leaves, and that SE and PKL globally restrict the competence to respond to genes that promote morphogenesis.
The type I BMP receptor BMPRIB is required for chondrogenesis in the mouse limb
Authors: Yi Soyun E. , Daluiski Aaron , Pederson Ron , Rosen Vicki , Lyons Karen M. 
Published: April 2021

ABSTRACT
Mice carrying a targeted disruption of BmprIB were generated by homologous recombination in embryonic stem cells. BmprIB−/− mice are viable and, in spite of the widespread expression of BMPRIB throughout the developing skeleton, exhibit defects that are largely restricted to the appendicular skeleton. Using molecular markers, we show that the initial formation of the digital rays occurs normally in null mutants, but proliferation of prechondrogenic cells and chondrocyte differentiation in the phalangeal region are markedly reduced. Our results suggest that BMPRIB-mediated signaling is required for cell proliferation after commitment to the chondrogenic lineage. Analyses of BmprIB and Gdf5 single mutants, as well as BmprIB; Gdf5 double mutants suggests that GDF5 is a ligand for BMPRIB in vivo. BmprIB; Bmp7 double mutants were constructed in order to examine whether BMPRIB has overlapping functions with other type I BMP receptors. BmprIB; Bmp7 double mutants exhibit severe appendicular skeletal defects, suggesting that BMPRIB and BMP7 act in distinct, but overlapping pathways. These results also demonstrate that in the absence of BMPRIB, BMP7 plays an essential role in appendicular skeletal development. Therefore, rather than having a unique role, BMPRIB has broadly overlapping functions with other BMP receptors during skeletal development.
Drosophila bunched integrates opposing DPP and EGF signals to set the operculum boundary
Authors: Dobens Leonard L. , Peterson Jeanne S. , Treisman Jessica , Raftery Laurel A. 
Published: April 2021

Abstract
The Drosophila BMP homolog DPP can function as a morphogen, inducing multiple cell fates across a developmental field. However, it is unknown how graded levels of extracellular DPP are interpreted to organize a sharp boundary between different fates. Here we show that opposing DPP and EGF signals set the boundary for an ovarian follicle cell fate. First, DPP regulates gene expression in the follicle cells that will create the operculum of the eggshell. DPP induces expression of the enhancer trap reporter A359 and represses expression of bunched, which encodes a protein similar to the mammalian transcription factor TSC-22. Second, DPP signaling indirectly regulates A359 expression in these cells by downregulating expression of bunched. Reduced bunched function restores A359 expression in cells that lack the Smad protein MAD; ectopic expression of BUNCHED suppresses A359 expression in this region. Importantly, reduction of bunched function leads to an expansion of the operculum and loss of the collar at its boundary. Third, EGF signaling upregulates expression of bunched. We previously demonstrated that the bunched expression pattern requires the EGF receptor ligand GURKEN. Here we show that activated EGF receptor is sufficient to induce ectopic bunched expression. Thus, the balance of DPP and EGF signals sets the boundary of bunched expression. We propose that the juxtaposition of cells with high and low BUNCHED activity organizes a sharp boundary for the operculum fate.
Nodal signaling patterns the organizer
Authors: Gritsman Kira , Talbot William S. , Schier Alexander F. 
Published: April 2021

ABSTRACT
Spemann’s organizer plays an essential role in patterning the vertebrate embryo. During gastrulation, organizer cells involute and form the prechordal plate anteriorly and the notochord more posteriorly. The fate mapping and gene expression analyses in zebrafish presented in this study reveal that this anteroposterior polarity is already initiated in the organizer before gastrulation. Prechordal plate progenitors reside close to the blastoderm margin and express the homeobox gene goosecoid, whereas notochord precursors are located further from the margin and express the homeobox gene floating head. The nodal-related genes cyclops and squint are expressed at the blastoderm margin and are required for prechordal plate and notochord formation. We show that differential activation of the Nodal signaling pathway is essential in establishing anteroposterior pattern in the organizer. First, overexpression of cyclops and squint at different doses leads to the induction of floating head at low doses and the induction of both goosecoid and floating head at higher doses. Second, decreasing Nodal signaling using different concentrations of the antagonist Antivin inhibits goosecoid expression at low doses and blocks expression of both goosecoid and floating head at higher doses. Third, attenuation of Nodal signaling in zygotic mutants for the EGF-CFC gene one-eyed pinhead, an essential cofactor for Nodal signaling, leads to the loss of goosecoid expression and expansion of floating head expression in the organizer. Concomitantly, cells normally fated to become prechordal plate are transformed into notochord progenitors. Finally, activation of Nodal signaling at different times suggests that prechordal plate specification requires sustained Nodal signaling, whereas transient signaling is sufficient for notochord development. Together, these results indicate that differential Nodal signaling patterns the organizer before gastrulation, with the highest level of activity required for anterior fates and lower activity essential for posterior fates.
Roles of Hoxa1 and Hoxa2 in patterning the early hindbrain of the mouse
Authors: Barrow Jeffery R. , Stadler H. Scott , Capecchi Mario R. 
Published: April 2021

ABSTRACT
Early in its development, the vertebrate hindbrain is transiently subdivided into a series of compartments called rhombomeres. Genes have been identified whose expression patterns distinguish these cellular compartments. Two of these genes, Hoxa1 and Hoxa2, have been shown to be required for proper patterning of the early mouse hindbrain and the associated neural crest. To determine the extent to which these two genes function together to pattern the hindbrain, we generated mice simultaneously mutant at both loci. The hindbrain patterning defects were analyzed in embryos individually mutant for Hoxa1 and Hoxa2 in greater detail and extended to embryos mutant for both genes. From these data a model is proposed to describe how Hoxa1, Hoxa2, Hoxb1, Krox20 (Egr2) and kreisler function together to pattern the early mouse hindbrain. Critical to the model is the demonstration that Hoxa1 activity is required to set the anterior limit of Hoxb1 expression at the presumptive r3/4 rhombomere boundary. Failure to express Hoxb1 to this boundary in Hoxa1 mutant embryos initiates a cascade of gene misexpressions that result in misspecification of the hindbrain compartments from r2 through r5. Subsequent to misspecification of the hindbrain compartments, ectopic induction of apoptosis appears to be used to regulate the aberrant size of the misspecified rhombomeres.
Conditional inactivation of VEGF-A in areas of collagen2a1 expression results in embryonic lethality in the heterozygous state
Authors: Haigh Jody J. , Gerber Hans-Peter , Ferrara Napoleone , Wagner Erwin F. 
Published: April 2021

ABSTRACT
VEGF-A has been implicated in regulating the initial angiogenic invasion events that are essential for endochondral bone formation. VEGF-A mRNA expression was indeed found in the sclerotome of the developing somite and in the limb-bud mesenchyme at E10.5 in mouse development but declined during chondrogenesis and became upregulated in hypertrophic chondrocytes prior to angiogenic invasion. To determine the functional importance of VEGF-A expression in the developing chondrogenic tissues, VEGF-A was conditionally inactivated during early embryonic development using Collagen2a1-Cre transgenic lines. Deletion of a single VEGF-A allele in Collagen2a1-Cre-expressing cells results in embryonic lethality around E10.5. This lethality is characterized by aberrant development of the dorsal aorta and intersomitic blood vessels, along with defects in the developing endocardial and myocardial layers of the heart.
A small percentage of VEGFFlox/+, Collagen2a1-Cre fetuses survive until E17.5, show aberrant endochondral bone formation and develop a heart phenotype resembling a dilated form of ischemic cardiomyopathy. These results provide insights into the function of VEGF-A in heart and endochondral bone formation and underscore the importance of tightly controlled levels of VEGF-A during development.
Increased cell death and delayed development in the cerebellum of mice lacking the rev-erbAα orphan receptor
Authors: Chomez Patrick , Neveu Isabelle , Mansén Anethe , Kiesler Eva , Larsson Lars , Vennström Björn , Arenas Ernest 
Published: April 2021

ABSTRACT
The rev-erbAα gene, belonging to the steroid receptor superfamily of transcription factors, is highly conserved during evolution but little is known so far about its functions in development or in adult physiology. Here, we describe genetically altered mice lacking the rev-erbAα gene. These animals do not show any obvious phenotype in either fat tissue or skeletal muscle, despite the known regulation of rev-erbAα expression during adipocyte and myotube differentiation in vitro. However, during the second week of life, the cerebellum of rev-erbAα mutants presents several unexpected abnormalities, such as alterations in the development of Purkinje cells, delay in the proliferation and migration of granule cells from the external granule cell layer and increased apoptosis of neurons in the internal granule cell layer. Interestingly, the expression pattern of rev-erbAα suggests that the abnormalities observed in the external granule cell layer could be secondary to Purkinje cell alterations. Taken together, our data underline the importance of rev-erbAα expression for the appropriate balance of transcriptional activators and repressors during postnatal cerebellar development.