bluuebunny/crossref_metadata_2025_split huggingface dataset:
Lineage-tracing cells born in different domains along the PD axis of the developing Drosophila leg
Authors: Weigmann Katrin , Cohen Stephen M. 
Published: April 2021

Abstract
Patterning of the developing limbs by the secreted signaling proteins Wingless, Hedgehog and Dpp takes place while the imaginal discs are growing rapidly. Cells born in regions of high ligand concentration may be displaced through growth to regions of lower ligand concentration. We have used a novel lineage-tagging method to address the reversibility of cell fate specification by morphogen gradients. We find that responses to Hedgehog and Dpp in the wing disc are readily reversible. In the leg, we find that cells readily adopt more distal fates, but do not normally shift from distal to proximal fate. However, they can do so if given a growth advantage. These results indicate that cell fate specification by morphogen gradients remains largely reversible while the imaginal discs grow. In other systems, where growth and patterning are uncoupled, nonreversible specification events or ‘ratchet’ effects may be of functional significance.
Regeneration of isthmic tissue is the result of a specific and direct interaction between rhombomere 1 and midbrain
Authors: Irving Carol , Mason Ivor 
Published: April 2021

ABSTRACT
The midbrain-hindbrain boundary, or isthmus, is the source of signals that are responsible for regional specification of both the midbrain and anterior hindbrain. Fibroblast growth factor 8 (Fgf8) is expressed specifically at the isthmus and there is now good evidence that it forms at least part of the patterning signal. In this study, we use Fgf8 as a marker for isthmic cells to examine how interactions between midbrain and hindbrain can regenerate isthmic tissue and, thereby, gain insight into the normal formation and/or maintenance of the isthmus. We show that Fgf8-expressing tissue with properties of the isthmic organiser is generated when midbrain and rhombomere 1 tissue are juxtaposed but not when midbrain contacts any other rhombomere. The use of chick/quail chimeras shows that the isthmic tissue is largely derived from rhombomere 1. In a few cases a small proportion of the Fgf8-positive cells were of midbrain origin but this appears to be the result of a local respecification to a hindbrain phenotype, a process mimicked by ectopic FGF8. Studies in vitro show that the induction of Fgf8 is the result of a direct planar interaction between the two tissues and involves a diffusible signal.
The Phox2 homeodomain proteins are sufficient to promote the development of sympathetic neurons
Authors: Stanke Matthias , Junghans Dirk , Geissen Markus , Goridis Christo , Ernsberger Uwe , Rohrer Hermann 
Published: April 2021

ABSTRACT
The development of sympathetic neurons is controlled by a network of transcriptional regulators, including the paired homeodomain proteins Phox2a and Phox2b. To understand the role of Phox2 proteins in more detail, the effect of Phox2 overexpression was analysed in the avian peripheral nervous system. Phox2a expression in neural crest cultures elicited a strong increase in the number of sympathoadrenergic cells. Expression of Phox2a in the chick embryo promoted the generation of additional neurons expressing the noradrenergic marker genes DBH and TH, pan-neuronal genes SCG10 and NF160 and cholinergic genes ChAT and VAChT. Phox2a-induced neurons were found in ectopic locations such as dorsal root ganglia and peripheral nerve. Sympathoadrenergic development could be elicited in cultures of E5 dorsal root ganglia, demonstrating the presence of Phox2a-responsive cells in non-autonomic peripheral ganglia. Phox2b induced ectopic neurons in the chick embryo in the same way as Phox2a. These results show that Phox2 proteins are sufficient to promote sympathetic neuron generation and control, directly or indirectly, the expression of a large number of genes characteristic for sympathetic neurons.
Regulation of neuronal K+ currents by target-derived factors: opposing actions of two different isoforms of TGFβ
Authors: Cameron Jill S. , Dryer Laurence , Dryer Stuart E. 
Published: April 2021

ABSTRACT
The developmental expression of macroscopic Ca2+-activated K+ currents in chick ciliary ganglion neurons is dependent on an avian ortholog of TGFβ1, known as TGFβ4, secreted from target tissues in the eye. Here we report that a different isoform, TGFβ3, is also expressed in a target tissue of ciliary ganglion neurons. Application of TGFβ3 inhibits the functional expression of whole-cell Ca2+-activated K+ currents evoked by 12 hour treatment with either TGFβ1 or β-neuregulin-1 in ciliary ganglion neurons developing in vitro. TGFβ3 had no effect on voltage-activated Ca2+ currents. A neutralizing antiserum specific for TGFβ3 potentiates stimulation of Ca2+-activated K+ currents evoked by a target tissue (iris) extract in cultured ciliary ganglion neurons, indicating that TGFβ3 is an inhibitory component of these extracts. Intraocular injection of TGFβ3 causes a modest but significant inhibition of the expression of Ca2+-activated K+ currents in ciliary ganglion neurons developing in vivo. Further, intraocular injection of a TGFβ3-neutralizing antiserum stimulates expression of Ca2+-activated K+ currents in ciliary ganglion neurons developing in vivo, indicating that endogenous TGFβ3 regulates the functional expression of this current. The normal developmental expression of functional Ca2+-activated K+ currents in ciliary ganglion neurons developing in vivo is therefore regulated by two different target-derived isoforms of TGFβ, which produce opposing effects on the electrophysiological differentiation of these neurons.
Specification of hematopoietic and vascular development by the bHLH transcription factor SCL without direct DNA binding
Authors: Porcher Catherine , Liao Eric C. , Fujiwara Yuko , Zon Leonard I. , Orkin Stuart H. 
Published: April 2021

AbstractTranscription factors, such as those of the basic-helix-loop-helix (bHLH) and homeodomain classes, are primary regulators of cell fate decisions and differentiation. It is considered axiomatic that they control their respective developmental programs via direct binding to cognate DNA sequences in critical targets genes. Here we test this widely held paradigm by in vivo functional assay of the leukemia oncoprotein SCL, a bHLH factor that resembles myogenic and neurogenic proteins and is essential for both hematopoietic and vascular development in vertebrates. Contrary to all expectation, we find that SCL variants unable to bind DNA rescue hematopoiesis from gene-targeted SCL−/− embryonic stem cells and complement hematopoietic and vascular deficits in the zebrafish mutant cloche. Our findings establish DNA-binding-independent functions of SCL critical for transcriptional specification, and should encourage reassessment of presumed requirements for direct DNA binding by other transcription factors during initiation of developmental programs.
A two-step mechanism generates the spacing pattern of the ciliated cells in the skin of Xenopus embryos
Authors: A. Deblandre Gisèle , Wettstein Daniel A. , Koyano-Nakagawa Naoko , Kintner Chris 
Published: April 2021

Abstract
The skin of Xenopus embryos contains a population of specialized ciliated cells that are distributed in an evenly spaced pattern. Here we describe two successive steps that govern the differentiation and the generation of the spacing pattern of these ciliated cells. The first step occurs in the inner or sensorial layer of the non-neural ectoderm where a subset of cells are chosen to differentiate into ciliated-cell precursors. This choice is under the control of lateral inhibition mediated by a Suppressor of Hairless-dependent Notch signaling pathway, in which X-Delta-1 is the putative ligand driving the selection process, and a new Enhancer- of-Split-related gene is an epidermal target of Notch signaling. Because nascent ciliated-cell precursors prevent neighboring cells from taking on the same fate, a scattered pattern of these precursors is generated within the deep layer of the non-neural ectoderm. Ciliated-cell precursors then intercalate into the outer layer of cells in the epidermis. We show that the intercalation event acts as a second step to regulate the spacing of the mature ciliated cells. We propose that the differentiation of the ciliated cells is not only regulated by Notch-mediated lateral inhibition, but is also an example where differentiation is coupled to the movement of cells from one cell layer to another.
FGF8 can activate Gbx2 and transform regions of the rostral mouse brain into a hindbrain fate
Authors: Liu Aimin , Losos Kasia , Joyner Alexandra L. 
Published: April 2021

Abstract
The mid/hindbrain junction region, which expresses Fgf8, can act as an organizer to transform caudal forebrain or hindbrain tissue into midbrain or cerebellar structures, respectively. FGF8-soaked beads placed in the chick forebrain can similarly induce ectopic expression of mid/hindbrain genes and development of midbrain structures (Crossley, P. H., Martinez, S. and Martin, G. R. (1996) Nature 380, 66-68). In contrast, ectopic expression of Fgf8a in the mouse midbrain and caudal forebrain using a Wnt1 regulatory element produced no apparent patterning defects in the embryos examined (Lee, S. M., Danielian, P. S., Fritzsch, B. and McMahon, A. P. (1997) Development 124, 959-969). We show here that FGF8b-soaked beads can not only induce expression of the mid/hindbrain genes En1, En2 and Pax5 in mouse embryonic day 9.5 (E9.5) caudal forebrain explants, but also can induce the hindbrain gene Gbx2 and alter the expression of Wnt1 in both midbrain and caudal forebrain explants. We also show that FGF8b- soaked beads can repress Otx2 in midbrain explants. Furthermore, Wnt1-Fgf8b transgenic embryos in which the same Wnt1 regulatory element is used to express Fgf8b, have ectopic expression of En1, En2, Pax5 and Gbx2 in the dorsal hindbrain and spinal cord at E10.5, as well as exencephaly and abnormal spinal cord morphology. More strikingly, Fgf8b expression in more rostral brain regions appears to transform the midbrain and caudal forebrain into an anterior hindbrain fate through expansion of the Gbx2 domain and repression of Otx2 as early as the 7- somite stage. These findings suggest that normal Fgf8 expression in the anterior hindbrain not only functions to maintain development of the entire mid/hindbrain by regulating genes like En1, En2 and Pax5, but also might function to maintain a metencephalic identity by regulating Gbx2 and Otx2 expression.
Compartments and organising boundaries in the Drosophila eye: the role of the homeodomain Iroquois proteins
Authors: Cavodeassi Florencia , Corral Ruth Diez del , Campuzano Sonsoles , Domínguez María 
Published: April 2021

Abstract
The Drosophila eye is patterned by a dorsal-ventral organising centre mechanistically similar to those in the fly wing and the vertebrate limb bud. Here we show how this organising centre in the eye is initiated – the first event in retinal patterning. Early in development the eye primordium is divided into dorsal and ventral compartments. The dorsally expressed homeodomain Iroquois genes are true selector genes for the dorsal compartment; their expression is regulated by Hedgehog and Wingless. The organising centre is then induced at the interface between the Iroquois-expressing and non- expressing cells at the eye midline. It was previously thought that the eye develops by a mechanism distinct from that operating in other imaginal discs, but our work establishes the importance of lineage compartments in the eye and thus supports their global role as fundamental units of patterning.
Expression and functional analysis ofCititf1, an ascidianNK-2class gene, suggest its role in endoderm development
Authors: Ristoratore Filomena , Spagnuolo Antonietta , Aniello Francesco , Branno Margherita , Fabbrini Floriana , Lauro Roberto Di 
Published: April 2021

AbstractIn solitary ascidians the fate of endoderm is determined at a very early stage of development and depends on cytoplasmic factors whose nature has not been determined. We have isolated a member of the NK-2 gene family, Cititf1, from the ascidian Ciona intestinalis, showing high sequence homology to mammalian TITF1. The Cititf1 gene was expressed in all endodermal precursors at the pregastrula and gastrula stages, and is thus the first specific regulatory endodermal marker to be isolated from an ascidian. Cititf1 expression was downregulated at the end of gastrulation to reappear at middle tailbud and larval stages in the most anterior and ventral parts of head endoderm, regions which give rise, after metamorphosis, to the adult endostyle, where Cititf1 mRNA was still present. Microinjection of Cititf1 mRNA into fertilized eggs resulted in tadpole larvae with abnormalities in head-trunk development consequent to the formation of excess endoderm, perhaps due to recruitment of notochord precursors to an endodermal fate. These data suggest that Cititf1 plays an important role in normal endoderm differentiation during ascidian embryogenesis.
Differential regulation of epaxial and hypaxial muscle development by Paraxis
Authors: Wilson-Rawls Jeanne , Hurt Carla R. , Parsons Sarah M. , Rawls Alan 
Published: April 2021

Abstract
In vertebrates, skeletal muscle is derived from progenitor cell populations located in the epithelial dermomyotome compartment of the each somite. These cells become committed to the myogenic lineage upon delamination from the dorsomedial and dorsolateral lips of the dermomyotome and entry into the myotome or dispersal into the periphery. Paraxis is a developmentally regulated transcription factor that is required to direct and maintain the epithelial characteristic of the dermomyotome. Therefore, we hypothesized that Paraxis acts as an important regulator of early events in myogenesis. Expression of the muscle-specific myogenin-lacZ transgene was used to examine the formation of the myotome in the paraxis−/− background. Two distinct types of defects were observed that mirrored the different origins of myoblasts in the myotome. In the medial myotome, where the expression of the myogenic factor Myf5 is required for commitment of myoblasts, the migration pattern of committed myoblasts was altered in the absence of Paraxis. In contrast, in the lateral myotome and migratory somitic cells, which require the expression of MyoD, expression of the myogenin-lacZ transgene was delayed by several days. This delay correlated with an absence of MyoD expression in these regions, indicating that Paraxis is required for commitment of cells from the dorsolateral dermomyotome to the myogenic lineage. In paraxis−/−/myf5−/− neonates, dramatic losses were observed in the epaxial and hypaxial trunk muscles that are proximal to the vertebrae in the compound mutant, but not those at the ventral midline or the non-segmented muscles of the limb and tongue. In this genetic background, myoblasts derived from the medial (epaxial) myotome are not present to compensate for deficiencies of the lateral (hypaxial) myotome. Our data demonstrate that Paraxis is an important regulator of a subset of the myogenic progenitor cells from the dorsolateral dermomyotome that are fated to form the non-migratory hypaxial muscles.
Disruption of an RNA helicase/RNAse III gene in Arabidopsis causes unregulated cell division in floral meristems
Authors: Jacobsen Steven E. , Running Mark P. , Meyerowitz Elliot M. 
Published: April 2021

Abstract
Arabidopsis thaliana floral meristems are determinate structures that produce a defined number of organs, after which cell division ceases. A new recessive mutant, carpel factory (caf), converts the floral meristems to an indeterminate state. They produce extra whorls of stamens, and an indefinite number of carpels. Thus, CAF appears to suppress cell division in floral meristems. The function of CAF is partially redundant with the function of the CLAVATA (CLV) and SUPERMAN (SUP) genes, as caf clv and caf sup double mutants show dramatically enhanced floral meristem over-proliferation. caf mutant plants also show other defects, including absence of axillary inflorescence meristems, and abnormally shaped leaves and floral organs. The CAF gene was cloned and found to encode a putative protein of 1909 amino acids containing an N-terminal DExH/DEAD-box type RNA helicase domain attached to a C-terminal RNaseIII-like domain. A very similar protein of unknown function is encoded by a fungal and an animal genome. Helicase proteins are involved in a number of processes, including specific mRNA localization and mRNA splicing. RNase III proteins are involved in the processing of rRNA and some mRNA molecules. Thus CAF may act through some type of RNA processing event(s). CAF gives rise to two major transcripts of 2.5 and 6.2 kb. In situ hybridization experiments show that CAF RNA is expressed throughout all shoot tissues.
The role of micromere signaling in Notch activation and mesoderm specification during sea urchin embryogenesis
Authors: Sweet Hyla C. , Hodor Paul G. , Ettensohn Charles A. 
Published: April 2021

Abstract
In the sea urchin embryo, the micromeres act as a vegetal signaling center. These cells have been shown to induce endoderm; however, their role in mesoderm development has been less clear. We demonstrate that the micromeres play an important role in the induction of secondary mesenchyme cells (SMCs), possibly by activating the Notch signaling pathway. After removing the micromeres, we observed a significant delay in the formation of all mesodermal cell types examined. In addition, there was a marked reduction in the numbers of pigment cells, blastocoelar cells and cells expressing the SMC1 antigen, a marker for prospective SMCs. The development of skeletogenic cells and muscle cells, however, was not severely affected. Transplantation of micromeres to animal cells resulted in the induction of SMC1-positive cells, pigment cells, blastocoelar cells and muscle cells. The numbers of these cell types were less than those found in sham transplantation control embryos, suggesting that animal cells are less responsive to the micromere-derived signal than vegetal cells. Previous studies have demonstrated a role for Notch signaling in the development of SMCs. We show that the micromere-derived signal is necessary for the downregulation of the Notch protein, which is correlated with its activation, in prospective SMCs. We propose that the micromeres induce adjacent cells to form SMCs, possibly by presenting a ligand for the Notch receptor.
The Drosophila tissue polarity gene starry night encodes a member of the protocadherin family
Authors: Chae Jeiwook , Kim Maeng-Jo , Goo Jae Hwan , Collier Simon , Gubb David , Charlton Jeannette , Adler Paul N. , Park Woo Jin 
Published: April 2021

Abstract
The tissue polarity genes control the polarity of hairs, bristles and ommatidia in the adult epidermis of Drosophila. We report here the identification of a new tissue polarity gene named starry night (stan). Mutations in this essential gene alter the polarity of cuticular structures in all regions of the adult body. The detailed polarity phenotype of stan on the wing suggested that it is most likely a component of the frizzled (fz) pathway. Consistent with this hypothesis, stan appears to be downstream of and required for fz function. We molecularly cloned stan and found that it encodes a huge protocadherin containing nine cadherin motifs, four EGF-like motifs, two laminin G motifs, and seven transmembrane domains. This suggests that Stan functions in signal reception, perhaps together with Fz.
A sequence motif distinct from Hox binding sites controls the specificity of a Hox response element
Authors: Li Xuelin , Veraksa Alexey , McGinnis William 
Published: April 2021

Abstract
Hox transcription factors, in combination with cofactors such as PBC proteins, provide diverse developmental fates to cells on the anteroposterior body axis of animal embryos. However, the mechanisms by which the different Hox proteins and their cofactors generate those diverse fates remain unclear. Recent findings have provided support for a model where the DNA binding sites that directly interact with Hox-PBC heterodimers determine which member of the Hox protein family occupies and thereby regulates a given target element. In the experiments reported here, we test the function of chimeric Hox response elements and, surprisingly, find evidence that runs counter to this view. A 21 bp cofactor binding sequence from an embryonic Deformed Hox response element, containing no Hox or Hox-PBC binding sites, was combined with single or multimeric sites that bind heterodimers of Labial-type Hox and PBC proteins. Normally, multimerized Labial-PBC binding sites are sufficient to trigger a Labial-specific activation response in either Drosophila or mouse embryos. Here we find that the 21 bp sequence element plays an important role in Deformed specificity, as it is capable of switching a Labial-PBC binding site/response element to a Deformed response element. Thus, cofactor binding sites that are separate and distinct from homeodomain binding sites can dictate the regulatory specificity of a Hox response element.
The deltaA gene of zebrafish mediates lateral inhibition of hair cells in the inner ear and is regulated by pax2.1
Authors: Riley Bruce B. , Chiang Ming-Yung , Heck Lisa Farmer and Rebecca 
Published: April 2021

Abstract
Recent studies of inner ear development suggest that hair cells and support cells arise within a common equivalence group by cell-cell interactions mediated by Delta and Notch proteins. We have extended these studies by analyzing the effects of a mutant allele of the zebrafish deltaA gene, deltaAdx2, which encodes a dominant-negative protein. deltaAdx2/dx2 homozygous mutants develop with a 5-to 6-fold excess of hair cells and a severe deficiency of support cells. In addition, deltaAdx2/dx2 mutants show an increased number of cells expressing pax2.1 in regions where hair cells are normally produced. Immunohistological analysis of wild-type and deltaAdx2/dx2 mutant embryos confirmed that pax2.1 is expressed during the initial stages of hair cell differentiation and is later maintained at high levels in mature hair cells. In contrast, pax2.1 is not expressed in support cells. To address the function of pax2.1, we analyzed hair cell differentiation in no isthmus mutant embryos, which are deficient for pax2.1 function. no isthmus mutant embryos develop with approximately twice the normal number of hair cells. This neurogenic defect correlates with reduced levels of expression of deltaA and deltaD in the hair cells in no isthmus mutants. Analysis of deltaAdx2/dx2; no isthmus double mutants showed that no isthmus suppresses the deltaAdx2 phenotype, probably by reducing levels of the dominant-negative mutant protein. This interpretation was supported by analysis of T(msxB)b220, a deletion that removes the deltaA locus. Reducing the dose of deltaAdx2 by generating deltaAdx2/ T(msxB)b220trans-heterozygotes weakens the neurogenic effects of deltaAdx2, whereas T(msxB)b220 enhances the neurogenic defects of no isthmus. mind bomb, another strong neurogenic mutation that may disrupt reception of Delta signals, causes a 10-fold increase in hair cell production and is epistatic to both no isthmus and deltaAdx2. These data indicate that deltaA expressed by hair cells normally prevents adjacent cells from adopting the same cell fate, and that pax2.1 is required for normal levels of Delta-mediated lateral inhibition.