bluuebunny/crossref_metadata_2025_split huggingface dataset:
The role of tinman, a mesodermal cell fate gene, in axon pathfinding during the development of the transverse nerve in Drosophila
Authors: Gorczyca Michael G. , Phillis Randall W. , Budnik Vivian 
Published: April 2021

ABSTRACT
During the development of peripheral nerves, pioneer axons often navigate over mesodermal tissues. In this paper, we examine the role of the mesodermal cell determination gene tinman on cells that provide pathfinding cues in Drosophila. We focus on a subset of peripheral nerves, the transverse nerves, that innervate abdominal segments. During wild-type embryonic development, the transverse nerve efferents associate with glial cells located on the dorsal aspect of the CNS midline (transverse nerve exit glia). These glial cells have cytoplasmic extensions that prefigure the transverse nerve pathway from the CNS to the body wall musculature prior to transverse nerve formation. Transverse nerve efferents extend along this scaffold to the periphery, where they fasciculate with projections from a peripheral neuron − the LBD. In tinman mutants, the transverse nerve exit glia appear to be missing, and efferent fibers remain stalled at the CNS midline, without forming transverse nerves. In addition, fibers of the LBD neurons are often truncated. These results suggest that the lack of exit glia prevents normal transverse nerve pathfinding. Another prominent defect in tinman is the loss of all dorsal neurohemal organs, FMRFamide-expressing thoracic structures which likely contain the homologs of the transverse nerve exit glia in the thoracic segments. Our results support the hypothesis that the exit glia have a mesodermal origin and that glia play an essential role in determining transverse nerve axon pathways.
Programming gene expression in developing epidermis
Authors: Byrne Carolyn , Tainsky Michael , Fuchs Elaine 
Published: April 2021

ABSTRACT
As the major proteins of adult keratinocytes, keratins provide biochemical markers for exploring mouse epidermal embryogenesis. Here, we used a modified method of whole-mount in situ hybridization to track skin-specific expression of endogenous keratin mRNAs through-out embryogenesis. To monitor transcriptional regulation, we coupled this with β-galactosidase expression of a human epidermal keratin promoter-driven transgene. These studies have radically changed our perception of how the program of gene expression becomes established during epidermal development. Specifically, we have discovered that (1) basal keratin (K5 and K14) genes are first detected at E9.5 in a highly regional fashion, and surprisingly as early as the single layered ectodermal stage; (2) the early patterns do not correlate with morphogenesis per se, but rather with regional variations in the embryonic origin of underlying mesenchyme, supporting morphogenetic criteria that early inductive cues are mesenchymal; (3) epidermal keratin genes are expressed in periderm, supporting the notion that this layer arises from ectodermal stratification, even though it is simple epithelial-like in morphology and is subsequently sloughed during development; (4) later embryonic patterns of K5 and K14 gene expression parallel proliferative capacity and not stratification; and (5) K1 and K10 mRNAs are first detected as early as E13.5, and their patterns correlate with differentiation and not stratification.
These patterns of epidermal gene expression led us to explore whether potential transcriptional regulators of these genes are expressed similarly. We show that AP2 (but not Sp1) cRNAs hybridize in a pattern similar to, but preceding that of basal keratin cRNAs. Finally, using gene expression in cultured cells, we demonstrate that AP2 has a strong inductive effect on basal keratin expression in a cellular environment that does not normally possess AP2 activity.
The intracellular domain of mouse Notch: a constitutively activated repressor of myogenesis directed at the basic helix-loop-helix region of MyoD
Authors: Kopan Raphael , Nye Jeffrey S. , Weintraub Harold 
Published: April 2021

ABSTRACT
We show that Myf-5 and mNotch mRNA are both present in the presomitic mesoderm before muscle cell commitment and before muscle structural gene activation. The failure of presomitic mesoderm to respond to Myf-5 and express myogenic properties implies that there may be a mechanism in presomitic mesoderm to suppress muscle differentiation. Here we show that ectopic expression of the intracellular domain of mNotch (mNotchIC) functions as a constitutively activated repressor of myogenesis both in cultured cells and in frog embryos. Mutagenesis experiments indicate that the target for inactivation by mNotch is the MyoD basic helix-loop-helix domain. mNotchIC contains a nuclear localization signal and localizes to the nucleus. Removal of the nuclear localization signal (NLS) reduces nuclear localization and diminishes the inhibition of myogenesis caused by Myf-5 or MyoD. Additional experiments show that the CDC10/SWI6/ankyrin repeats are also necessary for myogenic inhibition.
Ks1, an epithelial cell-specific gene, responds to early signals of head formation in Hydra
Authors: Weinziger Ruth , Salgado Luis M. , David Charles N. , Bosch Thomas C. G. 
Published: April 2021

ABSTRACT
As a molecular marker for head specification in Hydra, we have cloned an epithelial cell-specific gene which responds to early signals of head formation. The gene, designated ks1, encodes a 217-amino acid protein lacking significant sequence similarity to any known protein. KS1 contains a N-terminal signal sequence and is rich in charged residues which are clustered in several domains. ks1 is expressed in tentacle-specific epithelial cells (battery cells) as well as in a small fraction of ectodermal epithelial cells in the gastric region subjacent to the tentacles. Treatment with the protein kinase C activator 12-O-tetradecanoylphorbol-13-acetate (TPA) causes a rapid increase in the level of ks1 mRNA in head-specific epithelial cells and also induces ectopic ks1 expression in cells of the gastric region. Sequence elements in the 5′-flanking region of ks1 that are related to TPA-responsive elements may mediate the TPA inducibility of ks1 expression. The pattern of expression of ks1 suggests that a ligand-activated diacylglycerol second messenger system is involved in head-specific differentiation.
Early tagma-specific commitment of Drosophila CNS progenitor NB1-1
Authors: Prokop Andreas , Technau Gerhard M. 
Published: April 2021

ABSTRACT
The developing central nervous system of many species expresses distinct segment-specific characteristics. We recently described the entire embryonic lineage of Drosophila neuroblast NB1–1 and showed that the compo-sition of this lineage differs between the thoracic and abdominal tagmata with respect to the presence or absence of specific glial and neuronal components (Udolph, G., Prokop, A., Bossing, T. and Technau, G. M. (1993) Devel-opment 118, 765–775). Here, we demonstrate by heterotopic transplantations that tagma specificity of NB1-1 is deter-mined in the neuroectoderm at the early gastrula stage (stage 7). Heterogenetic transplantation and mutant analysis show that the activity of the homeotic genes Ubx or abd-A is required for the expression of the abdominal variant of the lineage. Heat induction of Ubx or abd-A expression or their derepression in Polycomb mutant embryos can override thoracic determination several hours after gastrulation (stage 10/11). At that stage antibody stainings reveal both proteins to be present in NB1-1 during normal development. Possible mechanisms confer-ring the early tagma-specific determination are discussed.
HOM-C/Hox genes and four interacting loci determine the morphogenetic properties of single cells in the nematode male tail
Authors: Chow King L. , Emmons Scott W. 
Published: April 2021

ABSTRACT
The copulatory structure of the C. elegans male tail includes a set of nine bilaterally symmetrical pairs of sense organs known as rays. Each ray comprises three cells, which are generated by a stereotyped cell sublineage expressed by 18 epidermal ray precursor cells. A pattern formation mechanism in the epidermis guides the specification of morphogenetic differences between the rays necessary for correct organelle assembly at specific positions within the epidermis. Expression of these ray dif-ferences was altered in mutations we described previously, resulting in displaced and fused rays. Here we show that two genes of the C. elegans HOM-C/Hox gene complex play a role in the pattern formation mechanism. Increasing or decreasing the gene dosage of mab-5, an Antennapedia homolog, and egl-5, an Abdominal B homolog, results in displacement and fusion of specific rays. These changes are interpreted as anterior or posterior transformations in ray identities. Mutations in the genes previously described are dominant modifiers of these effects. This suggests that these genes act in the same morphogenetic pathway as mab-5 and egl-5. Several lines of evidence, including cell ablation experiments, argue that the identity of each ray is specified cell-autonomously in the terminal cells of the ray lineages. mab-5 and egl-5, therefore, specify the morphogenetic properties of differentiating cells, without change in cell lineage or apparent cell type. Modifier genes may act upstream of mab-5 and egl-5 to regulate their expression. Alternatively, they may act at the same step in the pathway, as cofactors, or they may be target genes. Target genes could include genes specifying cell recognition and adhesion molecules governing ray organelle assembly.
Down-regulation of Drosophila Egf-r mRNA levels following hyperactivated receptor signaling
Authors: Sturtevant M. A. , O’Neill J. W. , Bier E. 
Published: April 2021

ABSTRACT
Internalization of ligand-receptor complexes is a well-documented mechanism for limiting the duration and magnitude of a signaling event. In the case of the EGF-Receptor (EGF-R), exposure to EGF or TGF-α results in internalization of up to 95% of the surface receptor pool within 5 minutes of exposure to ligand. In this report, we show that levels of Drosophila Egf-r mRNA are strongly down-regulated in epidermal cells likely to have recently undergone high levels of EGF-R signaling. The cells in which Egf-r mRNA levels are down-regulated express the rhomboid gene, which is thought to locally amplify EGF-R signaling. Widespread Egf-r mRNA down-regulation can be induced by ubiquitous expression of rhomboid or by eliminating the Gap1 gene. These results suggest that cells engaged in intense EGF-R/RAS signaling limit the duration of the signal through a combination of short-acting negative feedback mechanisms such as receptor internalization followed by a longer lasting reduction in receptor transcript levels. Control of Egf-r mRNA levels by altering transcription or mRNA stability is a new tier of regulation to be considered in analysis of EGF-R signaling during development.
Mice with targeted disruption of Hoxb-1 fail to form the motor nucleus of the VIIth nerve
Authors: Goddard, Judy M. , Rossel Mireille , Manley Nancy R. , Capecchi Mario R. 
Published: April 2021

ABSTRACT
Mice were generated with targeted disruptions in the hoxb-1 gene. Two separate mutations were created: the first disrupts only the homeodomain and the second inactivates the first exon as well as the homeodomain. The phenotypes associated with these two mutant alleles are indistinguishable in surviving adult mice. The predominant defect in these mutant mice is a failure to form the somatic motor component of the VIIth (facial) nerve, possibly through a failure to specify these neurons. The phenotype of hoxb-1 mutant homozygotes closely resembles features of the clinical profile associated with humans suffering from Bell’s Palsy or Moebius Syndrome. These animals should therefore provide a useful animal model for these human diseases.
Rhombencephalic neural crest segmentation is preserved throughout craniofacial ontogeny
Authors: Köntges Georgy , Lumsden Andrew 
Published: April 2021

ABSTRACT
To investigate the influence of hindbrain segmentation on craniofacial patterning we have studied the long term fate of neural crest (NC) subpopulations of individual rhom-bomeres (r), using quail-chick chimeras. Mapping of all skeletal and muscle connective tissues developing from these small regions revealed several novel features of the cranial neural crest. First, the mandibular arch skeleton has a composite origin in which the proximal elements are r1+r2 derived, whereas more distal ones are exclusively midbrain derived. The most proximal region of the lower jaw is derived from second arch (r4) NC. Second, both the lower jaw and tongue skeleton display an organisation which precisely reflects the rostrocaudal order of segmental crest deployment from the embryonic hindbrain. Third, cryptic intraskeletal boundaries, which do not correspond to anatomical landmarks, form sharply defined interfaces between r1+r2, r4 and r6+r7 crest. Cells that survive the early apoptotic elimination of premigratory NC in r3 and r5 are restricted to tiny contributions within the 2nd arch (r4) skeleton. Fourth, a highly constrained pattern of cranial skeletomuscular connectivity was found that precisely respects the positional origin of its constitutive crest: each rhombomeric population remains coherent throughout ontogeny, forming both the connective tissues of specific muscles and their respective attachment sites onto the neuro- and viscerocranium. Finally, focal clusters of crest cells, confined to the attachment sites of branchial muscles, intrude into the otherwise mesodermal cranial base. In the viscerocranium, an equally strict, rhombomere-specific matching of muscle connective tissues and their attachment sites is found for all branchial and tongue (hypoglossal) muscles. This coherence of segmental crest populations explains how cranial skeleto-muscular pattern can be implemented and conserved despite evolutionary changes in the shapes of skeletal elements.
Kinase-negative mutant epidermal growth factor receptor (EGFR) expression during embryonal stem cell differentiation favours EGFR-independent lineages
Authors: Wu Jie-Xin , Adamson Eileen D. 
Published: April 2021

ABSTRACT
EGF receptors are expressed on most fetal and adult cells but their precise roles are not well known. We previously reported that, in P19 embryonal carcinoma cells, the expression of kinase-negative EGFR inhibits retinoic acid (RA)-induced differentiation to nervous tissue, suggesting that EGFR plays a role in differentiation (J.-X. Wu and E. D. Adamson (1993) Dev. Biol. 159, 208-222). Embryo stem (ES) cells differentiate into a wide range of tissue types after the removal of the cytokine LIF from the culture medium. We demonstrate here that the induction of some early markers of differentiation, tissue-type plasminogen activator (tPA), AFP and keratins 8 and 19 is inhibited, whilst brachyury and myosin are increased, in clones containing kinase-negative mutant EGFR. After an extended period of differentiation, the cell types present in mutant and control cultures differed. Mutant clones produced frequent cardiac and skeletal muscle as the predominant differentiated cell types in vitro; other cells types were sparse or absent. Teratocarcinomas formed by EGFR-Δkinase-expressing ES cells contained frequent skeletal and cardiac muscle as well as apoptotic nuclei, while normal ES cells produced no detectable muscle and less apoptoses. Since mutant differentiated cultures had slower growth rates and increased levels of cell death, we concluded that: (1) inactive EGFR does not allow some cell types to survive and/or proliferate; (2) tissues that do not require EGFR for their survival, development or function predominate in long-term mutant cultures; (3) EGFR activity is not necessary for cardiac and skeletal muscle or endoderm formation and (4) Impaired survival of EGF-dependent lineages leads to preferential selection of muscle in differentiating ES cells.
Neither the homeodomain nor the activation domain of Bicoid is specifically required for its down-regulation by the Torso receptor tyrosine kinase cascade
Authors: Bellaïche Yohanns , Bandyopadhyay Rupa , Desplan Claude , Dostatni Nathalie 
Published: April 2021

ABSTRACT
Bicoid (Bcd) is a maternal morphogen responsible for patterning the head and thorax of the Drosophila embryo. Correct specification of head structure, however, requires the activity of the Torso receptor tyrosine kinase cascade, which also represses expression of Bcd targets at the most anterior tip of the embryo. Here, we investigate the role of both the homeodomain (HD) and the activation domain of Bcd in the anterior repression of its targets. When a Bcd mutant protein whose HD has been replaced by the Gal4 DNA-binding domain is expressed in early embryos, a reporter gene driven by Gal4 DNA-binding sites is first activated in an anterior domain and then repressed from the anterior pole. The down-regulation of Bcd-Gal4 activity requires torso function but does not depend on endogenous bcd activity, indicating that the Bcd protein alone and none of its targets is required to mediate the effect of torso. Functional analysis of a chimeric protein, whose activation domain has been replaced by a generic activation domain, indicates that the activation domain of Bcd is also not specifically required for its downregulation by Torso. We propose that Torso does not affect the ability of Bcd to bind DNA, but instead directs modification of Bcd or of a potential Bcd co-factor, which renders the Bcd protein unable to activate transcription.
Ectopic expression of wingless in imaginal discs interferes with decapentaplegic expression and alters cell determination
Authors: Johnston Laura A. , Schubiger Gerold 
Published: April 2021

ABSTRACT
We have expressed the segment polarity gene wingless (wg) ectopically in imaginal discs to examine its regulation of both ventral patterning and transdetermination. By experimentally manipulating the amount of Wg protein, we show that different thresholds of Wg activity elicit different outcomes, which are mediated by regulation of decapentaplegic (dpp) expression and result in alterations in the expression of homeotic genes. A high level of Wg activity leads to loss of all dorsal pattern elements and the formation of a complete complement of ventral pattern elements on the dorsal side of legs, and is correlated with repression of dpp expression. wg expression in dorsal cells of each disc also leads to dose-dependent transdetermination in those cells in homologous discs such as the labial, antennal and leg, but not in cells of dorsally located discs. When dpp expression is repressed by high levels of Wg, transdetermination does not occur, confirming that dpp participates with wg to induce transdetermination. These and other experiments suggest that dorsal expression of wg alters disc patterning and disc cell determination by modulating the expression of dpp. The dose-dependent effects of wg on dpp expression, ventralization of dorsal cells and transdetermination support a model in which wg functions as a morphogen in imaginal discs.
The Dichaete gene of Drosophila melanogaster encodes a SOX-domain protein required for embryonic segmentation
Authors: Russell Steven R. H. , Sanchez-Soriano Natalia , Wright Charles R. , Ashburner Michael 
Published: April 2021

ABSTRACT
We have cloned and characterised a member of the High Mobility Group superfamily of genes from Drosophila, Sox70D, which is closely related to the mammalian testis determining gene SRY. Sox70D corresponds to the dominant wing mutation Dichaete. Homozygous deletions of the Sox70D gene and recessive lethal Dichaete alleles have a variable embryonic segmentation phenotype. Dichaete is expressed in early embryos in a dynamic pattern reminiscent of gap and pair-rule genes and is required for the appropriate expression of the primary pair-rule genes even skipped, hairy and runt. The molecular nature of Dichaete and its expression pattern during early embryogenesis suggest that the gene plays a key role in early development; the variability in both the segmentation phenotype and the effects on pair-rule gene expression suggests that this role is to support the transcriptional regulation of key developmental genes rather than directly regulate any one of them.
An activated form of type I serine/threonine kinase receptor TARAM-A reveals a specific signalling pathway involved in fish head organiser formation
Authors: Renucci A. , Lemarchandel V. , Rosa F. 
Published: April 2021

ABSTRACT
The role of Transforming Growth Factor β (TGF-β)-related molecules in axis formation and mesoderm patterning in vertebrates has been extensively documented, but the identity and mechanisms of action of the endogenous molecules remained uncertain. In this study, we isolate a novel serine/threonine kinase type I receptor, TARAM-A, expressed during early zebrafish embryogenesis first ubiquitously and then restricted to dorsal mesoderm during gastrulation. A constitutive form of the receptor is able to induce the most anterior dorsal mesoderm rapidly and to confer an anterior organizing activity. By contrast, the wild-type form is only able to induce a local expansion of the dorsal mesoderm. Thus an activated form of TARAM-A is sufficient to induce dorsoanterior structures and TARAM-A may be activated by dorsally localized signals. Our data suggest the existence in fish of a specific TGF-β-related pathway for anterior dorsal mesoderm induction, possibly mediated by TARAM-A and activated at the late blastula stage by localized dorsal determinant.
Zebrafish tinman homolog demarcates the heart field and initiates myocardial differentiation
Authors: Chen Jau-Nian , Fishman Mark C. 
Published: April 2021

ABSTRACT
The fashioning of a vertebrate organ requires integration of decisions of cell fate by individual cells with those that regulate organotypic form. Logical candidates for this role, in an organ such as the heart, are genes that initiate the differentiation process leading to heart muscle and those that define the earliest embryonic heart field, but for neither class are genes defined.
We cloned zebrafish Nkx2.5, a homolog of the tinman homeodomain gene needed for visceral and cardiac mesoderm formation in Drosophila. In the zebrafish, its expression is associated with cardiac precursor cells throughout development, even in the early gastrula, where the level of zebrafish Nkx2.5 is in a gradient which spatially matches the regional propensity of ventral-marginal cells to become heart. Overexpression of Nkx2.5 causes formation of disproportionally larger hearts in otherwise apparently normal embryos. Transplanted cell expressing high levels of Nkx2.5 express cardiac genes even in ectopic locales. Fibroblasts transfected with myc-tagged Nkx2.5 express cardiac genes. These effects require the homeo-domain.
Thus, Nkx2.5 appears to mark the earliest embryonic heart field and to be capable of initiating the cardiogenic differentiation program. Because ectopic cells or transfected fibroblasts do not beat, Nkx2.5 is likely to be but one step in the determination of cardiac myocyte cell fate. Its overexpression increases heart size, perhaps by bringing cells on the edge of the field to a threshold level for initiation of cardiac differentiation.