bluuebunny/crossref_metadata_2025_split huggingface dataset:
Identification of separate slow and fast muscle precursor cells in vivo, prior to somite formation
Authors: Devoto Stephen H. , Melançon Ellie , Eisen Judith S. , Westerfield Monte 
Published: April 2021

ABSTRACT
We have examined the development of specific muscle fiber types in zebrafish axial muscle by labeling myogenic precursor cells with vital fluorescent dyes and following their subsequent differentiation and fate. Two populations of muscle precursors, medial and lateral, can be distinguished in the segmental plate by position, morphology and gene expression. The medial cells, known as adaxial cells, are large, cuboidal cells adjacent to the notochord that express myoD. Surprisingly, after somite formation, they migrate radially away from the notochord, becoming a superficial layer of muscle cells. A subset of adaxial cells develop into engrailed-expressing muscle pioneers. Adaxial cells differentiate into slow muscle fibers of the adult fish. We have named the lateral population of cells in the segmental plate, lateral presomitic cells. They are smaller, more irregularly shaped and separated from the notochord by adaxial cells; they do not express myoD until after somite formation. Lateral presomitic cells remain deep in the myotome and they differentiate into fast muscle fibers. Thus, slow and fast muscle fiber types in zebrafish axial muscle arise from distinct populations of cells in the segmental plate that develop in different cellular environments and display distinct behaviors.
Regulation and function of transcription factor GATA-1 during red blood cell differentiation
Authors: Briegel Karoline , Bartunek Petr , Stengl Gabi , Lim Kim-Chew , Beug Hartmut , Engel James Douglas , Zenke Martin 
Published: April 2021

ABSTRACT
The tissue-specific transcription factor GATA-1 is a key regulator of red blood cell differentiation. One seemingly contradictory aspect of GATA-1 function is that, while it is abundant in erythroid progenitor cells prior to the onset of overt differentiation, it does not significantly activate known GATA-1 target genes in those cells. To investigate the mechanisms underlying GATA-1 function during the transition from early to late erythropoiesis, we have examined its expression and activity in normal avian erythroid progenitor cells before and after induction of differentiation. In these primary progenitor cells, GATA-1 protein was predominantly located in the cytoplasm, while induction of differentiation caused its rapid relocalization to the nucleus, suggesting that nuclear translocation constitutes an important regulatory step in GATA-1 activation. As an alternative way of addressing the same question, we also ectopically expressed a GATA-1/estrogen receptor fusion protein (GATA-1/ER) in red blood cell progenitors, where nuclear translocation of, and transcriptional activation by, this hybrid factor are conditionally controlled by estrogen. We found that hormone-activated GATA-1/ER protein accelerated red blood cell differentiation, and concomitantly suppressed cell proliferation. These phenotypic effects were accompanied by a simultaneous suppression of c-myb and GATA-2 transcription, two genes thought to be involved in the proliferative capacity of hematopoietic progenitor cells. Thus, GATA-1 appears to promote differentiation in committed erythroid progenitor cells both by inducing differentiation-specific genes and by simultaneously suppressing genes involved in cell proliferation.
The chick limbless mutation causes abnormalities in limb bud dorsal-ventral patterning: implications for the mechanism of apical ridge formation
Authors: Grieshammer Uta , Minowada George , Pisenti Jacqueline M. , Abbott Ursula K. , Martin Gail R. 
Published: April 2021

ABSTRACT
In chick embryos homozygous for the limbless mutation, limb bud outgrowth is initiated, but a morphologically distinct apical ridge does not develop and limbs do not form. Here we report the results of an analysis of gene expression in limbless mutant limb buds. Fgf4, Fgf8, Bmp2 and Msx2, genes that are expressed in the apical ridge of normal limb buds, are not expressed in the mutant limb bud ectoderm, providing molecular support for the hypothesis that limb development fails in the limbless embryo because of the inability of the ectoderm to form a functional ridge. Moreover, Fgf8 expression is not detected in the ectoderm of the prospective limb territory or the early limb bud of limbless embryos. Since the early stages of limb bud outgrowth occur normally in the mutant embryos, this indicates that FGF8 is not required to promote initial limb bud outgrowth. In the absence of FGF8, Shh is also not expressed in the mutant limb buds, although its expression can be induced by application of FGF8-soaked beads. These observations support the hypothesis that Fgf8 is required for the induction of Shh expression during normal limb development. Bmp2 expression was also not detected in mutant limb mesoderm, consistent with the hypothesis that SHH induces its expression. In contrast, SHH is not required for the induction of Hoxd11 or Hoxd13 expression, since expression of both these genes was detected in the mutant limb buds. Thus, some aspects of mesoderm A-P patterning can occur in the absence of SHH and factors normally expressed in the apical ridge. Intriguingly, mutant limbs rescued by local application of FGF displayed a dorsalized feather pattern. Furthermore, the expression of Wnt7a, Lmx1 and En1, genes involved in limb D-V patterning, was found to be abnormal in mutant limb buds. These data suggest that D-V patterning and apical ridge formation are linked, since they show that the limbless mutation affects both processes. We present a model that explains the potential link between D-V positional information and apical ridge formation, and discuss the possible function of the limbless gene in terms of this model.
Developmental territories created by mutual antagonism between Wingless and Decapentaplegic
Authors: Theisen Heidi , Haerry Theodor E. , O’Connor Michael B. , Marsh J. Lawrence 
Published: April 2021

ABSTRACT
Drosophila appendages develop from imaginal discs which become subdivided into distinct regions during normal pat- terning. At least 3 axes of asymmetry are required to produce a chiral appendage such as a leg. The A/P com- partments provide one axis of asymmetry in all discs. In leg and antennal discs, the anterior compartment becomes asymmetric in the D/V axis with decapentaplegic (dpp) expression defining dorsal anterior leg, and wingless (wg) expression defining ventral anterior leg. However, unlike wing discs, no D/V compartment has been demonstrated in legs or antennae. How are the dorsal anterior and ventral anterior territories defined and maintained? Here we show that wg inhibits dpp expression and dpp inhibits wg expression in leg and eye/antennal discs. This mutual repression provides a mechanism for maintaining separate regions of wg and dpp expression in a developing field. We propose the term ‘territory’ to describe regions of cells that are under the domineering influence of a particular morphogen. Territories differ from compartments in that they are not defined by lineage but are dynamically main- tained by continuous morphogen signaling. We propose that the anterior compartment of the leg disc is divided into dorsal and ventral territories by the mutual antagonism between WG and DPP signaling.
The human β-globin locus control region confers an early embryonic erythroid-specific expression pattern to a basic promoter driving the bacterial lacZ gene
Authors: Tewari Rita , Gillemans Nynke , Harper Alex , Wijgerde Mark , Zafarana Gaetano , Drabek Dubravka , Grosveld Frank , Philipsen Sjaak 
Published: April 2021

ABSTRACT
The β-globin locus control region (LCR) is contained on a 20 kb DNA fragment and is characterized by the presence of five DNaseI hypersensitive sites in erythroid cells, termed 5′HS1-5. A fully active 6.5 kb version of the LCR, called the μLCR, has been described. Expression of the β-like globin genes is absolutely dependent on the presence of the LCR. The developmental expression pattern of the genes in the cluster is achieved through competition of the promoters for the activating function of the LCR. Transgenic mice experiments suggest that subtle changes in the transcription factor environment lead to the successive silencing of the embryonic ε-globin and fetal γ-globin promoters, resulting in the almost exclusive transcription of the β-globin gene in adult ery-thropoiesis. In this paper, we have asked the question whether the LCR and its individual hypersensitive sites 5′HS1-4 can activate a basic promoter in the absence of any other globin sequences. We have employed a minimal promoter derived from the mouse Hsp68 gene driving the bacterial β-galactosidase (lacZ) gene. The results show that the μLCR and 5′HS3 direct erythroid-specific, embryonic expression of this construct, while 5′HS1, 5′HS2 and 5′HS4 are inactive at any stage of development. Expression of the μLCR and 5′HS3 transgenes is repressed during fetal stages of development. The trans-genes are in an inactive chromatin conformation and the lacZ gene is not transcribed, as shown by in situ hybrid-ization. These data are compatible with the hypothesis that the LCR requires the presence of an active promoter to adopt an open chromatin conformation and with models proposing progressive heterochromatization during embryogenesis. The results suggest that the presence of a β-globin gene is required for LCR function as conditions become more stringent during development.
The Drosophila decapentaplegic and short gastrulation genes function antagonistically during adult wing vein development
Authors: Yu Kweon , Sturtevant Mark A. , Biehs Brian , François Vincent , Padgett Richard W. , Blackman Ronald K. , Bier Ethan 
Published: April 2021

ABSTRACT
TGF-β-related signaling pathways play diverse roles during vertebrate and invertebrate development. A common mechanism for regulating the activity of TGF-β family members is inhibition by extracellular antagonists. Recently, the Drosophila short gastrulation (sog) gene was shown to encode a predicted diffusible factor which antagonizes signaling mediated by the TGF-β-like Decapenta-plegic (Dpp) pathway in the early blastoderm embryo. sog and dpp, which are among the earliest zygotic genes to be activated, are expressed in complementary dorsal-ventral domains. The opposing actions of sog and dpp in the early embryo have been highly conserved during evolution as their vertebrate counterparts, chordin and BMP-4, function homologously to define neural versus non-neural ectoderm in Xenopus. Here we exploit the genetically sensitive adult wing vein pattern to investigate the generality of the antagonistic relationship between sog and dpp. We show that dpp is expressed in vein primordia during pupal wing development and functions to promote vein formation. In contrast, sog is expressed in complementary intervein cells and suppresses vein formation. sog and dpp function during the same phenocritical periods (i.e. 16-28 hours after pupariation) to influence the vein versus intervein cell fate choice. The conflicting activities of dpp and sog are also revealed by antagonistic dosage-sensitive interactions between these two genes during vein development. Analysis of vein and intervein marker expression in dpp and sog mutant wings suggests that dpp promotes vein fates indirectly by activating the vein gene rhomboid (rho), and that sog functions by blocking an autoactivating Dpp feedback loop. These data support the view that Sog is a dedicated Dpp antagonist.
The Drosophila Enhancer of zeste gene encodes a chromosomal protein: examination of wild-type and mutant protein distribution
Authors: Carrington Elizabeth A. , Jones Richard S. 
Published: April 2021

ABSTRACT
The Drosophila Enhancer of zeste [E(z)] gene is a member of the Polycomb-group and, as such, is involved in maintaining the transcriptional repression of the homeotic genes of the Antennapedia (ANT-C) and bithorax (BX-C) complexes. It has been proposed that Polycomb-group (Pc- G)-mediated silencing requires the formation of heteromeric protein complexes which modify the chromatin structure of target genes. We describe the in vivo distribution of the E(Z) protein and show it to be ubiquitously present in embryonic and larval nuclei. In salivary gland polytenized nuclei, the identifiable E(Z) chromosome binding sites are a subset of those described for other Polycomb-group proteins, suggesting that E(Z) may also participate in Polycomb-group complexes. E(Z) binds to chromosomes in a DNA sequence-dependent manner, as illustrated by the creation of a new E(Z)-binding site at the location of a P element reporter construct that previously has been shown to contain a Polycomb response element (PRE). We also present the sequences of one null and three temperature-sensitive E(z) alleles, describe the effects these mutations have on the in vivo distribution of E(Z) protein and discuss their implications concerning putative functional domains. Finally, we describe the effect a trithorax mutation has on E(Z) chromosome binding.
lin-12 and glp-1 are required zygotically for early embryonic cellular interactions and are regulated by maternal GLP-1 signaling in Caenorhabditis elegans
Authors: Moskowitz Ivan P. G. , Rothman Joel H. 
Published: April 2021

ABSTRACT
Cell-cell interactions mediated by LIN-12 and GLP-1, members of the LNG (LIN-12, Notch, GLP-1) family of receptors, are required to specify numerous cell fates during development of the nematode Caenorhabditis elegans. Maternally expressed GLP-1 participates in two of at least four sequential inductive interactions that specify the fates of early embryonic descendants of the AB founder cell. We report that GLP-1 and LIN-12, and apparently their ligand, LAG-2, as well as a downstream component, LAG-1, are required in the latter two inductions. We find that LAG-2 is expressed in the signaling cells and LIN-12 is expressed in cells receiving the inductions, consistent with their proposed roles as ligand and receptor, respectively.
Furthermore, we report that maternal GLP-1 activity is required (1) to repress early zygotic lag-2 expression and (2) to activate zygotic lin-12 expression in the early embryo. The patterning of both receptor and ligand expression by maternal GLP-1 signaling establishes competence for the zygotic LNG-mediated cellular interactions and localizes these interactions to the appropriate cells. We propose that activation of maternal GLP-1 regulates zygotic lin-12 and lag-2 expression by a regulatory mechanism analogous to that described for the post-embryonic gonad.
cdh-3, a gene encoding a member of the cadherin superfamily, functions in epithelial cell morphogenesis in Caenorhabditis elegans
Authors: Pettitt Jonathan , Wood William B. , Plasterk Ronald H. A. 
Published: April 2021

ABSTRACT
Several genes that encode members of the cadherin super-family have been identified in Caenorhabditis elegans. Based on the roles of cadherins in vertebrates and Drosophila, it is expected that they function in the control of epithelial morphogenesis, an event which is poorly understood at the molecular level in C. elegans. Reporter genes under the control of upstream sequences from one of these genes, cdh-3, are expressed in developing epithelial cells, but also in a number of neuroectodermal cells that extend processes along some of these epithelial cells. We generated a loss-of-function mutation in cdh-3 by transposon-mediated deletion mutagenesis. This mutation affects the morphogenesis of a single cell, hyp10, which forms the tip of the nematode tail. The lack of detectable defects associated with the other cells expressing cdh-3 reporter constructs hints at the existence of other genes that can compensate for cdh-3 loss of function.
Function of the Drosophila POU domain transcription factor Drifter as an upstream regulator of Breathless receptor tyrosine kinase expression in developing trachea
Authors: Anderson Michael G. , Certel Sarah J. , Certel Kaan , Lee Tzumin , Montell Denise J. , Johnson Wayne A. 
Published: April 2021

ABSTRACT
Organogenesis of the Drosophila tracheal system involves extensive directed cell migrations leading to a stereotypic series of interconnected tubules. Although numerous gene products have been shown to be essential for tracheal morphogenesis, direct functional relationships between participants have not been previously established. Both the breathless gene, encoding a Drosophila fibroblast growth factor receptor tyrosine kinase homologue, and the POU-domain transcription factor gene, drifter, are expressed in all tracheal cells and are essential for directed cell migrations. We demonstrate here that ubiquitously expressed Breathless protein under control of a heterologous heat-shock promoter is able to rescue the severely disrupted tracheal phenotype associated with drifter loss-of-function mutations. In the absence of Drifter function, breathless expression is initiated normally but transcript levels fall drastically to undetectable levels as tracheal differentiation proceeds. In addition, breathless regulatory DNA contains seven high affinity Drifter binding sites similar to previously identified Drifter recognition elements. These results suggest that the Drifter protein, which maintains its own expression through a tracheal-specific autoregulatory enhancer, is not necessary for initiation of breathless expression but functions as a direct transcriptional regulator necessary for maintenance of breathless transcripts at high levels during tracheal cell migration. This example of a mechanism for maintenance of a committed cell fate offers a model for understanding how essential gene activities can be maintained throughout organogenesis.
Functional cooperation between the non-paralogous genes Hoxa-10 and Hoxd-11 in the developing forelimb and axial skeleton
Authors: Favier Bertrand , Rijli Filippo M. , Fromental-Ramain Catherine , Fraulob Valérie , Chambon Pierre , Dollé Pascal 
Published: April 2021

ABSTRACT
The Abdominal B-related Hoxa-10 gene displays similar expression patterns in the differentiating forelimbs and hindlimbs of the mouse, with preferential expression around the humeral and femoral cartilages and more diffuse expression in distal regions. We found that a targeted disruption of Hoxa-10 has almost no effect in the forelimbs, while it affects the proximal hindlimb skeleton. The alterations were located along the dorsolateral side of the femur (labium laterale), with an enlargement and distal shift of the third trochanter, a misshapen lateral knee sesamoid, a supernumerary ‘ligament’ connecting these structures and an occasional duplication of the femoral trochlea. Some Hoxa-10−/− mutant mice developed severe degenerative alterations of the knee articulation upon ageing. Viable Hoxa-10/Hoxd-11 double mutant mice were produced by genetic intercrosses. The compound mutation resulted in synergistic forelimb phenotypic alterations, consisting of: (i) an exacerbation of Hoxd-11−/− phenotypic traits in the carpal and digital region, e.g. more pronounced truncations of the ulna styloid, pyramidal and pisiform bones and of some metacarpal and phalangeal bones and (ii) marked alterations in a more proximal region which is nearly unaffected in Hoxd-11−/− single mutants; the entire radius and ulna were truncated and thickened, with deformations of the ulna proximal extremity. Thus, functional redundancy can occur even between non-paralogous Abdominal B-related Hox genes. The double Hoxa-10/Hoxd-11 mutation also conferred full penetrance to the sacral and caudal vertebrae transforma-tions which are ∽50% penetrant in Hoxd-11−/− single mutants, revealing that functional cooperation can also occur between non-paralogous Hox gene products in axial skeleton patterning.
Specific and redundant functions of the paralogous Hoxa-9 and Hoxd-9 genes in forelimb and axial skeleton patterning
Authors: Fromental-Ramain Catherine , Warot Xavier , Lakkaraju Sudhakar , Favier Bertrand , Haack Herbert , Birling Céline , Dierich Andrée , Dollé Pascal , Chambon Pierre 
Published: April 2021

ABSTRACT
Using gene targeting, we have produced mice with a disruption of Hoxa-9 or Hoxd-9, two paralogous Abdominal B-related genes. During embryogenesis, these genes are expressed in limb buds and along the vertebral axis with anterior expression boundaries at the level of prevertebra #20 for Hoxa-9 and #23 for Hoxd-9. Skeletal analysis revealed homeotic transformations corresponding to ante-riorisations of vertebrae #21 to #25 (L1 to L5) in the lumbar region of Hoxa-9−/− mutants; vertebrae #23 to #25 (L3 to L5) in the lumbar region together with vertebrae #28, #30 and #31 (S2, S4 and Ca1) in the sacrum and tail were ante-riorized in Hoxd-9−/− mutants. Thus, anteriorisation of vertebrae #23 to #25 were common to both phenotypes. Subtle forelimb (but not hindlimb) defects, corresponding to a reduction of the humerus length and malformation of its deltoid crest, were also observed in Hoxd-9−/−, but not in Hoxa-9−/−, mutant mice. By intercrosses between these two lines of mutant mice, we have produced Hoxa-9/Hoxd-9 double mutants which exhibit synergistic limb and axial malformations consisting of: (i) an increase of penetrance and expressivity of abnormalities present in the single mutants, and (ii) novel limb alterations at the level of the forelimb stylopod and additional axial skeleton transfor-mations. These observations demonstrate that the two paralogous genes Hoxa-9 and Hoxd-9 have both specific and redundant functions in lumbosacral axial skeleton pat-terning and in limb morphogenesis at the stylopodal level. Taken all together, the present and previously reported results show that disruption of different Hox genes can produce similar vertebral transformations, thus support-ing a combinatorial code model for specification of vertebral identity by Hox genes.
Interactions between rhombomeres modulate Krox-20 and follistatin expression in the chick embryo hindbrain
Authors: Graham Anthony , Lumsden Andrew 
Published: April 2021

ABSTRACT
The rhombomeres of the embryonic hindbrain display compartment properties, including cell lineage restriction, genetic definition and modular anatomical phenotype. Consistent with the idea that rhombomeres are autonomous developmental units, previous studies have shown that certain aspects of rhombomere phenotype are determined early, at the time of rhombomere formation. By contrast, the apoptotic depletion of neural crest from rhombomeres 3 and 5 is due to an interaction with their neighbouring rhombomeres, involving the signalling molecule Bmp4. In this paper, we have examined whether inter-rhombomere interactions control further aspects of rhombomere phenotype. We find that the expression of Krox-20 and the repression of follistatin in r3 is dependent upon neighbour interaction, whereas these genes are expressed autonomously in r5. We further demonstrate that modulation of Krox-20 and follistatin expression is not dependent on Bmp4, indicating the existence of multiple pathways of interaction between adjacent rhombomeres. We also show that, although some phenotypic aspects of r3 are controlled by neighbour interactions, the axial identity of the segment is intrinsically determined.