bluuebunny/crossref_metadata_2025_split huggingface dataset:
Imprinting of Igf2 and H19 from a 130 kb YAC transgene
Authors: Ainscough Justin F-X. , Koide Tsuyoshi , Tada Masako , Barton Sheila , Surani M. Azim 
Published: April 2021

ABSTRACT
A stringent test for imprint control elements is to examine their function at ectopic loci in transgenic experiments. Igf2 and H19 are part of a larger imprinting region and as a first step, we examined these reciprocally imprinted genes in transgenic experiments using a 130 kb YAC clone. After paternal inheritance, H19 was appropriately repressed and Igf2 was expressed, irrespective of copy number or genetic background. After maternal inheritance H19 was consistently expressed, albeit with some variability. The levels of H19 expression per copy of the transgene inversely correlated with Igf2 (-lacZ) expression in cis. The consistent imprinting of H19 from this YAC contrasts with the previously described imprinting of mini-H19 transgenes, which only occurs at multi-copy loci, is inconsistent, and is prone to genetic background effects. We propose a novel model in which silencing of the H19 gene is the default state and its activation after maternal inheritance is the key mechanistic event for imprinting in this region. In addition, in situ analysis of the Igf2-lacZ reporter indicates that additional mesoderm-specific enhancers are present within the YAC clone. No obvious phenotype was detected from the excess gene dosage of H19.
Macrophages induce apoptosis in normal cells in vivo
Authors: Diez-Roux Graciana , Lang Richard A. 
Published: April 2021

ABSTRACT
It is well established that macrophages have a function in scavenging apoptotic bodies from cells undergoing programmed cell death. Here we show that macrophages can also induce apoptosis of normal cells. Using injected toxic liposomes to eliminate macrophages in the anterior chamber of the rat eye, we provide direct evidence that, in vivo, macrophages induce apoptosis in normal vascular endothelial cells during programmed capillary regression. Macrophage elimination resulted in the survival of endothelial cells that normally would die and the persistence of functional capillaries. Furthermore, replacement of eliminated macrophages with bone-marrow-derived macrophages ‘rescued’ lack of capillary regression. Viability of the persistent target cells was demonstrated through their lack of apoptotic morphology, expression of intracellular esterases and synthesis of DNA. These results uncover a new function for macrophages in the remodeling of tissues through the induction of programmed cell death and provide direct evidence of a key role for macrophages in capillary regression.
Ectopic expression of the Drosophila Bam protein eliminates oogenic germline stem cells
Authors: Ohlstein Benjamin , McKearin Dennis 
Published: April 2021

ABSTRACT
The Drosophila germ-cell lineage has emerged as a remark-able system for identifying genes required for changes in cell fate from stem cells into more specialized cells. Previous work indicates that bam expression is necessary for cystoblast differentiation; bam mutant germ cells fail to differentiate, but instead proliferate like stem cells. This paper reports that ectopic expression of bam is sufficient to extinguish stem cell divisions. Heat-induced bam+ expression specifically eliminated oogenic stem cells while somatic stem cell populations were not affected. Together with previous studies of the timing of bam mRNA and protein expression and the state of arrest in bam mutant cells, these data implicate Bam as a direct regulator of the switch from stem cell to cystoblast. Surprisingly, ectopic bam+ had no deleterious consequences for male germline cells suggest-ing that Bam may regulate somewhat different steps of germ-cell development in oogenesis and spermatogenesis. We discuss a model for how bam+ could direct differentiation based on our data (McKearin and Ohlstein, 1995) that Bam protein is essential to assemble part of the germ-cell-specific organelle, the fusome. We propose that fusome biogenesis is an obligate step for cystoblast cell fate and that Bam is the limiting factor for fusome maturation in female germ cells.
cut interacts with Notch and Protein kinase A to regulate egg chamber formation and to maintain germline cyst integrity during Drosophila oogenesis
Authors: Jackson Stephen M. , Blochlinger Karen 
Published: April 2021

ABSTRACT
Communications between the germline and the soma during Drosophila oogenesis have been previously shown to be essential for the formation of egg chambers and to establish polarity in the developing oocyte. In this report, we demonstrate that the function of a somatically expressed gene, cut, is critical for maintaining the structural integrity of germline-derived cells and their arrangement within an egg chamber. Genetic manipulations of cut activity resulted in defective packaging of germline-derived cysts into egg chambers and disintegration of the structural organization of oocyte-nurse cell complexes to generate multinucleate germline-derived cells. We also found that cut interacts genetically with the Notch gene and with the catalytic subunit of Protein kinase A gene during egg chamber morphogenesis. Since cut expression is restricted to the somatic follicle cells and cut mutant germline clones are phenotypically normal, we propose that the defects in the assembly of egg chambers and the changes in germline cell morphology observed in cut mutant egg chambers are the result of altered interactions between follicle cells and germline cells. cut encodes a nuclear protein containing DNA-binding motifs, and we suggest that it participates in inter-cellular communications by regulating the expression of molecules that directly participate in this process.
The Drosophila neurogenic gene big brain, which encodes a membrane-associated protein, acts cell autonomously and can act synergistically with Notch and Delta
Authors: Doherty Dan , Jan Lily Yeh , Jan Yuh Nung 
Published: April 2021

ABSTRACT
In the developing nervous system of Drosophila, cells in each proneural cluster choose between neural and epidermal cell fates. The neurogenic genes mediate the cell-cell communication process whereby one cell adopts the neural cell fate and prevents other cells in the cluster from becoming neural. In the absence of neurogenic gene function, most, if not all of the cells become neural. big brain is a neurogenic gene that encodes a protein with sequence similarity to known channel proteins. It is unique among the neurogenic genes in that previous genetic studies have not revealed any interaction between big brain and the other neurogenic genes. Furthermore, the neural hypertrophy in big brain mutant embryos is less severe than that in embryos mutant for other neurogenic genes.
In this paper, we show by antibody staining that bib is expressed in tissues that give rise to neural precursors and in other tissues that are affected by loss of neurogenic gene function. By immunoelectron microscopy, we found that bib is associated with the plasma membrane and concentrated in apical adherens junctions as well as in small cytoplasmic vesicles. Using mosaic analysis in the adult, we demonstrate that big brain activity is required autonomously in epidermal precursors to prevent neural development. Finally, we demonstrate that ectopically expressed big brain acts synergistically with ectopically expressed Delta and Notch, providing the first evidence that big brain may function by augmenting the activity of the Delta-Notch pathway. These results are consistent with bib acting as a channel protein in proneural cluster cells that adopt the epidermal cell fate, and serving a necessary function in the response of these cells to the lateral inhibition signal.
Cell determination strategies in the Drosophila eye
Authors: Freeman Matthew 
Published: April 2021

ABSTRACT
Cells in the Drosophila eye are determined by inductive signalling. Here I describe a new model of eye development that explains how simple intercellular signals could specify the diverse cell types that constitute the ommatidium. This model arises from the recent observation that the Drosophila homologue of the EGF receptor (DER) is used reiteratively to trigger the differentiation of each of the cell types – successive rounds of DER activation recruit first the photoreceptors, then cone and finally pigment cells. It seems that a cell’s identity is not determined by the specific signal that induces it, but is instead a function of the state of the cell when it receives the signal. DER signalling is activated by the ligand, Spitz, and inhibited by the secreted protein, Argos. Spitz is initially produced by the central cells in the ommatidium and diffuses over a small distance. Argos has a longer range, allowing it to block more distal cells from being activated by low levels of Spitz; I have termed this interplay between a short-range activator and a long-range inhibitor ‘remote inhibition’. Since inductive signalling is common in many organisms and its components have been conserved, it is possible that the logic of signalling may also be conserved.
Regulation of a dpp target gene in the Drosophila embryo
Authors: Rusch Jannette , Levine Michael 
Published: April 2021

ABSTRACT
In Drosophila, two TGF-β growth factors, dpp and screw, function synergistically to subdivide the dorsal ectoderm into two embryonic tissues, the amnioserosa and dorsal epidermis. Previous studies have shown that peak dpp activity is required for the localized expression of zerknüllt (zen), which encodes a homeodomain transcription factor. We present evidence that zen directly activates the amnioserosa-specific expression of a downstream target gene, Race (Related to angiotensin converting enzyme). A 533 bp enhancer from the Race promoter region is shown to mediate selective expression in the amnioserosa, as well as the anterior and posterior midgut rudiments. This enhancer contains three zen protein binding sites, and mutations in these sites virtually abolish the expression of an otherwise normal Race-lacZ fusion gene in the amnioserosa, but not in the gut. Genetic epistasis experiments suggest that zen is not the sole activator of Race, although a hyperactivated form of zen (a zen-VP16 fusion protein) can partially complement reduced levels of dpp activity. These results suggest that dpp regulates multiple transcription factors, which function synergistically to specify the amnioserosa.
Genetic evidence that the retinoid signal is transduced by heterodimeric RXR/RAR functional units during mouse development
Authors: Kastner Philippe , Mark Manuel , Ghyselinck Norbert , Krezel Wojciech , Dupé Valérie , Grondona Jesus M. , Chambon Pierre 
Published: April 2021

ABSTRACT
We describe here the analysis of congenital malformations in compound mutant fetuses bearing null alleles in one RXR (α β or γ) and one RAR (α β or γ) isotype gene. A marked synergy was observed between the effects of mutations in RXRα and RARs, as a large number of developmental defects previously found mainly in RAR single and compound mutants were recapitulated in specific RXRα/RAR compound mutants. Several malformations were seen only in one type of RXRα/RAR mutant combination, whereas others were seen in several types of RXRα/RAR double mutants. No synergy was observed between the effects of mutations of either RXRβ or RXRγ mutations and those of any of the RAR mutations. These genetic data suggest that RXR/RAR heterodimers are the functional units transducing the retinoid signal for a large number of RA-dependent processes, and furthermore, that RXRα is the main RXR implicated in the developmental functions of RARs. The significance of these observations is discussed with respect to the problem of functional specificity and redundancy among retinoid receptors in vivo.
Ectopic application of recombinant BMP-2 and BMP-4 can change patterning of developing chick facial primordia
Authors: Barlow Amanda J. , Francis-West Philippa H. 
Published: April 2021

ABSTRACT
The facial primordia initially consist of buds of undifferentiated mesenchyme, which give rise to a variety of tissues including cartilage, muscle and nerve. These must be arranged in a precise spatial order for correct function. The signals that control facial outgrowth and patterning are largely unknown. The bone morphogenetic proteins Bmp-2 and Bmp-4 are expressed in discrete regions at the distal tips of the early facial primordia suggesting possible roles for BMP-2 and BMP-4 during chick facial development. We show that expression of Bmp-4 and Bmp-2 is correlated with the expression of Msx-1 and Msx-2 and that ectopic application of BMP-2 and BMP-4 can activate Msx-1 and Msx-2 gene expression in the developing facial primordia. We correlate this activation of gene expression with changes in skeletal development. For example, activation of Msx-1 gene expression across the distal tip of the mandibular primordium is associated with an extension of Fgf-4 expression in the epithelium and bifurcation of Meckel’s cartilage. In the maxillary primordium, extension of the normal domain of Msx-1 gene expression is correlated with extended epithelial expression of shh and bifurcation of the palatine bone. We also show that application of BMP-2 can increase cell proliferation of the mandibular primordia. Our data suggest that BMP-2 and BMP-4 are part of a signalling cascade that controls outgrowth and patterning of the facial primordia.
In vivo functional analysis of the Hoxa-1 3′ retinoic acid response element (3′ RARE)
Authors: Dupé Valerie , Davenne Marc , Brocard Jacques , Dollé Pascal , Mark Manuel , Dierich Andrée , Chambon Pierre , Rijli Filippo M. 
Published: April 2021

ABSTRACT
Retinoids are essential for normal development and both deficiency and excess of retinoic acid (RA) are teratogenic. Retinoic acid response elements (RAREs) have been identified in Hox gene promoters suggesting that endogenous retinoids may be involved in the direct control of Hox gene patterning functions. In order to test this hypothesis, we have mutated the Hoxa-1 3′ RARE using the Cre-loxP targeting strategy, and studied its functional role during mouse development. We find that this enhancer plays an important role in the early establishment of the Hoxa-1 anterior expression boundary in the neural plate. This early disturbance in Hoxa-1 activation results in rhombomere and cranial nerve abnormalities reminiscent of those obtained in the Hoxa-1 total knockout, although their severity and penetrance are lower, thus providing strong evidence for direct control of Hox gene function by retinoids during normal development. Interestingly, we also find that the Hoxa-1 expression response to RA treatment is not entirely controlled by the RARE, suggesting the existence of other retinoid-induced factors mediating the Hoxa-1 response to RA and/or the presence of additional RAREs. Interestingly, although the RARE is not required for the spatiotemporal control of colinear expression of the Hoxa genes, it is absolutely required for correct Hoxa-2 expression in rhombomere 5.
In vitro lens transdifferentiation of Xenopus laevis outer cornea induced by Fibroblast Growth Factor (FGF)
Authors: Bosco Luigi , Venturini Giorgio , Willems Daniela 
Published: April 2021

ABSTRACT
It has been shown that lens regeneration from outer cornea of larval Xenopus laevisis dependent on neural retina both in vivo and in tissue culture. The isolated outer cornea cultured in the presence of bovine brain-derived acidic Fibroblast Growth Factor (aFGF) is able to reprogram the differentiation into lens fibers, although this transdifferentiative process is not coupled with the formation of a normally organized lens. The capacity of aFGF to promote lens differentiation from cornea is not linked to its mitogenic activity. The cultured corneal cells can transdifferentiate into lens fibers in the presence of aFGF when DNA replication and cell proliferation are prevented by addition of aphidicolin, a specific inhibitor of DNA polymerase in eukaryotes, to the culture medium.
Induction of the primary dorsalizing center in Xenopus by the Wnt/GSK/β-catenin signaling pathway, but not by Vg1, Activin or Noggin
Authors: Fagotto François , Guger Kathleen , Gumbiner Barry M. 
Published: April 2021

ABSTRACT
The molecular nature of the primary dorsalizing inducing event in Xenopus is controversial and several secreted factors have been proposed as potential candidates: Wnts, Vg1, Activin and Noggin. Recent studies, however, have provided new insight into the activity of the dorsalizing region, called the Nieuwkoop Center. (1) The activity of this dorsalizing center involves an entire signal transduction pathway that requires maternal β-catenin (Heasman, J., Crawford, A., Goldstone, K., Garner-Hamrick, P., Gumbiner, B., McCrea, P., Kintner, C., Noro, C. Y. and Wylie, C. (1994)Cell 79, 791-803). (2) A transcription factor with potent dorsalizing activity, Siamois, is expressed within the Nieuwkoop Center (Lemaire, P., Garrett, N. and Gurdon, J. B. (1995)Cell 81, 85-94). We have used these two properties of the Nieuwkoop Center to evaluate the dorsalizing activity of the four secreted factors Wnt8, Vg1, Activin and Noggin. The requirement for β-catenin was tested by coexpressing a cadherin, which sequesters β-catenin at the cell membrane and specifically blocks its intracellular signaling activity (Fagotto, F., Funayama, N., Glück, U. and Gumbiner, B. M. (1996)J. Cell Biol. 132, 1105-1114). Induction of Siamois expression was detected by RT-PCR. Of the four growth factors, only Wnt was sensitive to inhibition of β-catenin activity and only Wnt could induce Siamois expression. Therefore, Wnt is able to induce a bonafide Nieuwkoop Center, while Vg1, Activin and Noggin probably induce dorsal structures by a different mechanism.
To order the steps in the Nieuwkoop Center signaling cascade, we have tested the relationship between β-catenin and GSK, a serine-threonine kinase that has been implicated in axis formation in a step downstream of Wnt. We found that GSK acts upstream of β-catenin, similar to the order of these components in the Wingless pathway in Drosophila. We have also examined the relationship between the Wnt/β-catenin pathway and Siamois. We show that β-catenin induces expression of Siamois and that the free signaling pool of β-catenin is required for normal expression of endogenous Siamois. We conclude that the sequence of steps in the signaling pathway is Wnt ⊣ GSK ⊣ β-catenin→ Siamois.
Direct neural induction and selective inhibition of mesoderm and epidermis inducers by Xnr3
Authors: Hansen Carin S. , Marion Christopher D. , Steele Kirsten , George Sean , Smith William C. 
Published: April 2021

ABSTRACT
During gastrulation in amphibians, secreted factors from Spemann’s organizer act on dorsal ectoderm to induce the central nervous system. A number of secreted factors produced by Spemann’s organizer have recently been identified. The TGFβ family member Xnr3 is similar in amino acid sequence to the mouse factor nodal and is expressed in a restricted group of cells in the superficial layer of Spemann’s organizer. Xnr3, unlike the related factors nodal, Xnr1 and Xnr2, lacks mesoderm-inducing activity. We report here that Xnr3 can directly induce neural tissue in Xenopus ectoderm explants (animal caps). Injection of animal caps with either Xnr3 RNA or plasmids induces the expression of the pan-neural genes NCAM and nrp1, as well as the anterior neural marker Cpl1. A growing body of evidence suggests that neural induction in Xenopus proceeds as the default in the absence of epidermis inducers. The best candidates for the endogenous epidermis inducers are BMP-4 and BMP-7. The neural inducing activity of Xnr3 can be inhibited by overexpression of BMP-4, as has been observed with the neural inducers noggin, chordin and follistatin. Furthermore, Xnr3 can block mesoderm induction by BMP-4 and activin, but not by Xnr2. The structural basis underlying the divergent activities of Xnr2 and Xnr3 was analyzed using site-directed mutagenesis. Mutations introduced to the conserved cysteine residues characteristic of the TGFβ family were found to inactivate Xnr2, but not Xnr3. The most unique feature of Xnr3 is the absence of a conserved cysteine at the C terminus of the protein. This feature distinguishes Xnr3 from other TGFβ family members, including Xnr2. However, we observed that changing the C terminus of Xnr3 to more closely resemble other TGFβ family members did not significantly alter its activity, suggesting that other structural features of Xnr3 distinguish its biological activity from Xnr2.
Coordinate actions of BMPs, Wnts, Shh and Noggin mediate patterning of the dorsal somite
Authors: Marcelle Christophe , Stark Michael R. , Bronner-Fraser Marianne 
Published: April 2021

ABSTRACT
Shortly after their formation, somites of vertebrate embryos differentiate along the dorsoventral axis into sclerotome, myotome and dermomyotome. The dermomyotome is then patterned along its mediolateral axis into medial, central and lateral compartments, which contain progenitors of epaxial muscle, dermis and hypaxial muscle, respectively. Here, we used Wnt-11 as a molecular marker for the medial compartment of dermomyotome (the ‘medial lip’) to demonstrate that BMP in the dorsal neural tube indirectly induces formation of the medial lip by up-regulating Wnt-1 and Wnt-3a (but not Wnt-4) expression in the neural tube. Noggin in the dorsal somite may inhibit the direct action of BMP on this tissue. Wnt-11 induction is antagonized by Sonic Hedgehog, secreted by the notochord and the floor plate. Together, our results show that the coordinated actions of the dorsal neural tube (via BMP and Wnts), the ventral neural tube/notochord (via Shh) and the somite itself (via noggin) mediates patterning of the dorsal compartment of the somite.
Overexpression of FGF-2 modulates fiber cell differentiation and survival in the mouse lens
Authors: Stolen Craig M. , Jackson Mark W. , Griep Anne E. 
Published: April 2021

ABSTRACT
During mammalian embryogenesis, the ocular lens forms through a temporally and spatially regulated pattern of differentiation which is thought to be coordinated at least in part by the FGF-1 and FGF-2 members of the fibroblast growth factor (FGF) family. Previous transgenic experiments in which FGF-1 or dominant negative FGF receptors were overexpressed in the lens indicated that FGF-1 could induce differentiation while differentiated lens cells rely upon FGF signaling for their survival. In this study, we asked if the 17.5 kDa FGF-2 protein was capable of inducing differentiation of lens cells in transgenic mice. Unexpectedly, differentiation was inhibited by lens-specific expression of a transgene encoding a secreted form of the 17.5 kDa bovine FGF-2 protein under the transcriptional control of the murine αA-crystallin promoter (αAIgFGF-2 transgenic mice). To address the possibility that FGF-2 functions as a modulator of fiber cell survival, αAIgFGF-2 transgenic mice were crossed to transgenic mice exhibiting extensive apoptosis in the lens due to the functional inactivation of the retinoblastoma protein (αAE7 transgenic mice). The level of apoptosis in the lenses of double trans-genic mice was substantially reduced as compared to the level in lenses from αAE7 only mice. These studies indicate that FGF-2 can act as a modulator of the later stages of differentiation including fiber cell survival. Additionally, they imply that control of lens development by FGFs is a complex process in which FGF-1 and FGF-2 play distinct roles.