bluuebunny/crossref_metadata_2025_split huggingface dataset:
Aggregation chimeras demonstrate that the primary defect responsible for aganglionic megacolon in lethal spotted mice is not neuroblast autonomous
Authors: Kapur Raj P. , Yost Cynthia , Palmiter Richard D. 
Published: April 2021

ABSTRACT
The lethal spotted (ls) mouse has been used as a model for the human disorder Hirschsprung’s disease, because as in the latter condition, ls/ls homozygotes are born without ganglion cells in their terminal colons and, without surgical intervention, die early as a consequence of intestinal obstruction. Previous studies have led to the conclusion that hereditary aganglionosis in ls/ls mice occurs because neural crest-derived enteric neuroblasts fail to colonize the distal large intestine during embryogenesis, perhaps due to a primary defect in non-neuroblastic mesenchyme rather than migrating neuroblasts themselves. In this investigation, the latter issue was addressed directly, in vivo, by comparing the distributions of ls/ls and wild-type neurons in aggregation chimeras. Expression of a transgene, D H-nlacZ, in enteric neurons derived from the vagal neural crest, was used as a marker for ls/ls enteric neurons in chimeric mice. In these animals, when greater than 20% of the cells were wild-type, the ls/ls phenotype was rescued; such mice were neither spotted nor aganglionic. In addition, these ‘rescued’ mice had mixtures of ls/ls and wildtype neurons throughout their gastrointestinal systems including distal rectum. In contrast, mice with smaller relative numbers of wild-type cells exhibited the classic ls/ls phenotype. The aganglionic terminal bowel of the latter mice contained neither ls/ls nor wild-type neurons. These results confirm that the primary defect in ls/ls embryos is not autonomous to enteric neuroblasts, but instead exists in the non-neuroblastic mesenchyme of the large intestine.
Regulation of development and differentiation by the extracellular matrix
Authors: Adams Josephine C. , Watt Fiona M. 
Published: April 2021

Abstract
Introduction
Evidence that cell-ECM interactions regulate
differentiation and development
Developmental mutations
Experimental perturbation of embryonic development
Cell and organ cultures
Regulatory mechanisms
ECM diversity
Interactions of growth factors with the ECM
ECM receptors
Non-integrin receptors
Integrins
Signal transduction
Cytoskeleton
Second messengers
‘ECM-response elements’
Conclusion
Regional repression of a Drosophila POU box gene in the endoderm involves inductive interactions between germ layers
Authors: Affolter Markus , Walldorf Uwe , Kloter Urs , Schier Alexander F. , Gehring Walter J. 
Published: April 2021

Abstract
An induction process occurring between the mesodermal and the endodermal germ layers has recently been described in the regulation of the Drosophila homeotic gene labial (lab). We report here that proper spatial regulation of the Drosophila POU box gene pdm-1 products also involves interaction between these two germ layers. pdm-1 transcripts are initially present in both the anterior and the posterior endodermal midgut primordia. Upon fusion of the two primordia, transcripts disappear from two regions in the endoderm, a central domain and an anterior domain. The anterior repression domain of pdm-1 is independent of the expression of known homeotic genes and genes encoding secreted signalling molecules in the visceral mesoderm, both for its positioning and its repression. Repression in the central domain requires both the homeotic gene Ultrabithorax (Ubx) and the decapentaplegic (dpp) gene, which encodes a secreted protein. Both of these genes are also required for lab induction. However, the analysis of pdm-1 expression in various mutant backgrounds indicates that the regulation of lab and pdm-1 across germ layers is controlled by different genetic cascades. Our study indicates that dpp is not the signal that dictates central pdm-1 repression across germ layers and suggests that in the same midgut region, different signalling pathways result in the differential activation or repression of potential transcription factors.
Cross regulation of decapentaplegic and Ultrabithorax transcription in the embryonic visceral mesoderm of Drosophila
Authors: Hursh Deborah A. , Padgett Richard W. , Gelbart William M. 
Published: April 2021

Abstract
The Drosophila decapentaplegic gene (dpp) encodes a TGF-β family member involved in signal transduction during embryonic midgut formation. The shortvein (shv) class of cis-regulatory dpp mutants disrupt expression in parasegments 4 and 7 (ps4 and ps7) of the embryonic visceral mesoderm (VM) surrounding the gut and cause abnormalities in gut morphogenesis. We demonstrate that cis-regulatory elements directing expression in ps4 and ps7 are separable and identify DNA fragments that generate ps4 and ps7 expression patterns using reporter gene constructs. dpp reporter gene expression in both ps4 and ps7 is autoregulated as it requires endogenous dpp+ activity. Reporter gene ps7 expression requires the wild-type action of Ultra bithorax (Ubx), and abdominal-A. Furthermore, the expression of certain Ubx reporter genes is coincident with dpp in the VM. Both the mis-expression of Ubx reporter genes in the developing gastric caecae at ps4 and its normal expression in ps7 are dependent upon endogenous dpp+ activity. We conclude that dpp both responds to and regulates Ubx in ps7 of the visceral mesoderm and that Ubx autoregulation within this tissue may be indirect as it requires more components than have previously been thought.
Analysis of genetic mosaics in developing and adult Drosophila tissues
Authors: Xu Tian , Rubin Gerald M. 
Published: April 2021

Abstract
We have constructed a series of strains to facilitate the generation and analysis of clones of genetically distinct cells in developing and adult tissues of Drosophila. Each of these strains carries an FRT element, the target for the yeast FLP recombinase, near the base of a major chromosome arm, as well as a gratuitous cellautonomous marker. Novel markers that carry epitope tags and that are localized to either the cell nucleus or cell membrane have been generated. As a demonstration of how these strains can be used to study a particular gene, we have analyzed the developmental role of the Drosophila EGF receptor homolog. Moreover, we have shown that these strains can be utilized to identify new mutations in mosaic animals in an efficient and unbiased way, thereby providing an unprecedented opportunity to perform systematic genetic screens for mutations affecting many biological processes.
Lithium perturbation and goosecoid expression identify a dorsal specification pathway in the pregastrula zebrafish
Authors: Stachel Scott E. , Grunwald David J. , Myers Paul Z. 
Published: April 2021

Abstract
The zebrafish dorsoventral axis can first be distin-guished at gastrulation, upon formation of the embry-onic shield, the site of the organizer. We have asked whether the shield is specified before gastrulation. First, we show that brief exposure of premidblastula embryos to lithium, which is known to shut down the phospho-inositol signaling pathway, produces excessive shield formation and extreme hyper-dorsal development. Second, we show that the zebrafish goosecoid homeobox gene is activated at or just after the midblastula in a localized domain of cells that subsequently populate the most anterior region of the incipient shield and axial hypoblast. goosecoid expression is elevated and radialized by early lithium treatment, suggesting that goosec -oid plays a role in establishing the organizer and shield. Our results demonstrate that the zebrafish dorsal axis is signaled by a pathway initiated in the cleavage-stage embryo. Furthermore, they provide novel insights into anterior morphogenesis.
Chimeric analysis of T (Brachyury) gene function
Authors: Wilson Valerie , Rashbass Penny , Beddington Rosa S. P. 
Published: April 2021

Abstract
To investigate T(Brachyury) gene function, a chimeric analysis of midgestation (9.5–11.5 days post coitum) embryos has been performed. Embryonic stem (ES) cell lines homozygous or heterozygous for the T gene have been introduced into wild-type host embryos by blasto-cyst injection, and the resulting chimeras scored for morphological abnormality and extent of colonization by T/T cells. As observed previously in earlier stage chimeras (Rashbass, P., Cooke, L. A., Herrmann, B. G. and Beddington, R. S. P. (1991) Nature 353, 348-350), 9.5-11.5 dpc T/T +/+ chimeras exhibit many morpho-logical features of intact T/T mutants. In addition, a dramatic bias of T/T cells towards caudal regions (such as tail and allantois) was observed in all chimeras tested. This is likely to result from accumulation of nascent T/T mesoderm cells with time near the primitive streak, possibly because of altered migration or adhesion proper-ties. T/+ cells colonized rostral regions efficiently, but a slight bias towards the distal end of the tail was still evident. No such bias was observed in control chimeras. The presence of T/T cells in the allantois resulted in its failure to form a correct placental connection and thus arrested later development. In contrast, chimeras in which T/T cells were present predominantly in the tail developed normally but exhibited severe tail abnormalities such as foreshortening, branching and haemorrhagic cavities. Moreover, in these embryos, much higher levels of chimerism were present in the distal end of the tail than in younger (9.5 dpc) embryos. Later in gestation, such abnormal tails probably degenerated, giving rise to neonates with absent or severely abnormal tails but no evidence of chimerism. In situ analysis of T expression in the tail reveals that normally T is expressed highly in the tailbud (the growing portion of the tail) during its elongation between 9.5 and 11.5 dpc. Thus, evidence both from chimeras and from T expression in the tail suggest that T may play a role in the correct deployment of cells emerging from the tailbud.
Isolation and characterisation of murine homologues of the Drosophila seven in absentia gene (sina)
Authors: Della Neil G. , Senior Paul V. , Bowtell David D. L. 
Published: April 2021

Abstract
The seven in absentia gene (sina) is required for formation of the R7 photoreceptor cell in the developing eye of Drosophila melanogaster. The sina protein contains a putative zinc finger domain and localises to the cell nucleus in Drosophila. We report here the identification of a family of genes in the mouse (designated Siah) with extensive sequence homology to Drosophila sina. The Siah genes fall into two main groups: Siah-1, which consists of four closely related members, two of which appear to be functional, and Siah-2, which contains a single functional member. The predicted Siah proteins show an unusually high degree of conservation with sina over the majority of their lengths, diverging significantly only at their amino terminal ends. The Siah-1 and Siah-2 genes are widely expressed at a low level in the embryo and adult. Analysis of Siah-2 by hybridisation histo-chemistry shows that it is expressed at a higher level in a restricted number of sites during development, including the olfactory epithelium, retina, forebrain and pro-liferating cartilage of developing bone. The striking degree of sequence homology observed between the Drosophila and murine genes implies strong conservation pressure on the Siah genes and suggests that they play a significant role in vertebrate development.
Ventral spinal cord inhibition of neurite outgrowth from embryonic rat dorsal root ganglia
Authors: Fitzgerald Maria , Kwiat Geoffrey C. , Middleton Jacqueta , Pini Adrian 
Published: April 2021

Abstract
Organotypic culture of embryonic rat lumbar spinal cord and dorsal root ganglia has been used to demonstrate an inhibitory effect of ventral spinal cord on neurite growth from dorsal root ganglion explants. When dorsal root ganglion explants from 14 – 15 day old embryos were cultured alone or in close proximity to a dorsal cord explant, the pattern of dorsal root ganglion neurite outgrowth was typically radial. However, when E14 – 15 dorsal root ganglion explants were cocultured for 22 – 24 hours in proximity to a ventral spinal cord explant from the same embryo, few, if any, dorsal root ganglion neurites grew in the direction of the ventral cord explant. This inhibitory effect appeared to be developmentally regulated; it was diminished or absent in cocultures prepared from 18 day old embryos. In contrast, in cocultures of dorsal cord and ventral cord explants from E14-15 embryos, dorsal cord neurites grew abundantly toward the ventral cord explant suggesting that the inhibition is not likely to be due to a nonspecific neurotoxic effect and that the activity responsible selectively inhibits dorsal root ganglion neurite outgrowth. We conclude that a diffusible, primary afferent inhibitory factor(s) produced by embryonic ventral horn may be responsible for the inhibition. Our results are discussed with respect to the possible involvement of inhibition in the normal development of primary afferent innervation of the spinal cord.
Mechanisms of dorsal-ventral axis determination in Drosophila embryos revealed by cytoplasmic transplantations
Authors: Roth Siegfried 
Published: April 2021

Abstract
The establishment of the dorsal-ventral pattern in Drosophila embryos depends on a signal transduction process: a putative extracellular ligand released into the perivitelline space surrounding the embryo binds to the Toll receptor. Toll activation triggers the formation of the nuclear gradient of dorsal protein, the morphogen of the dorsal-ventral axis. Here, I analyse the dorsal protein distribution and the expression of zygotic dorsal-ventral genes in Toll− embryos that have been injected with wild-type cytoplasm under a variety of different injection conditions. Injections into two positions within a single embryo lead to the formation of two dorsal-ventral patterns in one embryo, allowing the analysis of interactions between pattern-forming processes. The results of single and double injections suggest that the spatial information for the embryonic dorsal-ventral axis is largely derived from spatial cues present in the extraembryonic compartment, which restrict the release of the putative Toll ligand. They argue against a Toll-dependent pattern-formation process employing local self-enhancement and lateral inhibition to enhance a weak initial asymmetry. The putative Toll ligand appears to originate from a ventrally restricted zone which extends along the entire anterior-posterior axis. Ligand diffusion or its graded release are required to determine the slope of the nuclear dorsal protein gradi-ent. Both the Toll receptor and the putative ligand of Toll are in excess in wild-type embryos. Since spatial information for the embryonic dorsal-ventral axis is already present in the vitelline membrane or the perivitelline space, it is most likely generated during oogen-esis. Oogenic pattern formation is also responsible for the perpendicular orientation the dorsal-ventral axis maintains with respect to the anterior-posterior axis.
Analysis of Hox-4.5 and Hox-3.6 expression during newt limb regeneration: differential regulation of paralogous Hox genes suggest different roles for members of different Hox clusters
Authors: Simon Hans-Georg , Tabin Clifford J. 
Published: April 2021

Abstract
Adult urodele amphibians can regenerate their limbs and tail. Based on their roles in other developing sys-tems, Hox genes are strong candidates for genes that play a role in regulating pattern formation during regeneration. There are four homologous clusters of Hox genes in vertebrate genomes. We isolated cDNA clones of two newt homeobox genes from homologous positions within two Hox clusters; Hox-4.5 and Hox-3.6. We used RNase protection on nonamputated (normal) and regenerating newt appendages and tissue to com-pare their transcriptional patterns. Both genes show increased expression upon amputation with similar kinetics. Hox-4.5 and Hox-3.6 transcription is limited to the mesenchymal cells in the regenerates and is not found in the epithelial tissue. In addition to regenerat-ing appendages, both genes are transcriptionally active in adult kidney of the newt. Striking differences were found in the regulation of Hox-4.5 and Hox-3.6 when they were compared in unamputated limbs and in regenerating forelimbs versus regenerating hindlimbs.
Hox-4.5 is expressed in the blastema of regenerating fore- and hindlimbs, but Hox-4.5 transcripts are not detectable in normal limbs. In contrast, Hox-3.6 tran-scripts are found exclusively in posterior appendages, but are present in normal as well as regenerating hindlimbs and tails. Hox-4.5 is also expressed at a higher level in proximal (mid-humerus) regenerates than in distal ones (mid-radius). When we proximalized the positional memory of a distal blastema with retinoic acid, we find that the early expression level of Hox-4.5 is also proximalized. When the expression of these genes is compared to the expression of two previously reported newt Hox genes, a consistent pattern emerges, which can be interpreted in terms of differential roles for the dif-ferent Hox clusters in determining regenerative limb morphology.
Maintenance of ZPA signaling in cultured mouse limb bud cells
Authors: Anderson Rosalie , Landry Michael , Muneoka Ken 
Published: April 2021

Abstract
The positional signal localized to the posterior (zone of polarizing activity or ZPA) region of the vertebrate limb is transiently expressed during development and a decline in ZPA signaling is accelerated when posterior cells are dis-sociated and cultured in vitro. The evidence that cultured posterior cells display a precocious decline in ZPA signaling when compared to in vivo studies suggests that a factor present in the limb bud maintains or stabilizes ZPA sig-naling during limb outgrowth and that this maintenance factor is lost and/or exhausted in in vitro studies. We have developed a new culture technique, ‘microdissociation’, which preserves extracellular components that we have found to be necessary for ZPA signal maintenance. Our data suggest that the limb bud ectoderm produces a maintenance activity that becomes stored in the extracellular matrix where it acts on limb bud cells to stabilize the activity of the ZPA signal. Using our initial characterization of this maintenance activity, we have identified a growth factor, FGF-2 (bFGF), that can replace all of the ZPA signaling maintenance activity observed in microdissociate cultures. The existence of various members of the FGF family in the developing limb strongly argues a role for FGF in stabiliz-ing ZPA signaling in vivo.
Contractile protein gene expression in primary myotubes of embryonic mouse hindlimb muscles
Authors: Ontell Marcia , Ontell Martin P. , Sopper Maggie M. , Mallonga Rosa , Lyons Gary , Buckingham Margaret 
Published: April 2021

Abstract
The time course of contractile protein [actin, myosin heavy chain (MHC) and myosin light chain (MLC)] gene expression in the hindlimb muscles of the embryonic mouse (&lt;15 days gestation) has been correlated with the expression of genes for the myogenic regulatory factors, myogenin and MyoD, and with morphogenetic events. At 14 days gestation, secondary myotubes are not yet present in crural muscles (M. Ontell and K. Kozeka (1984) Am. J. Anat. 171, 133-148; M. Ontell, D. Bourke and D. Hughes (1988)Am. J. Anat. 181, 267-278); there-fore, all transcripts for contractile proteins found in these muscles must be produced in primary myotubes. In situ hybridization, with 35S-labeled antisense cRNAs, demonstrates the versatility of primary myotubes in that transcripts for (1) α-cardiac and α-skeletal actin, (2) MHCembryonic, MHCperinatal and MHC /slow, and (3) MLC1A, MLC1F and MLC3F are detectable at 14 days gestation. While the general patterns of early activation of the cardiac genes and early activation of the genes for the developmental isoforms are preserved in both myotomal and limb muscles (D. Sassoon, I. Garner and M. Buckingham (1988)Development 104, 155-164 and G. E. Lyons, M. Ontell, R. Cox, D. Sassoon and M. Buckingham (1990)J. Cell Biol. 111, 1465-1476 for myotomal muscle), there are a number of differences in contractile protein gene expression. For example, in the myotome, when myosin light chain genes are initially transcribed, hybridization signal with probe for MLC1A mRNA is greater than that with probe for MLC1F tran-scripts, whereas the relative intensity of signal with these same probes is reversed in the hindlimb. The order in which myosin heavy chain genes are activated is also different, with MHCembryonic and MHCperinatal preced-ing the appearance of MHC β/slow transcripts in limb muscles, while MHCembryonic and MHC /slow appear simultaneously in the myotomes prior to MHCperinatal. In the myotome, an intense hybridization signal for α-cardiac and a weak signal for α-skeletal actin tran-scripts are detectable prior to myosin mRNAs, whereas in the limb α-cardiac actin transcripts accumulate with myosin transcripts before α-skeletal actin mRNA is detectable. These differences indicate that there is no single coordinate pattern of expression of contractile protein genes during initial formation of the muscles of the mouse. The fact that different myogenic factors are present initially in myotomes than are present initially in the hindlimb (cf. M. E. Buckingham (1992)Trends Genet. 8, 144-149) suggests that there may be subtle dif-ferences in the capacity of these factors to activate dif-ferent muscle genes. These results are discussed in the context of muscle cell lineages.
Acidic and basic FGF in ocular media and lens: implications for lens polarity and growth patterns
Authors: Schulz Mark W. , Chamberlain Coral G. , Iongh Robbert U. de , McAvoy John W. 
Published: April 2021

ABSTRACT
We have shown previously that FGF induces lens epithelial cells in explant culture to proliferate, migrate and differentiate into fibre cells in a progressive concentration-dependent manner. In situ, these processes occur in a distinct anterior-posterior pattern in clearly defined regions of the lens. Thus anterior-posterior differences in the bio-availability of FGF in the lens environment may play a role in determining lens polarity and growth patterns. In this study, using heparin chromatography and western blotting (or ELISA), we established that both acidic and basic FGF are present in the aqueous and vitreous (the ocular media that bathe the anterior and posterior compartments of the lens, respectively). In addition, substantially more FGF was recovered from vitreous than from aqueous. Both forms of FGF were also detected in lens fibre cells and capsule. A truncated form of basic FGF (less than 20×103Mr) predominated in every case with traces of higher Mr forms in lens cells. For acidic FGF, the classical full-length form (about 20×103Mr) predominated in lens cells and a truncated form was found in vitreous. The capsule contained a higher Mr form. Using our explant system, we also tested the biological activity of ocular media and FGF fractions obtained from vitreous and lens cells. Vitreous but not aqueous contained fibre-differentiating activity. Furthermore, virtually all the fibre-differentiating activity of vitreous was shown to be FGF-associated, as follows: (a) this activity remained associated with FGF during fractionation of vitreous by heparin and MonoS chromatography and (b) the activity of the major FGF-containing fraction was blocked by antibodies to acidic and basic FGF. Posterior, but not anterior, capsule was shown to have mitogenic activity, which was neutralised by FGF antibodies and associated only with the cellular surface. These results support our hypothesis that FGF is involved in determining the behaviour of lens cells in situ. In particular, a key role for FGF in determining lens polarity and growth patterns is suggested by the anterior-posterior differences in the bio-availability of FGF in the ocular media and capsule.