bluuebunny/crossref_metadata_2025_split huggingface dataset:
Developmental loss of functional laminin receptors on retinal ganglion cells is regulated by their target tissue, the optic tectum
Authors: Cohen James , Nurcombe Victor , Jeffrey Peter , Edgar David 
Published: April 2021

ABSTRACT
The ability of chick retinal ganglion cells (RGCs) to extend neurites on tissue culture substrata of the extracellular matrix protein laminin is lost during embryonic development. In order to establish the mechanism responsible for the loss of response, the number of high affinity (KD 10−9M) laminin receptors on both the cell bodies and neurites of RGCs were determined throughout this period by a ligand binding assay using radiolabelled laminin. It was found that the loss of response paralleled a decrease in receptor numbers on both the cell bodies and the neurites of the RGCs. Bilateral tectalablation at embryonic day 6 resulted in the subsequent maintenance of laminin-stimulated neurite outgrowth, together with a partial inhibition of the loss of laminin receptors. Thus, the loss of response of the RGCs to laminin reflects a decrease in the numbers of laminin receptors on these neurons, and furthermore, this downregulation is in turn dependent on innervation of the target tissue.
Another role for melanocytes: their importance for normal stria vascularis development in the mammalian inner ear
Authors: Steel Karen P. , Barkway Chris 
Published: April 2021

ABSTRACT
The stria vascularis of the mammalian cochlea is composed primarily of three types of cells. Marginal cells line the lumen of the cochlear duct and are of epithelial origin. Basal cells also form a continuous layer and they may be mesodermal or derived from the neural crest. Intermediate cells are melanocyte-like cells, presumably derived from the neural crest, and are scattered between the marginal and basal cell layers. The marginal cells form extensive interdigitations with the basal and intermediate cells in the normal adult stria. The stria also contains a rich supply of blood vessels.
We investigated the role of melanocytes in the stria vascularis by studying its development in a mouse mutant, viable dominant spotting, which is known to have a primary neural crest defect leading to an absence of recognisable melanocytes in the skin. Melanocytes were not found in the stria of most of the mutants examined, and from about 6 days of age onwards a reduced amount of interdigitation amongst the cells of the stria was observed. These ultrastructural anomalies were associated with strial dysfunction. In the normal adult mammal, the stria produces an endocochlear potential (EP), a resting dc potential in the endolymph in the cochlear duct, which in mice is normally about + 100 mV. In our control mice, EP rose to adult levels between 6 and 16 days after birth. In most of the mutants we studied, EP was close to zero at all ages from 6 to 20 days.
Melanocyte-like cells appear to be vital for normal stria vascularis development and function. They may be necessary to facilitate the normal process of interdigitation between marginal and basal cell processes at a particular stage during development, and the lack of adequate interdigitation in the mutants may be the cause of their strial dysfunction. Alternatively, melanocytes may have some direct, essential role in the production of an EP by the stria. Melanocytes may be important both for normal strial development and for the production of the EP. We believe this is the clearest demonstration yet of a role for migratory melanocytes other than their role in pigmentation.
Genetic structure of the abd-A gene of Drosophila
Authors: Busturia Ana , Casanova Jordi , Sánchez-Herrero Ernesto , González Rosa , Morata Ginés 
Published: April 2021

ABSTRACT
We report the embryonic and adult phenotypes of a number of mutations of the abd-A gene of the bithorax complex. Some of them result in loss of abd-A function in the whole abd-A domain and are usually lethal. These probably eliminate or inactivate abd-A protein products. Other mutations affect only part of the abd-A domain. These are viable, appear to map outside the abd-A transcription unit, and presumably alter the normal spatial regulation of abd-A products.
We propose a model of abd-A structure based on a protein-coding region and two cis-regulatory regions. Regulatory region 1, 3′ to the transcription unit, contains positive and negative regulatory elements. Regulatory region 2, 5′ to the transcription unit, establishes the correct level of abd-A activity in the abdominal metameres.
Myosin light chain gene expression in developing and denervated fetal muscle in the mouse
Authors: Barton Paul J. R. , Harris A. John , Buckingham Margaret E. 
Published: April 2021

ABSTRACT
We have investigated the accumulation of mRNA transcripts of the atrial (or embryonic) myosin light chain MLC1A (MLCLmb), and the two adult fast muscle myosin light chains (MLC1F and MLC3F) during fetal skeletal muscle development in the mouse. In 15-day fetal muscle, MLC1A is the predominant mRNA detectable, by 18 days MLC1F has become the major transcript and MLC3F mRNA is detectable for the first time. By 12 days after birth, MLC1A transcripts are undetectable and MLC1F and MLC3F are similar in abundance. In fetuses treated with β-bungarotoxin and which therefore develop in the absence of functional nerve, MLC1A and MLC1F undergo normal transitions but MLC3F mRNA accumulation is significantly retarded. This demonstrates that these myosin light chain mRNAs accumulate with differing kinetics, and that MLC3F mRNA accumulation is nerve-dependent during fetal development. The results are discussed in terms of secondary muscle fibre formation, and in relation to the independent regulation of MLCIF and MLC3F mRNAs which are transcribed from the same gene.
Expression of the SMP antigen by oligodendrocytes in the developing avian central nervous system
Authors: Cameron-Curry P. , Dulac C. , Le Douarin N. M. 
Published: April 2021

ABSTRACT
Expression of the avian antigen SMP (Schwann cell Myelin Protein, Mr 75–80 000), first characterized in the PNS with a monoclonal antibody as an early and strictly specific Schwann cell marker, was further studied in the CNS.
Comparing SMP immunoreactive areas in the different parts of the CNS with those expressing the Myelin Basic Protein (MBP), we showed a strict colocalisation of both phenotypes. In vitro, MBP+ oligodendrocytes express the surface antigen SMP as well.
SMP cellular expression was followed in situ and in culture using nervous tissues from embryos at different stages. We were thus able to detect an early expression of this marker by oligodendroblasts before the first appearance of MBP immunoreactivity.
We have also identified a subpopulation of SMP+/ MBP– and SMP+/GC– cells, which persists under our culture conditions as precursors remaining in an immature state.
Temporal and tissue-specific expression of the proto-oncogene c-fos during development in Xenopus laevis
Authors: Mohun T. J. , Garrett N. , Taylor M. V. 
Published: April 2021

ABSTRACT
We describe the isolation and complete sequence of the Xenopus c-fos proto-oncogene, c-fos expression throughout Xenopus development was analysed using a homologous probe derived from the cloned gene, c-fos RNA is accumulated during oogenesis to reach a plateau of 2 x105 transcripts per stage VI oocyte, suggesting an unusual stability of the c-fos message. The amount of RNA per embryo decreases substantially after fertilisation to reach a level corresponding to less than 0.1 molecule per cell at the tailbud stage. Subsequently, at the swimming tadpole stage, the amount of c-fos mRNA increases; an increase that is correlated with the start of skeleton formation. In the newly metamorphosed frog-let, c-fos mRNA shows a marked tissue-specific distribution, with the highest level in intestine and lowest in gall bladder, lung and spleen. We also demonstrate that the Xenopus c-fos gene is serum-inducible in Xenopus cultured cells, a property attributable to a promoter sequence known as the Serum Response Element (SRE). A protein activity (indistinguishable from Serum Response Factor) in both whole cell and nuclear Xenopus embryo extracts binds specifically to the SRE and is present at an approximately constant level throughout early development. Our results suggest roles for c-fos in aspects of both the rapid cell proliferation and cell differentiation characteristic of early Xenopus development.
The contribution made by cells from a single somite to tissues within a body segment and assessment of their integration with similar cells from adjacent segments
Authors: Bagnall K. M. , Higgins S. J. , Sanders E. J. 
Published: April 2021

ABSTRACT
Somites represent the first visual evidence of segmentation in the developing vertebrate embryo and it is becoming clear that this segmental pattern of the somites is used in the initial stages of development of other segmented systems such as the peripheral nervous system. However, it is not known whether the somites continue to contribute to the maintenance of the segmental pattern after the dispersal of the somitic cells. In particular, the extent to which cells from a single somite contribute to all of the tissues of a single body segment and the extent to which they mix with cells from adjacent segments during their migration is not known. In this study, we have replaced single somites in the future cervical region of 2-day-old chick embryos with equivalent, similarly staged quail somites. The chimerae were then allowed to develop for a further 6 days when they were killed. The cervical region was dissected and serially sectioned. The sections were stained with the Feulgen reaction for DNA to differentiate between the chick and quail cells. The results showed that the cells from a single somite remained as a clearly delimited group throughout their migration. Furthermore, the sclerotome, dermatome and myotome portions from the single somites could always be recognised as being separate from similar cells from other somites. The somitic cells formed all of the tissues within a body segment excluding the epidermis, notochord and neural tissue. There was very little mixing of the somitic cells between adjacent segments. The segmental pattern of the somites is therefore maintained during the migration of the somitic cells and this might be fundamental to a mechanism whereby the segmentation of structures, such as the peripheral nervous system, is also maintained during development.
The molecular basis of positional signalling: introduction
Authors: Kay R. R. , Smith J. C. 
Published: April 2021

ABSTRACT
The importance of cell–cell interactions in embryonic development was first described by Driesch (1891), who showed that any of the blastomeres of the 2-cell or 4-cell sea-urchin embryo is capable of forming a complete embryo if cultured in isolation; this implied that in normal development each blastomere is aware of the other and will only form a half- or quarter-embryo, as appropriate. And it was only ten years later that Spemann (1901) discovered the phenomenon of embryonic induction, recently reviewed by Gurdon (1987) and defined as an interaction in which the differentiation of one group of cells is affected by a signal from an adjacent group. Thus the significance of cell signalling during development has been appreciated for almost a century, but, as has frequently been remarked, progress in the molecular analysis of the phenomenon has been slow compared with that in the younger disciplines of, for example, immunology and molecular biology.
Models for positional signalling with application to the dorsoventral patterning of insects and segregation into different cell types
Authors: Meinhardt Hans 
Published: April 2021

ABSTRACT
Models of pattern formation and possible molecular realizations are discussed and compared with recent experimental observations. In application to the dorsoventral patterning of insects, it is shown that a superposition of two pattern-forming reactions is required. The first system generates the overall dorsoventral polarity of the oocyte, the second generates the positional information proper with a stripe-like region of high concentration along the ventral side of the embryo. A single reaction would be insufficient since the two reactions require different parameters. The model accounts for the orientation of the DV axes of the oocytes in the ovary of Musca domestica and Sarcophaga, independent of the DV axis of the mother, for the formation of several ventral furrows in the absence of the primary gurken/ torpedo system in Drosophila, as well as for the good size regulation of the dorsoventral axis as observed in some insect species.
Segregation of a homogeneous cell population into different cell types requires autocatalytic processes that saturate at relatively low concentrations and nondiffusible substances responsible for the autocatalytic feedback loops. Thus, these loops can be realized directly on the gene level via their gene products, for instance, by the mutual repression of two genes. A balance of the two cell types is achieved by a long-ranging substance interfering with the self-enhancing process. This substance is expected to have a more or less homogeneous distribution. This model accounts for the reestablishment of the correct proportion after an experimental interference and the change of determination after transplantation. Applications to the segregation of prestalk and prespore cells in Dictyostelium and of neuroblast cells from the ventral ectoderm in Drosophila are provided.
The process of localizing a maternal messenger RNA in Xenopus oocytes
Authors: Yisraeli Joel K. , Sokol Sergei , Melton D. A. 
Published: April 2021

ABSTRACT
The maternal mRNA Vgl is localized to the vegetal pole during oogenesis in Xenopus. We have cultured oocytes in vitro to begin to understand how this localization occurs. Endogenous Vgl mRNA undergoes localization when oocytes are cultured in vitro, and synthetic Vgl mRNA injected into such oocytes is localized in the same fashion. Vgl mRNA is associated with a detergentinsoluble fraction from homogenized oocytes, suggesting a possible cytoskeletal association. The use of cytoskeletal inhibitors reveals a two-step process for localizing Vgl mRNA. Microtubule inhibitors such as nocodazole and colchicine inhibit the localization of Vgl mRNA in late stage in/early stage IV oocytes, but have no effect on Vgl mRNA once it is localized. The microfilament inhibitor cytochalasin B, however, has little effect on the translocation of Vgl mRNA in middle-stage oocytes but causes a release of the message in late-stage oocytes. We propose a model for the localization of Vgl mRNA in which translocation of the message to the vegetal cortex is achieved via cytoplasmic microtubules and the anchoring of the message at the cortex involves cortical microfilaments.
Cortical rotation of the Xenopus egg: consequences for the anteroposterior pattern of embryonic dorsal development
Authors: Gerhart J. , Danilchik M. , Doniach T. , Roberts S. , Rowning B. , Stewart R. 
Published: April 2021

ABSTRACT
We first review cortical-cytoplasmic rotation, a microtubule-mediated process by which the Xenopus egg, like other amphibian eggs, transforms its polarized cylindrical symmetry into bilateral symmetry within the first cell cycle after fertilization. This transformation, the earliest of many steps leading to dorsal development, involves the displacement of the egg’s cortex relative to its cytoplasmic core by 30° in an animal-vegetal direction. As rotation is progressively reduced by microtubuledepolymerizing agents, embryos develop with body axes progressively deleted for dorsal structures at the anterior end. With no rotation, ventralized embryos are formed. In an effort to comprehend this progressive effect on embryonic organization, we go on to review subsequent developmental processes depending on rotation, and we propose, with evidence, that reduced rotation leads to a reduced number of vegetal dorsalizing cells, which induce during the blastula stage a Spemann organizer region of smaller than normal size. The reduced organizer then promotes a reduced amount of cell rearrangement (morphogenesis) at gastrulation. Reduced morphogenesis seems the proximate cause of the incompleteness of axial pattern, as shown further by the fact that embryos that are normal until the gastrula stage, if exposed to inhibitors of morphogenesis, develop body axes that are progressively less complete in their anterior dorsal organization the earlier their gastrulation had been blocked. We discuss why axial pattern might depend systematically on morphogenesis.
Short-range positional signals in the developing Drosophila eye
Authors: Tomlinson Andrew 
Published: April 2021

ABSTRACT
Positional signals provided by immediate neighbours appear to direct developmental decisions in the eye of Drosophila. By a combined genetic and molecular approach the biochemical bases of the signal and reception mechanisms are being systematically dissected. Three key gene products have now been identified, sevenless is a transmembrane tyrosine kinase probably transducing positional signals that direct the R7 cell to its fate. The bride of sevenless gene product is on the signalling side of the mechanism and is required in R8 for R7 to develop. The type of protein bride of sevenless encodes is not yet known. The rough gene encodes a transcription factor on the signalling side required in R2 and RS for positional signals to be transmitted to neighbouring cells.
Formation and anatomy of the prestalk zone of Dictyostelium
Authors: Williams J. G. , Jermyn K. A. , Duffy K. T. 
Published: April 2021

ABSTRACT
The pDd63 and pDd56 genes encode extracellular matrix proteins which, respectively, surround the migratory slug and mature stalk cells. Both genes are dependent for their expression upon, and rapidly induced by, DIF, the stalk cell inducer. Using these genes as cell-autonomous markers, we have defined three distinct kinds of ‘prestalk’ cells localized to different parts of the anterior region of the slug. At least one, and probably both, prestalk cell types initially differentiates at the base of the aggregate. The most abundant of the two prestalk cell types then migrates into the tip, the precursor of the prestalk zone which arises at the apex of the aggregate. Thus we believe that morphogenesis of the prestalk zone, the primary pattern-forming event in Dictyostelium development, involves a combination of positionally localized differentiation and directed cell migration. To account for the positionally localized différentiation of prestalk cells, we invoke the existence of gradients of the known antagonists of DIF - cAMP and NH3. We further suggest that differences in the motility of pstA and pstB cells might result from differences in their chemotactic responsiveness to cAMP signals propagated from the tip.
The biological effects of XTC-MIF: quantitative comparison with Xenopus bFGF
Authors: Green J. B. A. , Howes G. , Symes K. , Cooke K. J. , Smith J. C. 
Published: April 2021

ABSTRACT
Mesoderm in Xenopus and other amphibian embryos is induced by signals from the vegetal hemisphere acting on equatorial or animal hemisphere cells. These signals are diffusible and two classes of candidate signal molecule have been identified: the fibroblast growth factor (FGF) and transforming growth factor β (TGF-β) types. In this paper, we compare the effects of cloned Xenopus basic FGF (XbFGF) and electophoretically homogeneous XTC-MIF (a TGF-β-like factor obtained from a Xenopus cell line) on animal pole expiants. We find that they have a similar minimum active concentration (0.1−0.2ng ml−1) but that, nonetheless, XTC-MIF is at least 40 times more active in inducing muscle. In general, we find that the two factors cause inductions of significantly different characters in terms of tissue type, morphology, gene expression and timing.
At low concentrations (0.1−1.0ngml-1) both factors induce the differentiation of ‘mesenchyme’ and ‘mesothelium’ as well as blood-like cells. These latter cells do not, however, react with an antibody to Xenopus globin. This raised the possibility that the identification of red blood cells in other studies on mesoderm induction might have been mistaken, but combinations of animal pole regions with ventral vegetal pole regions confirmed that genuine erythrocytes are formed. The identity of the blood-like cells formed in response to the inducing factors remains unknown. At higher concentrations XTC-MIF induces neural tissue, notochord, pronephros and substantial and often segmented muscle. By contrast, XbFGF only induces significant amounts of muscle above 24 ng ml”1 and even then this is much less than that induced by XTC-MIF.
For both factors an exposure of less than 30 min is effective. Competence of animal pole cells to respond to XbFGF is completely lost by the beginning of gastrulation (stage 10) while competence to XTC-MIF is detectable until somewhat later (stage 11). Since animal pole tissue is known to be able to respond to the natural inducer at least until stage 10, and perhaps until stage 10.5, this suggests that bFGF cannot be the sole inducer of mesoderm in vivo.
Taken together, these results are consistent with XTC-MIF being a dorsoanterior inducer and XbFGF a ventroposterior inducer, suggesting that body pattern is established by the interaction of two types of inducing signal. This model is discussed in view of the qualitative and quantitative differences between the factors.
The spatiotemporal distribution of N-CAM in the retinotectal pathway of adult goldfish detected by the monoclonal antibody D3
Authors: Bastmeyer Martin , Schlosshauer Burkhard , Stuermer Claudia A. O. 
Published: April 2021

Abstract
The spatiotemporal distribution of neural cell adhesion molecule (N-CAM) in the retinotectal system of adult goldfish was assessed by immunofluorescence using the monoclonal antibody (Mab) D3 against chick N-CAM. In immunoblots with extracts of cell surface membranes of fish brains, Mab D3 recognized a prominent band at 170K and a weak band at 130K (K=103Mr). N-CAM immunofluorescence on cells was restricted to the marginal growth zones of the retina and the tectum and, in normal fish, to the youngest axons from the new ganglion cells of the peripheral retinal margin. In fish with previously transected optic nerves (ONS), Mab D3 staining was found transiently on all axons from the site of the cut into the retinorecipient layers of the tectum, but disappeared from these axons 450 days after ONS.
Growing retinal axons in vitro exhibited N-CAM immunofluorescence throughout their entire extent, including their growth cones. Glial cells cultured from regenerating optic nerves were, however, unlabeled.
These data are consistent with the idea that N-CAM is involved in adhesive interactions of growing axons. The temporally regulated expression of N-CAM on the new retinal axons may contribute to the creation of the age-related organization of the axons in the retinotectal pathway of fish.