bluuebunny/crossref_metadata_2025_split huggingface dataset:
KTF-1, a transcriptional activator of Xenopus embryonic keratin expression
Authors: Snape A. M. , Jonas E. A. , Sargent T. D. 
Published: April 2021

ABSTRACT
Nuclear extracts from embryos of Xenopus laevis were shown to contain a protein activity, KTF-1, which binds in vitro to the promoter of the embryonic, epidermisspecific keratin gene, XK81A1. Mobility shift assays, methylation interference and footprinting analysis were used to show that the KTF-1 binding site contains an imperfect, palindromic sequence, ACCCTGAGGCT. This sequence occurs once in the XK81A1 promoter, 152-162 base pairs upstream of the transcription start site. A construct of the keratin gene in which this sequence was altered so that it no longer binds KTF-1 in vitro showed severely reduced transcription levels upon injection into Xenopus embryos, but retained epidermal specificity. Addition of KTF-1 binding sites also enhanced epidermal and non-epidermal activity of a heterologous promoter, Xenopus /J-globin, in embryos. These results suggest that KTF-1 is a general activator of embryonic keratin transcription, which acts in concert with other factors to produce high levels of epidermisspecific expression.
Expression of basic fibroblast growth factor in the nervous system of early avian embryos
Authors: Kalcheim Chaya , Neufeld Gera 
Published: April 2021

ABSTRACT
Basic fibroblast growth factor (bFGF) promotes the survival of a subpopulation of non-neuronal cells developing from trunk neural crest (Kalcheim, Devi Biol. 134, 1-10, 1989). It was therefore important to determine whether this factor is present in the nervous system at early developmental stages. Immunocytochemistry using specific polyclonal and monoclonal antibodies was combined with three highly sensitive assays: bFGF-induced proliferation of bovine adrenal cortex-derived capillary endothelial cells (ACE), a radioimmunoassay for bFGF (RIA) and Western blot analysis. bFGF immunoreactivity was localized to the cytoplasm of neuroepithelial cells derived from embryonic day 2 (E2) quail neural tubes and cultured for one day in a chemically defined medium. Specific staining was observed in young sensory neurons in cultures of neural crest clusters as well as in a subpopulation of non-neuronal cells. In cultured E7 dorsal root ganglia, immunostaining was confined to neuronal cell bodies and fibers. In situ, staining of spinal cord and ganglionic neurons appeared on E6 and increased In intensity towards E10. Various mesoderm-derived structures such as the limb buds, the mesenchyme dorsal to the neural tube, the vertebral muscles and cartilage showed specific staining patterns in addition to neural tissue. In agreement with the results of immunocytochemical studies, 1.4 ng bFGF per mg protein was detected in spinal cord extracts by RIA as early as E3, its concentration increased to 8.0ng mg−1 on ES and then to a maximum of 18.0 ng mg−1 protein on E10, this was followed by a subsequent decrease in concentration in older embryos. On the other hand, high levels of bFGF were present in vertebral tissues from E10 onwards. Extracts of immunopositive tissues were subjected to heparin-Sepharose affinity chromatography and eluted in a stepwise salt gradient. Fractions that eluted from the columns at 2 M NaCl contained a bFGF-like protein as revealed by their ability to stimulate the proliferation of ACE cells and by Western blot analysis. These data demonstrate that bFGF is expressed during early nervous system development in both central and peripheral neurons.
A study of meiosis in chimeric mouse fetal gonads
Authors: Dolci Susanna , Felici Massimo De 
Published: April 2021

ABSTRACT
The influence of somatic environment on the onset and progression of meiosis in fetal germ cells was studied in chimeric gonads produced in vitro by dissociationreaggregation experiments. Germ cells isolated from testes or ovaries of 11.5-13.5 days post coitum (dpc) CD-1 mouse embryos were loaded with the fluorescent supravital dye 5-6 carboxyfluorescein diacetate succinimyl ester (CFSE) and mixed with a cell suspension obtained by trypsin-EDTA treatment of gonads of various ages and of the same or opposite sex. Whereas 11.5 dpc donor germ cells appeared unable to survive in the chimeric gonads obtained, about 76 % of the CFSElabeled female germ cells obtained from 12.5 dpc donor embryos (premeiotic germ cells) found viable within host ovarian tissues showed a meiotic nucleus. In contrast, a smaller number (about 19 %) were in meiosis in chimeric testes. None or very few of donor male germ cells entered meiosis in testes or ovarian host tissues. Aggregation of meiotic 13.5 dpc female germ cells with testis tissues from 13.5 to 14.5 dpc embryos resulted in inhibition of meiotic progression and pyknosis in most donor germ cells.
These results support the existence of a meiosis-preventing substance or a factor causing oocyte degeneration in the fetal mouse testis, but not of a meiosisinducing substance in the fetal ovary.
Distribution of insulin-like growth factor peptides in the developing chick embryo
Authors: Ralphs J. R. , Wylie L. , Hill D. J. 
Published: April 2021

ABSTRACT
Growth factors are likely to be of major significance in developmental biology. Here, the distribution of insulin-like growth factor (IGF) peptides is described during development of the chick embryo. IGF was immunolocalised using a polyclonal antibody to human IGF I detected with a modified Vectastain ABC procedure. Under the conditions used, the antibody binds strongly to IGF I and weakly to IGF II; thus the distribution of IGF peptide, rather than the individual factors, is described.
Muscle, peripheral nerve and the notochord were labelled whenever present. Muscle label was associated with the myotubes and neural labelling with neurons; Schwann cells were unlabelled. IGF distribution changed during differentiation of connective tissues. Regions of mesenchyme destined to form cartilage labelled weakly or not at all, and cartilage condensations were unlabelled. In the limb, chondrocytes became labelled once cartilage rudiments had formed; however, in later development, label was absent in zones of rounded and flattened chondrocytes and appeared strongly at the onset of hypertrophy. Early osteogenic mesenchyme was also unlabelled, although later bone cells were strongly stained. In the neural tube, label was associated with differentiating neuroblasts and cell bodies and with axons, especially in the developing dorsolateral tracts.
These results show a possible correlation between IGF label and cell division in early mesenchyme; cartilage condensations, which have reduced mitotic indices, do not label. In other tissues, notably muscle and nerve but also later connective tissues, label is associated with differentiating, rather than dividing, cells.
Expression and function of the homoeotic genes Antennapedia and Sex combs reduced in the embryonic midgut of Drosophila
Authors: Reuter Rolf , Scott Matthew P. 
Published: April 2021

ABSTRACT
Drosophila homoeotic genes control the formation of external morphological features of the embryo and adult, and in addition affect differentiation of the nervous system. Here we describe the morphogenetic events in the midgut that are controlled by the homoeotic genes Sex combs reduced (Scr) and Antennapedia (Antp). The midgut is composed of two cell layers, an inner endoderm and an outer visceral mesoderm that surround the yolk. Scr and Antp are expressed in the visceral mesoderm but not in the endoderm. The two genes are required for different aspects of the midgut morphogenesis. In Scr null mutant embryos the gastric caeca fail to form. Scr is expressed in the visceral mesoderm cells posterior to the primordia of the gastric caeca and appears to be indirectly required for the formation of the caeca. Antp is expressed in visceral mesoderm cells that overlie a part of the midgut where a constriction will form, and Antp null mutant embryos fail to form this constriction. An ultrastructural analysis of the midgut reveals that the visceral mesoderm imposes the constriction on the endoderm and the yolk. The mesodermal tissue contracts within the constriction and thereby penetrates the layer of the midgut endoderm. Microtubules participate in the morphological changes of the visceral mesoderm cells. The analysis of the expression of Scr in Antp mutant embryos revealed a case of tissue-specific regulation of Scr expression by Antp. In the epidermis, Antp has been shown to negatively regulate Scr, but it positively regulates Scr in the visceral mesoderm.
Target-independent regulation of a novel growth associated protein in the visual system of the chicken
Authors: Schlosshauer Burkhard , Dütting Dieter , Wild Monika 
Published: April 2021

ABSTRACT
Using an immunosuppression technique, the monoclonal antibody 2A1 has been generated specific for a 140 ×103Mr cytoplasmic-membrane-associated protein as shown by subcellular fractionation and Western blot analysis. The antigen is initially confined to perikarya of postmitotic migratory ganglion cells of the embryonic chick retina as revealed by bromodeoxyuridine labeling. During the subsequent period of axon outgrowth, the antigen becomes restricted to ganglion cell axons but disappears during the innervation of the tectum opticum, suggesting a tectal inhibition of antigen expression in retinal axons. To analyse whether the tectum suppresses 2Al-antigen expression, optic nerves of chick embryos were severed to prevent tectal innervation. 2Al-immunoreactivity was determined in deflected axons in comparison to control axons. In addition, retinal axons were grown in vitro on a substratum consisting of alternating stripes of laminin and tectal membranes, in order to investigate whether retinal axons become devoid of the 2Al-antigen once they cross from laminin to tectal membranes. However, neither prevention of target innervation by optic nerve transection in vivo nor exposure of retinal axons to soluble or particulate tectal components in vitro modify 2Al-antigen regulation in ganglion cell axons, suggesting a retina inherent-control of gene expression. Antigen expression is essentially restricted to the period of axonal outgrowth and therefore the 2Al-protein is likely to be involved in processes essential for neurite extension, independent of the synaptic target.
Cytoskeletal protein and mRNA accumulation during brush border formation in adult chicken enterocytes
Authors: Fath Karl R. , Obenauf Steven D. , Burgess David R. 
Published: April 2021

ABSTRACT
We have explored the development of the brush border in adult chicken enterocytes by analyzing the cytoskeletal protein and mRNA levels as enterocytes arise from crypt stem cells and differentiate as they move toward the villus. At the base of the crypt, a small population of cells contain a rudimentary terminal web and a few short microvilli with long rootlets. These microvilli appear to arise from bundles of actin filaments which nucleate on the plasma membrane. The microvilli apparently elongate via the addition of membrane supplied by vesicles that fuse with the microvillus and extend the membrane around the actin core. Actin, villin, myosin, tropomyosin and spectrin, but not myosin I (previously called 110 kD; see Mooseker and Coleman, J. Cell Biol. 108, 2395-2400, 1989) are already concentrated in the luminal cytoplasm of crypt cells, as seen by immunofluorescence. Using quantitative densitometry of cDNA-hybridized RNA blots from cells isolated from crypts, villus middle (mid), or villus tip (tip), we found a 2- to 3-fold increase in villin, calmodulin and tropomyosin steady-state mRNA levels; an increase parallel to morphological brush border development. Actin, spectrin and myosin mRNA levels did not change significantly. ELISA of total crypt, mid and tip cell lysates show that there are no significant changes in actin, myosin, spectrin, tropomyosin, myosin I, villin or α-actinin protein levels as the brush border develops. The G-/F-actin ratio also did not change with brush border assembly. We conclude that, although the brush border is not fully assembled in immature enterocytes, the mgjor cytoskeletal proteins are present in their full concentration and already localized within the apical cytoplasm. Therefore brush border formation may involve reorganization of a pool of existing cytoskeletal proteins mediated by the expression or regulation of an unidentified key protein(s).
Vertebral Malformation in the Mouse Foetus Caused by Maternal Hypoxia During Early Stages of Pregnancy
Authors: Murakami Ujihiro , Kameyama Yoshiro 
Published: April 2021

ABSTRACT
The ddN strain of mice were kept in a chamber with reduced atmospheric pressure (225 mmHg) for 5 hours on their eighth (group A), ninth (group B), tenth (group C), eleventh (group D) or twelfth (group E) day of pregnancy and examined both for external malformations and for skeletal changes in the foetuses. For skeletal examinations they were cleared by the Dawson method. In group A, besides two cases of atlanto-occipital fusions, malformations of upper cervical vertebrae were seen. In group B, cervical vertebrae were chiefly involved in malformations, but the thoraco-lumbar ones were also disturbed. In group C, besides a few cervical involvements, lower thoracic and lumbar malformations were the most striking. In group D, malformations shifted to the sacro-caudal level, while in group E the malformations ranged from the lumbar to the caudal level, though they were low in frequency. These changes were fusion, adhesion, bifurcation, absence, reduction in size, asymmetry of the primordial posterior rami, disordered segmentation, etc. The primordium of the vertebral body was also involved. At the thoracic level ribs were also involved in deformities when their corresponding vertebrae were affected. In the lowest part of the thoracic level, the absence or vestigial of the rib was often seen in group C. In an overall picture, a clear-cut head-to-tail gradient shift of malformations occurs as the developmental stage of oxygen deficiency advances. This sequence is in good agreement with that shown by Ingalls et al. and by Degenhardt. Atlanto-occipital fusions and abnormalities in the upper cervical region recall the conditions seen in iniencephalia, Klippel-Feil syndrome and platybasia in human beings. Some of the malformations in the vertebrae at other levels resembled those in vertebral rachischisis in man.
Differentiation of the Yolk Sac of the Chick Studied by Electron Microscopy
Authors: Bellairs Ruth 
Published: April 2021

ABSTRACT
The marginal cells of the area opaca and early yolk sac are extended distally into long processes which may measure up to 500μ in length by as little as μ in depth. In whole mounts of blastoderms, examined by fight microscopy, these processes can be seen forming a clear rim to the blastoderm. They possess cytoplasmic granules, but no mitochondria or endoplasmic reticulum. It is suggested that these processes enable the blastoderm to migrate under the vitelline membrane. The endoderm of the region lying immediately proximal to the edge has been found to be composed of cells and not of a syncytium as is generally supposed. These cells are frequently separated by patches of modified yolk, consisting of a meshwork of membranes. These membranes possess a fine structure similar to that of myelin figures and it is suggested that they are formed by hydration of yolk lipids by water drawn through the vitelline membrane from the egg white. This meshwork corresponds with the region known at this stage as the periblast by some light microscopists. No evidence about the nature of the periblast in early cleavage is presented. The incidence of desmosomes in the area opaca appears to increase between 1 and 2 days of incubation. It is shown that each cell membrane retains its anatomical identity throughout the desmosome. Structural changes begin to take place in the intracellular yolk drops of the area vasculosa just before the establishment of the yolk sac circulation. These changes are considered to be the result of enzyme activity and it is suggested that partly digested yolk is carried in the blood stream to the area pellucida. These events exemplify the nicety of timing involved in many embryonic processes, for just as the intracellular yolk drops of the area pellucida become used up, so, it seems, new supplies of yolk start to arrive from the area vasculosa. Other changes which take place as the area opaca becomes colonized by mesoderm are described. They include: the re-arrangement of the ectoderm cells and changes in their shape; the loss of dorsal villi from the ectoderm cells and the appearance of more desmosomes and to nofilaments in them; changes in shape and arrangement of the endoderm cells, which become epithelial, acquiring desmosomes and tonofilaments. Pinocytic-like indentations appear at the lower border of the endoderm cells. The mesenchyme cells are described and it is noted that collagen-like fibrils appear at the same time.
Studies on Transplantations of Amphibian Anterior Pituitary into Chick Embryo. Analysis of Induction Capacity by Differential Solubility and Precipitation Method
Authors: Sherbet Gajanan V. 
Published: April 2021

ABSTRACT
An attempt at analysing the inductive capacity of the anterior pituitary gland of Rana tigrina, in order to understand the nature of its active principle, was made, having recourse to differential solubility and precipitation of the hormonal and the ribonucleic acid factors using half-saturated ammonium sulphate, 50 per cent pyridine and 2·5 per cent trichloroacetic acid. The study of the inductive capacity of the gland in its normal state and after a 24-hour treatment with the solvents was made by grafting experiments on chick primitive-streak embryos. The behaviour of control pituitary grafts taken from donors at different seasons, namely breeding and non-breeding, and those taken from female and male donors at the same season, and also the relationship found to exist between the volume of the graft and that of the induced neural tissue, have suggested that the active principle of induction is probably FSH glycoprotein, and that the RNA contained in the gland has only a facilitating action.
An Experimental Analysis of the Development of the Haploid Syndrome in Embryos of Xenopus laevis
Authors: Hamilton Louie 
Published: April 2021

ABSTRACT
The only observed effect of rearing haploid and diploid embryos of Xenopus laevis at 16°C instead of 22°C was retarded development. The same proportion of haploids (90–95 per cent) develop the syndrome (oedema, feeble heart, poorly coiled gut) and the stage expectancy is similar. Haploid tissues may live longer and develop more normally when telo-biosed to diploid tissues, but anterior diploid tissue promotes better development than the same quantity of posterior tissue. It is suggested that the haploid syndrome develops because haploids lack hybrid vigour completely, and cannot regulate the abnormalities caused by smaller cell size and/or unmasked recessive lethal genes. An hypothesis is put forward to explain the fact that haploid nuclei are more nearly spherical than diploid nuclei.
The Isolated Xenopus laevis Tail: A Preparation for Studying the Central Nervous System and Metamorphosis in Culture
Authors: Shaffer B. M. 
Published: April 2021

ABSTRACT
The Xenopus tail preparation described here was initially developed for studying the action of substances on the vertebrate nervous system. For this both physiological preparations and whole animals have their disadvantages. The former are short-lived; the latter may die before any major chemical or structural changes have had time to occur. It was therefore thought desirable to seek a relatively long-lived preparation that possessed a functional central nervous system, but yet was not dependent on the conduction of nerve impulses for its survival. The tail of a Xenopus laevis tadpole seemed to be highly suitable for this purpose, as it contained complete reflex arcs and was sufficiently small to carry out its necessary exchanges by diffusion. Moreover, it was so transparent that nerves and muscle striations could be studied microscopically during life. Although agents to which the skin was impermeable could easily be injected into the tail, it was thought best to seek media that would be suitable for partially flayed tails.
The Differential Growth-Response of Embryonic Chick Limb-Bone Rudiments to Triiodothyronine in vitro. III. Hormone Concentration
Authors: Lawson Kirstie 
Published: April 2021

ABSTRACT
Limb-bone rudiments from 6-day-old chick embryos were explanted in a medium of fowl plasma and embryo extract and the effect of various concentrations of T3 on the growth in length and wet weight of the rudiments was studied. Treatment with 0·01 to 0·32μg.T3/ml. produced a progressive retardation in the growth in length of the tibia, and a stimulation in the growth of the radius, which was maximal at intermediate concentrations. The growth in length of the ulna was increased by low levels of added hormone and retarded by high levels. The final wet weight of the tibia was slightly increased by low T3 concentrations and reduced by high doses. The final wet weights of the radius and ulna were greater than the controls at all T3 concentrations, but the greatest increase in the size of the ulna was reached at a lower dose level than that needed for the radius. These results suggested that the growth stimulation of the radius and retardation of the leg bones when exposed to the same concentration of T3 reflect a difference in sensitivity of the rudiments which may respond in a fundamentally similar way. The response of the ulna to 0 ·16μg. T3/ml. was a continuous process of growth stimulation followed by retardation. A difference in the threshold of response between the third metatarsus and radius was found at low concentrations of T3: the flattened cell zone of the metatarsus was affected by 0·0005 μg./ml. to which the radius was insensitive.