bluuebunny/crossref_metadata_2025_split huggingface dataset:
Control of muscle differentiation by embryonic neural tissues
Authors: Muchmore William B. 
Published: April 2021

ABSTRACT
Previous work has suggested that in the salamander embryonic spinal cord enhances and embryonic brain suppresses differentiation of muscle from somitic mesoderm. These results have been confirmed by means of transplantation and explantation experiments performed on early neurulae of Ambystoma maculatum. Transplantation of presumptive spinal cord into the hind-brain region results in increased size of post-otic myotomes. On the other hand, transplantation of presumptive forebrain into the trunk neural plate usually results in a striking decrease in size of trunk myotomes. Orthotopic transplants of neural plate have little or no effect upon the development of myotomes. Ventral ectoderm transplanted into the neural plate at stage is incorporated into the host spinal cord and adjacent myotomes are usually normal. Transplants of trunk neural plate over lateral mesoderm often results in increased size of myotomes without affecting the pronephros. Explants of large amounts of somite mesoderm in an ectodermal envelope readily differentiate into muscle. Inclusion of presumptive brain cells in such explants results in a conspicuous decrease in frequency of occurrence of muscle differentiation and in quantity of muscle actually formed. The control of muscle differentiation in the early embryo is considered in the light of the known influences exerted by the neural tissues.
Studies on kidney tubulogenesis. I. The effect of actinomycin D on tubulogenesis in vitro
Authors: Jainchill John , Saxén Lauri , Vainio Tapani 
Published: April 2021

ABSTRACT
The effects of actinomycin D upon the induction of tubulogenesis in mouse metanephrogenic mesenchyme by dorsal spinal cord have been studied. A drug concentration of 0 · 05 μg./c.c. was found to be optimal for inhibiting differentiation without being lethal for the cells. Treatment of both spinal cord and mesenchyme, or of mesenchyme only, for 30 min. just prior to recombination, inhibited tubulogenesis. Treatment of the spinal cord (inducer) only, either just prior to or up to 8 hr. before recombina-tion had no effect. Treatment of the spinal cord and mesenchyme for 30 min. with 0 · 05 μg./c.c. actinomycin at any time up to 20 hr. after recombination inhibited tubulogenesis. If 24 or more hours elapsed between recombination and treatment with the drug, however, differentiation could no longer be inhibited. In all cases exposure to actinomycin reduced tissue viability, but both spinal cord and liver (dummy inducer) protected the mesenchyme and increased cell viability in the latter, measured by neutral red uptake. In the discussion the significance of the change in the effect of exposure to actinomycin between 20 and 24 hr. after recombination is considered with reference both to other studies of this time period in the mesenchyme induction system, and to analogous results achieved with actinomycin in other systems.
Induction de l’endoderme pré-hépatique par le mésoderme de l’aire cardiaque chez l’embryon de poulet
Authors: Douarin par Nicole Le 
Published: April 2021

ABSTRACT
Dans des travaux antérieurs (Le Douarin, 1961, 1962) j’ai localisé les territoires présomptifs du foie chez l’embryon de Poulet de 9 à 15 somites. Ces territoires s’étendent de part et d’autre de l’axe somitique jusqu’au niveau du 15ème somite environ et se réunissent sur la ligne médioventrale dans le repli cardiaque. L’étude des potentialités histogénétiques des différentes régions de ces aires hépatiques a montré que seules les parties contenant le repli cardiaque peuvent fournir du foie lorsqu’elles sont isolées et transplantées en greffes coelomiques (Le Douarin, 1964). Il est apparu ainsi que le territoire présomptif endodermique du foie n’est pas aussi étendu que le territoire mésodermique. Il est localisé dès un stade précoce dans la lèvre antérieure de l’ombilic intestinal (Text-fig. 1).
Rhythmicity in the early swimming of anuran larvae
Authors: Corner Michael 
Published: April 2021

ABSTRACT
Observations were made upon two species of anurans, Xenopus laevis and Rana pipiens, of the early body movements and their modification after making sections through various levels of the central nervous system. Bursts of muscle contractions, effecting swimming, occur spontaneously and are identical to those evoked by tactile stimulation. Bursts are usually consistent in duration and occur at fairly regular intervals. In Rana they are generated by the spinal cord as well as by the hind-brain, but with a decreasing frequency at successively posterior levels. Early behavior in Xenopus is unchanged by removal of the forebrain and mid-brain, or by removal of the most anterior portion of the hind-brain. More extensive hind-brain removal alters the swimming pattern in most cases so that the bursts become either prolonged or abortive. Complete removal results in continual rather than periodic muscular activity. The early amphibian central nervous system is concluded to consist functionally of several excitatory and inhibitory rhythms acting upon an efferent mechanism which is capable of generating pulses at a constant mean frequency. Sensory input is held to alter briefly the net level of central excitation resulting from these endogenous rhythms.
Effects of Actinomycin D on the lens regenerating system
Authors: Yamada Tuneo , Roesel Marion E. 
Published: April 2021

ABSTRACT
Effects of actinomycin D on transformation of iris into lens in Wolffian lens regeneration of adult T. viridescens were studied by injection into the body cavity of lentectomized animals. One microgram of the antibiotic per gram body weight was injected every day or every other day for a 3- to 12-day period at various phases of lens regeneration Administration of actinomycin during the early phase of lens regeneration for a period longer than 4 days suppressed the progress of regeneration. Suppression was complete or partial depending upon the experimental conditions. Four daily injections of the above indicated amount were given at various phases of lens regeneration. When the treatment began after appearance of primary lens fiber cells, differentiation of those cells proceeded normally, while developmental arrest and disintegration were observed in the lens epithelium. The actinomycin-treatment given after the regenerate has formed a well-differentiated lens caused a degenerative inhibition of the lens epithelium, but no appreciable change in the morphology of lens fibers. The non-regenerating iris and lens did not show any morphological sign of abnormalities after the same treatment. Data are discussed in connection with information on syntheses of RNA, proteins, and DNA occurring in the lens-regenerating system. A change in the pattern of transcription of genetic information is suggested as a part of the mechanism of tissue transformation.
True hermaphroditism in chimaeric mice
Authors: Tarkowski Andrzej K. 
Published: April 2021

ABSTRACT
Histological examination of the reproductive systems of fourteen newborn chimaerae developed from fused eggs revealed eleven sexually normal animals and three true hermaphrodites. The genital apparatus of the hermaphrodites is described, the structure of the gonads being given special attention. Of the three hermaphrodites, one had one ovary with female sex ducts and an ovotestis with complete male ducts and incomplete female ones. The second had two ovotestes and a genital apparatus of nearly typically male type; the remnants of Müllerian ducts being retained only caudally. The third had one ovary with female sex ducts and one ovotestis with male sex ducts. The occurrence of true hermaphrodites strongly suggests that spontaneous true hermphroditism also develops from sex-chromosome mosaicism. The available literature on spontaneous hermaphroditism in rodents is critically reviewed. It is postulated that the frequencies of the four types of true hermaphroditism described (ovary-testis, ovary-ovotestis, testis-ovotestis, ovotestis-ovotestis) in mice and other rodents do not adequately reflect their actual incidence in nature in that the incidence of the lateral type of hermaphroditism is exaggerated. It is suggested that if the testicular tissue does, in fact, elaborate a morphogenetic stimulus influencing the differentiation of XX gonadal tissue, such a stimulus must be rather weak and act only near the site of its elaboration. The genetic sex of germ cells in chimaeric hermaphrodites remains unknown. It is postulated that the presence in the hermaphrodite gonads of oöcytes and male germ cells reflects only the secondary differentiation of germ cells, which need not reflect their genetic sex. While the ovarian tissue of the ovotestes examined contains only oöcytes, in the testicular tissue both oöcytes and spermatogonia are present. Initiation of meiosis of the female type in the testicular territory is attributed to the action of a meiotic stimulus elaborated by the ovarian tissue and diffusing through the testicular part.
The regenerative capacity of the tail in embryonic and post-natal lizards (Lacerta vivipara Jacquin)
Authors: Moffat (née Holder) Lynette A. , D’A. Bellairs A. 
Published: April 2021

ABSTRACT
The structure and development of the fracture planes in the tail of Lacerta vivipara are briefly described. The histological features of normal tail regeneration in baby and adult lizards are described. Regeneration occurs after autotomy or after amputation through either an intravertébral or an intervertebral plane, and becomes clearly visible after 2 to 3 weeks. The technique, based on the work of Panigel, of rearing embryos of lizards in a form of culture after removal from the mother, and of operating on them is described. In recent experiments over 40 per cent, of the embryos subjected to the operation of tail amputation at stages 30 – 32 in the normal table by Dufaure and Hubert survived to reach near hatching stages (39 – 40). A few hatched after periods of 17 to 24 days in culture at 28° C. Embryos operated on at very late stages generally succeeded in hatching. The effects of tail amputation during embryonic life were studied histologically in fifty-nine individuals. Almost all the embryos operated on at stages younger than 39 failed to regenerate after up to 36 days in culture, and showed appearances suggestive of rapid healing. Most of the embryos operated on at stages 39 – 40, very late in embryonic life, showed early regenerative changes. Others showed failure of regeneration, as in the younger embryos, and in a few specimens the results were doubtful. A possible reason for the lack of regenerative power in embryo lizards, and for its appearance at or shortly before hatching (or in nature, birth) is suggested. There is evidence that regeneration may depend upon the rate of healing and the extent of the wound surface. Substantial keratinization of the scales and stiffening of the sub-epidermal tissues occur towards the end of embryonic life. By preventing premature healing and helping to maintain a large wound surface such changes may provide the necessary conditions for regeneration. From the standpoint of natural selection the lack of regenerative power of the lizard embryo is not surprising, since regeneration would have no survival value until post-natal life.
Laminar specific attachment and neurite outgrowth of thalamic neurons on cultured slices of developing cerebral neocortex
Authors: Emerling Daniel E. , Lander Arthur D. 
Published: April 2021

ABSTRACT
In nervous system development, the growth cones of advancing axons are thought to navigate to their targets by recognizing cell-surface and extracellular matrix molecules that act as specific guidance cues. To identify and map cues that guide the growth of a particular axonal system, the thalamocortical afferents, an assay was devised to examine short-term interactions of dissociated embryonic thalamic cells with living, ∼150 μm slices of developing mouse forebrain. Thalamic cells rapidly (&lt;3 hours) and efficiently attached to and extended neurites on pre- and postnatal slices, but a broad zone throughout the neocortex was generally non-permissive for both thalamic cell attachment and the ingrowth of neurites. This zone coincided with the cortical plate at early stages (embryonic day 15), but later became restricted, in rostral-to-caudal fashion, to cortical laminae 2/3. Thus, at each stage, thalamic cells in vitro avoided just that area that thalamic axons confront, but generally do not enter, in vivo. In addition, neurites that extended on some layers were found to be significantly oriented in directions that coincide with the pathways that thalamic axons follow in vivo. These results imply that local adhesive cues and signals that affect process outgrowth are distributed among developing cortical laminae in a manner that could underlie much of the temporal and spatial patterning of thalamocortical innervation.
A Dictyostelium anterior-like cell mutant reveals sequential steps in the prespore prestalk differentiation pathway
Authors: Bichler Georg , Weijer Cornelis J. 
Published: April 2021

ABSTRACT
We have isolated Dictyostelium cell type proportioning mutants in a screen for cAMP signal transduction mutants. All mutants showed reduced numbers of prespore cells as analyzed with prespore-specific antibodies and prespore- and prestalk-specific reporter gene constructs. Formation of prestalk and prespore cells in the mutant HP1 is initially almost normal; however, many prespore cells redifferentiate as anterior-like cells leading to altered cell type proportions. Synergy experiments of HP1 transformant cells with wild-type Ax2 slugs showed the existence of stable subpopulations of cells in the prestalk and prespore regions of the slug. HP1 cells sort exclusively to the back of the prestalk and prespore zone in slugs. These cells will form the upper and lower cup regions of the culminate. Ax2 transformant cells sort to the tip of the anterior prestalk and prespore zone in HP1 slugs and will form the stalk and spores in the culminate.
These experiments show that upper and lower cup derive from cells in different differentiation pathways. The lower cup cell derive from prespore cells, which redifferentiate as anterior-like cells in the back of the prespore zone. The upper cup cells derive from cells from the back of the prestalk zone. Synergy experiments showed that the mutation in HP1 results in an altered sensitivity to proportioning signals. The mutation in HP1 may result in a reduced sensitivity to cAMP, which facilitates the redifferentiation of prespore cells via anterior-like to lower cup cells and inhibits the transition from upper cup to stalk cells.
Developmental control of allelic methylation in the imprinted mouse Igf2 and H19 genes
Authors: Feil Robert , Walter Jörn , Allen Nicholas D. , Reik Wolf 
Published: April 2021

ABSTRACT
The Insulin-like growth factor 2 (Igf2) and H19 genes are reciprocally imprinted and closely linked. Igf2 encodes a fetal growth-factor and is predominantly expressed from the paternal allele, while H19 is expressed from the maternal allele and encodes a transcript which may down-regulate cellular proliferation. One of the epigenetic modifications thought to be involved in parental imprinting is DNA methylation. Here we analyse methylation in two regions of the Igf2 gene, one approx. 3 kb upstream of the gene and one in the 3′ part of the gene. Both regions are more methylated on the expressed paternal chromosome. Genomic sequencing of individual chromosomes in the first region shows this parent-specific methylation to be highly mosaic; interestingly, individual sperm chromosomes carry different methylation patterns into the egg. In the more 3′ region, which is fully methylated in sperm, the level of methylation on the paternal allele is highly tissue-specific and is correlated with expression of the gene in fetal tissues. Hence, the paternal allele is highly methylated in fetal liver (high expression) but is undermethylated in fetal brain (virtually no expression). Adult choroid plexus, a brain tissue in which Igf2 is expressed from both alleles and H19 is not expressed, represents an apparent loss of imprinting. Here, both Igf2 and H19 adopt a paternal type methylation pattern on both parental chromosomes. Analysis of early-passage androgenetic and parthenogenetic embryonic stem (ES) cells shows that the methylation patterns of Igf2 and H19 on maternal and paternal chromosomes are very similar. Androgenetic and parthenogenetic teratomas derived from these ES cells show the appropriate paternal and maternal patterns, respectively, of allelic methylation in both genes. Our results suggest that allelic methylation patterns in Igf2 and H19 arise early in embryogenesis and change progressively during development. Some of these developmental changes are apparently under tissue-specific control.
Positioning adjacent pair-rule stripes in the posterior Drosophila embryo
Authors: Langeland James A. , Attai Sherwin F. , Vorwerk Kathy , Carroll Sean B. 
Published: April 2021

ABSTRACT
We present a genetic and molecular analysis of two hairy (h) pair-rule stripes in order to determine how gradients of gap proteins position adjacent stripes of gene expression in the posterior of Drosophila embryos. We have delimited regulatory sequences critical for the expression of h stripes 5 and 6 to 302 bp and 526 bp fragments, respectively, and assayed the expression of stripe-specific reporter constructs in several gap mutant backgrounds. We demonstrate that posterior stripe boundaries are established by gap protein repressors unique to each stripe: h stripe 5 is repressed by the giant (gt) protein on its posterior border and h stripe 6 is repressed by the hunchback (hb) protein on its posterior border. Interestingly, Krüppel (Kr) limits the anterior expression limits of both stripes and is the only gap gene to do so, indicating that stripes 5 and 6 may be coordinately positioned by the Kr repressor. In contrast to these very similar cases of spatial repression, stripes 5 and 6 appear to be activated by different mechanisms. Stripe 6 is criti-cally dependent upon knirps (kni) for activation, while stripe 5 likely requires a combination of activating proteins (gap and non-gap). To begin a mechanistic understanding of stripe formation, we locate binding sites for the Kr protein in both stripe enhancers. The stripe 6 enhancer contains higher affinity Kr-binding sites than the stripe 5 enhancer, which may allow for the two stripes to be repressed at different Kr protein concentration thresholds. We also demonstrate that the kni activator binds to the stripe 6 enhancer and present evidence for a competitive mechanism of Kr repression of stripe 6.
Mutations in the FASS gene uncouple pattern formation and morphogenesis in Arabidopsis development
Authors: Torres-Ruiz Ramón A. , Jürgens Gerd 
Published: April 2021

ABSTRACT
The pattern of cell division is very regular in Arabidopsis embryogenesis, enabling seedling structures to be traced back to groups of cells in the early embryo. Recessive mutations in the FASS gene alter the pattern of cell division from the zygote, without interfering with embryonic pattern formation: although no primordia of seedling structures can be recognised by morphological criteria at the early-heart stage, all elements of the body pattern are differentiated in the seedling. fass seedlings are strongly compressed in the apical-basal axis and enlarged circum-ferentially, notably in the hypocotyl. Depending on the width of the hypocotyl, fass seedlings may have up to three supernumerary cotyledons. fass mutants can develop into tiny adult plants with all parts, including floral organs, strongly compressed in their longitudinal axis. At the cellular level, fass mutations affect cell elongation and ori-entation of cell walls but do not interfere with cell polarity as evidenced by the unequal division of the zygote. The results suggest that the FASS gene is required for mor-phogenesis, i.e. oriented cell divisions and position-dependent cell shape changes generating body shape, but not for cell polarity which seems essential for pattern formation.
bcl-xLx is the major bcl-x mRNA form expressed during murine development and its product localizes to mitochondria
Authors: González-García Maribel , Pérez-Ballestero Rafael , Ding Liyun , Duan Linda , Boise Lawrence H. , Thompson Craig B. , Núñez Gabriel 
Published: April 2021

ABSTRACT
Most examples of cell death in animals are controlled by a genetic program that is activated within the dying cell. The apoptotic process is further regulated by a set of genes that act as repressors of cell death. Of these, bcl-2 is expressed in a variety of embryonic and postnatal tissues which suggests a critical role for bcl-2 in organogenesis and tissue homeostasis. Surprisingly, mutant mice with targeted disruption of bcl-2 appear normal at birth and complete maturation of lymphoid tissues before succumbing to fulminant lymphopenia and polycystic renal disease by 2-5 weeks of age. This suggests that there may be genes other than bcl-2 that can regulate apoptosis during development. To begin to investigate this possibility, we have cloned and characterized the murine bcl-x gene, whose human counterpart displays striking homology to bcl-2. The predicted murine bcl-xL gene product exhibits a high level of amino acid identity (97%) to its human counterpart. Just like Bcl-2, the murine bcl-xL gene product can act as a dominant inhibitor of cell death upon growth factor withdrawal. In addition, the bulk of the bcl-xL product localizes to the periphery of mitochondria as assessed by a bcl-xL-tag expression system, suggesting that both Bcl-2 and Bcl-xL proteins prevent cell death by a similar mechanism. bcl-xL is the most abundant bcl-x mRNA species expressed in embryonic and adult tissues. The levels of bcl-xL mRNA appear higher than those of bcl-2 during embryonal development and in several adult organs including bone marrow, brain, kidney and thymus. In addition to bcl-xL, we have identified another form of bcl-x mRNA, bcl-xβ, that results from an unspliced bcl-x transcript. bcl-xβ mRNA is expressed in various embryonic and postnatal tissues. Surprisingly, the expression of bcl-xS (a negative regulator of programmed cell death) was undetectable by a sensitive S1-nuclease assay and polymerase chain reaction analysis of mouse tissues. Based on its tissue and developmental patterns of expression, it appears that bcl-x may play an important role in the regulation of cell death during development and tissue homeostasis.