bluuebunny/crossref_metadata_2025_split huggingface dataset:
The mechanism of feather pattern development in the chick: II. Control of the sequence of pattern formation
Authors: Davidson Duncan 
Published: April 2021

ABSTRACT
During the development of the dorsal feather pattern, a wave of morphogenesis sweeps across the skin forming successive anteroposterior rows of feather primordia. The preceding paper in this series showed that the morphogenetic wave is almost immediately preceded by a wave of determination at which feathers sites are established row by row, (Davidson, 1983). The present paper reports an in vitro experimental investigation of the movement of these waves across the skin.
The waves pass undisturbed across a cut made before the pattern forms. Although cultured skin does not grow and consequently forms only a few rows of primordia, the morphogenetic wave takes the same time to cross the prospective feather tissue as in vivo, indicating that the passage of this wave through cultured skin reflects its traverse of the entire pattern in vivo.
These results show that the movement of the waves of determination and morphogenesis does not depend on the propagation of any signal across the skin immediately ahead of primordium formation. Their movement derives from a gradient in the temporal differentiation of the skin, established before stage 29. In this respect, the temporal control of feather development in the chick skin resembles the control of somite development in the amphibian paraxial mesoderm (Pearson & Elsdale, 1979). The present results therefore suggest that a programmed gradient of temporal differentiation across the prospective patterned tissue is a common component of the mechanisms which form regular, repetitious patterns in vertebrate embryos.
A prestalk-cell-specific acid phosphatase in Dictyostelium discoideum
Authors: Oohata Akiko A. 
Published: April 2021

ABSTRACT
A simple and reliable method of separating and quantifying acid phosphatase activities in D. discoideum is described, and one of the electrophoretically distinguishable forms of the enzyme is shown to be specific for prestalk cells. Accumulation of this product commences some 2-3 h later in development than the prespore specific enzyme UDP-galactose polysaccharide transferase. This finding is discussed in terms of recent observations on the control of prestalk cell differentiation in this organism.
Restriction of developmental potential and trochoblast ciliation in Patella embryos
Authors: Janssen-Dommerholt C. , Wijk R. Van , Geilenkirchen W. L. M. 
Published: April 2021

ABSTRACT
At the 64-cell-stage embryos of Patella develop a prototroch consisting of four groups of four cilia-bearing cells. Ciliogenesis of isolated blastomeres and trochoblasts was studied, as well as the effect on it of cleavage arrest caused by cytochalasin B treatment. Isolation of blastomeres or trochoblast cells has no influence on ciliogenesis; neither has arrest of cleavage in whole embryos after the third cleavage. However, cleavage arrest before third cleavage completely prevents ciliogenesis. Thus, third cleavage is decisive for the expression of the developmental potential of the primary trochoblasts. Impairment of DNA synthesis by aphidicolin in the S-phase preceding third cleavage also prevents ciliogenesis. It is concluded that a determinant for ciliogenesis as well as certain nuclear factors must be segregated into the micromeres at third cleavage for ciliogenesis to occur in the prototroch cells.
An SEM analysis of neural crest migration in the mouse
Authors: Erickson C. A. , Weston J. A. 
Published: April 2021

ABSTRACT
The cellular morphology and migratory pathways of the trunk neural crest are described in normal mouse embryos, and in embryos homozygous for Patch in which neural crest derivatives develop abnormally. Trunk neural crest cells initially appear in -day embryos as a unique cell population on the dorsal neural tube surface and are relatively rounded. Once they begin to migrate the cells flatten and orient somewhat tangentially to the neural tube, and advance ventrad between the somites and neural tube. At the onset of migration neural crest cells extend lamellipodia onto the surface of the tube while detaching their trailing processes from the lumenal surface. The basal lamina on the dorsal neural tube is discontinuous when cell migration begins in this region. As development proceeds, the basal lamina gradually becomes continuous from a lateral to dorsal direction and neural crest emigration is progressively confined to the narrowing region of discontinuous basal lamina. Cell separation from the neural tube ceases concomitant with completion of a continuous basement membrane. Preliminary observations of the mutant embryos reveal that abnormal extracellular spaces appear and patterns of crest migration are subsequently altered. We conclude that the extracellular matrix, extracellular spaces and basement membranes may delimit crest migration in the mouse.
Transfilter studies on the mechanism of epithelio-mesenchymal interaction leading to chondrogenic differentiation of neural crest cells
Authors: Smith Linda , Thorogood Peter 
Published: April 2021

ABSTRACT
Interaction with an epithelium is a prerequisite for avian cranial neural crest (NC) cells to differentiate into cartilage and bone (Bee & Thorogood, 1980). In order to investigate the causal mechanism we have selected one such interaction - that between mesencephalic NC and retinal pigmented epithelium (RPE) for further study. Premigratory NC cells were grown transfilter to RPE explants of different developmental ages and on Nuclepore filters of different pore size which either allowed or prevented penetration by cell processes. Initial scanning electron microscopy (SEM) observations established that pores of 0·8μm allowed the passage of cell processes through the filter whereas 0·2 μm pores did not.
The transfilter experiments demonstrated that chondrogenic differentiation of NC cells will occur only if the Nuclepore filters have a pore size large enough to permit the passage of cell processes. Furthermore SEM observations established that cell processes do traverse the Nuclepore filter when NC and RPE are grown in transfilter combination. The results indicate that the mechanism is not mediated by diffusable factors but rather is mediated either by direct contact between NC cells and non-diffusable matrix closely associated with RPE or by direct plasmalemmal contact between RPE and NC cells through discontinuities in the basement membrane. The results of these experiments also demonstrate that younger (stage 17) RPE is more effective at eliciting chondrogenesis from premigratory NC cells than older (stage 24) RPE and that the interaction between RPE and NC cells is a prolonged one, taking place over days rather than within hours. Both of these in vitro observations are compatible with the timing of events leading to scleral cartilage formation in vivo.
Nature of the hypoblastic influence on the chick embryo epiblast
Authors: Mitrani E. , Shimoni Y. , Eyal-Giladi H. 
Published: April 2021

ABSTRACT
Stage XIII chick blastoderms deprived of the marginal zone, the area opaca and the posterior half of the hypoblast, when incubated further developed axes whose orientation in 50 % of the cases was according to the original blastoderm’s orientation, whilst in 50 % of the cases they developed at 90° from the posterior side. Those results illustrate the quantitative differences in inductivity between the anterior and the posterior hypoblastic halves. Normally the posterior region has the highest effect but other regions can also bring about the development of an embryonic axis if allowed to act upon the epiblast for a sufficiently long period of time. The possible ways in which a chick hypoblast influences the epiblast to develop an embryo are examined in the light of recent findings and of new experiments described below.
Expression of the yolk-protein genes in the mutant doublesex dominant (dsxD) of Drosophila melanogaster
Authors: Bownes Mary , Dempster Maureen , Blair Mairearad 
Published: April 2021

ABSTRACT
Adult flies mutant for doublesex dominant (dsxD) are intermediate in phenotype between males and females. The dsxD mutation acts in the heterozygous state to transform only flies with two X chromosomes into intersexes, XY flies are unaffected by the mutation. Yolkprotein synthesis, which normally occurs in the ovaries and fat bodies of females, but not in males unless stimulated with 20-hydroxy-ecdysone, is reduced. The dsxD fat body synthesizes less yolk proteins throughout adult life, and the gonads rarely make yolk proteins. Using cloned yolk-protein genes as probes for measuring transcript levels we have shown that expression of these genes in dsxD is regulated both transcriptionally and post-transcriptionally. We suggest that the dsxD locus regulates the expression of the yolk-protein genes from within the fat body cells and does not operate by modulating ecdysteroid titres in the adults.
A boundary model for pattern formation in vertebrate limbs
Authors: Meinhardt Hans 
Published: April 2021

ABSTRACTWe postulate that positional information for secondary embryonic fields is generated by a cooperative interaction between two pairs of differently determined cell types. Positional information is thus generated at the boundaries between cells of different determination. The latter are assumed to result from the primary pattern formation in the embryo. The application of this model to vertebrate limbs accounts for the pairwise determination of limbs at a particular location, with a particular handedness and alignment to the main body axes of the embryo. It accounts further for the gross difference in the regeneration of double anterior and double posterior amphibian limbs as well as for the formation of supernumerary limbs after certain graft experiments including supernumeraries in which the dorsoventral polarity changes or which consist of two anterior or two posterior halves. Our model provides a feasible molecular basis for the polar coordinate model and successfully handles recently found viola-tions, for instance formation of supernumerary limbs after ipsilateral grafting with 90° rotation. The most frequent types of developmental malformations become explicable. The models allow specific predictions which are fully supported by recent experiments (see the accompanying paper of M. Maden).
Tissue interactions in the organization and maintenance of the muscle pattern in the chick limb
Authors: Mauger Annick , Kieny Madeleine , Hedayat Ihsan , Goetinck Paul F. 
Published: April 2021

ABSTRACT
Recent investigations on a hereditary muscular dysgenesis (cn/cn) in the chicken (Kieny, Mauger, Hedayat & Goetinck, 1983) have suggested that limb muscle pattern development and subsequent maintenance are two independent steps in the formation of the musculature. The respective activities or muscle cells and connective tissue cells in the ontogeny of the musculature have been investigated in avian embryos 1) by in ovo administration of drugs interfering with collagen biosynthesis, and 2) by heterogenetic somite-exchange experiments between normal and mutant embryos.
None of the drugs administered to the chick embryo caused any disturbance of muscle pattern formation or maintenance whether treatment occurred before (5 days) or after (7-5 days) the muscle splitting period.
Heterogenetic implantations were performed at 2 days of incubation either at the leg or at the wing level. Somitic mesoderm from non-mutant quail embryo was grafted to replace a piece of somitic mesoderm in putative mutant (cn/cn) chick embryos. The introduction of normal myogenic cells into a mutant leg or wing led to a normally patterned musculature, which demonstrates that the muscular dysgenesis cn/cn results from a defect of the somitic myogenic cell line.
Role of theesc+gene product in ensuring the selective expression of segment-specific homeotic genes inDrosophila
Authors: Struhl Gary 
Published: April 2021

ABSTRACTThe product of the extra sex combs+ (esc+) gene is required during embryogenesis for the correct determination of segments in Drosophila. If this product is absent, most segments develop like the normal eighth abdominal segment. Here, I extend previous results (Struhl, 1981a) showing that this phenotype results in large part from indiscriminate expression of the bithorax-compiex genes which are normally active only in particular segments of the thorax and abdomen. In addition, I test whether the esc+ gene product is required for the correct expression of other homeotic genes. First, I have examined two genes of the Antennapedia- complex (Sex combs reduced+ and Antennapedia+): I find that both genes are normally required in only some of the body segments, but that in the absence of the esc+ gene product, both appear to function adventitiously in other segments. Second, comparing esc+ and esc+ embryos lacking both these genes as well as the bithorax-compiex, I find that additional homeotic genes (possibly those normally involved in specifying head segments) appear to be expressed indiscriminately when the esc+ gene product is absent. Finally, I present evidence that the products of the esc+ gene and the Poly comb+ gene (a second gene required for the correct regulation of the bithorax-complex) act independently. On the basis of these results, I propose a tentative outline of the roles and realms of action of all of these genes.
An analysis of contractile proteins in developing chick heart by SDS polyacrylamide gel electrophoresis and electron microscopy
Authors: Lim Soo-Siang , Woodroofe M. Nicola , Lemanski Larry F. 
Published: April 2021

ABSTRACT
Chick heart development was studied using transmission electron microscopy and SDS-polyacrylamide gel electrophoresis in combination with densitometry. Myosin heavy chain, α-actinin, actin and tropomyosin accumulations were analysed in developing hearts from preheartbeat stage 9 (Hamburger-Hamilton staging series) through 2 days after hatching. At the preheartbeat stage, electron microscopy revealed a significant number of thin filaments scattered throughout the cytoplasm of the myoblasts; however, very few thick filaments were seen. There was no obvious association between the two filament types. SDS-polyacrylamide tube gels of heart muscle homogenates demonstrated the presence of all five proteins in hearts at the preheartbeat stage. Further analyses of the proteins by gel densitometry indicated that both actin and myosin accumulated rapidly during heart development while a-actinin and tropomyosin levels remained relatively static. Our results show that detectable quantities of myosin heavy chain, α-actinin, actin and tropomyosin accumulate in myocardial cells prior to the appearance of myofibrils and initiation of the contractile function.
Evidence for a functional role of the cytoskeleton in determination of the dorsoventral axis in Xenopus laevis eggs
Authors: Ubbels Geertje A. , Hara K. , Koster C. H. , Kirschner M. W. 
Published: April 2021

ABSTRACT
A normal table of events of the first cleavage period in the fertilized egg (cf. Gerhart, 1980) has been completed (cf. Table I) by studying external and internal features. Through a cytological study of eggs fixed after video time-lapse observation such features can directly be correlated and it has been shown that the first postfertilization wave (PFW) reflects spermaster growth, which causes rearrangements of animal yolk material. This may, in conjunction with the interaction of the spermaster rays with the cortex, define, in time as well as in space, the asymmetric cortical contraction which we suppose to evoke asymmetry in the animal hemisphere by formation of the vitelline wall (Pasteels, 1964) and in the vegetal hemisphere by formation of the Vegetal Dorsalising Centre (Kirschner et al. 1981).
Neither prick-activated eggs nor fertilized eggs incubated in vinblastine develop a spermaster. Under these conditions abnormal cytoplasmic segregation may be directed by gravity alone. For normal development the activated egg must in some way, for instance through the sperm centriole, organize microtubule assembly into a monaster. The centriole acts as a microtubule-organizing centre in structuring the egg’s cytoskeleton, and through this directs localization of the various yolk components, in time as well as in space. In egg rotation experiments performed under appropriate conditions, the cytoskeleton is disturbed and yolk rearranges under gravity till a new equilibrium is established which determines a new dorsoventral polarity. Such experiments also show that neither the dorsal cytoplasm nor the grey crescent cortex act as the ultimate dorsal determinants, since their localization is unaltered upon rotation, whereas the overall yolk distribution is significantly changed.
Cytoplasmic and cortical factors participating in cleavage furrow formation in eggs of three amphibian genera; Ambystoma, Xenopus and Cynops
Authors: Sawai Tsuyoshi 
Published: April 2021

ABSTRACT
A cytoplasmic factor and a cortical factor participating in cleavage furrow formation had been previously found in Cynops eggs (Sawai, 1972). These were investigated in the present study in Ambystoma and Xenopus eggs, by the method of cytoplasmic or cortical transplantation. Results were practically similar to those previously obtained with Cynops, indicating that in all the species of eggs during cleavage, the cytoplasm localizing along the cleavage furrow possessed furrow-inducing activity, and the cortex was competent to form the furrow in response to the activity of the cytoplasmic factor. In the present work, the species specificity of the two further factors was examined among Cynops, Ambystoma and Xenopus eggs, and the factors were found to act across species.
The effect of vitamin A on the regenerating axolotl limb
Authors: Maden M. 
Published: April 2021

ABSTRACT
These experiments describe further investigations into the effects of vitamin A on regenerating limbs. The effects of different retinoids, the time of administration, concentration of vitamin A and histological, autoradiographic and histochemical studies are reported. The most obvious result of vitamin A treatment is to cause proximal elements to regenerate from distal amputation levels, that is to cause serial reduplication of pattern in the proximodis-tal axis. Retinoic acid was the most potent of the analogues tested and longer times of administration or higher concentrations cause a greater amount of serial reduplication. Various tissue changes have been found which include the inhibition of cell division, loss of cartilage metachromasia, changes in the mucous-secreting properties of the epidermis and an increased packing in the blastemal cells. The significance of these cellular effects in relation to the pattern-formation changes is discussed.
The fifth cell cycle of the mouse embryo is longer for smaller cells than for larger cells
Authors: Macqueen Hilary A. , Johnson Martin H. 
Published: April 2021

ABSTRACT
Newly-formed pairs of 16-cell blastomeres were collected by periodic observation of isolated 8-cell blastomeres. Any pairs formed by division were recovered and classified as being composed of 1/16 blastomeres that differed in size or were of similar size. All of the latter and some of the former were then cultured for periods of up to 20 h. The remaining pairs of different-sized blastomeres were disaggregated to larger or smaller cells. Some of these were reaggregated as smaller: smaller or larger: larger pairs, and these, together with the remaining isolated smaller and larger blastomeres were also cultured for up to 20 h. At hourly intervals, cultured cells were sampled and analysed for incidence of division. It was found that larger cells divided on average after 12 h whereas smaller cells divided on average after 14 h.
Sodium transport and the control of epiblast polarity in the early chick embryo
Authors: Stern Claudio D. , MacKenzie Debora O. 
Published: April 2021

ABSTRACT
The sodium transport properties of chick epiblast during gastrulation were studied by various techniques. It was found that the epiblast is capable of unidirectional apical to basal sodium transport, in towards the underlying intraembryonic space. The Na-K-ATPase was localized by [3H]ouabain binding and autoradiography near the basal surfaces of the cells, and the number of pump sites was quantified. The transport rate of sodium was determined with 22Na. Electrophysiological studies on embryos at primitive streak stages showed a trans-epithelial potential of about +16 ±5 mV (basal side positive) which was sensitive to strophanthidin. Applying similar voltages but of reverse polarity to isolated sheets of epiblast caused a rapid reversal of some of their morphological polarity markers as well as some of their physiological functions. The relevance of these results to development is discussed.
Neuronal cell death in grasshopper embryos: variable patterns in different species, clutches, and clones
Authors: Loer Curtis M. , Steeves John D. , Goodman Corey S. 
Published: April 2021

ABSTRACT
Previous studies showed that cell death plays an important role in adjusting the segmentspecific number of ganglionic neurones during grasshopper embryogenesis (Bate, Goodman & Spitzer, 1979; Goodman & Bate, 1981). In every segment, the single midline precursor 3 (MP3) divides once to produce two progeny. In some segments, one or both of these two progeny die; there is a general pattern of cell death of the MP3 progeny across the thoracic and abdominal segments.
In the present study we examined the pattern of cell survival versus death of the MP3 progeny in 472 embryos from four different species, from the genetically related offspring within different clutches of the same species and from the genetically identical offspring within isogenic clones of the same species. We find variability in the pattern of cell survival versus death amongst embryos of the same species, clutch and clone, suggesting a significant epigenetic influence on this pattern. However, our results also show significant differences in the pattern of cell death between different genera and species, and between different clones and clutches within a single species, suggesting a genetic influence on this pattern as well.
Light microscope observations on actin distribution during morphogenetic movements in the chick embryo*
Authors: Ostrovsky David , Sanger Joseph W. , Lash James W. 
Published: April 2021

ABSTRACT
The cellular distribution of actin during two morphogenetic processes in the chick embryo has been observed, using a high-resolution fluorescent technique, with heavy meromyosin as a probe. These cytoskeletal elements have been implicated in all cell and tissue movements in the embryo. It is now commonly accepted that microfilaments are necessary to provide the motive force for morphogenesis. Two morphogenetic movements in the early embryo have been studied at the light microscope level. During somitogenesis, the mesenchymal segmental plate becomes transformed into a meristic series of transient epithelial vesicles. Again, actin distribution is diffuse and random before the morphogenetic event. During epithelialization, actin becomes prominent in the apical regions of the epithelial cells. Cells in the somitic epithelial vesicles, the core cells, appear to be passive participants in this process, and consequently show no distinct cellular localization of actin.
Normal adenylate ribonucleotide content in mouse embryos homozygous for the t12 mutation
Authors: Spielmann Horst , Erickson Robert P. 
Published: April 2021

ABSTRACT
The recently improved firefly luciferase assay was used to determine ATP, ADP or AMP in single preimplantation mouse embryos from crosses yielding lethal t12/t12 embryos. Normal values of the three adenylate ribonucleotides were found in freshly collected 2-cell and 4-cell embryos and during in vitro culture to the blastocyst stage. A decrease in adenylate ribonucleotide content was seen in putative t12/t12 embryos only when they were degenerating.