bluuebunny/crossref_metadata_2025_split huggingface dataset:
Studies on the possible role of cyclic AMP in limb morphogenesis and differentiation
Authors: Kosher Robert A. , Savage Mary P. 
Published: April 2021

ABSTRACT
Recent studies indicate that one of the major functions of the apical ectodermal ridge (AER) of the embryonic chick limb bud is to maintain mesenchymal cells directly subjacent to it (i.e. cells extending 0·4 –0·5 mm from the AER), in a labile, undifferentiated condition, and that when mesenchymal cells are freed from the AER’s influence either artificially or as a result of normal polarized proximal to distal limb outgrowth, they are freed to commence cyto-differentiation. In a preliminary attempt to investigate at a molecular level the mechanism by which the AER exerts its ‘negative’ effect on the cytodifferentiation of subjacent mesenchymal cells, we have examined the effect of a variety of agents that elevate cyclic AM P levels on the morphogenesis and differentiation of the unspecialized subridge mesoderm in an organ culture system. In vitro in the presence of the AER, undifferentiated subridge mesoderm explants undergo remarkably normal morphogenesis characterized primarily by progressive polarized proximal to distal outgrowth and changes in the contour of the developing explant. In the presence of cyclic AMP derivatives, explants fail to undergo the polarized outgrowth and contour changes characteristic of control explants. In fact, in the presence of di butyryl-cyclic AMP and theophylline, AER-directed morphogenesis essentially ceases during the first day of culture. The cessation of AER-directed morphogenesis in the presence of cyclic AMP derivatives is accompanied by the histochemically and biochemically detectable precocious chondrogenic differentiation of the subridge mesenchymal cells. In control explants, cartilage differentiation only occurs in those proximal cells of the explant which gradually become located greater than 0·4 –0·5 mm from the AER. In contrast, in the presence of cyclic AMP derivatives, cartilage differentiation by cells within 0·4 –0·5 mm of the AER is detectable from the first day of culture, and by the third day cartilage formation has occurred throughout the entire explant. Overall, these results indicate that elevating the cyclic AMP content of the subridge mesenchymal cells enables the cells to overcome negative influences on cytodifferentiation and the positive influences on morphogenesis being imposed upon them by the AER. On the basis of this observation and previous studies, a testable model on the role of cyclic AMP in limb morphogenesis and differentiation is proposed.
Regulation and potency in the forelimb rudiment of the axolotl embryo
Authors: Slack J. M. W. 
Published: April 2021

ABSTRACTAnterior, posterior, dorsal and ventral halves of the pre-bud forelimb rudiment of tail-bud axolotl embryos can all give rise to normal limbs after the complementary half has been removed.A histological study of the regulation of the posterior half rudiment showed no requirement for mesodermal healing across the gap, and no proliferative zone. The development of the limb bud on the operated side lags behind that of the control bud for several weeks of larval life.When half limb rudiments and double half limb rudiments were grafted to the head they did not develop unless both the posterior and the dorsal margin were present. Double posterior and double dorsal halves could develop into duplications on this site, single halves formed normal or hypomorphic limbs.When half limb rudiments were grafted to the flank the anterior halves developed into normal limbs and the posterior halves into duplicate limbs.The results are interpreted to indicate that at the pre-bud stage the limb rudiment is a homogeneous group of cells with no internal regional subdivisions. Its regulative behaviour is thus similar to that of early embryos and different from the regeneration behaviour shown by adult organs.
Qualitative changes in DNA indicating differential DNA replication during early embryogenesis of the newt Triturus vulgaris
Authors: Lohmann Klaus , Schubert Lore 
Published: April 2021

ABSTRACT
During gastrulation of the newt Triturus vulgaris considerable changes in the melting behaviour and in the CsCl density gradient pattern of DNA occur. The melting curves of DNAs from mid to late gastrulae (stages 11 b–12c) deviate from the regular shape. Whereas the Tm values are identical in the stages 11 a (early gastrula) and 15 (early neurula), and correspond to the standard DNA (stage 36 = tailbud), a significant rise of Tm (0· 8–1·2 °C) has been recorded in the stages 12 a/b (yolk plug). The differences in melting behaviour become visible by the deviation of the curves above Tm. These deviations from the normal sigmoidal shape are caused by the fact that a portion of DNA melts at higher temperatures than usual. Therefore the thermal denaturation of DNA is completed at approximately 3–4 °C later than in standard DNA. Both the derivative curves and the plots on normal probability paper demonstrate a heterogeneity of DNA in the stages 11 b–12c which indicates the presence of an additional GC-rich satellite fraction. These findings are confirmed by CsCl density gradient studies. Thus, in the stages 12a/b a slight shoulder on the heavy side of the gradients occurs, being absent in the other stages. From these facts we have to conclude that there is a. stage-dependent multiplication and elimination of GC-rich sequences.
Changes in lectin-mediated agglutinability during primary embryonic induction in the amphibian embryo
Authors: Barbieri Francisco D. , Sánchez Sara S. , Pino Enrique J. Del 
Published: April 2021

ABSTRACT
The present study was undertaken to investigate structural alterations at the surface of presumptive neural cells after primary embryonic induction. For this purpose, plant lectin-mediated agglutinability of dissociated cells from the epiblast of Bufo arenarum gastrulae was tested. Two fragments of epiblast were excised from the same mid-gastrula: one from the dorsal side of the egg, making contact with the invaginating chordamesoblast and assumed to be composed of determined cells and the other from the ventral region of the egg, facing the blastocoele cavity and assumed to be composed of undetermined cells. Cells of the pooled fragments were dissociated in calcium-free Holtfreter’s solution with potassium oxalate and incubated in the presence of different concentrations of phytohemagglutinin and concanavalin A. Epiblast cells overlying the archenteron roof are less agglutinated with both lectins than undetermined cells. On the other hand, when egg fragments were removed from the dorsal and ventral regions of early gastrulae before the archenteron was formed, no significant difference in lectin-mediated agglutinability was observed, even after having been cultured in vitro in absence of inducing tissue. These results suggest that the target of the inducing signal generated in the mesoblast is likely to be located on the surface of epiblast cells. Additional experiments showed that cells pretreated with colchicine, cytochalasin B or colchicine and cytochalasin B simultaneously exhibit no significant variation in agglutinability, suggesting that the cytoskeleton was not be involved in the cell surface alteration here described.
Treatment of whole embryos or sandwich explants with concanavalin A or phytohemagglutinin has no effect on neural tube formation, suggesting that the carbohydrate-containing binding sites for these lectins are not involved in primary embryonic induction. Changes in cell agglutinability described in this paper are to be interpreted thus as a secondary expression of structural alterations in the cell surface concomitant with neural determination.
Somitogenesis in amphibian embryos: III. Effects of ambient temperature and of developmental stage upon pattern abnormalities that follow short temperature shocks
Authors: Cooke Jonathan , Elsdale Tom 
Published: April 2021

ABSTRACT
Temperature shocks of a few minutes duration at 37 °C to tail-bud embryos of Rana induce zones of abnormal segmentation along the somite files subsequently produced. The immediate result of a temperature shock is a temporary arrest of development as a whole, following which the schedule of somite determination and formation is resumed at the normal rate. It is during the period immediately following this that the zone of abnormal somite pattern is determined. Thus the length of the abnormal zone reflects the total time taken by the morphogenetic system to recover from the disturbance, and might depend upon variables affecting both the duration of the initial arrest and the duration of the recovery period itself.
Observations are presented demonstrating how the lengths of abnormal zones, caused by a temperature shock of any particular severity, are affected by three variables : (1) the ambient temperature to which the embryos were adapted before shock, (2) the ambient temperature of post-shock development, (3) the stage in somitogenesis, i.e. the number of somites already formed at the time of shock.
The data (in this and previous papers of the series) support models postulating that the spatial periodicity in cell behaviour, that is somite morphogenesis, reflects a normal interaction between two hidden aspects of development, one a wavefront of cellular activation passing down the body axis, and the other having the character of a temporal periodicity throughout the tissue. Temperature shock, as well as halting the wavefront (i.e. stopping development) temporarily, leads to a subsequent period during which there is only gradual recovery of normal co-ordination between the periodicity within cells of the tissue and the wavefront progress. It is the relative rate of this recovery, alone, that is responsible for variation in the length of the abnormal zone.
Developmental fate of a distinct class of chick myoblasts after transplantation of cloned cells into quail embryos
Authors: Womble Mark D. , Bonner Philip H. 
Published: April 2021

ABSTRACTA technique appropriate to investigation of the developmental fates of distinct embryonic cell types is described and the fate of a particular type of chick myoblast (CMR-I) examined. CMR-I myoblast clones are morphologically different from other chick myoblast clone types and can readily be identified in living cultures.After two weeks of culture CMR-I myoblast clones were collected, aggregated, and transplanted into the prospective dorsal thigh region of young quail embryos. After four days of growth, cells of the transplant-containing quail legs were grown as clones. Chick clones were located by Feulgen staining and identified as muscle or non-muscle and, if muscle, as CMR-I or not; 91 % of the chick clones recovered from transplants were muscle clones, and of these 97% were CMR-I. It was concluded that CMR-I myoblasts do not undergo a change in differentiated state identifiable by clonal analysis.Other transplant-containing quail legs were fixed, sectioned, and Feulgen stained. The locations of chick nuclei were determined. The only region in which chick nuclei appeared at significantly greater frequency than in control tissue was the dorsal thigh muscle, the region into which the cloned chick cells were placed originally. Dorsal thigh multinucleated myotubes exhibited the highest percentage of chick nuclei of all tissues examined. It was concluded that the fate of CMR-I myoblasts is fusion to form myotubes.
Palate morphogenesis:V. Effects of cholinergic agonists and antagonists on rotation in embryo culture
Authors: Wee Elizabeth L. , Phillips Nancy J. , Babiarz Bruce S. , Zimmerman Ernest F. 
Published: April 2021

ABSTRACT
Morphological studies have shown that the pterygopalatine ganglion in the day-14·5 mouse palatal shelf lies adjacent to the putative contractile system of region-2 cells in the posterior palate. It is of interest to learn whether the ganglion could influence rotation of the palate. Results of embryo culture experiments showed that acetylcholine appeared to play a role in posterior shelf rotation since cholinergic agents (pyridostigmine, bethanechol and carbachol) stimulated elevation of that end of the palate. To characterize the putative receptors mediating the effects of the cholinergic agonists on palate shelf elevation, muscarinic or nicotinic antagonists were introduced into the embryo culture system. Atropine, a muscarinic blocking agent, did not produce any significant effect on palate shelf rotation when tested in overnight and 2 h embryo cultures at 3 × 10−5 M and 10−4 M, respectively. Neither did atropine inhibit significantly the stimulation produced by 10−8 M bethanechol. Thus, the cholinergic effect was probably not on muscarinic receptors of the contractile system. However, hexaméthonium, a nicotinic antagonist, at 10−6 M and 10−4 M profoundly inhibited posterior shelf rotation to about 35 % of the control value in a 2 h incubation. In addition, 10−4 M hexaméthonium inhibited posterior palate rotation to 11 % of the control value after overnight culture. Furthermore, hexaméthonium was able to reverse the stimulation of posterior rotation produced by carbachol. Partial inhibition of palate rotation by hexaméthonium was also demonstrated when pregnant dams were injected with drug at doses approximately corresponding to 10−6 and 10−4 M. Hexaméthonium treatment resulted in approximately 30% of the palates not completely rotated at day 15·5 compared to only 9·3 % in the control. Hexaméthonium also produced a significant increase in the palate gap and a comparable decrease in palate fusion. These effects were slightly greater at the posterior end of the palate. Thus, the cholinergic ganglion in the posterior palate may play a role in regulating shelf rotation at that end through a nicotinic pathway.
Aggregation between teratocarcinoma cells and preimplantation mouse embryos
Authors: Stewart Colin 
Published: April 2021

ABSTRACT
The ability of two embryonal carcinoma (EC) cell lines, F9 and PCI3, to aggregate with preimplantation 8-cell mouse embryos is described. Both adhere to the embryonic cells and subsequently compact with the embryos. The aggregates form blastocysts in culture. The blastocysts sometimes contain the EC cells, located almost always in their inner cell mass. Differentiated derivatives of EC cells, namely PYS-1 and PYS-2, as well as STO fibroblasts do not aggregate with embryos.
A gradient of morphogenetic information involved in muscle patterning
Authors: Williams G. J. A. , Caveney S. 
Published: April 2021

ABSTRACT
The results of grafts performed in the larva of the beetle Tenebrio molitor reveal that the position at which certain adult muscle attachments form is specified by a regulative, rather than a mosaic, mechanism. The results of grafts involving the rotation of squares of integument through 180° or 90°, or the antero-posterior transposition of two adjacent rectangles of integument, show that the site of muscle attachments in the antero-posterior axis of an abdominal sternite is specified by an epidermal segmental gradient of positional information. This gradient is presumed to be identical to the gradient which specifies cuticular patterns in this insect. There is a good correlation between the effect of grafts on adult muscle morphology and cuticular patterns.
Formation of feathers on chick foot scales: a stage-dependent morphogenetic response to retinoic acid
Authors: Dhouailly Danielle , Hardy Margaret H. , Sengel Philippe 
Published: April 2021

ABSTRACTIn the chick embryo, large scales (scuta) form on days 9 –11 on the anterior face of the shank and the upper surface of the toes; smaller scales (scutella) appear on day 11 on the posterior face of the shank; most of the smallest scales (reticula) form on days 12 and 13 on the plantar surface of the foot.A single injection of 125 μg of retinoic acid (RA) into the amniotic cavity caused the formation of feathers on the foot scales in locations and percentages differing according to the age of embryos at the time of treatment. Injection at 10 days caused feathers to form on the feet in 57 % of the embryos, almost all of which bore feathers on their scuta and scutella; a few reticula were occasionally affected. When treated at 11 days, 48 % of embryos had feathered feet, the tarsometatarsal scutella and digital reticula being most frequently affected. Treatment at 12 days resulted in feathers on the feet of 15 % of the embryos, all of which bore feathers on the reticula only, while the scuta and scutella were not affected.It was concluded that the foot skin regions which were affected by RA treatment were those in which scale morphogenesis was starting or about to start at the time of injection. These regions contained pre-placodal or placodal stages of scuta and scutella, and the preelevation or elevation stages of reticula.
Scanning electron microscopy of wound healing inXenopusand chicken embryos
Authors: Stanisstreet Martin , Wakely Jennifer , England Marjorie A. 
Published: April 2021

ABSTRACTWound closure in the ectoderm of Xenopus early neurulae and chick primitive-streak embryos has been studied by scanning electron microscopy (SEM). Initial gaping of the wound and a cobble-stone appearance of cells peripheral to the wound in both Xenopus and chick confirm that the ectoderm is under lateral tension at these stages. Healing is rapid: in Xenopus embryos wound closure has started within 5 min of wounding; in chick healing is almost complete within 30 min in some cases. The SEM observations suggest that in Xenopus embryos changes in cell shape are the major mechanism for wound closure. In chick embryos wound healing is also accompanied by changes in the shape of the marginal cells, but evidence is presented that in this system cell proliferation is important. The mechanisms of wound healing in Xenopus and chick embryonic ectoderm are compared with those of wound healing in other tissues.
The in vitro transmission frequency of the t12 mutation in the mouse
Authors: McGrath James , Hillman Nina 
Published: April 2021

ABSTRACT
Male mice which are heterozygous for a recessive lethal mutation ( + /tL) transmit the tL mutation in non-Mendelian ratios. In the present studies, spermatozoa obtained from + t12 males were used to fertilize ova from + t12 females in vitro. The frequency of transmission of the t12 mutation determined from these in vitro studies was compared with the frequency of transmission of this mutation in normal and delayed matings. The data show that the transmission frequency of the t12 mutation, in vitro, is Mendelian and is the same as the transmission frequency of the t12 mutation in vivo when matings are delayed until the time of ovulation.
Immunohistochemical localization of cyclic AMP in the developing rodent secondary palate
Authors: Greene Robert M. , Shanfeld Joseph L. , Davidovitch Zeev , Pratt Robert M. 
Published: April 2021

ABSTRACT
During development of the mammalian secondary palate, medial-edge epithelia (MEE) from apposing palatal shelves adhere and undergo autolysis allowing palatal mesenchymal regions to unite. In a prior study (Greene & Pratt, 1979), we reported a transient increase in levels of cyclic AMP (cAMP) in the mouse and rat palate during epithelial adhesion and cell death. The objective of this study was to examine the distribution of cyclic AMP in the developing rodent secondary palate using immunohistochemistry to localize cyclic AMP. Staining for cAMP was observed in the epithelium just prior to and during epithelial fusion (day 16 in the rat; day 14 in the mouse). Cyclic AMP was distributed throughout the epithelial cytoplasm whereas no staining was seen in nuclei. Epithelial staining for cAMP was faint or absent 24 and 48 h prior to epithelial contact. Mesenchymal staining for cAMP was minimal and associated with the plasma membrane at all stages studied. These results demonstrate that elevated levels of cAMP in the rat and mouse palate during epithelial adhesion and cell death are mainly due to increases of the nucleotide in palatal epithelium. This observation suggests that a transient increase in epithelial cAMP may play a role in palatal epithelial differentiation.
Ommatidium assembly and formation of the retina-lamina projection in interspecific chimeras of cockroach
Authors: Nowel Mark S. 
Published: April 2021

ABSTRACT
By grafting operations, interspecific eye chimeras of the cockroaches Gromphadorhina portentosa and Leucophaea maderae were produced. Mechanisms involved in the development of both the compound eye and the retina-lamina projection have been studied. Most cell types composing the eyes of these cockroaches are cytologically distinguishable in the chimera; also, retinula axons forming the retina-lamina projection in the two species are of vastly different lengths. At the border between host and graft eye tissue, individual ommatidia are formed containing cells of both types. In particular, it is shown that the four cone cells can be found in any of the possible combinations of the two cell types. This shows that the cone cells within one ommatidium are not necessarily related by lineage. These results are in agreement with the hypothesis that cells within an ommatidium are determined by position rather than by a lineage mechanism. Furthermore, formation of mosaic ommatidia suggests that mechanisms governing eye formation are similar in these two species. The formation of the projection from donor retina to host lamina shows that axon elongation is not rigidly programmed, but that the axons grow until they reach a suitable target at which point connexions are made.
Chimaeric rabbits from immunosurgically-prepared inner-cell-mass transplantation
Authors: Babinet C. , Bordenave G. R. 
Published: April 2021

ABSTRACT
Rabbit inner cell masses (ICM’s) have been prepared by immunosurgery from 96-h-old blastocysts. Their properties are described. It is shown that ICM’s prepared this way retain their developmental potentialities. In particular if they are injected into host blastocysts, they appear to be able to participate in the development of the composite blastocysts thus obtained: upon implantation into a foster-mother the latter give rise, in a high proportion of cases, to chimaeric rabbits. Immunoglobulin allotypic markers as well as progeny test were used to assess chimaerism.
Expression of Forssman antigen in the post-implantation mouse embryo
Authors: Stinnakre M. G. , Evans M. J. , Willison K. R. , Stern P. L. 
Published: April 2021

ABSTRACT
The expression of Forssman antigen on the surface of cells of post-implantation mouse embryos between 5 and days old and of cells of the gonads from days has been followed using the monoclonal antiserum Ml/22.25. In the early post-implantation embryo a lineage-related distribution is found.
The inner cell mass of the blastocyst was previously shown to be Forssman antigen positive and its derivative tissues the epiblast of the 5-day embryo and the primary embryonic endoderm are also positive. The endoderm cells remain positive both over the embryonic and extraembryonic portions of the embryo but the epiblast becomes Forssman antigen negative as it differentiates into embryonic ectoderm. The extraembryonic ectoderm which is derived from the Forssman negative trophectoderm remains negative throughout. The primordial germ cells are Forssman antigen positive from their first appearance in the germinal ridge until day 14 when they become negative but after that time it is other cells not related by direct lineage which become Forssman antigen positive. These are tentatively identified as Sertoli cells precursors as it is the Sertoli cells which are the antigen-positive population in the adult testis.