bluuebunny/crossref_metadata_2025_split huggingface dataset:
Morphogenesis of the amphibian limb blastema: The relationship between pattern and form
Authors: Holder Nigel , Reynolds Susan 
Published: April 2021

ABSTRACT
A relationship between pattern formation and field shape is established following the formation of rounded blastemas on lower arm limb stumps after treatment with vitamin A. Pattern formation is not affected by alteration in blastemal shape caused by removal of the dermis from the thigh region of the leg. We conclude, therefore, that blastemal shape does not play a causal role in establishing limb pattern. Data relating the number of cells present between the cardinal axial poles of blastemas and the size of blastemas is discussed in terms of short arc intercalation and short range cell-cell interactions during pattern regulation.
Vibrissa dermal papilla cell aggregative behaviour in vivo and in vitro
Authors: Jahoda Colin A. B. , Oliver Roy F. 
Published: April 2021

ABSTRACT
Parallel cultures of adult rat vibrissa dermal papilla cells and skin fibroblasts revealed differences between the two cell types with respect to a number of criteria. In particular the dermal papilla cells demonstrated a distinctive single cell morphology, and at confluence formed cell aggregates radically different from regular fibroblast multilayering and patterning. This finding confirmed repeated observations of papilla cell clumping in short-term culture. The dermal papilla cells which are mitotically quiescent in situ were also shown to have a lower proliferative capacity than the skin fibroblasts. The affinity shown by papilla cells towards each other in culture reflected the behaviour demonstrated by isolated dermal papillae transplanted into ear dermis and into the collagenous capsule of the vibrissa follicle. In the absence of epidermal contact the papilla cells remained as recognizable rounded aggregates for the experimental period of up to nine months. Synthesis of extracellular material typical of that seen in situ was observed, particularly during the first weeks following transplantation. The collective behaviour of the dermal papilla cells revealed in this study may be significant for the morphogenetic activity of the papilla, and for papilla size during the hair cycle. It may also reflect the retention of embryonic-like properties by the dermal component of adult hair follicles.
The origin of intrahepatic bile duct cells in the mouse
Authors: Shiojiri Nobuyoshi 
Published: April 2021

ABSTRACT
The origin of the intrahepatic bile ducts in the embryonic mouse liver was investigated. At 12·5 and 13·5 gestation days in the C3H/Tw strain mouse, the liver parenchyma contains morphologically and histochemically homogeneous immature hepatocytes but not bile duct cells. When the liver fragments were cultured in the testis, immature hepatocytes differentiated into large hepatocytes for the most part and also into bile duct cells. In contrast, when the similar liver fragments were cultured under the skin of newborn mice, bile duct cells differentiated much earlier in all transplants than those cultured in the testis. These bile duct cells were considered to be the intrahepatic bile duct cells, since they did not form biliary glands but possessed a basal lamina and histochemical characteristics of intrahepatic bile duct cells of the normal liver. The origin of the endodermal epithelial cells in the mouse liver is discussed with special attention to the differentiation of the intrahepatic bile duct cells from the immature hepatocytes.
Skin glands in the axolotl: the creation and maintenance of a spacing pattern
Authors: Holder Nigel , Glade Richard 
Published: April 2021

ABSTRACT
The morphogenesis of skin glands in the larval axolotl is described at the light microscope level. The glands are derived from the epidermis, but are eventually located in the dermis. The glands are non-randomly arranged within the skin and the spacing pattern tends towards a hexagonal array in two dimensions. Analysis of the spacing pattern in animals of different sizes reveals that a clear relationship exists between gland size and the distance between glands. Occasionally, new small glands are inserted into the pattern, suggesting that the spacing of glands in under a dynamic control throughout the growth of the axolotl. The possible mechanisms underlying the creation and maintenance of the pattern are discussed.
Experimental Analysis of the Eye Morphogenesis in Mammals
Authors: Stroeva O. G. 
Published: April 2021

ABSTRACT
Owing to the great difficulties of experimental interference with the embryogenesis of mammals, the morphogenetic potentialities of the mammalian eye remain almost unstudied up to the present. The elucidation of whether the developing mammalian eye obeys the same rules that have been established for the lower vertebrates, or whether its development proceeds in another way, is interesting in many respects. It might allow us to answer a number of questions, e.g. how stable are the morphogenetic interactions within the vertebrates which result in the formation of homologous organs? How do the morphogenetic potentials of the parts of an organ alter in the course of evolution? Light might also be thrown on the development or loss of regenerative capacity in various forms. Lastly, we may find out to what extent the experiments on lower vertebrates, easily carried out on a large scale, are of use for the understanding of those processes which cause regularly recurring inborn malformations in man.
Néoblastes et limitation du pouvoir de regeneration céphalique chez la planaire Dendrocoelum lacteum
Authors: Kolmayer Simone , Stéphan-Dubois Françoise 
Published: April 2021

ABSTRACT
The regeneration of the planarian Dendrocoelum lacteum has been tested at three different levels of amputation : just behind the eyes, half-way between the eyes and the pharynx, and just in front of the pharyngeal base. The plana-rians always regenerate in the first case, never in the last case, and about 7 times out of 10 in the intermediate case. Experiments involving amputations and irradiations show that there are regeneration cells (neoblasts) in the regions behind the pharyngeal base, regions which are unable to regenerate. When they are not irradiated, these neoblasts are able to move towards the head and to restore the irradiated regions. They reconstitute a blastema with eyes, the number of cases directly depending on the prepharyngeal level of the section. The histology confirms the experimental results and demonstrates the processes of regression, of necrosis, and then of colonization of the irradiated regions.
The Developmental Capacity of Nuclei Taken from Differentiating Endoderm Cells ofXenopus Laevis
Authors: Gurdon J. B. 
Published: April 2021

ABSTRACTThe developmental potentiality of embryonic endoderm nuclei in X. laevis is shown to change as the tissue to which they belong becomes differentiated. This change has been demonstrated by taking nuclei from endoderm tissue in different stages of differentiation, and transplanting them into enucleated unfertilized eggs; the development of the resulting transplant-embryos indicates the developmental capacity of their nuclei. Since the proportion of total transplantations which become late blastulae is affected by the technique, the main conclusions have been drawn from the further development of late blastula transplant-embryos. The quality of recipient eggs, which is always variable, may also affect transplant-embryo development, and conclusions have therefore been mainly derived from selected experiments in which control donor nuclei have shown that egg quality was good. Reasons have been given for believing that non-hereditary nuclear qualities, such as their size and stage in mitosis, do not affect the conclusions drawn from transplantembryo development; their development is therefore solely dependent on the specific genetic qualities of the donor nuclei used. No decline in the developmental potentiality of endoderm nuclei was found in blastulae and gastrulae. However, the capacity of nuclei to form normal tadpoles decreased progressively from after gastrulation until the beginning of torsion in the gut of swimming tadpoles; at this late stage there was still a small proportion of undifferentiated nuclei from which normal tadpoles have been obtained. Thus nuclear differentiation affects an increasing proportion of nuclei to an increasing extent, as the endoderm becomes differentiated. Serial transplantation has shown that the changes involved in nuclear differentiation are heritable and, at least to a large extent, irreversible. These results are compared with those of Briggs & King who transplanted nuclei from endoderm cells of R. pipiens. In both Xenopus and Rana, nuclei are undifferentiated at the late blastula stage, but after this the rate and time of onset of nuclear differentiation is very different for the endoderm of the two species. These differences show that there is no exact correlation between nuclear differentiation and tissue differentiation. It is suggested that nuclear differentiation may be concerned in the processes which take place when individual cells become differentiated into their final functional state.
The distribution of endocrine cell progenitors in the gut of chick embryos
Authors: Rawdon B. B. , Kramer Beverley , Andrew Ann 
Published: April 2021

ABSTRACT
The aim of this experiment was to find out whether or not, at early stages of development, progenitors of the various types of gut endocrine cells are localized to one or more specific regions of the gastrointestinal tract. Transverse strips of blastoderm two to four somites in length were excised between the levels of somites 5 and 27 in chick embryos at 5- to 24-somite stages and were cultured as chorioallantoic grafts. The distribution of endocrine cells in the grafts revealed confined localization of progenitor cells only in the case of insulin-immunoreactive cells. The progenitors of cells with somatostatin-, pancreatic polypeptide-, glucagon-, secretin-, gastrin/CCK-, motilin-, neurotensin- and serotonin-like immunoreactivity were distributed along the length of the presumptive gut at the time of explantation; indeed, in many cases they were more widespread than are their differentiated progeny in normal gut of the same age. This finding indicates that conditions in grafts must differ from those that operate in the intact embryo. Also it may explain the occurrence of ectopic gut or pancreatic endocrine cells in tumours of the digestive tract.
Stages in the development of cat muscle spindles
Authors: Milburn Alice 
Published: April 2021

ABSTRACT
The structure of developing spindles has been examined in cat peroneal muscles by light and electron microscopy, beginning at the 34- to 38-day foetal stage.
By this stage α motoneurons have formed end-plates on primary myotubes. Secondary extrafusal myotubes then develop beneath the basal lamina of primary myotubes, and are innervated by motor axons early in their assembly. First-series secondary myotubes separate from primary myotubes prior to the development of subsequent series. The assembly of extrafusal fibres is completed by birth.
Intrafusal fibres assemble in a similar manner. At the 34- to 38-day foetal stage developing spindles consist of a single primary myotube containing a small accumulation of myonuclei beneath the terminals of the la afferent axon. Simple motor nerve terminals also innervate this myotube, which will ultimately become the bag2 fibre of the mature spindle. Secondary intrafusal myotubes then assemble beneath the basal lamina of the primary bag2 myotube, in the order presumptive bagi, long-chain, intermediate-chain and typical-chain fibres. Their assembly begins at the equator, beneath the sensory terminals, and spreads to the poles. The bagi and long-chain myotubes separate from the bag2 in the spindle pole prior to the development of the other chain fibres. The assembly of intrafusal fibres is completed by birth. The periaxial space begins to develop in the first postnatal week.
The development of tandem spindles containing b2c units is described. The role of sensory and motor innervation in the assembly and differentiation of mammalian intrafusal fibres is discussed.
Mutational analysis of patterning of oral structures in Tetrahymena: II. A graded basis for the individuality of intracellular structural arrays
Authors: Frankel Joseph , Nelsen E. Marlo , Bakowska Julita , Jenkins Leslie M. 
Published: April 2021

ABSTRACT
The ciliary arrays of the oral apparatus of the ciliated protozoan Tetrahymena thermophila each have their own unique ‘pattern signature’, which varies little so long as the number of arrays remains the same. In this study, we analyse the consequence of increases in the number of these arrays (membranelles) brought about by certain mutations. In oral apparatuses of mutant cells, the addition of a membranelle is associated with specific alterations in at least one of the other membranelles. The features that are altered include the relative lengths of membranelles, the state of ciliation of basal bodies located at specific positions within these membranelles, and the spatial configurations resulting from displacement of ciliary units during late oral development. The final organization of each membranelle depends upon its relative position along the length of the oral apparatus. This indicates that the membranelles are not individually ‘named’ by the organism, and suggests that the unit of pattern organization is the membranelle field as a whole. In the Discussion, we consider means for testing whether the same underlying idea might also apply to multicellular systems, such as the vertebrate limb, in which spatially ordered differences appear to be superimposed upon a fundamental repeating pattern.
Effects of radius—ulna removal on forelimb regeneration in Xenopus laevis froglets
Authors: Korneluk Robert G. , Liversage Richard A. 
Published: April 2021

ABSTRACT
Regeneration of boneless amputated forearms of adult newts was found to progress at a rate and to a degree comparable to amputated control limbs in which stump bones were not removed. In contrast, regeneration of boneless amputated Xenopus froglet forearms was significantly delayed and did not occur until two to three weeks following amputation. This is in comparison with the initiation of distal cartilage formation observed one week postamputation in control forelimbs of Xenopus froglets. The regeneration of cartilage in boneless forearms of adult newts was found to occur distal to the amputation level. In contrast, distal as well as proximal (centripetal) regeneration of cartilage was observed in the amputated boneless forearms of Xenopus. In froglets and newts, unamputated forelimbs in which forearm bones were extirpated did not initiate cartilage regeneration. Our findings support the hypothesis that forelimb regeneration in Xenopus froglets is primarily a tissue response. In comparison, limb regeneration in the adult newt is predominantly an epimorphic response.
The distribution of cytoplasmic actin in mouse 8-cell blastomeres
Authors: Johnson M. H. , Maro B. 
Published: April 2021

ABSTRACT
Three non-homogeneous patterns of cytoplasmic actin distribution have been demonstrated in pairs of 8-cell blastomeres. Newly formed blastomeres showed an actin distribution associated with the remnant of the previous mitotic spindle. Subsequently blastomeres showed a zonal clearing of actin from regions of intercellular contact, the extent of the clearing increasing with the extent of contact. A polarized distribution of actin was evident from the early to mid 8-cell stage and coincided with the movement of nuclei towards the point of intercellular contact. The detection of polar actin preceded by 2−4 h the detection of a surface polarity as assessed by the FITC-Con A binding pattern and the distribution of cortical microvillous actin. However, once a surface pole of microvilli had formed, it persisted under conditions which led to loss of polar cytoplasmic actin. Incubation in cytochalasin D (CCD) resulted in a dispersed homogeneous pattern of actin distribution but did not prevent the formation of surface poles as assessed both by the Con A binding pattern and detection of polar microvilli. However, the poles formed were less clearly defined and the density and length of microvilli within them was variable. Moreover, when CCD was added early during the 8-cell stage the position of the poles was frequently not on an axis perpendicular to the point of intercellular contact. Cytochalasin D also affected the movement of the nucleus that occurs during the process of polarization. On the basis of these experiments, we conclude that actin is likely to be involved in the events of polarization, but that its precise role remains to be determined.
Induction of hair follicles in mouse skin by rat vibrissa dermal papillae
Authors: Pisansarakit P. , Moore G. P. M. 
Published: April 2021

ABSTRACT
Rat vibrissa dermal papillae were transplanted between the epidermis and dermis of isolated embryonic mouse skin and then grafted onto nude mice. The papillae induced the formation of hair follicles which were larger than those of the host skin but smaller than vibrissa follicles. The potential of isolated dermal papillae to induce follicles with characteristics of those from which the papillae originated is discussed. One of the major factors affecting the sizes of induced follicles may have been related to the splitting of the papilla mass and dispersal of the cells by invading cords of epidermal cells from the host skin during induction.
Branching morphogenesis in the avian lung: electron microscopic studies using cationic dyes
Authors: Gallagher Betty C. 
Published: April 2021

ABSTRACT
The developing chick lung was examined in the electron microscope for intimate cell contacts between epithelium and mesenchyme, discontinuities in the basal lamina and substructure of the basement membrane. Cell filopodia were seen which crossed the basal lamina from both the epithelial and the mesenchymal cells. Ruthenium red and tannic acid staining of the basal lamina of the chick lung showed it to be thin and sometimes discontinuous at the tips compared to the more substantial basal lamina in the interbud areas. The bilaminar distribution of particles seen with ruthenium red is similar to those seen in the cornea and lens. With tannic acid staining, filaments could be seen which crossed the lamina lucida and connected with the lamina densa. Spikes perpendicular to the basal lamina were sometimes seen with a periodicity of approximately 110 nm. Alcian blue staining revealed structure similar to that seen by ruthenium red staining in the salivary and mammary glands, although the interparticle spacing was closer.
Collagen was located in areas of morphogenetic stability, as has been seen by other investigators in different tissues. Collagen was coated with granules (probably proteoglycan) at periodic intervals when stained with ruthenium red. The fibrils were oriented circumferentially around the mesobronchus and were assumed to continue into the bud, but the fibres curve laterally at the middle of a bud. This orientation is opposite to that seen by another investigator in the mouse lung.
In general, the observations made in the avian lung are similar to those seen in branching mammalian tissue. It is likely, therefore, that the chick lung uses strategies in its morphogenesis that are similar to those that have been elucidated previously in developing mammalian organs.
Positional signalling by Hensen’s node when grafted to the chick limb bud
Authors: Hornbruch Amata , Wolpert Lewis 
Published: April 2021

ABSTRACT
Hensen’s node from stage 4 to stage 10 shows polarizing activity when grafted to the anterior margin of the chick limb bud. It can specify additional digits though its action is somewhat attenuated when compared with the effect of a grafted polarizing region. At stage 10 the activity disappears from the node and is found both posterior to the node and in the future wing region of the flank. The ability of Hensen’s node to generate a positional signal suggests that the signal in the limb and early embryo may be similar. The results support the view of the polarizing region as a discrete signalling region.
What do dissociated embryonic cells of the starfish, Asterina pectinifera, do to reconstruct bipinnaria larvae?
Authors: Yamanaka H. , Tanaka-Ohmura Y. , Dan-Sohkawa M. 
Published: April 2021

ABSTRACT
The cellular events that take place during reconstruction of larval forms from dissociated embryonic cells of the starfish are investigated by thick and thin sections. Dissociated cells reaggregate, form an external epithelium (ectoderm), internal epithelial vesicles (endoderm), the blastocoel and the mesenchyme. The internal vesicles continue to fuse until there is only one large one suspended in the centre of the blastocoel. Eventually, the ectoderm invaginates at one or more sites and fuses with the endoderm to form blastopore(s).
Special emphasis is placed on the differences in cell behaviour during endoderm-to-endoderm and endoderm-to-ectoderm fusion.
Replacement of posterior by anterior endoderm reduces sterility in embryos from inverted eggs of Xenopus laevis
Authors: Cleine J. H. 
Published: April 2021

ABSTRACT
The genital ridges of Xenopus laevis tadpoles reared from eggs kept in an inverted position contain less than 40 % of the number of primordial germ cells (PGCs) of controls (Cleine & Dixon, 1985). It has been suggested that this reduction is caused by the germ cells’ ectopic position in the anterior endoderm of larvae from inverted eggs, from where they may be unable to migrate into the genital ridges (Cleine & Dixon, 1985). This hypothesis is tested here by interchanging anterior and posterior endodermal grafts between pairs of inverted embryos at the early tailbud stage. Replacement of anterior by posterior endoderm has no effect but replacement of posterior by anterior endoderm increases the number of PGCs in the genital ridges and significantly reduces the proportion of sterile embryos. In a control series, in which the same type of grafting was done with normal embryos, replacement of posterior by anterior endoderm reduced the number of germ cells to almost zero, but replacement of anterior by posterior endoderm nearly doubled it. These findings are explained in terms of the distribution of the germ cells in the endoderm at the time of grafting. The results firstly show that the position of the germ cells is crucial to successful migration and secondly they support the notion that germ plasm has a determinative role during early germ cell differentiation.