bluuebunny/crossref_metadata_2025_split huggingface dataset:
Myogenic differentiation in early chick wing mesenchyme in the absence of the brachial somites
Authors: Kenny-Mobbs Terry 
Published: April 2021

ABSTRACT
A controversy exists in the literature over the ability of wing mesenchyme of somatopleural origin to form skeletal muscle. Experimental approaches used in such studies leave open the possibility of postoperative accessibility of the experimental wings to somitic cell invasion. In the present study wing somatopleural tissue was isolated from HH stage-12 to -21 chick embryos and grown either in organ culture (OC) or on the chorioallantoic membrane (CAM) of host chicks, conditions under which postoperative entry of somitic cells is impossible. In the presence of axial and somitic tissues of the brachial region, the wing territories from all four stages underwent comparable growth and tissue differentiation. However, isolated wing regions showed a stagedependency in the differentiation of skeletal muscle but not of other limb tissues. The incidence and amount of skeletal muscle was markedly reduced in HH stage-12 and -15 isolated wing regions while myogenesis in HH stage-18 and -21 wing buds was not affected by the absence of the somitic tissues. These results are consistent with reported stages of somitic cell migration into wings with the exception of HH stage-12 explants which should have been muscleless if somitic cells are the sole source of wing myofibres. The possibility that somitic cells had been included in these explants was investigated by 1) testing the myogenic potential of lateral plate tissue adjacent to the wing, 2) altering the dissection procedure for isolating wing territories and 3) using antibodies to skeletal muscle myosin and actin to detect myotubes. The results from this series of experiments illustrate the need for extraordinary care in the isolation of wing regions when investigating limb– somite relationships and suggest that the myogenic capacity attributed to wing somatopleural cells in the past can be accounted for by either postoperative entry of somitic cells into experimental wings or inadvertent inclusion of somitic cells in the primordia when dissected. Overall, the results show that somitic cells are the sole source of wing myofibres for, in their absence, somatopleural cells form all mesodermally-derived wing cell types except skeletal myofibres.
The migration of neural crest cells and the growth of motor axons through the rostral half of the chick somite
Authors: Rickmann M. , Fawcett J. W. , Keynes R. J. 
Published: April 2021

ABSTRACT
We have studied the pathway of migration of neural crest cells through the somites of the developing chick embryo, using the monoclonal antibodies NC-1 and HNK-1 to stain them. Crest cells, as they migrate ventrally from the dorsal aspect of the neural tube, pass through the lateral part of the sclerotome, but only through that part of the sclerotome which lies in the rostral half of each somite. This migration pathway is almost identical to the path which presumptive motor axons take when they grow out from the neural tube shortly after the onset of neural crest migration. In order to see whether the ventral root axons are guided along this pathway by neural crest cells, we surgically excised the neural crest from a series of embryos, and examined the pattern of axon outgrowth approximately 24 h later. In somites which contained no neural crest cells, ventral root axons were still found only in the rostral half of the somite, although axonal growth was slightly delayed. These axons were surrounded by sheath cells, which had presumably migrated out of the neural tube, to a point about 50 μm proximal to the growth cones. With appropriate antibodies we found that the extracellular matrix components fibronectin and laminin are evenly distributed between the rostral and caudal halves of the somite. Neither of these molecules therefore plays a critical role in determining the specific pathway of neural crest cells or motor axons through the rostral half of the somite.
The effect of egg rotation on the differentiation of primordial germ cells in Xenopus laevis
Authors: Cleine J. H. , Dixon K. E. 
Published: April 2021

ABSTRACT
Eggs of X. laevis were rotated (sperm entrance point downwards) either through 90° (1×90 embryos) or 180° in two 90° steps (2×90 embryos) at approximately 25–30 min postfertilization after cooling to 13 °C. The embryos were kept in their off-axis orientation and cooled until the early gastrula stage. Rotation resulted in relocation of egg constituents with slight changes in the distribution of outer cortical and subcortical components and major changes in inner constituents where the heavy yolk and cytoplasm appeared to reorient as a single coherent unit to maintain their relative positions with respect to gravity. Development of rotated embryos was such that regions of the egg which normally give rise to posterior structures instead developed into anterior structures and vice versa. Germ plasm was displaced in the vegetal-dorsal-animal direction (the direction of rotation) and was segregated into dorsal micromeres and intermediate zone cells in 2×90 embryos and dorsal macromeres and intermediate zone cells in 1×90 embryos. In consequence, at the gastrula stage, cells containing germ plasm were situated closer to the dorsal lip of the blastopore after rotation - in 2×90 gastrulas around and generally above the dorsal lip. Hence, in rotated embryos, the cells containing germ plasm were invaginated earlier during gastrulation and therefore were carried further anteriorly in the endoderm to a mean position anterior to the midpoint of the endoderm. The number of cells containing germ plasm in rotated embryos was not significantly different from that in controls at all stages up to and including tail bud (stage 25). However at stages 46,48 and 49 the number of primordial germ cells was reduced in 1×90 embryos in one experiment of three and in 2×90 embryos in all experiments. We tested the hypothesis that the decreased number of primordial germ cells in the genital ridges was due to the inability of cells to migrate to the genital ridges from their ectopic location in the endoderm. When anterior endoderm was grafted into posterior endodermal regions the number of primordial germ cells increased slightly or not at all suggesting that the anterior displacement of the cells containing germ plasm was not the only factor responsible for the decreased number of primordial germ cells in rotated embryos. Other possible explanations are discussed.
Calcium and neurulation in mammalian embryos: II. Effects of cytoskeletal inhibitors and calcium antagonists on the neural folds of rat embryos
Authors: Smedley Martin J. , Stanisstreet Martin 
Published: April 2021

ABSTRACT
The role of calcium in neurulation in mammalian embryos has been studied by culturing rat embryos at 10·4 days of gestation, when the cephalic neural folds have elevated but not fused, in serum containing cytoskeletal inhibitors or calcium antagonists. The effects of these antagonists on the morphology of the cephalic neural folds have been examined by scanning electron microscopy. The different agents caused the cephalic neural folds to part to varying degrees. The neural folds were classified as intact (normal), open (folds parted up to 90° with each other), flattened (folds parted from 90° to 180°) or collapsed (folds parted more than 180°).
The microtubule inhibitors colchicine and nocodazole at 10−4M and 6·6×10−4M respectively cause the cephalic neural folds of 10·4-day embryos to collapse after 60 min. At 5·2×10−6M the microfilament inhibitor cytochalasin B causes the folds to open after 60 min. Longer term culture of 9·5-day embryos for 24 h in diazepam, which is reported to inhibit myosin synthesis, causes general developmental retardation including a delay in the closure of the neural tube.
Culture of 10·4-day rat embryos for 60 min in papaverine at 2·4 × 10−4 M or gallapomil (D-600) at 5·0×10−4M, agents which reduce the entry of calcium into cells, causes opening of the elevated cephalic neural folds. In contrast TMB-8, which is purported to perturb some intracellular calcium-dependent functions, does not cause opening of the elevated cephalic neural folds, even at high concentrations.
The results suggest that both microtubules and microfilaments are essential to the maintenance of the elevated cephalic neural folds in rat embryos. The results are also compatible with the idea that calcium ion flux across the membranes of the neuroepithelial cells might be important for the elevation of the neural folds, and thus for successful neurulation.
Axolotl retina and lens development: mutual tissue stimulation and autonomous failure in the eyeless mutant retina
Authors: Cuny Robert , Malacinski George M. 
Published: April 2021

ABSTRACT
During eye development in the axolotl (Ambystoma mexicanum Shaw), morphogenetic movements bring together tissues from head epidermis, neuroectoderm and neural crest. The stages 0 to 14 of axolotl eye development were expanded from Rabi’s (1898) stages 1 to 10 and correlated with Harrison’s (1969) stages. At the onset of neurulation (stage 13 of Harrison), the head epidermis is already determined to form skin, and the neuroectoderm is committed to form brain, because these tissues develop autonomously in 60% Leibovitz L-15 culture medium. However, a sequence of mutual tissue interactions is necessary to stimulate eye development. When head epidermis and neuroectoderm were cocultured, eyes developed, containing retinas with photoreceptors (stage 8) and lenses with secondary lens fibres (stage 8). The first event needed in this case appears to be the secretion of a growth factor from the head epidermis which stimulates retina development from the neuroectoderm. When neuroectoderm cultures were exposed to nondialysable extracts (30μgml−1) of an adult epidermis derivative, the bovine cornea, pigmented retinas (stage 6) and at higher concentrations (3000 µg ml−1) neural retinas developed (stage 6). In turn, lens formation is stimulated in the head epidermis by a retina-derived growth factor. A mutation that causes adult eyelessness (e eyeless, nonlethal, recessive) affects the earliest event in eye development (stage la), while a mutation that causes arrest of eye development (mi microphthalmic, lethal, recessive) acts in a later event (stage 8). Two possibilities have been considered in the case of mutation e: either the head epidermis does not secrete sufficient amounts of active growth factor, or the presumptive retina itself is defective. The latter statement turned out to be correct, because mutant e neural plates rarely developed early retina stages (stage 5) in organ culture when combined with wild-type head epidermis. On the other hand, wild-type neural plates formed advanced retinas (stage 8) in all cases when combined with mutant e head epidermis. As expected, no retina or lens developed when both neural plate and head epidermis were from mutant e donors. The heterozygous presence of genes e and r (renal insufficiency, lethal, recessive) produces duplications of the presumptive retina at the optic stalk. This observation is consistent with the notion that the mutation e, assisted by the r locus, causes a primary failure in the presumptive retinal region.
Lack of inactivation of a mouse X-linked gene physically separated from the inactivation centre
Authors: Lyon Mary F. , Zenthon J. , Evans E. P. , Burtenshaw M. D. , Wareham Kathryn A. , Williams E. D. 
Published: April 2021

ABSTRACT
Previous evidence had shown that, when a mammalian X-chromosome is broken by a translocation, only one of the two X-chromosome segments shows cytological signs of X-inactivation in the form of late replication or Kanda staining. In the two mouse X-autosome translocations T(X;4)37H and T(X;11)38H the X-chromosome break is in the A1 –A2 bands; in both, the shorter translocation product fails to exhibit Kanda staining. By in situ hybridization, the locus of ornithine carbamoyltransferase (OCT) was shown to be proximal to the breakpoint (i.e. on the short product) in T37H and distal to the breakpoint in T38H. Histochemical staining for OCT showed that in T38H the locus of OCT undergoes random inactivation, as in a chromosomally normal animal, whereas in T37H the OCT locus remains active in all cells. The interpretation is that, when a segment of X-chromosome is physically separated from the X-inactivation centre, it fails to undergo inactivation. This point is important for the understanding of the mechanism of X-inactivation, since it implies that inactivation is a positive process, brought about by some event that travels along the chromosome. It is also relevant to the interpretation of the harmful effects of X-autosome translocations and the abnormalities seen in individuals carrying such translocations.
The formation of mesodermal tissues in the mouse embryo during gastrulation and early organogenesis
Authors: Tam P. P. L. , Beddington R. S. P. 
Published: April 2021

ABSTRACTOrthotopic grafts of [3H]thymidine-labelled cells have been used to demonstrate differences in the normal fate of tissue located adjacent to and in different regions of the primitive streak of 8th day mouse embryos developing in vitro. The posterior streak produces predominantly extraembryonic mesoderm, while the middle portion gives rise to lateral mesoderm and the anterior region generates mostly paraxial mesoderm, gut and notochord. Embryonic ectoderm adjacent to the anterior part of the streak contributes mainly to paraxial mesoderm and neurectoderm. This pattern of colonization is similar to the fate map constructed in primitive-streak-stage chick embryos. Similar grafts between early-somite-stage (9th day) embryos have established that the older primitive streak continues to generate embryonic mesoderm and endoderm, but ceases to make a substantial contribution to extraembryonic mesoderm.Orthotopic grafts and specific labelling of ectodermal cells with wheat germ agglutinin conjugated to colloidal gold (WGA-Au) have been used to analyse the recruitment of cells into the paraxial mesoderm of 8th and 9th day embryos. The continuous addition of primitive-streak-derived cells to the paraxial mesoderm is confirmed and the distribution of labelled cells along the craniocaudal sequence of somites is consistent with some cell mixing occurring within the presomitic mesoderm.
Ventral duplication of the autopod: chemical induction by methoxyacetic acid in rat embryos
Authors: Scott William J. , Nau H. , Wittfoht W. , Merker H.-J. 
Published: April 2021

ABSTRACT
Administration of 2-methoxyethanol to pregnant rats on day 12 of gestation induced ventral duplication of the autopod, presumably via its oxidative metabolite, methoxyacetic acid. Morphological observations indicate that the limb bud periderm is severely damaged by methoxyacetic acid so that large patches of this structure are actually missing during an extended period of limb bud development. A high concentration of methoxyacetic acid (10 mM) was found in the extra-embryonic fluid and we postulate that the damage to the periderm was initiated from this extraembryonic exposure. The ventral duplication of the autopod is thought to arise through an attempt by the embryo to repair the periderm lesion.
Positional reorganization in compoundjanuscells ofTetrahymena thermophila
Authors: Frankel Joseph , Nelsen E. Marlo 
Published: April 2021

ABSTRACTThe janus mutations of Tetrahymena thermophila convert the large-scale organization of the dorsal surface of the cell into a mirror-image of the ventral surface, which is characterized by a second, abnormal, oral apparatus and by contractile vacuole pores to the left of the second oral area rather than the usual right. This conversion could be due either to a local change in the response to an unaltered positional system or to a more global reorganization of the system itself, janus homopolar doublets were used to distinguish between these two alternatives. Homopolar doublets can be made by fusing two similarly oriented cells in side-by-side parabiosis. Non-janus homopolar doublets typically possess two sets of normal oral structures with contractile vacuole pores to the right of each of them. In janus doublets, there are up to four sets of oral structures, with the abnormal oral structures located between the two sets of normal oral structures; contractile vacuole pores are situated to the right of the normal oral areas and to the left of the abnormal oral structures.Non-janus homopolar doublets are known to propagate their compound condition for a number of cell divisions, but also to regulate toward the singlet state through a progressive reduction in number of ciliary rows followed by loss of one of the two sets of major cell surface structures, janus homopolar doublets go through a corresponding regulation. As a consequence, the location of the abnormal oral structures relative to the normal ones is more variable in janus doublets than in janus singlets. Sometimes the abnormal oral structures shift to a position close to their normal counterparts and then the intervening CVP sets disappear. There is evidence for occasional fusion of an abnormal oral area with an adjacent normal oral apparatus, a condition that may be transitional to the singlet state. These observations are inconsistent with the idea of a fixed positional system and strongly suggest a global reorganization of the surface pattern in a manner consistent with predictions of an intercalation model that was first proposed to explain the regulation of non-janus doublets to singlets.
Brachial muscles of dystrophic chick embryos atypically sustain interaction with thoracic nerves
Authors: Butler Jane , Cosmos Ethel 
Published: April 2021

ABSTRACT
Previous analyses of experimental chick embryos of normal lineage demonstrate the inability of brachial muscles to sustain a successful union with foreign nerves derived from a thoracic neural tube segment transplanted to the brachial region at day 2 in ovo (day 2E). The present experiments were performed to determine if mutant chick embryos afflicted with hereditary muscular dystrophy would respond similarly to this experimental manipulation. Using the same criteria applied to our analysis of experimental normal embryos, our results demonstrated that dystrophic brachial muscles were capable of maintaining a compatible union with foreign thoracic nerves throughout the experimental period analysed. Significant muscle growth occurred, intramuscular nerve branches were maintained, motor endplates formed and wing motility was equivalent to that of unoperated dystrophic embryos. Thus, foreign nerves rejected by normal brachial muscles were accepted by brachial muscles of the mutant dystrophic embryo.
The effect of the zone of polarizing activity (ZPA) on the anterior half of the chick wing bud
Authors: Wilson D. J. , Hinchliffe J. R. 
Published: April 2021

ABSTRACTRemoval of the posterior half of the chick wing bud between stages 17-22 results in failure of the anterior distal tissue to survive and differentiate. This observation has been interpreted in terms of a requirement by the anterior half of a factor supplied by the posterior half of the limb containing the zone of polarizing activity (ZPA). This relationship has been tested by grafting ZPA tissue to the posterior surface of the anterior half after posterior half removal. Grafts made proximally on the cut surface did not significantly improve survival and development, nor did the ZPA prevent the expansion of the cell death in the ANZ beyond its normal boundaries into the distal mesenchyme. However, when grafted distally the ZPA inhibited cell death in the apical mesenchyme and caused the anterior mesenchyme to change its normal prospective fate (radius and digit 2). In all these cases, in addition to digit 2, digit 3 and frequently also digit 4 differentiated. The anterior half went on to develop a full set of digits and zeugopod parts in almost 50 % of cases, although no skeleton resulting from this regulation of the anterior half had totally size regulated. These results demonstrate a developmental ‘rescue’ effect by the ZPA, and further support the view that the ZPA has a central and unique function in normal limb bud development, controlling survival and differentiation of the mesenchyme along the anteroposterior axis.
M-phase-promoting factor activation
Authors: Meikrantz William , Schlegel Robert A. 
Published: April 2021

ABSTRACT
Two decades ago, Hartwell and co-workers isolated a number of cell division cycle (cdc) mutants in Saccharomyces cerevisiae on the basis of their arrest at specific, morphologically distinguishable points in the cell cycle. These temperature-sensitive mutants provided the first identification and temporal ordering of genes required for progress through the cell cycle, and permitted the first molecular definition of a cell cycle restriction point, START, passage through which requires the function of the CDC28 gene. Interestingly, CDC28 was found to be required not only for leaving stationary phase and commencing DNA replication, but also for the events of nuclear division (Hartwell et al., 1974; Hartwell and Weinert, 1989; Reed et al., 1985). Similarly, in the fission yeast Schizosaccharomyces pombe, the homologous cdc2 gene was found to be necessary for executing both the G1/S and G2/M transitions (Nurse et al., 1976; Nurse and Bisset, 1981; Beach et al., 1981). CDC28/cdc2, and their homologs in species spanning the plant and animal kingdoms, encode protein kinases of approximately 34 kDa (Hindley and Phear, 1984; Reed et al., 1985; Simanis and Nurse, 1986), referred to hereafter simply as p34. In animal cells, increasingly sophisticated molecular techniques have led to the identification of a family of p34-related genes (Pines and Hunter, 1991), some of which are clearly distinct from CDC28 or cdc2 and may mediate some of the G1/S functions previously attributed exclusively to CDC28/cdc2 (Elledge and Spottswood, 1991; Fang and Newport, 1991; Koff et al., 1991; Lehner and O’Farrell, 1990; Paris et al., 1991; Tsai et al., 1991).
Morphological and immuno-cytochemical characterization of a hetero-spheroid composed of fibroblasts and hepatocytes
Authors: Takezawa Toshiaki , Yamazaki Manabu , Mori Yuichi , Yonaha Tomohide , Yoshizato Katsutoshi 
Published: April 2021

ABSTRACT
A novel method for the preparation of spheroids containing two types of cells (hetero-spheroid) has been successfully developed by utilizing a collagen-conjugated thermo-responsive polymer, poly-N-isopropyl acrylamide (PNIPAAm), as a cell substratum. PNIPAAm solidifies above its lower critical solution temperature (LCST, about 30°C), and instantly dissolves into the culture medium below its LCST. We firstly seeded and cultured human dermal fibroblasts on the substratum up to a confluent state and then seeded rat primary hepatocytes onto the fibroblast monolayer. The hetero-spheroid was prepared by detaching the hepatocyte-attached fibroblast monolayer at a temperature below LCST and culturing it on the non-adhesive substratum. The surface area of the substratum and the seeding population ratio of each cell precisely and reproducibly regulated the size and the cell composition of the resulting hetero-spheroid, respectively. Histological and immuno-cytochemical observations of spheroids revealed characteristic organizations of fibroblasts and hepatocytes within a spheroid because the latter cells expressed albumin for up to at least 3 weeks. TEM study of the hetero-spheroid showed the presence of structures morphologically similar to the Disse’s space and the bile canaliculus, which are features characteristic of liver. These findings suggest that the method described above is useful for making a hetero-spheroid that morphologically and functionally resembles tissues or organs in vivo, i.e. an organoid.