bluuebunny/crossref_metadata_2025 huggingface dataset:
Distribution of microvilli on dissociated blastomeres from mouse embryos: evidence for surface polarization at compaction
Authors: Reeve W. J. D. , Ziomek C. A.
Published: April 2021

Cells of mouse embryos develop a polarization of microvillous distribution at compaction. Cells of the 4-cell embryo show a uniform pattern of fluorescent-ligand binding and an even distribution of microvilli. Each cell of the early 8-cell embryo has a uniform distribution both of microvilli and of fluorescent ligand. During the 8-cell stage, there is a progressive increase in the incidence of cells which show microvilli restricted to a region normally on the exposed surface of the embryo. When late 8-cell embryos were disaggregated to single cells, and these sorted by pattern of fluorescent-ligand binding, each of the four patterns of staining related consistently to a characteristic distribution of microvilli as viewed by scanning electron microscopy. The 16-cell embryo possessed an inside population of uniformly labelled cells with a sparse microvillous distribution, and an outside population of cells, each of which had a microvillous pole.
Naturally occurring abnormalities (Bruchdreifachbildungen) in the chelae of three species of Crustacea (Decapoda) and a possible explanation
Authors: Shelton P. M. J. , Truby P. R. , Shelton R. G. J.
Published: April 2021

Naturally occurring abnormalities (Bruchdreifachbildungen) in decapod crustacean appendages are described. They are similar to the range of structures experimentally produced by cutting notches in the sides of insect legs (Bohn, 1965). It is argued that they result from failure of wounds to heal. Regeneration from a free surface along the proximodistal axis is always in a distal direction. Surfaces regenerating circumferentially can regenerate in either direction around the circumference. Regeneration will proceed until the two surfaces of the wound meet. Then, where the two surfaces on either side are non-congruent, intervening tissues will be intercalated. This explanation accounts for the range of structures observed after notching experiments (Bohn, 1965) and seen in crustacean Bruchdreifachbildungen. The explanation says that regeneration will occur wherever wounds fail to heal. This avoids the difficulties of the complete circle rule (French, Bryant & Bryant, 1976) and explains why appendages with mirror-image symmetry are often capable of regeneration.
Active role of embryonic facial epithelium: New evidence of cellular events in morphogenesis
Authors: Millicovsky Guillermo , Johnston Malcolm C.
Published: April 2021

Epithelial cells of the C57B1/6J mouse embryo participate in a temporal sequence of events associated with the approximation, fusion and consolidation of components of the facial primordia into a definitive structure. These cells lose their surface microvilli, and after a brief period of quiescence they begin to fill the grooves separating facial constituents by producing a series of surface projections that increase in size and complexity as the process of fusion nears termination. Cessation of surface activity and the restoration of epithelial microvilli indicate the end of the temporal sequence. Significantly, the epithelial cells of primary palates of embryos with genetically- and phenytoin-induced cleft lip remain unchanged and do not participate in fusion. This epithelial sequence has not been described previously and we suggest that all of its steps may be critical to the normal development of the mammalian face.
The developmental capacity of blastomeres from 4- and 8-cell sheep embryos
Authors: Willadsen S. M.
Published: April 2021

The developmental capacity of (a) single blastomeres of 4-cell embryos, (b) pairs of blastomeres of 8-cell embryos and (c) single blastomeres of 8-cell embryos was studied. The blastomeres were inserted into evacuated foreign zonae pellucidae, embedded in agar, transferred to ligated oviducts of dioestrous ewes, and recovered when their total age was to days. At lecovery the majority of embryos belonging to categories (a) and (b) had developed into small blastocysts, whereas most embryos of category (c) were vesicular forms with no clearly observable inner cell mass.

The viability of embryos which had continued their development during culture in the sheep oviduct was tested by their transfer to the uterine horns of recipient ewes which had come into oestrus on the same day as the respective embryo donors. Three lambs were produced after transfer of eight embryos of category (a) deriving from two parent embryos. These three lambs derived from a single 4-cell embryo. Nine lambs were produced after transfer of 16 embryos of category (b) deriving from four parent embryos. Four of these lambs derived from a single 8-cell embryo. When ewes which had come into oestrus one or two days after the respective embryo donors were used as recipients for 16 embryos of category (a) and 16 embryos of category (b) one and five lambs, respectively, were produced.

Finally, two lambs were produced after transfer of 31 embryos of category (c). These lambs derived from two different parent embryos.

The principal conclusions drawn from the study are that at least some individual blastomeres from 4- and 8-cell sheep embryos can give rise to an entire conceptus, and that the viability of embryos produced by blastomere separation depends more on the degree of reduction in cell number than on the stage of development at which separation is performed.
The control of somitogenesis in mouse embryos
Authors: Tam P. P. L.
Published: April 2021

Somitogenesis in the mouse embryo commences with the generation of presumptive somitic mesoderm at the primitive streak and in the tail-bud mesenchyme. The presumptive somitic mesoderm is then organized into somite primordia in the presomitic mesoderm. These primordia undergo morphogenesis leading to the segmentation of somites at the cranial end of the presomitic mesoderm. Somite sizes at the time of segmentation vary according to the position of the somite in the body axis: the size of lumbar and sacral somites is nearly twice that of upper trunk somites and of tail somites. The size of the presomitic mesoderm, which is governed by the balance between the addition of cells at the caudal end and the removal of somites at the cranial end, changes during embryonic development.

Somitogenesis is disturbed during the compensatory growth of mouse embryos which have suffered a drastic size reduction at the primitive-streak and early-organogenesis stages. The formation of somites is retarded and the upper trunk somites are formed at a smaller size. The embryo also follows an entirely different growth profile, but a normal body size is restored by the early foetal stage. The somite number is regulated to normal and this is brought about by an altered rate of somite formation and the adjustment of somite size in proportion to the whole body size. It is proposed that axis formation and somitogenesis are related morphogenetic processes and that embryonic growth controls the kinetics of somitogenesis, namely by regulating the number of cells allocated to each somite and the rate of somite formation.
The possible mechanism of cell positioning in mouse morulae: an ultrastructural study
Authors: Sołtyńska Maria S.
Published: April 2021

Ultrastructure of the mouse morula at the time of formation of the outer cell layer is described.

Analysis of relative positions of sister blastomeres, still connected with cytoplasmic bridge, suggests that cell division may occur both tangentially and perpendicularly in relation to the embryo surface. However, there are observations suggesting that active cell movement may be involved in cell positioning already after mitosis. These observations include: (1) the flexure of cytoplasmic bridge, (2) the presence of bundles of filaments in external blastomeres at the late cytokinesis and (3) a striking difference in loose versus tight packing of blastomeres within the embryo.
The timetable of innervation and its control in the chick wing bud
Authors: Swanson Gavin J. , Lewis Julian
Published: April 2021

How is the timing of nerve outgrowth controlled during development? This question has been examined by grafting early limb buds between chick embryos of different ages, before innervation, and assessing the morphological pattern of nerves at later stages. Grafted limbs continued to develop according to their own timetable and were invaded by nerves from the host. Irrespective of the age of the host, the development of the pattern of innervation followed the time course appropriate to the age of the grafted limb. Young nerves in an old limb showed accelerated development; old nerves in a young limb showed retarded development. The process of innervation is apparently governed not by the intrinsic developmental timetable of the neurons, but rather by the rate of construction of pathways for them in the peripheral tissue, and by the times at which their specific targets, such as muscles, differentiate.
The retinotectal fibre pathways from normal and compound eyes in Xenopus
Authors: Fawcett J. W. , Gaze R. M.
Published: April 2021

Horseradish peroxidase was used to demonstrate the nature of the retinotectal fibre pathways from normal eyes and from compound double nasal (NN), double temporal (TT) and double ventral (VV) eyes in Xenopus. From normal eyes, nasal fibres were widespread in the optic tract and mostly entered the tectum through the medial and lateral brachia. Ventral retinal fibres approached the tectum via the medial brachium and dorsal retinal fibres passed through the lateral brachium, while temporal retinal fibres formed a narrow band in the centre of the tract and entered the tectum directly at its rostral border.

Fibres from NN eyes formed a wide tract and strong medial and lateral brachia. Fibres from VV eyes all entered the tectum via the medial brachium and fibres from TT eyes formed a narrow tract and entered the tectum directly from its rostral extremity. Thus fibres from each type of compound eye followed pathways to the tectum that were appropriate to the embryonic origin of the retina forming the compound eye.
L’Otocyste exerce-t-il une action inductrice sur le mésenchyme somitique chez l’embryon de Poulet?
Authors: Benoit par Jean A. A.
Published: April 2021

L’épithélium auditif induit normalement le cartilage de la capsule otique, à partir du mésenchyme céphalique, chez l’embryon de poulet (Benoit, 1955). Ce pouvoir inducteur peut-il s’exercer à l’égard du mésenchyme axial du tronc? Nous avons tenté de résoudre ce problème en greffant des otocystes au contact des somites, ou en associant otocystes et somites en culture in vitro.
Myogenic cell movement in the developing avian limb bud in presence and absence of the apical ectodermal ridge (AER)
Authors: Gumpel-Pinot Madeleine , Ede D. A. , Flint O. P.
Published: April 2021

Fragments of quail wing bud containing myogenic cells of somitic origin and fragments of quail sphlanchopleural tissue were introduced into the interior of the wing bud of fowl embryo hosts. No movement of graft into host tissue occurred in the control, but myogenic cells from the quail wing bud fragments underwent long migrations in an apical direction to become incorporated in the developing musculature of the host. When the apical ectodermal ridge (AER), together with some subridge mesenchyme, was removed at the time of grafting, no such cell migration occurred. The capacity of grafted myogenic cells to migrate in the presence of AER persists to H.H. stage 25, when myogenesis has begun, but premyogenic cells in the somites, which normally migrate out into the early limb bud, do not migrate when somite fragments are grafted into the wing bud. Coelomic grafts of apical and proximal wing fragments showed that apical sections of quail wing buds become invaded by myogenic cells of the host, but grafts from proximal wing bud regions do not.
SEM localization of cell-surface-associated fibronectin in the cranium of chick embryos utilizing immunolatex microspheres
Authors: Meier Stephen , Drake Christopher
Published: April 2021

Fibronectin has been localized to basement membranes and cell surfaces with the light microscope by fluorescent staining of thick sections, and with the TEM by immunoperoxidase reaction. However, these methods are limited because it is difficult to appreciate the patterned distribution of fibronectin from sectioned material. We have developed a probe for fibronectin that facilitates its identification with the SEM. Our probe consists of two parts; the first component is a derivatized methacrylate microsphere 90 nm in diameter, linked to purified sheep anti-rabbit IgG. The second component is anti-fibronectin IgG raised in rabbits. Stage-3 to -12 chick embryos were fixed and the ectoderm covering the cranial mesoderm was removed. Embryos were treated with testicular hyaluronidase, exposed to rabbit antifibronectin IgG and finally to sheep anti-rabbit IgG conjugated microspheres. As expected, the basal lamina of surface and neural ectoderm as well as the remaining fibrous ECM were heavily decorated with microspheres, whereas control embryos treated with preimmune serum were beadless. Fibronectin was localized on the cell soma and processes of primary mesenchyme as early as stage 3. In addition, it was possible to decorate to various extents, populations of prosencephalic, mesencephalic, and rhombencephalic cranial neural crest cells. Our studies suggest that fibronectin is present in the cranium of chick embryos at earlier times than heretofore realized, and that fibronectin accumulates in a cranial to caudal gradient that reflects the sequential differentiation of the embryonic axis.
Cell death in the dorsal part of the chick optic cup. Evidence for a new necrotic area
Authors: García-Porrero Juan A. , Colvée Elvira , Ojeda José L.
Published: April 2021

The spatiotemporal pattern of morphogenetic cell death during the early development of the chick retina was studied by means of the neutral red vital staining and light microscopy. A modification of the conventional procedure of vital staining, which consisted of the injection of the dye into the neural tube lumen, was used for this purpose. In addition to the two areas of cell death known from previous literature, the first located in the ventral part of the optic cup and the second located in the insertion of the optic stalk with the diencephalon, a new area of cell death was described. This third necrotic area was located in the protruding dorsal part of the optic cup rim and was present throughout the stages 15 to 18. The area consisted of dying cells, fragments and phagocytosed cells.

We suggest that this dorsal area of cell death could stop the intense dorsal growth of the optic cup and/or reshape the optic cup rim. Moreover, this area may influence the production of cell degeneration in the dorsal part of the invaginating lens placode.
An in situ cell marker for clonal analysis of development of the extraembryonic endoderm in the mouse
Authors: Gardner R. L.
Published: April 2021

Conditions were found for staining whole mid-gestation capsular parietal endoderms and visceral yolk sacs for malic enzyme activity that gave excellent discrimination between wildtype (Mod-1+/Mod-1+) cells and mutant (Mod-ln/Mod-ln) cells that lack the cytoplasmic form of the enzyme. Reciprocal blastocyst injection experiments were undertaken in which single primitive endoderm cells of one genotype were transplanted into embryos of the other genotype. In addition, Mod-1+/Mod-1+ early inner cell mass (ICM) cells were injected into Mod-ln/Mod-ln blastocysts, either in groups of two or three singletons or as daughter cell pairs. A substantial proportion of the resulting conceptuses showed mosaic histochemical staining in the parietal endoderm, visceral yolk sac, or in both these membranes. Stained cells were invariably intimately intermixed with unstained cells in the mosaic parietal endoderms. In contrast, one or both of two distinct patterns of staining could be discerned in mosaic visceral yolk sacs. The first, a conspicuously‘coherent’ pattern, was found to be due to endodermal chimaerism; the second, a more diffuse pattern, was attributable to chimaerism in the mesodermal layer of this membrane. The overall distribution of cells with donor staining characteristics resulting from primitive endoderm versus early ICM cell injections was consistent with findings in earlier experiments in which allozymes of glucosephosphate isomerase were used as markers.

The conspicuous lack of phenotypically intermediate cells in predominantly stained areas of mosaic membranes suggested that the histochemical difference between Mod-1+/Mod-1+ and Mod-ln/Mod-ln genotypes was cell-autonomous. This conclusion was strengthened by the results of staining mixed in vitro cultures of parietal endoderm in which presence or absence of phagocytosed melanin granules was used as an independent means of distinguishing wild type from null cells.

By substituting tetranitro blue tetrazolium for nitro blue tetrazolium in the incubation medium, satisfactory differential staining was obtained for both the extraembryonic endoderm and other tissues of earlier postimplantation wild type versus null embryos.

Finally, absence of cytoplasmic malic enzyme activity does not appear to have a significant effect on the viability or behaviour of mutant cells.
Arrest of intravitelline mitoses in Drosophila embryos by u.v. irradiation of the egg surface
Authors: Togashi Shin , Okada Masukichi
Published: April 2021

The intravitelline mitosis in Drosophila was arrested at the anaphase within the span of a single cell cycle after irradiation with 300 nm u.v. Embryos at and before the 8-nucleus stage were influenced by the u.v. only when irradiated anteriorly, while at and after the 16-nucleus stage, embryos are sensitive to either anterior or posterior irradiation. In embryos anteriorly irradiated at or before the 8-nucleus stage all nuclei in the embryo were prevented from performing mitosis. When irradiated at or after the 16-nucleus stage, inhibition of the intravitelline mitosis is limited to the nuclei in approximately anterior-half region of embryos in anterior irradiation, and to those in approximately posterior-half region in posterior irradiation, resulting in incomplete blastoderm formation. Sites sensitive to 300 nm u.v. are postulated to be present in the peripheral cytoplasmic region of the embryo and not in the nucleus, because the half-attenuation thickness of 300 nm u.v. light for the Drosophila egg cytoplasm is and nuclei are at least 50 μm away from the periphery at the stage of irradiation. In addition lateral irradiation of a portion of an egg where there is no nucleus underneath was also effective in arresting division of nuclei in the sameegg. It is suggested that the effects of 300nm u.v. may not be conveyed to the nuclei from the periphery by simple diffusion of a substance, and a hypothesis is proposed for the involvement of cytoskeletal elements associated with the u.v. sensitive sites on the surface to the control mechanism of the intravitelline mitosis of the Drosophila embryo.
The mode of cell death associated with cavitation in teratocarcinoma-derived embryoid bodies
Authors: Boyd Sheilagh M. , Hooper M. L. , Wyllie A. H.
Published: April 2021

Cell death occurring in embryoid bodies derived from the embryonal carcinoma cell line, PSA4, which undergo cavitation, and in those from the related cell line S2, which do not undergo cavitation, was classified as apoptosis or necrosis by ultrastructural criteria. Both modes of cell death were seen in PSA4 embryoid bodies while apoptosis alone was seen in S2 embryoid bodies. No significant difference was found between PS A4 and S2 embryoid bodies either in apoptotic incidence score or in the spatial distribution of apoptotic events. We therefore conclude that although apoptosis and tissue modelling coexist in PSA4 embryoid bodies, necrosis rather than apoptosis is causally related to formation of the cavity.
Influence of injected pluripotential (EK) cells on haploid and diploid parthenogenetic development
Authors: Kaufman M. H. , Evans M. J. , Robertson E. J. , Bradley A.
Published: April 2021

A number of pluripotential embryo-derived EK cells were introduced into the blastocoele of haploid and diploid parthenogenetic embryos which were subsequently transferred to suitable recipients. At autopsy on day 10 or 11 of pseudopregnancy 22 % of decidua in the diploid series contained somite-stage embryos while an additional 12 % contained abnormal egg cylinder-like sacs. In the haploid series, 7 % of the decidua contained somite-stage embryos and an additional 5 % contained abnormal ‘sacs’. In ‘injected’ diploid and haploid ‘controls’ in which the zonae were pierced with an empty injection pipette 3 % and 0 % respectively of decidua in these two series contained somite-stage embryos, while an additional 17 % and 3 % respectively of decidua in these two series contained abnormal sacs. GPI analysis revealed that the EK cells were incorporated into somite-stage conceptuses in only one third of the diploids and in none of the haploid embryos. Although the presence of EK cells considerably increases the chance of normal embryonic development taking place, a detectable contribution from the EK cells into the resulting somite-stage embryo is apparently not necessary. Possible mechanisms allowing successful early post-implantation development to occur in this study are discussed.
Diploid gynogenesis in Xenopus laevis and the localization with respect to the centromere of the gene for periodic albinism a
p
Authors: Thiébaud Ch. H. , Colombelli B. , Müller W. P.
Published: April 2021

Diploid gynogenetic Xenopus laevis were obtained by inseminating the eggs with u.v. irradiated spermatozoa, and treating them with hydrostatic pressure to inhibit the expulsion of the second polar body. A u.v. dose of 3000ergs/mm2 genetically inactivates the spermatozoa without loss of their ability to activate egg development.

The use of a genetic marker on very large samples of eggs made it possible to verify the efficiency of the methods employed. The comparison of the development of diploid gynogenetic embryos with that of haploid gynogenetic, triploid and diploid controls makes it very probable that the relatively high mortality or abnormal development obtained with the pressurized eggs is not due to partial homozygosity but rather to physical damage to the egg structure by this treatment. Altogether about 2500 developing eggs were used.

In addition diploid gynogenetic reproduction from females heterozygous for a known mutation allows the mapping of the gene concerned relative to the centromere on the basis of the recombination rate. For this experiment we used the recessive mutation causing periodic albinism (ap) and found the position of this gene to be between 44 map units from the centromere and the end of the chromosome.
Analysis of upper beak defects in chicken embryos following with retinoic acid
Authors: Tamarin A. , Crawley A. , Lee J. , Tickle C.
Published: April 2021

Implanting inert carriers soaked in retinoic acid into the anterior margin of the developing limb of chicken embryos leads to orofacial malformations as well as affecting pattern formation in the limb. Using anion-exchange beads as carriers, and soaking solutions of 1–10 mg/ml retinoic acid, almost 100% of the embryos have malformations of the face. The effects on the treated limbs range from symmetrical patterns of duplicated digits (maximum number of digits being four) to truncations in which no digits were formed at all.

Typically, in the malformed faces the upper beak is completely absent, no nostrils are present and the front of the face forms a scalloped rim of tissue above the mouth. By reference to normal beak development, the seven bulges of tissue that make up the rim can be identified as derivatives of the masses of tissue that normally would fuse to form the upper beak. The roof of the mouth consists of three bulges of tissue flanked by widely separated palatal shelves. The defect can thus be classified as severe bilateral clefting of the primary palate.

By examining the morphology of the faces of treated embryos, the origin of the defect can be traced to failure of the frontonasal mass to enlarge. Thus, the oronasal fissures are very wide and fusion across them to form the primary palate cannot occur.

The way in which retinoic acid brings about the defect is discussed in relation to possible mechanisms involved in the production of cleft palate. The parallel is noted between the associated effects of retinoic acid on beak and limb morphogenesis and the chick mutation cpp, that also affects both face and limbs.
Characterization of exocoelomic fluid protein from rat conceptuses cultured in rat and human sera: a measure of yolk sac activity during organogenesis
Authors: Huxham I. M. , Beck F.
Published: April 2021

Fluid from the extraembryonic coelom of 11·5-day rat embryos cultured in 100% rat serum, 100% human serum and 90% human serum supplemented with 10% rat serum between days 9·5 and 11·5 postconception were compared using polyacrylamide gel electrophoresis and crossed immunoelectrophoresis. The protein composition of the exo-coelomic fluids differed considerably from one another and from each of their respective culture sera. The majority of proteins in the exocoelom were derived from macromolecular transport but some contribution was made from protein synthesis by the conceptus. Eighteen proteins normally found in rat serum were found in the exocoelom of conceptuses cultured in 100% rat serum. Eighteen proteins were found in the exocoelom of rat conceptuses cultured in 100% human serum, of which ten were derived from human serum and eight were proteins normally found in rat serum. Analysis of fluid from conceptuses cultured in 90% human serum supplemented with 10% rat serum showed eleven human serum proteins and ten rat serum proteins. Differences in the composition of both human and rat proteins between the latter two fluids were also evident.
Protein synthetic patterns of tissues in the early chick embryo
Authors: Lovell-Badge Robin H. , Evans Martin J. , Bellairs Ruth
Published: April 2021

Tissues dissected from early chick embryos were labelled in vitro with [35S]methionine, and their patterns of polypeptide synthesis investigated using the technique of two-dimensional (2-D) polyacrylamide gel electrophoresis. Apart from providing a preliminary description of the molecular changes associated with the processes of gastrulation and segmentation in the chick embryo, this study has revealed a number of polypeptides that may be useful as markers of cell type or function.

The protein synthetic patterns of hypoblast from early and late gastrulae (stages 2 and 4, respectively: Hamburger & Hamilton, 1951) and of definitive endoblast and junctional endoblast from late gastrulae all resemble one another closely, but differ markedly from that of the epiblast at either stage. The lower layer tissues are characterized by the presence of eleven polypeptides that are largely absent from the epiblast. These findings are discussed with reference to current theories on the origins of the lower layer tissues.

Comparisons between the 2-D patterns for tissues dissected from gastrulae and from embryos undergoing segmentation (stage 12) have revealed ten polypeptides showing stage-specific rather than tissue-specific expression. Apart from these ten polypeptides, the 2-D patterns for epiblast and ectoderm were practically identical, and distinguishable from those of other tissues by a lack of any unique polypeptides. On the other hand, stage-4 endoblast and stage-12 endoderm differed in the expression of many polypeptides.

One polypeptide was found that may be considered as a marker of mesodermal cell type, as it was present in lateral plate, segmental plate and somitic mesoderm, but not in tissues of the other germ layers. Lateral plate could be distinguished from the other mesodermal tissues in the expression of a number of polypeptides, but the similarity in the 2-D patterns for segmental plate and somites suggest that the separation of somites from the anterior end of the segmental plate is not accompanied by the synthesis of new polypeptides.
Growth stimulation of the immature chick oviduct by androgens : the vagina as a new target tissue
Authors: Grau Yves , Reichhart Jean-Marc , Thiebold Jean
Published: April 2021

Testosterone when injected alone stimulates growth of the vagina but is inactive upon the other segments of the oviduct of the immature chicken. This action of testosterone can already be detected in embryos: it is expressed by the beginning of differentiation of the vaginal mesenchyme cells into smooth muscle cells. In the treated immature chicken, stimulation of growth is considerable and is specifically caused by androgens (testosterone and 5-α-dihydrotestos-terone); the vaginal mesenchyme differentiates into two smooth muscular layers and vaginal epithelium cells differentiate into ciliated cells and goblets cells. [3H]testosterone binding has been found in the vagina of the immature chicken (data not shown). The characteristics of testosterone binding to cytoplasmic components of the chick vagina are consistent with its identity as a testosterone receptor.
Pattern regulation in fragments of Drosophila wing discs which show variable wound healing
Authors: Dale Leslie , Bownes Mary
Published: April 2021

When complementary fragments of the imaginal wing disc of Drosophila are cultured for several days prior to inducing metamorphosis, usually one fragment will regenerate while the second duplicates. It has been proposed that wound healing plays an important part in disc regulation by initiating cell proliferation and determining the mode of regulation (regeneration/ duplication). To test the latter proposal 15 types of wing disc fragments were examined for variability both in the mode of wound healing and the mode of pattern regulation. Two modes of wound healing were observed, regular - the two wound edges heal with each other, and irregular - each wound edge heals with itself. When cultured separately fragments that healed regularly regenerated, while fragments that healed irregularly duplicated. This suggests that the mode of wound healing determines the mode of pattern regulation.
Trophectodermal carcinoma: mouse teratocarcinoma-derived tumour stem cells differentiating into trophoblastic and yolk sac elements
Authors: Damjanov I. , Damjanov A. , Andrews P. W.
Published: April 2021

The retransplantable tumour line derived from a spontaneous ovarian murine teratocarcinoma (Fekete & Ferigno, 1952) was cloned and characterized using light and electron microscopic and immunohistochemical techniques. Grown in ascites, the tumour consisted predominantly of stem cells and a small number of differentiated derivatives. The stem cells expressed surface reactivity with antibody to SSEA-3 and Forssman antigen, alkaline phosphatase, focal cytoplasmic reactivity with antibody to SSEA-1, and varying amounts of cytoplasmic glycogen and 3 betahydroxysteroid dehydrogenase. Their cytoskeleton reacted with antibodies to keratin and vimen-tin. The differentiated derivatives formed approximately 5–15 % of the total cell population in ascites and appeared either as giant cells or were characterized by their reactivity with antibodies to H-2 or α-foetoprotein or intracellular and pericellular laminin or high levels of 3 betahydroxysteroid dehydrogenase activity. Solid tumours produced from subcutaneously injected cells had a variegated appearance suggesting, that like the limited differentiation in the ascites, the stem cells can give rise to trophoblastic, as well as parietal and visceral yolk sac elements. On the basis of the presented data the tumour stem cells were considered as representing malignant equivalents of the common precursor of trophoblastic, visceral and parietal yolk sac cells most likely corresponding to trophectoderm. Accordingly, the tumour was designated as trophectodermal carcinoma.
Pioneering and pathfinding by an identified neuron in the embryonic leech
Authors: Kuwada John Y.
Published: April 2021

Numerous investigations of pathfinding by embryonic neurons, including many leech neurons, have demonstrated that pathfinding is precise. Neurons project the correct number of growth cones which grow to their target areas by making specific choices along the way. However, one leech mechanosensory neuron, the dorsal P (PD) neuron, is unusual in the sense that it initially projects an excessive number of growth cones. One of the growth cones will form the peripheral axon while the others are eliminated. This suggests that PD is one of the earliest neurons to project a peripheral axon, i.e., it may pioneer a peripheral nerve, and that it searches with its multiple growth cones for an external cue which can guide it to its target area. Examination of the early PD axon with light and electon microscopy reveals that it indeed is the first growth cone in its nerve and that it grows in contact with a large non-neuronal (DV) cell until it reaches its target area. The DV cell has a unique morphology and location: a large cell body with thin flat processes extending from the edge of the ganglion to the target area of the PD. It is also present with its unique morphology prior to axonal outgrowth by the PD neuron. These features suggest that the DV cell may be an attractive substrate and/or axonal guidance cue for the PD peripheral axon and therefore for the entire peripheral nerve.
In vitro analysis of interactions between sensory neurons and skin: evidence for selective innervation of dermis and epidermis
Authors: Verna J.-M.
Published: April 2021

Axons from dorsal root ganglion cells cultured in a serum-free medium on poly-L-lysine or collagen substrates interact differently with dermis and epidermis. The orientation of neurite growth is not changed by encountering mesenchymal cells migrating from the outgrowth zone of a dermal explant, and neurites form close membrane associations with some dermal cells; in contrast, neurites strongly avoid epidermis and deviate around the edge of an epidermal explant. When cultures are grown on polylysine this avoidance behaviour occurs at a distance from the epidermis. It is suppressed in the presence of necrotic epidermal cells. We suggest that this avoidance is due to epidermal diffusible factor(s) which bind preferentially to polylysine. The possibility of an absence of specific recognition cues between neurites and epidermal cells is discussed.
In vitro differentiation of neuronal precursor cells from amphibian late gastrulae: morphological, immunocytochemical studies, biosynthesis, accumulation and uptake of neurotransmitters
Authors: Duprat Anne-Marie , Kan Paulette , Foulquier Françoise , Weber Michel
Published: April 2021

Neuronal differentiation has been studied in dissociated cell cultures from early neurulae of Pleurodeles waltl and Ambystoma mexicanum. Cocultures were prepared from the neural primordium and underlying chordamesoderm. NP and NF cultures were prepared from isolated neural plate and neural folds, respectively.

Neuronal precursors in NP and NF cultures had distinctive aggregation properties already evident after 1–2 days in culture. After 10–15 days, mature neurones and synapses were observed by electron microscopy in the three culture types. The expression of neurofilament polypeptides and tetanus-toxin-binding sites was also present in these cultures. A small percentage of neurones contained cytochemically detectable catecholamine. Many neurones took up tritiated dopamine with a high affinity.

Quantitative measurement of [3H]acetylcholine synthesis and storage from [3H]choline were negative at the early neurula stage and in 5 to 15-day-old NF cultures, and remained low in 5 to 15-day-old NP cultures. Acetylcholine production in cocultures increased linearly with time and was always much higher than in NP cultures.

These results suggest that, at the early neurula stage, some neuronal precursors have acquired the capacity to express a high degree of morphological and biochemical differentiation even in the absence of further chordamesoderm influence. However, the chordamesodermal cells in the cultures increased acetylcholine synthesis.
An allelic difference determines reciprocal patterns of expression of binding sites for Dolichos biflorus lectin in inbred strains of mice
Authors: Ponder Bruce A. J. , Festing Michael F. W. , Wilkinson Maureen M.
Published: April 2021

We used staining of tissue sections by lectin conjugates to screen inbred strains of mice for polymorphisms which could be used as histological markers of chimaerism. We found one polymorphism, which involves reciprocal patterns of expression of binding sites for the N-acetyl-galactosamine-binding lectins from Dolichos biflorus (DBA), Helixpomatia (HPA) and Wisteria floribunda (WFA) on intestinal epithelium and vascular endothelium. The polymorphism is due to alleles at a single locus, designated Dlb-1 (for Dolichos lectin binding). Of 29 inbred strains examined, 3 are D1b-1a (type strain RIII-ro; gut epithelium - ve, vascular endothelium + ve), and 26 are D1b-1b (type strain C57BL/6J; gut epithelium + ve, vascular endothelium − ve). In RIII-ro and C57BL/6J embryos, the polymorphic difference is not clearly present until day 11 of gestation. Before then, embryos of both strains express binding sites on gut epithelium and on endothelium.

The temporal and tissue-specific patterns of expression of lectin-binding sites may result from differences in expression of an N-acetyl galactosaminosyl transferase. If so, elucidation of the genetic basis of the polymorphism might provide an insight into the mechanisms of developmental regulation of glycosyltransferase activity.
Embryonic axis orientation in the mouse and its correlation with blastocyst relationships to the uterus: II. Relationships from 4¼ to 9½ days
Authors: Smith L. J.
Published: April 2021

Each of the three primary axes of the primitive streak ( days p.cf) to C-shaped ( days) stage mouse embryo has a specific relationship to the uterine horn axes. By a retrograde analysis of younger sectioned embryos it has been possible to construct an axis fate map for the implanting day blastocyst and to show how its implantation in one or the other of two specific orientations to the ends and walls of the horn leads to these embryo-horn relationships. The implanting blastocyst axis fate map can be related to an axis fate map of the attached blastocyst (Smith, 1980) since these too are in one or the other of two orientations to the ends and walls of the horn. It is suggested that the asymmetries of the attached and implanting blastocysts that allowed the distinctive attachment and implantation orientations to be recognized, are the initial expressions of a three-dimensional system of positional information that is present in the attached blastocyst.
A model for chondrogenic condensations in the developing limb: the role of extracellular matrix and cell tractions
Authors: Oster G. F. , Murray J. D. , Maini P. K.
Published: April 2021

The hyaluronate component of the extracellular matrix is a powerfully hydrophilic polymer, capable of osmotically swelling and deswelling by a volume factor of 5 or more. At the time of cartilage condensation in the limb bud the chondrocytes start to produce hyaluronidase, an enzyme which degrades hyaluronate. The consequent deswelling brings the chondrocytes closer together -close enough for intercellular cell tractions to become effective and intercellular junctions to form. By analysing the physicochemical situation we show how these processes, principally the coupling of the osmotic deswelling with cellular traction forces, can produce cartilage condensation patterns resembling those in the early limb bud. In distinction from our earlier model for chondrogenic condensations this mechanism does not depend on cell motions other than convective transport by contraction.
The cytoskeleton of Xenopus oocytes and its role in development
Authors: Wylie C. C. , Brown Derek , Godsave S. F. , Quarmby J. , Heasman Janet
Published: April 2021

Much is known about determinative events in early amphibian embryos, perhaps more than any other animal group. However, as yet, little attention has been focused on the cytoarchitecture of the oocyte, and the way in which this could regulate asymmetries in the egg, which in turn could lead to developmentally important interactions.

The changing cytoarchitecture of the Xenopus oocyte is described with the emphasis on the following: - firstly the polarity; the oocyte is not radially symmetrical at early stages of oogenesis, but shows marked polarity. Secondly, several cytoskeletal elements change their distribution during oogenesis, and again during maturation to form a fertilizable egg. Thirdly, monoclonal antibody methods show that the oocyte develops several asymmetries which are retained in the egg and early embryo, and may be lineage related.
Cell lineage labels and region-specific markers in the analysis of inductive interactions
Authors: Smith J. C. , Dale L. , Slack J. M. W.
Published: April 2021

This paper reviews work with cell lineage labels and cell-type specific markers in the analysis of inductive interactions in early amphibian development. Our results provide clear evidence for the existence of three such interactions. Mesodermal induction occurs in the early blastula and results from the action of vegetal pole cells on the animal hemisphere. At least two mesodermal rudiments are formed, one dorsal and one ventral. During the next interaction, which we call dorsalization, the ventral mesodermal rudiment becomes subdivided into several territories under the influence of the dorsal marginal zone, or organizer. Finally, during gastrulation, the involuting organizer induces neural tissue from the overlying ectoderm. This interaction is called neural induction.

Although these phenomena can readily be demonstrated under experimental conditions, direct evidence that they occur in normal development awaits an understanding of the molecular basis of induction.
Development of Haemoglobin by De-embryonated Chick Blastoderms Cultured in vitro and the Effect of Abnormal RNA upon its Synthesis
Authors: O′ Brien B. R. A.
Published: April 2021

A simple in vitro histogenesis is described in which the protein haemoglobin is synthesized in the developing blood-islands of a de-embryonated blastoderm. The spread of the blastoderm which follows de-embryonation when it is cultured on the vitelline membrane according to the New technique is eliminated by transfer to an agar gel medium. Cell-division and differentiation in the blood-islands was not inhibited to the same extent as it was in the other tissues present. The erythroblasts multiply, differentiate, and synthesize haemoglobin. The RNA base analogue and antimetabolite 8-azaguanine effectively blocks the synthesis of haemoglobin up to but not including developmental stage 8 on the Hamburger-Hamilton scale. Stages 9 and 10 synthesize haemoglobin in the presence of this analogue. The inhibition by 8-azaguanine is in part removed when the normal base guanine is included with it in the medium. The inhibition is not removed to any extent by incubation with guanine either before or after contact with azaguanine. It is concluded that there is a period in developmental stage 8 of only 1 or 2 hours that represents the border line between RNA analogue inhibition and non-inhibition. It is considered that during this period the RNA associated mechanisms or templates for haemoglobin production begin to operate. The amino-acid analogue fluorophenylalanine but not thienylalanine inhibited haemoglobin synthesis. Incubation following de-embryonation in RNAse had little effect on the synthesis. Chloramphenicol proved to be ineffective as an inhibitor of protein synthesis in this system. The data presented are discussed in relation to the sequence in which haemoglobin becomes detectable in the nucleolus, the nucleus, and the cytoplasm of the developing erythroblast. Haemoglobin development is observed directly in the living system and histochemically by the peroxidatic oxidation of o-dianisidine.
Atypical Spindles in Reinnervated Rat Muscles
Authors: Hník P. , Zelená J.
Published: April 2021

In young rats, following lesions of a peripheral nerve at birth, immature muscle spindles disintegrate during a short transition period (Zelená, 1957), and even after several months of reinnervation the reinnervated muscles are usually found to contain no spindles (Zelená & HNÍK, 1960). Nevertheless, occasional small spindles of atypical structure are observed in some of these muscles. In the present report, the structure and morphological characteristics of these atypical spindles were studied and compared with normal spindles. Since differences in fast and slow muscles may include differences in muscle receptors (Voss, 1937; Maruseva, 1947; Hagbarth & Wohlfahrt, 1952; Freimann, 1953; Cooper, 1960), the number, size, and distribution of spindles were studied in two muscles representing the two functional groups.
Development of gynogenetic and parthenogenetic inner cell mass and trophectoderm tissues in reconstituted blastocysts in the mouse.
Authors: Barton Sheila C. , Adams Catharine A. , Norris M. L. , Surani M. A. H.
Published: April 2021

The developmental potential of inner cell mass (ICM) and trophectoderm (TE) derived from parthenogenetic or biparental gynogenetic embryos was examined in reconstituted blastocysts with normal TE or ICM, respectively. The results demonstrate that when a normal ICM was introduced inside a trophectoderm vesicle derived from parthenogenetic or gynogenetic blastocysts, postimplantation development was characterized by the almost complete failure of trophoblast proliferation and without compensating cellular contribution from the normal ICM to the outer trophoblast lineage. Consequently, the normal ICMs also failed to develop adequately and only a few retarded embryos were detected on day 11–12 of pregnancy. In most respects, development of these reconstituted blastocysts resembled that obtained with unoperated gynogenetic and a parthenogenetic blastocyst. By contrast, an ICM from a parthenogenetic or gynogenetic embryo introduced inside a normal trophectoderm vesicle induced substantial proliferation of the trophoblast but again without a detectable cellular contribution from the ICM to the outer trophoblast lineage. However, with the improved development of the trophoblast, both the parthenogenetic and gynogenetic ICMs developed substantially better and without a detectable cellular contribution from the TE to the embryo. Almost all the embryos developed at least up to the 25-somite stage and many of them reached the 30- to 40-somite stage. Some of the most advanced day-11 and -12 gynogenones and parthenogenones yet seen have now been obtained in this way. Nevertheless, all the embryos were still smaller than the equivalent control embryos and showed signs of some tissue degeneration. The yolk sac was also suboptimal with poor blood supply and may need to be improved to obtain further improvement in the development of the embryos. The combined results demonstrate that the trophoblast proliferates very poorly even in the presence of a normal ICM, if the TE tissue lacks a paternal genome. However, ICM tissues which lack a paternal genome can develop to an advanced embryonic stage if they are introduced inside a normal trophectoderm vesicle. The results give further insight into the differential roles of maternal and paternal genomes during development of the embryo and extraembryonic tissues in the mouse.