bluuebunny/crossref_metadata_2025 huggingface dataset:
Lethality of a tritiated amino acid in early mouse embryos
Authors: Wiebold Janet L. , Anderson Gary B.
Published: April 2021

2- to 4-cell and morula- to blastocyst-stage mouse embryos were cultured for 1 h in tritiated leucine at two specific activities and their subsequent development followed in vitro and in vivo (after transfer to recipients), respectively. 2- to 4-cell embryos that incorporated an average of 42 d.p.m. per embryo were impaired in their ability to develop to the morula and blastocyst stage. Recipients receiving morulae and blastocysts that had incorporated an average of 384 d.p.m. per embryo failed to produce young. Reduction of the specific activity improved the viability of embryos both in vitro and in vivo but development was still less than that of unlabelled embryos. Protein degradation curves were different for both 2- to 4-cell and morula- to blastocyst-stage embryos labelled at the two different specific activities. Most studies using tritiated amino acids have employed higher specific activities than those used here and they may have to be reevaluated due to the possibility of radiation-induced artifacts.
Cell proliferation in condensing scleral ectomesenchyme associated with the conjunctival papillae in the chick embryo
Authors: Kamp Maarten Van De , Hilfer S. Robert
Published: April 2021

The role of cell proliferation in the formation of scleral ectomesenchymal condensations underlying the conjunctival papillae was examined with in vivo tritiated thymidine labelling in chick embryos ranging in age from 8 days 0 h to 10 days 12 h. Percentages of labelled nuclei were determined in both ectomesenchyme and the deeper fibrous sclera for short-term and continuous tritiated thymidine incubations. During formation of the ectomesenchymal condensations the percentages of labelled nuclei were consistently higher within the condensations than in corresponding non-condensing ectomesenchyme between papillae. The consistent differences of labelling percentages observed within the condensing versus noncondensing ectomesenchyme were not found in the fibrous sclera at any stage. All areas of both the ectomesenchyme and fibrous sclera showed decreases in the percentages of labelled nuclei from 8 days Oh to 10 days 12h, although the decline in the ectomesenchymal condensations beneath papillae occurred more slowly than in areas between papillae. The data suggest that the conjunctival papillae directly influence the proliferation in the subjacent condensing ectomesenchyme but have no effect on the ectomesenchyme between papillae or any region of the deeper fibrous sclera. The observations of this investigation are discussed in relation to other studies of the development of the pre-ossicular mesenchyme.
Relationship between timing of posterior neuropore closure and development of spinal neural tube defects in mutant (curly tail) and normal mouse embryos in culture
Authors: Copp Andrew J.
Published: April 2021

The relationship between timing of closure of the posterior neuropore (PNP) and development of spinal neural tube defects (NTD) has been studied in individual mutant curly tail mouse embryos maintained in culture. Moderate delay in PNP closure results in development of tail flexion defects whereas extreme delay of PNP closure is associated with development of open NTD. Experimental enlargement of the PNP at the stage of 25 to 29 somites leads to delayed PNP closure and development of tail flexion defects in 36 % and 38 % respectively of non-mutant A/Strong embryos. In curly tail embryos, the effect of experimental enlargement of the PNP summates with the genetic predisposition to produce an increased incidence of spinal NTD among which open defects are proportionately more common. These results indicate that a causal relationship exists between delay in PNP closure and development of spinal NTD in mouse embryos. The method described for distinguishing between prospective normal and abnormal curly tail embryos at a stage prior to the appearance of malformations provides an opportunity to study the morphogenetic processes that precede the development of genetically determined spinal NTD.
The fate of larval chondrocytes during the metamorphosis of the epibranchial in the salamander, Eurycea bislineata
Authors: Alberch P. , Lewbart G. A. , Gale Emily A.
Published: April 2021

The metamorphosis of the epibranchial cartilage, a skeletal component of the hyobranchial apparatus, in the salamander Eurycea bislineata entails a combination of the reabsorption of a larval cartilaginous element with the simultaneous genesis of an adult cartilage in the same place. In this study we focus on the fate of the larval chondrocytes. Two hypotheses are considered: one, larval cells simply die off during metamorphosis, or, alternatively, they dedifferentiate and participate in the formation of the adult element.

Thyroxine treatment and experimental tissue manipulation coupled with measurements of thyroxine levels using radioimmunoassay show that, within 24 h after T4 treatment, larval chondrocytes in the epibranchials exhibit large autophagocytic vacuoles, disruption of the rough endoplasmic reticulum, abnormally shaped mitochondria, abundance of lysosomes and nuclear degeneration, all symptoms of the onset of cell death. In conclusion, evidence from light microscopy, TEM and SEM show that the larval chondrocytes in response to rising levels of thyroid hormones undergo a process of lysosomal autophagocytosis and do not participate in the formation of adult structures.
DNA replication and compaction in the cleaving embryo of the mouse
Authors: Smith Roger K. W. , Johnson Martin H.
Published: April 2021

The effects of aphidicolin, a reversible inhibitor of DNA polymerase alpha, both on replication and on development of the mouse embryo from the 2- and 4-cell stages to the compacted late 8-cell stage have been assessed. The continuous presence of aphidicolin from G1 of the 4-cell stage resulted in inhibition of DNA replication and prevention of division from 4 to 8 cells, but was without effect on the timing or incidence of cell flattening, surface polarization and cytoplasmic polarization. The continuous presence of aphidicolin from Gx of the 2-cell stage resulted in inhibition of DNA replication, division, and polarization. Some slight intercellular flattening in a few embryos did occur. If addition of aphidicolin was delayed by 10 h to early in G2 of the 2-cell stage, further rounds of replication were blocked and some embryos failed to cleave to 4-cells. Nevertheless, almost all embryos showed evidence of flattening and polarization regardless of cell number. In contrast, if aphidicolin was added in G] of the 2-cell stage and removed after 10 h, the cells showed delayed DNA replication, little evidence of division, and no cell flattening or polarization. We conclude that DNA replication at the 2-cell stage may be essential for the components of compaction studied, but that DNA replication at the 4- and 8-cell stages is not.
A clonal analysis of the requirement for the trithorax gene in the diversification of segments in Drosophila
Authors: Ingham P. W.
Published: April 2021

The requirement for the trithorax gene during imaginal cell proliferation has been analysed by clonal analysis. Clones carrying the allelic Regulator of bithorax and trithorax mutations were induced by mitotic recombination at different developmental stages. The results indicate that the trithorax gene is required at least until the beginning of the third larval instar to ensure the correct differentiation of head, thoracic, and abdominal structures, and are consistent with a role for the gene in maintaining the appropriate levels of Antennapedia and bithorax complex expression.
Prostaglandin synthesis during the course of limb cartilage differentiation in vitro
Authors: Gay Steven W. , Kosher Robert A.
Published: April 2021

In the present study we have used radiometric thin layer chromatography (TLC) and radioimmunoassay (RIA) to examine the synthesis of various prostaglandins (PGs) during the progressive chondrogenic differentiation limb mesenchymal cells undergo in micromass culture. Throughout the 3-day culture period, [3H]arachidonic acid (AA) is metabolized to compounds which comigrate with authentic PGE2, PGF2α, 6-keto-PGF1α, TxB2, and PGD2. In micromass cultures prepared from the cells of whole stage-23/24 wing buds, all 3H-AA metabolites are produced in relatively small amounts during the initial period of culture, i.e. prior to the formation of extensive prechondrogenic cellular aggregates. Concomitant with maximum aggregate formation and the initiation of cartilage differentiation, there is a striking and progressive increase in the production of all the major classes of PGs from 3H-AA. PG production from 3H-AA is also at a maximum during the onset of chondrogenesis in micromass cultures prepared from the distal subridge mesenchymal cells of stage-25 wing buds in which more rapid, extensive, and homogeneous cartilage differentiation occurs. To complement these TLC studies, RIA has been used to examine the amount of various PGs synthesized from endogenous substrates by micromass culture homogenates at various times during in vitro chondrogenesis. These RIA studies also indicate that PG production is highest during periods of culture which coincide with the onset of overt chondrogenesis in both stage-23/24 whole limb and stage-25 subridge mesoderm micromass cultures. RIA indicates that PGE2 is the predominant PG produced from endogenous substrates during 1 h incubations at the onset of chondrogenesis, while radiometric TLC indicates compounds which comigrate with PGF2α are the major class of 3H-AA metabolites which accumulate during that time. This qualitative difference very likely reflects metabolism of parent PG compounds during the long (12 h) labelling and postlabelling incubations utilized in the TLC analyses. The temporal correlation between PG production and the initiation of chondrogenesis in vitro is consistent with previous studies implicating PGs in the regulation of limb cartilage differentiation.
Monoclonal antibodies to the cells of a regenerating limb
Authors: Kintner Chris R. , Brockes Jeremy P.
Published: April 2021

Monoclonal antibodies were raised against differentiated cells, and blastemal cells from regenerating limbs of adult newts (Notophthalmus viridescens) and screened for specific staining by immunocytochemistry. In addition to antibodies that identify muscle, Schwann cells and cartilage, two reagents were specific for subpopulations of blastemal cells. One of these latter antibodies, termed 22/18, has provided new evidence about the origin of blastemal cells from Schwann cells and myofibres, and also identifies blastemal cells whose division is persistently dependent on the nerve supply.
The function and mechanism of convergent extension during gastrulation of Xenopus laevis
Authors: Keller R. E. , Danilchik Michael , Gimlich Robert , Shih John
Published: April 2021

The processes thought to function in Xenopus gastrulation include bottle cell formation, migration of cells on the roof of the blastocoel, and autonomous convergent extension of the circumblastoporal region. A review of recent and classical results shows that only the last accounts for the bulk of the tissue displacement of gastrulation, including spreading of the marginal zone toward the blastopore, involution of the marginal zone, and closure of the blastopore. Microsurgical manipulation and explantation studies, analysed by time-lapse video and cine microscopy, shows that the dorsal circumblastoporal region contains two regions which show either autonomous or semiautonomous convergent extension. The dorsal involuting marginal zone (IMZ) undergoes convergence (narrowing) and extension (lengthening) after its involution, beginning at the midgastrula stage and continuing through neurulation, such that it simultaneously extends posteriorly across the yolk plug and narrows the blastoporal circumference. Concurrently, the corresponding region of the overlying non-involuting marginal zone (NIMZ) begins a complementary convergent extension, but at a greater rate, which spreads vegetally to occupy surface area vacated by the IMZ. Tissue recombination experiments show that the deep cells of the dorsal IMZ bring about convergent extension. Labelling of small populations of these cells with a cell lineage tracer shows that convergent extension involves intercalation of deep cells to form a longer, narrower array. Direct time-lapse video and cine micrography of deep cells in cultured explants show that convergent extension involves radial and circumferential intercalation. Removal of the entire blastocoel roof of the early gastrula, including all or part of the NIMZ, shows that convergent extension of the IMZ alone can bring about its involution and blastopore closure. The role of convergent extension in gastrulation of other amphibians and other metazoans and its significance to related problems in early development are discussed.
Maturation promoting factor and cell cycle regulation
Authors: Ford C. C.
Published: April 2021

Cell cycles in early amphibian embryos are characterized by the absence of Gi and G2 phases. The simple cycle of S phase and mitosis does show similarities with other systems, particularly in the presence of cytoplasmic components advancing nuclei into DNA synthesis and mitosis. Maturation-promoting factor induces nuclear envelope breakdown and subsequent chromosome condensation. Cytoplasmic factors appear during maturation which are capable of inducing DNA synthesis, and arrest of the nuclear division cycle in metaphase (cytostatic factor). The timing of appearance of these activities is considered and their relationship in integrating DNA synthesis during early cleavage is discussed.
The Differential Growth Response of Embryonic Chick Limb-bone Rudiments to Triiodothyroninein vitro
Authors: Lawson Kirstie
Published: April 2021

The cartilaginous limb-bone rudiments of the 6-day-old embryonic chick show a differential growth response to treatment with triiodothyronine (T3) during 8 days’ culture in vitro. The growth in length and wet weight of the tibia is reduced by l · 6 × 10–4g. T3/l. of medium, but the growth of the radius is increased. Tibia and radius explanted at comparable histogenetic stages respond differently to T3, but the responses are slightly modified by the stage of development at which the rudiments are exposed to the hormone: tibiae from 5-to -day-old embryos show a transitory stimulation of growth in length, followed by retardation, while increase in the growth in length of radii from 7- and 8-day-old embryos is less than that of radii from 6-day-old embryos. Five small limb-bone rudiments of a similar size (third metatarsus, radius, ulna, third metacarpus, and fourth metacarpus) respond differentially to T3. It is therefore unlikely that the differential growth-response of the tibia and radius is a result of the limited nutritional conditions in vitro.
Sur l’origine du sang et des vaisseaux chez Lebistes reticulatus (Téléostéen)
Authors: Colle-Vandevelde par A.
Published: April 2021

The erythroblasts of the Teleost Lebistes reticulatus, when visualized with the Unna-Brachet technique, appear at the 2-somite stage of development. The earliest visible erythropoiesis is then located in the ventral part of the border of the blastodisc. Along this border it rapidly extends towards the posterior extremity of the embryo, where it appears continuous with the elements of the ‘Intermediare Zellenmasse’ of Oellacher.

The blood-forming rudiment in the embryo itself becomes visible only at the stage of 5 somites, and takes the shape of an inverted Y whose long limb is localized in the midline of the posterior somitic region of the embryo; the two branches of the Y taking their origin in the posterior part of the extra-embryonic tissue on both sides of the terminal node.

Blood-circulation becomes apparent at the 15–17-somite stage, and at the surface of the yolk the blood-cells then move towards the venous side of the heart. The closure of the blastopore occurs around the stage of 18 somites, when the blood-circulation is already established.

These observations do not correspond with what is found in other Teleosts where the blood-forming rudiment appears to be situated only in the dorsal part of the body. It would now seem possible to relate this extraordinary origin to the situation which prevails in other Vertebrates.
Transplantation et Régénération chez la Planaire Dendrocoelum lacteum
Authors: Stéphan-Dubois par Françoise , Gilgenkrantz Fernand
Published: April 2021

A graft of prepharyngeal origin, implanted behind the mouth, tends to dominate the posterior fragment obtained by postbuccal section. If this section runs through the graft, the latter regenerates a head at its free anterior border while the host edges undergo a regulation of form. After a similar section, the graft having previously been irradiated with X rays, the postpharyngeal host region provides the graft with the necessary material for regeneration and the final result is identical with the preceding one, except that regeneration is delayed for about twelve days during which the healthy neoblasts are migrating across the irradiated graft. If the section goes between mouth and graft, no regeneration is possible at the level of section. The graft bulges dorsally, develops eyes, and its movements draw the posterior part along. A graft of postpharyngeal origin, implanted at the anterior level of a decapitated and X-irradiated worm, supplies the host with its own healthy cells, but it remains unable to perform any head regeneration from a free border running through itself.
Comparison of the Different Teratogenic Effects of Three Commercial Samples of Trypan Blue
Authors: Beck F.
Published: April 2021

Three commercial preparations of trypan blue were injected into Wistar rats at days of pregnancy. The amount of azo dye (in terms of titratable azo linkage) administered was the same in each series. Two of the dye preparations were found to have well-marked teratogenic properties while the third was almost totally inactive. Control rats were injected with normal saline. One of the teratogenic dyes had a lower Ld50 (Kärber) than the non-teratogenic dye.
Le rôle du mesonephros de l’embryon de Poulet dans la nutrition de cellules cancéreuses
Authors: Wolff par Etienne , Wolff Emilienne
Published: April 2021

Nous avons montré que plusieurs souches cancéreuses humaines, HeLa, KB, Osgood, Fogh, peuvent être cultivées sur des organes embryonnaires de poulet explantés in vitro. Le mesonephros de 8 à 9 jours est un des plus favorables à la prolifération des cellules cancéreuses (Et. Wolff & Em. Wolff, 1958, 1959). Rappelons que celles-ci ne se multiplient pas et ne survivent pas, si elles sont placées directement sur les milieux nutritifs propres aux cultures organotypiques. Par contre, elles se nourrissent des tissus du mesonephros cultivés sur ces milieux. C’est donc l’organe embryonnaire, non le milieu de culture, qui est responsable du succès de la culture. Les cellules cancéreuses se comportent comme des parasites vis-à-vis des cellules de l’organe embryonnaire. Elles se substituent à elles, par un processus encore mal élucidé, car les cellules normales au milieu desquelles pénètrent les cellules cancéreuses ne montrent pas de phénomènes de dégénérescence. Pourtant elles disparaissent en grand nombre, car des territoires considérables du mesonephros sont envahis par les cellules tumorales, qui se substituent à elles et n’en laissent subsister aucune.
Membrane organization in the preimplantation mouse embryo
Authors: Pratt Hester P. M.
Published: April 2021

The preimplantation mouse blastocyst consists of two differentiated tissues, the troph-ectoderm (a structurally and functionally polarized epithelium) and the inner cell mass. The divergence of these two cell types can be traced back to a contact dependent polarization of the surface and cytoplasm at the 8-cell stage. Membrane/cytocortical organization during this preimplantation period has been studied using freeze fracture in conjunction with the sterol-binding antibiotic filipin in an attempt to discern the molecular basis and origin of these surface asymmetries.

The distribution of filipin reactivity within the different membrane domains showed that the surface polarity exhibited by trophectoderm and by blastomeres of the 8-cell stage is underlain by a heterogeneity in molecular organization of the membrane/cytocortex which may originate prior to the appearance of any overt surface polarity.

The results are discussed in terms of the likely basis of this membrane/cytocortical asymmetry, its probable origins and the use of the preimplantation mouse embryo as a model system for studying the assembly of a polarized epithelium.
Genetic analysis of developmental mechanisms in hydra : XVI. Effect of food on budding and developmental gradients in a mutant strain L4
Authors: Takano Jun , Sugiyama Tsutomu
Published: April 2021

Effect of food was examined on the budding rate and the developmental gradients of a mutant hydra strain L4.

This mutant strain has very high levels of head-inhibition potential gradient along its body axis (Takano & Sugiyama, 1983). It also has a reduced budding capacity when it is cultured using brine shrimp nauplii as food, but its budding capacity is significantly improved when a small amount of tubifex worm tissue is added to its diet of brine shrimp (Takano, 1984).

To test whether or not this change of budding rate is correlated with the change in the levels of the head-activation or head-inhibition potential gradients, L4 animals were cultured on the diet of brine shrimp with or without addition of tubifex worm tissue and the budding rates and the gradient levels were examined in these animals.

The results showed that food affected the budding rate in L4 without affecting its gradient levels. This suggests that the gradient levels and the budding rate in L4 are uncorrelated to each other, and that therefore the high levels of head-inhibition potential are not the cause for the low budding rate in this strain (cf., Takano & Sugiyama, 1983).
Isolation, characterization and localization of a lectin within the vitelline membrane of the hen’s egg
Authors: Cook Geoffrey M. W. , Bellairs Ruth , Rutherford Nicholas G. , Stafford Caroline A. , Alderson Thomas
Published: April 2021

A lectin with an affinity for certain sulphated polysaccharides, such as fucoidin and dextran sulphate, has been isolated from the vitelline membrane of hens’ eggs and purified to hom­ogeneity as assessed by two-dimensional gel electrophoresis. Polyclonal and monoclonal anti­bodies have been raised to the lectin and used in indirect immunofluorescence microscopy to localize the agglutinin in the outer layer of the vitelline membrane, where the lectin persists prior to the breakdown of the vitelline membrane. The qu antity of lectin extracted from the two layers of the membrane, which have been separated by the method of Bellairs, Harkness & Harkness (1963), correlated well with the results of immunofluorescence microscopy. Sodium dodecyl sulphate-polyacrylamide gel electrophoresis of the two layers of the membrane indicates that each layer has a distinctive polypeptide composition, the outer layer containing in particular lysozyme and avidin.

The evidence obtained in this study indicates that the lectin is not involved in adhesion of the blastoderm to the vitelline membrane; neither is it involved in the expansion of the blastoderm nor in maintaining the strength of the membrane. The possible roles in promoting transport of solutes across the membrane as well as providing bactericidal properties to the egg are discussed.
Cell division during intercalary regeneration in the cockroach leg
Authors: Anderson Hilary , French Vernon
Published: April 2021

In a series of grafting operations on cockroach legs, epidermal cells from different positions or from the same position on the circumference of the femur were placed together. Where cells from different positions were confronted, new cuticular structures corresponding to the positions which would normally have lain between them were formed during the following moults. At the control junctions, where cells from the same positions were placed together, no new structures were formed.

Grafted legs were examined histologically at various times after the operation. The events following grafting fell into four phases: wound healing - when epidermal cells migrated over the wound to re-establish epidermal continuity and cells adjacent to the wound divided to compensate for cell emigration; intercalation - when cell divisions took place at the host-graft borders where there was a positional discrepancy; proliferation - when the general growth of the epidermis occurred by widespread cell division; cuticle secretion - when apolysis occurred, cell division ceased, and cuticle secretion began.

The results show that intercalary regeneration is associated with local cell division at the graft-host borders, and that these divisions are not confined to the normal proliferative phase of the moult cycle, but begin much earlier in the cycle, as soon as wound healing is complete.

These results support epimorphic models (such as the Polar Coordinate Model) of pattern regulation, where change of positional value is tied to cell division, but they do not discount the possibility of a limited initial morphallactic phase.
Eyelid development and fusion induced by cortisone treatment in mutant, lidgap-Miller, foetal mice. A scanning electron microscope study
Authors: Harris M. J. , Juriloff D. M.
Published: April 2021

In normal mice the eyelids grow across the eye and fuse together during days 15 and 16 of gestation, and the mice are born with their eyes closed. In mutant lgM1/lgM1 (lidgap-Miller) foetuses this growth and fusion does not occur and the mice are born with their eyes open. A single prenatal treatment with cortisone on day 14 of gestation masks the genetic defect, and the mice are born with their eyes closed. In the present study, a scanning electron microscope was used to investigate: (1) whether eyelid closure in cortisone-treated lgM1/lgM1 foetuses differs from that in normal foetuses of the CBA/J and ICR/M1 strains and, if so, how; and (2) how developing eyelids of untreated lgM1/lgM1 foetuses differ from normal.

The induced closure differs from normal. During their growth, eyelids of treated mutant foetuses have a deficiency of rounded periderm cells at their margins; the margin cells agglomerate and flatten prematurely. In closed eyes of treated mutants there is a gap between periderm cells of the upper and lower eyelids along part of the fusion line. Fusion is completed late, during day 17. Maturation of the head periderm is advanced in treated lgM1/lgM1foetuses on day 16, relative to normal CBA/J and untreated lgM1/lgM1 foetuses.

Untreated lgM1/lgM1 foetuses differ from normal in that the eyelids never cover the eye and lack rounded periderm cells at their perimeter. The periderm cells present form a flattened band along the eyelid margin rather than, as in normal eyelids, along the fusion line.

The results of the cortisone study suggest that the route to eyelid closure in mice may not be narrowly canalized either in cell morphology or number, or in timing, and that closed eyes may be achieved after cortisone treatment in lgM1/lgM1 foetuses as part of an induced maturation of the periderm.
The precision of pathway selection by developing peripheral axons in the axolotl
Authors: Freeman J. M. , Davey D. F.
Published: April 2021

At the time of hindlimb development in the axolotl there is a well-established but still developing trunk innervation. The trunk innervation is primarily composed of the segmental nerves, each of which consists of a dorsal and a ventral ramus and its branches. At a few segmental levels in the region of the hindlimb a large number of additional axons arise to innervate the limb. To reach the limb, they must grow via the ventral rather than the dorsal rami.

The precision with which this pathway is selected was determined by counting axons in the dorsal and ventral rami at limb segmental levels, prior to and during the period of maximum axon proliferation. If outgrowth is highly directed rather than random, then the ratio of ventral/ dorsal ramus axons should increase significantly during the period when large numbers of additional axons are produced. In addition, since the dorsal trunk varies little in size between limb segments and immediately caudal ‘non-limb’ segments, the number of axons in the dorsal rami can be compared at the two levels. Mistaken projections should result in inordinately large axon numbers in dorsal rami at limb compared to non-limb levels.

The results show that there is approximately a tenfold increase in the ratio of ventral/dorsal ramus axons at the time of maximum outgrowth to the limb, thus the mode of distribution at the ventral-dorsal branch point is significantly altered in favour of growth toward the limb, and outgrowth appears to be highly directed rather than random. Moreover at this time there is no discernible increase in the number of dorsal ramus axons at limb levels while those at non-limb levels increase fourfold. The apparent growth of all axons into the ventral ramus suggests the presence of a strong, non-specific attraction.
The handedness and origin of supernumerary limb structures following 180° rotation of the chick wing bud on its stump
Authors: Javois Lorette C. , Iten Laurie E.
Published: April 2021

The pattern of differentiated wing structures formed following 180° rotation of the undifferentiated wing bud tip on its base was examined in detail. These analyses were performed to determine the handedness and origin of the supernumerary structures which arise. In contrast to the variable classes of symmetric and/or asymmetric limb anatomies observed following the same operation with amphibian regeneration blastemas, wings of predictable handedness were observed. Both the graft and stump contributed cells to the supernumerary structures. These results are discussed in the light of two current models describing the developing chick limb and analysed diagrammatically within the framework of one of these models, the polar coordinate model.
Tetrasomy 16 in the mouse: a more severe condition than the corresponding trisomy
Authors: Debrot Sylvain , Epstein Charles J.
Published: April 2021

Although an understanding of the phenotypic similarities and differences between individuals trisomic and tetrasomie for the same chromosome or chromosome segment is of considerable theoretical interest with regard to the relationship of the phenotypic features of aneuploid states to changes in the dosage of specific genes, the data obtainable from human cases of tetrasomy do not permit firm conclusions to be drawn. However, a mouse model system based on the intercrossing of animals doubly heterozygous for two Robertsonian translocation (metacentric) chromosomes with monobrachial homology can be used to generate both tetrasomie and trisomic embryos simultaneously. With mice carrying the two metacentric chromosomes, Rb(11.16)2H and Rb(16.17)32Lub, which share chromosome 16 in common, embryos with tetrasomy 16 and trisomy 16 have been generated. The rate of non-disjunction in both males and females was 34 to 36 %, and the observed overall frequency of tetrasomies in embryos up to 10 days of age was 3·3 %, very close to the expected 3·1 %. Although trisomy 16 and tetrasomy 16 embryos could not be distinguished by size from one another or from diploid embryos at the sixth day of gestation, the tetrasomy 16 embryos were very small and delayed in development at day 10 and clearly distinguishable from the trisomics. Fusion of the anterior neuropore had not occurred, rotation of the embryo was incomplete, and somite formation was retarded. By day 12, all of the tetrasomy 16 embryos were either dead or dying. By contrast, virtually all trisomy 16 embryos were alive at day 10, although about 60 % were retarded in development. The same was also the case on day 12 for trisomy 16 embryos obtained from mothers that were naturally mated. However, super ovulation of the mothers, which caused a doubling of the number of implants, resulted in a significant decrease in the frequency of trisomy 16 embryos and possibly of tetrasomy 16 embryos as well. This finding is consistent with the suggestion that the viability of aneuploid embryos, which may be at a proliferative disadvantage, is highly dependent upon intrauterine conditions. These exogenous factors notwithstanding, it is clear that tetrasomy 16 has much more deleterious effects on embryonic development than does trisomy 16 and that four doses of the genes on chromosome 16 result in developmental derangements greater than are produced by three doses of the same genes.
Non-random spatial arrangement of clone sizes in chimaeric retinal pigment epithelium
Authors: Schmidt Günter H. , Wilkinson Maureen M. , Ponder Bruce A. J.
Published: April 2021

Clonal analysis of whole-mount preparations of entire retinal pigment epithelium (RPE), using SWR↔C57BL/6JLac and DDK↔C3H/Bi mouse aggregation chimaeras in which one of the two parental components predominated, revealed a markedly non-random spatial arrangement of patch (clone) sizes. Single-cell and small patches predominated in an area around the optic nerve head while large patches occurred most frequently near the periphery. Mechanisms are discussed which may explain these results. Patch size frequency distributions were concave and skewed. Singletons were the most frequent size class, but a wide range of sizes and a smaller number of much larger patches were also always found. The results preclude the use of statistical methods previously employed to calculate clone sizes from the geometric means of observed patch sizes. Instead, the median and interquartile range may provide the best summary of the observed patch size frequency distributions. Our findings support a stochastic model of tissue growth.
Interaction between the leg and surrounding thorax in the beetle
Authors: French Vernon
Published: April 2021

Interactions between the insect leg and surrounding thoracic epidermis were studied in the beetle, Tenebrio, by grafting the entire larval prothoracic leg into the metathoracic leg site in various orientations.

Control grafts simply heal, but A/P reversed grafts lead to regeneration of supernumerary legs of host orientation in A and P positions. M/L reversed grafts also give supernumeraries, again with host orientation but in M (or MP) and L (or LA) positions. The differences in structure between adult prothoracic and metathoracic legs allow the origin of these super-numeraries to be analysed at coxa and tarsus level. The A/P supernumeraries are consistent and complementary in structure, of host origin on the host side and graft origin on the graft side, and with the borders in apparently constant midmedial and midlateral positions. The M/L super- numeraries, however, are variable and often non-complementary in structure. The results of the A/P and M/L reversals are similar to those found at a more distal level in Tenebrio legs and the legs of several hemimetabolous insects, suggesting that the arrangement of positional values and A and P compartments extends from the epidermis of the leg onto the surrounding thorax.

The results of a 180° rotation of the entire leg, however, differ from those found at a more distal level in that the grafted leg rarely derotated and two (or occasionally one or three) supernumeraries are formed in a wide variety of positions, some with constant and others with variable orientation. These results are not readily explained by current models of insect leg formation and regeneration.
Distribution of fibronectin, laminin and entactin in the environment of migrating neural crest cells in early mouse embryos
Authors: Sternberg J. , Kimber S. J.
Published: April 2021

The distribution of the extracellular matrix molecules fibronectin, laminin and entactin was studied in frozen sections of -day mouse embryos in order to relate their presence to neural crest cell migration. It was found that all three components were present in basement mem-branes, laminin and entactin being mainly restricted to these. Fibronectin was present at high levels in basement membranes and extracellular spaces throughout the embryo, including the regions of neural crest cell migration. Fibronectin is known to affect migration in a variety of cell systems, so its presence in the.embryo at the time of migration may indicate that it is influencing cell movement. This influence is likely to be via the cell surface through interactions with other matrix components such as glycosaminoglycans, and possibly entactin and laminin.
Comparison of the effects of vitamin A on limb development and regeneration in Xenopus laevis tadpoles
Authors: Scadding S. R. , Maden M.
Published: April 2021

The purpose of these experiments was to compare the effects of vitamin A on developing and regenerating limbs in Xenopus laevis tadpoles. Each tadpole had one hindlimb amputated to induce regeneration while the contralateral developing limb was left intact. Tadpoles at stages 50 through 54 were treated by immersion in retinol palmitate at doses ranging from 0·3 to 75i.u.ml−1, for periods ranging from 1 to 14 days. Developing limbs usually became hypomorphic as a result of the treatment, with results varying with stage and treatment from slight phalange derangements to total disruption of pattern, or complete inhibition of limb development. Regenerating limbs gave a variety of responses including hypomorphic regeneration, proximodistal or anteroposterior duplication of skeletal elements, or complete suppression of regeneration. The response to retinol palmitate of developing limbs was clearly different from regenerating limbs. Hypotheses which might explain the results were discussed and a hypothesis which proposed a dual action of vitamin A affecting both the cell cycle and the mechanism of pattern regulation was proposed.
Pattern formation in 8-cell composite embryos of Xenopus laevis
Authors: Kageura H. , Yamana K.
Published: April 2021

We have shown in defect experiments that an 8-cell embryo of Xenopus laevis consists of three kinds of cells, that is, animal, vegetal dorsal and vegetal ventral cells, and that cells of different kinds are distinctly different in their developmental capacity. Complete pattern formation occurs in any defect embryo which contains at least two animal, one vegetal dorsal and one vegetal ventral cell. In the present transplantation experiments, we replaced one or two cells of one 8-cell embryo by those of another to obtain 29 series of composite embryos, in which the cell composition of an embryo and/or the dorsoventral orientation of individual cells differed from those of a normal 8-cell embryo. The resulting embryos were examined macroscopically when controls reached stage 26 (tailbud stage) and later.

The results showed that both the two animal dorsal cells or one vegetal dorsal cell could be replaced by animal ventral cells or a vegetal ventral cell, respectively, without any detectable effect on pattern formation, irrespective of the ventrodorsal direction of the ventral cells. On the other hand, replacement of an animal ventral or a vegetal ventral cell by an animal dorsal or a vegetal dorsal cell, respectively, made most composite embryos twins. Twins were also formed when a left-handed vegetal dorsal cell was replaced by a right-handed counterpart and vice versa. In these composite embryos, the dorsoventral orientation of the transplanted cell was different from that of a resident dorsal cell or cells of a recipient, and several lines of evidence show that the dorsal cell transplanted in an off-axis orientation is responsible for twin formation. Thus, dorsal cells have the capacity to form dorsal axial structures at later stages and this capacity is localized on the dorsal side, and endows the cells with polarity. On the other hand, ventral cells did not have this capacity or polarity, judging from the fact that their orientation had no effect on pattern formation. One vegetal dorsal or ventral cell could be replaced by an animal dorsal or ventral cell, respectively, without any marked effect. However, replacement of two vegetal cells by animal ones and of one or two animal cells by vegetal ones resulted in deficiency of vegetal cells and oedema and in deficiency of animal cells and incomplete invagination, respectively.

Twin formation in composite embryos with animal dorsal cells in place of animal ventral ones is discussed in consideration of findings in recombination experiments by Nieuwkoop.
Pattern of skeletal muscle regeneration after reautotransplantation of regenerated muscle
Authors: Gulati Adarsh K.
Published: April 2021

Autotransplantation of rat extensor digitorum longus muscle results in initial myofibre degeneration and subsequent regeneration from precursor myosatellite cells. To determine what effect a reinjury would have on the regenerative response, in the present.study, once transplanted and regenerated muscles were reinjured by reautotransplantion. In rats, four weeks after initial transplantation, when the regeneration was complete, the extensor digitorum longus muscle was transplanted again and the pattern of regeneration in reautotransplanted and once auto transplanted muscles was compared. Muscles were analysed 2, 4, 7, 14 and 30 days after autotransplantation and reautotransplantation. Both autotransplanted and reautotransplanted muscles underwent degeneration and regeneration; however, the pattern of regeneration in these two transplants was quite different. In autotransplants, a thin myogenic zone, marked by activated myoblasts, was first seen at 4 days. By 7 days the width of myogenic zone increased but still many degenerating myofibres were present in the central region of the muscle. By 14 days the muscle was filled with regenerated myotubes and myofibres. The reautotransplanted muscles underwent similar regenerative events; however, the rate of regeneration was considerably faster. The myogenic zone was apparent as early as 2 days and was much larger at 4 days, and by 7 days the entire muscle was filled with regenerated myotubes and myofibres which matured at later time intervals. Furthermore, the decrease in muscle weight in reautotransplanted muscles was not as much as that seen after autotransplantation. These findings reveal that not only is skeletal muscle capable of regeneration after a second injury, but the rate of this regeneration is much faster. This increased rate and recovery may be due to a conditioning effect of the first injury.
The growth of supernumerary legs in the cockroach
Authors: Truby Paul R.
Published: April 2021

When the anteroposterior axis of a cockroach leg is reversed at a graft by exchanging a left leg for a right leg at the mid-tibia level, regeneration occurs in the region of the graft/host junction. This results in the formation of a pair of lateral supernumerary legs. In these experiments the patterns of cell division which take place during supernumerary leg formation were observed in sections of regenerating legs of the cockroach Leucophaea maderae. Early patterns of cell division resemble those seen in control grafts in which no axial reversal had been carried out during grafting. These cell divisions are associated with the process of wound healing. Later, a large area of the epidermis proximal to the graft/host junction becomes activated and shows a rapid rate of cell division. This area forms two outgrowths which grow by cell division throughout their epidermis to form the epidermis of the supernumerary legs.

The results are more consistent with the view that the formation of supernumerary legs involves dedifferentiation of the epidermis in the region of the graft/host junction to form a blastema, rather than being due to local cell division at the point of maximum pattern discontinuity. This conclusion is used to offer an explanation for the range of different types of outcome of left-right grafts that has been observed.
Proximal–distal sequence of development of the skeletal tissues in the penis of rat and the inductive effect of epithelium
Authors: Murakami Ryutaro , Mizuno Takeo
Published: April 2021

The penis of adult rats comprises the corpus cavernosum penis and the proximal and distal segments of os penis which are situated proximal–distally in this order. Androgens are necessary for the phenotypic differentiation of these tissues. In the present study, genital tubercular mesenchyme of foetal rats was recombined with or without homologous or heterologous epithelia and transplanted beneath the kidney capsule of syngeneic adult male rats, and the development of the corpus cavernosum penis and the os penis in the transplants was examined. Only in the presence of epithelia can the genital tubercular mesenchyme acquire the capacity for differentiation into the corpus cavernosum penis, the proximal segment of os penis, and the distal segment of os penis in this chronological order. The inductive effect of epithelium is a permissive step in the differentiation of the os penis of rat. The epithelium seems to be necessary for the process of rudiment formation of the os penis and the corpus cavernosum penis.
The effects of two retinoids on limb regeneration in Pleurodeles waltl and Triturus vulgaris
Authors: Lheureux Emile , Thoms Stephen D. , Carey Frederick
Published: April 2021

The effects of two vitamin A analogues, retinol palmitate and retinoic acid, on pattern formation during limb regeneration in larvae of two European newts, P. waltl and T. vulgaris are described. The response of the regenerating limb to retinoid treatment differed according to the larval stage of development for P. waltl. Young larval limbs, which were anterior limb buds at the time of amputation, duplicated transversely while limbs of older larvae duplicated proximodistally. Proximodistal duplications were usually limited to the production of supernumerary carpals or a second zeugopod. Complete limbs regenerating from a distal amputation plane were rarely seen. T. vulgaris larvae regenerated limbs with either one or the other type of duplication, but never both on the same limb, at all larval stages tested.

When larval P. waltl were kept in normal laboratory light during the treatment with retinol palmitate suspended in the rearing water the percentage of limbs which duplicated was very small for young larvae and increased with the age of the larvae used. Keeping the animals in the dark during the treatment period greatly increased the percentage of duplicate limbs obtained on the young larvae but not on the older larvae. This result is discussed in terms of the photodegradation of the retinoid and the length of the sensitive period for the regenerating limb.

A dose–response relationship between the dose of retinol palmitate and either the percentage of limbs duplicated or the degree of duplication was not found. Such a relationship, however, was observed when retinoic acid was injected intraperitoneally into stage-54+ P. waltl larvae. Additionally, this technique revealed a peak of sensitivity to retinoic acid on the 6th day after amputation.

Limb regeneration in older larvae was temporarily blocked by retinoid treatment. The limbs showed little or no regression and began blastemal development shortly after the treatment ended. Limbs of young larvae, however, often regressed. Such regressions were followed by blastemal formation and middle- to late-bud blastemas were found at the end of 11 or 14 days treatments with retinol palmitate.