bluuebunny/crossref_metadata_2025 huggingface dataset:
The polarity of the dental lamina in the regenerating salamander jaw
Authors: Graver Heber T.
Published: April 2021

In and amputated lower jaws of larval Ambystoma maculatum the dental lamina (DL) is replaced from both the anterior and posterior ends of the regenerate area, while in adult Triturus viridescens the DL is regenerated from the posterior stump tissues only. One-fourth and mandibular jaw amputations were performed in such a manner that a short stump of jaw, devoid of DL, remained. Larvae exhibited a posterior regrowth of the DL, while in adults the lamina accumulated at the edge of the regenerate but did not enter the new tissue.

Transplantation of a section of jaw from the left to the right side of the mandible resulted in the DL of the inserted piece having a reversed polarity in its new position. In both larval and adult forms, the DL of the transplant established connexions both anteriorly and posteriorly with lamina present. Transverse amputations through the inserted piece resulted in regeneration from the DL in the transplant in an anterior direction. Transplantation of a section of edentulous tissue into normal jaw tissue of the opposite side, or transplantation of a section of normal tissue into the edentulous area of the opposite side resulted in no anterior or posterior regrowth of the DL into the edentulous area.

Collectively the results indicate that no anterior – posterior polarity exists in the DL of the larval salamander jaw, since regeneration can occur equally well in both directions. The DL of the adult salamander jaw exhibits an anterior – posterior polarity allowing for regrowth in an anterior direction only.
Inhibition of nuclear migration in the absence of microtubules in the chick embryo
Authors: Messier Paul-Emil , Auclair C.
Published: April 2021

Interkinetic nuclear migration was studied in cells of the forming neural tube of cultured chick embryos aged from 1 to 7 pairs of somites. In specimens that were first exposed to 2°C for 3 h, then treated with 4 × 10−3 M monoiodoacetamide and finally transferred to new media to be reincubated for 1 – 2·5 h, it was found that microtubules were absent and nuclear movements blocked. These findings point to microtubules as essential structures for interkinetic nuclear migration. Their relation to the problem of neurulation is discussed.
Cell death and the development of limb form and skeletal pattern in normal andwingless(ws) chick embryos
Authors: Hinchliffe J. R. , Ede D. A.
Published: April 2021

The wingless condition resulting from the action of the sex-linked wingless (ws) gene arises from the precocious appearance of cell death in the anterior necrotic zone (ANZ) of the forelimb-bud at stage 19 (3 days) and its progressive extension beyond its normal area during stages 20 – 23. A similar though less pronounced effect occurs in the hindlimb-bud. Although some wingless hindlimb-buds are normal, others are affected by the precocious appearance of cell death in the ANZ.

The ws wingless mutant resembles the different wingless mutant investigated by Zwilling (1956) in that the apical ectodermal ridge (AER) is absent in most ws wing-buds. AER absence could be due to ws mesenchymal cell death interfering with the production of apical ectodermal maintenance factor (AEMF), which Zwilling claims is necessary to maintain the AER which plays an essential role in inducing limb outgrowth.

Wingless mutant phenotypes range from birds with rudimentary wings and normal legs through a modal type with forelimbs absent and hindlimbs normal to wingless and legless forms showing a high degree of expressivity. Individual wingless embryos vary in the degree to which the precocious ANZ appearing at 3 days is extended into the limb-bud and the wide range of wingless phenotypic expression is attributed to this variation.

Electron microscopic and histochemical analysis of the cell death process in wingless wing-buds revealed the presence of both isolated dead cells and macrophages, which contained intense acid phosphatase activity. These findings are interpreted as showing that isolated dead cells are ingested by neighbouring mesenchymal cells which thus become transformed into macrophages, first ingesting and then digesting further dead cells.

A study was made of the origin of the anomalous hindlimb condition, including absence or reduction of the tibia and digits, characteristic of severely affected wingless embryos. Autoradiographic analysis of the pattern of 35SO4 uptake revealed that at stage 24/5 wingless hindlimb-buds which were smaller than normal had a normal prospective fibula region, but that the prospective tibia region was small or absent. Thus the effect of a precocious hindlimb ANZ at stages 19 – 22 is to reduce or delete the pre-axial prospective tibia at stage 24/5.
Cortical-nuclear interactions in cephalopod development: cytochalasin B effects on the informational pattern in the cell surface
Authors: Arnold John M. , Williams-Arnold Lois D.
Published: April 2021

Cytochalasin B (CB) was applied to early developmental stages of the egg of the squid Loligopealei and defects in cleavage and/or organogenesis were produced. If CB was applied in relatively high dosages (2·0 μg/ml) or for long periods (30 min) to embryos in early cleavage the existing furrows irreversibly disappeared. If precleavage embryos were similarly treated the streaming pattern which forms the blastodisc was interrupted and patches of clear cytoplasm appeared on the zygote surface. Short low dosage pulses (0·2 μg/ml for 10 min) produced cleavage effects correlated with the time of pulsing. If pulsed within 30 min of first cleavage the first furrow did not appear in the majority of cases but the second furrow appeared synchronously with the controls and appeared normal in all respects. If pulsed approximately 30 min or longer before cleavage the first furrow usually appeared on time as a weak surface line. Second cleavage appeared normally. However, the asymmetrical pattern of third cleavage was ‘equalized’ and the blastomeres tended to be of equal size. It was concluded that there are subtle cytoplasmic movement patterns, sensitive to CB, which position the nuclei before each cleavage and thereby determine the cleavage pattern.

If embryos were pulsed (0·2 μg/ml for 10 min) at various times during early development, anomalies in differentiation at organogenesis (3–4 days later) were produced which correlated with the time of pulsing. Pulses after germinal layer formation (stage 11) produced no noticeable effects and pulses before the cytoplasmic streaming which produces the blastodisc similarly had very little or no effect. However, pulses during blastodisc formation or early cleavage produced severely affected embryos in which organ displacement, poor tissue and organ differentiation, or organ deficiencies were common. Pulsed embryos were scored and the time of pulsing correlated with the severity of effects. The nuclei of the inductive yolk epithelium were abnormal, frequently being rounded, clumped and/or containing clumped or abnormally diffuse chromatin. It was concluded that the streaming pattern which forms the blastodisc in some way fixes or enhances a pre-existing pattern of developmental information which resides in or at the surface of the egg. Once this pattern is established it is insensitive to CB but it can still be demonstrated by other techniques. This informational pattern apparently influences the nuclei of the yolk epithelium that come to lie in specific regions and controls the expression of their genome so that specific organs are programmed.
Isozymes of lactate dehydrogenase (LDH) in skeletal tissues of the embryonic and newly hatched chick
Authors: Coffin Patricia A. , Hall Brian K.
Published: April 2021

The time of appearance and the relative activity of isozymes of LDH were studied in portions of the skeleton of the embryonic and newly hatched chick by starch-gel electrophoresis. The following tissues were examined for presence or absence of isozymes: mesenchyme of the hind limb as it separated into chondrogenic and myogenic tissue; the development of the cartilaginous model of the tibia and its subsequent replacement by bone; the development of the quadratojugal (a membrane bone) with and without secondary cartilage.

LDHX and LDH2 were present in all tissues from the earliest time at which the tissues could be detected histologically. Thus these isozymes are ubiquitous. They were also the predominant isozymes during the first and second weeks of development of all the tissues and continued to predominate in the quadratojugal after hatching.

LDH3, LDH4, LDH5 appeared after the initial differentiation of the tissues, arose at earlier ages in cartilage than in bone, and became the predominant isozymes earlier in cartilage (14 days of incubation) than in bone (20 days of incubation).

These patterns of isozymes were related to metabolic activity of the developing tissues, especially to aerobic and anaerobic glycolysis.
Genetic inhibition of mesenchymal cell death and the development of form and skeletal pattern in the limbs oftalpid3(ta3) mutant chick embryos
Authors: Hinchliffe J. R. , Thorogood P. V.
Published: April 2021

Vital staining reveals that in homozygous (ta3/ta3) talpid3 embryos, the areas of mesen-chymal cell death which occur regularly in normal limb development are absent or reduced.

The necrotic locus in the central mesenchyme (the ‘opaque patch’) which in the normal chick limb reaches maximum development at stages 24 and 25 is absent or much reduced in talpid3 fore-and hindlimb-buds. Autoradiographic studies, following application of a 2 h pulse of 40 μCi of35SO4 to the vitelline circulation, show that normal tibia and fibula incorporate 35SO4 into chondroitin sulphate at stage 24 and more strongly at stage 26 during the process of chondrogenesis. The mesenchyme in the opaque patch region of normal limbs ceases to incorporate 35SO4 into chondroitin sulphate at stage 24. Talpid3 mesenchyme cells in the equivalent position at stages 24 and 26 continue to incorporate 35SO4, remain viable and become chondrogenic. It is suggested that absence or reduction of this central necrotic locus in talpid3 is causally related to the fusion of radius/ulna and (in some cases) of tibia/fibula characteristic of the later stages (28–35) of talpid3 limb development. This evidence supports the hypothesis that cell death in the opaque patch plays a morphogenetic role in separation of radius/ulna and tibia/fibula.

The digital plate of stage 32 normal limbs is characterized by massive necrosis of the interdigital tissue. In talpid3 forelimbs of stages 30–35 interdigital necrosis is absent, and there is no regression of the tissue between the digits (‘soft tissue syndactyly’). In talpid3 hindlimbs of stage 30–35 interdigital necrosis is either absent or much reduced, and there is little or no erosion of the soft tissue between the digits. This evidence supports the hypothesis that the morphogenetic role of interdigital cell death is in causing separation of the digits through shaping and remodelling the contours of the digital plate.
Zur Geschlechtsbestimmung und Gametogenese von Boneilia viridis Rolando
Authors: Leutert Rudolf
Published: April 2021

Sex differentiation and gametogenesis in Boneilia viridis Solando

Large numbers of trochophore larvae of Bonellia viridis (Echiurida) were cultivated either in pure sea water (‘Glaszuchten’) or in sea water containing an intact or fragmented proboscis of an adult female RüsselzuchtenThe ability of these larvae to differentiate into males or females was investigated.

Sex determination for the majority (43–83 %) is metagamic and phenotypic. These findings therefore confirm the results of Baltzer and disprove those of Wilczynski.

When larvae are exposed to the action of the female proboscis, 76 % become males. The sensitive period during which this determination can take place lasts from day 3 to day 16 of larval life. Exceptions to this rule are discussed.

The gametogenesis of Boneilia viridis has been investigated by electron microscopical methods.

In early stages the oogonia of the ovary are already in syncytial contact with the nurse cells. The possible functions of the nurse cells and follicle cells are discussed. Electron micrographs failed to reveal two types of eggs (male- and female-determined eggs, according to Wilczynski).

Spermiogenesis in Boneilia is described. The spermatogonia are situated in paired clusters in the coelomic cavity, and form a syncytial complex. After completion of spermiogenesis, the spermatozoa abandon their syncytial contact.

The fine structure of ripe spermatozoa is described and discussed.
Cell distribution in chimaeric mouse embryos before implantation
Authors: Garner Wendy , Mclaren Anne
Published: April 2021

Eight-cell mouse embryos labelled by prior cultivation in the presence of tritiated thymidine were aggregated with unlabelled 8-cell stages, and allowed to develop in vitro for two further cell divisions. Autoradiographic analysis of the resulting embryos showed that little or no mixing of the two cell populations took place during this period, either in the trophoblast or in the inner cell mass.
Stalk cell differentiation by cells from migrating slugs ofDictyostelium discoideum: special properties of tip cells
Authors: Town C. D. , Stanford E.
Published: April 2021

When fragments of migrating slugs of D. discoideum are disaggregated and spread on agar containing 1 mM cyclic AMP, cells from all parts of the slug form stalk cells with high efficiency. When cyclic AMP is not added to the agar, normal fruiting of dissociated slug cells can be prevented by overlaying them with cellophane. Under these conditions only cells from the anterior 10% of the slug (the ‘tip’) give rise to appreciable numbers of stalk cells, all other cells remaining amoeboid.

By separating distinct cell populations with cellophane we have shown that tip cells can induce cells from other parts of the slug to differentiate into stalk cells. The ability of tips to induce stalk cells is independent of tip age, but the proportion of cells induced depends both on the age of the slug and the part of the slug from which they are derived. The proportion induced is greater in older slugs than in newly formed ones, and in the older slugs is greater in the cells from fronts than from backs.

The active substance released by the tip cells may be cyclic AMP.
The establishment of the oral-aboral axis in the ctenophore embryo
Authors: Freeman Gary
Published: April 2021

In a small percentage of normal embryos and in a higher percentage of embryos centrifuged prior to the first cleavage the positions of the polar bodies and the site of the first cleavage furrow do not coincide. These cases have been used to establish whether polar body formation sites or first cleavage initiation sites correlate best with the oral-aboral axis of the embryo. In all cases when the first cleavage is initiated at a site different from the site where the polar bodies were given off, the pattern of the first four cleavages is normal, the segregation of comb plate potential at these stages is normal, and the larvae that form are normal. The extent to which comb plate potential is localized along the oral-aboral axis of the embryo prior to the first cleavage, during the first cleavage and at the 2-cell stage was also examined. These experiments demonstrate that the oral-aboral axis is established at the time of the first cleavage, that cleavage plays a causal role in setting up the axis, and that comb plate-forming potential begins to be localized in the aboral region of the embryo at this time.
Genetic analysis of developmental mechanisms in hydra: III. Characterization of a regeneration deficient strain
Authors: Sugiyama Tsutomu , Fujisawa Toshitaka
Published: April 2021

Mutant hydra strains showing abnormal development can be isolated through sexual inbreeding of wild hydra. One such mutant strain, called reg-16, regenerates tentacles very poorly following amputation of the head and foot. Tentacle regeneration, however, is significantly enhanced by subdividing the regenerating fragment longitudinally.

Lateral tissue implants that induce head formation in wild-type hydra either regress or induce foot formation in reg-16 polyps. These results suggest that regeneration deficiency in reg-16 is due to a defective polarity gradient.

A chimaeric strain of hydra was produced by combining interstitial cells (and thus their differentiation products, nerve cells and nematocytes) of reg-16 hydra with epithelial cells of another strain which is capable of normal regeneration. The chimaeras regenerate normally, suggesting that the defect of reg-16 is not located in the interstitial or nerve cells.
Limb-somite relationship : effect of removal of somitic mesoderm on the wing musculature
Authors: Chevallier Alain , Kieny Madeleine , Mauger Annick
Published: April 2021

The aim of this study is to test the ability of the intrinsic wing musculature to develop in the absence of somitic mesoderm.

The experiments were performed on 2-to 2·5-day chick embryos either by replacing the somitic mesoderm adjacent to the wing field with a piece of 9-day chick embryonic midgut or by destroying, through local X-irradiation, not only the somitic mesoderm of the wing level, but also at least three somites (or presumptive somites) anterior and/or three presumptive somites posterior to the wing level.

The replacement of somitic tissue scarcely affected the organogenesis of the forearm musculature, at least when both bones were present. In the other experiments, radio-destruction severely impaired the development of the forearm muscles, which were seldom all present and in most cases were entirely missing. The absence of a given muscle involves the simultaneous absence of the corresponding tendons.

The possible origins of the muscles that formed despite the removal of the somitic mesoderm are discussed.
Cleavage in the chick embryo
Authors: Bellairs Ruth , Lorenz F. W. , Dunlap Tania
Published: April 2021

Chick embryos ranging from the stage of first cleavage to that of about 700 cells were removed from the oviduct and examined by transmission electron microscopy. Beneath the cell membrane is a yolk-free cortical region containing microfilaments. Beneath this lies cytoplasm which contains yolk spheres which are graded in size, the dorsal ones being smaller than the ventral ones. The subgerminal periblast possesses a greater proportion of yolk to cytoplasm than do the cells proper, but it merges with the cytoplasm at the incomplete borders of the ‘open’ cells.

Specialized accumulations of membranes lie in the marginal periblast, and it is suggested that they play a role in cell membrane formation.

(This paper is dedicated to Professor Silvio Ranzi on the occasion of his 75th birthday)
Monomeric and aggregate proteoglycans in the chondrogenic differentiation of embryonic chick limb buds
Authors: Vasan N. S. , Lash J. W.
Published: April 2021

Proteoglycan heterogeneity was studied during the in vivo differentiation of embryonic chick limb cartilage. Recently, it has been shown that during the differentation of limb cartilage the proportion of the aggregated form of proteoglycans increases whereas the unassociated monomeric forms decrease, and this has been related to the synthesis of two link proteins at a specific stage of differentation. In this study it is suggested that the appearance of the aggregate formation is also due to synthesis of a stable hyaluronic acid binding region of the core protein. Thus, it can be concluded that differential gene expression for these proteins takes place as a differentiation phenomenon.
The Effect of Unilateral Blockage of a Pronephric Duct upon the Development of the Pronephroi in Triturus helveticus
Authors: Fox H.
Published: April 2021

Larvae of Triton helveticus, 20 days after the pronephric duct on one side has been blocked at the caudal bud stage, do not differ from controls in total length or nose-to-cloacal length. The unblocked functional pronephros of the other side shows significantly higher mean values for the following measurements when compared with control pronephroi in sham-operated animals: antero-posterior length, nuclear population, total volume of cells, total volume of lumina, overall volume of the pronephros, internal surface area of tubules, calculated individual cell volume, and antero-posterior length of the posterior nephrostome base. The blocked pronephros also shows significantly higher values than controls in all these measurements, except that it is the anterior nephrostome base and not the posterior which significantly increases in antero-posterior length, and that the calculated individual cell volume significantly falls. The glomus adjacent to the functional pronephros and that adjacent to the blocked pronephros do not differ significantly in size and shape. Both groups show a significant superiority in mean total volume over the controls. The pronephric duct of the functional pronephros, when its partner is blocked, is expanded along its length, like the duct of the remaining pronephros when a larva has undergone unilateral pronephrectomy. The remainder of the duct behind the lesion of the blocked pronephros is degenerate, and has a flattened reduced lumen like the duct remaining when its ipsilateral pronephros has been extirpated. There is no evidence that a blocked pronephros in situ exercises any inhibition on growth of its functional partner. In compensatory growth local intra-tubular tension may be an important influence.
The cellular effect of 5-bromodeoxyuridine on the mammalian embryo
Authors: Bannigan John , Langman Jan
Published: April 2021

It is well known that 5-bromodeoxyuridine (BUdR) when injected into pregnant animals may cause exencephaly, cleft palate, and limb abnormalities. Similarly, it is well established that the drug when added to a culture medium may prevent differentiation of embryonic cell systems without affecting cell division or cell viability. The goal of our experiments was to examine whether the congenital malformations resulting from BUdR treatment were due to lack of differentiation of certain cell lines or were due to other mechanisms. The effects of BUdR on proliferating and differentiating cells in the 12-day mouse embryo were therefore examined and special attention was given to the proliferating cells of the rhombic lip which give rise to the Purkinje cells.

When the embryos were treated with BUdR the mitotic index of the neuroepithelium of the rhombic lip doubled in value 3 h after treatment and remained high until 24 h later. By using the colchicine index it was calculated that the mitotic duration in the BUdR-treated embryos lasted at least 2 h and that in the control embryos less than 1 h. When the cell generation time in the BUdR treated animals was calculated the length of the S-phase was increased by about 50%. It was thus concluded that BUdR caused an increase in the duration of the S-phase and mitosis, together making the cell cycle 5 h longer than normal.

Eighteen hours after treatment many neuroepithelial cells became degenerative. By radioautography it was demonstrated that the degenerating cells were in their second DNA-synthetic phase following BUdR injection and that cells which incorporated BUdR and were differentiating into neurons were not affected. By injecting [3H]BUdR it was found that many cells which incorporated the analogue were able to leave the proliferative population after their first cell division. They migrated to the periphery where they developed into apparently normal Purkinje cells. The additive effects of cell death and retardation of the cell cycle caused a 15% deficit of Purkinje cells in the postnatal cerebellum but the BUdR did not interfere with their differentiation. Thus, contrary to the BUdR effect on cultures of embryonic cells, in vivo the drug causes cell death and a delay in the cell cycle time. Our experiments therefore seem to indicate that the congenital malformations caused by BUdR in the mammalian embryo are caused by cell death and growth retardation rather than by interference with the process of differentiation.
Autoradiographic study of macromolecular synthesis in the fusion epithelium of the developing rat primary palatein vitro
Authors: Figueroa Alvaro A. , Pratt Robert M.
Published: April 2021

The facial processes involved in primary palate formation undergo epithelial fusion in a manner morphologically analogous to that observed during secondary palate formation. We have used whole embryo culture to analyze the synthesis of macromolecules (DNA, protein, glycoprotein) in the primary palate, based on the incorporation of various labeled precursors. The results of this study demonstrate that changes in the synthesis of macromolecules occur during the fusion of the facial processes, which resemble those previously reported to occur during secondary palate development. These changes include cessation of DNA synthesis in cells in a restricted zone of the epithelium, concomitant with maintenance of glycoprotein synthesis. These findings indicate that the molecular events underlying the development of the primary and secondary palate may be similar.
Selection of appropriate medial branch of the optic tract by fibres of ventral retinal origin during development and in regeneration: An autoradiographic study inXenopus
Authors: Straznicky C. , Gaze R. M. , Horder T. J.
Published: April 2021

The formation of the branches of the optic tract has been studied with the use of [3H]-proline autoradiography, during development and during regeneration of the optic nerve in Xenopus with one compound ventral (VV) eye made by the embryonic fusion of two ventral eye fragments.

The formation of the optic pathway was abnormal in that the lateral branch failed to develop, suggesting that fibres from a VV retina selectively entered the tectum via the medial branch during development. Three months after section of the optic nerve of a VV eye, regenerated fibres were present both in the contralateral and ipsilateral tecta. On the ipsilateral side regenerated fibres entered the tectum via the medial branch only. Retinal fibres entered the contralateral tectum through both branches in some animals and through the medial branch only in others.

It is concluded that mechanical factors alone are insufficient to explain the phenomenon of selection of the appropriate medial branch by fibres of ventral retinal origin either during development or in regeneration. Some form of fibre-substrate interaction seems to be necessary; and this ability of fibres from a VV eye to take the path appropriate for ventral retina argues strongly that the VV eye is not a regulated system in terms of cell specificities.
Cell number in relation to primary pattern formation in the embryo of Xenopus laevis: I. The cell cycle during new pattern formation in response to implanted organizers
Authors: Cooke Jonathan
Published: April 2021

Results are presented which offer strong evidence that extensive alteration of the fates of embryonic Xenopus cells occurs independently of the schedule of cell division, after operations which lead to a doubling of the axial pattern of mesodermal differentiation in the gastrula. The experimental strategy was to make estimates of total mesodermal cell numbers and mitotic index in closely matched sets, each of three synchronous sibling embryos, fixed during the ten hours following the close of gastrulation. Within each set two embryos, an unoperated control and a sham-operated embryo whose own dorsal-lip (organizer) cells had been replaced with an equivalent graft, were developing normally. The third, experimental embryo had received an organizer implant to replace an equivalent number of cells from its ventral marginal zone, and was thus developing two axial mesodermal patterns of differentiation in relation to two dorsal midlines, the extra pattern embracing much host tissue. Mitotic index was also determined, in specific regions and throughout the mesoderm, in similar sets of embryos but at mid-gastrula stages.

The conclusions are justified by the results of a control investigation which show that there is normally no difference in cell cycle time along the presumptive dorso-ventral mesodermal, dimension, during the interval between time of operations and the determination of patterm The lack of any enhancement of mesodermal cell number in late embryos with dual axia patterns, or intervening enhancement of mitotic index in younger operated embryos, thus suggests that new patterns may be determined in the Xenopus gastrula without generation of extra cells.

The results are discussed in relation to recent ideas about pattern formation, and the concepts of morphallaxis and epimorphosis.
Enzyme analysis of mouse extra-embryonic tissues
Authors: Sherman Michael I. , Atienza-Samols Sui Bi
Published: April 2021

We have separated for enzyme analysis the following layers that surround the conceptus at midgestation: decidua, trophoblast, parietal endoderm (including Reichert’s membrane), visceral endoderm, yolk-sac mesoderm and amnion. Measurement of several catabolic enzyme activities )N-acetyl-β,D-hexosaminidase, β-glucuronidase, alkaline and acid phosphatases and non-specific esterases) in these tissues indicates that they are biochemically distinct, perhaps reflecting the different functions that they perform in providing the embryo proper with a desirable environment for differentiation and development. Our studies also provide an example of how visceral endoderm cells can effectively block passage of maternal macromolecules (in this case a serum esterase) in the fetal circulation. Finally, since there is often difficulty in distinguishing among early embryonic and extra-embryonic cell types produced in teratocarcinoma cultures, we have considered how our observations might be of use in this respect, particularly in discriminating between visceral and parietal endoderm.
Investigation of the lethal yellowAy/Ayembryo using mouse chimaeras
Authors: Papaioannou Virginia , Gardner Richard L.
Published: April 2021

Chimaeric combinations of normal and mutant embryonic tissues were used to investigate the lethal effect of the yellow gene. The homozygous mutant embryos could not be identified before implantation. Therefore, embryos from both intercross matings and control backcross matings were used to provide inner cell masses (ICMs) for injection into genetically marked blastocysts of the CFLP random-bred stock. All conceptuses obtained from reimplanted blastocysts were analysed at mid-gestation for the presence of donor isozyme of glucose phosphate isomerase. A similar proportion of chimaeras were found in the experimental and control series, indicating rescue of the lethal Ay/Ay ICM tissue. The reciprocal experiment also produced a similar proportion of chimaeras but there was a 25 % postimplantational loss of injected embryos evidenced by empty decidual swellings. The results suggest that the yellow mutation primarily affects the trophectoderm which cannot be rescued by a normal ICM, whereas Ay/Ay ICM is capable of survival in a chimaera at least until mid-gestation.
Genetical Studies on the Skeleton of the Mouse1 : XXII. The Development of Danforth’s Short-tail
Authors: Grüneberg Hans
Published: April 2021

An embryological investigation of the semi-dominant gene for Danforth’s short-tail in the mouse shows that, contrary to the results of earlier investigations, the syndrome can be understood as a unitary system dependent on a single root cause. The effects of the gene are similar in heterozygotes and homozygotes, but more extreme in the latter. The most fundamental anomaly probably resides in the primitive streak. This gives rise to a structurally abnormal notochord with a reduced calibre. The abnormality of the notochord increases in intensity in a cranio-caudal direction. At a somewhat later stage the notochord disintegrates all along its length. The process starts in the cervical region where it is also most complete. As a direct result of the disintegration of the notochord there is a reduction of the nuclei pulposi of the intervertebral disks and a reduction of the centra of the vertebrae, particularly in the cervical region; the dens epistrophei is virtually absent, and as a result of this anomaly, an atypical but fully functional horse-shoe articulation is formed between the first two cervical vertebrae with yet more remote effects on neighbouring muscles. The abnormality of the notochord is responsible for regressive processes (cell pyknosis) which at a later stage lead to the loss of part or the whole of the tail. The abnormality of the notochord is also responsible for a considerable reduction of the cloaca and the tail-gut. The cloaca is too small for the development of a urorectal septum and hence persists; the shrinkage of the cloaca also leads to a (? secondary) separation from the cloacal membrane; this results in absence of the bladder, urethra, and genital papilla. Finally, there is an arrest or delay in the establishment of contact between the reduced cloaca and the Wolffian ducts; it is suggested that this may interfere with the growth of the ureter buds and thus, in turn, lead to the absence of the metanephros. Further minor effects of the Sd gene include right-to-left connexions between paraxial mesoderm or somites in the tail, a slight effect on the ventral ectodermal ridge of the tail, and a statistical effect on the metoptic roots of the ala orbitalis of the presphenoid. All these effects are clearly secondary, but the mechanism of the last two of them is not understood in detail.
The Conversion of Yolk into Cytoplasm in the Chick Blastoderm as shown by Electron Microscopy
Authors: Bellairs Ruth
Published: April 2021

Three main types of yolk drop are present in the area pellucida of the chick blastoderm. They have been given the names ‘complex yolk drop’, ‘type A yolk drop’, and ‘type B yolk drop’. Together they have been called secondary yolk to distinguish them from the extra-embryonic or primary yolk. It is concluded that the complex yolk drops are early stages in the conversion of yolk. They contain granular material which resembles that found in the primary yolk. Type A drops are present in the complex yolk drops and appear to be formed from the granular material. Type B drops, mitochondria, vacuoles, and membranes are also found within the complex drops. The membranes around the complex drops appear to break down, releasing the contents of the yolk drops into the cell. Most type A drops appear to become converted into a number of circular, or possibly tubular, bodies. These are believed to be predominantly lipoproteins. It is concluded that the membrane around each type A drop breaks down and these circular bodies are then released into the cytoplasm where they may contribute to the endoplasmic reticulum. Other type A drops are composed of numbers of micro-particles. They closely resemble the cytoplasmic micro-particles and may become part of them. Evidence is presented for considering these micro-particles to be precursors of ribonucleoproteins. The type B drops persist in the cytoplasm after the complex drops and the type A drops have almost completely disappeared. Evidence is presented for considering them to be fatty drops. Primary yolk from the hen’s egg has also been examined.
Type-specific Morphogenesis of Cartilages developed from Dissociated Limb and Scleral Mesenchymein vitro1
Authors: Weiss Paul , Moscona Aron
Published: April 2021

The emergence of definite organ and tissue structure during development implies that the component units—cells and intercellular materials—assume patterned space relations. These reveal themselves in geometric features of position, proportions, orientation, grouping, alignment, and so on. The ordering processes involved are variously referred to as ‘organization’, ‘differentiation’, ‘morphogenesis’, ‘field action’, and the like. Such terms, while useful as identifying labels for the respective problems, are largely lacking in concrete operational meaning. To realize this, one need only consider how little is known about the practical devices and tools by which any given product of development is achieved. The study of the ‘biotechnology’ of developmental mechanisms has indeed been lagging behind the preoccupation with general principles.
Teratogenic Effects of Trypan Blue on Hamster Embryos1
Authors: Ferm Vergil H.
Published: April 2021

Little information is available in the literature on the susceptibility of the hamster embryo to teratogens. Desoxycorticosterone acetate apparently has some teratogenic activity (Tedford & Risely, 1950), but the degree and type of abnormality produced by this agent in the hamster have not been recorded. Orsini (1952) has described naturally-occurring urogenital anomalies which appear in females of a piebald strain of the golden hamster.
On Regeneration after the Amputation of Abnormal Structures
Authors: Newth D. R.
Published: April 2021

Supernumerary limbs induced in the flank of larvae of Triturus helveticus by homoplastic grafts of nasal placode are frequently abnormal in structure. Some are highly polydactylous, others hypodactylous, and yet others are mere protuberances whose character as limbs cannot be assumed from their appearance in vivo. The amputation of such induced formations at a level close to the flank of the larva is usually followed by regeneration. The regenerates so formed are, in most cases, more nearly normal in structure than the original inductions they are replacing. A second amputation and regeneration may completely restore normality. The possibility of explaining these results in terms of the known peculiarities of supernumerary induced limbs is discussed.
The Origin of the Acoustic Ganglion in the Sheep
Authors: Batten E. H.
Published: April 2021

The acoustic ganglion arises from placodal cells which detach from the otic vesicle between the 6 ·0-mm. and 14·0-mm. stages. The accepted view that it develops from a common ‘acustico-facial’ neural crest is rejected. The initial rudiment of the acoustic ganglion is a mass of detached placodal cells which lies at the base of the vesicle and is distinctly separated from the facial crest by a zone of mesenchyme. After the 8·0-mm. stage the detachment and migration of placodal cells becomes more vigorous and the enlarging acoustic ganglion becomes secondarily apposed to the geniculate ganglion. Nevertheless, these ganglia retain their separate identity through cytological differences which rest on the fact that the young neuroblasts are already present in the geniculate ganglion before a distinct acoustic rudiment is evident. This contrast wanes gradually after the 11·0-mm. stage when the placodal cells begin to differentiate into acoustic neuroblasts. It is concluded that the acoustic ganglion arises exclusively from placodal cells and the participation of facial crest cells in the root portion, if it occurs at all, is probably negligible. The definitive vestibular ganglion is derived from the pars superior together with the lateral zone of the pars inferior in which the earliest neuroblasts appear. The definitive cochlear ganglion begins to develop rather later and arises from the remaining medial zone of the pars inferior with the addition of further diffuse placodal contributions from the base of the vesicle.
Skeletal Regeneration in Amphibians
Authors: Goss R. J.
Published: April 2021

In order to investigate the replacement of skeletal elements in the Amphibia, bones were removed from the extremities of anuran tadpoles, and larval and adult urodeles. Following the extirpation of tibiae from the hind limbs of R. pipiens tadpoles, skeletal regeneration occurred in only a few of the smaller legs. Ulnae removed from the forelimbs of adult T. viridescens were not replaced even when the bone had been previously fractured or when it was replaced by blastema tissue from amputated arms. Cartilaginous skeletal regeneration did occur, however, after extirpation of ulnae from the forelimbs of larval A. maculatura. Likewise, ulnae removed from young forelimb regenerates of adult Triturus were regularly reconstituted, but as such regenerates grew older the percentage of ulna replacement progressively diminished. In view of these results, it is concluded that in order for skeletal regeneration to occur the extirpated structure must be cartilaginous, and it must be removed from a limb otherwise capable of regeneration after amputation. This, together with the evidence that skeletal regeneration, like total limb regeneration, is dependent upon adequate innervation, substantiates the contention that these two phenomena are different manifestations of the same process. It is suggested that the absence of skeletal regeneration is dependent upon the developmental state of surrounding tissues, such that in larval or recently regenerated urodele limbs sufficient potential chondroblasts persist after skeletal extirpation to ensure replacement, while in adult limbs chondrogenic cells, being restricted to the periosteum, are nearly all removed with the bone.
Supplemented eggshell restores calcium transport in chorioallantoic membrane of cultured shell-less chick embryos
Authors: Tuan Rocky S.
Published: April 2021

It was previously reported (Tuan, 1980a) that the development-specific expression of calcium transport and related functions in the chick embryonic chorioallantoic membrane (CAM) requires the continuous presence of the eggshell, the calcium source of the embryo. To further understand the mechanism of action of the eggshell on the CAM functions, this study reports the effects of eggshell supplementation on chick embryos maintained in shell-less cultures. The cultured embryos were able to accumulate and utilize the exogenous shell calcium, applied directly onto the CAM, for skeletal formation. In the region of the CAM directly adhering to the added shell, calcium transport activity, calcium-binding protein (CaBP) activity, and vitamin K-dependent y-glutamyl carboxylase activity were significantly restored. These results strongly suggest that the proximity of shell calcium may regulate expression of calcium transport and related functions in the chick embryonic CAM.
Neurulation in the Mexican salamander (Ambystoma mexicanum) : a drug study and cell shape analysis of the epidermis and the neural plate
Authors: Brun Rudolf B. , Garson John A.
Published: April 2021

We analysed the neurulation movements in the Mexican salamander Ambystoma mexicanum. Embryos were exposed to colchicine or nocodazole prior to neural fold formation. Exposure to these drugs prevented the anterior neural folds from closing. Neurulation however proceeded normally in the posterior regions of the embryo. We were unable to find apically constricted cells in the neural plate of colchicine-blocked neurulae. Only rounded-up neural plate cells were present (semithin sections). This situation was typical in embryos exposed to colchicine prior to neural fold formation. Concentrations of colchicine up to 2 ·5 × 10-3 were not capable of blocking neurulation once the neural folds were formed. The wedge-shaped cells were present in similar numbers to those found in controls. We quantified the cell shape changes in the neural plate and in the epidermis in both controls and drug-arrested embryos. The comparison of these to classes of data shows that epidermal spreading is prevented by colchicine but only slightly affected by nocodazole. Embryos blocked in late neurulation by exposure to these drugs can resume neurulation following neural plate excision in nocodazole but not in colchicine. We conclude from this observation that the epidermis contributes to raising and closing of the neural folds. The presence of neural folds in absence of wedge-shaped cells in the neural plate is also taken as evidence that neurulation is not exclusively driven by forces generated in or acting on the neural plate. Our view on the concerted interplay of various embryonic components is illustrated in a summarizing diagram (Fig. 11).
Nuclear position in the cells of the mouse early embryo
Authors: Reeve W. J. D. , Kelly F. P.
Published: April 2021

The nuclei of preimplantation mouse embryos were identified after labelling with either DAPI or Hoechst 33258. During the 4- and 8-cell stages the peripherally located nuclei become clustered nearer the centre of the embryo. This nuclear migration towards the base of each cell was also observed during the development of couplets of 2/4 and 2/8 cells. Most blastomeres isolated from compact 8-cell embryos contained a nucleus located in their basal half away from the microvillous pole. The displacement may be critical for the generation of a range of sizes of blastomeres in the 16-cell embryo.
Spreading of a sperm surface antigen within the plasma membrane of theeggafter fertilization in the rat
Authors: Gaunt Stephen J.
Published: April 2021

The rat sperm surface antigen 2D6, located over the entire surface of the spermatozoon, is shown by use of a monoclonal antibody in indirect immunofluorescence experiments to spread laterally over the surface of the egg after fusion of sperm and egg plasma membranes at fertilization. Freshly fertilized eggs, obtained from superovulated rats 14h after hCG injection, showed the 2D6 antigen to have spread in a gradient over a discrete fan-shaped area of the egg surface anterior to the protruding sperm tail. Eggs at a later stage of sperm incorporation, obtained 20 h after hCG injection, showed that the spread of antigen had extended to cover most or all of their surfaces. By 40 h after hCG injection, the approximate time that fertilized eggs cleaved to form 2-cell embryos, most of the 2D6 antigen had been lost from the cell surface. Fertilized eggs, but not unfertilized eggs or 2-cell embryos, were lysed by 2D6 monoclonal antibody in the presence of guinea pig complement. A model for sperm-egg fusion is presented to account for the observed pattern of spreading shown by the 2D6 antigen. The possible role of sperm antigens on the egg surface is discussed.
Effect of glucose on beta cell proliferation and population size in organ culture of foetal and neonatal rat pancreases
Authors: Kaung Hue-Lee Cheng
Published: April 2021

The effect of glucose on growth of the beta cell population was characterized in rat pancreatic organ culture. The effect was monitored by measuring [3H]thymidine labelling indices of beta cells during the culture period and by quantitation of beta cell population size at the end of the culture period. Foetal and neonatal pancreases and different glucose levels were compared.

Glucose was found to be effective in stimulating the beta cell proliferation and beta cell population increase at 300 mg/100 ml in 18-day foetal pancreatic explants, but not in 3-day neonatal explants, when compared to the control level of 100mg/100ml. A higher level of glucose (500 mg/100 ml) was ineffective and may even inhibit beta cell population growth. The higher than control levels of glucose (300 mg/100 ml and 500 mg/100 ml) were able to stimulate insulin secretion in neonatal tissue, but not in foetal tissue, although foetal tissue may develop such response later in culture. These results suggest that glucose stimulates beta cell proliferation and insulin secretion through different mechanisms. They further show that the potentiality for beta cell proliferation under glucose stimulation decreases with age of the explants and that the capacity for beta cell to proliferate as a function of glucose stimulation is limited.