bluuebunny/crossref_metadata_2025 huggingface dataset:
The teratogenic effects of sugars on the chick embryo
Authors: Hughes A. F. , Freeman R. B. , Fadem T.
Published: April 2021

The effect of treatment of chick embryos during the first day of incubation with a number of sugars is described. To some embryos solid sugars were applied in opened eggs; for others the substances were injected in solution. By both methods, all sugars tested were found to be teratogenic, but no apparent general differences between mono-, di-, and trisaccharides were found. Nor were there any correlations between those which can be metabolised at these stages and their teratogenicity.

The range of defects produced is similar to those found when embryos of this age are treated with other substances. In embryos treated with [14C]sucrose, some of the label is retained within the tissues in a bound, insoluble form. Possible implications of this finding are suggested.
Experimental study of the formation of the heart tube in the chick embryo
Authors: Argüello Carlos , De La Cruz MaríA V. , Sánchez Gómez Concepción
Published: April 2021

A study was made of the development of the heart tube beginning from Hamburger & Hamilton (1951) stage 8+ up to stage 12. We used labelling with particles of iron oxide followed with time-lapse cinemicrophotography, staining with methylene blue, serial section and cutting the embryo in two halves.

Our results led to the conclusion that the tubular heart is formed by the addition of precardiac material into its posterior end, but in addition it is necessary to consider the fusion of the myocardium in a cephalic direction, starting with the fusion of both heart primordia at the rostral end. By this fusion the most anterior part of the heart up to stage 12 is formed.
Experimental cardiac morphogenesis: I. Development of the ventricular septum in the chick
Authors: Harh Jung Y. , Paul Milton H.
Published: April 2021

An experimental technique utilizing microfiber markers and radioautography was used to study the morphogenesis of the ventricular septum in the chick embryo heart from stages 22 to 33 of Hamburger & Hamilton (1951). Fibers placed in the myocardium of the primitive ventricles of 4-day-old embryos within 250 μm to each side of the future site of the ventricular septum resulted in shortening of the distance between the two fibers until both were found within the myocardium of the septum at 7 days. The fibers coated with tritiated thymidine labeled the myocytes of the trabeculae immediately adjacent to where the fibers were placed and showed that when trabeculae were labeled within the 400–500 μm width centered on the ventricular septum, they aggregated together. The labeled myocytes in the trabeculae were found from the smooth crest to the most apical portion of the septum. These findings suggest that the muscular ventricular septum is formed by aggregation and coaptation of trabeculae and is of a single developmental origin.
Local autonomy of gastrulation movements after dorsal lip removal in two anuran amphibians
Authors: Cooke Jonathan
Published: April 2021

The time-course of the remaining gastrulation movements has been investigated after removal of the dorsal lip, the presumptive foregut endoderm and the anterior mid-dorsal mesoderm as a plug-shaped mass of cells from beginning gastrulae of Xenopus laevis and Bombina orientalis. This embryonic region has been previously studied in its role as an organizer, when grafted into a host gastrula marginal zone.

There is usually no effect of the removal of these cells, the first morphogenetically active ones, either upon rate of subsequent completion of the external aspects of gastrulation, or upon the internal evolution of the presumptive mesodermal mantle. This finding is discussed in connexion with results of a previous paper on pattern formation in early Xenopus development, since it may help to distinguish between possible types of explanation for those results.
Differentiation in vitro of sympathetic cells from chick embryo sensory ganglia
Authors: Newgreen D. F. , Jones R. O.
Published: April 2021

This study was carried out in order to determine what factors control the differentiation of certain neural crest cells in the chick embryo. Emphasis was placed on the morphologically and biochemically divergent sensory and sympathetic pathways of differentiation. Embryos were precisely staged according to Hamburger & Hamilton (1951) and it was observed that sensory ganglia with somites, explanted at stages 21–24, gave rise to cells showing formaldehyde-induced fluorescence in more than 25% of explants. These cells were identical in properties to the fluorescent cells of the sympathetic system of embryos of similar age, and appeared by 12 days in vitro. These fluorescent cells did not appear when somites and sensory ganglia explants were maintained separately.

The incidence of fluorescent cells in combined explants was considerably reduced or absent when cultures were maintained for 7 days or less, or when the explants were obtained from stage 25–26 embryos. Furthermore, when neural tube was also included in the cultures, the appearance of fluorescent cells was markedly inhibited. The requirement for somitic tissue to induce fluorescent cells in combined explants can be replaced by forelimb-bud tissue.

The origin of these cells and the factors that control their differentiation in vitro are discussed with reference to the neural crest origin of the sensory ganglion, and the possible conditions pertaining in vivo in this region.
Determination in regenerating tissues of Dugesia dorotocephala: the influence of nerve cord grafts
Authors: Sperry Pamela J. , Ansevin Krystyna D.
Published: April 2021

Lateral fragments which contained no nerve cord were isolated from the postpharyngeal body section of Dugesia dorotocephala and fused with nerve cord grafts soon after isolation and at daily intervals through 8 days of regeneration. Fragments fused soon after isolation formed ‘headless’ regenerates but had normal body proportions. If the lateral cordless fragment was allowed to regenerate for 1 day or longer before fusion with the nerve cord fragment, the head always developed and the body proportions were normal. Therefore, head structures become determined in the lateral fragment within the first 24 h of regeneration; during this time these tissues can also respond to the head-inhibiting influence of the nerve cord. The competence to form particular structures of the postcerebral body regions must emerge after head-forming competence is lost, that is about 24h after isolation; however, it persists at least through the first 8 days of regeneration. Normal body proportions can be induced by nerve cord grafts throughout the first 8 days of regeneration.

Lateral fragments fused at any time after isolation with another fragment containing no nerve cord developed head structures but failed to differentiate tissues of the postcerebral regions. This confirms that the nerve cord is responsible for inhibition of head structures and induction of differentiation of body regions and normal body proportions.
Fate maps and the pattern of cell division: a calculation for the chick wing-bud
Authors: Lewis J. H.
Published: April 2021

Given the growth rate throughout an embryonic rudiment, one can calculate how its parts must shift as it gets bigger, and so plot fate maps showing their future positions. The calculation is done here for the chick wing-bud from stage 18 to stage 25, using published data for mitotic index and cell packing density, and new measurements of size and shape. Two main findings are: (1) the wing-bud in this period elongates almost uniformly along itsproximo-distal axis. (2) Each limb segment derives from the tissue generated by one cell division cycle in the ‘progress zone’ at the tip.
Time, place and positional value in the chick limb-bud
Authors: Summerbell D. , Lewis J. H.
Published: April 2021

Quantitative experimental evidence is presented for the progress zone theory of limb development. The theory, here formulated mathematically, states that the parts of the limb are specified in proximo-distal succession by an autonomous timing mechanism operating in a ‘progress zone’ of undifferentiated growing mesenchyme under the influence of the apical ectodermal ridge. By the exchange of distal tips between young and old wing-buds, it is shown that there are no long-range morphogenetic signals from proximal to distal tissue. The width of the progress zone is calculated, and it is found autoradiographically that practically all its cells are dividing.
Recherches sur l’origine des différentes lignées de cellules sanguines chez l’Amphibien Urodèle Pleurodeles waltlii
Authors: Deparis Pierre , Jaylet André
Published: April 2021

Studies on the origin of various blood cell lines in the salamander Pleurodeles waltlii
Epithelial autolysis during implantation of the mouse blastocyst: an ultrastructural study
Authors: El-Shershaby A. M. , Hinchliffe J. R.
Published: April 2021

An ultrastructural investigation was made of cell death in the uterine epithelium during the implantation of the mouse blastocyst. Cell death occurs in two phases: (i) early individual cell death, and (ii) later general cell death.

Individual dead epithelial cells are phagocytosed and digested by trophoblast cells. At 95 h post coitum (p.c.) there are 1–4 dead cells; at 105 h and 113 h, 6–8 dead cells, and at 116 h, 2–3 dead cells. No lysosomal involvement could be identified in the death of these cells.

The general breakdown of the uterine epithelium around the implanting blastocyst is first recognizable at the ultrastructural level at 113 hp.c., and continues until the adjacent deteriorated epithelium has been phagocytosed by the trophoblast cells at 119 h p.c. Ultrastructurally, from I13h p.c. cytoplasmic portions of epithelial cells are trapped within cytosegrosomes, and there is an increase in size of the dense lysosomal bodies found in viable epithelial cells at 105 h p.c. The dense bodies, which are positively stained for acid phosphatase enzyme at 105 h p.c., increase in diameter approximately 3–5 times between 105 h p.c. and 119 h p.c. These results provide evidence of intracellular digestion of small portions of the cytoplasm possibly through the formation of cytosegrosomes which then fuse with residual bodies already present. Thus the evidence favours a process of autolytic breakdown of the uterine epithelium around the implanting blastocyst.
The function of the ectodermal apical ridge and distinctive characteristics of adjacent distal mesoderm in the avian wing-bud
Authors: Cairns John M.
Published: April 2021

Blocks of mesoderm about 0 ·1 mm in diameter were isolated from various regions of chick wing-buds of stages 17 through 22 and cultured individually, or sometimes in pairs, wells. Cell deaths had occurred after 10 h of culture in those explants that had come from the region associated with the thickest part of the ectodermal ridge, and after 11 –12 h in all other mesoderm. When the adjacent ectodermal ridge was left attached to the mesodermal block there were almost no cell deaths for up to 24 h of culture. When the dorsal ectoderm immediately proximal to the apical ridge was left attached, but no ridge was present, cell deaths occurred just as they did in mesoderm with no ectoderm. When a number (usually six) of complete ridges were suspended in a wire basket at the top of a well, cell deaths did not occur in a test mesodermal block at the bottom of the well (six of eight cases). These experiments support previous evidence for a special function of the ectodermal apical ridge in limb morphogenesis, and indicate that there is a chemical messenger.

The cells that migrated from distal mesodermal explants (the band up to 0 ·15 mm from the apical ridge) differed sharply in morphology and behavior from those coming from explants from any more proximal region. Within the proximal mesoderm there was a less striking variation along the antero-posterior axis. These observations reveal that there is present even at early stages a detailed pattern within the mesoderm of the limb-bud. The particularly striking and distinctive characteristics of that mesoderm closest to the apical ectodermal ridge provide new possibilities for the understanding of the function of the ridge in limb morphogenesis.
Mitochondrial and other ultrastructural changes in the developing Habrobracon embryo
Authors: Amy Robert L.
Published: April 2021

Cells of the wasp, Habrobracon juglandis, were studied by electron microscopy with the view to comparing ultrastructural changes, especially those found in mitochondria, that occur during the first two-thirds of the 29 h embryonic period. In 1-to 2-h embryos (the earliest studied) mitochondria are distributed principally in the periplasm and typically are arranged in clumps with their long axes parallel to each other. Based on a study of profiles occurring in thin sections, most appear to be elongate with poorly developed cristae, have dense matrices and are longer than those of later stages. At 3 –4 h of age, in incipient blastoderm cells, the mitochondria are distributed throughout the cytoplasm with 40% located lateral to the nuclei and 42 % concentrated in a subnuclear position. Most (81 %) exhibit spherical profiles, with well-developed cristae and less dense matrices than those found at earlier ages. In fully formed blastodermal cells (7 –8 h), mitochondria are similar morphologically except that a lower percentage (53 %) are spherical; almost half (48 %) have migrated to a supranuclear location. In early gastrula cells (11 –12 h) no significant variations from the blastoderm condition were apparent. Mitochondria in the oldest cells studied (18 – 19 h) show somewhat greater structural complexity and variability. The number per cell section is drastically reduced compared to earlier ages, but this, at least in part, is related to a reduction in cell size. Changes observed in other cellular constituents are also described. Comparisons are made with similar variations reported in other developing organisms and their possible significance is discussed.
The development of animals homozygous for a mutation causing periodic albinism (a
p) in Xenopus laevis
Authors: Hoperskaya Olga A.
Published: April 2021

This paper describes the development of a mutant strain associated with periodic albinism (ap) in the clawed toad Xenopus laevis. The most outstanding feature of this mutation is the instability of the albino state. In the course of the development there is a succession of three periods of pigment expression: (1) complete absence of melanin pigment, (2) appearance of melanin in the pigmented epithelium of the eyes and in small quantities in skin melanophores, (3) disappearance of most pigment granules. Repeated spawnings show that the mutant syndrome is inherited as a recessive trait. Possible ways of analysing pigment cell differentiation with the use of the mutation described are discussed.
Adult amphibian epidermal proteins: biochemical characterization and developmental appearance
Authors: Reeves O. Raymond
Published: April 2021

The keratin-like proteins (KLPs) from the epidermis of adult frogs of the species Xenopus laevis have been isolated and biochemically characterized by means of polyacrylamide gel electrophoresis, amino acid analysis, tryptic peptide mapping, amino-terminal end-group analysis and isoelectric focusing. One particular protein fraction of rather unusual amino acid composition found only in epidermal tissue was isolated in quantity by preparative gel electrophoresis and monospecific antibodies prepared against it. Using this anti-KLP antibody preparation it was possible to show that at least one kind of keratin-like protein characteristic of the adult epidermis first appears within the larval epidermis during metamorphosis. This is the first reported biochemical characterization of a tissue-specific protein from adult amphibian skin.
In vitro differentiation of a homogeneous cell population—the epidermis of Xenopus laevis
Authors: Reeves O. R. , Laskey R. A.
Published: April 2021

A simple culture technique is described for obtaining homogeneous populations of differentiating epidermal cells from adult amphibian skin. This population of cells continues its normal differentiation, namely keratinization, in vitro. By the third day of culture more than 99·9 % of the cells in the population contain immunoreactive keratin. During the next 5 –7 days of culture these cells synthesize increasing amounts of a tissue-specific keratin-like protein until this protein constitutes more than 25 % of the total extractable carboxymethylated proteins of these cells. Under the conditions described cell division does not occur during the course of differentiation. When vitamin A is added to the culture medium the rate of keratinization is decreased; when its antagonist citral is added, keratinization is accelerated. These factors influence only the rate but not the direction of differentiation.
Diploid parthenogenetic mouse embryos produced by heat-shock and Cytochalasin B
Authors: Bałakier Hanna , Tarkowski Andrzej K.
Published: April 2021

Swiss albino and C57BL/10 eggs from induced ovulations, and spontaneously ovulated A eggs, were activated in vitro by a heat shock of 44 °C for 5 or 7·5 min and cultured in the presence of 10 μg/ml of Cytochalasin B (CB) for 5-8 h. The activation rate was about 70% in Swiss albino, 40% in C57BL and 90% in A eggs. CB suppressed second polar body (2P.B.) formation in over 90% of activated eggs, with the majority containing two pronuclei. When eggs were placed in CB-free medium their surface became wrinkled and they formed protrusions of various sizes, which in some eggs detached to form enucleate or pronucleate cytoplasmic fragments; some eggs broke down completely into fragments. In most eggs, however, the surface smoothed out in a few hours and suppression of 2P.B. appeared to be permanent. The rate of development of these eggs after transplantation to the oviduct was delayed in terms both of cell divisions and of the time of blastocyst formation. Out of 41 implants collected on the 8th–10th day of pregnancy only two healthy looking egg-cylinders were found on the 8th and 9th day; both were retarded, at the stage characteristic for the 7th day of normal development. The reasons for delayed preimplantation development and low implantation rate are discussed. The present experiments corroborate earlier observations that parthenogenetic mouse embryos, even if diploid, rarely survive in the uterus beyond the egg-cylinder stage.
Ultrastructural observations of lethal yellow (A
y
/A
y
) mouse embryos
Authors: Calarco Patricia G. , Pedersen Roger A.
Published: April 2021

A V /A V embryos were identified by the presence of large excluded blastomeres (Pedersen, 1974) and examined cytologically and ultrastructurally. Cell organelles, inclusions and junctions in the excluded blastomeres were compared with those of non-excluded cells of Av/Av embryos and control embryos. Excluded blastomeres always had the fine structural characteristics of earlier developmental stages and may have arrested at the 4-to 8-cell stage or slightly later. Interior cells (inner cell mass) were observed in all mutant blastocysts. Non-excluded cells of Av/Av embryos were normal until degenerative changes appear in the late blastocyst stage. The mode of action of the + Av gene was not determined, but evidence from this study and others indicates that the effects of + Av gene action occur over a wide range of time in early cleavage and implantation.
Réversibilité de la dédifférenciation observée dans les cultures cellulaires de foie embryonnaire d’oiseau
Authors: Houssaint E.
Published: April 2021

Reversibility of the morphological and functional dedifferentiation occurring in cultures of avian embryonic liver cells

Primary cell cultures are established from 8-day quail embryo livers. During the first three days the culture is made up of areas of epithelial-like cells and scattered fibroblasts. The cytoplasm of the epithelial cells shows a high glycogen content as detected by the PAS reaction controlled with salivary amylase digestion. During the following days an important increase in the number of fibroblastic cells is observed. After 6–7 days of cultivation, the epithelial cells have disappeared and the culture is entirely fibroblastic. PAS technique does not show any trace of glycogen in these cultures which have been prolonged up to 45 days.

Six-to 45-day primary cultures entirely made up of fibroblasts were associated with hepatic or pulmonary mesenchyme in organotypic culture for 3–4 days. In some cases the explant was first cultivated in vitro for 2 days and then grafted into a 5-day-old chick embryo on the chorioallantoic membrane for 6 days. In the secondary cultures hepatocytes showing an epithelial arrangement and a high glycogen content were observed.

It appears from this observation that some of the primary culture fibroblasts are in fact dedifferentiated parenchymal cells. Such a dedifferentiation is a reversible phenomenon since the cells retain the ability to express their initial determination if they are placed in convenient environmental conditions. The role of the specific tissular arrangement in the stability of the differentiated state is discussed.
Implantation and early postimplantation development of the bank vole Clethrionomys glareolus, Schreber
Authors: Ławożdżeński Wac , Mystkowska Ewa T.
Published: April 2021

The development of the bank vole Clethrionomys glareolus is described from implantation to the formation of the foetal membranes. The embryonic development of this species combines features of primitive rodent species, for example Geomys bursarius and highly specialized ones, for example Mus musculus. The egg-cylinder is formed by invagination into the blastocoelic cavity of the inner cell mass and polar trophoblast overlying it; this resembles in many respects the early stages of development of primitive species. The fully formed egg-cylinder, however, resembles that of the mouse and the formation of foetal membranes is also similar to that in Muridae. It is concluded that in the bank vole and also in other rodents, the extra-embryonic ectoderm of the egg-cylinder is derived from the polar trophoblast rather than from the inner cell mass.
Increased production of genetic mosaics inHabrobracon juglandisby cold shock of newly oviposited eggs
Authors: Petters R. M. , Grosch D. S.
Published: April 2021

Eggs from an ebony stock exposed to 5·5 °C prior to syngamy exhibited increased production of genetic mosaics in comparison with untreated eggs from the same females. No increase in mosaic production occurred for cold-shocked cleavage-stage embryos from the ebony stock or from pre-cleavage cold-shocked eggs from a wild-type stock. Heat shock of pre-syngamy eggs also failed to increase the production of genetic mosaics. These findings are consistent with predictions based on the post-cleavage fertilization theory of mosaic origin in Habrobracon or with a hypothesis of differential mortality.
Patches in the livers of chimaeric mice
Authors: West J. D.
Published: April 2021

Sections of adult chimaeric livers have been histochemically stained for β-glucuronidase activity and patches of two cell populations visualized. A one-dimensional clonal analysis has been used to estimate the number of coherent clones in the adult liver. The data are consistent with a total of 9–22 million regular, coherent clones, comprising 10–34 nuclei, or a smaller number of irregular, branched coherent clones. Both of these alternatives suggest considerable cell mixing during liver morphogenesis.
A simplified procedure for preparing myogenic cells for culture
Authors: Caplan Arnold I.
Published: April 2021

A procedure involving mechanical agitation referred to as vortexing is compared to a trypsin procedure for obtaining myogenic cells for culture. The vortex procedure appears to be at least as useful as the trypsin procedure and has several advantages including speed, the elimination of chemical disruptive agent, elimination of collagen coating of culture dishes and earlier onset of fusion.
Fish swimbladder: an excellent mesodermal inductor in primary embryonic induction
Authors: Kawakami Izumi
Published: April 2021

Swimbladder of the crucian carp, Carassius auratus, was found to be better as a vegetali-zing tissue than other tissues, such as guinea-pig bone marrow, when presumptive ectoderm of Trituras gastrulae was used as reacting tissue.

Swimbladder usually induced assemblies of highly organized mesodermal tissues, such as notochord, somites and pronephric tubules, some of which were covered by mesodermal epithelium without an epidermal covering.

A special character of the effect of swimbladder was the rather frequent induction of solid balls of undifferentiated cells, which were identified as mesodermal or mesodermal and probably endodermal. These findings show that swimbladder has a strong and fast spreading vegetalizing effect on the responding presumptive ectoderm.
Direct exposure of mouse embryonic limb-buds to 5-bromodeoxyuridinein vitroand its effect on chondrogenesis: increasing resistance to the analog at successive stages of development
Authors: Agnish Narsingh D. , Kochhar Devendra M.
Published: April 2021

The inhibitory effect of 5-bromodeoxyuridine (BudR)-an analog of thymidine-on embryonic mouse limb-buds was studied in vitro employing an organ-culture system. The effect was found to be dose-related and also depended on the developmental stage of the donor embryos. Limbs at an early stage of development (early 11th-day embryos, somite stage 26 –29) were extremely sensitive to the analog. Treatment with low levels (2 –4 μg ml) and for a relatively short period of time in culture (2-3 days) completely and irreversibly suppressed chondrogenesis in these explants. Limbs from older embryos (somite stage 40 and up) were found to be much less sensitive to the inhibitory effect of the drug; a prolonged exposure to a much higher dose (100 –150 μg ml) resulted in an incomplete suppression of chondrogencsis. Only a 20% inhibition was observed in the cultures of limbs from mid-13th-day mouse embryos. After continuous growth in vitro, the limbs became progressively resistant to the analog and towards the end of the culture period had become refractory to the drug. The time of complete insensitivity appeared earlier in the cultures of the limbs taken from older embryos than in the explants of younger limbs. These studies show that as limbs continue to differentiate in vivo or in vitro, they become increasingly resistant to the inhibitory effect of BudR. in at least as far as the effect on the process of chondrogenesis is concerned. It is suggested that the relative sensitivity or insensitivity to the inhibitory effect of BudR may prove to be a useful parameter in evaluating the developmental stage of an organ.
Evidence that blood pressure controls heart rate in the chick embryo prior to neural control
Authors: Rajala G. M. , Kalbfleisch J. H. , Kaplan S.
Published: April 2021

Blood, pressure increases will increase heart rate in intact chick embryos, prior to the development of neural control. Similarly, in surgically isolated hearts, increases in intraventricular fluid pressure will increase the rate of beat. However, fluid pressure applied equally to both interior and exterior surfaces of the isolated heart does not result in increased heart rate. Therefore, we conclude that the increased pressure stretches the heart muscle and that this stretch stimulates the increased heart rate.

While heart rate is clearly influenced by blood pressure, the reverse is not true. Propranolol reduces the heart rate to about half normal in intact embryos but does not significantly alter the blood pressure.
A method for enucleating oocytes ofXenopus laevis
Authors: Ford C. C. , Gurdon J. B.
Published: April 2021

A method is described for the enucleation and complete healing of Xenopus oocytes so that the enucleated oocytes withstand multiple injections and culture for several days. The oocytes are defolliculated and enucleated manually and allowed to heal in a potassium phosphate buffer. Oocytes enucleated in this way support RNA synthesis by injected HeLa-cell nuclei 3 days later. This method is valuable in providing a low-background system in which transcription of injected nuclei can be studied.
Evaluation of the technique of immunosurgery for the isolation of inner cell masses from mouse blastocysts
Authors: Handyside A. H. , Barton S. C.
Published: April 2021

Inner cell masses (ICMs) immunosurgically-isolated from -day mouse blastocysts were examined for trophoblast cell contamination and developmental capacity. Blastocysts were preincubated in rabbit anti-mouse antiserum, washed thoroughly and then incubated in complement. The ICMs were then easily dissected by drawing through a fine pipette.

Various experiments confirmed that the trophectoderm had been completely removed by this treatment. Firstly, the ICMs did not bind a fluorescein-conjugated antibody directed against rabbit IgG, indicating the absence of cells exposed to the rabbit antiserum during the immunosurgical procedure. Secondly, ICMs dissected from blastocysts preincubated in a suspension of melanin granules did not include any of the trophoblast cells that had phagocytosed the granules. And, thirdly, the protein synthetic profile of these ICMs was similar to microsurgically dissected ICMs, and in particular, trophoblast specific spots were absent.

The developmental capacity of immunosurgically-isolated ICMs was tested by injecting them into blastocysts and transferring to the uterus of -day pseudopregnant recipients. Extensive chimaerism was detected in the majority of implants, 5-6 days after transfer, but only in ICM-derived tissues. This demonstrates both the lack of trophoblast cell contamination and functional viability of these ICMs.
The Time and Place of Fertilization of the Golden Hamster Egg
Authors: Strauss Fritz
Published: April 2021

The middle and caudal third of the ampulla tubae are the regions where most of the eggs of Mesocricetus auratus Waterhouse are fertilized. The earliest fertilization resulting from evening matings prior to ovulation (assuming the ovulation peak to be at 3 a.m.) were obtained at 2 hours after ovulation. When copulation occurred the morning after ovulation, fertilized ova were not obtained at 2 hours after mating, but they were at 4 hours. The time of fertilization is most frequently between the 2nd and 10th hour after ovulation. About 91 per cent, of the eggs are fertilized during this period. On the basis of existing data it is not possible to speak of a family-specific or even an order-specific fertilization site for the mammalian egg.
The Initial Formation and Subsequent Development of the Double Visual Cells in Amphibia
Authors: Saxén Lauri
Published: April 2021

The investigation deals with the development and structure of the double visual cells of two amphibians, Rana temporaria and Trituras vulgaris. The double cells of these species, which belong to the ‘double cone’ type described by previous investigators, are encountered later in development than the single visual cells. They are formed through the fusion of two visual cell progenitors. The results support the theory previously advanced by the present author that the accessory component is a rod-like receptor. Thus the name ‘double cone’ gives an erroneous impression both with regard to the origin of this cell, and probably also with regard to its function. The glycogen droplet in the accessory component, the paraboloid, is apparently a lens-like organ. The function of the double cell is still, however, open to speculation.
Teratogenic Effects of Trypan Blue on Amphibian Embryos
Authors: Waddington C. H. , Perry M. M.
Published: April 2021

Trypan blue, at concentrations around 0·025 per cent., was allowed to act on cleavage, gastrula, and early neurula stages of Xenopus, Axolotl, and Triturus alpestris and palmatus for various periods (about 24 or 48 hours). A variety of abnormalities were produced, of which the most striking were: (a) Oedema, (b) Microcephaly, (c) Prevention of elongation of the tail bud. (d) Vacuolation and swelling of the epidermal cells and fusion of the epidermis to the mesoderm, (e) Degeneration of the neural tissue (and to a lesser extent of the mesoderm) with appearance of vacuoles in the cells, (f) Suppression of gastrulation. (g) Mesodermalization of the notochord, similar to that produced by lithium. It seems unlikely that all these effects are consequences of one single original action. Some of the abnormalities (particularly (d) and (e), and to a lesser extent (b) and (g)) can be produced when the exposure to the dye occurs after gastrulation. In view of the lithium-like effect, Professor S. Ranzi of Milan has tested the action of trypan blue on the viscosity of protein solutions and their resistance to the action of urea, and found that it behaves similarly to other ‘vegetalizing’ agents. The incidence of these types of abnormality differs in the different amphibia investigated, as it also appears to do in the various stocks of mice which have been studied.
Analysis of the Determination of the Olfactory Placode in Amblystoma punctatum
Authors: Haggis Alex J.
Published: April 2021

This study deals with the tissue factors engaged in the induction of the nasal organs in embryos of Amblystoma punctatum. Isolations and heterotopic transplantations of a large area of head ectoderm, including all the nose primordium of one side, demonstrate that the nose primordium is not determined before stage 21. By unilaterally excising nasal primordia, and either allowing the surrounding head ectoderm to heal over the wound, or replacing the excised primordium with anterior flank ectoderm from embryos at stages 13 to 25, it was demonstrated: (1) that heterotopic head ectoderm of all the stages studied is competent for nose formation, (2) that anterior flank ectoderm from stage 13 is able to react to nose-inducing stimuli, while (3) anterior flank ectoderm from stages beyond 14 no longer has this ability. The nose competence of heterotopic head ectoderm progressively decreases with increasing age. Transplantations of competent ectoderm in place of the excised nasal primordium at stages 15 to 27 show that nose-inducing capabilities are retained within the nasal region until the latest stages studied here. In some instances, early flank ectoderm, grafted into the nose region, was induced to form a brain fragment associated with a nasal organ. The latter was evidently induced secondarily by the former. Isolates of the prospective nasal ectoderm, previous to stage 21, differentiate a nose only if part of the adjacent forebrain anlage is included in the explants. Removal of the presumptive forebrain, with or without the underlying archenteron roof, could result in (1) complete absence of noses if the telencephalon is absent, (2) absence of one nose if the cerebral hemisphere is absent or very small, or (3) synrhiny or monorhiny if the forebrain is a small medial vesicle. The removal of the anterior one-seventh of the archenteron roof alone did not directly affect the number of noses present but tended to produce hypomorphic forebrains which in turn were associated with subnormal nose formations. The capability of prospective forebrain and the most anterior portion of the archenteron roof to induce nose was tested by wrapping these tissues, separately or together, in competent ectoderm. Nose inductions occurred only in those explants which contained brain, whether mesoderm was present or not. On the other hand, ectodermal explants enclosing head mesoderm alone showed no inductions. The frequency of nose inductions in explants containing presumptive forebrain was much higher than in those with mesoderm in addition to brain. Mesenchyme seemed to prevent rather than promote nose induction. The data taken together support the view that inductive stimuli emanating from the prospective forebrain are solely responsible for the emergence of the olfactory organs.
Differentiation and Metamorphosis of the Imaginal Optic Glomeruli in Drosophila
Authors: Shatoury H. H. El
Published: April 2021

A description has been given of the differentiation and metamorphosis of the optic glomeruli. The giant ganglion cells of the larval brain degenerate at the end of the third instar after differentiation to the imaginal brain primordia is completed. The outer eye glomerulus was found to differentiate from the brain and not from the optic bud. The ‘fenestrated zone’ of the outer eye ganglion is an artefact, and develops from the histolytic products of the larval tissues in the head. The condition in the mutant eyeless is discussed.
Régénération du tissu musculaire strié dans des pertes de substance expérimentales de l’œsophage chez le chien
Authors: Picard D. , Henry E. , Cotte G. , Inglesakis J. A.
Published: April 2021

When part of the dog’s thoracic œsophagus is surgically removed, and the defect is covered by a graft of pericardium, sutured to the adventitia without drawing together the edges of the wound, there occurs a very rapid reconstitution of the striated muscle tunic. The regeneration involved in this reconstitution occurs exclusively by a process of outgrowth, which initially gives rise to thin strands of little differentiated muscle, growing rapidly in length. These observations, made on the region of junction which can confidently be declared to be free from pre-existing musclefibres or fragments of muscle-fibres, throw doubt on the existence of the mode of regeneration called ‘discontinuous’, particularly on muscle-fibre neogenesis by differentiation of mesenchyme in situ. On the contrary, they support the opinion of Pfuhl, of Clark, and of Adams, Brown, & Pearson, that regeneration of mammalian striped muscle occurs exclusively by ‘continuous’ outgrowth. In these experiments, besides the immediate regeneration which re-establishes muscular continuity, there is a delayed outgrowth (lasting up to 7| months). We do not know the significance of this: it may be the consequence of continuous micro-trauma from the sutures, or it may be a very slow perfection of the anatomical and functional reconstitution of the muscular tunic.
Cell proliferation during morphogenetic change; analysis of frontonasal morphogenesis in the chick embryo employing DNA labeling indices
Authors: Minkoff Robert , Kuntz Amy J.
Published: April 2021

The role of cell proliferation was analyzed in the chick embryo system employing DNA labeling indices during the invagination of the olfactory placode and the development of the lateral and medial nasal processes. Chick embryos were labeled for 1 h with [3H]thymidine and processed histologically and autoradiographically. The percentage of labeled mesenchymal cells in delineated areas within and adjacent to the nasal processes was determined. From analysis of labeling indices of each area at successive developmental stages, it was concluded that cell proliferation of mesenchyme, as measured by DNA labeling indices, did not appear to increase during the formation of the nasal processes, and that cell proliferation actually declined during the later stages of nasal process formation.

Differences were also found between the labeling indices of the mesenchyme of the nasal processes as compared to that of adjacent areas. These differences tended to become greater as development progressed. In all of the areas studied, cell proliferation declined during the later stages of development but the magnitude of the decline was greater in the areas adjacent to the nasal processes. Differential rates of decline, rather than acceleration of cell proliferation, therefore, appears to be operative as a morphogenetic mechanism during early primary palate formation.
Development of interspecific hybrids ofMus
Authors: West John D. , Frels William I. , Papaioannou Virginia E. , Karr James P. , Chapman Verne M.
Published: April 2021

Artificial insemination has been used to produce interspecific mouse hybrids. Mus musculus × Mus cervicolor cervicolor hybrids failed to complete more than a few cleavage divisions but both M. musculus × M. dunni and M. musculus × M. caroli hybrids completed preimplantation development. These hybrid embryos are heterozygous for various X-linked enzymes and may provide a useful genetic system for studying X-chromosome inactivation during early development. Further development of M. musculus × M. caroli hybrids was studied: several completed foetal development; a few survived to maturity but none has yet reproduced.
Embryonic malformations in rats, resulting from maternal diabetes: preliminary observations
Authors: Deuchar Elizabeth M.
Published: April 2021

Diabetes mellitus was induced in female Wistar rats by injections of either alloxan or streptozotocin, and their embryos were found to have significantly higher incidences (7·5%) of brain and heart abnormalities (non-closure of neural folds, and deformities of heart chambers) at mid-gestation than controls (2·2%). There were also increased numbers of resorptions (25% in diabetic animals: 7·2% in controls). Both drugs produced similar abnormalities. External and X-ray examination of 488 foetuses from streptozotocin-treated animals at 20 days showed eight cases of exomphalos, two cases of micrognathia with tongue protrusion, and 34 cases of incomplete sacral ossification. This last deformity occurred also in foetuses of mildly diabetic animals, and has been seen occasionally in infants of human diabetic mothers. Other evidence suggests that skeletal deformities may be due to hyperinsulinism in the foetuses of diabetic mothers. Even a mild or pre-diabetic condition may set the foetus at risk.
DNA synthesis during the first stages of anterior regeneration in the polychaete annelid Owenia fusiformis (dedifferentiation and early phases of differentiation)
Authors: Marilley Monique , Thouveny Yves
Published: April 2021

We have analysed DNA synthesis in early phases of regeneration in a marine Polychaete Annelid, Owenia fusiformis. The length and efficiency of the prereplicative phase was found to vary with the diurnal rhythm of activity of the animal; that is, it depends on the initial state of the cell population at the moment of the onset of proliferative stimulation. When animals were operated on at 12 a.m., the duration of the prereplicative phase of the first cells stimulated to proliferate was found to be 12 h. The remaining cells entered the S-phase progressively in waves until the 3rd day following amputation when nearly 100% of the blastema cells were stimulated. At that time the cell-cycles of these dividing cells were found to be highly synchronized. Blastema differentiation takes place on the 4th day and is initiated by stomodeum formation. During the differentiation phase, DNA synthesis is restricted to small areas of the regenerating part. The system described is viewed as a new instrument for investigating the control of the cell cycle in synchronized and subsequently differentiating tissue cells.
In vitro development of inner cell masses isolated immunosurgically from mouse blastocysts: II. Inner cell masses from 3·5- to 4·0-day p.c. blastocysts
Authors: Hogan Brigid , Tilly Rita
Published: April 2021

This paper describes the development in culture of inner cell masses isolated immunosurgically from C3H/He mouse blastocysts immediately after collection between 3 ·5 and 4 ·0 days p.c. By 24 –48 h most of the inner cell masses isolated from half-expanded blastocysts, and about 50 % of those from expanded blastocysts, regenerate an outer layer of trophecto-derm-like cells and so resemble mini-blastocysts. With further in vitro culture these structures attach to the substratum and give rise to trophoblast-like giant cells, together with clusters of parietal endoderm cells or inner cell masses surrounded by visceral endoderm.

Many of the inner cell masses from the remaining expanded blastocysts develop into floating structures with an outer layer of endoderm cells, and by 7 days consist of a large fluid filled cyst surrounding a collapsed vesicle of epithelial cells. Mesodermal cells line the cysts and form numerous blood islands. When mechanically disrupted, and grown as attached sheets of cells, these cystic structures give rise to patches of trophoblast-like giant cells similar to those described in the previous paper.

These results suggest that the inner cell mass of normal mouse blastocysts contains cells which are capable of giving rise to trophoblast in culture.
A method for isolating uncontaminated nuclei from all stages of developingXenopus laevisembryos*
Authors: Farzaneh F. , Pearson C. K.
Published: April 2021

A method for isolating nuclei from Xenopus laevis embryos has been developed. This procedure enables the isolation of nuclei, free from contamination with yolk and pigment granules, at all stages of embryonic development. Using this method the nuclear yield is 60– 70% of the estimated number of cells in the embryo. The DNA, RNA, histone and non-histone protein content of these nuclei during embryogenesis (from early cleavage to the swimming tadpole stage) has been measured.
In vitro studies of mouse embryos bearing mutations in the T complex: t6
Authors: Wudl Linda R. , Sherman Michael I.
Published: April 2021

Cultured blastocysts homozygous for the t6 mutation lose their inner cell mass within a few days of attachment to the culture dish. At about the same time it becomes apparent that putative t6-mutant trophoblast cells and their nuclei fail to enlarge to the degree of their normal counterparts. These abnormalities in mutant embryos are reflected by an abrupt drop on the seventh equivalent gestation day in the rate of increase of β-glucuronidase activity. The failure of t6/t6 trophoblast nuclei to enlarge normally appears to be due partially to endoreduplication at a slower rate than normal trophoblast nuclei and partially to pre-mature cessation of DNA synthesis. Analyses indicate that this abnormality is not reversed when mutant embryos are placed in chimeric association with normal ones. Trophoblast outgrowths from mutant and normal trophectodermal vesicles are similarly distinguishable by differences in outgrowth and nuclear size as well as DNA content and synthesis. Despite the fact that t6/t6 embryos and trophectodermal vesicles are phenotypically different from normals from early times in culture, the trophoblast cells in the mutant structures acquire and continue to produce two enzymes characteristic of trophoblast differentiation, Δ 5,3 β -hydroxysteroid dehydrogenase and plasminogen activator.

On the basis of these and previous observations, we propose that the primary effect of the t6 mutation is to cause a metabolic lesion which kills inner cell mass cells relatively quickly but which has a more gradual effect upon trophoblast cells. The fact that phenotypically recognizable t6/t6 trophoblast cells can survive for several days before dying makes this a potentially useful system in which to search for the t6 gene product(s).