bluuebunny/crossref_metadata_2025 huggingface dataset:
Metabolic Characteristics of the Heart-forming Areas of the Early Chick Embryo
Authors: Duffey Lowell M. , Ebert James D.
Published: April 2021

The inhibition of early development by sodium fluoride and antimycin A has been analysed in the early chick embryo cultured in vitro. The relatively specific inhibition of the development of the heart by sodium fluoride, originally reported by Spratt (1950), has been extended to include early streak stages, head process stage, and head fold stage embryos in order to determine the period during development at which the heart-forming tissues become fluoride-sensitive. (a) Fluoride-sensitive areas corresponding to the bilateral prospective heartforming areas arise in the early streak stages. (b) The locations of fluoride-sensitive loci in subsequent stages mirror the sites of highest cardiogenic potency and the areas of highest levels of the cardiac proteins, myosin and actin. In very low concentrations, antimycin A has a striking inhibitory action on the mesoderm of the chick embryo grown in vitro. The brain is free of gross developmental abnormalities in embryos in which all mesodermal derivatives, including heart, have degenerated. The action of antimycin A cannot be prevented by the addition of d-α- tocopherol; however, the effects of this inhibitor can be prevented by doubling the albumen content of the medium. It is suggested, in consonance with recent findings by Nason et al., that a lipid bound to albumin functions in the restoration of activity in the DPN- and succinate-cytochrome c reductases. The results, together with recent information on the specificity of action of the inhibitors, provide a basis for a re-examination of the working hypothesis of Spratt (1950) which holds that brain is dependent primarily on oxidative metabolism and heart on glycolysis. The inhibition of heart by antimycin A reveals a pronounced dependence of this tissue on pathways for DPN oxidation. The combined results of Spratt and the authors, correlated with information on the action of antimycin A and other respiratory poisons, suggest that fundamental differences exist between brain and heart in their respective electron to oxygen transport systems.
Correcting the Genetically Determined Sterility of W
V
W
V Male Mice
Authors: Veneroni Giorgio , Bianchi Angelo
Published: April 2021

In the house-mouse the genotype WvWv is usually sterile. Young male mice of this genotype have been treated with high dosages of f.s.h. (follicle-stimulating hormone) or with f.s.h. associated with testosterone propionate; in some, a unilateral orchidectomy was carried out. Most of the animals thus treated showed a significant recovery in spermatogenesis; some of them, mated to fertile females, had offspring. Untreated WvWv males of our colony have always proved sterile. The sterility-inducing action of the Wv-factor is believed to be accounted for by a deficiency in f.s.h. secretion and/or to a low sensitivity of the germinative tissue to f.s.h. in addition to a deficiency of the primordial sex cells. The treatments did not increase testis size: apparently they stimulated the few derivatives of the primordial sex cells without increasing their number. But this may be sufficient to abolish the sterility of the WvWvmales.
Complete Heterospermic Androgenesis in Silkworms as a Means for Experimental Analysis of the Nucleus-Cytoplasm Problem
Authors: Astaurov B. L. , Ostriakova-Varshaver V. P.
Published: April 2021

In the course of the last 70 years many outstanding biologists have tried to obtain so-called heterospermic merogons, or androgenetic hybrids, developing as a result of interaction between the cytoplasm of one (maternal) and the nuclear material of another (paternal) species. The successful achievement of this experiment was considered the experimentum crucis for the solution of certain fundamental questions of heredity and development pertaining to the so-called nucleus-cytoplasm problem. The most important of these questions was that of the cytoplasmic versus nuclear localization of the physical elements which condition the specific hereditary characters of parental forms and their transmission through successive generations.
Correction of the maternal effect linked to theacmutation, by injury of the egg, in the salamanderPleurodeles waltlii
Authors: Fernandez Maria
Published: April 2021

At the gastrula stage, deep irregular furrows appear on the animal hemisphere in embryos arising from ac/ac females and characterize a maternal effect (Beetschen, 1970). Disturbed morphogenetic movements (epiboly and invagination) frequently elicit exogastrulation or anomalies of later embryonic development. Pricking the animal hemisphere of the uncleaved egg with a micropipette prevents the occurrence of anomalies during gastrulation and neurulation in many embryos. Injection of normal oocyte nuclear sap or of normal egg cytoplasm into mutant female eggs does not improve that result. The partial correction of the maternal effect therefore appears to be consecutive to the injury of the cortical cytoplasm and/or the plasma membrane. Assuming that activation could be deficient, an electric shock was applied to freshly laid fertilized mutant eggs. It did not correct ectodermal anomalies but nevertheless seemed to increase the corrective effect of pricking when both treatments were applied.
Palate Morphogenesis: IV. Effects of serotonin and its antagonists on rotation in embryo culture
Authors: Wee Elizabeth L. , Babiarz Bruce S. , Zimmerman Stephen , Zimmerman Ernest F.
Published: April 2021

Previous studies have localized non-muscle contractile systems in the posterior (region 2) and the anterior (region 3) ends of mouse palates at the time of shelf movement. In order to determine whether these contractile systems function in shelf rotation, effects of pharmacologic agents have been analyzed in embryo culture. First, it was shown that the posterior end of the palate rotates before the anterior end, and its rotation in culture was proportionally greater as development of the embryo progressed. Generally, the posterior end of the palate was more easily inhibited in embryo culture than the anterior end. Serotonin at 10−8 M to 10−5 M was shown to significantly stimulate rotation at the anterior end of the palate after 2 h in embryo culture. The effect on the posterior palate was less pronounced. To investigate further the role of this neurotransmitter on palate shelf rotation, serotonin antagonists were employed. Methysergide (10−4M) inhibited anterior shelf rotation to 12% of control values (P 0·005), while not significantly affecting the posterior end. Ergotamine (10−6 M) significantly inhibited the stimulation induced by 10−5 M serotonin (P 0·025). Cyproheptadine (10−9 M) partially inhibited anterior and posterior shelf rotation in embryo culture. When injected into the pregnant dam, cyproheptadine partially inhibited shelf rotation and fusion. The palate was examined histologically after embryo culture. In the presence of 10−4 M methysergide, the elongated contractile cells in region 3 at the anterior and midpalatal mesenchyme were prevented from rounding. Thus, serotonin may be regulating rotation of the anterior end of the palate by an effect on a cell-mediated process.
Segmental innervation of the chick forelimb following embryonic manipulation
Authors: Bennett M. R. , Lindeman R. , Pettigrew A.G.
Published: April 2021

A number of studies have shown that the segmental innervation of some muscles in the developing limb undergoes some modification during the earliest stages of ontogeny. These observations can be interpreted in support of the hypothesis that the motor axons and muscles are matched during this period of development. As a further test of this suggestion we have made a quantitative examination of the motor innervation of the chick forelimb under conditions of controlled abnormal development.

Embryos were surgically manipulated at stages before the motor axons invade the limb. The operations were controlled such that forelimbs were induced with segments deleted or reduplicated or simply that a segment of the spinal cord had been deleted. In preparations with abnormal limbs the motor innervation of the muscles present was the same as for those muscles in the normal limb. Where a spinal segment had been deleted the limbs developed normally and their innervation was completed by the remaining brachial segments.

These results suggest that any particular matching property of a developing muscle does not develop as a consequence of its position in the limb relative to those segments of the limb proximal to it. Furthermore, that some muscles which are normally innervated by two spinal segments can be completely innervated by one of those spinal segments, in the absence of the other, suggests that any matching between growing axons and developing muscle cells is hierarchical rather than strictly all-or-nothing.
Growth and differentiation of an embryonal carcinoma cell line (C145b)
Authors: Papaioannou V. E. , Evans E. P. , Gardner R.L. , Graham C. F.
Published: April 2021

Several cell and tumour lines were isolated from a single-embryo-derived teratocarcinoma and their karyotypes and differentiation in adult hosts recorded. The majority of cells contained normal karyotypes by banding. The cells were injected into blastocysts and although they sometimes colonized the yolk sac, they never colonized the embryo. Thus the possession of a normal karyotype is not a sufficient condition for embryo colonization. The loss of growth capacity was investigated by studying differentiation and tumourigenicity in a variety of circumstances. The change in appearance from an EC cell morphology to a big flat cell in culture leads to retardation of growth in adult hosts. When EC cells are injected into a blastocyst, the ability to grow progressively both in culture and in adult hosts is lost.
An autoradiographic analysis of the development of the chick trigeminal ganglion
Authors: D’Amico-Martel Adele , Noden Drew M.
Published: April 2021

The avian trigeminal ganglion, which is embryonically derived from the neural crest and epidermal placodes, consists of two topographically segregated classes of immature neurons, large and small, during the second week of incubation, and two neuronal cell types, dark and light, interspersed throughout the mature ganglion. In order to establish the times of terminal mitosis of trigeminal sensory neurons, embryos were treated with [3H]thymidine during the first week of incubation and their ganglia fixed on embryonic day 11. The embryonically large, distal, placodal-derived neurons are generated between days 2 and 5, while the small, proximal, neural crest-derived neurons are formed mostly between days 4 and 7.

By comparing the locations of labeled cells in ganglia treated with isotope but fixed on day 18 of incubation with their 11-day counterparts, we have proved that there are no morphogenetic rearrangements of neurons during the final week of incubation. Thus, no unique relationship exists between the two neuron types in the mature ganglion and the two cell classes in the immature trigeminal. Therefore, both the light and the dark neurons in the mature trigeminal ganglion arise from neural crest as well as placodal primordia.
Estrogen target cells in gonads of the chicken embryo during sexual differentiation
Authors: Gasc Jean-Marie
Published: April 2021

Estrogen target cells were searched for in the differentiating gonads of the chicken embryo in order (1) to establish at the cellular level that steroid hormones can play a physiological role in gonadal sexual differentiation, and (2) to localize their sites of action. An autoradiographic technique carried out with frozen sections was employed to demonstrate the presence of binding sites for radiolabelled hormone in the nuclei of the target cells.

Target cells for [3H]estradiol are found similarly in gonads of both male and female embryos from (stage 27 of H and H) to 7 days of incubation. Estrogen target cells are observed in the germinal epithelium of the left but not the right gonad, and in the medulla of both the right and left gonads. In the medulla, numerous cells inside the cords are a target for estradiol. The germ cells, difficult to identify unmistakably in the experimental conditions, do not seem to be a target for estrogen hormones. A 100-fold excess of unlabelled estradiol abolishes the nuclear labelling, which is only slightly reduced after a similar excess of unlabelled dihydrotestosterone. It is concluded that the nuclear binding sites have a limited capacity for steroid hormones and are specific for estrogen hormones. The lack of clear and consistent nuclear labelling after [3H]dihydrotestosterone injection confirms the specificity of the [3H]estradiol nuclear labelling. At day 10 of incubation, only the undifferentiated remnant of the germinal epithelium in the left testis still displays labelled cells after [3H]estradiol injection.

These observations confirm the determinative role currently ascribed to the estrogen hormones in the cortical differentiation, but they also emphasize that this role extends to the medulla of both gonads. In light of this presence of estrogen receptor sites in the medullary cords as well as in the germinal epithelium, one can assign the estrogen hormones more specific and diversified roles than currently believed. These roles also appear very precocious in the process of gonadal differentiation. Finally, the absence of target cells for estrogen hormones in the germinal epithelium of the right gonad accounts for the lack of cortical differentiation on the right side.
On the role of germ cells in planarian regeneration:I. A karyological investigation
Authors: Gremigni V. , Miceli C. , Puccinelli I.
Published: April 2021

Specimens from a polyploid biotype of Dugesia lugubris s.l. were used to clarify the role and fate of germ cells during planarian regeneration. These specimens provide a useful karyological marker because embryonic and somatic cells (3n = 12) can be easily distinguished from male (2n = 8) and female (6n = 24) germ cells by their chromosome number. We succeed in demonstrating how primordial germ cells participate in blastema formation and take part in rebuilding somatic tissues. This evidence was obtained by cutting each planarian specimen twice at appropriate levels. The first aimed to induce primordial germ cells to migrate to the wound. The second cut was performed after complete regeneration and aimed to obtain a blastema from a cephalic or caudal area devoid of gonads. A karyological analysis of mitotic cells present in each blastema obtained after the second cut provided evidence that cells, originally belonging to the germ lines, are still present in somatic tissues even months after complete regeneration. The role of primordial germ cells in planarian regeneration was finally discussed in relation to the phenomenon of metaplasia or transdifferentiation.
An interaction between dorsal and ventral regions of the marginal zone in early amphibian embryos
Authors: Slack J. M. W. , Forman D.
Published: April 2021

When small explants from early gastrulae of Xenopus laevis are allowed to develop in a buffered salt solution there is a considerable difference between the patterns of differentiation obtained from different dorsoventral levels of the marginal zone. These patterns of differentiation correspond to the fates of the different regions in the course of normal development. They are not altered if several explants of the same type are fused before culture.

If a ventral marginal zone explant from Xenopus is cultured in contact with a piece of dorsal marginal zone from the axolotl, it forms structures more dorsal in character than it would in isolation or in normal development. This behaviour is shown only feebly with other regions of the axolotl gastrula. A piece of dorsal marginal zone from Xenopus is not affected in its development by culture in contact with an explant of ventral marginal zone from the axolotl. The dorsalization of ventral marginal zone explants is shown only if there is a large area of direct contact with the dorsal explant and if the pieces remain in contact for a period of 48 h or more.

It is proposed that this in vitro interaction is the same as the dorsoventral component of action of the ‘organizer’ graft discovered by Spemann and Mangold.
Morphological study of cleft palate development in 5-fluorouracil-treated hamster fetuses
Authors: Shah Ravindra M. , Wong David T. W.
Published: April 2021

Morphogenesis of palate was studied in normal and 5-fluorouracil-treated hamster fetuses. The results showed that normal palatal development was completed between days .12 and 13 of gestation. In 5-fluorouracil-assaulted palate the reorientation of shelves from a vertical to horizontal plane was delayed. Crown-rump length, gestational age and fetal weight were reliable predictors of the stages of normal palatal development, whereas the morphological rating system was not. Following 5-fluorouracil treatment, however, crown-rump length, weight and morphological rating were poor indicators of the stage of palatal development.
The site of action of the naked locus (N) in the mouse as determined by dermal-epidermal recombinations
Authors: Raphael Kathryn A. , Pennycuik Pamela R.
Published: April 2021

The dermal-epidermal recombination technique was used to determine the site of action of the naked (N) locus in the skin of the mouse. The skin of athymic (nude) mice was used as a host site for growth of recombined epidermis and dermis from 13- and 14-day N/+ and +/+ embryos. Grafts that contained mutant epidermis lost their hair by 26 days after grafting (at the end of the first hair cycle) and again after 47 days (at the end of the second hair cycle); grafts that contained normal epidermis retained hair throughout the experiment. It was concluded that the N locus acts in the epidermis.
Tissue interactions and the initiation of osteogenesis and chondrogenesis in the neural crest-derived mandibular skeleton of the embryonic mouse as seen in isolated murine tissues and in recombinations of murine and avian tissues
Authors: Hall Brian K.
Published: April 2021

Mandibular processes from 9- to 13-day-old embryonic mice formed both bone and cartilage when grafted to the chorioallantoic membranes of host embryonic chicks. Isolated ectomesenchyme, taken from 9-day-old embryos did not form bone or cartilage, while older ectomesenchyme formed both. Recombination of the epithelial and ectomesenchymal components confirmed that the presence of the epithelium was a sufficient stimulus for the initiation of both chondro- and osteogenesis. Recombinations between components of mouse and chick mandibular processes showed that 9-day-old mouse ectomesenchyme could respond to chick epithelium but that, although older murine epithelia could initiate osteogenesis from the avian ectomesenchyme, epithelia from 9-day-old embryos could not. These results indicated that an epithelial–ectomesenchymal interaction was responsible for the initiation of both osteo- and chondrogenesis within the mandibular arch of the mouse; that the interaction began at 10 days of gestation; that the ectomesenchyme was capable of responding at 9 days, but that the epithelium did not acquire its ability to act on the ectomesenchyme until 10 days of gestation.
Changes in the surface coat of mesenchymal cells of mouse limb buds after enzymatic cell separation
Authors: Kohnert-Stavenhagen Evamaria , Zimmermann Bernd
Published: April 2021

Isolation of cells is nowadays performed by enzymatic means. The influence of such enzymes on the surface coat of mesenchymal and blastemal cells during the dissociation of limb buds from 11-day-old mouse embryos was studied electron microscopically after staining with ruthenium red. EGTA or collagenase failed to bring about cell separation. The surface coat seemed to be unchanged after collagenase treatment. After EGTA an increase in extracellular filaments was observed. The proteases a-chymotrypsin, dispase II, papain, pronase P and trypsin (0·2%, 37 °C, 20 min) succeeded in completely dissociating limb buds. Apart from single granules, there was a detachment of the surface coat from the cells in all cases studied. Hyaluronidase led to only partial separation, but the detachment of the surface coat was almost complete, indicating a GAG-rich surface layer on these cells.
Ectoderm and mesoderm interactions in the limb bud of the chick embryo studied by transfilter cultures: cartilage differentiation and ultrastructural observations
Authors: Gumpel-Pinot Madeleine
Published: April 2021

The wing mesoderm of the chick embryo cultured in vitro without ectoderm is able to differentiate into cartilage from stage 17 (Hamburger & Hamilton, 1951). But before this stage the presence of ectoderm is necessary.

In transfilter cultures of wing-bud ectoderm and mesoderm, the mesodermal response as measured by chondrogenesis was directly related to the pore size (0·2-1 μm) of the filter. Filters of 0·2 μm pore size and 10 μm thickness gave no increase in chondrogenesis over that of mesoderm cultures alone.

The lower face of filters on the upper face of which mesoderm or ectoderm had been cultured was observed by scanning electron microscopy. With ectoderm, no cell processes crossed the filter. In contrast, with mesoderm, cell processes crossed the filter and this was also related to pore size. A good correlation was observed between the mass and density of processes crossing the filter and the mesodermal response.

It is concluded that induction of cartilage in limb mesoderm cannot be classified as a Tong-range transmission’ system. It requires ectoderm and mesoderm to be separated by a very narrow gap and this condition can be brought about in vitro by extension of mesodermal processes through the filter close to the ectoderm.

The results are discussed in relation to a possible role of the basement membrane and associated extracellular matrix in limb cartilage induction.
Changes in the oxidative metabolism during maturation of amphibian oocytes
Authors: Legname Arnaldo H. , Salomón De Legname Hortensia
Published: April 2021

Some aspects of oxidative metabolism during cytoplasmic maturation of the Bufo arenarum oocyte have been studied.

During the autumn-winter period (immature oocyte), carbohydrates are degraded through the glycolytic pathway, followed by the classical tricarboxylic acid cycle.

During the spring-summer period (mature oocyte), carbohydrates are mainly used through the pentose phosphate cycle, while the tricarboxylic acid cycle operates as the glutamic-aspartic cycle.

The oxidative phosphorylation of ADP does not seem to change during oocyte maturation. Although maturation does not alter the absolute values of ATP and citrate in the oocyte, it determines their different compartmentalization, which, through phosphofructokinase, in turn regulates the glycolytic activity of the oocyte.

Oxygen uptake decreases by about 40 % during maturation, while simultaneously, a marked increment in respiratory stimulation by 2,4-dinitrophenol is observed.
An atlas of notochord and somite morphogenesis in several anuran and urodelean amphibians
Authors: Youn B. Woo , Keller R. E. , Malacinski G. M.
Published: April 2021

A scanning electron microscopic, comparative survey of notochord and somite formation including some details of change in cell morphology and arrangement, was made of selected stagesof twospecies of anuranamphibians(Xenopuslaevis and Ranapipiens) and two speciesof urodeles (Ambystoma mexicanum and Pleurodeles waltlii). The ectoderm or neural plate was removed from fixed embryos and the dorsal aspect of the developing notochord and somite mesoderm was photographed. Micrographs of comparable stages of all species were arranged together to form an atlas of notochord and somite formation. Similar morphogenetic events occur in the same sequence in the four species. Notochordal cells become distinguishable from paraxial mesodermal cells by shape, closeness of packing, and arrangement. Notochordal elongation is accompanied by a decrease in cross-sectional area and by cell rearrangement. Somitic mesoderm becomes distinguished from lateral mesoderm by a change in cell shape and orientation, followed by segmentation of somites. The schedule of somite formation was compared and related to the staging series for each species. The urodeles differ from the anurans in that the notochordal region in the early neurula stages is triangular, with the broadest part in the posterior region of the embryo. In anurans it is uniform in width. This difference may reflect differences in gastrulation and in the mechanism of elongation of the posterior part of the embryo in the neurula.
Ultrastructural aspect of size dependent regulation of surface pattern of complex ciliary organelle in a protozoan ciliate
Authors: Bakowska Julita , Jerka-Dziadosz Maria
Published: April 2021

A regulation is shown for size and number of the elements of complex ciliary structures forming the oral apparatus (OA) of a ciliate Paraurostyla weissei. Morphometric investigations were performed on oral ciliature of normal and size-reduced cells. Those constituents of the OA which exist as single structures, such as the inner and outer preoral membranelles, are not eliminated. Both shorten and the outer membranelle becomes narrower. Within the adornal zone of membranelles in size-reduced cells some frontal and ventral membranelles become eliminated, whereas the respective ratio of these types remains size invariant. In each individual adoral zone of membranelles there are membranelles of different length specificially located along the ventral part. Membranelles from small cells are significantly smaller than those of normal cells.

The number of kinetosomes is reduced in all four rows constructing an adoral membranelle. The analysis showed that regardless of cell size, the number of kinetosomes in the two inner rows of a membranelle is linearly and proportionately related. Regulation of the size of all components of the oral ciliature in P. weissei occurs at the time when the primordia of oral ciliature are formed.

The results are discussed in relation to recent ideas about pattern formation and size dependent regulation of the number and size of pattern elements.
Sterility in mutant (tLx/tLy) male mice II. A morphological study of spermatozoa
Authors: Nadijcka Mary , Hillman Nina
Published: April 2021

A comparative light and electron microscopic study was done on cauda epididymal spermatozoa obtained from correspondingly-aged sterile t6/tw32, and fertile T/tw32, T/t6 and BALB/c, mice. The results show that all of the males, regardless of age, contained defective gametes and that all contained the same types of aberrant gametes. The oldest males of each genotype contained more abnormal gametes than the younger males of the same genotype. No unique spermatozoan defect and no increased frequency of a specific spermatozoan defect was noted which could be correlated with the sterility of the t6/tw32 animals.
Sterility in mutant (tLx/tLy) male mice III.In vitrofertilization
Authors: Mcgrath James , Hillman Nina
Published: April 2021

Mice which are heterozygous for two complementary lethal t mutations (t6/tw32) exhibit complete male sterility. Experiments have been conducted to determine if spermatozoa from these heterozygous males can fertilize oviducal ova in vitro. The experiments have been designed so that specific barriers which are present during in vivo fertilization can be sequentially removed and the fertilizing ability of the spermatozoa tested after each barrier is eliminated. Our results show that spermatozoa from t6/tw32 males are unable to effect fertilization even after all of the barriers normally imposed by the female reproductive tract have been removed.
Extracellular matrix synthesis in the chick embryo lateral plate prior to and during limb outgrowth
Authors: Stephens Trent D. , Vasan N. S. , Lash James W.
Published: April 2021

Little is known at the present time about the molecular basis and mechanisms of morphogenesis. The present study is an attempt to determine what influence the extracellular matrix has on the initial outgrowth of the limb bud. Stage -12 to -18 chick embryo lateral plates were examined in relation to proline and sulfate incorporation into collagen and proteoglycan. The flank and limbs incorporated the same amount of labeled proline and sulfate before stage 16. At stage 16 the flank began to incorporate more of both isotopes until at stage 18 there was twice as much incorporation into the flank as into the limbs. The flank and limbs contained the same type of collagen during the period examined. The limbs contained both large and small proteoglycans but the flank contained only small proteoglycans. These data suggest that the extracellular matrix in the flank and limb regions may play a role in limb outgrowth and that the limb buds at these stages may be more inclined toward cartilage development.
Influence de la méthode d’élevage sur la différenciation nerveuse d’un fragment d’ectoblast
Authors: Denis par H.
Published: April 2021

Au cours d’un récent travail (Denis, 1957), exécuté sur Pleurodeles waltii, nous avons soumis un fragment d’ectoblaste prélevé au pôle animal d’une jeune gastrula, à l’influence inductrice du chordo-mésoblaste troncal d’une jeune neurula (stade H. 14–15). Ce greffon, quand il est implanté sur le ventre d’un hôte du même stade, peut se neuraliser entièrement. Les protocoles d’expériences amenaient à conclure qu’un contact inducteur de durée très réduite doit suffire pour amorcer la transformation nerveuse de l’ectoblaste. La neuralisation, cependant, est loin de se produire dans toutes les expériences: elle exige, pour se réaliser, des conditions bien spéciales: il faut que le greffon demeure ramassé sur lui-même et résiste à l’étirement provoqué par l’allongement de son hôte.
Inversion of the Dorso-ventral Axis in Amphibian Embryos by Unilateral Restriction of Oxygen Supply
Authors: Løvtrup S. , Pigon A.
Published: April 2021

According to the hypothesis advanced by Løvtrup (1958) the supply of oxygen is one of the factors responsible for the determination of bilateral symmetry in amphibian embryos. The protein coat covering the outside of the egg is known to have a very low permeability (Holtfreter, 1943), and it was suggested in the hypothesis that the formation of the grey crescent consists in a stretching of this coat by which the permeability is increased (cf. the work of Dalcq & Dollander (1948) and of Dollander & Melnotte (1952) on permeability of Nile blue), in this way the radial symmetry of the egg is changed to a bilateral symmetry from a metabolic point of view. As a consequence of the increase in permeability those oxidative, energy-supplying processes which are associated with gastrulation are enabled to proceed at a higher rate at one side of the egg. This hypothesis can of course only be valid for eggs which require oxygen for gastrulation. In some amphibian species, particularly in toads, gastrulation may occur under anaerobic conditions (Waddington, 1956). It seems necessary to assume that the bilateral symmetry is somehow built into the structure of these eggs.
Molecular studies on cells of the trophectodermal lineage of the postimplantation mouse embryo
Authors: Johnson M. H. , Rossant J.
Published: April 2021

Embryonic ectoderm (EmE), extraembryonic ectoderm (EE), ectoplacental cone diploid cells (EPC) and secondary giant cells (GC) were isolated from -day mouse embryos and their polypeptide synthetic profile assessed by fluorography of 2D polyacrylamide gels. Fifty polypeptides showed different distributions amongst the tissues, permitting characterization of each tissue by an array of polypeptide markers typical for the tissue at that developmental stage. The three tissues on the presumptive trophectoderm lineage did not show identical synthetic patterns. However, culture of EE cells in vitro resulted in conversion of their polypeptide synthetic profile to that of EPC after 2 days and of GC after 6 days, whilst culture of EPC cells converted their polypeptide synthetic profile to that of GC after only 4 days. These changes in polypeptide synthesis correlated well with the ploidy levels of the tissues at different times in culture.
Interaction of epiblast and hypoblast in the formation of the primitive streak and the embryonic axis in chick, as revealed by hypoblast-rotation experiments
Authors: Azar Yehudit , Eyal-Giladi Hefzibah
Published: April 2021

Three types of experiments were performed to determine the interaction between the epiblast and hypoblast for primitive streak formation: (1) Hypoblasts of blastoderms from stages XIII E.G & K to 3 H & H were separated from the epiblasts and rotated by 90° counterclockwise; (2) hypoblasts from stages XIII E.G & K to 3 H & H blastoderms were rotated by 180°; (3) hypoblasts were exchanged between blastoderms of different developmental stages and placed at 90° counterclockwise to the axis of the recipient epiblast. In all blastoderms studied only a single PS developed. After rotation of the hypoblast by 90°, the direction of the PS was according to the orientation of the hypoblast at stage XIII, whereas at older stages it gradually shifted towards the axis of the epiblast. At stage 3− H & H the PS is already imprinted in the epiblast and cannot be shifted. After rotation of the hypoblast by 180° the PS originated at the point near the marginal zone at which the inductive part of the hypoblast interacted with a competent epiblast. Conclusions are drawn about the dynamics of the inductiveness of the hypoblast and the competence of the epiblast for the PS formation and orientation.
Spreading of hemiretinal projections in the ipsilateral tectum following unilateral enucleation: a study of optic nerve regeneration inXenopuswith one compound eye
Authors: Straznicky Charles , Tay David
Published: April 2021

Right compound eyes were formed in Xenopus embryos at stages 32–33 by the fusion of two nasal (NN), two ventral (VV) or two temporal (TT) halves. Shortly after metamorphosis the optic nerve from the compound eye was sectioned and the left intact eye removed. The retinotectal projections from the compound eye to the contralateral and ipsilateral tecta were studied by [3H]proline autoradiography and electrophysiological mapping between 6 weeks and 5 months after the postmetamorphic surgery. The results showed that NN and VV eyes projected to the entire extent of both tecta. In contrast, optic fibre projection from TT eyes, although more extensive than the normal temporal hemiretinal projection, failed to cover the caudomedial portion of the tecta. The visuotectal projections in all three combinations corresponded to typical reduplicated maps to be expected from such compound eyes, where each of the hemiretinae projected across the contralateral and ipsilateral tecta in an overlapping fashion. The rapid expansion of the hemiretinal projections of the compound eyes in the ipsilateral tectum following the removal of the resident optic fibre projection suggests that tectal markers may be carried and deployed by the incoming optic fibres themselves.
The mechanism of mouse egg-cylinder morphogenesisin vitro
Authors: Copp A. J.
Published: April 2021

The number of trophoblast giant cells in outgrowths of mouse blastocysts was determined before, during and after egg-cylinder formation in vitro. Giant-cell numbers rose initially but reached a plateau 12 h before the egg cylinder appeared. A secondary increase began 24 h after egg-cylinder formation. Blastocysts whose mural trophectoderm cells were removed before or shortly after attachment in vitro formed egg cylinders at the same time as intact blastocysts but their trophoblast outgrowths contained fewer giant cells at this time. The results support the idea that egg-cylinder formation in vitro is accompanied by a redirection of the polar to mural trophectoderm cell movement which characterizes blastocysts before implantation. The resumption of giant-cell number increase in trophoblast outgrowths after egg-cylinder formation may correspond to secondary giant-cell formation in vivo. It is suggested that a time-dependent change in the strength of trophoblast cell adhesion to the substratum occurs after blastocyst attachment in vitro which restricts the further entry of polar cells into the outgrowth and therefore results in egg-cylinder formation.
Control of neurite extension by embryonic heart explants
Authors: Ebendal Ted
Published: April 2021

The dynamics of neurite outgrowth elicited by embryonic chick heart explants in sympathetic, spinal, ciliary and Remak’s ganglia were investigated in collagen gel cocultures. Neurites emerged preferentially on the side facing the heart explants even after only 6 h and continued to increase in density and length for the next 2 days. Removal of the heart explants after only initial stimulation resulted in less-dense neurite outgrowth. Washing of such cultures led to retraction or degeneration of neurites, effects which could be countered by again adding heart explants. Addition of a second set of heart explants on the back of ganglia initiated a second wave of neuritic outgrowth locally. Ganglia extracted from gels separate from their fibre halos and transferred to a second gel did not regenerate neurites unless again stimulated by heart explants. Neurites from additional, distally positioned ganglia failed to advance into parts of the gel shadowed from the heart explants by proximal ganglia. The asymmetry of neurite outgrowths may be explained by local chemokinetic stimulation of extension, possibly in combination with chemotactic orientation of fibre tips up concentration gradients. The results show that the extension of several categories of ganglionic neurites was reversible, being controlled by the concentration of a soluble neuronotrophic factor released from a developing end organ.
Embryogenesis of an insect nervous system II: A second class of neuron precursor cells and the origin of the intersegmental connectives
Authors: Bate C. M. , Grünewald E. B.
Published: April 2021

The intersegmental connectives in the locust central nervous system are initiated by the axons of early differentiating neuron trios. Using a combination of electron microscopy and fluorescent dye injection we have shown that the axons of these cells grow out anteriorly and posteriorly in each segment along a basement membrane, and link together at the segment borders to form continuous longitudinal pathways on each side of the developing nervous system. These early neurons are the progeny of a second class of precursor cell, the midline precursors, which are distinct from the segmental neuroblasts. Like the neuroblasts, the midline precursors are arranged in a standard segmentaliy repeated pattern. This and the standard pattern of axon outgrowth in different segments suggest that the nervous system develops to a common, segmentaliy repeated programme.
Foetal megakaryoblastic abnormality associated with congenital limb amputation in the br/br rabbit
Authors: Ehrensperger Maud , Petter Claude , Keuky Lim
Published: April 2021

Recent research on the br/br rabbit is summarized. In all homozygous individuals, limb amputations result from in utero haemorrhages which develop in the extremities and lead to necrosis. An inner-ear abnormality is observed in about 25% of the cases. By studying a large number of gestations and birth, we observed that homozygous crossings result in about 100% amputated animals while crossings between heterozygous and homozygous rabbits result in about 50% of the young being abnormal.

Observations of megakaryoblastic cells in 15- and 17-day foetal liver show a predominance of immature cells in 15-day br/br foetuses. This abnormality disappears on day 17. The possible role of megakaryoblastic cells in br/br rabbit amputation is discussed.
On the control of the trophoblastic giant-cell transformation in the mouse: homotypic cellular interactions and polyploidy
Authors: Ilgren E. B.
Published: April 2021

Trophoblastic tissues grown under different conditions in vitro display distinct patterns of cellular growth. Thus, trophoblast cultured on ‘bacteriological grade’ plastic surfaces remained in suspension culture as rounded tissue fragments. Such tissues maintained numerous cell contacts and remained, in turn, largely diploid. Trophoblast explanted on a ‘tissue-culture grade’ substrate formed monolayers. These contained fewer cell contacts and had more giant nuclei than the rounded tissues. Finally, if trophoblast was dissociated and grown as attached single cells, so that cell contact was minimal or absent, the single-cell preparations contained more giant nuclei than tissues grown either as monolayers or in suspension. These results suggest that changes in tissue shape and the number of cell contacts can modify the growth of mouse trophoblast and alter its ability to become giant.
Effect of culture conditions on diploid to giant-cell transformation in postimplantation mouse trophoblast
Authors: Rossant J. , Tamura-Lis W.
Published: April 2021

Diploid extraembryonic ectoderm and ectoplacental cone from the 7·5-day mouse embryo were grown in vitro under a variety of culture conditions in an attempt to discover conditions which maintain trophoblast in a diploid state and prevent giant-cell formation. It was found that maintenance of tissue integrity was not enough to keep the tissues dividing and diploid, but that the presence of inner-cell-mass derivatives did have some effect. This effect was only apparent when trophoblast cells were entirely enclosed by embryonic tissues. Monolayers of embryonic or embryonal carcinoma cells did not prevent giant-cell formation. Diploid extraembryonic ectoderm and ectoplacental cone responded differently: ectoplacental cells eventually formed trophoblast giant cells even when enclosed by embryonic cells whereas extraembryonic ectoderm cells apparently could be maintained in a diploid condition. This and other differences in properties between extraembryonic ectoderm and ectoplacental cone are discussed with reference to a new model for the postimplantation trophoblast lineage in the mouse.
Transdifferentiation of chicken embryo neural retina into pigment epithelium: indications of its biochemical basis
Authors: Pritchard D. J.
Published: April 2021

Neural retina from 8- to 9-day embryo chickens was grown in long-term cell culture in an experiment to test the hpothesis that one step during the in vitro transdifferentiation of neural retina into pigment cells occurs in response to stimulation of tricarboxylic acid (TCA) cycle activity. Time-lapse photography showed that pigment-cell formation occurs through the intermediate stages of ‘undistinguished cells’, ‘pavement epithelium’ and ‘potential pigment cells’. Mitosis of undistinguished cells to pavement epithelium was proportional to malonate over most of the tested range of concentrations and was inhibited by succinate, which respectively depress and stimulate the TCA cycle. Conversely mitosis of pavement epithelium to potential pigment cells occurred in proportion to succinate concentration over most of the tested range and was inhibited by malonate, in support of the hypothesis under test.

Melanin synthesis begins in a minority of ‘pigment leader cells’ uniquely stimulated by the lowest concentration of malonate, although higher concentrations blocked pigment synthesis in all cell types. The pigment leader cells appear to act as centres of influence upon neighbouring potential pigment cells, which subsequently also beome pigmented. Lactate inhibited most or all of the steps in formation of pigment epithelium.

Between three and five mitoses occur in the production of pigment cells, whereas multilayers and lentoid bodies seem to be formed by expansion of undistinguished cells, probably without mitosis.

The observations lead to a general theory that metaplastic conversion between cell types in eye tissues may require the physical isolation of overtly differentiated, multipotent cells from ‘leader’ cells which normally hold them in physiological subjugation.
Amphibian pronephric duct morphogenesis: segregation, cell rearrangement and directed migration of theAmbystomaduct rudiment
Authors: Poole T. J. , Steinberg M. S.
Published: April 2021

The axolotl pronephric duct rudiment is readily accessible to both SEM observation and surgical manipulation. The rudiment segregates from the dorsal part of the lateral mesoderm and then extends caudally along the ventrolateral border of the segmenting somites, eventually contacting the cloacal wall. The marked thinning of the rudiment which accompanies this migration is paralleled by a corresponding reduction in cell number across the duct’s diameter and by caudad translocation and elongation of vital dye marks applied to the duct mesoderm. Duct extension thus involves appreciable cell rearrangement. The morphology of duct mesoderm and its substratum (somite and lateral mesoderm) suggests that active locomotion of cells near its tip marshals the duct’s caudad elongation. Filopodia and small focal areas of intercellular contact may mediate the adhesions between duct cells which must be broken and reformed as the cells rearrange.
Positional signalling along the anteroposterior axis of the chick wing. The effect of multiple polarizing region grafts
Authors: Wolpert L. , Hornbruch Amata
Published: April 2021

We have proposed that positional information along the anteroposterior axis is specified by a signal from the polarizing region and that position may be specified by the concentration of a diffusible morphogen. While this model can account for a variety of results it is now clear that a model based on intercalation by growth of positional values can do the same. The distinction between the two models lies in whether a grafted polarizing region can alter existing positional values and in the distance over which it exerts its influence. The two models make different predictions as to the effect of grafting two polarizing regions. The intercalation model predicts that this effect will be the sum of two single grafts, whereas the morphogen model predicts different results depending on how close together the two polarizing regions are placed. The pattern of digits following grafts of two polarizing regions show that it is sensitive to the distance between the grafts and consistent with a model based on long-range interaction, such as a diffusible morphogen.
The control of growth and the development of pattern across the anteroposterior axis of the chick limb bud
Authors: Summerbell Dennis
Published: April 2021

Two grafts of zone of polarizing activity (ZPA) were made to host limb buds. The grafts define the width of the shared responding field lying between them. They cause a change in the growth pattern of the bud so that there is an increase in the width of the tissue between the grafts. Concurrently they redefine (respecify) cell states in the responding tissue so as to cause formation of a mirror-image reduplicate hand between them. The number and type of digits formed depends on the initial distance between the grafts.

The results suggest that the initial presumptive hand field is very small (∼ 300μm), that it is not a classical morphallactic system, and that it is able to regulate its growth pattern. A point-source diffusion model is presented.