bluuebunny/crossref_metadata_2025_split huggingface dataset:
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

ABSTRACTThe 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

ABSTRACTSome 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

ABSTRACTA 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

ABSTRACTA 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

ABSTRACTA 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

ABSTRACTMice 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

ABSTRACTLittle 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

ABSTRACT
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

ABSTRACTAccording 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

ABSTRACTEmbryonic 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

ABSTRACTThree 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

ABSTRACTRight 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

ABSTRACTThe 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

ABSTRACTThe 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

ABSTRACTThe 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

ABSTRACT
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

ABSTRACT
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

ABSTRACT
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

ABSTRACT
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.