bluuebunny/crossref_metadata_2025_split huggingface dataset:
Polymorphism and specificity of positioning of contractile vacuole pores in a ciliate,Chilodonella steini
Authors: Kaczanowska Janina 
Published: April 2021

ABSTRACTThe unicellular ciliate Chilodonella steini has a well-defined flat and ciliated ventral field. During divisional morphogenesis two sets of new contractile vacuole pores (CVPs) are formed on this field. During final pattern formation some of these CVP primordia and the old parental set of CVPs are completely resorbed. Primary pattern of distribution of the CVP primoidia and final pattern of distribution of the matured CVPs manifest an intraclonal polymorphism.From analysis of this polymorphism some features of mechanism(s) of CVP pattern determination are deduced:There is a strict, short-distance negative control of appearance of CVP primordia at sites of oral morphogenesis and around the ventral field. Certain indeterminacy of large-scale patterning of CVP primordia is observed over the area competent to yield CVP formation. However, within this area three longitudinal sectors with a high probability of occurrence of CVP primordia are alternated with sectors nearly deprived of their occurrence. Positive control of probability of occurrence and of specificity of location is found for certain CVP primordia. An interaction of mechanism of positioning on cellular longitudes and latitudes is proposed to account for these facts. The resorption of supernumerary CVP primordia does not alter the character of the global map of distribution of CVP primordia achieved during primary pattern formation. The primordia located at some latitudes persist, whereas others are resorbed at random. It is suggested that all CVP primordia which do not mature at the time of stabilization of divisional morphogenesis are resorbed. Thus the global map of CVPs distribution would result from the sum of the individual determinations of the fates of each CVP primordium, superimposed on an initial spatially non-uniform distribution of CVP primordia.
Morphallaxis in an epimorphic system: size, growth control and pattern formation during amphibian limb regeneration
Authors: Maden M. 
Published: April 2021

ABSTRACT
An essential component of most theories of pattern formation in epimorphic systems is that growth and pattern formation are strictly linked. Furthermore it has been assumed that epimorphic systems display size dependence, i.e. the pattern elements are always of a fixed size. These assumptions are challenged in the work described here on amphibian limb regeneration. The sizes of elements regenerating from small and large limbs and from normal and partially denervated limbs have been measured along with a detailed study of their subsequent growth stages. It is shown that the size of elements within one group of animals is remarkably constant even though their final, adult size is very different. But between groups of animals (large versus small or normal versus partially denervated) their sizes vary considerably. Therefore this classical epimorphic system is not size dependent, calling for a revision of current theoretical concepts. The similarities between this type of behaviour and that in morphallactic systems is discussed as well as similarities with growth control in limb development.
Control of growth related to pattern specification in chick wing-bud mesenchyme
Authors: Cooke Jonathan , Summerbell Dennis 
Published: April 2021

ABSTRACTThe distribution of raised mitotic index, and the co-incidence of this with lowered cell packing density, has been studied across the anteroposterior dimension of the terminal 500μm of chick wing buds following various numbers of hours signalling from an anteriorly grafted extra Zone of Polarizing Activity (ZPA). The results show propagation of the situation that causes these correlated phenomena, from graft-host interface essentially right across the limb mesenchyme, frequently within 8 h. This contrasts with the much slower and more local succession of changes in position memory, for differentiation of a duplicated limb pattern, that also occurs in mesenchyme relatively close to the graft after this operation. The results are discussed, in relation to current ideas about the control of pattern during limb development.
Pattern formation and growth in the regenerating limbs of urodelean amphibians
Authors: Holder Nigel 
Published: April 2021

ABSTRACT
The results of numerous types of grafting experiments involving the amputation of symmetrical limbs are described. These experiments were designed to test the tenets of the polar coordinate model. The analysis of the results of these grafts coupled with a quantitative analysis of blastemal shape strongly indicates that pattern regulation during amphibian limb regeneration can be understood in terms of the model.
Morphogenetic behaviour of the rat embryonic ectoderm as a renal homograft
Authors: Švajger Anton , Levak-Švajger Božica , Kostović-Knežević Ljiljana , Bradamante Želimir 
Published: April 2021

ABSTRACTHalves of transversely or longitudinally cut primary ectoderm of the pre-primitive streak and the early primitive streak rat embryonic shield developed after 15–30 days in renal homografts into benign teratomas composed of various adult tissues, often in perfect organspecific associations. No clear difference exists in histological composition of grafted halves of the same embryonic ectoderm.The primary ectoderm of the pre-primitive streak rat embryonic shield grafted under the kidney capsule for 2 days displayed an atypical morphogenetic behaviour, characterized by diffuse breaking up of the original epithelial layer into mesenchyme. Some of these cells associated into cystic or tubular epithelial structures.The definitive ectoderm of the head-fold-stage rat embryo grown as renal homograft for 1–3 days gave rise to groups of mesenchymal cells. These migrated from the basal side of the ectoderm in a manner which mimicked either the formation of the embryonic mesoderm or the initial migration of neural crest cells. This latter morphogenetic activity was retained in the entire neural epithelium of the early somite embryo but was only seen in the caudal open portion of the neural groove at the 10- to 12-somite stage.The efficient histogenesis in grafts of dissected primary ectoderm and the atypical morphogenetic behaviour of grafted primary and definitive rat embryonic ectoderm were discussed in the light of current concepts on mosaic and regulative development, interactive events during embryogenesis and positioning and patterning of cells by controlled morphogenetic cell displacement.
Catch-up growth
Authors: Williams J. P. G. 
Published: April 2021

ABSTRACT
Catch-up growth, defined as growth velocity above the statistical limits of normality for age or maturity during a defined period of time, is distinguished from compensatory growth since it makes up for a potential loss rather than an actual loss and is seen in the whole body as opposed to specific organs. The cellular explanation for catch-up based on the work of Winick is described and a recent challenge to this explanation is briefly discussed. The mechanism of mismatch between actual size and ‘planned’ size suggested by Tanner is described and tested. In a series of experiments conducted in rats of different ages the degree of mismatch and the role of catch-up are compared for two different parameters, body weight and nose-rump length. It was found that the two parameters behaved differently and it is suggested that while the concept of mismatch is still acceptable the idea of a single central mechanism is not supported. It is suggested that the mismatch mechanism is a cellular phenomenon.
Abnormal neural fold development in trisomy 12 and trisomy 14 mouse embryos
Authors: Putz Barbara , Morriss-Kay Gillian 
Published: April 2021

ABSTRACTThe early development of the exencephalic malformation in trisomy 12 (Tsl2) and trisomy 14 (Tsl4) mouse embryos was examined by means of scanning electron microscopy and compared with cranial neural tube formation in euploid litter-mates. Embryos from normal laboratory mice were used as additional controls.The euploid control embryos of the trisomy-inducing breeding system showed a slight delay and some variation in the timing of cranial neurulation. The pre-exencephalic trisomic embryos showed hypoplasia, and lower somite number when compared with euploid littermates; there was also a retardation of development of the whole neural tube, when related to the somite stage. External differences from the control embryos were observed at the late pre-somite stage, when the anterior part of the neural plate showed a crumpled appearance. At 6 somites the lateral edges of the forebrain were everted instead of elevated in Tsl2 and Tsl4 embryos. At later stages, however, the forebrain showed a tendency towards the normal morphogenetic pattern, so that the optic vesicles were eventually formed and the most anterior part fused. The caudal forebrain and the midbrain were more permanently affected by the disturbance of trisomic conditions and grew laterally, failing to appose or fuse in the midline in both Tsl2 and Tsl4 embryos. Hindbrain morphogenesis was different in Tsl2 and Tsl4 excencephaly : in Tsl2 embryos it did not close rostral to the otic pits, whereas in Tsl4 embryos it showed a normal closure up to the hindbrain/midbrain junction.These observations support the hypothesis that in mammalian embryos the mechanism of neural tube formation of the future brain region is more complex than that of the spinal neural tube and therefore may be more likely to react to a general delay of neurulation with a gross malformation.Tsl2 and Tsl4 exencephaly are due to a primary non-closure of the neural tube.
Interactions between compound and normal eye projections in dually innervated tectum: a study of optic nerve regeneration inXenopus
Authors: Straznicky Charles , Tay David 
Published: April 2021

ABSTRACTRight compound eyes were formed in Xenopus embryos at tailbud stages by the fusion of two nasal (NN), two temporal (TT) or two ventral (VV) halves. The left eye was kept intact. Two to four weeks after metamorphosis the optic nerve from the intact eye was severed to induce bilateral optic nerve regeneration. The contralateral retinotectal projections from the compound eye and the induced ipsilateral projections from the intact eye to the same (dually innervated) tectum were studied by [3H]proline autoradiography and visuotectal mapping from 3 to 6 months after the postmetamorphic surgery. The results showed that the NN, TT and VV projections, in the presence of optic fibres from the intact eye failed to spread across the whole extent of the dually innervated tectum. Unexpectedly the bulk of the regenerating projection from the intact eye was confined to the previously uninnervated parts of the dually innervated tecta, the caudomedial region in TT, the rostrolateral region in NN and the lateral region in VV eye animals. The partial segregation of the two populations of optic fibres in the dually innervated tectum has been taken as a further indication of the role of fibre-fibre and fibre-tectum interactions in retinotectal map formation.
Postembryonic development of the visual system ofPeriplaneta americana
Authors: Stark Robert J. , Mote Michael I. 
Published: April 2021

ABSTRACTThe compound eyes of Periplaneta americana are connected by optic fibre tracts to an optic lobe composed of three sequential ganglia, the lamina, the medulla and the lobula respectively. The eyes and optic ganglia are organized into repeating sub-units arranged in a regular pattern. During postembryonic development, the number of subunits in the eye (ommatidia) increases from between 50 and 60 to over 2000, with a concomitant increase in the size of the optic lobe ganglia. The patterns of cell growth and proliferation were examined in serial section autoradiagraphs prepared following long and short exposures to [3H]thymidine during each developmental stage. Aspects of structural differentiation were examined in reduced silver-stained sections of nymphs at each developmental stage. Growth of the eye and optic ganglia resulted from the continuous proliferation of new cells throughout postembryonic development. Unlike other body tissues, growth of this system was independent of the moulting cycle. The pattern of growth observed in the optic ganglia directly reflected the growth of the eye. Growth of the compound eye occurs from a special zone of proliferation and differentiation located along all but its posterior margin. The lamina and medulla both grow by cell proliferation from a single neuroblast region located at the apex of the angle subtended by them. Cells which proliferate distally from this region differentiate into lamina neurons, while those that proliferate proximally differentiate into medulla neurons. Axons growing from these two adjacent regions meet at and add new new fibres to the distal end of the medulla neuropil. Specificity of the interneuronal connexions appears to result from a precise temporospatial sequencing of growth with the formation of the optic ganglia dependent on retinal development.
The proportion and distribution of polarizing zone cells causing morphogenetic inhibition when coaggregated with anterior half wing mesoderm in recombinant limbs
Authors: Frederick Jeanne M. , Fallon John F. 
Published: April 2021

ABSTRACT
Previous work demonstrated that dissociated polarizing zone cells inhibit morphogenesis when dispersed among dissociated anterior wing mesoderm cells in recombinant limbs. In the present study the proportions and distribution of polarizing zone mesoderm which inhibit morphogenetic expression in recombinant limb buds were determined. Completely dissociated and pelleted anterior half wing mesoderm packed into leg ectodermal jackets produced slender, digit-like outgrowths of bilateral symmetry in 60 % of the cases. This represented the baseline with which recombinants containing polarizing zone cells were compared. The inhibitory influence was first detected when polarizing zone cells constituted 16 – 18 % of the mesodermal component of recombinant limb buds; at this percentage the incidence of distally complete outgrowths dropped to 23 % of the cases. The addition of 20 – 36 % polarizing mesoderm to dissociated anterior half wing gave reduced incidence (9 %) of distally complete outgrowths. Percentages greater than 36 % polarizing zone cells led to the total failure of distally complete limb-like morphogenesis in all cases. Further, when more than 60 % polarizing mesoderm was dispersed with anterior half mesoderm, the outgrowths obtained were small, fleshy, and completely deficient in limb character. Finally, the distribution of polarizing mesoderm in recombinant grafts was demonstrated to be random at all percentages examined through 8 days, using chick/quail and autoradiographic methods. In a separate set of experiments, flank mesoderm was not found to have the same inhibitory effect on recombinant limb morphogenesis as described for polarizing mesoderm.
Studies of early stages of differentiation of the cellular slime mouldDictyostelium discoideum
Authors: Sharpe P. T. , Treffry T. E. , Watts D. J. 
Published: April 2021

ABSTRACTCountercurrent distribution in a polymer, two-phase system has been used to study changes in the cell surface properties of amoebae of Dictyostelium discoideum. Amoebae harvested during exponential growth in axenic culture and during the subsequent first six hours of development on Millipore filters were distributed as a single peak. However, the position of the peak changed during the period of early development which showed that changes in cell surface properties were occurring. At aggregation (8 h), the peak markedly broadened, indicating considerable increase in cell surface heterogeneity amongst the amoebae, and heterogeneity was so great by 9 –10 h that the amoebae distributed as two peaks. Amoebae from one peak were shown to be precursors of spores while amoebae from the other peak appeared to be precursors of stalk cells. Similarly, amoebae from the trailing and leading edges of the broad peak, formed from amoebae beginning to aggregate (8 h), were found to have different fates. Thus cell differentiation had been found at times of development prior to formation of aggregates having apical tips or anterior-posterior polarity and neither of these features of aggregates can be essential for initiation of cell differentiation. It is therefore concluded that differentiation is not initiated in D. discoideum in response to ‘positional information’.
Calcium and wound healing in Xenopus early embryos
Authors: Stanisstreet Martin 
Published: April 2021

ABSTRACT
The role of calcium in the healing of wounds made in the ectoderm of Xenopus neurulae has been studied. Embryos have been wounded in the presence of calcium inhibitors, and the effects on wound healing observed by scanning electron microscopy. In addition, unwounded embryos have been exposed to a local application of ionophore A23187 to simulate the possible calcium fluxes following wounding. Lanthanum, which competes for calcium channels, inhibits wound healing. EDTA, which binds divalent cations, also inhibits wound healing, but its effect can be reversed by the addition of excess calcium. Local application of ionophore A23187, which promotes transport of calcium across biological membranes, results in a local change in cell shapes. These observations lend support to the hypothesis that wound healing in amphibian early embryos, which is effected by changes in cell shapes similar to those seen in certain examples of normal morphogenesis, is initiated by a local influx of calcium into cells.
Turnover of embryonic messenger RNA in preimplantation mouse embryos
Authors: Kidder Gerald M. , Pedersen Roger A. 
Published: April 2021

ABSTRACTWe have estimated the average half-life of embryonic messenger RNA in mouse embryos at two stages of preimplantation development. Embryos were collected at 48 and 75 h post-hCG and cultured overnight in the presence of [3H] uridine. Beginning at 65 –68 h (morulae) or 92 –94 h (early blastocysts), the label was withdrawn and replaced with unlabelled uridine, and samples were taken at intervals thereafter for RNA isolation. Label in cytoplasmic, poly(A)-containing RNA was measured after binding to oligo(dT)-cellulose, and was normalized to label in 28S and 18S ribosomal RNA, separated on sucrose gradients. The stability of rRNA in both stages was verified directly, as was the integrity and purity of the isolated mRNA. With morulae, the mRNA decay curve was monophasic, with an average half-life of 9 ·5 ±0 ·9 h. In three experiments with early blastocysts the decay curve appeared to be biphasic, consisting of short-lived (less than 6 h) and long-lived (30 –50 h) components; in two other experiments a short-lived component was not evident. In all cases, however, the overall average half-life of mRNA in early blastocysts, determined by linear regression assuming monophasic kinetics, was greater than that in morulae. Our data indicate that the stability of embryonic mRNA increases by at least twofold during the morula-to-blastocyst transition. The results are considered in terms of the transcriptional dependency of early mouse embryos and the regulation of maternal and embryonic mRNA.
Interaction of granule, Purkinje and inferior olivary neurons in Lurcher chimaeric mice : I.Qualitative studies
Authors: Wetts Richard , Herrup Karl 
Published: April 2021

AbstractHeterozygous lurcher (+/Lc) mutant mice lose 100% of their Purkinje cells (PCs), 90% of their granule cells, and 75 % of their inferior olivary neurons. In order to determine the primary site of Lc gene action, lurcher ↔ wild-type aggregation chimaeras were produced. The cerebella of the three chimaeras examined were intermediate or normal in size compared to + /Lc and wild-type cerebella. The PCs were reduced in number. Using the β-glucuronidase locus (Gus) as a cell marker, all of the PCs present were identified as having descended from the wild-type embryo. It appears that all of the + /Lc PCs degenerated. Hence, the Lc gene acts directly on PCs to cause their degeneration.The inferior olivary nuclei of the chimaeras seemed to have fewer neurons than wild-type but more than + /Lc animals. As revealed by β-glucuronidase histochemistry, both + /+ and + /Lc cells were present, and the ratio of genotypes was similar to the ratio seen in other regions of the brain. The evidence suggests that the death of olivary neurons in lurcher is secondary to another defect, probably the loss of PCs. β-glucuronidase is not an accurate cell marker for granule cells, and so no conclusion concerning the action of the Lc gene on granule cells could be made with these chimaeras.
Normal anterior pattern formation after barrier placement in the chick leg: further evidence on the action of polarizing zone
Authors: Rowe Donene A. , Fallon John F. 
Published: April 2021

ABSTRACT
Impermeable barriers were inserted into the stage-20 to -21 leg bud to test whether or not such an interruption of diffusion of the proposed morphogen from the polarizing zone would result in failure of leg elements to develop anterior to the barrier. Tantalum foil was placed at somite levels 30/31 or mid-31 through the dorsoventral extent of the leg bud separating anterior from posterior mesoderm and ectodermal ridge. In the resulting legs, structures developed anterior to the level of the barrier. For example, legs with foil at the 30-/31-somite level developed digits 1 and 2. We conclude that either the barrier is not an effective block of diffusion of polarizing zone morphogen or that the influence of the polarizing zone is not required for determination of leg structures at these stages.
Importance of trophoblast genotype for survival of interspecific murine chimaeras
Authors: Rossant J. , Mauro V. M. , Croy B. A. 
Published: April 2021

ABSTRACTInterspecific chimaeras between Mus musculus and Mus caroli were made by injection of M. musculus inner cell masses (ICMs) into M. caroli blastocysts, and by aggregation of 8-cell embryos. Both types of chimaera were transferred to M. musculus recipients: the former did not survive to term, but viable chimaeras were produced following embryo aggregation. Previous experiments have shown that chimaeras produced by injection of M. caroli ICMs into M. musculus blastocysts are viable, whereas M. caroli blastocysts cannot survive in the M. musculus uterus. These results indicate that the presence of tropho-blast cells of maternal uterine genotype allows M. caroli ↔ M. musculus chimaeras to survive in the M. musculus uterus. It is suggested that M. musculus trophoblast components may protect the M. caroli embryonic cells from maternal immune rejection.