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J Cooke

Publications and source records attributed to J Cooke.

At least 127 records · Page 7Linked to original sources
PubMed1985

Early specification for body position in mes-endodermal regions of an amphibian embryo.

Specification for development of the body pattern in the amphibian embryo has usually been thought of as a prolonged process, initiated from an ooplasmic localisation of some kind in what will become the dorsal-anterior midline. The evidence has been interpreted as suggesting that this initial localisation is centred in what will become anterior endoderm, but gives rise by an inductive process in early blastula stages to an overlying organising centre which eventually controls the genesis of mesodermal pattern. Neurectodermal development (especially, the position and pattern of the central nervous system) is seen as controlled considerably later, by inductive signals from submigrating mesoderm at gastrulation. Current work tends to confirm that this sequence of inductive influences can occur at least in experimental situations. It also suggests, however, that in the normal development of the rather small egg of Xenopus, genesis of positional cues that specify the body pattern contributions within the more vegetal material (mes-endoderm) is a rather rapid, widespread and direct consequence of events occurring in the interval between fertilisation and cleavage. Possible molecular bases of early nuclear responses to position within egg material, and the more problematic nature of the positional system itself, are discussed.

Animals↗
PubMed1985

Studies of zinc metabolism in pregnant and lactating rats.

The metabolism of 65Zn administered intramuscularly (Expt 1) or enterally (Expt 2) at the beginning of pregnancy in rats given a control or marginal-Zn diet was measured. In Expt 2 a comparison was also made between pregnant and non-pregnant rats. The loss of 65Zn (assumed to represent labile body Zn) was markedly reduced in animals fed on a marginal-Zn diet compared with controls, and this effect occurred very rapidly, i.e. within 48 h of introducing the marginal-Zn diet. Pregnancy itself had a much less important effect on 65Zn turnover than diet. Transfer of 65Zn to the litter was significantly greater in the animals fed on a marginal-Zn diet compared with controls but total Zn transfer was reduced. The effect of length of time on a marginal-Zn diet on fetal growth and composition was examined. Compared with controls, fetal weight was significantly greater in litters from mothers fed on a marginal-Zn diet during the last 4, 7 or 14 d of pregnancy, but no different in litters from mothers fed on a marginal-Zn diet throughout pregnancy. There were no differences in the proportions of protein or fat in the fetuses from mothers fed on the control or marginal-Zn diets but the Zn concentration was lower in litters from mothers fed on a marginal-Zn diet during part or all of the pregnancy when compared with controls. The transfer of 65Zn from mothers to litters during birth and the first 3 d of lactation was measured. There were no differences in maternal or litter 65Zn just before or just after birth, but within 72 h maternal 65Zn had significantly decreased and litter 65Zn increased. Increases in litter size were associated with greater total litter 65Zn but reduced individual fetal 65Zn. These experiments demonstrate the importance of an adequate daily supply of Zn during pregnancy. Although there is room for adaptation to a marginal-Zn intake (by reducing Zn excretion) the maintenance of Zn homeostasis is only possible in the absence of other forms of stress, such as pregnancy, to the body. The consequence of insufficient Zn at times of rapid fetal growth on carbohydrate and lipid metabolism warrants further investigation.

Animals↗
PubMed1985

Subpulmonary pleural effusions in children after cardiac surgery.

Postoperative chest radiographs on 100 children who had undergone cardiac operations were evaluated to determine the frequency of subpulmonary effusions after surgery. Of the 83 patients in whom adequate erect postoperative radiographs were available, 9 (11%) had effusions confirmed by lateral decubitus radiographs. On the frontal chest x ray film, the evidence of an effusion was an increase in distance between the diaphragm and air in the gastric fundus, or an apparent elevation of the right hemidiaphragm. None of the patients examined echocardiographically had associated pericardial effusions. When a subpulmonary effusion was detected diuretic treatment was started or continued. None of the patients had radiographic evidence of residual fluid when they were seen two weeks after their discharge from hospital.

Adolescent↗
PubMed1985

The system specifying body position in the early development of Xenopus, and its response to early perturbations.

Evidence is presented that the system setting up preliminary specifications for contributions to the axial body plan, across vegetal regions of the Xenopus embryo, acts in a widespread way at early stages. Mechanisms that regulate the spatial profile of this primary positional variable, and thus ensure the constancy and harmony of the body plans normally achieved, have lost this integrative ability by the 4-cell stage one hour after the plasm shifts that precede first cleavage and symmetrize the egg. Abnormal, partial or distorted profiles of the positional system across whole eggs or isolates, recorded by these times, are retained to give correspondingly partial or imbalanced mes/endodermal pattern at tailbud larval stages. There is evidence that subsequent 'back-up' positional interactions, which can heal gross positional discontinuities in isolated presumptive lateral half-eggs and so restore bilateral symmetry, also do this at the price of loss of complete pattern specification. This is probably because of an asymmetrical principle whereby relatively activated (dorsoanterior specified) material can raise the level of originally posterior material on contact, whereas the reverse interaction cannot occur. The observations are discussed in relation to apparently different behaviour in certain other amphibian embryos, and to our knowledge of other positional interactions, normal and also experimentally provoked, such as those that set up the germ layers.

Animals↗
PubMed1985

Dynamics of the control of body pattern in the development of Xenopus laevis. II. Timing and pattern in the development of single blastomeres (presumptive lateral halves) isolated at the 2-cell stage.

Xenopus embryos have been selected in which the first cleavage plane is tending strongly to correspond with that of bilateral symmetry for the future larval pattern. The two blastomeres produced by this cleavage have been separated and allowed to develop as reciprocal pairs of presumptive lateral-half isolates. The early development and the time course of the gastrulation movements, and the qualitative and quantitative aspects of larval mesodermal patterns, have been studied in relation to synchronously fertilized controls. The result is restoration of bilateral symmetry for developmental potential, and production of a pair of small gastrulae and larvae with qualitatively complete body plans but 50% of control cell numbers each (see Kageura & Yamana, 1983). Most commonly, however, the resulting small patterns deviate from the normal range in their proportions in at least one of two ways. The notochord territory is rarely, if ever, under-represented (i.e. notochords contain at least 50% control cell numbers) but it is frequently over-represented, in some cases approximating that of control whole embryos. Reciprocal pairs of isolates thus tend, on average, to produce more notochordal tissue than they would have if developing normally. Secondly, the balance of cell population sizes assigned to somites up and down the axis is altered so that relatively anterior members of the series are less scaled down than those in trunk and tail regions. The mesodermal plan developed by a lateral-half isolate is thus characteristically intermediate between that of a small, harmonious larva (the proportional presumptive fates of the materials, apart from loss of bilaterality), and that of the mosaically developing presumptive dorsoanterior cell pair from the 4-cell stage, discussed in the previous paper. A minority of the lateral isolates does develop a harmonious and thus well-regulated body plan, however, and the normality or otherwise of the schedules of gastrulation timing in isolates seems a good predictor of their morphogenetic performance in this respect. The results are discussed as informing us about the dynamics of the interactions, prior to gastrular stages, that underlie the normal mesoderm development.

Animals↗
PubMed1985

Dynamics of the control of body pattern in the development of Xenopus laevis. III. Timing and pattern after u.v. irradiation of the egg and after excision of presumptive head endo-mesoderm.

A series of Xenopus egg batches has been exposed to doses of u.v. (2537A) light on the vegetal hemisphere at precleavage stages, calculated to result in a range of minimal axial deficiency syndromes in the developing larvae. At the time of onset of gastrulation in synchronously fertilized but non-irradiated batch members, each experimental group was regularly scanned so that small subsamples of embryos could be set aside as showing particular, progressive degrees of delay in onset of the visible gastrulation movements. Such sampling was found to have preselected embryos showing generally progressive degrees of pattern impairment at larval stages, and this observation was extended by histological examination of the anterior axial anatomy. Such examination was also made of the least abnormal-looking members of a series of larvae resulting from excision of the presumptive head endo-mesoderm, traditionally called 'the organizer', from stage-10 gastrulae (Cooke, 1975). The results support the notion that production of the most anterior endo-mesodermal pattern parts (and of their inductive capacities in giving rise to the brain pattern) occurs only in material whose timing, in the onset of gastrulation activity, is close to the normal onset time after fertilization. Either an early failure of the egg to generate a location with the 'position value' corresponding with this extreme of the pattern, or the much later excision of the region from a physiologically normal gastrula, results in a system of pattern formation permanently truncated at its apical (head and dorsal) end. There is no evidence for any dynamic, in the system ascribing position value, that will cause regulative restoration of this cellular state (the most extreme 'activation' for development) in response to its absence after precleavage stages. An earlier statement (Cooke, 1975) that this could occur was based upon inadequate analysis of larvae with an often misleading external anatomy. The present results are discussed as supporting the overall view of the early Xenopus patterning system that has been developed in the previous two papers of the series.

Animals↗
PubMed1985

Dynamics of the control of body pattern in the development of Xenopus laevis. I. Timing and pattern in the development of dorsoanterior and posterior blastomere pairs, isolated at the 4-cell stage.

Xenopus embryos have been selected in which the second cleavage is occurring in a frontal plane, i.e. one tending to lie at right angles to the prospective plane of bilateral symmetry for the body pattern. Some of these have been used to deduce a map of the disposition of materials for the normal mesodermal pattern (the normal 'fate map') by injecting blastomeres to found fluorescently marked clones from 4- to 32-cell stages. Other such 4-cell embryos have been separated into two isolates across this second cleavage; in fate-map terms, prospective dorsoanterior and posterior isolates. These have been allowed to develop to control axial larval stages, with examination of the time schedule of their gastrulation movements in relation to cofertilized whole controls. The patterns of mesoderm produced have been examined and interpreted in the light of quantitative knowledge about the normal pattern, and our current understanding of the map. A meaningful fate map exists for the egg material even at this early, essentially acellular stage, and it differs appreciably from what might have been expected in view of that traditionally shown for early gastrula stages. The patterns developed in the isolates show that at least in many eggs, widespread information that positively specifies material as to its body position is available from at most 1 h after the events that give rise to bilateral symmetry upon fertilization. This information usually leads to a mosaic development of the appropriate mesodermal part-pattern in dorsoanterior isolates, and frequently allows development that approximates to this in the reciprocal posterior part. Regulation, i.e. the replacement of removed information to specify a development more complete than the normal contribution in isolates, is not observed. The results suggest a revision of former claims for regulative ability in at least this amphibian embryo. They also imply that systems for ascribing position value (positional information) to early embryonic tissue can be diverse in dynamics, even among embryos whose body plans are obviously homologous as are those of vertebrates.

Animals↗
PubMed1983

Evidence for specific feedback signals underlying pattern control during vertebrate embryogenesis.

Experiments are described in which sectors including dorsolateral mesoderm from early-neurula-stage amphibian embryos are grafted to the mid-ventral region of gastrula-stage hosts. The grafted tissue pursues an autonomous developmental sequence, though integrated into the host mesodermal mantle, so that such embryos develop a ventral strip of ectopic somite tissue, occasionally with a pronephric formation at one side. When the proportions in which mesodermal tissue has been assigned to the four basic territories of the host's mediolateral pattern are assayed, a significant deficit in somite is characteristically found, though the phenomenon is variable in magnitude. It seems that the size of the host's pronephric territory may be diminished in a similar way, if an earlier differentiating ectopic pronephros is already joined to the system. These phenomena are discussed in relation to theories of biological pattern formation.

Ambystoma mexicanum↗
PubMed1983

The positional coding system in the early eye rudiment of Xenopus laevis, and its modification after grafting operations.

In a series of Xenopus embryos, 60-90 degrees sectors at various positions distributed around the eye rudiment were replaced with sectors grafted from the opposite position in the rudiment on the same side of the head of a donor. The majority of the operations were carried out before stage 28 (Nieuwkoop & Faber, 1956), and many before stage 26. The patterns of retinotectal connectivity which then developed were assayed electrophysiologically soon after metamorphosis. The visuotectal maps were frequently compound, giving evidence that many parts of the rudiment had already been equipped with distinct tissue positional codes by the time operations were performed (i.e. before neurogenesis). Although graft-derived sectors of retina connected to tectal sectors that were more nearly appropriate for their original positions in the rudiment than for their translocated ones, the 'handedness' of these ectopic components of the compound maps tended to bear a mirror-image relation to the major map, rather than the point-symmetrical one to be expected from a complete autonomy of mapping functions in grafted tissue. The results are discussed in relation to possible modes of organization of the developing eye, considered as a pattern-forming system.

Animals↗
PubMed1981

The problem of periodic patterns in embryos.

A segmented body-plan has developed at least twice during metazoan evolution: in the lineage including annelids and arthropods, where the segment is the unit of body structure, and in the ancestors of vertebrates, where a primary segmentation of the middle, mesodermal cell layer of the embryo imposes a spatially periodic character upon derivatives of other layers. The mechanism controlling the development of these periodic patterns has the property that the number of the serially homologous structures formed within each species is largely independent of the linear dimension, or scale, at which pattern formation occurs in individual cases. In this they contrast with other patterns of dispersed, homologous structures occurring in animal epidermis and dermis. The performance of various classes of model for the control of number in vertebrates somite formation are compared, in the light of experimentally and naturally observable properties of this aspect of pattern.

Animals↗
PubMed1981

Scale of body pattern adjusts to available cell number in amphibian embryos.

In many embryos, the removal of cells whose descendants would normally have formed entire parts of the body pattern is followed by apparently normal morphogenesis, which implies an ordered readjustment of the activities of the remaining cells before their potentialities become restricted. Special cell lineages cannot underly the generation and regulation of pattern in such embryos. It is proposed instead that there must be some regulatory communication system in the developing embryo that normally ensures an appropriate spatial pattern of differentiation but which is also able to adjust to the removal, addition or transposition of material at a sufficiently early stage. Precise models for such a mechanism have recently been suggested, and have been tested experimentally. I have performed surgical manipulations at pre-gastrula embryonic stages in two distinctly related amphibian types, Xenopus and Ambystoma, and report here an assessment of the regulation achieved in terms of pattern proportions. The results are problematical for most current theories of pattern control.

Ambystoma↗