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Biomedical subjects

J Cooke

Publications and source records attributed to J Cooke.

At least 145 records · Page 8Linked to original sources
PubMed1981

Control of growth related to pattern specification in chick wing-bud mesenchyme.

The 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 500 mum 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 the the graft after this operation. The results are discussed, in relation to current ideas about the control of pattern during limb development.

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PubMed1980

Cell cycle and experimental pattern duplication in the chick wing during embryonic development.

Transient stimulation of cell division within chick wingbud mesenchyme is associated with the reorganization of limb pattern that follows insertion of a small graft from the posterior zone of limb polarizing activity into the anterior border of a host bud. This increase is initiated as an enhanced rate of entry to S phase, correlated with a decrease in packing density among mesenchyme cells, through much of the limb rudiment a few hours after the operations.

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PubMed1980

Somitogenesis in amphibian embryos. III. Effects of ambient temperature and of developmental stage upon pattern abnormalities that follow short temperature shocks.

Temperature shocks of a few minutes duration at 37 degrees C to tail-bud embryos of Rana induce zones of abnormal segmentation along the somite files subsequently produced. The immediate result of a temperature shock is a temporary arrest of development as a whole, following which the schedule of somite determination and formation is resumed at the normal rate. It is during the period immediately following this that the zone of abnormal somite pattern is determined. Thus the length of the abnormal zone reflects the total time taken by the morphogenetic system to recover from the disturbance, and might depend upon variables affecting both the duration of the initial arrest and the duration of the recovery period itself. Observations are presented demonstrating how the length of abnormal zones, caused by a temperature shock of any particular severity, are affected by three variables; (1) the ambient temperature to which the embryos were adapted before shock, (2) the ambient temperature of post-shock development, (3) the stage in somitogenesis, i.e. the number of somites already formed at the time of shock. The data (in this and previous papers of the series) support models postulating that the spatial periodicity in cell behaviour, that is somite morphogenesis, reflects a normal interaction between two hidden aspects of development, one a wavefront of cellular activation passing down the body axis, and the other having the character of a temporal periodicity throughout the tissue. Temperature shock, as well as halting the wavefront (i.e. stopping development) temporarily, leads to a subsequent period during which there is only gradual recovery of normal co-ordination between the periodicity within cells of the tissue and the wavefront progress. It is the relative rate of this recovery, alone, that is responsible for variation in the length of the abnormal zone.

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PubMed1979

Patients' reactions to a two-way mirror in general practice.

From a survey of 200 patients in two general practices it would appear that the patients' reaction to the use of a two-way mirror is on the whole not unfavourable. The results suggest, however, that in the very personal setting expected of general practice people suffering from psychiatric problems (especially depression) should be given every opportunity to decline consultation in front of the mirror and if any patient becomes upset, then the mirror should be 'turned off' immediately. Internal examinations should not take place when the mirror is in use.

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PubMed1979

Cell number in relation to primary pattern formation in the embryo of Xenopus laevis. I. The cell cycle during new pattern formation in response to implanted organizers.

Results are presented which offer strong evidence that extensive alteration of the fates of embryonic Xenopus cells occurs independently of the schedule of cell division, after operations which lead to a doubling of the axial pattern of mesodermal differentiation in the gastrula. The experimental strategy was to make estimates of total mesodermal cell numbers and mitotic index in closely matched sets, each of three synchronous sibling embryos, fixed during the ten hours following the close of gastrulation. Within each set two embryos, an unoperated control and a sham-operated embryo whose own dorsal-lip (organizer) cells had been replaced with an equivalent graft, were developing normally. The third, experimental embryo had received an organizer implant to replace an equivalent number of cells from its ventral marginal zone, and was thus developing two axial mesodermal patterns of differentiation in relation to two dorsal midlines, the extra pattern embracing much host tissue. Mitotic index was also determined, in specific regions and throughout the mesoderm, in similar sets of embryos but at mid-gastrula stages. The conclusions are justified by the results of a control investigation which show that there is normally no difference in cell cycle time along the presumptive dorso-ventral mesodermal, dimension, during the interval between time of operations and the determination of pattern. The lack of any enhancement of mesodermal cell number in late embryos with dual axia patterns, or intervening enhancement of mitotic index in younger operated embryos, thus suggests that new patterns may be determined in the Xenopus gastrula without generation of extra cells. The results are discussed in relation to recent ideas about pattern formation, and the concepts of morphallaxis and epimorphosis.

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PubMed1979

Cell number in relation to primary pattern formation in the embryo of Xenopus laevis. II. Sequential cell recruitment, and control of the cell cycle, during mesoderm formation.

Morphological evidence is presented that definitive mesoderm formation in Xenopus is best understood as extending to the end of the neurula phase of development. A process of recruitment of cells from the deep neurectoderm layers into mesodermal position and behaviour, strictly comparable with that already agreed to occur around the internal blastoporal 'lip' during gastrula stage 20 (earliest tail bud). Spatial patterns of incidence of mitosis are described for the fifteen hours of development between the late gastrula and stage 20--22. These are related to the onset of new cell behaviours and overt cyto-differentiations characterizing the dorsal axial pattern, which occur in cranio-caudal and then medio-lateral spatial sequence as development proceeds. A relatively abrupt cessation of mitosis, among hitherto asynchronously cycling cells, precedes the other changes at each level in the presumptive axial pattern. The widespread incidence of cells still in DNA synthesis, anterior to the last mitoses in the posterior-to-anterior developmental sequence of axial tissue, strongly suggests that cells of notochord and somites in their prolonged, non-cycling phase are G2-arrested, and thus tetraploid. This is discussed in relation to what is known of cell-cycle control in other situations. Best estimates for cell-cycle time in the still-dividing, posterior mesoderm of the neurula lie between 10 and 15 h. The supposition of continuing recruitment from neurectoderm can resolve an apparent discrepancy whereby total mesodermal cell number nevertheless contrives to double over a period of approximately 12 h during neurulation when most of the cells are leaving the cycle. Because of pre-existing evidence that cells maintain their relative positions (despite distortion) during the movements that form the mesodermal mantle, the patterns presented in this paper can be understood in two ways: as a temporal sequence of developmental events undergone by individual, posteriorly recruited cells as they achieve their final positions in the body pattern, or alternatively as a succession of wavefronts with respect to changes of cell state, passing obliquely across the presumptive body pattern in antero-posterior direction. These concepts are discussed briefly in relation to recent ideas about pattern formation in growing systems.

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PubMed1979

The orientation of the visuotectal map in Xenopus: developmental aspects.

Rotations and translocations of the eye anlage were performed in Xenopus embryos of stages ranging from 21/22 to 30. Some of the operations involved grafting wild-type eye anlagen into albino host orbits. Operations were performed under a variety of operating media and conditions. In later larval life, or after metamorphosis, the visuotectal maps from the operated eyes were recorded electrophysiologically. Results fell into two classes. In the majority, the orientation of the visuotopic map corresponded to the orientation of the eye at the time of recording. In the minority the visuotopic maps were 'compound', consisting of two parts each with its own independent orientation. The organization of the compound maps was such that one component was oriented in correspondence with the orientation of the eye, while the other component was normally oriented. Histological analysis and observations on genetically marked grafts indicated that the component parts of the compound eye were of dual cellular origin. The component giving the rotated (or translocated) map belonged to the originally operated eye tissue; whereas the component giving the normally oriented map was derived from newly grown eye tissue coming from the optic stalk. In no case was a normally oriented map obtained from a rotated or translocated eye. The results are discussed in relation to mechanisms proposed to account for the determination of map-related retinal specificity.

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PubMed1978

Somite abnormalities caused by short heat shocks to pre-neurula stages of Xenopus laevis.

This paper describes the small disturbances, in the regular pattern of the somites and the fissures between them, that are seen following short (around 300 s) heat shocks at 37.5 degrees C delivered to pre-neurula stages of Xenopus laevis. Affected groups of cells still finally differentiate as somite muscle, but the normally precise spatio-temporal sequence in which they move beforehand to give rise to the actual pattern of somite blocks, is disrupted. Examination of the position and sizes of patches of disrupted morphogenesis, in relation to the precise embryonic stage at shock, leads to certain conclusions about the nature of the disturbance induced by a brief period at high temperature, in cells due to form somites. The pattern of results is compared with that produced by similar temperature shocks given to tail-bud (later) staged embryos. The discussion includes a brief consideration of how the various results of heat shocks, given at different embryonic stages, might be understood in terms of one particular model (Cooke & Zeeman, 1976) for the spatio-temporal control of the developing somite pattern.

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