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

Development ◽  
1978 ◽  
Vol 45 (1) ◽  
pp. 283-294
Author(s):  
Jonathan Cooke
Keyword(s):  
High Temperature ◽  
Xenopus Laevis ◽  
Temporal Sequence ◽  
Embryonic Stage ◽  
Regular Pattern ◽  
Tail Bud ◽  
Heat Shocks ◽  
Similar Temperature ◽  
Spatio Temporal ◽  
Small Disturbances

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 °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.

Mitotic activity of germ cells during normal development of Xenopus laevis tadpoles

Development ◽  
1975 ◽  
Vol 34 (3) ◽  
pp. 687-694
Author(s):  
Ken-Ichi Ijiri ◽  
Nobuo Egami
Keyword(s):  
Xenopus Laevis ◽  
Germ Cell ◽  
Mitotic Activity ◽  
Germ Cells ◽  
Regional Difference ◽  
Normal Development ◽  
Uniform Value ◽  
Interesting Conclusion ◽  
Spatio Temporal ◽  
Gland Development

Data on the spatio-temporal pattern of germ cell proliferation in Xenopus laevis tadpoles were obtained, tracing the germ cells from the cloacal position forward. This spatial pattern in germ cell distribution and its change during normal development clearly coincided with histological observations of germ gland development. By application of regression lines to the analysis of this complex pattern, an interesting conclusion about the mitotic activity of germ cells was suggested. While the mitotic activity of germ cells before sexual differentiation shows a regional difference along the germ-cell-containing ridge (GCCR), the doubling time of sexually differentiated gonia seems to show a uniform value over the whole GCCR

Retrieval of spatio-temporal sequence in asynchronous neural network

1990 ◽  
Vol 41 (6) ◽  
pp. 3346-3354 ◽  
Author(s):  
Hidetoshi Nishimori ◽  
Tota Nakamura ◽  
Masatoshi Shiino
Keyword(s):  
Neural Network ◽  
Temporal Sequence ◽  
Spatio Temporal

The role of water-regulating mechanisms in the development of the haploid syndrome in Xenopus laevis

Development ◽  
1972 ◽  
Vol 28 (2) ◽  
pp. 449-462
Author(s):  
Louie Hamilton ◽  
P. H. Tuft
Keyword(s):  
Xenopus Laevis ◽  
Cell Number ◽  
Gastrula Stage ◽  
Tail Bud ◽  
Volume Changes ◽  
Membrane Area ◽  
Flow Through ◽  
The Difference ◽  
Haploid Embryos

The uptake of water by haploid and diploid sibling embryos of Xenopus laevis has been investigated by measuring the density changes which occur during the development of intact embryos from the blastula to the late tail-bud stage, and of explants from which most of the presumptive endoderm has been removed. The results show that up to the mid-gastrula stage there is no difference between the haploid and diploid embryos; but from then on, whereas the diploid volume increases steadily, the haploid gastrulae undergo a series of cyclical volume changes due to loss of fluid through the blastopore. It is concluded that this is the result of an excessive inflow of water through the haploid ectoderm, because it was found that the volume of haploid ectodermal explants increased much more rapidly than the volume of similar diploid explants. Excess flow through the haploid ectoderm also accounts for other characteristics of the haploid syndrome – microcephaly and lordosis. It is suggested that it is the doubling of the cell number in haploid embryos with the consequent 25% increase in aggregate cell membrane area which accounts for the difference between the uptake of water by the two types of embryos. It is also suggested that changes in the rate of water flow through the ectoderm and endoderm which are thought to account for the accumulation of water in the blastocoel and archenteron in the normal diploid embryo arise in a similar way.

The effect of egg rotation on the differentiation of primordial germ cells in Xenopus laevis

Development ◽  
1985 ◽  
Vol 90 (1) ◽  
pp. 79-99
Author(s):  
J. H. Cleine ◽  
K. E. Dixon
Keyword(s):  
Xenopus Laevis ◽  
Germ Cells ◽  
Germ Plasm ◽  
Primordial Germ Cells ◽  
Intermediate Zone ◽  
Gastrula Stage ◽  
Tail Bud ◽  
Axis Orientation ◽  
Early Gastrula ◽  
Number Of Cells

Eggs of X. laevis were rotated (sperm entrance point downwards) either through 90° (1×90 embryos) or 180° in two 90° steps (2×90 embryos) at approximately 25–30 min postfertilization after cooling to 13°C. The embryos were kept in their off-axis orientation and cooled until the early gastrula stage. Rotation resulted in relocation of egg constituents with slight changes in the distribution of outer cortical and subcortical components and major changes in inner constituents where the heavy yolk and cytoplasm appeared to reorient as a single coherent unit to maintain their relative positions with respect to gravity. Development of rotated embryos was such that regions of the egg which normally give rise to posterior structures instead developed into anterior structures and vice versa. Germ plasm was displaced in the vegetal-dorsal-animal direction (the direction of rotation) and was segregated into dorsal micromeres and intermediate zone cells in 2×90 embryos and dorsal macromeres and intermediate zone cells in 1×90 embryos. In consequence, at the gastrula stage, cells containing germ plasm were situated closer to the dorsal lip of the blastopore after rotation — in 2×90 gastrulas around and generally above the dorsal lip. Hence, in rotated embryos, the cells containing germ plasm were invaginated earlier during gastrulation and therefore were carried further anteriorly in the endoderm to a mean position anterior to the midpoint of the endoderm. The number of cells containing germ plasm in rotated embryos was not significantly different from that in controls at all stages up to and including tail bud (stage 25). However at stages 46, 48 and 49 the number of primordial germ cells was reduced in 1×90 embryos in one experiment of three and in 2×90 embryos in all experiments. We tested the hypothesis that the decreased number of primordial germ cells in the genital ridges was due to the inability of cells to migrate to the genital ridges from their ectopic location in the endoderm. When anterior endoderm was grafted into posterior endodermal regions the number of primordial germ cells increased slightly or not at all suggesting that the anterior displacement of the cells containing germ plasm was not the only factor responsible for the decreased number of primordial germ cells in rotated embryos. Other possible explanations are discussed.

Spatio-temporal deixis and cognitive models in early Indo-European

2018 ◽  
Vol 29 (1) ◽  
pp. 1-44
Author(s):  
Annamaria Bartolotta
Keyword(s):  
Cognitive Models ◽  
Temporal Sequence ◽  
Point Mapping ◽  
The Past ◽  
European Languages ◽  
Linguistic Evidence ◽  
Future Events ◽  
Spatial Terms ◽  
Spatio Temporal ◽  
Temporal Events

AbstractThis paper is a comparative study based on the linguistic evidence in Vedic Sanskrit and Homeric Greek, aimed at reconstructing the space-time cognitive models used in the Proto-Indo-European language in a diachronic perspective. While it has been widely recognized that ancient Indo-European languages construed earlier (and past) events as in front of later ones, as predicted in the Time-Reference-Point mapping, it is less clear how in the same languages the passage took place from this ‘archaic’ Time-RP model or non-deictic sequence, in which future events are behind or follow the past ones in a temporal sequence, to the more recent ‘post-archaic’ Ego-RP model that is found only from the classical period onwards, in which the future is located in front and the past in back of a deictic observer. Data from the Rigveda and the Homeric poems show that an Ego-RP mapping with an ego-perspective frame of reference (FoR) could not have existed yet at an early Indo-European stage. In particular, spatial terms of front and behind turn out to be used with reference not only to temporal events, but also to east and west respectively, thus presupposing the existence of an absolute field-based FoR which the temporal sequence is metaphorically related to. Specifically, sequence is relative position on a path appears to be motivated by what has been called day orientation frame, in which the different positions of the sun during the day motivate the mapping of front onto ‘earlier’ and behind onto ‘later’, without involving ego’s ‘now’. These findings suggest that early Indo-European still had not made use of spatio-temporal deixis based on the tense-related ego-perspective FoR found in modern languages.

scholarly journals Transfer of Primordial Germ-cells between Two Subspecies of Xenopus laevis

Development ◽  
1962 ◽  
Vol 10 (4) ◽  
pp. 641-651
Author(s):  
A. W. Blackler
Keyword(s):  
Xenopus Laevis ◽  
Germ Cells ◽  
Nuclear Membrane ◽  
Rana Temporaria ◽  
Primordial Germ Cells ◽  
Staining Technique ◽  
Tail Bud ◽  
Ventral Region ◽  
Large Size ◽  
The Poor

In Anura the primordial germ-cells are discernible in the dorsal crest endoderm of tail-bud stages of development and may be traced from this position throughout their migration into the undifferentiated gonadal rudiment. These facts have been established by the descriptive studies of a number of workers (see review by Johnston, 1951), the cells being recognizable by their large size, the retention of yolk platelets long after their disappearance in neighbouring cells, the sharply denned and often kidney-shaped nuclear membrane, and the poor staining affinity of the nuclear contents. By means of the application of the Altmann-Volkonsky staining technique, Bounoure (1934) was able to demonstrate that germ-cells of the dorsal crest endoderm are the lineal descendants of certain cells found in the ventral region of the blastula. This discovery has been confirmed for Rana temporaria (the species investigated by Bounoure) by Blackler (1958), and extended to other Anuran species by Nieuwkoop (1956 a, b), Blackler (1958), and Di Berardino (1961).

Sign in / Sign up

Export Citation Format

Share Document