Somitogenesis in amphibia

Development ◽  
1979 ◽  
Vol 53 (1) ◽  
pp. 245-267
Author(s):  
Tom Elsdale ◽  
Murray Pearson
Keyword(s):  
Refractory Period ◽  
Behavioural Change ◽  
Paraxial Mesoderm ◽  
Gastrula Stage ◽  
Tail Bud ◽  
Temperature Shock ◽  
Sensitive Periods ◽  
Set Up ◽  
Specific Length

A somite pre-pattern is established shortly before visible segmentation. The pre-pattern results from the interaction of two components: a wave of cell behavioural change that passes along the axis, and, an underlying co-ordination of the cells that is the basis for their association into large somite-sized groupings. The evidence is derived from studies of the zones of abnormal segmentation that follow temperature shocks delivered between the neurula and tail-bud stages (Pearson & Elsdale, 1979). Temperature shock given earlier at the mid-gastrula stage is however ineffective in inducingabnormalities in somitogenesis. Shocks given before the mid-gastrula stage reveala prior period of sensitivity stretching back into the blastula. Thus early and late sensitive periods can be defined separated by a short refactory period. Quite different patterns in the distribution of somite abnormalities characterize the results of shock during the two sensitive periods, suggesting different aetiologies. It is concluded that the wave of rapid cell change is set up early in embryogenesis during theblastula stage, and each cell of the prospective paraxial mesoderm carries a determination to change after a specific length of time, i.e. a countdown is set in each cell. As a result of the movements of gastrulation, the prospective paraxial mesoderm cells become laid out along the axis of the neurula in the order (antero-posterior sequence) in which they will change. The achievement of the correct redistribution of the cells depends crucially on the conservation of the sequence in the blastula by the maintenanceof topological integrity throughout gastrulation. It is suggested that early shock disturbs gastrulation movements, causing some mixing up of the cells resulting in incoherenceof the wavefront. Whereas early shocks are thus assumed to affect the wave, the evidencesuggests that late shock undoes co-ordination. It is concluded therefore that co-ordination is established later, after the refractory period, around the late gastrula stage.

scholarly journals Epha1 is a cell surface marker for neuromesodermal progenitors and their early mesoderm derivatives

2019 ◽  
Author(s):  
Luisa de Lemos ◽  
André Dias ◽  
Ana Nóvoa ◽  
Moisés Mallo
Keyword(s):  
Cell Surface ◽  
Transcriptional Profiling ◽  
Surface Marker ◽  
Cell Surface Marker ◽  
Paraxial Mesoderm ◽  
Molecular Signature ◽  
Tail Bud ◽  
Molecular Fingerprint ◽  
Simple Method ◽  
Cell Subpopulations

ABSTRACTThe vertebrate body is built during embryonic development by the sequential addition of new tissue as the embryo grows at its caudal end. During this process, the neuro-mesodermal progenitors (NMPs) generate the postcranial neural tube and paraxial mesoderm. Recently, several approaches have been designed to determine their molecular fingerprint but a simple method to isolate NMPs from embryos without the need for transgenic markers is still missing. We isolated NMPs using a genetic strategy that exploits their self-renew properties, and searched their transcriptome for cell surface markers. We found a distinct Epha1 expression profile in progenitor-containing areas of the mouse embryo, consisting of two cell subpopulations with different Epha1 expression levels. We show that Sox2+/T+ cells are preferentially associated with the Epha1 compartment, indicating that NMPs might be contained within this cell pool. Transcriptional profiling showed enrichment of high Epha1-expressing cells in known NMP and early mesoderm markers. Also, tail bud cells with lower Epha1 levels contained a molecular signature suggesting the presence of notochord progenitors. Our results thus indicate that Epha1 could represent a valuable cell surface marker for different subsets of axial progenitors, most particularly for NMPs taking mesodermal fates.

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.

scholarly journals Ventral tail bud mesenchyme is a signaling center for tail paraxial mesoderm induction

2004 ◽  
Vol 229 (3) ◽  
pp. 600-606 ◽  
Author(s):  
Chunqiao Liu ◽  
Vladimir Knezevic ◽  
Susan Mackem
Keyword(s):  
Paraxial Mesoderm ◽  
Mesoderm Induction ◽  
Tail Bud ◽  
Signaling Center

Somitogenesis in amphibia

Development ◽  
1983 ◽  
Vol 76 (1) ◽  
pp. 157-176
Author(s):  
Tom Elsdale ◽  
Duncan Davidson
Keyword(s):  
Central Region ◽  
Tail Bud ◽  
Temperature Shock ◽  
Anteroposterior Axis ◽  
Tissue Change ◽  
Narrow Zone ◽  
Tail Tip

Following neurulation, the frog segments c.40 somites and concurrently undergoes a striking elongation along the anteroposterior axis. This elongation (excluding the head) is largely the result of a presegmental extension of posterior tissue with a lesser contribution from the extension of segmented tissue. Presegmental extension is entirely the result of activity within a narrow zone of extension that occupies the central region in the tail bud. Within the zone of extension, a minimum of six prospective somites undergo an eight- to ten-fold extension along the axis. The zone passes posteriorly across the tissue of the tail tip. The anterior of the tail bud contains three extended prospective somites in the course of segmentation. The anterior boundary of the zone of extension coincides in space exactly with the anterior boundary of the zone of abnormal segmentation that results from temperature shock. This means that extension ceases immediately before the sudden tissue change associated with segmentation.

The somitogenetic potential of cells in the primitive streak and the tail bud of the organogenesis-stage mouse embryo

Development ◽  
1992 ◽  
Vol 115 (3) ◽  
pp. 703-715 ◽  
Author(s):  
P.P. Tam ◽  
S.S. Tan
Keyword(s):  
Primitive Streak ◽  
Mouse Embryos ◽  
Paraxial Mesoderm ◽  
Tail Bud ◽  
Matrix Interaction ◽  
Cell Matrix ◽  
Age Related ◽  
Somite Formation ◽  
Lateral Mesoderm ◽  
Host Embryo

The developmental potency of cells isolated from the primitive streak and the tail bud of 8.5- to 13.5-day-old mouse embryos was examined by analyzing the pattern of tissue colonization after transplanting these cells to the primitive streak of 8.5-day embryos. Cells derived from these progenitor tissues contributed predominantly to tissues of the paraxial and lateral mesoderm. Cells isolated from older embryos could alter their segmental fate and participated in the formation of anterior somites after transplantation to the primitive streak of 8.5-day host embryo. There was, however, a developmental lag in the recruitment of the transplanted cells to the paraxial mesoderm and this lag increased with the extent of mismatch of developmental ages between donor and host embryos. It is postulated that certain forms of cell-cell or cell-matrix interaction are involved in the specification of segmental units and that there may be age-related variations in the interactive capability of the somitic progenitor cells during development. Tail bud mesenchyme isolated from 13.5-day embryos, in which somite formation will shortly cease, was still capable of somite formation after transplantation to 8.5-day embryos. The cessation of somite formation is therefore likely to result from a change in the tissue environment in the tail bud rather than a loss of cellular somitogenetic potency.

scholarly journals Lineage tracing axial progenitors using Nkx1.2CreERT2 mice defines their trunk and tail contributions

2018 ◽  
Author(s):  
Aida Rodrigo Albors ◽  
Pamela A. Halley ◽  
Kate G. Storey
Keyword(s):  
Spinal Cord ◽  
Lineage Tracing ◽  
Paraxial Mesoderm ◽  
Mouse Line ◽  
Tail Bud ◽  
Dynamic Nature ◽  
Transgenic Mouse Line ◽  
Continuous Generation ◽  
Axis Elongation

AbstractThe vertebrate body forms by continuous generation of new tissue from progenitors at the posterior end of the embryo. In mice, these axial progenitors initially reside in the epiblast, from where they form the trunk; and later relocate to the chordo-neural hinge of the tail bud to form the tail. Among them, a small group of bipotent neuromesodermal progenitors (NMPs) are thought to generate the spinal cord and paraxial mesoderm to the end of axis elongation. The study of these progenitors, however, has proven challenging in vivo due to their small numbers and dynamic nature, and the lack of a unique molecular marker to identify them. Here, we report the generation of the Nkx1.2CreERT2 transgenic mouse line in which the endogenous Nkx1.2 promoter drives tamoxifen-inducible CreERT2 recombinase. We show that Nkx1.2CreERT2 targets axial progenitors, including NMPs and early neural and mesodermal progenitors. Using a YFP reporter, we demonstrate that Nkx1.2-expressing epiblast cells contribute to all three germ layers, mostly neuroectoderm and mesoderm excluding notochord; and continue contributing neural and paraxial mesoderm tissues from the tail bud. This study identifies the Nkx1.2-expressing cell population as the source of most trunk and tail tissues in the mouse; and provides a key tool to genetically label and manipulate this progenitor population in vivo.

scholarly journals Warburg-like metabolism coordinates FGF and Wnt signaling in the vertebrate embryo

2017 ◽  
Author(s):  
Masayuki Oginuma ◽  
Philippe Moncuquet ◽  
Fengzhu Xiong ◽  
Edward Karoly ◽  
Jérome Chal ◽  
...  
Keyword(s):  
Aerobic Glycolysis ◽  
Embryonic Axis ◽  
Paraxial Mesoderm ◽  
Metabolic Adaptation ◽  
Fgf Signaling ◽  
Tail Bud ◽  
Temporal Regulation ◽  
Mammalian Embryos ◽  
Spatio Temporal

Mammalian embryos transiently exhibit aerobic glycolysis (Warburg effect), a metabolic adaptation also observed in cancer cells. The role of this particular type of metabolism during vertebrate organogenesis is currently unknown. Here, we provide evidence for spatio-temporal regulation of aerobic glycolysis in the posterior region of mouse and chicken embryos. We show that a posterior glycolytic gradient is established in response to graded transcription of glycolytic enzymes downstream of FGF signaling. We demonstrate that glycolysis controls posterior elongation of the embryonic axis by regulating cell motility in the presomitic mesoderm and by controlling specification of the paraxial mesoderm fate in the tail bud. Our results suggest that Warburg metabolism in the tail bud coordinates Wnt and FGF signaling to promote elongation of the embryonic axis.

scholarly journals Cdx1andCdx2have overlapping functions in anteroposterior patterning and posterior axis elongation

Development ◽  
2002 ◽  
Vol 129 (9) ◽  
pp. 2181-2193 ◽  
Author(s):  
Eric van den Akker ◽  
Sylvie Forlani ◽  
Kallayanee Chawengsaksophak ◽  
Wim de Graaff ◽  
Felix Beck ◽  
...  
Keyword(s):  
Vertebral Column ◽  
Hox Genes ◽  
Early Embryo ◽  
Paraxial Mesoderm ◽  
Thoracic Vertebrae ◽  
Tail Bud ◽  
Anteroposterior Patterning ◽  
C Elegans ◽  
Axis Elongation ◽  
Posterior Shift

Mouse Cdx and Hox genes presumably evolved from genes on a common ancestor cluster involved in anteroposterior patterning. Drosophila caudal (cad) is involved in specifying the posterior end of the early embryo, and is essential for patterning tissues derived from the most caudal segment, the analia. Two of the three mouse Cdx paralogues, Cdx 1 and Cdx2, are expressed early in a Hox-like manner in the three germ layers. In the nascent paraxial mesoderm, both genes are expressed in cells contributing first to the most rostral, and then to progressively more caudal parts of the vertebral column. Later, expression regresses from the anterior sclerotomes, and is only maintained for Cdx1 in the dorsal part of the somites, and for both genes in the tail bud. Cdx1 null mutants show anterior homeosis of upper cervical and thoracic vertebrae. Cdx2-null embryos die before gastrulation, and Cdx2 heterozygotes display anterior transformations of lower cervical and thoracic vertebrae. We have analysed the genetic interactions between Cdx1 and Cdx2 in compound mutants. Combining mutant alleles for both genes gives rise to anterior homeotic transformations along a more extensive length of the vertebral column than do single mutations. The most severely affected Cdx1 null/Cdx2 heterozygous mice display a posterior shift of their cranio-cervical, cervico-thoracic, thoraco-lumbar, lumbo-sacral and sacro-caudal transitions. The effects of the mutations in Cdx1 and Cdx2 were co-operative in severity, and a more extensive posterior shift of the expression of three Hox genes was observed in double mutants. The alteration in Hox expression boundaries occurred early. We conclude that both Cdx genes cooperate at early stages in instructing the vertebral progenitors all along the axis, at least in part by setting the rostral expression boundaries of Hox genes. In addition, Cdx mutants transiently exhibit alterations in the extent of Hox expression domains in the spinal cord, reminding of the strong effects of overexpressing Cdx genes on Hox gene expression in the neurectoderm. Phenotypical alterations in the peripheral nervous system were observed at mid-gestation stages. Strikingly, the altered phenotype at caudal levels included a posterior truncation of the tail, mildly affecting Cdx2 heterozygotes, but more severely affecting Cdx1/Cdx2 double heterozygotes and Cdx1 null/Cdx2 heterozygotes. Mutations in Cdx1 and Cdx2 therefore also interfere with axis elongation in a cooperative way. The function of Cdx genes in morphogenetic processes during gastrulation and tail bud extension, and their relationship with the Hox genes are discussed in the light of available data in Amphioxus, C. elegans, Drosophila and mice.

scholarly journals Studies on the flexor reflex.-IV. After-discharge

1931 ◽  
Vol 107 (754) ◽  
pp. 586-596 ◽  
Keyword(s):  
Refractory Period ◽  
Afferent Nerve ◽  
Tetanic Stimulation ◽  
Flexor Reflex ◽  
General Technique ◽  
Reflex Pathway ◽  
Neon Tube ◽  
Set Up ◽  
Reflex Discharge ◽  
Antidromic Volley

In many preparations the flexor reflex elicited by the application of a moderately strong break-shock to an ipselateral afferent nerve has an after-discharge following the initial reflex discharge, even when the strength of the break-shock it such that it sets up no more than a single centripetal volley (Sherrington, 1921, a ; 1921, b ; Adrian and Forbes, 1922). The prolonged excitatory condition which must occur at some part of the central reflex pathway clearly has some affinity to the persistence of the c. e. s. which forms the basis of facilitation (Eccles and Sherrington, 1930). It is of interest therefore to investigate the effect of an antidromic volley on after-discharge. It must, however, be remembered that an antidromic volley set up during an after-discharge will be prevented from reaching some motoneurones by meeting centrifugal (reflex) impulses. Denny-Brown (1929, p. 273) observed that an antidromic volley set up during the after-discharge of either a flexor or extensor reflex (in response to a tetanic stimulation) was followed by a period of quiescence owing to a temporary lapse of the after-discharge. The duration of this period seemed to be too long for a central refractory period set up by the antidromic volley, so he suggested that there might be a temporary exhaustion of the central exciting agent (c. e. s.). II. Method. The general technique is as described previously (Eccles and Sherrington, 1931, a ). In all cases the muscle (tibialis anticus) has been completely deafferented. Tetanic stimuli have been provided by a neon-tube oscillator.

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