The formation of the gonadal ridge in Xenopus laevis

Development ◽  
1976 ◽  
Vol 35 (1) ◽  
pp. 139-148
Author(s):  
C. C. Wylie ◽  
M. Bancroft ◽  
J. Heasman
Keyword(s):  
Surface Morphology ◽  
Xenopus Laevis ◽  
Germinal Epithelium ◽  
Coelomic Lining ◽  
Dorsal Mesentery ◽  
Do So

This paper studies the surface morphology of the developing gonadal ridge in X. laevis between stages 44 and 49 (Nieuwkoop & Faber, 1956). During this period the primordialgerm cells (PGCs) move laterally from the dorsal mesentery of the gut to the position of thepresumptive gonadal ridge. As they do so the coelomic lining cells lateral to the mesenterydifferentiate into a specialized, longitudinally orientated band, stretching nearly the fulllength of the dorsal mesentery on each side. The PGCs migrate beneath this band of cells, which thus becomes the germinal epithelium of the gonadal ridge. We have demonstrated by irradiation experiments that this specialized band of cells can differentiate independently, in the absence of the PGCs.

The formation of the gonadal ridge in Xenopus laevis

Development ◽  
1976 ◽  
Vol 35 (1) ◽  
pp. 125-138
Author(s):  
C. C. Wylie ◽  
J. Heasman
Keyword(s):  
Xenopus Laevis ◽  
Primordial Germ Cells ◽  
Somatic Cells ◽  
Passive Movement ◽  
Morphological Data ◽  
Cell Surfaces ◽  
Coelomic Cavity ◽  
Coelomic Lining ◽  
Well Differentiated ◽  
Cytoplasmic Processes

In Xenopus laevis tadpoles, between stages 44 and 49 (Nieuwkoop & Faber, 1956), the primordial germ cells (PGCs) migrate from the dorsal mesentery of the gut to the site of the presumptive gonadal ridge. This paper describes the process at the light- and electronmicroscope levels. The PGCs in the mesentery, which at first are very large and yolk-laden, seem to lie entirely within the cellular matrix of the mesentery, although this is not obvious in light micrographs. Where the PGCs bulge out into the coelomic cavity, they stretch the somatic cell covering to a thin, cytoplasmic layer. The somatic cells of the mesentery are held together around them at this stage by well-differentiated desmosomes. At this, and subsequent stages, the PGCs have cytoplasmic processes, roughly the size of microvilli, which are irregularly distributed over their surfaces, and which are inserted between surrounding somatic cells. Whether these processes play any role in locomotion or exploration of the substrate is uncertain. As the PGCs move laterally from the root of the mesentery to the presumptive gonadal ridge, the coelomic lining cells which cover them, initially with a very thin squamous layer, differentiate to form the cuboidal cells of the germinal epithelium. Several interesting ultrastructural features of these cells, and the PGCs, are described, particularly in the light of their surface interaction. In the light of the morphological data presented here, particularly of the cell surfaces involved, we conclude that both active locomotion by the PGCs and passive movement by the morphogenetic movements of the cells around them contribute to the establishment of the early gonadal ridge.

Transfer of Primordial Germ-cells in Xenopus laevis

Development ◽  
1961 ◽  
Vol 9 (4) ◽  
pp. 634-641
Author(s):  
A. W. Blackler ◽  
M. Fischberg
Keyword(s):  
Xenopus Laevis ◽  
Germ Cells ◽  
Germ Line ◽  
Primordial Germ Cells ◽  
Dorsal Region ◽  
Blastula Stage ◽  
Early Embryonic Stage ◽  
Sex Cells ◽  
Fertilized Egg ◽  
Dorsal Mesentery

There have been many claims for the segregation of Anuran primordial germcells at an early embryonic stage. Most authors agree that these cells may be distinguished with ease in the most dorsal region of the larval endoderm and, somewhat later in development, at the base of the dorsal mesentery and in the undifferentiated gonad (see review by Johnston, 1951). Bounoure (1934) and Blackler (1958) claim to have traced the origin of the primordial germ-cells as early in development as the late blastula stage and to have recognized cell inclusions that become restricted to the germ line at all stages between the fertilized egg and the late blastula. As pointed out by Everett (1945), some workers in this field of embryological study have firmly denied the existence of primordial germ-cells, while others have been cautious of accepting the principle that these cells give rise to any of the definitive sex-cells (gametes).

Mesoderm-inducing factors and the control of gastrulation

Development ◽  
1992 ◽  
Vol 116 (Supplement) ◽  
pp. 127-136 ◽  
Author(s):  
J. C. Smith ◽  
J. E. Howard
Keyword(s):  
Xenopus Laevis ◽  
Molecular Basis ◽  
Model System ◽  
Inductive Interaction ◽  
Inducing Factors ◽  
Gastrulation Movement ◽  
Mesoderm Inducing Factors ◽  
Suitable System ◽  
Do So

One of the reasons that we know so little about the control of vertebrate gastrulation is that there are very few systems available in which the process can be studied in vitro. In this paper, we suggest that one suitable system might be provided by the use of mesoderm-inducing factors. In amphibian embryos such as Xenopus laevis, gastrulation is driven by cells of the mesoderm, and the mesoderm itself arises through an inductive interaction in which cells of the vegetal hemisphere of the embryo emit a signal which acts on overlying equatorial cells. Several factors have recently been discovered that modify the pattern of mesodermal differentiation or induce mesoderm from presumptive ectoderm. Some of these mesoderm-inducing factors will also elicit gastrulation movements, which provides a powerful model system for the study of gastrulation, because a population of cells that would not normally undertake the process can be induced to do so. In this paper, we use mesoderm-inducing factors to attempt to answer four questions. How do cells know when to gastrulate? How do cells know what kind of gastrulation movement to undertake? What is the cellular basis of gastrulation? What is the molecular basis of gastrulation?

Observations on the migration and proliferation of gonocytes in Xenopus laevis

Development ◽  
1976 ◽  
Vol 36 (1) ◽  
pp. 197-207
Author(s):  
Michiko Kamimura ◽  
Kohji Ikenishi ◽  
Minoru Kotani ◽  
Toru Matsuno
Keyword(s):  
Xenopus Laevis ◽  
Developmental Stages ◽  
Primordial Germ Cell ◽  
Cell Mass ◽  
Cell Formation ◽  
Initial Step ◽  
Peripheral Region ◽  
Genital Ridge ◽  
Tail Bud ◽  
Dorsal Mesentery

The process of primordial germ cell formation in the normal course of development of Xenopus laevis was examined with a light microscope on paraffin and Epon sections of embryos or tadpoles, extending over the period from the gastrula to the feeding tadpole stage. Positional changes of gonocytes with development were nearly the same as those reported on the same species by Bladder (1958) and Whitington & Dixon (1975). The following points were newly demonstrated. Gonocytes which have been located in a deep endodermal position till mid tail-bud stage come to be located in a rather peripheral region of the endoderm cell mass at stage 31 (late tail-bud), suggesting that the initial step of migration of the gonocytes towards the future genital ridge has already begun at this stage. Gonocytes at stages 33/34 and 35/36 were observed in a more dorsal part of the endoderm than at stage 31. Gonocytes which seem to have begun their migration are roundish in external shape and have a large intercellular space around them. At stage 40 gonocytes were located in the dorsal endodermal crest, and at stage 41 gonocytes were found with cell bodies extending over both the dorsal endoderm crest and the dorsal mesentery, indicating that the separation of the gonocytes from the endoderm was in progress at this stage. The present results seem to indicate that gonocytes migrate not passively but actively from the deep endodermal position to the genital ridge, passing through the dorsal mesentery. Counting the number of gonocytes at successive stages of development revealed that gonocytes proliferated exponentially throughout the developmental stages from gastrula to tadpole.

scholarly journals Microtubule-dependent pushing forces contribute to long-distance aster movement and centration in Xenopus laevis egg extracts

2020 ◽  
Vol 31 (25) ◽  
pp. 2791-2802 ◽  
Author(s):  
Taylor Sulerud ◽  
Abdullah Bashar Sami ◽  
Guihe Li ◽  
April Kloxin ◽  
John Oakey ◽  
...  
Keyword(s):  
Xenopus Laevis ◽  
Cytoplasmic Dynein ◽  
Long Distance ◽  
Egg Extracts ◽  
Do So

In this work, we demonstrate that microtubule asters are able to center in a variety of cell geometries and can do so over long distances, even when the activity of cytoplasmic dynein is inhibited. This observation, along with additional characterizations of aster movements, is consistent with a microtubule-based pushing mechanism.

Holding replication studies to mainstream standards of evidence

2018 ◽  
Vol 41 ◽  
Author(s):  
Duane T. Wegener ◽  
Leandre R. Fabrigar
Keyword(s):  
Replication Studies ◽  
Replication Research ◽  
Standards Of Evidence ◽  
Do So

AbstractReplications can make theoretical contributions, but are unlikely to do so if their findings are open to multiple interpretations (especially violations of psychometric invariance). Thus, just as studies demonstrating novel effects are often expected to empirically evaluate competing explanations, replications should be held to similar standards. Unfortunately, this is rarely done, thereby undermining the value of replication research.

An Established Epithelial Cell Line (NPC/HK1) from a Nasopharyngeal Carcinoma - II. A Sem Study

1982 ◽  
Vol 40 ◽  
pp. 224-225
Author(s):  
Li C.L. ◽  
Chew E.C. ◽  
Huang D.P. ◽  
Ho H.C. ◽  
Mak L.S. ◽  
...  
Keyword(s):  
Nasopharyngeal Carcinoma ◽  
Epithelial Cell ◽  
Surface Morphology ◽  
Cell Line ◽  
Epithelial Cell Line ◽  
Present Communication ◽  
Cells In Culture ◽  
Sem Study ◽  
Well Differentiated

An epithelial cell line, NPC/HK1, has recently been successfully established from a nasopharyngeal carcinoma of the moderately to well differentiated squamous type. The present communication reports on the surface morphology of the NPC/HK1 cells in culture.

Specimen Collection Effect in Scanning Electron Microscopy Images

1972 ◽  
Vol 30 ◽  
pp. 448-449
Author(s):  
J. Temple Black ◽  
Jose Guerrero
Keyword(s):  
Surface Morphology ◽  
Secondary Electron Emission ◽  
Secondary Electrons ◽  
Charge Effects ◽  
Material Density ◽  
Specimen Collection ◽  
The Subject ◽  
Curved Paths ◽  
Subject Material ◽  
Microscopy Images

In the SEM, contrast in the image is the result of variations in the volume secondary electron emission and backscatter emission which reaches the detector and serves to intensity modulate the signal for the CRT's. This emission is a function of the accelerating potential, material density, chemistry, crystallography, local charge effects, surface morphology and especially the angle of the incident electron beam with the particular surface site. Aside from the influence of object inclination, the surface morphology is the most important feature In producing contrast. “Specimen collection“ is the name given the shielding of the collector by adjacent parts of the specimen, producing much image contrast. This type of contrast can occur for both secondary and backscatter electrons even though the secondary electrons take curved paths to the detector-collector.Figure 1 demonstrates, in a unique and striking fashion, the specimen collection effect. The subject material here is Armco Iron, 99.85% purity, which was spark machined.

Binucleate Spermiogenesis in the Mouse

1972 ◽  
Vol 30 ◽  
pp. 112-113
Author(s):  
John J. Wolosewick
Keyword(s):  
Electron Microscopy ◽  
Phosphate Buffer ◽  
Seminiferous Epithelium ◽  
Mouse Testis ◽  
Germinal Epithelium ◽  
Intercellular Bridges ◽  
Adult Mice ◽  
Cervical Dislocation ◽  
Human And Mouse

Classically, the male germinal epithelium is depicted as synchronously developing uninucleate spermatids conjoined by intercellular bridges. Recently, binucleate and multinucleate spermatids from human and mouse testis have been reported. The present paper describes certain developmental events in one type of binucleate spermatid in the seminiferous epithelium of the mouse.Testes of adult mice (ABP Jax) were removed from the animals after cervical dislocation and placed into 2.5% glutaraldehyde/Millonig's phosphate buffer (pH 7.2). Testicular capsules were gently split and separated, exposing the tubules. After 15 minutes the tissue was carefully cut into cubes (approx. 1mm), fixed for an additional 45 minutes and processed for electron microscopy.

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