The migration of presumptive primordial germ cells through the endodermal cell mass in Xenopus laevis: A light and electron microscopic study

Development ◽  
1980 ◽  
Vol 59 (1) ◽  
pp. 1-17
Author(s):  
Michiko Kamimura ◽  
Minoru Kotani ◽  
Kenzo Yamagata
Keyword(s):  
Xenopus Laevis ◽  
Germ Cells ◽  
Intercellular Space ◽  
Primordial Germ Cells ◽  
Cell Mass ◽  
Light And Electron Microscopy ◽  
Morphological Characteristics ◽  
Light Microscope Level ◽  
Cytoplasmic Processes ◽  
Germinal Plasm

Presumptive primordial germ cells (pPGCs) were examined during migration from their deep endodermal position to the endodermal crest in Xenopus laevis, using light and electron microscopy with Epon sections, and several morphological characteristics of pPGCs, associated with their migration, were revealed. pPGCs displayed polymorphism, with smooth contours. The intercellular space around the pPGCs was large and variable in width and cytoplasmic processes from pPGCs were occasionally observed in it. It was shown quantitatively that pPGCs at the migratory stage had a tendency to move with the leading end, towards which the nucleus was localized, dragging the germinal plasm behind. These polarized pPGCs were frequently associated with large intercellular spaces, both at their leading and trailing ends. Cytoplasmic processes of polarizing pPGCs found in the large intercellular space at the leading end were conspicuous. Ultrastructurally, the nuclei of pPGCs were euchromatic, and the nucleolus was prominent. The germinal plasm at the light microscope level corresponded to the cytoplasmic area near the nucleus where a large number of mitochondria with well-developed cristae and most of the other organelles were aggregated. Centrioles and centriole-associated microtubules observed in the aggregate were thought to be important structures responsible for the cell polarization mentioned above. It was demonstrated quantitatively that the size of mitochondria in pPGCs was larger on average than that of mitochondria in neighbouring somatic endodermal cells. Numerous irregularly shaped small yolk platelets characterized pPGCs. These ultrastructural features suggested that pPGCs were in an activated metabolic state. It was concluded that the migration of pPGCs was attributable to active movement with high cell metabolism, causing the formation of cell processes and intracellular polarization.

The formation of the gonadal ridge in Xenopus laevis

Development ◽  
1976 ◽  
Vol 35 (1) ◽  
pp. 149-157
Author(s):  
C. C. Wylie ◽  
T. B. Roos
Keyword(s):  
Xenopus Laevis ◽  
Germ Cells ◽  
Primordial Germ Cells ◽  
Time Lapse ◽  
Active Movement ◽  
Surface Phenomena ◽  
Cytoplasmic Processes

Previous studies have described the morphology, including the ultrastructure, of primordial germ cells (PGCs), and the cells with which they associate to form the gonadal ridge, in Xenopus laevis. In order to test their capacity for active movement we have studied single, isolated PGCs in vitro. Time-lapse studies of these cells reveal that they are motile, using broad cytoplasmic processes. The fact that these cells are very large and easy to manipulate in vitro makes them an attractive subject of study, particularly with respect to the mechanism of their movement and the surface phenomena which guide them to the site of the gonadal ridge.

Relationship between the amount of the ‘germinal plasm’ and the number of primordial germ cells in Xenopus laevis

Development ◽  
1974 ◽  
Vol 31 (1) ◽  
pp. 89-98
Author(s):  
Kazuyuki Tanabe ◽  
Minoru Kotani
Keyword(s):  
Xenopus Laevis ◽  
Germ Cell ◽  
Germ Cells ◽  
Primordial Germ Cells ◽  
The Other ◽  
Direct Proportion ◽  
Sensitive Material ◽  
Cell Stage ◽  
Other Hand ◽  
Germinal Plasm

Tadpoles of Xenopus laevis completely lacking primordial germ cells were obtained by irradiating the vegetal hemisphere of early 2-cell eggs with u.v. (wavelength, 253·7 nm; dose, ca. 6000 ergs/mm2). An increasing number of primordial germ cells were observed as the stage at irradiation advanced from early 2-cell to early 4-cell stages. Furthermore, early 2-cell eggs irradiated with doses ranging from 750 to 6000 ergs/mm2 grew into tadpoles carrying a decreasing number of primordial germ cells in accord with the increase of the dose. On the other hand, tadpoles developed from eggs irradiated immediately after being centrifuged at 150 g for 1 min at early 2-cell stage to displace the ‘germinal plasm’ deeper into the cytoplasm, carried a considerable number of primordial germ cells. These facts were interpreted to suggest the presence of u.v.-sensitive germ cell determinant in the ‘germinal plasm’. It was revealed by varying the area of irradiation that the number of primordial germ cells decreased in direct proportion to the increase of the area irradiated. It was concluded that the amount of the u.v.-sensitive material(s) contained in the ‘germinal plasm’ determined the number of primordial germ cells in tadpoles.

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.

An ultrastructural study of primordial germ cells, oogonia and early oocytes in Xenopus laevis

Development ◽  
1971 ◽  
Vol 26 (2) ◽  
pp. 195-217
Author(s):  
Kawakib A. K. Al-Mukhtar ◽  
Andrew C. Webb
Keyword(s):  
Xenopus Laevis ◽  
Granular Material ◽  
Germ Cells ◽  
Primordial Germ Cells ◽  
Cell Diameter ◽  
Oocyte Diameter ◽  
Nuclear Pores ◽  
Synaptonemal Complexes ◽  
Balbiani Body ◽  
Germ Cell Differentiation

Electron-microscope observations on the differentiation of germ cells in Xenopus laevis have revealed that the Balbiani body, cytoplasmic nucleolus-like bodies and groups of mitochondria associated with granular material previously reported only in older amphibian oocytes, are also present in the primordial germ cells, oogonia and early meiotic (pre-diplotene) oocytes of this species. Although there is considerable morphological reorganization of the gonad as a whole at the time of sex determination, little visible change in the ultrastructure of the primordial germ cells appears to take place during their transition to oogonia. Both primordial germ cells and oogonia have highly lobed nuclei and their cytoplasm contains a conspicuous, juxtanuclear organelle aggregate (consisting for the most part of mitochondria), which is considered to represent the precursor of the Balbiani body. In marked contrast, the transition from oogonium to oocyte in Xenopus is characterized by a distinctive change in nuclear shape (from lobed to round) associated with the onset of meiosis. During leptotene the oocyte chromatin becomes visibly organized into electron-dense axial elements (representing the single unpaired chromosomes) which are surrounded by a fibrillar network. Towards the end of leptotene, these axial elements become attached to the inner surface of the nuclear membrane in a localized region adjacent to the juxtanuclear mitochondrial aggregate. Zygotene is marked by the initiation of axial element pairing over short regions, resulting in the typical synaptonemal complex configuration of paired homologous chromosomes. The polarization of these tripartite ribbons within the nucleus becomes more pronounced in late zygotene, producing the familiar Bouquet arrangement. The synaptonemal complexes are more extensive as synapsis reaches a climax during pachytene, whereas the polarization is to some extent lost. The fine structure of synaptonemal complexes in the Xenopus oocyte is essentially the same as that described in numerous other plant and animal meiocytes. It is not until the beginning of the extended diplotene phase that any appreciable increase in cell diameter takes place. During early diplotene (oocyte diameter approximately 50 µm), the compact Balbiani body characteristic of the pre-vitellogenic anuran oocyte is formed by condensation of the juxtanuclear mitochondrial aggregate. Electron-dense, granular material appears to pass between nucleus and cytoplasm via nuclear pores in all stages of Xenopus germ cell differentiation studied. There is a distinct similarity in electron density and granular content between this ‘nuage material’ associated with the nuclear pores and the cytoplasmic aggregates of granular material in association with mitochondria or in the form of nucleolus-like bodies.

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.

Electron microscopic studies on the structure of motile primordial germ cells of Xenopus laevis in vitro

Development ◽  
1978 ◽  
Vol 46 (1) ◽  
pp. 119-133
Author(s):  
Janet Heasman ◽  
C. C. Wylie
Keyword(s):  
Xenopus Laevis ◽  
Germ Cells ◽  
Primordial Germ Cells ◽  
Structural Features ◽  
Culture Conditions ◽  
Structural Basis ◽  
Electron Microscopic ◽  
Microscopic Studies

Primordial germ cells (PGCs) of Xenopus laevis have been isolated from early embryos and kept alive in vitro, in order to study the structural basis of their motility, using the transmission and scanning electron microscope. The culture conditions used mimicked as closely as possible the in vivo environment of migrating PGCs, in that isolated PGCs were seeded onto monolayers of amphibian mesentery cells. In these conditions we have demonstrated that: (a) No significant differences were found between the morphology of PGCs in vitro and in vivo. (b) Structural features involved in PGC movement in vitro include (i) the presence of a filamentous substructure, (ii) filopodial and blunt cell processes, (iii) cell surface specializations. These features are also characteristic of migratory PGCs studied in vivo. (c) PGCs in vitro have powers of invasion similar to those of migrating PGCs in vivo. They occasionally become completely surrounded by cells of the monolayer and, in this situation, bear striking resemblance to PGCs moving between mesentery cells to the site of the developing gonad in stage-44 tadpoles. We conclude that as far as it is possible to assess, the behaviour of isolated PGCs in these in vitro conditions mimics their activities in vivo. This allows us to study the ultrastructural basis of their migration.

Nuclear transplantation of male primordial germ cells in the mouse

Development ◽  
1989 ◽  
Vol 107 (2) ◽  
pp. 407-411 ◽  
Author(s):  
Y. Tsunoda ◽  
T. Tokunaga ◽  
H. Imai ◽  
T. Uchida
Keyword(s):  
Germ Cells ◽  
Inner Cell Mass ◽  
Primordial Germ Cells ◽  
Cell Mass ◽  
Blastocyst Stage ◽  
Nuclear Transplantation ◽  
Embryonic Genome ◽  
Donor Nucleus ◽  
Implantation Sites ◽  
Genome Activation

We examined the developmental ability of enucleated eggs receiving embryonic nuclei and male primordial germ cells (PGCs) in the mouse. Reconstituted eggs developed into the blastocyst stage only when an earlier 2-cell nucleus was transplanted (36%) but very rarely if the donor nucleus was derived from a later 2-cell, 8-cell, or inner cell mass of a blastocyst (0–3%). 54–100%, 11–67%, 6–43% and 6–20% of enucleated eggs receiving male PGCs developed to 2-cell, 4-cell, 8-cell and blastocyst stage, respectively, in culture. The overall success rate when taking into account the total number of attempts at introducing germ cells was actually 0–6%. Live fetuses were not obtained after transfer of reconstituted eggs to recipients, although implantation sites were observed. The developmental ability of reconstituted eggs in relation to embryonic genome activation and genomic imprinting is discussed.

Primordial germ cells of Xenopus laevis are not irreversibly determined early in development

1985 ◽  
Vol 112 (1) ◽  
pp. 66-72 ◽  
Author(s):  
C.C. Wylie ◽  
Janet Heasman ◽  
Alison Snape ◽  
Melinda O'Driscoll ◽  
Stephen Holwill
Keyword(s):  
Xenopus Laevis ◽  
Germ Cells ◽  
Primordial Germ Cells
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