Observations on the origin of the ‘germinal cytoplasm’ in Xenopus laevis

Development ◽  
1969 ◽  
Vol 22 (2) ◽  
pp. 229-251
Author(s):  
Renata Czołowska
Keyword(s):  
Xenopus Laevis ◽  
Germ Cells ◽  
Rana Pipiens ◽  
Rana Temporaria ◽  
Primordial Germ Cells ◽  
Rana Esculenta ◽  
Bufo Bufo ◽  
Discoglossus Pictus ◽  
Early Appearance ◽  
Vegetative Pole

The early appearance of the ‘germinal cytoplasm’ and its behaviour during the formation of cells which are thought to represent the primordial germ cells have been described in detail for Rana temporaria by Bounoure (1927, 1934, 1939) and Blackler (1958). These observations were extended to Xenopus laevis (Nieuwkoop, 1956; Nieuwkoop & Faber, 1956; Blackler, 1958), Bufo bufo (Blackler, 1958), Rana pipiens (Berardino, 1961), Discoglossus pictus (Gipouloux, 1962 a) and Rana esculenta (Hammer, cited by Blackler, 1965 b). The above findings agree with respect to the earliest detection of the ‘germinal cytoplasm’. Its first appearance was noticed as early as in the fertilized, unsegmented egg, where small, distinctly staining islands of cytoplasm are localized just under the cell membrane in an area around the vegetative pole of the egg. During cleavage the ‘germinal cytoplasm’ is distributed between the vegetative blastomeres directly surrounding the vegetative pole.

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).

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.

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
Sign in / Sign up

Export Citation Format

Share Document