Cytological analyses of factors which determine the number of primordial germ cells (PGCs) in Xenopus laevis

Development ◽  
1985 ◽  
Vol 90 (1) ◽  
pp. 251-265
Author(s):  
Yasuko Akita ◽  
Masami Wakahara
Keyword(s):  
Xenopus Laevis ◽  
Germ Cells ◽  
Germ Plasm ◽  
Primordial Germ Cells ◽  
Somatic Cells ◽  
Cell Stage ◽  
Unknown Mechanism ◽  
Fertilized Egg ◽  
Number Of Cells ◽  
Experimentally Induced

Correlation of the number of primordial germ cells (PGCs) at stage 47 with the amount of germ plasm at the 8-cell stage and with the number of the germ-plasm-containing cells (GPCCs) was analysed using two different laboratory-raised colonies of Xenopus laevis, HD and J groups. The average number of PGCs in J group tadpoles was significantly larger than that in HD group tadpoles. The amount of germ plasm in J group embryos was also demonstrated to be larger than in HD group embryos. The amount of germ plasm was related positively to the number of GPCCs at the 8-cell stage and to the resulting number of PGCs; embryos which contained larger amounts of germ plasm developed larger numbers of PGCs at stage 47. The average number of PGCs in experimentally induced triploid tadpoles was exactly twothirds of that in normal diploid tadpoles. Furthermore, in somatic cells (e.g. epidermis, muscle, pancreas), the number of cells in the triploid was also two-thirds of that in diploid tadpoles. These findings suggest that the number of PGCs is regulated by at least two different mechanisms: first, the number of PGCs is primarily specified by the intrinsic amount of germ plasm in the fertilized egg. Second, it is regulated by an unknown mechanism which controls the total number of cells of whole embryos, such as the nucleocytoplasmic ratio.

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.

Events in the germ cell lineage after entry of the primordial germ cells into the genital ridges in normal and u.v.-irradiated Xenopus laevis

Development ◽  
1977 ◽  
Vol 41 (1) ◽  
pp. 33-46
Author(s):  
Brigitta Züst ◽  
K. E. Dixon
Keyword(s):  
Xenopus Laevis ◽  
Germ Cell ◽  
Germ Cells ◽  
Dorsal Root ◽  
Primordial Germ Cells ◽  
Cell Lineage ◽  
Cell Stage ◽  
Comparison Of The Results ◽  
New Generation

Approximately 20–25 primordial germ cells leave the endoderm between stages 38–41 and localize in the dorsal root of the mesentery by stage 43/44. At this time all the cells contain large quantities of yolk which is gradually resorbed. The cells begin dividing between stages 48–52. The number and size of the germ cells were measured in tadpoles between stages 48–54 of development. The results indicate that in females the germ cells divide more often than in males. In both sexes the mitoses are grossly unequal, leading to the formation of a new generation of germ cells which are considerably smaller (one-tenth to one-fifth) than the size of the primordial germ cells at stage 48. The germ cells in male tadpoles at stage 54 are larger than in female tadpoles at the same stage. In tadpoles which developed from eggs irradiated in the vegetal hemisphere with u.v. light at the 2- to 4-cell-stage, primordial germ cells migrate into the genital ridges much later (stage 46–48) than in unirradiated embryos. They also differ morphologically from germ cells in control animals at this stage in that they are approximately one-tenth the size, lacking yolk in the cytoplasm and have a more highly lobed nucleus. Comparison of the results in unirradiated and irradiated animals suggests that the germ cell lineage is composed of a series of ordered, predictable events, and serious disruption of one of the events deranges later events.

scholarly journals DEADSouth protein localizes to germ plasm and is required for the development of primordial germ cells in Xenopus laevis

Biology Open ◽  
2012 ◽  
Vol 2 (2) ◽  
pp. 191-199 ◽  
Author(s):  
T. Yamaguchi ◽  
A. Taguchi ◽  
K. Watanabe ◽  
H. Orii
Keyword(s):  
Xenopus Laevis ◽  
Germ Cells ◽  
Germ Plasm ◽  
Primordial Germ Cells

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).

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.

Quantitative studies of germ plasm and germ during early embryogenesis of Xenopus laevis

Development ◽  
1975 ◽  
Vol 33 (1) ◽  
pp. 57-74
Author(s):  
P. McD. Whitington ◽  
K. E. Dixon
Keyword(s):  
Germ Cells ◽  
Germ Plasm ◽  
Primordial Germ Cells ◽  
Early Embryogenesis ◽  
Daughter Cells ◽  
Quantitative Studies ◽  
Endodermal Cells ◽  
Early Gastrula ◽  
Number Of Cells ◽  
Direct Counts

The germ plasm in the egg is partitioned between the first four blastomeres by the first two cleavage planes. Although the blastomeres divide 10–11 times through the rest of cleavage, as shown by reduction in their size, the number of presumptive primordial germ cells (p.p. germ cells) does not increase significantly. During and as a result of the formation of the first two cleavage planes, the germ plasm aggregates together and moves towards and along the cleavage furrows. At subsequent mitoses, the germ plasm is localized at one of the poles of the spindle and hence is segregated to only one of the daughter cells, thus explaining how mitosis occurs without increase in the number of cells with germ plasm. Early in gastrulation, the germ plasm moves to a perinuclear position, therefore ensuring that as mitosis continues, both daughter cells receive germ plasm and the number of p.p. germ cells increases. Direct counts of the number of p.p. germ cells and measurements of their volume suggest that they divide twice between early gastrula and the stage at which they leave the endoderm. The p.p. germ cells behave similarly to the adjacent endodermal cells until they begin to migrate to the gonad, an event which may represent the first overt signs of differentiation. Measurements of the volume of germ plasm suggest that there is no change through cleavage. The general conclusion is drawn that during cleavage, the morphogenetic determinant germ plasm is segregated to a few cells by the normal processes of cleavage and that subsequently these cells undergo a small number of cloning divisions which are contemporaneous with the first signs of differentiation.

Replacement of posterior by anterior endoderm reduces sterility in embryos from inverted eggs of Xenopus laevis

Development ◽  
1986 ◽  
Vol 94 (1) ◽  
pp. 83-93
Author(s):  
J. H. Cleine
Keyword(s):  
Cell Differentiation ◽  
Xenopus Laevis ◽  
Germ Cell ◽  
Germ Cells ◽  
Germ Plasm ◽  
Primordial Germ Cells ◽  
Inverted Position ◽  
Control Series ◽  
Germ Cell Differentiation ◽  
Tailbud Stage

The genital ridges of Xenopus laevis tadpoles reared from eggs kept in an inverted position contain less than 40 % of the number of primordial germ cells (PGCs) of controls (Cleine & Dixon, 1985). It has been suggested that this reduction is caused by the germ cells' ectopic position in the anterior endoderm of larvae from inverted eggs, from where they may be unable to migrate into the genital ridges (Cleine & Dixon, 1985). This hypothesis is tested here by interchanging anterior and posterior endodermal grafts between pairs of inverted embryos at the early tailbud stage. Replacement of anterior by posterior endoderm has no effect but replacement of posterior by anterior endoderm increases the number of PGCs in the genital ridges and significantly reduces the proportion of sterile embryos. In a control series, in which the same type of grafting was done with normal embryos, replacement of posterior by anterior endoderm reduced the number of germ cells to almost zero, but replacement of anterior by posterior endoderm nearly doubled it. These findings are explained in terms of the distribution of the germ cells in the endoderm at the time of grafting. The results firstly show that the position of the germ cells is crucial to successful migration and secondly they support the notion that germ plasm has a determinative role during early germ cell differentiation.

The effect of u.v. irradiation of the vegetal pole of Xenopus laevis eggs on the presumptive primordial germ cells

Development ◽  
1975 ◽  
Vol 34 (1) ◽  
pp. 209-220
Author(s):  
Brigitta Züst ◽  
K. E. Dixon
Keyword(s):  
Xenopus Laevis ◽  
Germ Cells ◽  
Germ Plasm ◽  
Primordial Germ Cells ◽  
Cell Lineage ◽  
Initial Effect ◽  
Vegetal Pole ◽  
Cortical Regions ◽  
The Individual

The initial effect of u.v. irradiation of the vegetal pole was to inhibit cleavage in the vegetal hemisphere although karyokinesis was not substantially affected. In this way a syncytium formed in the vegetal hemisphere which broke down into individual cells some time between morula and late blastula. The movement of the germ plasm from the peripheral cortical regions into the interior of the egg was not appreciably delayed although aggregation of the germ plasm did not take place until the individual presumptive primordial germ cells were formed when the syncytium broke down. The method of segregation of the germ plasm and formation of the presumptive primordial germ cells was therefore very different in irradiated embryos from the normal orderly processes which depend on normal cleavage patterns. After neurula, the number of presumptive primordial germ cells declined rapidly and at stage 43/44, when the genital ridges in normal embryos contain primordial germ cells, the genital ridges in irradiated embryos were sterile. These results raise the question whether derangement of the segregation of the presumptive primordial germ cells is solely responsible for the later abnormalities in the cell lineage or whether u.v. irradiation affects the germ plasm and therefore indirectly the germ cells.

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