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.

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.

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.

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).

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

An autoradiographic analysis of nucleic acid synthesis in the presumptive primordial germ cells of Xenopus laevis

Development ◽  
1977 ◽  
Vol 37 (1) ◽  
pp. 13-31
Author(s):  
Marie Dziadek ◽  
K. E. Dixon
Keyword(s):  
Xenopus Laevis ◽  
Germ Cells ◽  
Rna Synthesis ◽  
Primordial Germ Cells ◽  
Acid Synthesis ◽  
Tail Bud ◽  
Blastula Stage ◽  
Autoradiographic Analysis ◽  
The One ◽  
Xenopus Laevis Embryos

Microinjection of [3H]thymidine into Xenopus laevis embryos between late blastula (stage 10) and early tadpole (stage 44) showed that the presumptive primordial germ cells synthesise DNA between stages 10–33. The percentage of labelled cells was highest between stages 10 and 16, declined sharply between stages 22 and 26 and rose again between stages 26 and 33. The fluctuations in the labelling patterns together with increase in the number of presumptive primordial germ cells and direct observation of germ cells in mitosis suggested that the germ cells divide three times between stages 10 and 44. The first divisions probably take place during gastrulation (stages 10–12), the second relatively synchronously at about stages 22–24 and the third series again relatively synchronously about stages 37–39. This period of proliferative activity is distinguishable on the one hand from the cleavage divisions in which the number of germ cells does not increase and on the other hand from the next proliferative phase by a period of mitotic inactivity. Microinjection of [3H]uridine showed that the presumptive primordial germ cells synthesize RNA only in mid-gastrula to early tail-bud-stage embryos. There is no obvious simple causal relationship between RNA synthesis and the movement of the germ plasm to the nucleus, or with division of the germ cells or with their migration out of the endoderm.

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.

An ultrastructural study of germ plasm in spermatogenesis of Xenopus lœvis

Development ◽  
1974 ◽  
Vol 32 (3) ◽  
pp. 573-592
Author(s):  
J. B. Kerr ◽  
K. E. Dixon
Keyword(s):  
Fine Structure ◽  
Mechanism Of Action ◽  
Germ Cells ◽  
Nuclear Membrane ◽  
Germ Plasm ◽  
Germ Line ◽  
Primordial Germ Cells ◽  
Pachytene Spermatocyte ◽  
Gastrula Stage ◽  
Nuclear Pores

Spermatogonia and primary diplotene and zygotene spermatocytes contain an electrondense, finely granular substance which is usually closely associated with mitochondria; small patches of this substance also occur close to the nuclear membrane, often in the nuclear pores, and within the nucleus of primary spermatogonia. The fine structure of this substance is very similar to the fine structure of germ plasm in other stages of development, and since an ontogenetic continuity with germ plasm can be demonstrated, it was concluded that this substance is also germ plasm. The substance disappears about pachytene, earlier than in oogenesis where it persists until mid-diplotene, a difference which may be due to the fact that the oocyte stores large quantities of germ plasm in its cortex for the next generation of primordial germ cells. If the presence of the substance in the nuclear pores and within the nucleus is an indicator of synthesis of germ plasm, then synthesis stops in the secondary spermatogonium, which correlates with the subsequent absence of germ plasm from the pachytene spermatocyte stages. It is suggested that the function of the germ plasm in specifying germ line cells is carried out between the gastrula stage and the beginning of meiosis. The three events which take place during this period are (i) the migration of the presumptive primordial germ cells from the endoderm to the genital ridges, (ii) mitosis of the primordial germ cells and subsequently of the oogonia and spermatogonia in the developing gonads and (iii) preparations for meiosis. It is suggested that the mechanism of action of the germ plasm may be in the control of one or more of these processes. Other types of granular cytoplasmic deposits are also described, and their possible relationship to germ plasm discussed.

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