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.

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.

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 Formative pluripotent stem cells show features of epiblast cells poised for gastrulation

Cell Research ◽  
2021 ◽  
Author(s):  
Xiaoxiao Wang ◽  
Yunlong Xiang ◽  
Yang Yu ◽  
Ran Wang ◽  
Yu Zhang ◽  
...  
Keyword(s):  
Stem Cells ◽  
Germ Cells ◽  
Pluripotent Stem Cells ◽  
Primordial Germ Cells ◽  
Embryonic Stem ◽  
Large Set ◽  
Mouse Escs ◽  
Epiblast Stem Cells ◽  
Early Gastrula

AbstractThe pluripotency of mammalian early and late epiblast could be recapitulated by naïve embryonic stem cells (ESCs) and primed epiblast stem cells (EpiSCs), respectively. However, these two states of pluripotency may not be sufficient to reflect the full complexity and developmental potency of the epiblast during mammalian early development. Here we report the establishment of self-renewing formative pluripotent stem cells (fPSCs) which manifest features of epiblast cells poised for gastrulation. fPSCs can be established from different mouse ESCs, pre-/early-gastrula epiblasts and induced PSCs. Similar to pre-/early-gastrula epiblasts, fPSCs show the transcriptomic features of formative pluripotency, which are distinct from naïve ESCs and primed EpiSCs. fPSCs show the unique epigenetic states of E6.5 epiblast, including the super-bivalency of a large set of developmental genes. Just like epiblast cells immediately before gastrulation, fPSCs can efficiently differentiate into three germ layers and primordial germ cells (PGCs) in vitro. Thus, fPSCs highlight the feasibility of using PSCs to explore the development of mammalian epiblast.

Germ plasm and the origin of the primordial germ cells in the oriental river prawn Macrobrachium nipponense

2021 ◽  
Author(s):  
Ying Chen ◽  
Xiang Fang ◽  
Xiao-Qing Tian ◽  
Zheng Cui ◽  
Hai-Yang Feng ◽  
...  
Keyword(s):  
Germ Cells ◽  
Germ Plasm ◽  
Primordial Germ Cells ◽  
Macrobrachium Nipponense ◽  
Oriental River Prawn

The positional effect of presumptive primordial germ cells (pPGCs) on their differentiation into PGCs in Xenopus

Development ◽  
1988 ◽  
Vol 102 (3) ◽  
pp. 527-535
Author(s):  
K. Ikenishi ◽  
Y. Tsuzaki
Keyword(s):  
Germ Cells ◽  
Germ Plasm ◽  
Germ Line ◽  
Anterior Part ◽  
Primordial Germ Cells ◽  
Positional Effect ◽  
In Series

To determine whether the location of ‘germ plasm’-bearing cells [presumptive primordial germ cells (pPGCs)] is crucial for their differentiation into PGCs in Xenopus, [3H]thymidine-labelled pPGCs were implanted into the anterior or posterior halves of the endoderm in unlabelled host neurulae. Labelled PGCs in the genital ridges of experimental tadpoles were investigated by autoradiography. When the labelled pPGCs were implanted into posterior halves of the endoderm where host pPGCs are situated, 65 and 77% of the experimental tadpoles (designated as p-tadpoles) had the labelled PGCs in series I and II, respectively. When implanted into the anterior halves, 20 and 27% of the experimental tadpoles (a- tadpoles) had the labelled PGCs in series I and II, respectively. In p-tadpoles, the average numbers of labelled PGCs per tadpole were 8á7 in series I and 10 in series II, whereas they were 2á0 in a-tadpoles of both series. Both the proportion and the average number in p-tadpoles of both series were significantly different from those in a-tadpoles. In both series, labelled PGCs in p-tadpoles were found to be distributed throughout the genital ridges while those in a-tadpoles were localized only in the anterior part of the ridges. These facts indicate that the location of pPGCs in the endoderm affects their successful migration into the genital ridges, and that not only the presence of the germ plasm but also the proper location in endoderm are prerequisites to PGC differentiation of the germ line cells.

Partial characterization of ‘primordial germ cell-forming activity’ localized in vegetal pole cytoplasm in anuran eggs

Development ◽  
1977 ◽  
Vol 39 (1) ◽  
pp. 221-233
Author(s):  
Masami Wakahara
Keyword(s):  
Germ Cells ◽  
Germ Plasm ◽  
Primordial Germ Cells ◽  
Primordial Germ Cell ◽  
Differential Centrifugation ◽  
Rana Chensinensis ◽  
Crude Homogenate ◽  
Germinal Granules ◽  
Vegetal Pole

Larvae of Rana chensinensis developed from fertilized eggs which had been subjected to ultraviolet (u.v.) irradiation on their vegetal hemisphere at a dose of 20000 ergs/mm2 within 60 min of fertilization contained no primordial germ cells (PGCs) when examined histologically at the stage when the operculum was complete (8 days after fertilization at 18 °C, stage 25 according to Shumway, 1940). The morphogenetic ability of vegetal pole cytoplasm from non-irradiated eggs to establish the PGCs was tested by injecting some fractions of this cytoplasm into the vegetal hemisphere of u.v.-irradiated eggs. Crude homogenate of the vegetal pole cytoplasm without large yolk platelets was able to restore the PGCs when injected into u.v.-irradiated eggs, but a similar fraction from animal half cytoplasm had no ability to form PGCs. The ‘PGC-forming activity’ demonstrated in the crude homogenate of the vegetal pole cytoplasm was not abolished by dialysis, lyophilization and heating to 90 °C for 10 min. When the homogenate was fractionated by differential centrifugation in 0·25 M sucrose, the ‘PGC-forming activity’ was recovered mainly in the precipitate of 15000g for 30 min. The precipitate of 7000 g for 10 min had also a little ‘activity’. The possibility was discussed that the ‘PGC-forming activity’ demonstrated in the vegetal pole cytoplasm was associated with the germinal granules in the germ plasm rather than the mitochondria.

Histological and quantitative changes in the annual testicular cycle of Triturus marmoratus marmoratus

1990 ◽  
Vol 68 (1) ◽  
pp. 63-72 ◽  
Author(s):  
Francisco Jose Saez ◽  
Benito Fraile ◽  
Ricardo Paniagua
Keyword(s):  
Endoplasmic Reticulum ◽  
Germ Cell ◽  
Germ Cells ◽  
Primordial Germ Cells ◽  
Light And Electron Microscopy ◽  
Second Phase ◽  
Glandular Tissue ◽  
Quantitative Studies ◽  
Quantitative Changes ◽  
Triturus Marmoratus

Eight male marbled newts (Triturus marmoratus marmoratus) were collected on the 15th of each month in 1987 and their testes were studied by light and electron microscopy. Quantitative studies also were performed to establish the annual testicular cycle and the total volume per testis occupied by each germ cell type throughout the year. Characteristic ultrastructural features of germ cells are the occurrence of a well-developed Golgi complex in primary spermatogonia; multiple small dictyosomes and nuclear blebs in primary spermatocytes; peripherally situated mitochondria; long strands of endoplasmic reticulum and subsurface cisternae in round spermatids; and abundant rough endoplasmic reticulum in follicular cells. Secondary spermatocytes have a short or absent interphase and are observed in the prophase. The annual testicular cycle comprises three periods: (i) germ cell proliferation (May–June), characterized by the formation of primary spermatocytes that undergo meiosis, giving rise to round spermatids; (ii) spermiogenesis (July–September), during which round spermatids develop into spermatozoa and the interstitial boundary cells are transformed into glandular tissue cells; and (iii) testicular quiescence (October–April) in which the testis contains only spermatozoa, glandular tissue, and a few primordial germ cells and spermatogonia. In the second phase of testicular quiescence (February–April) spermatozoa are released from the testis and proliferation of secondary spermatogonia occurs.

scholarly journals The spermatogenesis of acaris habena linton

1918 ◽  
Author(s):  
◽  
Hope Hibbard
Keyword(s):  
Germ Cells ◽  
Primordial Germ Cells ◽  
Growth Period ◽  
Number Of Cells

Text from pages 2-3: "In the development of spermatozoa, there are first differentiated in the embryo the primordial germ cells. These divide and subdivide until a large number of cells, known as spermatogonia, are formed. Then the cells begin to increase in size and following this growth period, there are two maturation divisions during which the chromatin content becomes reduced one half. The cells produced by these divisions become immediately the functional germ cells, or spermatozoa. It is the behavior of the chromosomes of Ascaris habena during the maturation divisions that is discussed in the following pages."

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