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).

Contribution to the Study of Germ-cells in the Anura

Development ◽  
1958 ◽  
Vol 6 (3) ◽  
pp. 491-503
Author(s):  
A. W. Blackler
Keyword(s):  
Life Cycle ◽  
Germ Cells ◽  
Germ Line ◽  
Primordial Germ Cells ◽  
Blastula Stage ◽  
The Subject ◽  
Sex Cells

The problems of the germ-line of cells are of long standing in animal biology, but of these two surpass the rest in importance. At what stage in the life-cycle do the primordial germ-cells make their appearance, and do these gonocytes give rise to all, some, or none of the definitive sex-cells? Since Nussbaum (1880, 1884) first discussed the continuity of the germ-cells from one generation to the next, study in this field of embryology has resulted in a measure of agreement that the primordial germ-cells make their appearance in the endoderm or mesoderm early in development. The subject has been extensively reviewed in recent years by Bounoure (1939), Dantschakoff (1941), Everett (1945), Nieuwkoop (1946), and Johnston (1951). In the invertebrates, the origin of the gonocytes during cleavage is well established for some species (e.g. Parascaris), but, for the vertebrates, only Bounoure (1934) makes a claim for the formation of the primordial germ-cells as early as the blastula stage.

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.

Further analysis of the effect of ultra-violet irradiation on the formation of the germ line in Xenopus laevis

Development ◽  
1983 ◽  
Vol 76 (1) ◽  
pp. 67-81
Author(s):  
V. Thomas ◽  
J. Heasman ◽  
C. Ford ◽  
D. Nagajski ◽  
C. C. Wylie
Keyword(s):  
Germ Cells ◽  
Germ Line ◽  
Primordial Germ Cells ◽  
Ultra Violet ◽  
The Other ◽  
Yolk Mass ◽  
Cell Numbers ◽  
Dorsal Axis ◽  
Vegetal Pole ◽  
Dorsal Mesentery

Ultra-violet (u.v.) irradiation of the vegetal pole of newly fertilized eggs has three documented effects: reduction of primordial germ cells (PGCs), cytological damage to the vegetal hemisphere and disruption of the normal mechanism by which the vegetal yolk mass induces the formation of the dorsal axis of the embryo. In this study, we find that 90° rotation of the egg for various periods after irradiation rescues the dorsal axial structures but does not restore the number of PGCs found in the dorsal mesentery of the gut; neither is there any correlation between reduced numbers of PGCs and disruption of cleavage at the vegetal pole. We therefore conclude that the effect on the germ line is separate from the other two phenomena. Secondly, 90° rotation of non-irradiated eggs was found to significantly reduce germ cell numbers migrating in the dorsal mesentery of the gut.

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.

Dual role of Ovol2 on the germ cell lineage segregation during gastrulation in mouse embryogenesis

Development ◽  
2022 ◽  
Author(s):  
Yuki Naitou ◽  
Go Nagamatsu ◽  
Nobuhiko Hamazaki ◽  
Kenjiro Shirane ◽  
Masafumi Hayashi ◽  
...  
Keyword(s):  
Germ Cells ◽  
Splice Variant ◽  
Epithelial To Mesenchymal Transition ◽  
Functional Relationship ◽  
Germ Line ◽  
Primordial Germ Cells ◽  
Cell Lineage ◽  
Animal Kingdom ◽  
Mesenchymal Transition

In mammals, primordial germ cells (PGCs), the origin of the germ line, are specified from the epiblast at the posterior region where gastrulation simultaneously occurs, yet the functional relationship between PGC specification and gastrulation remains unclear. Here, we show that Ovol2, a transcription factor conserved across the animal kingdom, balances these major developmental processes by repressing the epithelial-to-mesenchymal transition (EMT) driving gastrulation and the upregulation of genes associated with PGC specification. Ovol2a, a splice variant encoding a repressor domain, directly regulates EMT-related genes and consequently induces re-acquisition of potential pluripotency during PGC specification, whereas Ovol2b, another splice variant missing the repressor domain, directly upregulates genes associated with PGC specification. Taken together, these results elucidate the molecular mechanism underlying allocation of the germ line among epiblast cells differentiating into somatic cells through gastrulation.

Random X-chromosome inactivation in female primordial germ cells in the mouse

Development ◽  
1981 ◽  
Vol 64 (1) ◽  
pp. 251-258
Author(s):  
Andy McMahon ◽  
Mandy Fosten ◽  
Marilyn Monk
Keyword(s):  
X Chromosome ◽  
Germ Cells ◽  
Germ Line ◽  
Primordial Germ Cells ◽  
Phosphoglycerate Kinase ◽  
X Chromosome Inactivation ◽  
Yolk Sac ◽  
Chromosome Inactivation ◽  
X Chromosomes

The pattern of expression of the two X chromosomes was investigated in pre-meiotic germ cells from 12½-day-old female embryos heterozygous for the variant electrophoretic forms of the X-linked enzyme phosphoglycerate kinase (PGK-1). If such germ cells carry the preferentially active Searle's translocated X chromosome (Lyon, Searle, Ford & Ohno, 1964), then only the Pgk-1 allele on this chromosome is expressed. This confirms Johnston's evidence (1979,1981) that Pgk-1 expression reflects a single active X chromosome at this time. Extracts of 12½-day germ cells from heterozygous females carrying two normal X chromosomes show both the A and the B forms of PGK; since only one X chromosome in each cell is active, different alleles must be expressed in different cells, suggesting that X-chromosome inactivation is normally random in the germ line. This result makes it unlikely that germ cells are derived from the yolk-sac endoderm where the paternally derived X chromosome is preferentially inactivated. In their pattern of X-chromosome inactivation, germ cells evidently resemble other tissues derived from the epiblast.

Developmental expression of c-kit, a proto-oncogene encoded by the W locus

Development ◽  
1990 ◽  
Vol 109 (4) ◽  
pp. 911-923 ◽  
Author(s):  
A. Orr-Urtreger ◽  
A. Avivi ◽  
Y. Zimmer ◽  
D. Givol ◽  
Y. Yarden ◽  
...  
Keyword(s):  
Germ Cells ◽  
Receptor Tyrosine Kinase ◽  
Germ Line ◽  
Primordial Germ Cells ◽  
Mouse Embryos ◽  
Developmental Expression ◽  
Male Germ Line ◽  
Polypeptide Growth Factors ◽  
Adult Ovary

Developmental expression of the c-kit proto-oncogene, a receptor tyrosine kinase encoded by the W locus, was investigated by in situ hybridization in normal mouse embryos. Early after implantation transcripts were detectable only in the maternal placenta (6 1/2-7 1/2 days p.c.). Subsequently (8 1/2 days p.c.) numerous ectodermal (neural tube, sensory placodes) and endodermal (embryonic gut) derivatives expressed c-kit. Later transcripts were detected also in the blood islands of the yolk sac and in the embryonic liver, the main sites of embryonic hemopoiesis. Around midgestation, transcripts accumulated in the branchial pouches and also in primordial germ cells of the genital ridges. This complex pattern of expression remained characteristic also later in gestation, when c-kit was expressed in highly differentiated structures of the craniofacial area, in presumptive melanoblasts and in the CNS. In the adult ovary, maternal c-kit transcripts were detected. They were present in the oocytes of both immature and mature ovarian follicles, but not in the male germ line, where c-kit expression may be down regulated. Thus, c-kit activity is complex and appears in multiple tissues including those that also display defects in mutations at the W locus where c-kit is encoded. Correlation between W phenotypes and c-kit expression, as well as the regulation of the complex and multiple expression of polypeptide growth factors and receptors, is discussed.

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.

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