scholarly journals Mutations affecting early distribution of primordial germ cells in Medaka (Oryzias latipes) embryo

2004 ◽  
Vol 121 (7-8) ◽  
pp. 817-828 ◽  
Author(s):  
Takao Sasado ◽  
Chikako Morinaga ◽  
Katsutoshi Niwa ◽  
Ai Shinomiya ◽  
Akihito Yasuoka ◽  
...  
Keyword(s):  
Germ Cells ◽  
Primordial Germ Cells ◽  
Oryzias Latipes

Sex differentiation of germ cells in the teleost, Oryzias latipes, during normal embryonic development

Development ◽  
1972 ◽  
Vol 28 (2) ◽  
pp. 385-395
Author(s):  
Noriyuki Satoh ◽  
Nobuo Egami
Keyword(s):  
Germ Cells ◽  
Meiotic Prophase ◽  
Sex Differentiation ◽  
Primordial Germ Cells ◽  
Oryzias Latipes ◽  
The Other ◽  
Histological Structure ◽  
The Mean ◽  
Further Development ◽  
Normal Embryonic Development

Mitotic and meiotic activities of germ cells during early development in the medaka, Oryzias latipes, are dealt with in this report. Primordial germ cells were obviously distinguishable from somatic cells 3 days after fertilization and began to proliferate about 7 days after fertilization. The mean number of primordial germ cells increased during a period of 7–10 days after fertilization, reaching about 90 immediately before hatching. Newly hatched fry could be classified into two types according to the number and the nucleic activity of germ cells in the gonadal rudiment. One type consisted of fry containing about 100 germ cells and no cells in the meiotic prophase. In the other type of fry the number of germ cells increased by mitotic divisions and some of the cells began to enter into the meiotic prophase. During the course of further development the fry of the former type differentiated into males and the latter into females. Therefore it can be concluded that the morphological sex differentiation of germ cells occurs at the time of hatching. However, no sexual differences in the histological structure of somatic elements in the gonad are observable at that time.

An ultrastructural study of sex differentiation in the teleost Oryzias latipes

Development ◽  
1974 ◽  
Vol 32 (1) ◽  
pp. 195-215
Author(s):  
Noriyuki Satoh
Keyword(s):  
Body Length ◽  
Germ Cells ◽  
Leydig Cells ◽  
Sex Differentiation ◽  
Primordial Germ Cells ◽  
Somatic Cells ◽  
Oryzias Latipes ◽  
Follicle Cells ◽  
Animal Cells ◽  
Ultrastructural Characteristics

Electron-microscopic observations on sex differentiation during normal development in the medaka, Oryzias latipes, are presented in this report. Primordial germ cells in embryos 6–10 days after fertilization are clearly distinguishable from somatic cells by the presence in the cytoplasm of the former of germinal dense bodies, closely associated with large aggregations of mitochondria. The gonadal primordium is composed of the primordial germ cells and the enveloping somatic cells; no special ultrastructural relationships have been detected between these two cell types. The sex of an embryo cannot be decided by means of the electron microscope. The newly formed ovary is distinguishable in newly hatched fry of about 5 mm total body length. In the ovary, a layer of cells forming the ovarian wall encloses the ovarian matrix, consisting of oogonia and their surrounding follicle cells. There are often observable desmosomes between two neighbouring follicle cells. Although marked rearrangement of somatic cells takes place during sex differentiation of the gonad, few visible changes are observed in the ultrastructure of the primordial germ cells during their transition to oogonia. The transition from the oogonium to the oocyte is, however, characterized by a distinctive change in the nucleus, associated with the onset of meiosis. In the young ovary of 5-day-old fry, ooctye chromatin is visibly organized into electron-dense axial elements at the leptotene stage of meiotic prophase. But in the ovary of 10-day-old fry (about 6 mm body length), many oocytes at zygotene or pachytene stages are found, with synaptonemal complex configurations essentially the same as those described in numerous other meiosing plant and animal cells. In contrast, the testis of newly hatched male fry remains in an undifferentiated state, with the somatic cells simply enveloping the spermatogonia. No cells with the ultrastructural characteristics of Leydig cells (as observed in adult testis) can be distinguished in the young ovary or in the undifferentiated testis 10 days after hatching. Cells with the ultrastructural characteristics of adult Leydig cells are detectable for the first time in the matrix of the testis of 25-day-old young, about 8 mm in total length. When proliferation of spermatogonia has occurred, to form the typical testis of 45-day-old (about 15 mm), young, these cells appear in the interstitial region of the testis. Observations from the present study indicate that sex differentiation of germ cells and somatic cells in the gonad precedes the differentiation of steroid-secreting cells. Therefore, the hypothesis that sex hormones are natural sex-inducers is not supported by the present results. The possibility is emphasized that some intracellular mechanisms may be involved in the natural course of sex differentiation of the germ cells and the gonad in this fish.

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