Staging of Germ Cells

Evidence for the involvement of a Cdc2/Cyc B complex in the mitotic stages of germ cell development comes from studies in Drosophila. Cyc B transcripts are abundant and uniformly distributed in the early Drosophila embryo (Whitfield et al., 1989, 1990 Lehner and O Farrell, 1990b). Maternally derived Cyc B transcripts are also concentrated at the posterior pole of the oocyte. Later, during embryogenesis, Cyc B tran-... 

Great variation is found in the yield of mutations in the successive weekly matings following treatment, that is, in the response of the various stages of germ cell. This can arise from three main causes primary sensitivity, germinal selection, and metabolic factors. 

Second, Tazima tested the lethality of these mutations in homozygous condition. Mutants for testing were obtained by irradiating several stages of germ cells in both sexes. Among 116 tested, 37 were viable and 79 were accompanied by embryonic lethality. 

The degree of the mutation response to chemical compounds depends on several factors. The mutation curve rises with increasing dose, reaches a plateau at a certain dose (concentration), and then falls off. But what we actually found after treatment with various compounds was not simple due to the interaction of a number of variables. Major variables are dose of chemical, developmental stage of germ cells, metabolic activation of the chemical, and others. Since observed mutation frequencies are the product of interaction among all these factors, they vary more or less from experiment to experiment. 

With regard to the design of the test, mice are mated when 7-8 weeks old. By this age all germ cell stages are present. The test compound is normally administered by the IP route to maximize the likelihood of germ cell exposure. The preferred dose is just below the toxic level so long as fertility is not compromised. One lower dose should also be included. 

Vogel, E.W. Nivard, M.J.M. (1997) The response of germ cells to ethylene oxide, propylene oxide, propylene imine and methyl methanesulfonate is a matter of cell stage-related DNA repair. Environ, mol. Mutag., 29, 124-135... 

Mutation rates depend on the particular target gene, on the individual and the species, and on germ cell stage and sex. The role of germ cell stage is particularly important in the evaluation of human hazard. 

Cytotoxic chemotherapy is the cornerstone of therapy for metastatic testicular cancer. This type of cancer (known as a type of germ cell tumour as it is thought to be derived from cells in the germ cell lineage that are blocked in maturation) has been found to be extremely responsive to chemotherapeutic agents, in particular cisplatin and etoposide. There is no role for radiotherapy at this stage due to the advanced nature of the disease. 

Y. Tazima, Radiobiological studies in the silkworm. I. X-ray irradiation at pupal stage and sensitivity of germ cell, in Papers from Coordinating Committee for Research in Genetics, Vol. 2, pp. 153-162 (1951) (in Japanese). 

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