Germ cell development, stages

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-... 

Dominant lethal assays in mice were performed using o- and p-cresols. Male mice were given a single dose of o-cresol (0, 75, 250, or 750 mg/kg) or p- cresol (0, 100, 275, or 550 mg/kg) by gavage in corn oil and mated to untreated females in order to assess dominant lethal effects. The matings were continued for 6 weeks so that all stages of male germ cell development were tested. 

Dominant lethal tests are usually conducted in mice or rats. The mouse dominant lethal test is more economical, but the rat dominant lethal test is more informative, as corpora lutea may be accurately enumerated in pregnant female rats, but not in mice, to assess preimplantation loss. Although dominant lethal tests may be performed with treated females, the tests are commonly performed with treated males in order to identify stages sensitive to mutation induction during germ cell development because the knowledge of stage sensitivity is important for risk evaluation. In a typical dominant lethal test, males... 

Weber, R. (1961). In Symp. Germ Cells Earliest Stages Develop. (S. Ranzi, ed.), pp. 22 254. Baselli, Milano, Italy. 

A well-studied example of a tissue-specific DUB activity is fat facets, a UBP originally found in Drosophila [74]. It is important in eye development and germ-cell specification and is active only in specific cell types during certain stages of development [65, 75]. The lack of fat facets results in defective posterior patterning, germ-cell specification, and eye formation. Fat facets activity is required to prevent the inappropriate degradation of vasa and liquid facets. In this case, the role of the DUB appears to be defined by the restricted expression of its known substrates. 

Fig. 1. Dynamics of DNA methylation levels during mouse development. The methylation patterns of the oocyte and the rapidly demethylated after fertilization sperm create the combined methylation patterns in the early mouse zygote. During the first two to three cleavage divisions, the 5mC levels decrease further and stay low through the blastula stage. Post-implantation, the mouse embryo genome is methylated de novo the CpG islands remain mostly unmethylated. The primordial germ cells remain unmethylated. During gametogenesis specific parental (maternal or paternal) patterns of DNA methylation are established at imprinted loci (for further details see Refs. [13, 14]) (re-drawn from Ref [4]).

Most dominant lethals probably result from multiple chromosomal breaks in the germ cells. Frequencies are typically much higher in postspermatogonial stages,104 and often there are characteristic patterns of dominant lethality with regard to different stages of sperm development.104 The results can be very useful in determining... 

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