Comparable results were obtained by Garcia-Castro and coworkers for murine germ cells (García-Castro et al., 1997).
Next, we investigated CCDC6 expression in the GC1 cells, derived from immortalized type B murine germ cells that were found to express good levels of CCDC6.
Hence, even though it seems likely that 5hmC and TET proteins have an important role during fetal germ cell development, Tet1 is dispensable in the development of normal murine germ cells.
Cyclin D1 is expressed in murine germ cells from post natal day 3, which coincides with the appearance of spermatogonia in testis and therefore may control the proliferation and differentiation of these cells.
Next, the resistance to DNA damage-induced apoptosis and the production of reactive oxygen species has been investigated in GC1 cells, derived from immortalized type B murine germ cells, following CCDC6 silencing.
Finally, Nipbl was recently shown to bind chromosomal axes during zygotene in murine germ cells, where it co-localised with cohesin and components of the SC (Kuleszewicz et al. 2013).
This is similar to the observations in the mouse that some degree of methylation was retained in the IAP, Line1 and SineB1 loci in murine germ cells in the undermethylated state [ 7, 8, 15].
To evaluate the coordination of sex-specific transcriptional states during this important interval in germ cell differentiation, we examined placement of the activating histone modification H3K4me3 and the repressive histone modification H3K27me3 in XX and XY murine germ cells before and during the initiation of sex differentiation.
There is a possibility that all of these marks are transiently reverted in mouse gonocytes at a later foetal age, however, it is not likely, given that the subset of murine germ cells, recognised later as stem spermatogonia, do retain some features of PGC, including high expression of pluripotency genes.
However, Pou5f1 (Oct3/4), although best known for its expression by the murine germ-cell lineage and cell lines derived therefrom, is also expressed by both embryonic ectoderm and neuroepithelium (50), and it plays a permissive role in all germ layers in zebrafish (51).
The in vitro culture conditions allowing survival and initial proliferation of murine primordial germ cells from 10.5 days post coitum embryos, which include the use of a murine embryonal fibroblast (STO) feeder, were applied to 21 human seminomas, composed of tumour cells which are considered as the malignant counterparts of human primordial germ cells.
