Germline-specific expression of the Oct-4/green fluorescent protein (GFP) transgene in mice

The Pic-1, Oct-1,2, Unc-86 (POU) transcription factor Oct-4 is specifically expressed in the germ cell line, and a previous study has indicated that t he expression of the lacZ gene inserted into an 18 kb genomic fragment enco mpassing the Oct-4 gene can come close to mimicking the endogenous embryoni c expression pattern of Oct-4 in transgenic mice. In the present study tran sgenic mice expressing green fluorescent protein (GFP) in the germ cell lin e were generated using the same Oct-4 genomic fragments and the expression pattern was analyzed in detail through all stages of germ cell development. The GFP expressing primordial germ cells were first detected as early as 8 .0 days post-coitum (d.p.c.; early head fold stage) at the base of the alla ntois in living embryos. The GFP expression was thereafter found in both ma le and female germ cells at all developmental stages except in male germ ce lls after differentiating into type A spermatogonia in the postnatal testis . There was also a lower level of expression in female germ cells in the pr ophase of the first meiotic division. These transgenic mice therefore prove d to be powerful tools for isolating living germ cells at various developme ntal stages to study their nature and to isolate new genes.