Molecular genetic analysis on the regulatory mechanism for germ-soma differentiation in mammals

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We have established techniques to specifically mark and purify totipotent stem cells as well as primordial germ cells (PGC) from mouse embryos. Using purified PGCs and embryonic cells collected from 16 different developmental stages, representative cDNA libraries have been constructed, and cDNA clones were subjected to one pass sequencing to obtain EST sequences. Homology search of the EST from PGC-expressed genes against GenBank non-redundant database revealed that approximately one third of the cDNA represents novel sequences, and we found a number of known genes whose expression were not known in the PGC in our EST collection. Large-scale RT-PCR expression analysis of about 100 PGC-expressed genes was carried out to examine temporal changes in expression of those genes during germ cell development. We could define distinct gene clusters showing co-expression at specific stages of germ line development. In order to analyze organization of the PGC-expressed genes, 〜2,000 genes have been mapped onto mouse genome. Interestingly, there is a tendency that PGC-expressed genes are clustered on the genome. We have made custom cDNA array using PGC-EST sequences and have done expression analysis, and found that PGC-expressed genes are expressed abundantly in embryonic stem (ES) cells. Taken together, PGC may have expression profile similar to that of ES cell or early embryo like blastocyst implying that these cells share some common regulatory mechanisms for gene expression.