Developmentally regulated expression of mil-1 and mil-2, mouse interferon-induced transmembrane protein like genes, during formation and differentiation of primordial germ cells

In all multicellular organisms, germ cells originating from a fertilized egg have the highly specialized role of transmitting genetic information to the next generation. In many animal species, the establishment of the germ cell lineage is regulated by the maternally inherited germplasm. In mammals, however, germline determination is not based on the unequal distribution of maternal determinants. In the processes of mammalian germ cell formation and subsequent differentiation, the molecular basis of the acquisition of germ cell status is not well understood. Since migrating primordial germ cells (PGCs) are lineage-restricted to the germline, they have already acquired a germ cell specific fate distinct from that of pluri/multi-potent stem cells. However, there have been no molecules known to be expressed in migrating PGCs but not in the inner cell mass of blastocysts. Such molecules should be involved in early germ cell development, and they should make good markers for following the process of PGC formation. To identify such molecules, we performed a subtracted cDNA screening with migrating PGCs and blastocysts in mice, and isolated 11 clones preferentially expressed in PGCs. Here, we report the identification of two genes with similarity to human interferon-induced transmembrane protein (Ifitm) genes, and expression patterns of these genes in forming and in differentiating PGCs. During germ cell formation, mouse Ifitm like (mil)-1 was expressed in putative PGC ancestors in embryos at 6.5-7.5 days post coitum. In migrating PGCs, mil-1 expression was continuously observed and mil-2 expression was first detected during germ cell differentiation.