Satomi S. Tanaka

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.

Regulation of expression of mouse interferon‐induced transmembrane protein like gene‐3, Ifitm3 (mil‐1, fragilis), in germ cells

Mouse interferon‐induced transmembrane protein (IFITM) gene, Ifitm3 (previously known as mil‐1 and fragilis), is expressed in primordial germ cells (PGCs), in their precursors, and in germ cells of the fetal gonads (Saitou et al. [ 2002 ] Nature 418:293–300; Tanaka and Matsui [ 2002 ] Mech Dev 119S:S261–S267). By examining the expression of green fluorescent protein transgene under the control of DNA sequences flanking exon 1, we have identified domains that direct Ifitm3 transcription in PGCs and their precursors in gastrula stage and 13.5 days post coitum embryos. Germ cell‐specific expression is achieved by the activity of a consensus element unique to the Ifitm genes, which may act to suppress Ifitm3 expression in somatic tissues. The lack of any influence of the interferon‐stimulable response elements on transgene expression in the germ‐line suggests that interferon‐mediated response is not critical for activating Ifitm3. Developmental Dynamics 230:651–659, 2004.

Sall4 is essential for mouse primordial germ cell specification by suppressing somatic cell program genes

The Spalt‐like 4 (Sall4) zinc finger protein is a critical transcription factor for pluripotency in embryonic stem cells (ESCs). It is also involved in the formation of a variety of organs, in mice, and humans. We report the essential roles of Sall4 in mouse primordial germ cell (PGC) specification. PGC specification is accompanied by the activation of the stem cell program and repression of the somatic cell program in progenitor cells. Conditional inactivation of Sall4 during PGC specification led to a reduction in the number of PGCs in embryonic gonads. Sall4del/del PGCs failed to translocate from the mesoderm to the endoderm and underwent apoptosis. In Sall4del/del PGC progenitors, somatic cell program genes (Hoxa1 and Hoxb1) were derepressed, while activation of the stem cell program was not impaired. We demonstrated that in differentiated ESCs, Sall4 bound to these somatic cell program gene loci, which are reportedly occupied by Prdm1 in embryonic carcinoma cells. Given that Sall4 and Prdm1 are known to associate with the histone deacetylase repressor complex, our findings suggest that Sall4 suppresses the somatic cell program possibly by recruiting the repressor complex in conjunction with Prdm1; therefore, it is essential for PGC specification. Stem Cells 2015;33:289–300