Normal germ line establishment in mice carrying a deletion of the Ifitm/Fragilis gene family cluster

The family of interferon-inducible transmembrane proteins (Ifitm) consists of five highly sequence-related cell surface proteins, which are implicated in diverse cellular processes. Ifitm genes are conserved, widely expressed, and characteristically found in genomic clusters, such as the 67-kb Ifitm family locus on mouse chromosome 7. Recently, Ifitm1 and Ifitm3 have been suggested to mediate migration of early primordial germ cells (PGCs), a process that is little understood. To investigate Ifitm function during germ cell development, we used targeted chromosome engineering to generate mutants which either lack the entire Ifitm locus or carry a disrupted Ifitm3 gene only. Here we show that the mutations have no detectable effects on development of the germ line or on the generation of live young. Hence, contrary to previous reports, Ifitm genes are not essential for PGC migration. The Ifitm family is a striking example of a conserved gene cluster which appears to be functionally redundant during development.