The germ cell lineage is the sole cell lineage through which genomic information is transmitted into successive generations. To this end, germ cells undergo various specific differentiation steps including meiosis, whose regulation seems to correlate closely with fundamental mechanisms that create differences between germ cells and somatic cells. In mammals, meiosis is triggered by extra-embryonic stimuli such as retinoic acid, which may induce various intracellular molecular cascades promoting meiosis. In addition, the specific epigenetic status arranged in germ cells before and after induction of meiosis, including meiosis-specific transcription control based on histone methylation by a novel histone methyltransferase Meisetz, is also critical for its proper progression.