Issue Information.

Cover Photograph: Live‐cell fl uorescence imaging to show X chromosome inactivation (XCI) at an E6.25 mouse embryo. Green and red show maternally and paternally derived X chromosome, respectively. Either the maternally or paternally derived X chromosomes begin to be silenced randomly in the epiblast. However, in the visceral endoderm and extraembryonic ectoderm, the paternal X chromosome is inactivated selectively by imprinted XCI, and only the maternal X chromosome (green) is active (See Kobayashi pp. 493–500). [ABSTRACT FROM AUTHOR]