Taming the transposon: H3K9me3 turns foe to friend in human development.

In this issue of Cell Stem Cell, Xu et al. and Yu et al. use low-input epigenetic profiling techniques to map H3K9me3 deposition in early human development.

A mouse-specific retrotransposon drives a conserved Cdk2ap1 isoform essential for development.

Retrotransposons mediate gene regulation in important developmental and pathological processes. Here, we characterized the transient retrotransposon induction during preimplantation development of eight mammals. Induced retrotransposons exhibit similar preimplantation profiles across species, conferring gene regulatory activities, particularly through long terminal repeat (LTR) retrotransposon promoters.