Non-canonical imprinting in the spotlight

Classical genomic imprints are regulated by parent-specific DNA methylation levels inherited from the gametes in mammals. Imprints control gene expression in a parent-of-origin manner and are essential for development. A distinct class of so-called 'non-canonical' imprints was recently discovered; these are seemingly regulated by histone methylation and govern parent-specific expression of developmentally important genes, most notably in the placenta. This new class of imprinted genes expands the repertoire of asymmetric parental contributions in mammalian embryogenesis, and raises new questions about the functionality of imprinted gene regulation in mammalian development. In this Spotlight, we summarize the latest findings regarding non-canonical imprinting, mainly from the mouse model, and discuss what we know about the conservation of this phenomenon and how it impacts mammalian development.