Nimble and Ready to Mingle: Transposon Outbursts of Early Development.

Transposable elements are the largest individual constituent of mammalian genomes. These elements are highly diverse, a consequence of the multiplicity of genomic habitats that they inhabit and of the complex evolutionary histories that they have developed therein. Intriguingly, a surge of transposable element transcription occurs during mammalian preimplantation development, contributing to the establishment of totipotency and pluripotency and to the activation of the embryonic genome. However, it remains an open question how such an evolutionarily divergent set can mediate such conserved developmental processes. Here, we review transposable element diversity across mammals and their evolutionary significance. We also discuss the implications that their high evolutionary divergence has for the regulation of preimplantation development across mammals.