LINE1 and its host: one cell's junk is another cell's treasure.

LINE1 (L1) retrotransposons have gained notoriety for their involvement in a slew of pathologies. While improper de-repression of L1 transcription may drive disease, mammalian cells have coopted L1 activation into mechanisms essential for cell function. New findings published by Mangiavacci et al (2024) in The EMBO Journal reveal the role of L1 RNA in stimulating osteogenic activity during bone repair in both mice and humans, highlighting a previously undescribed beneficial regulatory role for L1 activity.