Lin28a mRNA is expressed in embryonic epidermis and limb buds, but its expression declines in these tissues after birth. The authors observed that epidermal hair regrowth (after shaving) and digit repair (following amputation 2 days after birth) were increased in an inducible Lin28a-transgenic mouse (iLin28a Tg), which expresses low levels of Lin28a in the absence of induction. Inducing Lin28a in adult mice enabled them to undergo hair regrowth even during the resting phase of the hair follicle cycle. Moreover, wounds in the pinnal tissues of the adult outer ear showed enhanced repair in the iLin28a Tg mouse, and repair was further increased when Lin28a expression was actually induced. Thus, the re-expression of Lin28a in mice enhances tissue repair.
LIN28A represses the biogenesis of let-7 microRNAs, so Shyh-Chang et al. asked whether LIN28A enhanced tissue repair through this mechanism. They observed a decrease in let-7 expression after injury to mouse digits and pinnal tissues. In addition, the induced expression of let-7 in a transgenic mouse decreased the level of pinnal tissue repair, suggesting that let-7 must be repressed for this to occur. However, as repressing let-7 alone did not increase pinnal tissue repair or hair regrowth, LIN28A must influence additional factors to promote these biological processes.
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