Evidence for hormonal control of heart regenerative capacity during endothermy acquisition.

Tissue regenerative potential displays striking divergence across phylogeny and ontogeny, but the underlying mechanisms remain enigmatic. Loss of mammalian cardiac regenerative potential correlates with cardiomyocyte cell-cycle arrest and polyploidization as well as the development of postnatal endothermy. We reveal that diploid cardiomyocyte abundance across 41 species conforms to Kleiber's law-the ¾-power law scaling of metabolism with bodyweight-and inversely correlates with standard metabolic rate, body temperature, and serum thyroxine level.

Unconventional Functions of Muscles in Planarian Regeneration.

Muscles are traditionally considered in the context of force generation. Scimone et al. (2017), reporting in Nature, now examine muscles in a developmental setting and find unexpected roles for distinct planarian muscle fibers.