LIN28 (lin-28 homolog) was first discovered in the nematode C. elegans. It is a heterochronic protein in C. elegans involved in the timing of developmental events and choice of stage specific cell fates. LIN28 e, Xenopus/Amphibian,pression has been found to be regulated post-transcriptionally by miRNAs in both nematodes and mammals. In humans it is e, Xenopus/Amphibian,pressed in embryonic stem cells and its e, Xenopus/Amphibian,pression decreases during differentiation. It is negatively regulated by retinoic acid in neuronal differentiation.