The gene lin-28 was originally identified through a mutant of the nematode Caenorhabditis
elegans displaying defects in developmental timing. It is expressed stage-specifically in
tissues throughout the animal and is required for cell fates to be expressed at the
appropriate stage of larval development. lin-28 encodes a cytoplasmic protein with a unique
pairing of RNA-binding motifs. Diverse animals possess Lin-28 homologues and mouse Lin-
28 is expressed in embryos, embryonic stem cells and embryonal carcinoma cells, but not in …