The Caenorhabditis elegans heterochronic gene lin-14 encodes a nuclear protein that forms a temporal developmental switch.

During wild-type development, a protein product of the Caenorhabditis elegans heterochronic gene lin-14 is localized to nuclei of specific somatic cells in embryos and early larvae, but is absent in late larvae and adult soma. Gain-of-function lin-14 mutations cause the level of lin-14 protein to remain high throughout development, resulting in developmental reiterations of early cell lineages. The normal down-regulation of the lin-14 nuclear protein level encodes a temporal switch between early and late cell fates.