背景资料：LIN-41, also called tripartite motif-containing 71 (TRIM71), which was first identified in Caenorhabditis elegans, is responsible for the timing of cell fate determination. By encoding microRNAs (miRNAs), the heterochronic genes let-7 and lin-4 downregulate the gene encoding LIN-41. The miRNAs bind to six complementary sites on the 3' untranslated region (UTR) of the LIN-41 gene. This downregulation positively regulates the timing of the expression of LIN-29, an adult specification transcription factor.