Two small RNAs regulate the timing of Caenorhabditis elegans development. Transition from the first to the second larval stage fates requires the 22-nucleotide
lin-4 RNA, and transition from late larval to adult cell fates requires the 21-nucleotide
let-7 RNA. The
lin-4 and
let-7 RNA genes are not homologous to each other, but are each complementary to sequences in the 3' untranslated regions of a set of protein-coding target genes that are normally negatively regulated by the RNAs. Here we have detected
let-7 RNAs of approximately 21 nucleotides in samples from a wide range of animal species, including vertebrate, ascidian, hemichordate, mollusc, annelid and arthropod, but not in RNAs from several cnidarian and poriferan species, Saccharomyces cerevisiae, Escherichia coli or Arabidopsis. We did not detect
lin-4 RNA in these species. We found that
let-7 temporal regulation is also conserved:
let-7 RNA expression is first detected at late larval stages in C. elegans and Drosophila, at 48 hours after fertilization in zebrafish, and in adult stages of annelids and molluscs. The
let-7 regulatory RNA may control late temporal transitions during development across animal phylogeny.AD - Department of Molecular Biology, Massachusetts General Hospital, Harvard Medical School, Boston 02114, USA.FAU - Pasquinelli, A EAU - Pasquinelli AEFAU - Reinhart, B JAU - Reinhart BJFAU - Slack, FAU - Slack FFAU - Martindale, M QAU - Martindale MQFAU - Kuroda, M IAU - Kuroda MIFAU - Maller, BAU - Maller BFAU - Hayward, D CAU - Hayward DCFAU - Ball, E EAU - Ball EEFAU - Degnan, BAU - Degnan BFAU - Muller, PAU - Muller PFAU - Spring, JAU - Spring JFAU - Srinivasan, AAU - Srinivasan AFAU - Fishman, MAU - Fishman MFAU - Finnerty, JAU - Finnerty JFAU - Corbo, JAU - Corbo JFAU - Levine, MAU - Levine MFAU - Leahy, PAU - Leahy PFAU - Davidson, EAU - Davidson EFAU - Ruvkun, GAU - Ruvkun GLA - engPT - Journal ArticleCY - ENGLANDTA - NatureJID - 0410462RN - 0 (RNA, Helminth)RN - 63231-63-0 (RNA)SB - IMSB - S