title: Pre-miRNA loop nucleotides control the distinct activities of mir-181a-1 and mir-181c in early T cell development.
abstract: BACKGROUND
  Mature miRNAs can often be classified into large families, consisting of members with identical seeds (nucleotides 2 through 7 of the mature miRNAs) and highly homologous approximately 21-nucleotide (nt) mature miRNA sequences. However, it is unclear whether members of a miRNA gene family, which encode identical or nearly identical mature miRNAs, are functionally interchangeable in vivo.
  
  
  RESULTS
  We show that mir-181a-1, but not mir-181c, can promote CD4 and CD8 double-positive (DP) T cell development when ectopically expressed in thymic progenitor cells. The distinct activities of mir-181a-1 and mir-181c are largely determined by their unique pre-miRNA loop nucleotides-not by the one-nucleotide difference in their mature miRNA sequences. Moreover, the activity of mir-181a-1 on DP cell development can be quantitatively influenced by nucleotide changes in its pre-miRNA loop region. We find that both the strength and the functional specificity of miRNA genes can be controlled by the pre-miRNA loop nucleotides. Intriguingly, we note that mutations in the pre-miRNA loop regions affect pre-miRNA and mature miRNA processing, but find no consistent correlation between the effects of pre-miRNA loop mutations on the levels of mature miRNAs and the activities of the mir-181a-1/c genes.
  
  
  CONCLUSIONS
  These results demonstrate that pre-miRNA loop nucleotides play a critical role in controlling the activity of miRNA genes and that members of the same miRNA gene families could have evolved to achieve different activities via alterations in their pre-miRNA loop sequences, while maintaining identical or nearly identical mature miRNA sequences.
authors.affiliation: Department of Microbiology and Immunology, Baxter Laboratory of Genetic Pharmacology, Stanford University School of Medicine, Stanford, California, USA.
authors.forename: Gwen
authors.initials: G
authors.lastname: Liu
authors.forename: Hyeyoung
authors.initials: H
authors.lastname: Min
authors.forename: Sibiao
authors.initials: S
authors.lastname: Yue
authors.forename: Chang-Zheng
authors.initials: CZ
authors.lastname: Chen
mesh_terms: D000818:Animals; D001483:Base Sequence; D002454:Cell Differentiation / Q000235:genetics*; D002478:Cells, Cultured; D006410:Hematopoiesis / Q000235:genetics; D006801:Humans; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D035683:MicroRNAs / Q000737:chemistry / Q000502:physiology*; D008954:Models, Biological; D008969:Molecular Sequence Data; D009690:Nucleic Acid Conformation; D012689:Sequence Homology, Nucleic Acid; D013601:T-Lymphocytes / Q000378:metabolism / Q000502:physiology*
chemical_list: D035683:MicroRNAs; C529100:mirn181 microRNA, mouse