MicroRNA-Directed Cleavage of HOXB8 mRNA,Soraya Yekta,I-hung Shih, David P.Bartel23 APRIL 2004 VOL 304 SCIENCE,Hox genes in mammals,The vertebrate homeotic complex comprises four distinct Hox gene clusters (Hox A, B, C, D) that are organized into thirteen homology The chromosomal organization of the genes in each Hox cluster reflects its anterior-posterior expression in the body plan (spatial colinearity). In general, members of the same subgroup are expressed at the same time and have the same anterior boundary of expression,The current model for the biogenesis and post-transcriptional suppression of microRNAs and siRNAs,Recent progress,In plant, most miRNAs anneal to their targets with nearly complete complementarity at a single site,leading to mRNAs cleavage and degradationThe extent of complementarity between the siRNA/miRNA and its target can determine the mechanism of silencing,miR-196 in Vertebrate,The sequence and genomic context of the vertebrate miR-196 family,Bold: residues of the mature miRNA; Red: miRNAs validated by cloning. Asterisks: perfectly conserved residues,Overview of the 5 RACE Procedure,RNAse protection assay,The Northern blot probes total RNA from 7-day, 11-day, 15-day, and 17-day mouse embryos (lanes 14, respectively) M :33P-labeled RNA size markers,Expression of miR-196 during mouse embryonic development.,MiR-196directed cleavage of HOXB8 mRNA(1),black Absolutely conserved nucleotides; red complementary site ; pink G:U wobble,MiR-196directed cleavage of HOXB8 mRNA(2),perfect antisense sequence of miR-196a: miR-196a-as perfect antisense sequence of miR-1d: miR-1d-as miR-1d expressed in skeletal muscle cells,MiR-196directed cleavage of HOXB8 mRNA(3),Additional HOX genes predicted to be regulatory targets of miR-196(1),Wide red bars extensive complementarity, narrow bars seed matches, Asterisks slightly relaxed seed matches that permit G:U wobble,Sequence alignment of the miR-196 complementary site, and a representative complementary seed and flanking regions in the 3 UTRs of HOXC8 and HOXD8 genes.,Black:absolutely conserved nucleotides Red: miR-196 complementary site and the seed Pink:G:U wobbles,Additional HOX genes predicted to be regulatory targets of miR-196(2),Additional HOX genes predicted to be regulatory targets of miR-196(3),Discussion,Transcriptional repression may also involved Genetic model of mRNA cleavage in vivo The difference of miRNA and siRNA The mechanism of miRNA function,Thank you!,