MicroRNAs(MIRNAs)are about 22 nucleotides small regulatory RNAs, which produced from hairpin-like precursors, and suppressing translation of target genes by binding to mRNA. MicroRNAs perform the role of gene regulation. Upstream regions of gense afe associated with transcription, and it is known that they could have one or many transcript start sites in eularyotes, and named these promoter regions, and CpG islands are often associated with promoter regions. In this research, we look for mouse (Mus musculus),rat(Rattus norvegicus), chicken(Gallus gallus)and wester claw frog (Xenopus tropicalis）CpG-island-associated miRNA are 10%(37/373),10.7%(25/234), 16.7%(25/149) and 6.2%(11/177) for mouse, rat, chicken and weater claw frog respectively.Furthermore, most of these CpG-island-associated miRNA genes are located near the intronic and intergenic regions. For mouse, among the seven promoter-associated miRNA genes four are CpG-island-associated as well. Mouse has 30 pre-miRNAs overlap with the first intron of a gene, rat has six(among them two are correlated with CpG islands), wester claw fong has three, and chicken has none.
