title: Evolutionary relationships between miRNA genes and their activity.
abstract: BACKGROUND
  The emergence of vertebrates is characterized by a strong increase in miRNA families. MicroRNAs interact broadly with many transcripts, and the evolution of such a system is intriguing. However, evolutionary questions concerning the origin of miRNA genes and their subsequent evolution remain unexplained.
  
  
  RESULTS
  In order to systematically understand the evolutionary relationship between miRNAs gene and their function, we classified human known miRNAs into eight groups based on their evolutionary ages estimated by maximum parsimony method. New miRNA genes with new functional sequences accumulated more dynamically in vertebrates than that observed in Drosophila. Different levels of evolutionary selection were observed over miRNA gene sequences with different time of origin. Most genic miRNAs differ from their host genes in time of origin, there is no particular relationship between the age of a miRNA and the age of its host genes, genic miRNAs are mostly younger than the corresponding host genes. MicroRNAs originated over different time-scales are often predicted/verified to target the same or overlapping sets of genes, opening the possibility of substantial functional redundancy among miRNAs of different ages. Higher degree of tissue specificity and lower expression level was found in young miRNAs.
  
  
  CONCLUSIONS
  Our data showed that compared with protein coding genes, miRNA genes are more dynamic in terms of emergence and decay. Evolution patterns are quite different between miRNAs of different ages. MicroRNAs activity is under tight control with well-regulated expression increased and targeting decreased over time. Our work calls attention to the study of miRNA activity with a consideration of their origin time.
authors.affiliation: Department of Cardiology, Gansu Provincial Hospital, Lanzhou 730000, China.
authors.forename: Yan
authors.initials: Y
authors.lastname: Zhu
authors.forename: Geir
authors.initials: G
authors.lastname: Skogerbø
authors.forename: Qianqian
authors.initials: Q
authors.lastname: Ning
authors.forename: Zhen
authors.initials: Z
authors.lastname: Wang
authors.forename: Biqing
authors.initials: B
authors.lastname: Li
authors.forename: Shuang
authors.initials: S
authors.lastname: Yang
authors.forename: Hong
authors.initials: H
authors.lastname: Sun
authors.forename: Yixue
authors.initials: Y
authors.lastname: Li
mesh_terms: D019143:Evolution, Molecular; D020869:Gene Expression Profiling; D005796:Genes / Q000235:genetics*; D006801:Humans; D054643:INDEL Mutation / Q000235:genetics; D035683:MicroRNAs / Q000145:classification / Q000235:genetics* / Q000502:physiology*; D059645:Mutation Rate; D020641:Polymorphism, Single Nucleotide / Q000235:genetics; D013045:Species Specificity; D013997:Time Factors
chemical_list: D035683:MicroRNAs