title: Phylogenetic analysis of CDK and cyclin proteins in premetazoan lineages.
abstract: BACKGROUND
  The molecular history of animal evolution from single-celled ancestors remains a major question in biology, and little is known regarding the evolution of cell cycle regulation during animal emergence. In this study, we conducted a comprehensive evolutionary analysis of CDK and cyclin proteins in metazoans and their unicellular relatives.
  
  
  RESULTS
  Our analysis divided the CDK family into eight subfamilies. Seven subfamilies (CDK1/2/3, CDK5, CDK7, CDK 20, CDK8/19, CDK9, and CDK10/11) are conserved in metazoans and fungi, with the remaining subfamily, CDK4/6, found only in eumetazoans. With respect to cyclins, cyclin C, H, L, Y subfamilies, and cyclin K and T as a whole subfamily, are generally conserved in animal, fungi, and amoeba Dictyostelium discoideum. In contrast, cyclin subfamilies B, A, E, and D, which are cell cycle-related, have distinct evolutionary histories. The cyclin B subfamily is generally conserved in D. discoideum, fungi, and animals, whereas cyclin A and E subfamilies are both present in animals and their unicellular relatives such as choanoflagellate Monosiga brevicollis and filasterean Capsaspora owczarzaki, but are absent in fungi and D. discoideum. Although absent in fungi and D. discoideum, cyclin D subfamily orthologs can be found in the early-emerging, non-opisthokont apusozoan Thecamonas trahens. Within opisthokonta, the cyclin D subfamily is conserved only in eumetazoans, and is absent in fungi, choanoflagellates, and the basal metazoan Amphimedon queenslandica.
  
  
  CONCLUSIONS
  Our data indicate that the CDK4/6 subfamily and eumetazoans emerged simultaneously, with the evolutionary conservation of the cyclin D subfamily also tightly linked with eumetazoan appearance. Establishment of the CDK4/6-cyclin D complex may have been the key step in the evolution of cell cycle control during eumetazoan emergence.
authors.affiliation: State Key Laboratory of Genetic Engineering, Institute of Genetics, School of Life Sciences, Fudan University, Shanghai 200433, PR China. lihuancao@fudan.edu.cn.
authors.forename: Lihuan
authors.initials: L
authors.lastname: Cao
authors.forename: Fang
authors.initials: F
authors.lastname: Chen
authors.forename: Xianmei
authors.initials: X
authors.lastname: Yang
authors.forename: Weijin
authors.initials: W
authors.lastname: Xu
authors.forename: Jun
authors.initials: J
authors.lastname: Xie
authors.forename: Long
authors.initials: L
authors.lastname: Yu
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D018844:Cyclin-Dependent Kinases / Q000737:chemistry / Q000145:classification* / Q000235:genetics; D016213:Cyclins / Q000737:chemistry / Q000145:classification* / Q000235:genetics; D056890:Eukaryota / Q000145:classification* / Q000201:enzymology / Q000235:genetics*; D019143:Evolution, Molecular; D005658:Fungi / Q000145:classification* / Q000201:enzymology* / Q000235:genetics; D008969:Molecular Sequence Data; D005810:Multigene Family; D010802:Phylogeny
chemical_list: D016213:Cyclins; D018844:Cyclin-Dependent Kinases