Phylogenetic Analysis Of Rb And CDK Proteins In Premetazoan Lineages

The RB-E2F pathway is conserved in most eukaryotic lineages, including animals and plants. E2F and RB family proteins perform crucial functions in cycle controlling, differentiation, development and apoptosis. The cyclin-dependent kinases (CDKs) together with cyclin family are thought to be the cornerstone in cell cycle control. Here, we performed a comprehensive evolutionary analysis of E2F, RB, CDK and cyclin familyFor E2F, RB family, several interesting facts were revealed. First, orthologues of RB, E2F, and DP family are present in several representative unicellular organisms and all multicellular organisms we checked. Second, ancestral E2F, RB genes duplicated before placozoans and bilaterians diverged, thus E2F family was divided into E2F4/5 subgroup (including repressive E2Fs:E2F4 and E2F5) and E2F1/2/3 subgroup (including active E2Fs:E2F1, E2F2 and E2F3), RB family was divided into RB1 subgroup (including RB1) and RBL subgroup (including RBL1 and RBL2). Third, E2F4 and E2F5 share more sequence similarity with the predicted E2F ancestral sequence than E2F1, E2F2 and E2F3; E2F4 and E2F5 also possess lower evolutionary rates and higher purification selection pressures than E2F1, E2F2 and E2F3. Fourth, for RB family, the RBL subgroup proteins possess lower evolutionary rates and higher purification selection pressures compared with RB subgroup proteins in vertebrates. Protein evolutionary rates and purification selection pressures are usually linked with protein functions. We speculated that function conducted by E2F4/5 subgroup and RBL subgroup proteins might mainly represent the ancient function of RB-E2F pathway, and the E2F1/2/3 subgroup proteins and RB1 protein might contribute more functional diversification in RB-E2F pathway. Our results will enhance the current understanding of RB-E2F pathway and will also be useful to further functional studies in human and other model organisms.For CDK and cyclin families, we found that CDK family could be divided into 8 subfamilies,7 CDK subfamilies (CDK1/2/3, CDK5, CDK7, CDK 20, CDK8/19, CDK9, CDK10711) are conserved in metazoans and fungi, however, CDK4/6 subfamily is only found in eumetazoans. For cyclin family, it was found that cyclin C, H, L, Y subfamily, and cyclin K and T as a whole subfamily, are general conserved in animal, fungi, and amoeba Dictyostelium discoideum. However, cyclin B, A, E, D subfamilies, which are recognized as cell cycle related cyclins, are found to own different evolutionary histories. Cyclin B subfamily is general conserved in D. discoideum, fungi, and animals; cyclin A subfamily and cyclin E subfamily are both present in animal and its unicellular relatives, such as choanoflagellate Monosiga brevicollis and filasterean Capsaspora Owczarzaki, but absent in fungi and amoeba D. discoideum; Cyclin D subfamily, though its orthologs could be found as early as in no opisthokontan organism apusozoa Thecamonas trahens. In opisthokonta, cyclin D subfamily is only conserved in eumetazons, and absent in fungi, choanoflagellates, and basal metazoan Amphimedon queenslandica. Thus, our data indicated that the emergence of CDK4/6 subfamily is linked simultaneously with eumetazoans appearance, and the evolutionary conservation of cyclin D subfamily, the binding pattern of CDK4/6 subfamily, also is tightly linked with eumetazoans occurrence. We speculated that the emerging CDK4/6 and cyclin D complex might be a key evolutionary step of cell cycle controlling during the progress of eumetazoa emergence.