Atypical cyclins: the extended family portrait

Abstract

Regulation of cell division is orchestrated by cyclins, which bind and activate their catalytic workmates, the cyclin-dependent kinases (CDKs). Cyclins have been traditionally defined by an oscillating (cyclic) pattern of expression and by the presence of a characteristic "cyclin box" that determines binding to the CDKs. Noteworthy, the Human Genome Sequence Project unveiled the existence of several other proteins containing the "cyclin box" domain. These potential "cyclins" have been named new, orphan or atypical, creating a conundrum in cyclins nomenclature. Moreover, although many years have passed after their discovery, the scarcity of information regarding these possible members of the family has hampered the establishment of criteria for systematization. Here, we discuss the criteria that define cyclins and we propose a classification and nomenclature update based on structural features, interactors, and phylogenetic information. The application of these criteria allows to systematically define, for the first time, the subfamily of atypical cyclins and enables the use of a common nomenclature for this extended family.

Postnatal Involution and Counter-Involution of the Thymus

“…Approximately 30 members of cyclin family proteins, defined by the cyclin box domain, are known in human and mice (69,70). Among the cyclin family proteins, cyclin A, cyclin B, cyclin D, and cyclin E are canonical cyclins, which interact with cell-cycle-related CDKs and regulate cell division (71,72). These canonical cyclins regulate distinct phases of cell cycle; cyclin A regulates S and G2 phases, cyclin B regulates M phase, cyclin D regulates G1 phase, and cyclin E regulates G1 and S phases (73)(74)(75)(76).…”

Beyond What Your Retina Can See: Similarities of Retinoblastoma Function between Plants and Animals, from Developmental Processes to Epigenetic Regulation

“…Interestingly, there is a different number of genes encoding for each cell cycle protein suggesting the emergence of different and novel lineage-dependent proteins between plants and animals [ 78 ]. For example, it is known that Arabidopsis has 10 genes that code for cyclin-D (CYCD) classified into seven subtypes [ 127 , 128 ], while in humans there are only three [ 129 ]. In contrast, nine E2F are found in humans (three activators and six repressors), and only six in Arabidopsis.…”

Cyclin-dependent kinases and rare developmental disorders

“…Over 30 cyclins have been identified in humans, on the basis of the presence of a cyclin box domain that is responsible for binding and activating CDKs. Functional and phylogenetic studies distinguish 3 subfamilies of CDK and cyclin proteins (cell cycle, transcriptional, atypical) that form combinatorial interactions mostly within each subfamily [ 3 ]. Overexpression and/or dysfunction of CDKs or cyclins have been reported in a very large number of human cancers and other diverse pathologies.…”