Final Activity Report Summary - CYCLIN A2 (Impact of Cyclin A2 deregulation in mouse physiology, cellular transformation and cancer)
The cell cycle allows the division of a cell into two daughter cells bearing identical genomic material to the parental cell. This process is subdivided in several phases: growth and preparation of the DNA in G1 phase, doubling of the DNA in S phase, preparation of the division in G2 and halving of the genome during mitosis (M phase). The cell cycle is a complex process that is highly regulated by cyclin-dependent kinases (Cdks). Cdks function at different phases of the cell cycle and are regulated by their association with specific cofactors, among which the cyclins play a dual role of activators and targeting agents towards specific proteins. Different cyclins exhibit distinct expression patterns that contribute to the temporal coordination of each cell cycle event. Two forms of cyclin A exist in mammals. Cyclin A2 is ubiquitously expressed, and activates Cdk2 or Cdk1 kinases to promote both S phase progression and G2/M transition, respectively. In contrast, cyclin A1 pairs with CDK1 only, and is present in germ cells in testis. Cyclin A2 whose expression is more ubiquitous, is essential for embryonic development, the embryos depleted for this protein dying at day 5.5 of development. This early embryonic lethality has prevented the elucidation of cyclin A2 function in whole mammalian organisms.
Moreover, several observations hint at Cdk-independent activities for cyclins functions. In order to address the physiological role of cyclin A2 in mammalian development, growth and health, and identify new cyclin A2 functions, we are generating mouse models with replacement of the endogenous gene by mutant cyclin A2 alleles compromised for their interaction with Cdk2 and/or Cdk1. As a starting point, we have generated several cyclin A2 mutants (11) presenting different interaction profiles with Cdk1 and/or Cdk2 and other well-known cyclin A2 partners. We have generated cyclin A2 deficient cells and determined that cyclin A2 depletion leads to an accumulation of the cells in G2/M phases and increased cell motility. Reintroduction, in these cells, of a cyclin A2 mutant unable to bind Cdk1 and Cdk2 restored cell migration to a normal level. We are currently studying the effect of this mutant on cell cycle progression. These in vitro studies are a pre-requisite allowing for the selection of the mutants that will be used to generate our mouse models.
At the same time, we have started to generate genetically modified stem cells in order to create our mouse models. These mouse models will serve as natural readouts of the regulation and function of cyclin A2 in development, life and growth of a mammalian organism, and will provide several useful cellular models for cell cycle studies.
Moreover, several observations hint at Cdk-independent activities for cyclins functions. In order to address the physiological role of cyclin A2 in mammalian development, growth and health, and identify new cyclin A2 functions, we are generating mouse models with replacement of the endogenous gene by mutant cyclin A2 alleles compromised for their interaction with Cdk2 and/or Cdk1. As a starting point, we have generated several cyclin A2 mutants (11) presenting different interaction profiles with Cdk1 and/or Cdk2 and other well-known cyclin A2 partners. We have generated cyclin A2 deficient cells and determined that cyclin A2 depletion leads to an accumulation of the cells in G2/M phases and increased cell motility. Reintroduction, in these cells, of a cyclin A2 mutant unable to bind Cdk1 and Cdk2 restored cell migration to a normal level. We are currently studying the effect of this mutant on cell cycle progression. These in vitro studies are a pre-requisite allowing for the selection of the mutants that will be used to generate our mouse models.
At the same time, we have started to generate genetically modified stem cells in order to create our mouse models. These mouse models will serve as natural readouts of the regulation and function of cyclin A2 in development, life and growth of a mammalian organism, and will provide several useful cellular models for cell cycle studies.