Differential splice isoforms of mouse CDK2 play functionally redundant roles during mitotic and meiotic division

In most mammals, the cell cycle kinase; cyclin-dependent kinase 2 (CDK2) is expressed as two major isoforms due to the inclusion or exclusion of an alternatively spliced exon. The shorter CDK2 isoform: CDK2S, is expressed constitutively during the cell cycle and can be detected in many different tissue types. In contrast, the longer isoform: CDK2L, shows preferential expression in meiotically dividing cells of the germ cells and upon S-phase entry during mitotic cell division. Both CDK2L and CDK2S form heteromeric complexes with cyclins A2 and E1 in vitro . However, complexes comprised of each isoform differ considerably in their kinase activity towards known CDK substrates. It is currently unknown whether the long and short isoforms of CDK2 play functionally different roles in vivo during either mitotic and meiotic divisions as conventional knockout methodology leads to the loss of both isoforms. In this study, we find that both CDK2L and CDK2S are sufficient to support both mitotic and meiotic division when expressed in the absence of the other. This data contributes to the explanation of the apparent tolerance of the evolutionary loss of CDK2L expression in humans.