In Vivo DNA Re-replication Elicits Lethal Tissue Dysplasias

Mammalian DNA replication origins are "licensed" by the loading of DNA helicases, a reaction that is mediated by CDC6 and CDT1 proteins. After initiation of DNA synthesis, CDC6 and CDT1 are inhibited to prevent origin reactivation and DNA overreplication before cell division. CDC6 and CDT1 are highly expressed in many types of cancer cells, but the impact of their deregulated expression had not been investigated in vivo. Here, we have generated mice strains that allow the conditional overexpression of both proteins. Adult mice were unharmed by the individual overexpression of either CDC6 or CDT1, but their combined deregulation led to DNA re-replication in progenitor cells and lethal tissue dysplasias. This study offers mechanistic insights into the necessary cooperation between CDC6 and CDT1 for facilitation of origin reactivation and describes the physiological consequences of DNA overreplication.We thank all members of the DNA Replication and Chromosome Dynamics Groups for discussions, S. Ruiz and I. Blanco for their help with mouse work, B. Urcelay for technical support, M. Udriste for assistance with IHC quantifications, U. Cronin and D. Martınezfor assistance with flow cytometryexperiments, M. Canamero for the initial histopathology analyses, and O. Fernandez-Capetillo for comments on the manuscript. Research was supported by MINECO grants BFU2013-49153-P, BFU2016-80402-R, and CSD2007- 00015 to J.M. and MINECO predoctoral fellowships to S.M. and S.BS