DUE-B Is Dispensable for Early Development and DNA Replication in Vertebrates

The DNA Unwinding Element-Binding protein (DUE-B) is a Cyclin Dependent Kinase (CDK) and Dbf4-Dependent Kinase (DDK) substrate that has been implicated in the control of DNA replication initiation. Previous studies reported that knocking down DUE-B in HeLa cells perturbs the G1-to-S phase transition, while depleting DUE-B from interphase Xenopus egg extracts impairs replication initiation. Based on these findings, the prevailing view is that DUE-B is a vertebrate-specific DNA replication initiation factor. Here, we asked whether due-b was an essential vertebrate gene in vivo , and whether it was critical for proper embryonic development in the zebrafish Danio rerio . We have generated due-b mutant zebrafish through genome-editing TALENs that fail to express due-b mRNA or protein. These mutant zebrafish are viable and survive to adulthood. They do not display outward developmental phenotypes, and when stressed with replication inhibitors, do not differ from their wild-type counterparts. Cell cycle analysis demonstrates that DNA replication occurs normally. Consistent with the zebrafish data, immunodepleting DUE-B from Xenopus nuclear egg extract did not impair DNA replication. Taken together, our findings indicate that DUE-B is dispensable for DNA replication and early development in vertebrates.