Due-B Is dispensable for early development and genome duplication 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. Knockdown of DUE-B in HeLa cells perturbs the G1-to-S phase transition and immunodepletion of due-b in Xenopus egg extracts blocks replication initiation. Combined prior evidence has suggested that Due-b may be 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. Our 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. Our data indicate that Due-b is not a core essential component of the DNA replication initiation machinery required for vertebrate development. Instead, it may be a mechanistically redundant protein or play a specialized role in DNA replication control.