A vertebrate gene, ticrr, is an essential checkpoint and replication regulator

Abstract

Eukaryotes have numerous checkpoint pathways to protect genome fidelity during normal cell division and in response to DNA damage. Through a screen for G2/M checkpoint regulators in zebrafish, we identified ticrr (for TopBP1-interacting, checkpoint, and replication regulator), a previously uncharacterized gene that is required to prevent mitotic entry after treatment with ionizing radiation. Ticrr deficiency is embryonic-lethal in the absence of exogenous DNA damage because it is essential for normal cell cycle progression. Specifically, the loss of ticrr impairs DNA replication and disrupts the S/M checkpoint, leading to premature mitotic entry and mitotic catastrophe. We show that the human TICRR ortholog associates with TopBP1, a known checkpoint protein and a core component of the DNA replication preinitiation complex (pre-IC), and that the TICRR-TopBP1 interaction is stable without chromatin and requires BRCT motifs essential for TopBP1's replication and checkpoint functions. Most importantly, we find that ticrr deficiency disrupts chromatin binding of pre-IC, but not prereplication complex, components. Taken together, our data show that TICRR acts in association with TopBP1 and plays an essential role in pre-IC formation. It remains to be determined whether Ticrr represents the vertebrate ortholog of the yeast pre-IC component Sld3, or a hitherto unknown metazoan replication and checkpoint regulator.[Keywords: DNA replication; S/M checkpoint; G2/M checkpoint; pre-RC; pre-IC; TopBP1; SLD3] Supplemental material is available at http://www.genesdev.org.

Mcm10 interacts with Rad4/Cut5TopBP1 and its association with origins of DNA replication is dependent on Rad4/Cut5TopBP1

“…These observations raise additional questions about the order of assembly of additional pre-initiation factors at origins of DNA replication. In budding yeast the Rad4 TopBP1 homologue Dpb11 has been shown to interact with both Sld2 and Sld3 and those events have been shown to be CDK-dependent and similar data have recently been reported in metazoans (6,7,8,10,11,12,49). Chromatin association of Cdc45 has been previously shown to be dependent upon Mcm10, Rad4 TopBP1 , Sld3 and the GINS complex (22,23,24,47).…”

“…2C). In contrast whilst Rad4 TopBP1 associated with origin DNA at the point of DNA replication initiation it was never found associated with DNA distal to 10 this site (Fig. 2D).…”

“…Phosphorylation of Sld2 promotes formation of a pre-loading complex containing Dpb11, the heteromeric GINS complex, DNA Pol and Sld2 itself (9). The metazoan orthologue of Sld3, Treslin/Ticrr, has been shown to interact with TopBP1 and to be required for DNA replication (10,11,12). Cdc45 recruitment appears to require direct interaction with Mcm complex and the mcm5-bob1-1 mutation results in DDK-independent loading of Cdc45 and the bypass of the DDK requirement for initiation of DNA replication (13,14,15).…”

GINS and Sld3 Compete with One Another for Mcm2-7 and Cdc45 Binding

“…In the future it will be useful to investigate whether Sld3 modulates the catalytic functions or nucleic acid binding properties of Mcm2-7. The human homolog of Sld3 is not known with certainty, but Treslin and Ticrr have recently been identified as possible Sld3 homologs in higher eukaryotes (27,28 (29) (Fig. 7).…”

Direct Role for the Replication Protein Treslin (Ticrr) in the ATR Kinase-mediated Checkpoint Response

“…TopBP1 contains multiple BRCT motifs (nine in humans), which mediate protein-protein interactions, and pairs of BRCT domains act as phosphopeptide-binding motifs (10,11). In addition to its checkpoint function, TopBP1 is also a replication protein (12).…”