Udu Deficiency Activates DNA Damage Checkpoint

Abstract

Udu has been shown to play an essential role during blood cell development; however, its roles in other cellular processes remain largely unexplored. In addition, ugly duckling (udu) mutants exhibited somite and myotome boundary defects. Our fluorescence-activated cell sorting analysis also showed that the loss of udu function resulted in defective cell cycle progression and comet assay indicated the presence of increased DNA damage in udu tu24 mutants. We further showed that the extensive p53-dependent apoptosis in udu tu24 mutants is a consequence of activation in the Atm-Chk2 pathway. Udu seems not to be required for DNA repair, because both wild-type and udu embryos similarly respond to and recover from UV treatment. Yeast two-hybrid and coimmunoprecipitation data demonstrated that PAH-L repeats and SANT-L domain of Udu interacts with MCM3 and MCM4. Furthermore, Udu is colocalized with 5-bromo-2 -deoxyuridine and heterochromatin during DNA replication, suggesting a role in maintaining genome integrity. INTRODUCTIONugly duckling (udu tu24 ) mutant was first isolated from the 1996 Tü bingen screen and has been shown to exhibit a short body-axis with massive cell death (Hammerschmidt et al., 1996). Another udu allele, udu sq1 , was isolated in a genetic screen aiming at mutants with defects in hematopoiesis (Liu et al., 2007). Positional cloning revealed that Udu protein encodes a novel nuclear factor consisting of three conserved regions (CR-1, CR-2, and CR-3) that do not share similarity with any known domains, two paired amphipathic ␣-helix like (PAH-L) repeats, and one putative SW13, ADA2, N-Cor and TFIIIB like (SANT-L) domain. The C-terminal PAH-L and SANT-L domains have been shown to be essential in primitive erythroid cell development (Liu et al., 2007). The PAH domain, first identified in yeast SIN3 (Wang et al., 1990), has been demonstrated to mediate protein-protein interactions (Spronk et al., 2000). SIN3 has no intrinsic DNA binding ability and has to be targeted to gene promoters by interacting with DNA binding proteins, thereafter positively and negatively regulating genes involved in diverse cellular functions (Silverstein and Ekwall, 2005). The SANT domain is a highly conserved motif with similarity to Myb DNA binding domain (Aasland et al., 1996), which has been shown to be critical in regulating chromatin accessibility (Boyer et al., 2002(Boyer et al., , 2004.The DNA damage response pathway is a cellular surveillance system that senses the presence of damaged DNA and elicits checkpoint activation and subsequent lesion repair in preventing amplification or loss of genes or chromosomes (Zhou and Elledge, 2000). The critical components of DNA damage checkpoint are two phosphatidyl inositol 3-kinaselike kinase family proteins: Ataxia telangiectasia mutated (ATM) and ATM-and Rad3-related (ATR) (Abraham, 2003;Shiloh, 2003). ATR functions as a sensor and transducer in response to UV light and presumably to genotoxic agents that give rise to stalled replication forks, and subsequently activates Checkp...

The Developmental Regulator Protein Gon4l Associates with Protein YY1, Co-repressor Sin3a, and Histone Deacetylase 1 and Mediates Transcriptional Repression

“…Further, analysis of mice engineered to lack YY1 in B cell progenitors has demonstrated that YY1 has a role in immunoglobulin gene rearrangement (36), a process that requires DNA repair. With regard to Gon4l, studies of zebrafish bearing null mutations in the Gon4l ortholog ugly duckling have provided evidence that this protein is important for cell division and genome stability in addition to the regulation of gene expression (11,12). These findings, combined with our observations linking Gon4l to Sin3a and YY1, suggest that Gon4l may be important for pathways in addition to those that mediate gene repression.…”

“…Thus, it is likely that other cofactors for Gon4l remain to be identified. Of note in this regard, a recent report provided evidence that the PAH repeats and SANT domain of zebrafish Gon4l mediate interaction with the proteins MCM3 and MCM4 (12), which are important for DNA replication but likely function in additional pathways (40).…”

“…For example, a null mutation in the zebrafish Gon4l ortholog disrupts the expression of critical erythroid genes and severely impairs primitive erythropoiesis (11). Also, studies of mutant zebrafish have suggested that the absence of Gon4l results in cell cycle arrest and increased cellular apoptosis in developing embryos (11,12). The mechanisms underlying these latter effects are not known, but they could reflect disruption of gene regulation during development.…”

GON4L Drives Cancer Growth through a YY1–Androgen Receptor–CD24 Axis

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Muscle wasted: a novel component of theDrosophilahistone locus body required for muscle integrity

“…SANT and homeodomains function in the regulation of transcription (Boyer et al, 2004;Hueber and Lohmann, 2008). Interestingly, BLAST searches revealed that the PAH repeats of Mute-L are 28% identical to that of zebrafish Ugly duckling (Udu), a nuclear protein required for somite development (Lim et al, 2009;Liu et al, 2007) and 27% identical to that of human GON4L or YARP (YY1AP-related protein 1), a nuclear protein with suggested transcriptionalregulator-like functions (supplementary material Fig. S1).…”