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XB-ART-39064
Proc Natl Acad Sci U S A January 20, 2009; 106 (3): 749-54.
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A distinct H2A.X isoform is enriched in Xenopus laevis eggs and early embryos and is phosphorylated in the absence of a checkpoint.

Shechter D , Chitta RK , Xiao A , Shabanowitz J , Hunt DF , Allis CD .


Abstract
Histone H2A.X is an H2A variant present in multicellular organisms that is specifically phosphorylated on the serine in the C-terminal consensus sequence, canonically "SQEY," in response to DNA damage. We have recently shown the significance of phosphorylation of the penultimate tyrosine for maintenance and processing of the DNA damage response in mammalian cells. Here, we report the identification of distinct H2A.X variants in the eggs and early embryos of the frog Xenopus laevis that contain a C-terminal SQEF, among other changes; we have denoted these proteins as "H2A.X-F." H2A.X-F is present only in late-staged oocytes, eggs, and premidblastula transition embryos and is not present in somatic cells. Similar unannotated isoforms were identified in other rapidly developing aquatic species, such as Xenopus tropicalis, goldfish, and zebrafish, and in Arabidopsis and chickpea. Furthermore, we demonstrate by mass spectrometry and phospho-specific antibodies that H2A.X-F is phosphorylated in the absence of exogenous DNA damage, in both actively dividing, unperturbed embryos and cell-free egg extract in the absence and presence of DNA damage and S-phase checkpoint conditions. We propose that this isoform may be involved in modulating the cellular response to the rapid early cell cycles in externally developing species.

PubMed ID: 19131518
PMC ID: PMC2630098
Article link: Proc Natl Acad Sci U S A
Grant support: [+]

Species referenced: Xenopus tropicalis Xenopus laevis
Genes referenced: h2ac21 h2axl
Antibodies: Atm Ab3 H2afj Ab1 H2afx Ab1 Hist1h4a Ab3 Hist1h4a Ab4

References [+] :
Almouzni, Nuclear assembly, structure, and function: the use of Xenopus in vitro systems. 1993, Pubmed, Xenbase