Garrick David, Samara Vassiliki, McDowell Tarra L, Smith Andrew J H, Dobbie Lorraine, Higgs Douglas R, Gibbons Richard J
MRC Molecular Haematology Unit, Weatherall Institute of Molecular Medicine, John Radcliffe Hospital, Oxford, OX3 9DS, UK.
Gene. 2004 Feb 4;326:23-34. doi: 10.1016/j.gene.2003.10.026.
Mutations in the ATRX gene cause a severe X-linked mental retardation syndrome that is frequently associated with alpha thalassemia (ATR-X syndrome). The previously characterized ATRX protein (approximately 280 kDa) contains both a Plant homeodomain (PHD)-like zinc finger motif as well as an ATPase domain of the SNF2 family. These motifs suggest that ATRX may function as a regulator of gene expression, probably by exerting an effect on chromatin structure, although the exact cellular role of ATRX has not yet been fully elucidated. Here we characterize a truncated (approximately 200 kDa) isoform of ATRX (called here ATRXt) that has been highly conserved between mouse and human. In both species, ATRXt arises due to the failure to splice intron 11 from the primary transcript, and the use of a proximal intronic poly(A) signal. We show that the relative expression of the full length and ATRXt isoforms is subject to tissue-specific regulation. The ATRXt isoform contains the PHD-like domain but not the SWI/SNF-like motifs and is therefore unlikely to be functionally equivalent to the full length protein. We used indirect immunofluorescence to demonstrate that the full length and ATRXt isoforms are colocalized at blocks of pericentromeric heterochromatin but unlike full length ATRX, the truncated isoform does not associate with promyelocytic leukemia (PML) nuclear bodies. The high degree of conservation of ATRXt and the tight regulation of its expression relative to the full length protein suggest that this truncated isoform fulfills an important biological function.
ATRX基因的突变会导致一种严重的X连锁智力迟钝综合征，该综合征常与α地中海贫血相关（ATR-X综合征）。先前鉴定的ATRX蛋白（约280 kDa）既包含一个类植物同源结构域（PHD）锌指基序，也包含SNF2家族的一个ATP酶结构域。这些基序表明，ATRX可能作为基因表达的调节因子发挥作用，可能是通过对染色质结构产生影响，尽管ATRX的确切细胞作用尚未完全阐明。在这里，我们鉴定了一种截短的（约200 kDa）ATRX异构体（在此称为ATRXt），它在小鼠和人类之间高度保守。在这两个物种中，ATRXt的产生是由于未能从初级转录本中剪接内含子11，并使用了近端内含子聚腺苷酸化信号。我们表明，全长和ATRXt异构体的相对表达受到组织特异性调节。ATRXt异构体包含类PHD结构域，但不包含SWI/SNF样基序，因此其功能不太可能与全长蛋白等效。我们使用间接免疫荧光法证明，全长和ATRXt异构体共定位于着丝粒周围异染色质区域，但与全长ATRX不同，截短的异构体不与早幼粒细胞白血病（PML）核体相关。ATRXt的高度保守性及其相对于全长蛋白的严格表达调控表明，这种截短的异构体具有重要的生物学功能。
