The 3D positioning of ANT2 and ANT3 genes within female X chromosome territories correlates with gene activity

The three-dimensional positioning of the X-chromosomal adenine nucleotide t ranslocase genes, ANTE and ANT3, were compared in the active and inactive X chromosome territories (Xa and Xi) of female human amniotic fluid cell nuc lei. ANT2 is located in Xq24-q25 and is transcriptionally active on Xa, but inactive on Xi. ANT3 is located in the pseudoautosomal region Xp22.3 and e scapes X-inactivation. Three-color fluorescence in situ hybridization, conf ocal laser scanning microscopy, and three-dimensional image analysis reveal ed that transcriptionally active ANTS and ANT3 genes were positioned more p eripheral within their chromosome territory than the inactive ANTS gene, Th e position of the latter was significantly more interior in the Xi territor y. Although the volumes of both X territories were similar, 3D distances be tween ANTE and ANT3 were significantly smaller in Xi compared to Xa territo ries reflecting different territory shapes. Our data show a correlation bet ween 3D positioning and transcriptional activity of these X-specific genes. (C) 1999 Academic Press.