Comparative XIST expression. A schematic of XIST exons transcribed from human (based on NR_001564) and lemur (aye-aye, Coquerel's sifaka, gray mouse lemur, black lemur, and ring-tailed lemur) fibroblast cell lines is shown relative to known mouse and cow exons (NR_001463 and NR_001464, respectively) (Chureau et al. 2002). Numbers above exons correspond to known numbered exons in human, mouse, and cow based on these RefSeqs. The general phylogeny along the left was compiled from Murphy et al. (2007), Horvath et al. (2008), and Perelman et al. (2011). (Dark gray boxes) Exons transcribed in a species; (light gray boxes) conservation of DNA sequence with no verified expression. Putative splice donor and acceptor sites are indicated for each exon–intron splice junction. (Open boxes) Regions that are not expressed in the lemurs and for which there is not a complete genome sequence. (NN) The orangutan genome sequence has a short gap of N's at the putative start of this exon. (#) The black lemur exon ends 5 bp downstream from all other species (except mouse, which extends 4 bp downstream) and the following splice junction is a TA instead of a GT. (&) The black lemur exon starts 3 bp upstream and the adjacent splice junction is TT instead of AG. ($) The ring-tailed lemur starts 96 bp upstream of human and black lemur. (**) The ring-tailed lemur exon extends 8 bp past all others. (%) The mouse exon starts 16 bp downstream from the human, cow, and ring-tailed lemur orthologous exon. (!) The mouse exon starts 271 bp upstream of the human and the black lemur exons. (*) The cow exon starts 67 bp downstream with a TA instead of AG at the splice junction. (@) The cow exon starts 64 bp upstream of the human and black lemur.
