title: Genes flanking Xist in mouse and human are separated on the X chromosome in American marsupials.
abstract: X inactivation, the transcriptional silencing of one of the two X chromosomes in female mammals, achieves dosage compensation of X-linked genes relative to XY males. In eutherian mammals X inactivation is regulated by the X-inactive specific transcript (Xist), a cis-acting non-coding RNA that triggers silencing of the chromosome from which it is transcribed. Marsupial mammals also undergo X inactivation but the mechanism is relatively poorly understood. We set out to analyse the X chromosome in Monodelphis domestica and Didelphis virginiana, focusing on characterizing the interval defined by the Chic1 and Slc16a2 genes that in eutherians flank the Xist locus. The synteny of this region is retained on chicken chromosome 4 where other loci belonging to the evolutionarily ancient stratum of the human X chromosome, the so-called X conserved region (XCR), are also located. We show that in both M. domestica and D. virginiana an evolutionary breakpoint has separated the Chic1 and Slc16a2 loci. Detailed analysis of opossum genomic sequences revealed linkage of Chic1 with the Lnx3 gene, recently proposed to be the evolutionary precursor of Xist, and Fip1, the evolutionary precursor of Tsx, a gene located immediately downstream of Xist in eutherians. We discuss these findings in relation to the evolution of Xist and X inactivation in mammals.
authors.affiliation: Institute of Cytology and Genetics, Russian Academy of Sciences, Siberian Department, Novosibirsk, Russia.
authors.forename: Alexander I
authors.initials: AI
authors.lastname: Shevchenko
authors.forename: Irina S
authors.initials: IS
authors.lastname: Zakharova
authors.forename: Eugeny A
authors.initials: EA
authors.lastname: Elisaphenko
authors.forename: Nicolay N
authors.initials: NN
authors.lastname: Kolesnikov
authors.forename: Siobhan
authors.initials: S
authors.lastname: Whitehead
authors.forename: Christine
authors.initials: C
authors.lastname: Bird
authors.forename: Mark
authors.initials: M
authors.lastname: Ross
authors.forename: Jennifer R
authors.initials: JR
authors.lastname: Weidman
authors.forename: Randy L
authors.initials: RL
authors.lastname: Jirtle
authors.forename: Tatiana V
authors.initials: TV
authors.lastname: Karamysheva
authors.forename: Nicolay B
authors.initials: NB
authors.lastname: Rubtsov
authors.forename: John L
authors.initials: JL
authors.lastname: VandeBerg
authors.forename: Nina A
authors.initials: NA
authors.lastname: Mazurok
authors.forename: Tatyana B
authors.initials: TB
authors.lastname: Nesterova
authors.forename: Neil
authors.initials: N
authors.lastname: Brockdorff
authors.forename: Suren M
authors.initials: SM
authors.lastname: Zakian
mesh_terms: D000818:Animals; D002460:Cell Line; D002874:Chromosome Mapping; D022202:Chromosomes, Artificial, Bacterial; D041321:Chromosomes, Human, X; D048293:Didelphis / Q000235:genetics*; D019143:Evolution, Molecular; D005260:Female; D005347:Fibroblasts; D015723:Gene Library; D050172:Genes, X-Linked; D006801:Humans; D008297:Male; D051379:Mice; D042282:Microdissection; D027501:Monocarboxylic Acid Transporters / Q000235:genetics; D048309:Monodelphis / Q000235:genetics*; D062085:RNA, Long Noncoding; D022661:RNA, Untranslated / Q000235:genetics*; D014960:X Chromosome / Q000235:genetics*; D049951:X Chromosome Inactivation
chemical_list: D027501:Monocarboxylic Acid Transporters; D062085:RNA, Long Noncoding; D022661:RNA, Untranslated; C077885:XIST non-coding RNA