Transcriptional silencing of the @entity1 inactive X chromosome is induced by the @entity6630 gene within the @entity1 X-inactivation center. The @entity6630 allele must be turned off on one X chromosome to maintain its activity in cells of both sexes. In the @entity19 placenta, where X inactivation is imprinted (the paternal X chromosome is always inactive), the maternal @entity23675 allele is repressed by a cis-acting antisense transcript, encoded by the @entity69510 gene. However, it remains to be seen whether this antisense transcript protects the future active X chromosome during random inactivation in the embryo proper. We recently identified the @entity1 @entity68597 gene and showed that it lacks key regulatory elements needed for the imprinting function of @entity19 @entity69510 . Now, using RNA FISH for cellular localization of transcripts in @entity1 fetal cells, we show that human @entity68597 antisense transcripts are unable to repress @entity6630 . In fact, @entity68597 is transcribed only from the inactive X chromosome and is coexpressed with @entity6630 . Also, @entity68597 is not maternally imprinted in placental tissues, and its transcription persists in placental and fetal tissues, throughout embryogenesis. Therefore, the repression of @entity23675 by @entity19 @entity69510 has no counterpart in @entity1 , and @entity68597 is not the gene that protects the active X chromosome from random inactivation. Because @entity1 @entity68597 cannot imprint X inactivation in the placenta, it serves as a mutant for @entity19 @entity69510 , providing insights into features responsible for antisense activity in imprinted X inactivation.

Species differences in XXXX / @entity68597 reveal the roles of these genes in X-chromosome inactivation.

@entity1 :: ('9606', 'Species') :: ['humans', 'human'] @entity6630 :: ('7503', 'Gene') :: ['XIST'] @entity68597 :: ('9383', 'Gene') :: ['TSIX'] @entity19 :: ('10090', 'Species') :: ['mouse', 'murine'] @entity69510 :: ('22097(Tax:10090)', 'Gene') :: ['Tsix'] @entity23675 :: ('213742(Tax:10090)', 'Gene') :: ['Xist']
@entity68597 :: (9383,Gene) :: ['TSIX']
