Details

Autor(en) / Beteiligte

• Warshawsky, David
• Stavropoulos, Nicholas
• Lee, Jeannie T.

Titel

Further examination of the Xist promoter-switch hypothesis in X inactivation: Evidence against the existence and function of a P 0 promoter

Ist Teil von

• Proceedings of the National Academy of Sciences - PNAS, 1999-12, Vol.96 (25), p.14424-14429

Erscheinungsjahr

1999

Link zum Volltext

Quelle

EZB Electronic Journals Library

Beschreibungen/Notizen

• The onset of X inactivation coincides with accumulation of Xist RNA along the future inactive X chromosome. A recent hypothesis proposed that accumulation is initiated by a promoter switch within Xist. In this hypothesis, an upstream promoter (P 0 ) produces an unstable transcript, while the known downstream promoter (P 1 ) produces a stable RNA. To test this hypothesis, we examined expression and half-life of Xist RNA produced from an Xist transgene lacking P 0 but retaining P 1 . We confirm the previous finding that P 0 is dispensable for Xist expression in undifferentiated cells and that P 1 can be used in both undifferentiated and differentiated cells. Herein, we show that Xist RNA initiated at P 1 is unstable and does not accumulate. Further analysis indicates that the transcriptional boundary at P 0 does not represent the 5′ end of a distinct Xist isoform. Instead, P 0 is an artifact of cross-amplification caused by a pseudogene of the highly expressed ribosomal protein S12 gene Rps12 . Using strand-specific techniques, we find that transcription upstream of P 1 originates from the DNA strand opposite Xist and represents the 3′ end of the antisense Tsix RNA. Thus, these data do not support the existence of a P 0 promoter and suggest that mechanisms other than switching of functionally distinct promoters control the up-regulation of Xist .