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Primary non-random X inactivation associated with disruption of Xist promoter regulation
A E Newall1, S Duthie, E Formstone
1X inactivation Group, MRC Clinical Sciences Centre, ICSM, Hammersmith Hospital, Du Cane Road, London W12 ONN, UK.
Abstract:
In this report we demonstrate primary non-random X chromosome inactivation following targeted mutagenesis of a region immediately upstream of XIST promoter P(1). In heterozygous animals there is a preferential inactivation of the targeted X chromosome in 80--90% of cells. The phenotype correlates with inappropriate activation of XIST in a proportion of the mutant XY embryonic stem cells. Strand-specific analysis revealed increased sense transcription initiating upstream of XIST promoter P(1). There was, however, no discernible effect on transcription from the antisense Tsix gene. We demonstrate that the in vitro and in vivo phenotypes are specifically attributable to the presence of a PGKneo cassette at the targeted locus. These findings are discussed in the context of understanding mechanisms of XIST gene regulation in X inactivation.
Insights
Targeted mutagenesis near the XIST promoter P(1) induced preferential X chromosome inactivation in heterozygous animals. This suggests the PGKneo cassette influences XIST gene regulation and X inactivation mechanisms.
Area of Science:
- Genetics
- Epigenetics
- Molecular Biology
Background:
- X chromosome inactivation (XCI) is a crucial process in female mammals for dosage compensation.
- The XIST gene plays a central role in initiating and spreading XCI.
- Regulation of XIST expression is complex and not fully understood.
Purpose of the Study:
- To investigate the role of the region upstream of XIST promoter P(1) in XCI.
- To determine the effect of targeted mutagenesis on XIST regulation and XCI.
- To elucidate the contribution of the PGKneo cassette to observed phenotypes.
Main Methods:
- Targeted mutagenesis of a region upstream of XIST promoter P(1).
- Analysis of X chromosome inactivation patterns in heterozygous animals.
- Strand-specific transcription analysis of XIST and Tsix.
- Assessment of XY embryonic stem cells for XIST expression.
Main Results:
- Primary non-random X chromosome inactivation observed in 80-90% of cells in heterozygous animals.
- Inappropriate activation of XIST in mutant XY embryonic stem cells.
- Increased sense transcription upstream of XIST promoter P(1), with no effect on Tsix.
- Phenotypes were specifically linked to the PGKneo cassette insertion.
Conclusions:
- The region upstream of XIST promoter P(1) is critical for regulating XCI.
- The PGKneo cassette can interfere with XIST regulation, leading to non-random XCI.
- These findings provide insights into the mechanisms of XIST gene regulation during X inactivation.