XIST dampens X chromosome activity in a SPEN-dependent manner during early human development

Area of Science:

• Epigenetics and Gene Regulation
• Developmental Biology
• Genomics

Background:

• XIST (X-inactive specific transcript) lncRNA initiates X chromosome inactivation (XCI) in placental mammals.
• In human preimplantation embryos, XIST and XACT (X-active coating transcript) lncRNAs accumulate on both X chromosomes without silencing.
• XACT may antagonize XIST function, but its role remains unclear.

Purpose of the Study:

• To investigate the functions of XIST and XACT in naive human embryonic stem cells.
• To elucidate their roles in shaping X chromosome chromatin and transcriptional landscapes during early development.

Main Methods:

• Utilized naive human embryonic stem cells.
• Assessed the impact of XIST and XACT on X chromosome chromatin modifications and gene expression.
• Investigated SPEN-dependent mechanisms of XIST function.

Main Results:

• XIST triggers repressive histone modifications and dampens X-linked gene transcription in a SPEN-dependent manner.
• XACT deficiency did not significantly alter XIST activity or X-linked gene expression.
• XIST is functional prior to complete XCI, indicating a transient dosage compensation process.

Conclusions:

• XIST actively dampens gene expression before initiating full XCI.
• XACT does not appear to antagonize XIST function in this context.
• XCI and gene dampening share common regulatory factors.