Asynchronous replication, mono-allelic expression, and long range Cis-effects of ASAR6

Area of Science:

• Genetics
• Molecular Biology
• Epigenetics

Background:

• Mammalian DNA replication follows a temporal program, with most homologous genes replicating synchronously.
• Mono-allelically expressed genes (imprinted, allelically excluded, female X-linked) replicate asynchronously.
• The cis-acting elements regulating this asynchronous replication are largely unknown.

Purpose of the Study:

• To identify and characterize the cis-acting locus controlling replication timing on human chromosome 6.
• To investigate the function of the identified non-coding RNA gene, ASAR6, in replication timing and chromosome stability.

Main Methods:

• Identification of a cis-acting locus on chromosome 6.
• Characterization of the ASAR6 gene and its RNA product (e.g., expression, localization, processing).
• Functional studies involving ASAR6 disruption and ectopic integration in human and mouse cells.

Main Results:

• A novel locus encoding the large intergenic non-coding RNA ASAR6 was identified on chromosome 6.
• ASAR6 disruption caused delayed replication, delayed mitotic condensation, and activation of silent alleles of mono-allelic genes.
• ASAR6 resides in an asynchronously replicating domain and is expressed mono-allelically from the later-replicating allele.
• ASAR6 disruption led to chromosome 6 instability (bridged chromosomes, micronuclei).
• Ectopic ASAR6 integration induced delayed replication in mouse chromosomes.

Conclusions:

• ASAR6 is a key regulator of replication timing and chromosome stability on human chromosome 6.
• ASAR6's function extends beyond chromosome 6, as demonstrated by its effect on mouse chromosomes.
• This study reveals a novel mechanism involving non-coding RNA in coordinating replication timing and genome integrity.