The origin of the RB1 imprint

Area of Science:

• Genetics
• Epigenetics
• Primate evolution

Background:

• The human RB1 gene exhibits genomic imprinting, regulated by a differentially methylated CpG island in intron 2.
• This CpG island is part of PPP1R26P1, a retrocopy of the PPP1R26 gene, acting as a promoter for an alternative RB1 transcript.

Purpose of the Study:

• To investigate the evolutionary origin of the RB1 gene imprint.
• To analyze the presence and methylation patterns of PPP1R26 retrocopies across primate species.

Main Methods:

• In silico analyses to detect parental PPP1R26 and retrocopy PPP1R26P1 presence in various primate lineages.
• Deep bisulfite sequencing to determine methylation patterns of PPP1R26 and its retrocopies.
• Single Nucleotide Polymorphism (SNP) analysis for allele-specific methylation in marmosets.

Main Results:

• The parental PPP1R26 gene is found in Haplorrhini primates, while the PPP1R26P1 retrocopy is present in all studied Anthropoidea.
• The RB1 intron 2 retrocopy is differentially methylated across all examined primates, unlike other fully methylated retrocopies.
• An additional retrocopy on marmoset chromosome 4 also shows differential, allele-specific methylation.

Conclusions:

• The differential methylation of the RB1 intron 2 retrocopy is conserved across primates, suggesting its role in establishing the RB1 imprint.
• The epigenetic status of PPP1R26 retrocopies is influenced by their DNA sequence and integration site characteristics.
• This study provides insights into the mechanisms of imprinted gene regulation and retrocopy evolution in primates.