Monoallelically expressed noncoding RNAs form nucleolar territories on NOR-containing chromosomes and regulate rRNA expression.

Hao, Qinyu; Liu, Minxue; Daulatabad, Swapna Vidhur; Gaffari, Saba; Song, You Jin; Srivastava, Rajneesh; Bhaskar, Shivang; Moitra, Anurupa et al. · Elife · 2024

basic_science · Level V

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Abstract

Out of the several hundred copies of <i>rRNA</i> genes arranged in the nucleolar organizing regions (NOR) of the five human acrocentric chromosomes, ~50% remain transcriptionally inactive. NOR-associated sequences and epigenetic modifications contribute to the differential expression of rRNAs. However, the mechanism(s) controlling the dosage of active versus inactive <i>rRNA</i> genes within each NOR in mammals is yet to be determined. We have discovered a family of ncRNAs, SNULs (<i>S</i>ingle <i>NU</i>cleolus <i>L</i>ocalized RNA), which form constrained sub-nucleolar territories on individual NORs and influence rRNA expression. Individual members of the SNULs monoallelically associate with specific NOR-containing chromosomes. SNULs share sequence similarity to pre-rRNA and localize in the sub-nucleolar compartment with pre-rRNA. Finally, SNULs control rRNA expression by influencing pre-rRNA sorting to the DFC compartment and pre-rRNA processing. Our study discovered a novel class of ncRNAs influencing rRNA expression by forming constrained nucleolar territories on individual NORs.

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