Researchers within the Biocomplexity Institute of Virginia Tech have demonstrated that eggs actively silence hundreds of paternal genes that encode ribosomal RNA, the protein factories of the cell, and that this suppression is maintained throughout the organism's life.
The discovery, in Proceedings of the Royal Society B, reveals unorthodox behavior in inheritance and gene expression, including previously unknown conflicts between parental genomes. The information sheds light on cellular processes, evolution, and human disease.
Ribosomal RNA, known as rRNA, is evolutionary one of the most ancient genetic sequences on Earth, presumably preceding even DNA itself, the researchers said. It is central to metabolic health and if damaged can cause severe disease.
The researchers looked to African clawed frogs for insight into rRNA sequences, which generally are excessive, repetitive, and difficult to understand.
"African clawed frogs with their large, complex hybrid genomes are a gold mine for researchers interested in how both genome structure and regulation evolve," said Pawel Michalak, an associate professor at the Biocomplexity Institute and corresponding author of the study.
In the process of this study, the researchers discovered that maternal genes control rRNA in ways they hadn't anticipated. Shortly after fertilization, the egg keeps paternal genes from expressing themselves. While the paternal genes are passed down, they remain inactive unless they land on a maternal chromosome.
Originally, the research team was exploring another phenomenon occurring in African clawed frog genomes—nucleolar dominance. The nuleolus assembles ribosomal subunits and generates the rRNA in a cell.
Nucleoli are distinctive nuclear compartments where most rRNA is generated. Nucleolar dominance occurs when hybrid nucleoli are underdeveloped and production of rRNA is thus reduced. Newly generated African clawed frog hybrids between different species have only one nuclelous even though their purebred parents develop two nucleoli.
"To understand the link between maternal control of rRNA and nucleolar dominance will certainly require more work," said Michalak. "This study aligns with the institute's new focus in biocomplexity, tying in to research within the institute with RNA."
Originally founded in 2000 as the Virginia Bioinformatics Institute, the Biocomplexity Institute recently underwent a name change to underscore its commitment to understanding massively-interacting systems from molecules to policy. The work on RNA and maternal control is one example of how computational and genomic resources have contributed to our increased understanding of the complexities of heredity.
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Katarzyna Michalak et al. Nucleolar dominance and maternal control of 45S rDNA expression, Proceedings of the Royal Society B: Biological Sciences (2015). DOI: 10.1098/rspb.2015.2201