Identification of a new protein in ribosome generation

The researchers have identified a four-protein complex that appears to play a key role in generating ribosomes – organelles that serve as protein factories for cells – as well as a surprising part in neurodevelopmental disorders. These findings, published in Cell Reports, could lead to new ways to manipulate ribosome production, which could impact a variety of conditions that affect human health.

“Ribosomes are fundamental for life, but we’ve had an incomplete understanding of how they’re put together and how the process of ribosome production is regulated,” said lead author. “Our findings shed significant light on these questions.” 

The lead explained that ribosomes are present in varying amounts in every cell of every organism on Earth. Because of their key role as protein producers, variations from these natural set points can have deleterious consequences. For example, cancer cells tend to increase ribosome production to boost protein production necessary for unchecked cell division. In addition, a group of rare diseases known as ribosomopathies – characterized by abnormal ribosome production – manifests with a variety of symptoms including anemia, craniofacial defects, and intellectual disability.

Although every species has ribosomes, most of what’s known about ribosome biogenesis has come from the popular lab model, yeast. The basics of this process are the same for human ribosome biogenesis, th eauthor said, but the specifics are not. Consequently, the details that make human ribosome generation unique have been unknown.

To learn more about this process, the authors started by developing a technique that prompted old ribosomes to glow red and newly generated ribosomes to glow green. The researchers used this tool on several different human cell types, confirming different rates of ribosome production in each.

Using the gene editing tool called CRISPR, the researchers inactivated individual genes to identify those that might be key players in ribosome biogenesis. Their search turned up four genes known as CINPSPATA5L1C1orf109, and SPATA5. Further research showed that these genes come together into a complex that strips a placeholder protein from ribosomes when assembly is almost complete, allowing a different protein to take its place for ribosome maturation.

Previously, SPATA5’s function in cells had been unknown; however, mutations in this gene have been associated with neurodevelopmental disorders including microcephaly, hearing loss, epilepsy, and intellectual disability. When the researchers inserted two of these mutations into cells, causing them to create a mutant SPATA5 protein, the cells couldn’t generate the normal level of functional ribosomes – suggesting that these neurodevelopmental disorders could stem from ribosome problems.

The author said that they plan to study why the central nervous system appears to be more sensitive than other cell types to ribosomal disruptions and added that these findings could eventually lead to new treatments for cancer, ribosomopathies, and other conditions affected by over- or under-production of proteins.