Introns and Splicing

Continuing a theme from the last post, this next article, Introns regulate the production of ribosomal proteins by modulating splicing of duplicated ribosomal protein genes, by Petibon, Parenteau, Catala, and Elela examined the mechanism of how introns regulate the expression of dRPGs (duplicate ribosomal protein genes) and how it relates to the synthesis of ribosomal proteins (RPs). The article shows how introns can determine the ratio of ribosomal protein isoforms through regulation of splicing. The authors used yeast, Saccharomyces cerevisiae, as their medium for this study.

           In the introduction, the authors demonstrated explain how ribosome synthesis is a major undertaking that requires precise coordination without wasting energy or compromising quality. They continue with how the duplication of genes and deletions of certain duplicates can generate different transcription profiles and affect growth. Introns become a part of this dRPG process in defining the expression pattern. The initial idea was that introns lead to only inhibition of gene expression. However introns induced the expression of about half of the genes and inhibited the expression of the other half meaning that introns may act as gene-specific regulators.

 To test their hypothesis, the yeast was grown and manipulated using standard procedures. They tagged RPS9 genes as RPS9 genes can be introduced with intron deleting strains. They used to variants called RPS9A and RPS9B which acted as paralogs of each other. Going through the methods of the experiment the authors were able to observe the changes in RNA, proteins, splicing, and growth of the yeast form the various tests conducted.

            They found that introns play an important role in controlling or coordinating the expression of RPGs but the mechanism used to fluctuate the RPG expression is another mystery. The authors found that the intron is preferred tool for repression of the RPS9A gene and that the deletion of the intron allows for a greater expression of the RPS9A gene.  The splicing of the RPS9A and RPS9B was also examined and the results showed that splicing efficiency was greater when the intron was present.

            To test how splicing efficiency affected the production of mRNA and proteins, the authors looked at the secondary structures. By performing intron substitution on the RPS9 genes, these substitutions increased mRNA levels. They concluded that the expression levels are influenced by the intron structure and splicing. This study showed how the preservation of introns in yeast is crucial for gene regulation via gene splicing.  

            Going through this study made me realize that there is a lot more to gene splicing and regulation than I had originally thought. I was under the impression that gene splicing was relevant to expressing slight variation in proteins through exons but it turns out that introns are as equally involved in splicing. I have to give credit ot the teachers at OCC for making this topic easier to understand in the classroom otherwise it would be completely overwhelming. 

Sources:

Petibon, C., Parenteau, J., Catala, M., & Elela, S.A. (2016). Introns regulate the production of ribosomal proteins by modulating splicing of duplicated ribosomal protein genes. Oxford Journals. 44: 3878-3891.