Research at the University of Oxford has revealed that transposon expression within the brain is not random and is in fact impacted by surrounding genes.
Whilst previously thought to be ‘junk,’ researchers soon realised that the non-coding portion of the genome possessed a range of different genetic elements with functional properties. Included within these regions are transposable elements, or transposons. Transposons were first discovered by cytogeneticist Barbara McClintock in the 1950s. She later earned the Nobel Prize in Physiology in 1983 for her research. Transposons make up ~50% of eukaryotic genomes and comprise of a wide array of molecular functions. These elements often reside within intronic regions, where they can introduce splice sites. In turn, they lead to the production of chimeric mRNAs between the transposon and relevant gene.
Reliable measurements of both autonomous and nonautonomous transposon expression within somatic tissue is hindered by repetitive sequences. Nonetheless, developments in high-throughput single-cell transcriptomics has aided in our ability to assess the cellular expression of each transposon within the genome.
In a study, published in Genome Research, researchers used single-cell RNA-seq (scRNA-seq) to map transposon expression to individual cells in the Drosophila midbrain. The team combined this data with high-coverage genomic data to correlate transposon expression with genes within which they were inserted. They then confirmed these interactions by extracting mRNA from heads of the same strain and performed high-coverage bulk mRNA sequencing.
Interestingly, the team found that most transposons are expressed as parts of chimeric mRNAs with cellular genes. This suggests that somatic expression of these transposons is largely driven by cellular genes. They also found a range of neural genes for which a large amount of their mature mRNA transcript pool contained transposon sequences.
Dr Christopher Treiber, postdoctoral research scientist in the Centre for Neural Circuits and Behaviour at the University of Oxford, stated:
“We show that many transposons are spliced into cellular genes and thereby potentially change the structure and function of proteins in the brain.”
Specifically, the team identified 264 transposon harbouring genes in the Drosophila brain. Several of these disrupted expression and therefore, could impact neural function. For example, flies harbouring hobo in Sh and flea in cac could alter voltage-gated currents.
Image credit: By nico_blue – canva.com