Word of the Day: Retrotransposon

by Gabrielle DeMarco on March 24, 2011

I recently wrote an article introducing the newest member of the biology faculty at Rensselaer, Patrick Maxwell. Maxwell studies baker’s yeast (yes – the same exact stuff that makes bread rise, pictured above) to understand the process of aging.

Aging is a very complex and poorly understood process – at least at the genetic level. Everyone understands the macro-level signs of aging (the horror of more creases by your eyes or grey hairs on your head), but scientists are just scratching the surface in our understanding of what happens to us as we age at the genetic level. Obviously something happens to the DNA in our genome over time that leads to a series of degradations that build slowly and result in the inevitable.

The element of this process that Maxwell studys is the retrotransposon. I like to refer to it as “Selfish DNA” because it’s only goal seems to be preserving itself in the genome – even though this can often put the overall genome at risk. But, let’s not get ahead of ourselves. First, let’s break down the word as Maxwell did for me:

“Transposon” because it can move around or transpose to different parts of the genome.

“Retro” because it uses reverse transcription as the way it makes copies of itself. Specifically, it takes a DNA sequence, turns in into an RNA copy (transcription), and then that RNA copy is used to make a new DNA copy (reverse transcription).

The DNA copy is then inserted somewhere else in the genome – often someplace where it isn’t wanted, causing a genetic mutation. Think of this as the genetic version of cut-and-paste.

Maxwell is looking to understand if these small variations in the DNA can eventually grow to the point where they cause widespread damage to the organism, which is another way of saying whether they contribute to the overall aging of the organism.

If a retrotransposon is added to a DNA sequence instead of the proper DNA strand, it can cause a failure in the system when the organism doesn’t have the correct sequence that it needs to perform a specific task. This leads to instability in the genome.

Maxwell is studying retrotransposons in yeast as a model for what they may also do in humans. A key element of his work will be learning exactly how retrotransposons move around the genome.

One possibility for their mobility around the genome, Maxwell sayd, is if they literally hack out a space for themselves in the genome. Another possibility Maxwell will investigate is whether retrotransposons make sure to be in the right place, at the right time (the little opportunists!). How might this happen? When a cell is damaged, it looks to other parts of the genome for a patch or DNA “band aid” to replace the damaged sequence. You can thank each of your parents because chromosomes come in pairs (one from mom and one from dad) so that genetic patch can often be found in the other parent’s donated chromosome. However, retrotransposons might be so similar to the sequence the body is looking for that it gets scooped up instead of the pair chromosome’s sequence.

So now you (hopefully) know a little more about retrotransposons. Maxwell plans to expand his retrotransposon research to include other organisms, including humans.