Parasitic guardians: diagnosing telomere length variation in Drosophila

Xander at his workbench




Assistant Professor of Biology

Project Summary

Through my PURM experience I worked in a genetics lab studying fruit fly telomeres and their evolution. My project was aimed at highlighting the variation in telomere length of several naturally evolved lines of Drosophila melanogaster. Recent computational analysis has shown that what used to be thought of as a standard, constant telomere length across all chromosomes and all lines is not actually the case, and my project sought to identify this variance using cell biology. Specifically, I dissected salivary glands from larvae, where I was able to extract the large, endoreplicated polytene chromosomes from these glands. I then hybridized the chromosomes with a probe that would bind to the telomeric DNA sequence of HeT-A, and finally stained and imaged the probe to quantify the HeT-A variation. I discovered that this variation is indeed real, with long-telomere lines having telomeres over five times as large as those of short-telomere lines. I also found variance in how many chromosomes even have HeT-A at all, with some lines having the sequence on all chromosomes and some lines on only three. Such findings begin to question the importance of HeT-A and give us insight into the intergenomic conflict between selfish, retrotransposon telomeres and the rest of the genome. The polytene chromosomes I imaged are large, banded chromosomes which, when hybridized with a probe for HeT-A, are extremely beautiful examples of life at work. So while this experience taught me the basics of conducting fruit fly genetics research, what I really learned was a love for the beauty underlying science as well as for the complications that make up the details. Case in point: fluorescent in situ hybridization, the rather finnicky procedure used for imaging the telomere, was a long, convoluted procedure used to visualize the strange irregularities in telomere length. Everything is a balance between simplicity and complexity. Once of my most fascinating realizations from this project has been how the science of evolution can take place away from rocks and fossils. Through cell biology, we will have a better idea of how and why the telomere has evolved the way it has and be able to ask new questions to further the study of evolution. I never would have thought that research in genetics could lead to advances in evolution, an inspiring and fascinating concept.