Using light to describe the ancient world


Researchers labelled DNA in moa eggshells with a fluorescent dye. Moa didn't have green fluorescent bones - this is just a fun picture.

Researchers labelled DNA in moa eggshells with a fluorescent dye. Moa didn’t have green fluorescent bones – this is just a fun picture.

Many researchers use genetic information to study relationships between species. This works because there are tiny differences between the genetic code of a parent and an offspring – over many generations, these small changes eventually produce new species. Closely related species that shared a recent common ancestor will have the most similar genetic code (i.e. most similar DNA sequences). So, by figuring out similarities and differences between the genetic codes, researchers can understand evolutionary relationships between species.

This works really well for modern animals because researchers can easily collect DNA from living tissues. This is a little more challenging if researchers want to use DNA to learn the relationships of extinct animals. DNA degrades over time, so even if you find a fossil that is only a few hundred years old, it may no longer contain DNA. This was the challenge that Charlotte Oskam and colleagues faced when they studied ancient moa eggshells (Oskam et al. 2010). How could they know if DNA was present in the ancient eggshells? One method they explored was confocal fluorescence microscopy.

I will let these two clips explain:

To find out if ancient moa and elephant bird eggshells contained DNA, Oskam and colleagues immersed the shell fragments in a solution of fluorescent dye. The dye is colourless and it binds to DNA. When the dye-labelled DNA is irradiated with a blue laser it appears green. Sure enough, the ancient moa eggshells lit up green in the laser microscope.

“…Confocal imaging of elephant bird (Aepyornis) eggshell in cross section clearly demonstrated that DNA is distributed through the eggshell matrix as evidenced by the presence of fluorescent ‘hot-spots’. Imaging of the inner surface of moa eggshell (Dinornis) also shows foci of DNA…”

This is great, and a real time saver if it stops the researchers from analysing ancient egg shells that don’t have DNA in them. Imagine, though, how amazing it would be if we could find the ancient DNA without the need for a fluorescent dye….

Oskam CL, Haile J, McLay E, Rigby P, Allentoft ME, Olsen ME, Bengtsson C, Miller GH, Schwenninger J-L, Jacomb C, Walter R, Baynes A, Dortch J, Parker-Pearson M, Gilbert MTP, Holdaway RN, Willerslev E and Bunce, M. 2010. Fossil avian eggshell preserves ancient DNA. Proceedings of the Royal Society B: DOI: 10.1098/rspb.2009.2019


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