It is now possible to obtain proteins from preserved soft tissues like brains. The new method could reveal details of human history and prehistory, and of evolutionary history, that were previously impossible to know. That includes what animals ate, the microbes they had in their guts and even how human brain cells changed over evolutionary time.
鈥淭here are soft tissues preserved over half a billion years of Earth history,鈥� says at the University of Oxford. Such tissues could now be mined for proteins. 鈥淭he amount of biological information is just massive.鈥�
All living organisms contain a variety of proteins, molecules that play roles in everything from the beating of hearts to brain signalling. When organisms die, the proteins rot away. However, if tissue is preserved, some of them can survive.
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Researchers have already used such proteins to reveal information about long-dead organisms. However, so far they have mostly used those from hard tissues. 鈥淭he vast majority of the field is bones and teeth,鈥� says Morton-Hayward. , for instance what species a specimen belonged to and how closely species are related.
A handful of studies have looked at preserved skin and hair, in the form of leather and fur. However, these contain few proteins. 鈥淭he biological information that skin and hair contain is really limited,鈥� says Morton-Hayward.
In contrast, internal organs such as brains and livers contain 鈥渕ore than 75 per cent of all human proteins鈥�, says Morton-Hayward. However, there hasn鈥檛 been a reliable way to extract [the proteins] from preserved remains. 鈥淭here are soft tissues in fridges and freezers all over the world,鈥� she says, but they aren鈥檛 being studied.
In , Morton-Hayward and her colleagues showed that human brains are preserved surprisingly often in the archaeological record, in waterlogged graves, for example. In the wake of this, they obtained samples from preserved brains 鈥� including 456 that date back up to 300 years, all from an archaeological dig in Bristol, UK. Her team used 10 samples from these brains, each weighing 50 milligrams, and tried a series of different methods to see which would release the most protein.
They found that urea, a chemical found in urine, successfully broke down the brain cells and released the proteins within, without damaging them. The team then broke the proteins down into smaller fragments, which could be identified using a mass spectrometer. The most successful method identified 1205 proteins.
鈥淭his would be probably one of the first, if not the first, [study] to do that,鈥� says at the University of Copenhagen in Denmark. It 鈥減iqued my interest to see that this might be possible鈥�, she says.
While the team tested the method on brains, it should work equally well on other soft tissues such as liver or gut, says Morton-Hayward. Nevertheless, 脕smundsd贸ttir wants to see follow-up studies 鈥渢o figure out what protocol works best鈥�.
It isn鈥檛 clear how old soft tissue could be and still yield useful proteins. 鈥淲e don鈥檛 know the boundaries of how long proteins survive,鈥� says 脕smundsd贸ttir. The oldest yet obtained are 21 to 24 million years old, but those are . In soft tissues, proteins might only survive a few thousand years, she says.
Meanwhile, there are preserved soft tissues from the Cambrian Period (), including trilobite guts and arthropod nervous systems. 鈥淓ither there are proteins in there and we don鈥檛 have the techniques to gain access to them yet, or there are no proteins after a certain amount of time,鈥� says 脕smundsd贸ttir. 鈥淲hich one it is, we will have to wait and see.鈥�
A key challenge is to understand exactly how proteins decay, so that we can reconstruct from a degraded protein what the original was like, says Morton-Hayward.
PLoS One
