Prize winning Hereford bulls from cryogenically stored Embryo Transfer
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Cryopreservation on the farm and in the news

Hereford Bull, Normanton 1 Laertes, from Ashby-de-la-Zouch in Leicestershire. He was born from embryo transfer, and was Supreme Champion at Burwarton Show in 2016.
Hereford Bull, Normanton 1 Laertes, from Ashby-de-la-Zouch in Leicestershire. He was born from embryo transfer, and was Supreme Champion at Burwarton Show in 2016.

Almost all the milk we drink will come from cows whose father’s sperm was frozen. It is quite likely that their father himself was an embryo transfer bull, who started ‘life’ in frozen in liquid nitrogen, and many of the elite dairy cows will be ET cows with frozen and thawed embryos implanted into a surrogate mother.

In my own research, I use animal tissue culture lines from ‘frozen zoos‘ – using cells from rare animals who died at the end of their natural lives or were taken for veterinary treatment, and have then been stored in a freezer for convenience. Almost all the genes and other DNA sequences I work with to study the information encoded in them and their organization are kept within bacteria stored in a freezer. While most plants are most conveniently stored as seed, or grown in gardens or pots where the maintenance and welfare needs are small, some lines come from frozen tissue. For my banana research, where the varieties we eat do not produce seeds, all the different varieties are stored frozen, as well as being kept as plants in the field and in tissue culture. So an important and routine part of scientific research uses frozen cells which can be regenerated into living cells.

So where are we with human cryogenic preservation? I am certain to know some people who were born, since the mid-1980s, through in vitro fertilization. For some of those people, is likely that the eggs, sperm, or embryos they developed from were frozen or ‘cryogenically stored’. After some debate and with rigorous regulation now in most countries, sperm, eggs and embryos are now routinely stored from people and couples for various reasons. But news articles this week have brought to prominence the possibility of paying to store frozen your newly-dead body, with the prospect held out of revitalization at some time in the future.

I will leave the ethical and moral discussions to people qualified in that, but think about what we can do now and are likely to do soon? The science and technology to regenerate whole mammals from single cells other than embryos has become routine since ‘Dolly the sheep‘ pioneered the approach 1996 as the first mammal to have been regenerated adult cell, although for ethical and scientific reasons has not been used in humans. The technology means that no mammal species would die out in the future so long as some frozen cells have been stored.

The present state of technology is still some way from being applicable to whole mammals, or indeed vertebrates. There are some films on YouTube of frozen fish being placed into water and starting to swim, but these are likely to only be frozen on the surface. The internal organs are not frozen, being in the dormant state they would be in the cold water at the bottom of a pond in the winter. For single cells which are frozen and then brought back to life, we will normally add some anti-freeze – the same chemical as is used in a car radiator, ethylene glycol, or other simple, less toxic chemicals like glycerine or sugar – to stop ice crystals forming in the cells, and then the cells are cooled. They are stored at temperatures somewhat colder than a food freezer (-20 degrees C), typically either -80C in a special type of freezer, or -196C in liquid nitrogen. Cells can be stored for decades in these conditions, and are brought back to life by gentle warming. I expect the approaches to freezing and reanimating whole organisms will continue to improve in the next few years. Cryogenic preservation of sperm, eggs and embryos has revolutionized animal breeding and human reproduction in less than 30 years. It would be a major advance to freeze whole organs to transfer between people.

The ethical issues are being discussed on Radio Leicester in the show by Mike Allbut on Sunday 27 November (2h 6m 45s), and I recorded a short piece with Andrew Fewster about the opportunities within the programme broadcast at about 7.15am (1h 11m 20s).

Editor Pat Heslop-Harrison

Pat Heslop-Harrison is Professor of Molecular Cytogenetics and Cell Biology at the University of Leicester. He is also Chief Editor of Annals of Botany.

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