In 2022, Dr Berenice Bernal Juarez, researcher at the Animal Breeding and Genomics group (ABG) and working for the Centre for Genetic Resources, the Netherlands (CGN), received a MSCA postdoctoral fellowship to start the CRYOCHICK project.
The project is drawing to a close, so we contacted Dr Bernal Juarez to ask for an update on the project.
Cryopreservation of chicken reproductive material
The CRYOCHICK project was developed in collaboration with the NBGK (National Center for Biodiversity and Gene Conservation) in Hungary, with extensive experience in the cryopreservation of chicken sperm of native breeds and female chicken reproductive material (ovarian tissue, primordial germ cells), and The Roslin Institute in Scotland, with experience in the cryopreservation of chicken female primordial germ cells and gonadal germ cells.
Cryopreservation of chicken reproductive material is challenging for several reasons. Apart from the high cryosensitivity of spermatozoa and low post-thaw fertility (not all sperm cells survive the freeze-thaw cycle), the contraceptive effect of glycerol (a cryoprotectant that is used to protect the biological tissue from freezing damage) and the impossibility to freeze chicken oocytes and embryos are complicated impediments.
"Chicken sperm cells are not as cryotolerant as, for example, the sperm cells of bulls, which is mainly due to their morphology (the shape, size, and structure) and their plasma membrane composition," says Dr Bernal Juarez. "Chicken sperm cells are filiform and longer than bull sperm, being less capable to tolerate changes in volume, which makes them more susceptible to damage from osmotic or mechanical stress during freezing. These were some of the challenges we faced in this project. Another big challenge was that we cannot freeze the oocytes of birds. So the aim was to contribute in the improvement of freezing protocols of another kind of female reproductive material such as primordial germ cells (PGCs) or gonadal germ cells (GGCs)."
Preventing freezing damage
"We wanted to propose a new strategy where we shorten the supercooling phase," says Dr Bernal Juarez. "This basically means that we wanted to start the formation of the ice earlier than normal. For example, if the ice normally forms at -5 °C, we wanted it to start at -3 °C. The reason why we wanted to do this, is because we believe that the supercooling phase is very damaging. Previous studies have shown that this phase can significantly damage the sperm cells, so we wanted to shorten the phase and also use additional natural cryoprotectants that some animals in Arctic environments use to minimize freezing damage."
Valuable research for genebanks
The research that was carried out in the CRYOCHICK project is particularly valuable for genebanks, as cryopreservation of genetic material of different chicken breeds means that researchers can, for example, reintroduce lost traits in breeding populations. Also, avian populations face threats like avian influenza. Preserving reproductive cells ensures that valuable breeds can be restored, even if the live population is severely diminished. And, last but not least, traditional and heritage breeds may have unique genetic traits suited for specific environments. Without conservation efforts, these breeds could disappear, for example due to environmental changes or shifts in agricultural practices. Cryopreservation ensures that these genetic traits remain available for future generations.
Future
"I would really like to continue working with PGCs and GGCs, and I would like to apply for another grant to continue my research. We think there is still a lot of work to be done with PGCs and the protocols for freezing chicken sperm," says Dr Bernal Juarez. Although she will be returning to Spain, her native country, once the CRYOCICK project is finished, we - everyone from the animal genetic resources team at CGN - will definitely keep following Dr Bernal Juarez's research activities.
