Novel needle-in-straw vitrification can effectively preserve the follicle morphology, viability, and vascularization of ovarian tissue in Japanese quail (Coturnix japonica)

Cryopreservation of ovarian tissue has been the only effective way of ex situ conservation of female germplasm in avian species. A novel needle-in-straw (NIS) vitrification method was developed to store tissue in straws instead of cryovials. Fragments of ovarian tissue from one-week old Japanese quail were transfixed on an acupuncture needle. They were immersed in equilibration and vitrification solutions containing dimethyl sulphoxide, ethylene glycol and sucrose. A layer of tin foil was rolled over the tissue fragments and the tin foil package was plunged into liquid nitrogen and inserted into a pre-cooled, 0.5-ml straw which was stored in liquid nitrogen. Tissue was also preserved using a needle immersed vitrification (NIV) method, in which tissue fragments transfixed on needles without tin foil and were stored in cryovials filled with liquid nitrogen. Cryopreserved tissue was warmed at room temperature (RT) or 37 °C and the ratio of normal follicles to total visible follicles was determined by histological methods. In addition, cryopreserved and warmed tissue was cultured on the chorioallantoic membranes of fertilized chicken eggs for 5–6 days. The viability and vascularization of the grafts were evaluated. The tissue cryopreserved by NIS and warmed at RT showed comparable follicle morphology to fresh tissue and to that preserved by NIV and warmed at RT. No significant impairment on the viability or vascularization of the grafted tissue was observed. The NIS method allows tissue to be stored and transported safely and efficiently and can be used instead of cryovials in tissue cryobanking.