Cryopreservation of fluorescence activated cell sorted boar spermatozoa based on extracellular ubiquitination

The present study is focused on the methodology of fluorescence activated cell sorting (FACS) of spermatozoa stained by the antibody against extracellular surface marker ubiquitin (eUb) and subsequent protocol for their long term storage in liquid nitrogen (LN). High level of spermatozoa surface ubiquitination has been previously discussed as a negative quality marker. From a general point of view, any other outer membrane antigen would be compatible with our approach. Regarding our experimental design we found that only those insemination doses with at least 40% of motile spermatozoa after freezing and thawing (F/T) in the egg-yolk medium with lactose are suitable for the subsequent antibody staining and FACS. The sorting rate was sufficient for the preparation of up to 20 spermatozoa aliquots for intracytoplasmic sperm injections (ICSI). Two significantly different groups with good freezability were prepared and stored in LN (0.73% contamination of spermatozoa with high eUb level in non-ubiquitinated group and reversely 6.65% spermatozoa without eUb in highly ubiquitinated group). Sperm viability after FACS varied from 11 to 28% regardless of the used media (P = 0.15). Required viability of F/T sorted spermatozoa was obtained by using Solusem® extender as a load and collection medium. In this case 12% of viable spermatozoa with progressive motility in low eUb level group and 7% in high eUb level group (P < 0.05) were detected. Our approach allows obtaining sufficient number of viable spermatozoa for subsequent artificial fertilization by ICSI. This procedure could be used for a wide variety of spermatozoa sorting based on different surface markers.