Staining of sturgeon spermatozoa with trypsin inhibitor from soybean, Alexa Fluor® 488 conjugate for visualization of sturgeon acrosome

Trypsin-like activity, similar to acrosin, is present in sturgeon spermatozoa and can be a potential target for trypsin inhibitors. The objective of this work was to use a fluorescent soybean trypsin inhibitor (SBTI) conjugate with the Alexa Fluor® 488 dye for visualization of the sturgeon acrosome. After incubation with SBTI-Alexa, a strong signal was observed both in the acrosome and midpiece or implantation fossa region. We have also found that SBTI-Alexa staining can be combined with PI viability test. Detailed examination of staining pattern revealed that SBTI-Alexa can stain either acrosome or whole sperm. Staining of whole sperm correlated with dead staining (r² = 0.94, P < 0.01). However, in fresh semen most cells (93-97%) were not stained with SBTI-Alexa, probably due to intact acrosomes. Further studies should test if SBTI-Alexa can be applied to monitor the acrosome status during the acrosome reaction and cryopreservation.