Acrosome reaction of Chinese mitten-handed crab Eriocheir sinensis (Crustacea: Decapoda) spermatozoa: Promoted by long-term cryopreservation

The effects of three media, two temperatures, and fourteen durations of cryopreservation from 0 h to 450 d on in vitro acrosome reaction (AR) of spermatozoa in Chinese mitten-handed crab Eriocheir sinensis (Crustacea: Decapoda) were investigated. The spermatozoa of good quality were obtained from spermatophores by a glass homogenizer in an ice-bath and centrifugation at 4 °C. At 0 h, 2 h, 1 d, 3 d, 15 d, 30 d, 60 d, 90 d, 120 d, 150 d, 180 d, 270 d, 360 d, and 450 d of cryo-storage in Ca²⁺-free artificial seawater, 10% (v/v) glycerol, and 5% (v/v) dimethylsulfoxide at − 80 °C and in liquid nitrogen (− 196 °C), the changes in spermatozoal morphology, the time of beginning AR, and the time of maximum percentage of AR were observed. The relationships of the changes on AR presented with the different media, temperatures, and durations of cryopreservation were speculated. In this study, the cryopreserved spermatozoa all underwent AR in less than 1 h of settlement under room temperature while the percentage of AR in the control was only about 4.9%. Meanwhile, cryopreservation shortened both the time of beginning AR (from 30.11 min of the uncryopreserved spermatozoa to 0 min of cryopreserved spermatozoa on the 30th day) and the time of maximum percentage (from 59.88 min of the uncryopreserved spermatozoa to 0 min of cryopreserved spermatozoa on the 60th day). Whereas the effect of media on sperm cell AR was negligible (P > 0.05), the treatments of spermatozoa with short- and long-term cryopreservation resulted in extremely significant differences in the time of beginning AR as well as in the time of maximum percentage of AR (P < 0.01). The present data indicate that cryopreservation for long or short periods can promote the AR of sperm cells in E. sinensis and physiologically affect the ability to capacitate. It may be that the mechanism of AR in this study is the direct promotion of membrane fusion of the acrosomal cap, or destruction of the proteins inhibiting AR and activation of the proteins promoting AR, by cryopreservation. In addition, the results also show that cryopreservation can protect the spermatozoa because AR can occur in almost all sperm cells cryopreserved for less than 15 d.