The effect of negative pressure on the expression of AQN-1 protein in boar sperm was shown in Fig 1. The relative expression of AQN-1 gene in boar sperm was not significant (
P>0.05) at 0,3,5,7 and 7 days of semen preservation. As shown in Fig 1, as the retention time increased, the relative expression of the AQN-1 protein gene increased. And after 5 days of storage, the relative expression level of AQN-1 protein is higher than 0 or 3 days of the storage. In this study, there was no difference in the relative expression of AQN-1 protein gene among the experimental groups. But with the increase of preservation time, the relative expression of mRNA in sperm adhesion protein gene family increased. The results of previous experiments have shown that the relative expression of mRNA in sperm adhesion protein gene family is increasing with the increase of preservation time, which is consistent with the results of GAO (
GAO et al., 2014).
The effect of negative pressure on the expression of AQN-3 protein gene in boar spermatozoa was shown in Fig 2. There was no significant difference in the relative expression of AQN-3 protein gene in boar spermatozoa on 0 day and 3 days of preservation
(P>0.05). After preservation for 5 days, the relative expression of AQN-3 protein gene in P4 and P8 groups was higher than that in control group and P2 group (
P<0.05), but there was no significant difference between P4 and P8 groups (
P>0.05) and there was no significant difference between P2 group and control group (
P>0.05). On preservation for 7 days, the relative expression of AQN-3 protein gene in P2 or P4 group was significantly higher than control group
(P<0.05) and there was no significant difference in the relative expression of AQN-3 protein gene between P8 group and control group
(P>0.05). The relative expression of AQN-3 protein gene was lower than that of the control group after 3 to 5 days of preservation under -0.04 MPa. The previous results also showed that the sperm motility was the best when the preservation condition was proper, which may also be related to the low relative expression of AQN-3 protein gene
(Li et al., 2018; 2020).
The effect of negative pressure on the expression of AWN protein gene in boar spermatozoa was shown in Fig 3. There was no significant difference in the relative expression of AWN protein gene in all groups at the 0 day and 7 days of preservation (
P>0.05). The relative expression of AWN protein gene in P2 group and control group was significantly higher than P4 and P8 groups on the 3 day after preservation, but there was no significant difference between P2 group and control group and there was no significant difference between P4 and P8 group. On the 5 days of preservation, the relative expression of AWN protein gene in the control group was significantly higher than the other groups (
P<0.05). This results showed that the relative expression of AWN, PSP-I and PSP-II genes in negative pressure group was lower than control group. The expression of AQN-3 and AWN protein genes of negative pressure preservation group was higher than control group at 7 days after preservation, which may be related to the proportion of dead spermatozoa. It can be seen from the results of the previous experiment that the sperm motility of control group after preservation 7 days was lower than that negative pressure group, but the specific reasons need to be further studied.
The effect of negative pressure on the expression of PSP-I and PSP-II protein in boar spermatozoa was shown in Fig 4 and 5. There was no significant difference in the relative expression of PSP-I/ PSP-II
(P>0.05) in all groups on 0 and 3 days of preservation (
P>0.05). The relative expression of PSP-I gene in the control group was significantly higher than the other groups (
P<0.05) on the 5 days of preservation, but there was no significant difference in P2, P4 and P8 groups (
P>0.05). On the 7 days of preservation, the relative expression of PSP-I/ PSP-II protein gene in the control group was significantly higher than the other groups (
P<0.05), however, not significant in P4 and P8 groups (
P>0.05).
Centurion et al., (2003) showed that the porcine sperm adhesion protein gene family was involved in the regulation of sperm motility and the heterodimers formed by PSP-I protein and PSP-II protein could bind to heparin.
Carcia et al., (2006) found that the main functional group of PSP-I/PSP-II dimer in inhibiting sperm motility was the subunit structure of PSP-I and the ability of single subunit to inhibit sperm motility was better than that of PSP-I/PSP-II dimer. At the same time, AQN-3 may be a member of boar sperm motility inhibitor complex (
Shultz et al., 2006).
Song et al., 2014 found that the mRNA expression level of adhesion protein gene family in capacitated sperm was significantly higher than infertile sperm. The results of
GAO (2014) showed that the expression of adhesion protein gene family mRNA in low motility spermatozoa was significantly higher than that in high motility spermatozoa (
GAO et al., 2014).
Although mRNA of boar sperm has been widely reported, most studies have focused on the types of RNA, the structure of the expressed products. However, there are few studies on its biological function and mechanism and the biological function and mechanism of many sperm RNA still need to be studied. Some studies found that AQN-1, AQN-3 and AWN are related to sperm capacitation
(Lambard et al., 2004; Lalrintluanga et al., 2014). GAO reported that the expression of AQN-1, AQN-3, AWN, PSP-I and PSP-II genes in pig spermatozoa was negatively correlated with sperm motility
(GAO et al., 2014).