Acquiring the potential for motility is accompanied by profound changes in the testicular sperm proteome of sex-reversed female and normal male rainbow trout

Salmonid fish spermatozoa acquire the potential for motility during the transition from the testis to the spermatic duct. Due to the lack of a spermatic duct in sex-reversed females (srf) of rainbow trout, sperm resemble testicular semen and must be collected directly from the testes; consequently, they are immature with no or low potential for motility. Such potential can be acquired through artificial in vitro maturation-incubation of testicular sperm suspensions in buffered-saline solutions mimicking seminal plasma with high pH and containing bicarbonate (artificial seminal plasma (ASP)). The objective of this study was to investigate the effect of the in vitro maturation of sperm on the sperm quality parameters and sperm proteome, for both srf and normal males of rainbow trout. The incubation of sperm in ASP resulted in an increase in sperm motility parameters (from the mean values of 26 to 66% and 28 to 56% for srf and normal males, respectively), a decrease in the proportion of ROS-positive cells (from the mean values 12.9% to 9.1% for srf and from 17.9% to 12.2% for normal male sperm) and no effect on sperm viability maturation, resulting in profound changes in the sperm protein profile in srf and normal male sperm. The application of a 2D-DIGE approach revealed a slightly higher number of differentially abundant protein spots (126 protein spots) after the sperm motility acquisition of normal male sperm than that of srf sperm (116 protein spots). Most of the proteins that change in abundance after sperm incubation in ASP were similar for both srf and normal male sperm and were involved in a variety of pathways and functions including cytoskeleton and cell movement, metabolism and energy production, protein folding, turnover and molecule binding. The number of significant changes in the sperm proteome is related to the cytoskeleton, flagella and cell movement, and metabolic proteins demonstrate changes in the sperm motility apparatus during the short period of artificial in vitro maturation, indicating similarities to the protein changes that occur during the longer process of natural sperm maturation. The lack of differences in sperm quality between srf and normal males after incubation in ASP indicates the similar modes of sperm motility acquisition. The alterations in proteins after artificial maturation partially overlapped with the changes noticed after trout sperm motility activation, strongly suggesting the participation, at least partially, of the same proteins, both in the process of acquiring the spermatozoa ability to move and sperm movement.