Transferrin Identification in Sterlet (Acipenser ruthenus) Reproductive System

Simple Summary Sturgeon is an ancient and unique fish species. Most of sturgeon are listed as critically endangered species due to habitat alteration and overharvesting. Study of sturgeon reproductive system and sperm is important for aquaculture and conservation programs. Transferrin is recognized as a multiple task protein, positively correlated with spermatogenesis and sperm quality. Thus, we tried to detect transferrin in spermiating and out-of-spawning sterlet reproductive organs and sperm. Two transferrin genes, serotransferrin and melanotransferrin, have been identified in reproductive organs of sterlet males. The serotransferrin was expressed higher in reproductive organs of spermiating than out-of-spawning sterlet males. Furthermore, transferrin was detected in sterlet seminal plasma. This information contributes to the existing information on the variability of transferrin proteins and the potential role of transferrin in chondrostean fishes. Abstract Transferrins are a superfamily of iron-binding proteins and are recognized as multifunctional proteins. In the present study, transcriptomic and proteomic methods were used to identify transferrins in the reproductive organs and sperm of out-of-spawning and spermiating sterlet (Acipenser ruthenus) males. The results showed that seven transferrin transcripts were identified in the transcriptome of sterlet, and these transcripts were qualified as two different transferrin genes, serotransferrin and melanotransferrin, with several isoforms present for serotransferrin. The relative abundance of serotransferrin isoforms was higher in the kidneys and Wolffian ducts in the spermiating males compared to out-of-spawning males. In addition, transferrin was immunodetected in sterlet seminal plasma, but not in sterlet spermatozoa extract. Mass spectrometry identification of transferrin in seminal plasma but not in spermatozoa corroborates immunodetection. The identification of transferrin in the reproductive organs and seminal plasma of sterlet in this study provides the potential function of transferrin during sturgeon male reproduction.