Abstract
The composition of sperm proteins influences the fertilizing ability of sperm and hence the present study was conducted (i) to profile sperm proteins expression patterns in bulls of differing fertility index and (ii) to identify and relate the abundant sperm proteins with bull fertility. The semen samples were collected from Holstein-Friesian bulls (n = 12) varying in conception rate (CR) (high/low). The frozen semen straws (three ejaculates, from each bull) were used to study (a) sperm kinetic parameters, (b) plasmalemma integrity, (c) mitochondrial membrane potential, and (d) chromatin distribution. Three bulls were randomly selected from each group (n = 3) and the neat sperm pellets were subjected to percoll purification, followed by protein isolation using 0.1% Triton X100. The sperm kinetic parameters, plasmalemma integrity, mitochondrial membrane potential, and the chromatin distribution did not differ significantly between groups. The number of acidic (pI; 3.1–5.6, 37%) and basic (pI; 7.9–10.0, 27%) proteins and their pattern of expression varied significantly (p < 0.05) between high and low fertile bulls. The abundant sperm protein spots in 2D-gel electrophoresis (2DE) were identified as seminal plasma protein PDC-109 (i.e., protein with N-terminus aspartic acid, D and carboxy terminus cystine, having 109 amino acids) and its isoform and spermadhesin-1 (SPADH1). The western blot analysis confirmed the presence of PDC-109 isoform proteins at 15.4 kDa (pI 5.3 and 5.5). The seminal plasma protein PDC-109 was abundant in the low fertile when compared to the high fertile group (p < 0.05). This study suggests that the imbalance in acidic and basic sperm proteins may influence sperm fertility and sperm PDC-109 levels above a certain threshold affects bull fertility.
Acknowledgments
We are thankful to Nandini Sperm Station (NSS), Karnataka Milk Federation, Hessarghatta, Bengaluru, India for providing semen samples and conception rate data for the bulls.
Declaration of interest
LS is funded by an Innovation in Science Pursuit for Inspired Research (INSPIRE) fellowship by Department of Science and Technology, Ministry of Science and Technology, Government of India for pursuing Ph.D. programme at the Department of Biochemistry, Jain University, Bengaluru, Karnataka, India. The research work is supported by Indian Council of Agricultural Research-National Institute of Animal Nutrition and Physiology, Adugodi, Bengaluru, India. The authors declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research reported. The authors alone are responsible for the content and writing of manuscript.
Author contribution
Conceived and designed the experiments: LS, SS, JPR; Performed the experiments: LS; Analyzed the data: LS, SS, PS; Wrote the manuscript: LS, SS, JPR; Revised the manuscript: LS, SS, PS, JPR. All authors approved the manuscript.
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