TRANSCRIPTOMIC PROFILING OF CROSSBRED BULL SPERMATOZOA IN RELATION TO FERTILITY AND CAPACITATION
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Date
2020
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ICAR-SRS-NDRI, KARNAL
Abstract
Although the significance of bull infertility has been documented well, the underlying reasons for high incidence of infertility in crossbred bulls still remains elusive. The present investigation was carried out to identify fertility related sperm transcripts in HF crossbred bulls and to find out the ability of spermatozoa to undergo capacitation on exposure to oestrous oviductal fluid and its relationship with bull fertility. The present study identified a total of 13,563 transcripts in crossbred bull spermatozoa; after total hit normalization, a total of 776 transcripts were detected, of which 524 transcripts were common to both high- and low-fertile bulls, while 84 sperm transcripts were unique to high-fertile bulls and 168 transcripts were unique to low-fertile bulls. Among the co-expressed genes, 176 genes were up-regulated while 209 genes were down regulated in low-fertile bulls. Using bioinformatics analysis, we identified that the biological processes down-regulated in low fertile bull spermatozoa included multicellular organism development and spermatogenesis. Further, ribosomal pathway was upregulated whereas oxidative phosphorylation was down-regulated in low fertile bull spermatozoa. Moreover, sperm transcripts unique to high fertile bulls were involved in oxidative phosphorylation pathway and transcripts unique to low fertile bulls were involved in ribosomal pathway. Select transcripts (TPT1, PFN1, ZNF706, CRISP2, MDB4, TNP2, ADIPOR1 and TNP1) were validated using qPCR and found that the transcriptional abundance of ZNF706, CRISP2, MDB4, TNP2 and TNP1 genes were significantly (p<0.05) higher in high-fertile bulls compared to low-fertile bulls and were positively correlated with conception rate (p<0.01). During incubation of spermatozoa from above- and below-average bulls with NL-ODF, it was observed that the extent of reduction in sperm viability and acrosome reaction between 0 h and 4 h of incubation was lower in above average bulls compared to below average bulls. Further, the hallmarks of sperm capacitation were significantly higher in above- compared to below-average bulls at 4 h of incubation indicating the dual role of oviductal secretions on spermatozoa. Transcriptional abundance of genes related to sperm capacitation (CATSPER1, PEBP1, CRISP2, ADIPOR1, ADIPOR2 and IQCF1) were upregulated in below average bulls. Conception rate was positively correlated (p<0.01) with sperm viability, intracellular calcium level and acrosome intactness at 4 h incubation with NL-ODF. It was therefore concluded that oxidative phosphorylation was the most affected pathway in low-fertile bull spermatozoa and the sperm transcriptional abundance of ZNF706, CRISP2, MDB4, TNP2 and TNP1 genes was significantly related to bull fertility and thus these genes could serve as potential candidate biomarkers for fertility in crossbred bulls. Further, the ability to undergo capacitation upon exposure to NL-ODF varied with individual bulls and also significantly related to bull fertility.