Expression of sex hormone-binding globulin gene and its relation to serum testosterone concentration in Bubalus buffaloes

To be bioavailable and exert its roles, testosterone binds to the sex hormone-binding globulin (SHBG) synthesized mainly by the hepatic cells. We investigated the relation between blood testosterone, SHBG gene expression in the hepatic cells, and the genetic variations in SHBG gene on Egyptian Bubalus bubalis buffaloes. Serum testosterone concentration increased significantly with age up to 36 months, then slightly declined at 42 months. SHBG mRNA levels slightly fluctuated in the different ages and declined at 42 months. Levels of SHBG protein were higher at 30 months, declined gradually with age up to 36 months, then increased slightly at 42 months. Serum testosterone concentration positively correlated with male buffaloes’ age. SHBG protein level negatively correlated with male buffaloes’ age and serum testosterone concentration. The positions −703 and −674 of SHBG gene promoter were polymorphic and the allele ‒674T could be associated with increased transcription of SHBG gene. A 603 bp-region in the middle of SHBG gene was determined as highly polymorphic; with 3–10 polymorphic sites. Certain genotypes were associated with higher or lower serum testosterone concentration. These results are important for characterizing the genetic make-up of SHBG gene, which may facilitate identifying high- concentration testosterone bull genotypes.