Sex hormone‐binding globulins characterization and gonadal gene expression during sex differentiation in the rainbow trout, Oncorhynchus mykiss

Abstract

Sex hormone-binding globulin (SHBG) binds androgens and estrogens in the blood of many vertebrates, including teleost fish. In mammals, SHBG is synthetized in the liver and secreted into the blood. In fish, shbga also exhibits a hepatic expression. In salmonids, in which the gene has been duplicated, the recently discovered shbgb gene exhibits a predominantly ovarian expression. The present work aimed at gaining new insight into shbgb gene structure and expression during gonadal sex differentiation, a steroid-sensitive process, and Shbgb protein structure and binding characteristics; specifically, rainbow trout (Oncorhynchus mykiss) shbgb was analyzed. shbgb structure was analyzed in silico while expression was characterized during gonadal sex differentiation using all-male and all-female populations. We observed that shbgb gene and cognate-protein structures are similar to homologs previously described in zebrafish and mammals. The shbgb gene is predominantly expressed in differentiating female gonads, with increased expression around the end of ovarian differentiation. In the ovary, shbgb mRNA was detected in a subset of somatic cells surrounding the ovarian lamellae. Furthermore, Shbgb binds steroids with a higher selectivity than Shbga, exhibiting a higher affinity for estradiol compared to Shbga. In conclusion, Shbgb binding characteristics are clearly different from those of Shbga. Shbgb is expressed in the differentiating ovary during a period when the synthesis and action of testosterone and estradiol must be tightly regulated. This strongly suggests that Shbgb participates in the regulation of steroid metabolism and/or mediation, that is, needed during early gonadal development in rainbow trout.

RUNX1 maintains the identity of the fetal ovary through an interplay with FOXL2

“…For the rainbow trout, Runx1 expression during gonadal development was assessed by quantitative PCR 63 . Species-specific primers used are listed in Supplementary Table 3.…”

The unusual rainbow trout sex determination gene hijacked the canonical vertebrate gonadal differentiation pathway

“…Expression levels of sdY, foxl2b1, foxl2b2, nr5a1, and cyp19a1a were measured by qPCR as previously described (37). Gonads (15-20 pairs of gonads per time points) were sampled in triplicate at 33,35,37,40,44,50,61,85, and 125 dpf in both genetic all-male (XY) and all-female (XX) populations of rainbow trout. Total RNA was extracted using the RNAqueous-Micro Kit (Ambion, Life Technologies) for the 33-to 50-dpf samples and the RNAqueous-Kit (Ambion, Life Technologies) for the 61-to 125-dpf samples.…”

Dietary phytochemicals modulate skin gene expression profiles and result in reduced lice counts after experimental infection in Atlantic salmon

“…Finally, the present study suggested that GLs-mediated suppression of sex hormone-binding globulin beta, involved in regulation of sex hormone levels [ 66 ], may have increased the availability of steroid hormones in protected fish (Table 3 ). The sex steroid hormonal system in fish skin is important in wound healing in sea bream [ 67 ] and is associated with protection against lice in Atlantic salmon [ 39 ].…”