Evolution of sex hormone binding globulins reveals early gene duplication at the root of vertebrates
Sex hormone-binding globulin (Shbg) is an important vertebrate blood carrier protein synthetized in the liver and involved in the transport and local regulation of sex steroids in target tissues. A novel shbg gene (shbgb) with a predominant ovarian expression was recently characterized. Being initially found only in salmonids, this shbgb was originally thought to result from the Salmonid-specific whole genome duplication. Using updated transcriptomic and genomic resources we identified Shbgb orthologs in non-salmonid teleosts (European eel, arowana), holosteans (spotted gar, bowfin), polypteriformes (reedfish), agnatha (sea lamprey) and in amphibians, and found that the classical Shbg gene (Shbga) displays a predominant hepatic expression whereas Shbgb has a predominant gonadal expression. Together, these results indicate that these two Shgb genes most likely originate from a whole genome duplication event at the root of vertebrate evolution, followed by numerous and independent losses and by tissue expression specialization of Shbga and Shbgb paralogs. HighlightsO_LIPhylogeny, synteny and expression analyses shed new light on Shbg evolution in vertebrates. C_LIO_LIShbg diversity originates from a duplication event at the root of vertebrate evolution. C_LIO_LIThis duplication was followed by many independent losses of Shbg paralogs in vertebrates. C_LIO_LIShbg paralogs have acquired different tissue expression patterns. C_LI