Diversity and biological significance of sex hormone-binding globulin in fish, an evolutionary perspective.
In fish, two different genes, shbga and shbgb, exist that encode for very different proteins. Shbga is the ortholog of mammalian Shbg and was found in all investigated teleosts. In contrast, Shbgb is highly divergent and appears to be a salmonid-specific protein. Here, we review existing data on fish Shbga and Shbgb that have been obtained in chondrichthyes and osteichtyes. Even though other significant expression sites exist, existing data indicate that Shbga is mainly expressed in liver and subsequently secreted into the blood as a homodimer. In contrast, Shbgb is mainly expressed in the ovary, probably secreted as a monomer, and could contribute to the regulation of local steroid action. Binding studies indicate a specialization of circulating Shbg during evolution towards the preferential binding of estradiol and testosterone in teleosts. In contrast, specific fish steroids such as 11-oxo-androgens and oocyte maturation-inducing steroids that are crucial for reproduction are poorly bound by either form of Shbg.
Bobe
Julien
J
INRA, UR1037 SCRIBE, IFR140, Fish Reproduction Group, Ouest-Genopole, F-35000 Rennes, France. Julien.Bobe@rennes.inra.fr
Guiguen
Yann
Y
Fostier
Alexis
A
D000595:Amino Acid Sequence; D000818:Animals; D005075:Biological Evolution; D005399:Fishes / Q000235:genetics / Q000378:metabolism; D006801:Humans; D008969:Molecular Sequence Data; D010802:Phylogeny; D011485:Protein Binding; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D016415:Sequence Alignment; D012738:Sex Hormone-Binding Globulin / Q000235:genetics / Q000378:metabolism; D014018:Tissue Distribution
D020033:Protein Isoforms; D012738:Sex Hormone-Binding Globulin