Cloning of FSHβ, LHβ, and glycoprotein α subunits from the Russian Sturgeon ( Acipenser gueldenstaedtii), β-subunit mRNA expression, gonad development, and steroid levels in immature fish

The Russian sturgeon, Acipenser gueldenstaedtii, is a late-maturing Acipenseriformes. To elucidate the role of FSH and LH in its reproduction, we cloned its glycoprotein α-subunit (GPα) and gonadotropin β-subunits (FSHβ and LHβ) using 5′ and 3′ RACE-PCR. The nucleotide sequences of the Russian sturgeon (st) GPα, FSHβ, and LHβ are 345, 384, and 411 bp long, encoding peptides of 91, 115, and 114 amino acids, respectively. The deduced amino acid sequence of each mature subunit showed high similarity with those of other teleosts. Sequence analysis showed that stFSHβ is more similar to higher vertebrate FSHβs (35–37%) than to higher vertebrate LHβs (26–30%). The next objective of this work was to compare the development of sturgeon gonads at the very first stages of their growth with the expression of their gonadotropins. Sturgeons at ages 1, 2, 3 or 4 years were sacrificed. The expression of their gonadotropin β-subunits was determined using quantitative real-time PCR, and their gonads were examined histologically, followed by a determination of the plasma levels of estradiol in females and 11-ketotestosterone (11-KT) in males. The expression levels of stFSHβ subunit was found to be higher in fish at 3 and 4 years of age than in 1-year olds. mRNA levels of stLHβ were higher than those of stFSHβ in both genders. Moreover mRNA levels of stFSHβ detected in females were significantly higher than those found in males. Even at age 4 years, all female Russian sturgeons tested contained gonads at the pre-vitellogenic stage, with small oocytes and very low levels of estradiol in the plasma. However, among the males, at ages 3 and 4 years, we found testes that contained spermatids and spermatozoa. Those males were found to have significantly high GSI (gonadosomatic index; gonadal weight as a percentage of BW) levels, stLHβ expression and 11-KT levels.