Molecular characterization and quantification of the gonadotropin receptors FSH-R and LH-R from Atlantic cod (Gadus morhua).

In order to elucidate regulatory mechanisms during puberty final oocyte maturation and spawning, full-length sequences coding for the receptors for follicle-stimulating hormone (FSH-R) and luteinizing hormone (LH-R) were isolated from female Atlantic cod (Gadus morhua) by a RACE-PCR based strategy. The nucleotide and amino acid sequences showed high homologies with the corresponding sequences of other fish species but contained some distinct differences. Conserved features important for functionality, such as a long N-terminal extracellular domain (ECD), seven transmembrane domains and a short C-terminal intracellular domain, were identified in both predicted proteins. Partial genomic sequences for these genes were also determined, allowing the design of mRNA-specific quantitative PCR assays. Due to suspected alternative splicing during expression of these genes, additional real-time PCR assays detecting variants containing the membrane-anchoring domain were established. Besides the expected expression of FSH-R and LH-R mRNA in the gonads similarly strong signals for LH-R were also obtained in male gill, and in female and male brain. When relative expression was analysed at different stages of sexual maturation, levels for FSH-R increased moderately during gonadal growth whereas those of LH-R showed a high peak at spawning.