[Results and Discussion] Five sea bass ST cDNAs potentially involved in the addition of sialic acid to Fsh were isolated and cloned. Previously we observed that Fsh bioactivity during male and female early development was higher in females. Assuming that less sialylated Fsh has higher bioactivity, we studied the pituitary expression of the STs in 300 days old juvenile males and females. We observed that, albeit with different intensities, the expression was always lower in females. Results of treated pituitary cells suggest that high doses of LHRHa and E2 stimulate the expression of ST3GAL4 and ST6GAL1 whereas it was inhibited by high doses of T. Pituitary expression analysis of ST3GAL4 and ST6GAL1 along the reproductive cycle showed that ST6GAL1 has maximum expression during vitellogenesis and maturation in females and late recrudescence in males. While, ST3GAL4 had low expression levels during vitellogenesis and maturation in females and high levels at spermation and spermiogenesis in males.

[Introduction] FSH is synthesized and secreted by the pituitary as differently glycosylated forms that differ in their oligosaccharide structure. In mammals the bioactivity of less sialylated FSH is higher than that of more sialylated counterparts and these FSH glycosylation variants have complementary and specific actions on the developing follicles. The endocrine milieu likely regulates the composition of FSH carbohydrate moiety and GnRH and sexual steroids have been proposed as the main regulators of FSH microheterogeneity. Several enzymes are involved in the post-translational FSH glycosylation processing; particularly the sialyltransferases (STs) that transfer sialic acid residues into the FSH carbohydrate chain. Our aim was to clone the ST genes of the European sea bass (Dicentraruchus labrax) and to and study their expression patterns in pituitary at different reproductive stages

[Methods] The amino acid sequences of the stickleback STs were used as queries in TBLASTN searches against the sea bass genome database. The complete coding sequences of ST3GAL3 (2 variants), ST3GAL4, ST6GAL1 and ST8SIA2 were amplified by PCR from sea bass brain and pituitary cDNA libraries, and then cloned in the pGEM-T Easy vector and sequenced. Primary cell culture of adult sea bass pituitaries was treated with two doses of LHRHa (10 and 100 mM), Estradiol (E2) and Testosterone (T) (50 and 1000 mM). Gene expression of STs was analysed by qPCR in these cultures and in pituitaries of juvenile and adult sea bass.

[Conclusion] In sea bass, Fsh bioactivity could be dependent on the content of sialic acid, likely regulated by the endocrine milieu, adapting the function of Fsh to the moment needs.

Comunicación presentada en el 10th International Symposium on Reproductive Physiology of Fish, celebrado en Olhao, Portugal, del 25 al 30 de mayo de 2014

Funded by MICINN (Aquagenomics, CSD2007-00002) and MINECO (AGL2011-28890).

Peer Reviewed