Eel Kisspeptins: Identification, Functional Activity, and Inhibition on both Pituitary LH and GnRH Receptor Expression

Abstract

The European eel (Anguilla anguilla) presents a blockade of sexual maturation at a prepubertal stage due to a deficient production of gonadotropins. We previously initiated, in the eel, the investigation of the kisspeptin system, one of the major gatekeepers of puberty in mammals, and we predicted the sequence of two Kiss genes. In the present study, we cloned and sequenced Kiss1 and Kiss2 cDNAs from the eel brain. The tissue distributions of Kiss1 and Kiss2 transcripts, as investigated by quantitative real-time PCR, showed that both genes are primarily expressed in the eel brain and pituitary. The two 10-residue long sequences characteristic of kisspeptin, eel Kp1(10) and Kp2(10), as well as two longer sequences, predicted as mature peptides, eel Kp1(15) and Kp2(12), were synthesized and functionally analyzed. Using rat Kiss1 receptor-transfected Chinese hamster ovary cells, we found that the four synthesized eel peptides were able to induce [Ca 2+ ]i responses, indicating their ability to bind mammalian KissR-1 and to activate second messenger pathways. In primary culture of eel pituitary cells, all four peptides were able to specifically and dose-dependently inhibit lhβ expression, without any effect on fshβ, confirming our previous data with heterologous kisspeptins. Furthermore, in this eel in vitro system, all four peptides inhibited the expression of the type 2 GnRH receptor (gnrh-r2). Our data revealed a dual inhibitory effect of homologous kisspeptins on both pituitary lhβ and gnrh-r2 expression in the European eel.

Age of European silver eels during a period of declining abundance in Norway

“…Once a specific size is reached, a period of high growth probably triggers silvering (Durif et al, 2005; Huang et al, 1998). Recent work in reproductive endocrinology has identified the kisspeptin system as essential for the onset of puberty in mammals but also in teleost fish (Pasquier et al, 2018; Seminara et al, 2003; Zohar, Munoz‐Cueto, Elizur, & Kah, 2010). In eels, kisspeptins regulate the expression of gonadotropins.…”

Tachykinin-3 Genes and Peptides Characterized in a Basal Teleost, the European Eel: Evolutionary Perspective and Pituitary Role

“…Predicted eel TAC3 peptides [NKBa (10 aa), NKB-RPa (13 aa), NKBb (10 aa), and NKB-RPb (13aa)] were synthesized as previously described ( 47 ) (Table 1 ).…”

“…Dispersion and primary culture of pituitary cells, using 30–40 female eel pituitaries per cell culture experiment, were performed as described in Ref. ( 49 ) and as recently used for the test of eel kisspeptins ( 47 ). Cultures were performed in serum-free culture medium [M199 with Earle’s salt, sodium bicarbonate, 100 U/ml penicillin, 100 µg/ml streptomycin, and 250 ng/ml fungizone (Gibco, Illkirch, France) at 18°C under 3% CO 2 and saturated humidity].…”

“…The effects of the treatments were tested on three independent experiments performed on cell cultures from different batches of fish and figures display the results of representative experiments. For human NKB, a range of concentrations from 10 −12 to 10 −6 M was tested according to previous in vitro studies with neuropeptides ( 47 , 50 ). For synthetized eel NKB and NKB-RP peptides, 10 −7 M was chosen as submaximal response could be observed with 10 −6 M human NKB.…”

Age of European silver eels during a period of declining abundance in Norway

“…Once a specific size is reached, a period of high growth probably triggers silvering (Durif et al, 2005;Huang et al, 1998). Recent work in reproductive endocrinology has identified the kisspeptin system as essential for the onset of puberty in mammals but also in teleost fish (Pasquier et al, 2018;Seminara et al, 2003;Zohar, Munoz-Cueto, Elizur, & Kah, 2010). In eels, kisspeptins regulate the expression of gonadotropins.…”