Marina
Morini, David S. Peñaranda, M. Carmen Vílchez, Helge Tveiten, Anne-Gaelle
Lafont, Sylvie Dufour, Luz Pérez, Juan F. Asturiano
Abstract
Estradiol (E2)
can bind to nuclear estrogen receptors (ESR) or membrane estrogen receptors
(GPER). While mammals possess two nuclear ESRs and one membrane GPER, the
European eel, like most other teleosts, has three nuclear ESRs and two membrane
GPERs, as the result of a teleost specific genome duplication. In the current
study, the expression of the three nuclear ESRs (ESR1, ESR2a and ESR2b) and the
two membrane GPERs (GPERa and GPERb) in the brain-pituitary-gonad (BPG) axis of
the European eel was measured, throughout spermatogenesis.
The eels were
first transferred from freshwater (FW) to seawater (SW), inducing parallel
increases in E2 plasma levels and the expression of ESRs. This indicates that
salinity has a stimulatory effect on the E2 signalling pathway along the BPG
axis.
Stimulation of
sexual maturation by weekly injections of human chorionic gonadotropin (hCG)
induced a progressive decrease in E2 plasma levels, and different patterns of
expression of ESRs and GPERs in the BPG axis. The expression of nuclear ESRs
increased in some parts of the brain, suggesting a possible upregulation due to
a local production of E2. In the testis, the highest expression levels of the
nuclear ESRs were observed at the beginning of spermatogenesis, possibly
mediating the role of E2 as spermatogonia renewal factor, followed by a sharply
decrease in the expression of ESRs. Conversely, there was a marked increase
observed in the expression of both membrane GPERs throughout spermatogenesis,
suggesting they play a major role in the final stages of spermatogenesis.
