Developmental ontogeny of prolactin and prolactin receptor in the sea bream (Sparus aurata).

The expression of PRL and its receptor (PRLR) were characterised during sea bream embryonic and larval development, by semi-quantitative and quantitative RT-PCR, respectively, until 46 days post-hatch (DPH). Immunocytochemistry with antisera specific for sea bream PRLR was carried out with larval sections from hatching up to 46 DPH. A single transcript of PRL (1.35 Kb) and PRLR (2.8 Kb) identical to the transcripts previously characterised in adult tissue, are present in sea bream embryos and larvae. PRL expression is first detectable at neurula and in all samples collected thereafter. The lowest levels of PRL mRNA are detected in sea bream embryos up until neurula when expression starts to increase. The maximal levels of PRL expression were detected at 24 DPH. PRLR transcripts first appear at 12h post-fertilisation (0.002 rho mol/microg total larvae RNA) (blastula) and increase significantly during gastrulation (0.245 rho mol/microg total larvae RNA) reaching a maximum at 2 DPH (0.281 rho mol/microg total larvae RNA). After hatching a significant reduction in PRLR expression is observed which reaches a minimum at 4 DPH (0.103 rho mol/microg total larvae RNA), gradually increasing thereafter. Immunocytochemistry revealed the presence of PRLR in early post-hatching stages of larvae in tissues derived from all three germ layers.