Ontogeny of growth hormone protein and mRNA in the gilthead sea bream Sparus aurata

The ontogeny of growth hormone (GH) protein and mRNA was studied in the gilthead sea bream Sparus aurata by Northern blot, reverse transcription-polymerase chain reaction (RT-PCR) and Western blot analyses. Total RNA was prepared from a pool of larvae collected on different days after hatching, When hybridized to Sparus aurata GH cDNA, GH specific mRNA was first seen on day 3 post-hatching, Levels increased on subsequent days and reached the highest levels on day 9; thereafter a decrease was noted to similar levels between days 10 and 16. RT-PCR amplification of larval RNA showed an amplified fragment on day 3, which hybridized to Sparus aurata GH cDNA but not on days 1 and 2 after hatching. Soluble proteins were electrophoresed and immunoreacted with antibodies raised against purified Sparus GH. A faint band was detected on day 2 after hatching, which had an electrophoretic mobility very similar to recombinant tilapia GH or Sparus pituitary extract, The immunoreactive material increased on days 3, 4 and 6. Specificity of the immunoreaction was demonstrated by the ability of recombinant tilapia GH to compete with GH bound to the membrane and inability of normal rabbit serum (NRS) to detect GH on the membrane. Our results suggest that both GH mRNA and protein are expressed in Sparus aurata shortly after hatching.