Changes of gonadal CB1 cannabinoid receptor mRNA in the gilthead seabream, Sparus aurata, during sex reversal

Two cannabinoid receptor-like genes (CB1-Iike), named CB1A and CB1B, have been isolated in teleost fish, specifically in the puffer fish, Fugu rubripes. However, information on the physiological roles, such as the control of reproduction and development in fish is still scarce. Therefore, the aim of the present study was to investigate the presence of CBI-like mRNA in the gonads of a marine teleost species, the gilthead seabream, Sparus aurata, a hermaphrodite species in which the gonadal tissues first develop as testes, and then as functional ovary. We isolated an 890 bp fragment (GenBank accession number EF051620); that corresponded to the open reading frame of the teleost CBI receptor gene, encoding for the central portion of the protein, which was aligned with the other bony fish sequence. Using in situ hybridization, CBI-Iike mRNA was localized in both mature and sex-reversing gonads, and relative changes in CBI-like expression levels were detected through semi-quantitative RT-PCR. In the mature testis and in the testicular part of the sex-reversing gonad, CBI expression levels were found to be much higher compared to the ovarian portion. This suggests that the CB1 signaling is likely involved in the process of testicular regression of the S. aurata, but its actual role has yet to be determined. (c) 2006 Elsevier Inc. All rights reserved.