Résumé
The work presented here reports the expression of immune-related genes during ontogenesis in the oyster
Crassostrea gigas. Expression patterns of 18 selected genes showed that RNAs detected in oocytes and 2–4 cell embryos are of maternal origin and that gene transcription starts early after fertilization. The expression patterns of 4 genes (
Cg-timp,
Cg-tal,
Cg-EcSOD and
Drac3) suggested that hemocytes appear in the gastrula-trochophore stages. The localization of
Cg-tal expression suggested that hematopoietic cells were derived from vessels and/or artery endothelia cells. Moreover, a bacterial challenge affected the level of expression of genes. Indeed, a change in expression levels was observed for
Cg-LBP/BPI,
Cg-timp,
Drac3 and
Cg-MyD88 genes in larval stages upon exposure to non-pathogenic bacteria. In early juveniles, a modulation was also observed for
Cg-LBP/BPI,
Cg-timp,
Cg-MyD88 and for
Cg-tal, according to the concentration of bacteria. Altogether, the results showed that studying the appearance of immunocompetent cells through their ability to express immune-related genes is a tool to gain insight the ontogenesis of the oyster immune system.