Expression of immune-related genes in one phase of embryonic development of freshwater crayfish, Pacifastacus leniusculus

Crayfish do not have larval stage as other crustacean such as penaeid shrimp they spawn their eggs until hatching and what hatches out from the eggs are miniature crayfish known as juveniles. In order to address the question whether immune genes are initially expressed during the embryo development in the egg stage, the expression of some immune-related genes: prophenoloxidase (proPO), peroxinectin, hemocyanin, anti-lipopolysaccharide factor (ALF), plcrustin, astakine-1, 2 and transglutaminase (TGase) were determined in the middle phase of crayfish embryo development. Furthermore, immune challenge was used to determine the immune response of eggs by immersing them in a solution of the highly pathogenic bacterium Aeromonas hydrophila. Semi-quantitative RT-PCR analysis showed that all tested genes are present except proPO in this phase of crayfish embryo development and none of the genes tested changed their expression following immersion in A. hydrophila. The proPO transcript has been reported from hemocytes in crustaceans and it plays crucial roles in crustacean immune response. This may indicate that the development of immune-competent hemocytes in this stage of crayfish embryo is not completed and the egg shell as such plays an important role as a shield in protecting the embryo from bacteria and maybe also other pathogens.