Transfer of egg white proteins and activation of proteases during the development of Anas platyrhynchos domestica embryo.

The route of egg white transfer into the yolk and the mechanisms underlying the digestion of egg proteins are unexplored in the fertilized egg of the duck, Anas platyrhynchos domestica. Here, we investigated the route(s) of egg white transfer and we determined the type of activated proteases during duck embryo development. Initially, we tested the electrophoretic patterns of egg proteins throughout development. Then, we used lysozyme as a reference protein to follow egg white transfer and we measured its activity. After that, we determined the type of activated proteases by employing different types of protease inhibitors. Several presumptive egg white protein bands appeared in different egg compartments. Also, lysozyme activity was detected chronologically on day 15 in the extraembryonic fluid, on day 17 in the amniotic and intestinal fluids and on day 19 in the yolk. Furthermore, acidic aspartic proteases seemed to be activated at hatch in the intestine and late in development in the yolk. Our results suggest that the main route of egg white transfer into the yolk is through the amniotic cavity and intestinal lumen. Also, the transferred egg white and endogenous yolk proteins are probably digested by the activated acidic proteases in the intestine and yolk.