Protease activity in the egg yolk during the development of Meleagris gallopavo (Galliformes: Phasianidae) embryos

Abstract

The egg white and egg yolk are the two main sources of nutrients for the developing avian embryo. Egg white ultimately reaches egg yolk before being consumed by the embryo. Previously, in the turkey Meleagris gallopavo, we showed that the major egg white transfer into the yolk through the amnion and intestinal lumen of the embryo started on day 17 and became obvious on day 19. We also suggested that the transferred egg white and endogenous yolk proteins undergo digestion at late developmental stages. However, the protease activity throughout development and the type of activated proteases are completely unexplored in the yolk of turkey eggs. Here, we measured the general proteolytic activity in the egg yolk during different developmental stages using casein as a substrate. Furthermore, we determined the type of activated proteases by employing different types of protease inhibitors. Protease activity in the egg yolk was basal throughout development until day 19 when activity significantly increased, remaining high thereafter. Moreover, acidic aspartic protease(s) were primarily activated in the yolk. Our results suggest that the transferred egg white and endogenous yolk proteins are mostly degraded by the aspartic proteases that become highly activated late in development.

Fate of egg proteins during the development of Columba livia domestica embryo

“…Taken together, our results propose that the transferred egg white and endogenous yolk proteins are mostly degraded by the activated proteases late in development. Our findings are similar to those from chicken (Sugimoto & Yamada, ) and turkey (Shbailat et al., ), which showed elevation of protease activity after the major transfer of egg white into the yolk. In contrast, protease activity was detected before the transfer of egg white proteins in quail (Yoshizaki et al., ).…”

“…In the chicken Gallus gallus and turkey Meleagris gallopavo , the major transfer of egg white proteins through the amniotic sac and intestinal lumen into the yolk started on day 14 and day 17, respectively (Carinci & Manzoli‐Guidotti, ; Shbailat & Safi, ). This transfer was followed by a rapid increase in the activity of proteases after day 14 in chicken (Sugimoto & Yamada, ), and on day 19 and thereafter in turkey (Shbailat et al., ). On the other hand, in the quail Coturnix japonica , the activation of protease between days 6 and 12 preceded the major transfer of egg white through the embryo into the yolk, which occurred after day 12 (Yoshizaki et al., , ).…”

Transfer of egg white proteins and activation of proteases during the development ofAnas platyrhynchos domesticaembryo

“…Our results are similar to those obtained in turkey which showed the presence of high aspartic protease activity during the last stages of development in the egg yolk [21]. In contrast, neutral and serine proteases were activated late in development in the chicken egg yolk [27].…”

“…This increase was shortly after the major transfer of egg white through the amniotic cavity and intestinal lumen into the yolk which started on day 14 [5]. In turkey, the activity of acidic aspartic proteases in the egg yolk was high on incubation day 19 and afterwards [21], following the major transfer of egg white which began on day 17 [22]. On the other hand, in quail egg yolk, the activity of the acidic aspartic protease cathepsin D was high in the period between days 6 and 12 before the major transfer of egg white through the embryo into the yolk that occurred after day 12 [32,33].…”

“…The egg shell is deposited around the egg shell membranes seba Jamal shbailat and Razan ataallah abuassaf Acta Biologica Hungarica 69, 2018incubated at 37 °C for 24 hr before loading in the gel[21,32]. To test for the inhibition of protease activity, the intestinal fluid and egg yolk samples (60 μg each) were diluted (1:1) with 0.1 M citric acid-0.2 M dibasic sodium phosphate buffer (pH 3) mixed with a protease inhibitor at a final concentration of 0.4 mg/mL[21,32]. The mixture was incubated at 37 °C for 24 h before loading in the gel.…”