Transfer of egg white proteins with reference to lysozyme during the development ofMeleagris gallopavo(Galliformes: Phasianidae) embryos

Abstract

The egg white and egg yolk are the two main sources of nutrients for the developing avian embryo. The egg white should be transferred into the yolk in order to be consumed by the embryo. How the egg white ultimately reaches the egg yolk is largely unexplored in the turkey Meleagris gallopavo. Here, we explored the routes of egg white transfer in fertilized turkey eggs. Initially, we tested the electrophoretic pattern of the proteins in different egg compartments throughout development. Then, we used lysozyme as a reference protein to follow the egg white transfer, and we measured its activity using Micrococcus lysodeikticus as a substrate. We found that several presumptive egg white protein bands appeared in the different egg compartments. Also, the electrophoretic patterns in the intestinal fluid and thick yolk were marked by the disappearance of large bands and the appearance of small ones at late developmental stages. Moreover, we detected a chronological appearance of lysozyme activity in the different egg compartments. The activity appeared in the extraembryonic and amniotic fluids on day 15, in the intestinal fluid on day 16 and in the thick yolk on day 17, and it increased in general with the progress of development. Our results suggest that the main route of egg white transfer is albumen sac -extraembryonic cavity -amniotic cavity -intestinal lumen -egg yolk. Furthermore, the transferred egg white proteins seem to undergo digestion in the intestinal lumen and egg yolk at late developmental stages.

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

“…Although the reduction of the mRNA expression preceded that of the protein activity, a sufficient protein level was apparently present to maintain the enzymatic activity. We previously showed that three large electrophoretic protein bands disappeared while a small one appeared in the developmental period between days 24 and 26, which further supports the presence of proteolytic activity during this period (Shbailat & Safi 2015). Given that the amniotic fluid almost disappears from the intestinal lumen after day 26 (de Oliveira et al 2009;Shbailat & Safi 2015), it is possible that the egg white proteins and all their digested products are transferred from the intestinal lumen into the yolk together with all the secreted proteolytic enzymes.…”

“…to the obvious transfer of egg white proteins into the yolk (Shbailat & Safi 2015). Previously, we found that one small electrophoretic band (19.6 KDa) appeared at late developmental stages in the egg yolk, while a relatively large one (36.5 KDa) disappeared 1 day after hatching (Shbailat & Safi 2015). Therefore, we suggested the presence of proteolytic activity that caused the digestion of egg yolk proteins.…”

“…Levene's test of homogeneity of variances (P = 0.000), and one-way analysis of variance (ANOVA) test (F (29, 63) = 26.514; P = 0.000) showed that the variances and the means, respectively, were significantly different for different samples at different stages. to the obvious transfer of egg white proteins into the yolk (Shbailat & Safi 2015). Previously, we found that one small electrophoretic band (19.6 KDa) appeared at late developmental stages in the egg yolk, while a relatively large one (36.5 KDa) disappeared 1 day after hatching (Shbailat & Safi 2015).…”

“…In the turkey Meleagris gallopavo (Linnaeus, 1758), we found that although the direct transfer of egg white into the yolk seemed to occur early in development, even on day 0 before the embryo growth, the major transfer through the amnion and intestine of the embryo started on day 17 and became obvious on day 19 and thereafter (Shbailat & Safi 2015). However, it is completely unexplored when and what type of proteases are activated in the yolk in order to process the egg proteins before their transfer into the embryo.…”

“…The egg yolk consists of nearly 50% water, 33% fat, 15% protein, less than 1% carbohydrate, and the rest of various minerals and vitamins (Shenstone 1968;Vieira 2007). Egg white is ultimately transferred into the yolk before being consumed by the developing embryo (Saito et al 1965;Saito & Martin 1966;Baintner & Fehér 1974;Sugimoto et al 1978Sugimoto et al , 1984Sugimoto et al , 1989Sugimoto et al , 1999Burley & Vadehra 1989;Yoshizaki et al 2002Yoshizaki et al , 2004Ito et al 2003;Shbailat & Safi 2015). In chicken, the major transfer of egg white into the yolk through the amniotic sac and intestinal lumen of the embryo occurred after day 12 (McIndoe 1960;Saito et al 1965;Saito & Martin 1966;Carinci & Manzoli-Guidotti 1968;Baintner & Fehér 1974;Burley & Vadehra 1989;Sugimoto et al 1989).…”