Absorption, transportation and digestion of egg white in quail embryos

Abstract

The present study was done to reveal how egg white is taken up by embryonic tissues, the pathway through which egg white is transported, and the location where it is digested during the development of the quail Coturnix japonica. Antiserum against quail ovalbumin was raised in rabbit and used as a probe. By immunoelectron microscopy, the uptake of ovalbumin on a small scale by receptor-mediated endocytosis was observed in the ectodermal cells of the yolk sac on days four to seven of incubation. The uptake of egg white on a large scale by fluid-phase endocytosis took place in the cells generally referred to collectively as the 'albumen sac'. The ovalbumin was transported through the albumen sac into the extraembryonic cavity during days eight to 10, and then into the amniotic cavity through the amnion approximately on day 10. Ovalbumin was present in the intestinal lumen on days 11 and 14, but it was not digested in the intestinal epithelial cells. The ovalbumin was detected in the yolk of embryos after day 10. Immunoblot testing, as well as a fluoroimmunoassay, revealed that the location where the amount of ovalbumin was highest changed chronologically from the extraembryonic cavity on day 10 to the amniotic cavity on day 11, the intestinal lumen on day 12 and then to the yolk on day 13. Several low molecular proteins which cross-reacted with the antiserum were observed in the extracts of the yolk. The reaction producing these proteins depended on low pH (approximately 3.0) and was inhibited by pepstatin A. The ovotransferrin was similarly digested. These results indicate that egg white is, for the most part, transported through the albumen sac to the yolk via the extraembryonic cavity, the amniotic cavity, and the intestinal lumen, and is digested in the yolk by aspartic proteinases.

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

“…The two yolk portions (thin and thick) were diluted with five volumes of 0.87% sodium chloride (NaCl) solution containing 1 mM ethylenediaminetetraacetic acid-disodium salt, dihydrate (EDTA-Na 2 ; Yoshizaki et al 2002). The diluted samples were then homogenised using a tissue homogeniser (Omni International, Kennesaw, Georgia, USA), and the homogenate was centrifuged at 6000 rpm for 30 min at 4°C.…”

“…Egg yolk samples (60 µg) were diluted (1:1) with 0.1 M citric acid-0.2 M dibasic sodium phosphate buffer at different pH (pH 3-7), and then incubated at 37°C for 24 hr (Yoshizaki et al 2002). After that, the mixture was subjected to sodium dodecyl sulfatepolyacrylamide gel electrophoresis (SDS-PAGE) according to the protocol in Laemmli (1970), with slight modifications using 10% separation gels.…”

“…After that, the mixture was subjected to sodium dodecyl sulfatepolyacrylamide gel electrophoresis (SDS-PAGE) according to the protocol in Laemmli (1970), with slight modifications using 10% separation gels. To test for the inhibition of protease activity, the yolk samples (60 µg) were diluted (1:1) with 0.1 M citric acid-0.2 M dibasic sodium phosphate buffer (pH 3.5) with a protease inhibitor at a final concentration of 0.4 mg/mL following the procedure in Yoshizaki et al (2002) with some modifications. The mixture was incubated at 37°C for 24 hr before loading in the gel.…”

“…In contrast, in quail, the activation of acidic proteases preceded the major transfer of egg white into the yolk, which occurred after day 12 (Yoshizaki et al 2002(Yoshizaki et al , 2004Ito et al 2003). The activated proteases appeared to digest the egg white and yolk proteins before their transfer into the growing embryo (Sugimoto & Yamada 1986;Yoshizaki et al 2002Yoshizaki et al , 2004.…”

“…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).…”