Shibata Mitsuhiro, Iwasawa Atsushi, Yayota Masato
The United Graduate School of Agricultural Science, Gifu University, Gifu 501-1193, Japan.
Faculty of Applied Biological Sciences, Gifu University, Gifu 501-1193, Japan.
J Poult Sci. 2023 Aug 9;60(2):2023020. doi: 10.2141/jpsa.2023020. eCollection 2023.
Yolk sac membranes of layer eggs were collected daily (n = 7-9) from day three of incubation to day three post-hatch, and mRNA expression and activities were quantified for key gluconeogenesis enzymes (glucose-6-phosphatase, fructose-1,6-bisphosphatase, cytosolic and mitochondrial phosphoenolpyruvate carboxykinases, and pyruvate carboxylase). Lactate, triglycerides, non-esterified fatty acids, glycogen, and glucose in the yolk sac membrane, and blood glucose levels were also measured. The mRNA expression and activity were detected for all enzymes. Differences in expression levels and enzyme activities seemed to reflect the embryo's developmental environment and physiological demands at different developmental stages. During the first week to the mid-second week of incubation, the expression and activity of gluconeogenic enzymes and lactate concentrations were high, suggesting an active period of gluconeogenesis from lactate, reflecting possible hypoxia in the embryo before completed formation of the chorioallantoic capillaries. From the mid-second week to mid-third week, when embryos were in an aerobic state, the triglyceride and non-esterified fatty acid contents increased in the yolk sac. Triglycerides from yolk lipids are typically hydrolyzed to produce non-esterified fatty acids as an energy source, whereas the glycerol skeleton is used for gluconeogenesis. In the late third week, when embryos were considered to re-enter an anaerobic state, the mRNA expression and enzyme activity of only glucose-6-phosphatase were high and the amount of glycogen in the yolk sac was reduced. Therefore, it is suggested that gluconeogenesis activity is low during this period, and the carbohydrates stored in the yolk sac membrane are secreted into the blood as energy for hatching. This study confirmed the role of the yolk sac membrane as a vital gluconeogenic organ during chicken egg incubation.
从孵化第3天到孵化后第3天，每天收集蛋鸡的卵黄囊膜（n = 7 - 9），对关键糖异生酶（葡萄糖-6-磷酸酶、果糖-1,6-二磷酸酶、胞质和线粒体磷酸烯醇式丙酮酸羧激酶以及丙酮酸羧化酶）的mRNA表达和活性进行定量分析。同时测定卵黄囊膜中的乳酸、甘油三酯、非酯化脂肪酸、糖原和葡萄糖以及血糖水平。检测到所有酶的mRNA表达和活性。表达水平和酶活性的差异似乎反映了胚胎在不同发育阶段的发育环境和生理需求。在孵化的第一周中期到第二周中期，糖异生酶的表达和活性以及乳酸浓度较高，表明乳酸糖异生处于活跃期，这反映了在尿囊绒毛膜毛细血管完全形成之前胚胎可能存在缺氧情况。从第二周中期到第三周中期，胚胎处于需氧状态时，卵黄囊中甘油三酯和非酯化脂肪酸含量增加。卵黄脂质中的甘油三酯通常被水解以产生非酯化脂肪酸作为能量来源，而甘油骨架则用于糖异生。在第三周后期，当胚胎被认为重新进入厌氧状态时，只有葡萄糖-6-磷酸酶的mRNA表达和酶活性较高，卵黄囊中糖原含量减少。因此，提示在此期间糖异生活性较低，卵黄囊膜中储存的碳水化合物作为孵化能量分泌到血液中。本研究证实了卵黄囊膜在鸡蛋孵化过程中作为重要糖异生器官的作用。
