Department of Animal and Poultry Sciences, Virginia Tech, Blacksburg, VA 24061.
Department of Animal Sciences, The Robert H. Smith Faculty of Agriculture, Food and Environment, The Hebrew University of Jerusalem, Rehovot 76100, Israel.
Poult Sci. 2021 Mar;100(3):100821. doi: 10.1016/j.psj.2020.11.004. Epub 2020 Nov 20.
The yolk sac (YS) consists of the yolk, which supplies nutrients, and the YS tissue, which surrounds the yolk and provides essential metabolic functions for the developing embryo. The YS tissue is derived from the midgut of the embryo and consists of a layer of endodermal epithelial cells (EEC) in contact with the yolk contents, a mesodermal layer that contains the vascular system and an outer ectodermal layer. The YS tissue is a multifunctional organ that provides essential functions such as host immunity, nutrient uptake, carbohydrate and lipid metabolism, and erythropoiesis. The YS tissue plays a role in immunity by the transport of maternal antibodies in the yolk to the embryonic circulation that feeds the developing embryo. In addition, the YS tissue expresses high mRNA levels of the host defense peptide, avian β-defensin 10 during mid embryogenesis. Owing to its origin, the YS EEC share some functional properties with intestinal epithelial cells such as expression of transporters for amino acids, peptides, monosaccharides, fatty acids, and minerals. The YS tissue stores glycogen and expresses enzymes for glycogen synthesis and breakdown and glucogenesis. This carbohydrate metabolism may play an important role in the hatching process. The mesodermal layer of the YS tissue is the site for erythropoiesis and provides erythrocytes before the maturation of the bone marrow. Other functions of the YS tissue involve synthesis of plasma proteins, lipid transport and cholesterol metabolism, and synthesis of thyroxine. Thus, the YS is an essential organ for the growth, development, and health of the developing embryo. This review will provide an overview of the studies that have investigated the functionalities of the YS tissue at the cellular and molecular levels with a focus on chickens.
卵黄囊（YS）由卵黄组成，为胚胎提供营养，由卵黄囊组织组成，卵黄囊组织围绕卵黄并为胚胎提供必要的代谢功能。卵黄囊组织来源于胚胎的中肠，由一层与卵黄内容物接触的内胚层上皮细胞（EEC）、包含血管系统的中胚层和外胚层组成。卵黄囊组织是一个多功能器官，提供了必要的功能，如宿主免疫、营养吸收、碳水化合物和脂质代谢以及红细胞生成。卵黄囊组织通过将卵黄中的母体抗体转运到胚胎循环中，为发育中的胚胎提供营养，从而在免疫中发挥作用。此外，在胚胎中期发育过程中，卵黄囊组织表达高水平的宿主防御肽鸡β-防御素 10 的 mRNA。由于其起源，卵黄囊 EEC 与肠道上皮细胞具有一些功能特性，例如表达氨基酸、肽、单糖、脂肪酸和矿物质的转运体。卵黄囊组织储存糖原，并表达用于糖原合成和分解以及糖异生的酶。这种碳水化合物代谢可能在孵化过程中发挥重要作用。卵黄囊组织的中胚层是红细胞生成的部位，并在骨髓成熟之前提供红细胞。卵黄囊组织的其他功能包括血浆蛋白合成、脂质转运和胆固醇代谢以及甲状腺素合成。因此，卵黄囊是胚胎生长、发育和健康所必需的器官。本综述将概述在细胞和分子水平上研究卵黄囊组织功能的研究，重点是鸡。
