Transcriptome Profiling of the Chicken Yolk Sac during Late Embryogenesis

The yolk sac (YS) is an extra-embryonic tissue that surrounds the yolk, which digests and transports nutrients during incubation of the avian embryo.  Understanding the function and development of the YS may lead to enhanced nutrient uptake and optimized embryo development.  The objective of this project was to perform a transcriptome analysis of the YS during late embryonic development on embryonic (e) days 13, 15, 17, 19, and 21. Functional annotation as well as histological analysis revealed that two main cell types of the YS were analyzed: epithelial cells and erythropoietic cells.  There was up regulation of genes involved in lipid transport and metabolism between e13 and e19.  Genes associated with cytoskeletal structure were down regulated between e17 and e21, supporting histological evidence of degradation of YS epithelial cells towards hatch.  Expression patterns of hemoglobin synthesis genes indicated a high erythropoietic capacity of the YS between e13 and e15.  The YS also produced high levels of genes coding for plasma carrier proteins normally produced by the liver.  Expression of the sodium glucose transporter and the anionic amino acid transporter increased from e13 to e19.  During the final week of chick embryonic development, the YS plays the role of several organs that have not yet reached their full functional capacity.  The YS is a multifunctional organ that acts as the intestine in digestion and transport of nutrients, the liver in production of plasma carrier proteins and the bone marrow in the synthesis of blood cells.