Embryonic cholesterol esterification is regulated by a cyclic AMP-dependent pathway in yolk sac membrane-derived endodermal epithelial cells

Genetic and epigenetic differentiation in response to genomic selection for avian lay date

Anthropogenic climate change has led to globally increasing temperatures at an unprecedented pace and, to persist, wild species have to adapt to their changing world. We, however, often fail to derive reliable predictions of species' adaptive potential. Genomic selection represents a powerful tool to investigate the adaptive potential of a species, but constitutes a 'blind process' with regard to the underlying genomic architecture of the relevant phenotypes. Here, we used great tit (Parus major) females from a genomic selection experiment for avian lay date to zoom into this blind process. We aimed to identify the genetic variants that responded to genomic selection and epigenetic variants that accompanied this response and, this way, might reflect heritable genetic variation at the epigenetic level. We applied whole genome bisulfite sequencing to blood samples of individual great tit females from the third generation of bidirectional genomic selection lines for early and late lay date. Genomic selection resulted in differences at both the genetic and epigenetic level. Genetic variants that showed signatures of selection were located within genes mostly linked to brain development and functioning, including LOC107203824 (SOX3-like). SOX3 is a transcription factor that is required for normal hypothalamo-pituitary axis development and functioning, an essential part of the reproductive axis. As for epigenetic differentiation, the early selection line showed hypomethylation relative to the late selection line. Sites with differential DNA methylation were located in genes important for various biological processes, including gonadal functioning (e.g., MSTN and PIK3CB). Overall, genomic selection for avian lay date provided insights into where within the genome the heritable genetic variation for lay date, on which selection can operate, resides and indicates that some of this variation might be reflected by epigenetic variants.

Centennial Review: The chicken yolk sac is a multifunctional organ

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.