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An avian egg is composed of an egg shell, the yolk and albumen or egg-white. The albumen contains 88.5% water and about 10.5% proteins and may be regarded as the main protein source for the developing embryo. Hill (1993) proposed that albumen removal can be used as a unique avian model to investigate the direct effect of reduced protein availability during embryogenesis on growth and development. In the present research, albumen was replaced by saline in fertile eggs from layer-type chickens to maintain the embryonic water levels and only decrease embryonic protein availability (albumen-deprived group). Results were compared to a mock-treated sham group and a non-treated control group. The present research was used to investigate the importance of albumen during embryonic development in birds. Furthermore, it was examined if our chicken model can be used as a model for prenatal protein undernutrition by comparison with mammalian models. In these mammalian models, the maternal diet is manipulated (i.e. low protein diet) leading to nutritional as well as maternal effects on the offspring, whereas in the chicken model only nutritional effects are applied. Although chick weight at hatch was not significantly reduced, the body weight of the laying hens was reduced until adulthood when reared in floor pens. When transferred to battery cages at the onset of laying, with limited possibility for exercise, the albumen-deprived hens exhibited catch-up growth and increased body weight, compared to the control and the sham hens. Irrespective of posthatch conditions, the reproductive performance of the albumen-deprived hens was seriously diminished as both the laying rate and egg weight were reduced. In addition, the quality of the eggs was inferior as demonstrated by the increased number of second-grade eggs. The eggs from the albumen-deprived hens had increased proportional yolk and decreased proportional albumen content. At 10 weeks of age, a decreased glucose tolerance was observed, indicating a decreased insulin production or insulin resistance. These differences however disappeared with age due to age-related loss of glucose-tolerance in all of the hens. The chick weight of the offspring was reduced as expected based on the reduced egg weight, but in addition the relative chick to egg weight was also reduced, perhaps as a consequence of the differences in egg composition. To gain insight into the programming of these physiological and zootechnical effects, molecular techniques were employed. Firstly, a screening for differential proteins in the liver of newly-hatched chicks using Two-Dimensional Difference Gel Electrophoresis (2-D DIGE) revealed not only changed abundance of proteins important for amino acid metabolism as expected, but also of enzymes related to energy and glucose metabolism. Interestingly, GLUT1, a glucose transporter, and phosphoenolpyruvate carboxykinase 2 (PCK2) and fructose-1,6-bisphosphatase 1 (FBP1), two out of three regulatory enzymes of the gluconeogenesis were dysregulated in the albumen-deprived chicks. No parallel differences in gene expressions causing the differences in protein abundance could be detected pointing to post-transcriptional or post-translational regulation of the observed differences. A candidate gene approach examining the gene expression of peroxisome proliferator-activated receptor alfa and gamma (PPARalfa and PPARgamma), glycogen synthase 2 (GYS2), glycogen phosphorylase 1 (PYGL1) and glucocorticoid receptor (NR3C1) revealed no differences in gene expression. A genome-wide screening for differences in gene expression was performed in the liver of adult hens using RNA-Sequencing (RNA-Seq). Grouping of the differentially expressed (DE) genes according to biological function revealed the involvement of embryonic and organismal development, organ morphology, organ and tissue development, reproductive system development and function, corresponding well with the observed phenotypic differences. Molecular pathways that were altered were amino acid metabolism; molecular transport, small molecule biochemistry, cell death and survival, cell-to-cell signaling and interaction, carbohydrate metabolism and protein synthesis. Involvement of amino acid and carbohydrate metabolism was previously observed in the 2-D DIGE results. Three central genes in some of these pathways interacting with many DE genes were ubiquitin C (UBC), glucocorticoid receptor (NR3C1), and Embryonic lethal, abnormal Vision, Drosophila-like 1 (ELAVL1). DNA methylation of 9 DE genes and 3 key central genes was examined by Methylated DNA Immunoprecipitation followed by qPCR (MeDIP-qPCR). The DNA methylation of one fragment located around the transcription start site of the UBC gene was increased in the albumen-deprived hens compared to the control hens.In conclusion, it has been demonstrated that embryonic albumen removal leads to both long-term effects on body weight and reproductive performance as well as transgenerational effects on body weight and that these effects could not be overcome by adequate posthatch management conditions. Comparison of the strictly nutritional chicken model to mammalian models (manipulating the diet of the mothers) of prenatal protein undernutrition reveals both similar and distinct results. To examine whether the latter might be due to absence of the maternal effects, comparison with a chicken model of low-protein diet is required.

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