Transcriptional regulation of albumen biosynthesis in the magnum of broiler breeder hens
Broiler chicken production is crucial to meet the increasing global food demand. Hyperphagic and obese broiler breeder hens have a short production cycle, which is challenged by age-associated egg quality and fertility decline, affecting hatchability. A fertilized egg is a comprehensive set of essential elements to nurture and develop a healthy chick. Egg albumin occupies most of the egg content, which is synthesized and secreted by the magnum. The genetic regulation of albumin biosynthesis in broiler breeder hens and its alteration with age might reveal the genetic marker that will produce quality eggs in subsequent generations. Hence, the objective of the study is to determine the differentially expressed genes (DEGs) and pathways involved in albumin biosynthesis in the magnum (young vs aged). The magnum tissues were collected from the broiler breeder hens at peak production, identified as the young group (35 weeks, N=30), and from the declined production, recognized as the aged group (50 weeks, N=30). Five samples from each group (n=5) were used for RNA sequencing and analyzed to get DEGs and associated pathways. The significantly upregulated genes with a putative function in quality egg formation were confirmed using qPCR. Seventy-five up-regulated and 52 down-regulated genes were determined. The top 20 most upregulated genes and top 20 most downregulated genes, based on their putative function, were categorized into five groups: egg white synthesizing (AMDHD1, FER, CTNNA3), molecular communication (VAPA), oviduct tissue regeneration (ADAM19, CFAP100, AMD1, TM4SF19, SLC39A13, VMO1), and defense (ZBTB46, STAM2, OVoDA3). “Post-translational protein phosphorylation” was the most significantly enriched Reactome pathway involving DNAJC3, PPP3CA, TF, SPARCL1, PDIA6, SGPP2, HSP90B1, and PNPLA2 genes.  The study successfully identified DEGs, genetic networks, and pathways that can be used as genetic markers to select quality egg producing broiler breeder hens. Overall design: RNA sequencing of the broiler breeder magnum to compare between peak (35 weeks) and declining (50 weeks) production to see the traanscriptomic variation of the magnum.