RNA sequencing-based analysis of the laying hen uterus revealed the novel genes and biological pathways involved in the eggshell biomineralization.

Eggshell is the outermost calcified covering of an egg that protects it from microbial invasion and physical damage, and is critical for egg quality. However, understanding of the genes/proteins and the biological pathways regulating the eggshell formation is still obscure. We hypothesized that the transcriptomic analysis of the chicken uteri using RNA-sequencing may reveal novel genes and biological pathways involved in the eggshell biomineralization. RNA-sequence analysis using uteri of laying hens at 15-20 h post-ovulation (layers, n = 3) and non-laying (non-layers, n = 3) hens was carried out. About 229 differentially expressed genes (DEGs) were up-regulated in the layers compared to the non-layers. Kyoto Encyclopedia of Genes and Genomes (KEGG) and Ingenuity Pathway Analysis (IPA) revealed more than ten novel genes and biological pathways related to calcium transport and mineralization in the uterus. Based on the enriched pathways and molecular function analysis, 12 DEGs related to eggshell mineralization were further analyzed in the uteri of layers (3 h and 15-20 h post-ovulation), non-layers and molters using qPCR. Expressions of OC-116 (regulator of mineralization), OTOP2 (modulator of cellular calcium influx), CALCB (intracellular release of Ca-ions), STC2 (increases alkaline phosphatase activity), and ATP2C2 (cellular import of Ca-ions) were significantly higher in the uteri of laying hen at 15-20 h post-ovulation. This study identified the involvement of novel genes and their proposed biological pathways in the regulation of eggshell formation.