Rapid communication: MicroRNA co-expression network reveals apoptosis in the reproductive tract during molting in laying hens

The aim of this study was to determine the regulatory mechanisms of molting and recrudescence via studying the micro-RNA (miRNA) expression in the oviduct of laying hens. We performed a cDNA microarray analysis in the magnum tissue from the oviduct to identify the whole miRNA profiles through the molting and recrudescence periods. A total of 35 laying hens (47-wk-old) were divided into 7 groups (0 d: a control group; 6 and 12 d: 2 molting-period groups fed on a high-zinc diet; and 20, 25, 30, and 35 d: 4 recrudes-cence-period groups fed on a normal diet after a 12-d period on a high-zinc diet). An miRNA co-expression network (miRCN) was generated using the differen- tially expressed miRNA (DEM) according to the entire data integration. The significantly co-expressed miR-NA (n = 111) were highly differentially expressed from 12 to 20 d, which was a transition period between molting and recrudescence, while their expression patterns were contrary to the estrogen changes. The targets of highly connected miRNA (n = 12) indicated the significant biological pathways and gene ontology (GO) terms, such as MAPK and Wnt signaling and magne-sium-ion binding, which are associated with apoptotic activities. These results suggest that the miRNA of the miRCN might play a role in the apoptotic progression of the reproductive tract during molting.