Transcriptome analysis revealed potential mechanisms of differences in physiological stress responses between caged male and female magpies.

BACKGROUND: Under caged conditions, birds are affected more severely by environmental stressors such as dietary structure, activity space, human disturbances, and pathogens, which may be reflected in the gene expression in peripheral blood or other tissues. Elucidating the molecular mechanism of these stress responses will help improve animal welfare.

RESULTS: In the present study, the blood transcriptomes of six male and five female caged magpies (Pica pica) were sequenced, and a total of ~ 100 Gb in clean reads were generated using the Illumina HiSeq 2000 sequencer. A total of 420,291 unigenes were identified after assembly, of which 179,316 were annotated in five databases, 7471 were assigned to 269 Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways, and 566 were assigned to the Clusters of Orthologous Groups (COG) functional classification "defense mechanisms". Analysis of differentially expressed genes (DEGs) showed that 2657 unigenes were differentially expressed between males and females (q < 0.1), and these DEGs were assigned to 45 KEGG pathways involving stress resistance, immunity, energy metabolism, reproduction, lifespan regulation, and diseases. Further analysis revealed that females might be more sensitive to stress through upregulation of c-Jun N-terminal kinases (JNKs) and 5'AMP-activated protein kinase (AMPK), and were also possibly more sensitive to dynamic changes in energy. Females expressed higher major histocompatibility complex (MHC) class II levels than males, enhancing resistance to pathogens, and the DEGs related to reproduction included MAPK, CaMK, CPEB, and Cdc25. The genes related to stress, energy, and immunity were also likely related to the regulation of longevity. The upregulated JNKs in females might prolong lifespan and relieve antioxidant stress. Females may also activate the AMPK pathway and implement dietary restrictions to prolong lifespan, whereas males may upregulate SIRT1 and CRAB to increase lifespan.

CONCLUSIONS: Female magpies might be more sensitive to stress and dynamic changes in energy thus enhanced resistance to pathogens, and the genes related to stress, energy, and immunity were also possibly related to the regulation of longevity. Further confirmations with techniques such as RT-qPCR and western blot are necessary to validate the above arguments.