Transcriptome analysis across reproductive stages in peripheral blood of female brown bears: a pilot study.

Brown bears (Ursus arctos) mate in late spring to early summer, and their embryos enter diapause until winter. Embryonic diapause (i.e., delayed implantation) enables them to postpone parturition until suitable conditions are met. In this pilot study, whether gene expression levels vary across reproductive stages in female brown bears was tested. Peripheral blood samples were periodically collected from five captive female brown bears across reproductive stages, and their transcriptome profiles were determined. Results showed immune-related genes and pathways, including several nuclear factor kappa B-associated ones, may downregulate during late delayed implantation, although these immune system changes are unrelated to progesterone levels. Thus, we propose a possibility that the maternal immune system of brown bears fluctuates before implantation to maintain embryo survival. Further sampling effort will show the molecular mechanism of embryonic diapause in brown bears.