Expression of glycogenic genes in the oviduct of Chinese brown frog (Rana dybowskii) during pre-brumation.

The oviduct of Chinese brown frog (Rana dybowskii) displays seasonal morphological and functional changes, which expands specifically during pre-brumation. To uncover the molecular mechanism underlying this phenomenon, we firstly confirmed the increased weight and enlarged diameter of the oviduct in pre-brumation by morphological observation. Interestingly, the glycogen content in the oviduct increased significantly during pre-brumation, indicating Rana dybowskii stores energy in the oviduct before brumation. Transcriptome analysis further identified the differentially expressed genes in the synthesis and metabolism pathways of carbohydrates in the oviduct during pre-brumation. Based on that evidence, we focused on the mRNA and protein expression of glycogenic genes in the oviduct of Rana dybowskii. qPCR confirmed that the expression of glycolysis and glycogenesis-related genes were up-regulated while gluconeogenesis-related genes were down-regulated during pre-brumation. Western blot data showed that glucose transporter GLUT1 and glycogen synthesis-regulation proteins including GYS, and p-GSK-3ß were highly expressed in the oviduct during pre-brumation. Moreover, immunohistochemical data showed that GLUT1, GYS, p-GYS, GSK-3ß and p-GSK-3ß were expressed regionally in the oviduct of Rana dybowskii. The data suggests that glycogen synthesis may be involved in the oviductal expansion of Rana dybowskii during the pre-brumation.