GSK3β expression and phosphorylation during neuronal maturation in the rat dorsal root ganglion.

Glycogen synthase kinase 3β (GSK-3β) protein is a key regulator of neurogenesis, neuronal differentiation and polarisation during neurodevelopment. Sensory neurons in dorsal root ganglion (DRG) undergo a series of development stages during its maturation. In this study, we investigated the dynamic changes in GSK-3β expression and phosphorylation of its N-terminal serine-9 residue (p-GSK-3β (S9)) during DRG development. Sprague-Dawley (SD) rats were divided according to the following ages: Embryonic 13(th) (E13), E15, E19, Postnatal 1(st) (P1), P3, P7, P14, P21 and P60 days. GSK-3β was detected by immunohistochemistry and double immunofluorescence on DRGs. Western blotting was used to determine the quantity of GSK-3β and p-GSK-3β (S9) expression. It was found that GSK-3β immunopositive cells in the DRG appeared as early as E13 development phase, and gradually increased to a peak level at P3, at which almost all neurons were GSK-3β positive, and then stayed at a high level to the experiment day 60. GSK3β expression was cell-type-specific during DRG maturation and exhibited cytoplasmic staining in the neuronal cell body and the axon. Glial cells consistently remained negative in DRGs at all stages. Western blot analysis revealed that GSK3β expression stayed the same during DRG maturation. In contrast, p-GSK-3β (S9) expression was stage-specific and decreased from E13 to P60 (P < 0.01). Taken together, these results suggest that GSK-3β expression is stage-specific and cell-type-specific during DRG maturation.