Abstract:
Myelin is a key component of the nervous system where it discontinuously insulates axons and increases the speed of action potential propagation. The absence or insufficiency of myelin sheathing causes hereditary neuropathies. For the initiation and maintenance of myelin sheathing, axon – Schwann cell contact seems to be essential and growth factor-mediated signaling has been proposed to mediate intercellular communication. Nerve regeneration paradigms and in vitro models point to the importance of FGFs and neurotrophins in myelination. However, their roles in the initiation and progression of myelination in vivo are not yet clear. Therefore, we studied expression of FGF1, FGF2, FGF9, FGFR1-4, and BDNF in adult and postnatal DRG during the period of active myelination. Our results show a gradual increase in FGF1 and FGF2 transcripts during early myelination, there after no modulations were evident. In contrast, FGF9 transcript levels increased until P10, then gradually decreased to basal levels in adulthood. FGF1 protein was first observed on P4, its levels increased for 10 days, then gradually decreased to basal levels in adults. Transcript levels of FGFR1 increased until P10 and then stabilized while FGFR2 transcript was present at all time points with no significant change. FGFR3 and BDNF transcript levels were unchanged during active myelination period, followed by a significant decrease. FGFR4 transcript levels were barely detectable. The observed profiles suggest that FGF1 and FGF2 might be important for both the formation and maintenance, while BDNF and FGF9 might be implicated primarily in the formation of the myelin sheath.
