Repulsive Effects Of FGF3 On The Inhibitory GABAergic Axons In The Prethalamus

Objective To study the guidance effects of fibroblast growth factor 3(FGF3)on the GABAergic inhibitory axons in the prethalamus,and explore the effect of FGF3 on the formation of thalamic axonal network.Methods Expression and localization of FGF3 and GABAergic marker gene PV in chicken embryonic diencephalon were detected by immunofluorescence.Early orientation of GABAergic axons was tracked by Di I.Three-dimensional gel co-culture experiment was carried out to investigate guidance effects of FGF3 on early prethalamic GABAergic axons.Electroporation of FGF3-RNAi vectors further confirmed the correct targeting function of FGF3 to early prethalamic GABAergic axons.Results Prethalamic GABAergic cells are adjacent to the FGF3+ hypothalamas,located above the hypothalamus.Di I tracing experiments reveal that GABAergic inhibitory axons have already extended into the thalamus at E6.Compared with the blank control group,FGF3 not only significantly promoted the growth of GABAergic nerve fibers in the prethalamus,but also repelled the newborn prothalamic axons to the dorsal thalamus(P<0.0001).The number of prethalamic axons is significantly less in proximal section(towards FGF3 beads)than in distal section(away from FGF3 beads)(P<0.0001).Moreover,the guidance effects of FGF3 on prethalamic axons can be blocked by the FGF pathway inhibitor SU5402.Electroporation inhibited the expression of FGF3 in the developing hypothalamus,resulting in disordered axonal growth of GABAergic axons.Conclusions FGF3 expressed in hypothalamus can function as a chemical directing molecule to guide the pathway selection of GABAergic nerve fibers in the adjacent prethalamus.