Pax3 RNA is expressed in neural crest when Schwann cell (SC) precursor
s migrate to the PNS. Pax3 RNA and SC markers were monitored in sciati
c nerves of mice during development and nerve repair. An inverse corre
lation was observed between expression of Pax3 RNA and myelin basic pr
otein (MBP). Inverse correlation was also observed in SC primary cultu
res. Treating cultures with forskolin, an adenylate cyclase agonist, r
epressed Pax3 RNA, GFAP, NGFR, N-CAM, and L1 and elevated MBP. Subsequ
ent microinjection with Pax3 expression vector elevated Pax3 RNA, GFAP
, NGFR, N-CAM, and L1 and repressed MBP. Thus, Pax3 is likely involved
in the differentiation pathway to myelinating SCs. Pax3 repressed a 1
.3 kb MBP promoter fragment in cotransfection assays, suggesting that
it represses MBP transcription.