Abstract
Schwann cells of the adult rat superior cervical ganglia (SCG) synthesize negligible levels of the major myelin glycoprotein, P~0~, in vivo. This suggests that the sympathetic axons of the SCG are deficient in one of more components involved in the regulation of myelin protein expression. Here we have compared the ability of neurites from neonatal rat SCG and embryonic rat dorsal root ganglia (DRG) to induce Schwann cell expression of myelin proteins after growth in culture using a serumโfree medium. Steadyโstate P~0~ mRNA levels in the SCG and DRG culture paradigms were determined with a sensitive polymerase chain reaction (PCR) assay that amplified cDNA produced by reverse transcription of mRNA. This semiquantitative assay showed a linear response to increasing amounts of P~0~ and actin mRNA and required substantially less cellular RNA than typical hybridization techniques. Using the PCR assay, we found that SCG cultures contained significantly lower amounts of P~0~ mRNA than did DRG cultures. To further confirm that SCG cultures have negligible expression of myelin proteins, immunoblot analyses were done to examine the steadyโstate levels of both P~0~ and myelin basic protein. While nonmyelinating DRG cultures had readily detectable amounts of these myelinโspecific proteins, neither could be demonstrated in the SCG cultures. The data indicate that SCG neurites lack one or more signals needed to induce myelin protein expression. Employing SCG and DRG cultures in comparative biochemical studies should prove useful in identifying the axonal molecule(s) involved in the regulation of myelin protein expression. ยฉ 1992 WileyโLiss, Inc.