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Role of axons in the regulation of P O biosynthesis by Schwann cells
Author(s) -
Brunden K. R.,
Windebank A. J.,
Poduslo J. F.
Publication year - 1990
Publication title -
journal of neuroscience research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.72
H-Index - 160
eISSN - 1097-4547
pISSN - 0360-4012
DOI - 10.1002/jnr.490260202
Subject(s) - basal lamina , schwann cell , biology , mannose , neurite , glycoprotein , microbiology and biotechnology , biosynthesis , myelin , neuron , cell culture , axon , chemically defined medium , biochemistry , in vitro , anatomy , neuroscience , central nervous system , enzyme , genetics , ultrastructure
The role of axons in the expression of the major myelin glycoprotein, P O , has been investigated using neuron/Schwann cell cultures. These cultures were either nonmyelinating or myelinating due to growth in defined medium or in medium containing serum and chick embryo extract, respectively. The neurons and Schwann cells used in the studies were derived from embryonic day 15 rat dorsal root ganglia (DRG), and the Schwann cells from these ganglia are shown not to synthesize appreciable levels of P o prior to growth in culture. Myelinating cultures of Schwann cells and neurons grown together for 18–21 days synthesize P o that is readily identified by immunoblotting. The nonmyelinating cultures, which do not assemble basal lamina, also synthesize P o that is detectable by either [ 3 H]mannose precursor incorporation or by immunoblotting. The steady‐state level of P o in the nonmyelinating cultures is less than that of the myelinating cultures, and the P o that is synthesized by the former appears to be catabolized shortly after its biosynthesis. Since nonmyelinating Schwann cells synthesize P o when in contact with neurites in vitro, we have examined the ability of such nonmyelinating cells to express the glycoprotein in vivo. Very little steady‐state P o is detected in immunoblots of the adult rat cervical sympathetic trunk (CST), a nerve in which approximately 99% of the axons are nonmyelinated. Similarly, the amounts of [ 3 H]mannose and [ 3 H]amino acids that are incorporated into newly synthesized P o are much lower in the CST than in the adult sciatic nerve. The Schwann cells of the CST are induced to synthesize myelin after growth in serum‐containing medium with embryonic DRG neurites that are devoid of endogenous Schwann cells due to prior treatment with an antimitotic agent. Immunoblot analysis of these cultures reveals a level of P o that is comparable to that of myelinating DRG Schwann cell/neuron cultures. These data indicate that DRG neurites supply a signal that can initiate the synthesis of P o in the absence of basal lamina and myelination. Furthermore, this signal may be reduced or altered in the CST.