Title

The effects of the shiverer mutation on myelin gene expression in the PNS

Date of Completion

January 2000

Keywords

Biology, Molecular|Biology, Neuroscience|Biology, Cell

Degree

Ph.D.

Abstract

Western blot analysis was used to examine the steady state level of myelin proteins from the peripheral nervous system (PNS) of the myelin basic protein (MBP)-deficient mutant mouse shiverer (shi). PNS myelin from homozygous shiverer (shi/shi) mice contains 3–6 times the amount of connexin-32 (CX32), myelin-associated glycoprotein (MAG), E-cadherin, proteolipid protein (PLP) and its spliced form DM20, normally present in wild type (wt). There is a gene dosage effect of MBP protein as heterozygous shiverer (+/shi) mice, which accumulate half the wt amount of MBP, have only 2–3 times as much of these proteins as wt mice. With the exception of PLP, the affected proteins are normally localized in the Schwann cell perikaryon and the uncompacted compartments of myelin. Immunofluoresence studies reveal that CX32 and MAG proteins are localized normally in the shi/shi nerve. The level of proteins present in the compact regions of myelin, protein zero (P0) and peripheral myelin protein-22 (PMP22), is not affected by the shi mutation. ^ Ribonuclease protection assays were performed to quantitate the steady state level of myelin mRNAs in wt and shi/shi nerves. A 2.5 fold increase in the level of PLP/DM20 mRNA suggests that some transcriptional regulation of PLP/DM20 gene expression exists in the shi/shi nerve as compared to wt. No differences were found in the level of CX32, MAG, and PMP22 mRNAs between wt and shi/shi nerves. Thus, the upregulation of CX32 and MAG proteins in the shi/shi PNS is not due to increased transcription of the corresponding genes. ^ As previous studies had indicated that MBP might bind to CX32 mRNA, experiments were performed to examine the possibility that MBP acts as an RNA-binding protein and inhibits the translation of CX32 mRNA. In vitro translation of CX32 mRNA is inhibited in the presence of MBP. Additionally, microinjection of CX32 mRNA into wt and shi/shi oligodendrocytes demonstrates that translation of CX32 mRNA is decreased in the presence of MBP. Thus, an inhibitory role of MBP on the expression of myelin proteins is suggested by data in this study. ^