Effects of Monensin and Colchicine on Myelin Galactolipids

Abstract

Monensin and colchicine have been used in a variety of systems to disrupt functioning of the Golgi apparatus and transport of Golgi-derived vesicles to the plasma membrane. In this study the effects of monensin and colchicine on the synthesis of cerebroside and sulfatide and their appearance in myelin were examined to determine whether these myelin components are processed through the Golgi apparatus. Brain slices from rats 17 days old were incubated with [3H]galactose and [35S]-sulfate to label cerebroside and sulfatide. Myelin was isolated on sucrose density gradients. Fractions highly enriched in cerebroside and sulfatide were prepared from homogenates and myelin fractions by lipid extraction, alkaline methanolysis, and in some cases TLC. Monensin at 0.1 microM had no significant effect on synthesis of these galactolipids as measured by incorporation of [3H]-galactose into cerebroside or [35S]sulfate into sulfatide in homogenates. However, appearance of [35S]sulfatide in the myelin fraction was reduced to 49% of control, while appearance of [3H]cerebroside was not significantly reduced. Colchicine from 1 mM to 0.1 microM had effects similar to monensin, that is, appearance of [35S]sulfatide in myelin was depressed, but again [3H]cerebroside was not affected. Incorporation of [35S]sulfate into sulfatide in homogenate was 93% of control, while appearance of [35S]sulfatide in the myelin fraction was depressed to 58% of control. The inhibition of appearance of sulfatide in myelin by colchicine and monensin is consistent with the view that sulfation of cerebroside occurs in the Golgi and that sulfatide is transported via Golgi-derived vesicles to the forming myelin membrane.(ABSTRACT TRUNCATED AT 250 WORDS)

Vesicular transport of myelin proteolipid and cerebroside sulfates to the myelin membrane

“…Evidence exists suggesting that cerebroside sulfates and PLP are delivered to the myelin membrane through similar mechanisms. The transport of either of these components is disrupted by monensin (Townsend and Benjamins, 1983;Townsend et al, 1982Townsend et al, , 1984Sat0 et al, 1986) and by colchicine (Bizzozero et al, 1982b;Townsend et al, 1982Townsend et al, , 1984. Furthermore, recent studies from our laboratories strongly suggested the possibility of an associated or coupled transport of both components.…”

Stabilization of myelin mRNAs as measured in a brain slice system

“…Brain slice preparations have been used previously to study myelin protein processing and the incorporation of fatty acids and phospholipids into myelin (Benjamins et al, 1978;Townsend et al, 1984;Townsend et al, 1982;Miller et al, 1977). In this report, the use of brain slices has been extended to measure the turnover rates of myelin mRNAs.…”

Transport of proteolipid protein to the plasma membrane does not depend on glycosphingolipid cotransport in oligodendrocyte cultures

“…GalCer is synthesized by the enzyme ceramide galactosyl transferase (CGT) in the endoplasmic reticulum (Stahl et al, 1994;Schaeren-Wiemers et al, 1995b), and because sulfation of GalCer occurs in the Golgi (Benjamins et al, 1982;Tennekoon et al, 1983;Farrer et al, 1995), GalCer has to pass through the Golgi for synthesis of sulfatide (Van der Bijl et al, 1996). Finally, sulfatide (Townsend et al, 1984) and presumably also GalCer are transported via vesicular transport to the myelin membrane. A mechanism proposed for the sorting and trafficking of proteins and lipids in polarized epithelial cells involves an association of membrane proteins with glycolipid-enriched microdomains in the trans-Golgi network (TGN) and the subsequent budding and transport via carrier vesicles to specific plasma membrane domains (Simons and Wand-inger-Ness, 1990).…”