Research

Glycosphingolipids

Many lines of evidence suggest that glycosphingolipids (GSLs), complex glycosylated lipids derived from ceramide, participate in several key cellular events leading to neuronal development, cell growth and proliferation, apoptosis and cell migration. However, the molecular mechanisms that underlie these effects are almost entirely unknown.

GSLs are amphipathic molecules consisting of a ceramide lipid moiety anchored to the membrane linked to one or more oligosaccharides protruding away from the membrane.GSLs are present on virtually all mammalian cell plasma membranes and are highly enriched in neurons. GSLs have been suggested to regulate signalling in a number of ways: 1) by interacting directly with signalling molecules; this has been shown, for example, for the growth factor FGF2; 2) By altering intracellular sorting and/or transport of proteins involved in signalling, since GSLs interfere with transport/sorting of other proteins such as the vesicular stomatitis virus G protein and of an enzyme essential for melanin synthesis; 3) by regulating the levels of the GSL precursor ceramide, which is implicated in apoptosis, cell-cycle arrest and cell proliferation; 4) via bioactive metabolites. These findings imply that GSLs play an important and complex role in many basic cellular processes and suggest that they have a crucial function during development and cell differentiation. Indeed, knockout experiments in mice showed that GSLs are essential for embryonic development and for correct tissue differentiation at gastrulation. However, the GSL requirement for these functions as well as the mechanisms and the molecular partners mediating their effects are unknown.


The precursor of the majority of GSLs, Glucosylceramide, is synthesized on the cytoplasmic face of the Golgi apparatus by Ceramide Glucosyltransferase, which transfers a glucose residue to ceramide. After its synthesis, glucosylceramide is modified by a series of Golgi glycosyltransferases to produce higher-order GSLs. To clarify the cellular roles and to determine the cellular requirements for GSLs, we have engineered C. elegans strains, which are unable to synthesize these complex lipids. Animals without CGT function arrest growth at an early larval stage. We are characterizing the phenotype of animals with no Ceramide Glucosyltransferase function and determining the tissues where CGT activity is essential.



A worm expressing a green fluorescent pro-
tein (GFP)-tagged form of Ceramide Glucosyl Transferase.