Glycosphingolipids dependent regulatory circuits controlling gene expression

Glycosphingolipids (GSLs) are a heterogeneous group of membrane lipids formed by a ceramide backbone covalently linked to a glycan moiety. According to the LIPID MAPS Structure Database, more than 400 different glycans can be assembled on ceramide in vertebrates. Although, in principle, every cell could produce the whole GSL repertoire individual cell types usually show high fidelity in their expression of a few selected GSL species which can dramatically change under stimuli or given physiological circumstances. The mechanisms by which this specificity is accomplished primarily involve the controlled expression of the relevant synthetic enzymes, while the structure of the genetic programs leading to this coordination is poorly understood. Taking advantage of the ability of the B subunit of Shiga and Cholera toxin to bind globoside Gb3 and ganglioside GM1 respectively, we have devised a fluorescence-based assay for the evaluation of GSLs expression in individual cells. Coupling Single-cell analysis to lipidomics and transcriptomics we uncovered a self-contained GSL regulatory circuit by which globo-series GSLs dampen ganglio-series GSL production. Such regulation is accomplished by the control of repressive epigenetic marks of the promoters of key ganglio series GSLs synthetic enzymes. Specifically we identified AUTS2 (a gene mutated in autism) as a Gb3 repressed gene controlling GM3 synthase expression through the regulation of H2AK119 ubiquitination at GM3 synthase promoter. Our observations ascribe an unreported property of GSLs to control transcriptional programs influencing their own synthesis through an epigenetic event. Our future plan is to understand the physiological meaning of this GSL metabolic circuit and to dissect its molecular details.