Survival strategies of a sterol auxotroph

Abstract

SUMMARYThe high sterol concentration in eukaryotic cell membranes is thought to influence membrane properties such as permeability, fluidity and microdomain formation. Drosophila cannot synthesize sterols, but do require them for development. Does this simply reflect a requirement for sterols in steroid hormone biosynthesis, or is bulk membrane sterol also essential in Drosophila? If the latter is true, how do they survive fluctuations in sterol availability and maintain membrane homeostasis? Here, we show that Drosophila require both bulk membrane sterol and steroid hormones in order to complete adult development. When sterol availability is restricted, Drosophila larvae modulate their growth to maintain membrane sterol levels within tight limits. When dietary sterol drops below a minimal threshold, larvae arrest growth and development in a reversible manner. Strikingly, membrane sterol levels in arrested larvae are dramatically reduced (dropping sixfold on average) in most tissues except the nervous system. Thus, sterols are dispensable for maintaining the basic membrane biophysical properties required for cell viability; these functions can be performed by non-sterol lipids when sterols are unavailable. However, bulk membrane sterol is likely to have essential functions in specific tissues during development. In tissues in which sterol levels drop, the overall level of sphingolipids increases and the proportion of different sphingolipid variants is altered. These changes allow survival, but not growth, when membrane sterol levels are low. This relationship between sterols and sphingolipids could be an ancient and conserved principle of membrane homeostasis.

Membrane lipidome of an epithelial cell line

“…Recent in vivo data from Drosophila suggest that SPs also get more hydroxylated in response to sterol depletion to maintain the physical properties of their membranes (34). Along the same lines, increased saturation of the hydrocarbon chains would increase interaction with Chol (35) and longer fatty acids could promote interleaflet coupling of a raft assembly (36).…”

The Ecdysteroidome of Drosophila: influence of diet and development

“…Drosophila melanogaster WT (Oregon-K) embryos were treated as described (Carvalho et al, 2012(Carvalho et al, , 2010. Dechorionated embryos were transferred to plates containing standard lab food consisting of malt, soy, cornmeal and yeast.…”

“…Lipid-depleted media (LDM) was added to 24-well plates (1 ml to each well) as described (Carvalho et al, 2010). Sterols in ethanol (15 μl of 1 mM stock solutions) were spiked on top of dried media and evaporated under air stream.…”

Acsl, the Drosophila ortholog of intellectual-disability-related ACSL4, inhibits synaptic growth by altered lipids

“…Like MacCer, sterol is also a constituent of lipid rafts and plays a crucial role in synapse development (Hering et al, 2003;Mauch et al, 2001;Rietveld et al, 1999); thus, we determined whether sterol depletion could suppress the NMJ overgrowth in Acsl mutants. Drosophila does not synthesize sterols, which are obtained from yeast-containing food (Carvalho et al, 2010); we therefore used methyl-β-cyclodextrin (MβCD), a cyclic oligosaccharide that efficiently decreases sterol level in various cell lines (Hebbar et al, 2008;Sharma et al, 2004). Feeding control larvae (Acsl KO /+) with 20 mM MβCD resulted in fewer and larger boutons at NMJs, whereas NMJ overgrowth was fully suppressed in Acsl KO /Acsl 05847 mutants by MβCD treatment (Fig.…”