There is substantial evidence from studies in humans that genetic variation that contributes to an individual's naive level of response to ethanol strongly impacts their susceptibility to become alcoholic. Our laboratory uses worms to study the genetic influences on the level of acute ethanol response. There are at least two components to the level of response to ethanol, initial sensitivity (measured at 10 minutes exposure), and a robust development of acute functional tolerance (AFT, measured at 30 and 50 minutes). We have used a forward genetic screen to isolate mutants that fail to develop AFT, and have recovered 16 recessive mutations that identify at least 14 complementation groups. We cloned the first of these,
eg613, which is a mutation in the gene
ctbp-1, a transcriptional repressor. CTBP-1 acts with PAG-3 and ZAG-1 to repress transcription (Nicholas, H. et al., J Mol Biol 375:1-11). We also recovered alleles of
pag-3 and
zag-1 from our screen, demonstrating that we are able to identify genetic pathways using this approach. The gene encoding the triacylglycerol (TAG) lipase LIPS-7 has been shown to be inappropriately upregulated in a
ctbp-1 mutant strain, resulting in decreased TAG levels (Chen, S. et al., PNAS 106(5): 1496-501). We demonstrated that dysregulation of
lips-7 is at least partially responsible for the failure of
ctbp-1(
eg613) to develop AFT, and that loss of function of
lips-7 results in fast development of AFT. TAGs are used as fat stores in the worm, so we tested if other mutations that alter fat levels also impact AFT, and found that there was no correlation between overall fat levels and AFT. We hypothesized that
lips-7 might also be altering membrane composition and/or structure, which has been shown in worms and other systems to influence the function of membrane-bound proteins. Such modulation of function may represent a mechanism for developing tolerance to the depressive effects of ethanol. Supporting this hypothesis, we found that worms reared on cholesterol-depleted media were unable to develop AFT. We also found that altering
lips-7 levels modulated the function of two gain-of-function mutations in the ethanol-sensitive BK channel, SLO-1. Together, these data suggest a model in which the lipid bilayer plays an important role in the ability of proteins to modulate their function in response to ethanol treatment.