Generation of a ceramide synthase 6 mouse lacking the DDRSDIE C-terminal motif

The important membrane lipid, ceramide, is generated by a family of homologous enzymes, the ceramide synthases (CerSs), multi-spanning membrane proteins located in the endoplasmic reticulum. Six CerS isoforms exist in mammals with each using a subset of acyl-CoAs for (dihydro)ceramide synthesis. A number of mice have been generated in which one or other CerS has been genetically manipulated, including complete knock-outs, with each displaying phenotypes concomitant with the expression levels of the CerS in question and the presumed biological function of the ceramide species that it generates. We recently described a short C-terminal motif in the CerS which is involved in CerS dimer formation; deleting this motif had no effect on the ability of the CerS to synthesize ceramide in vitro. In the current study, we generated a CerS6 mouse using CRISPR-Cas9, in which the DDRSDIE motif was replaced by ADAAAIA. While levels of CerS6(ADAAAIA) expression were unaffected in the CerS6(ADAAAIA) mouse, and CerS6(ADAAAIA) was able to generate C16-ceramide in vitro, ceramide levels were significantly reduced in the CerS6(ADAAAIA) mouse, suggesting that replacing this motif affects an as-yet unknown mechanism of regulation of ceramide synthesis via the DDRSDIE motif in vivo. Crossing CerS6(ADAAAIA) mice with CerS5 null mice led to generation of viable mice in which C16-ceramide levels were reduced by up to 90%, suggesting that depletion of C16-ceramide levels is compensated for by other ceramide species with different acyl chain lengths.