Increase in DHS1P leads to retinal degeneration in w¹¹¹⁸ photoreceptors accompanied by a decrease in Rh1 and TRP levels, and Sk2 overexpression increases the DHS1P level. (A) Transmission electron micrograph of photoreceptors of w¹¹¹⁸ fed sphingosine, S1P, DHS, and DHS1P. 100% of rhabdomeres are intact in w¹¹¹⁸ fed sphingosine and S1P, 90% of rhabdomeres are intact in DHS-fed flies, and 27% are intact in DHS1P-fed flies. (B) Rh1 and TRP are reduced in flies fed DHS1P compared with solvent and flies fed with other lipids. (C) Rh1 and TRP levels are reduced by 40% in w¹¹¹⁸ flies fed DHS1P compared with solvent. Bars denote standard deviation; n = 3. (D) UFLC MS/MS measurements show that Sk2 overexpressors have a higher level of DHS1P compared with control or Sk1 overexpressors. Bars denote standard error; n = 3.