LCBs are synthesized during S and G2 phases in human cells. (a) Sphingolipid synthesis pathway in human cells showing the levels of lipid molecules measured by mass spectroscopy in 106 cells. (b) Gene expression of the enzymes involved in de novo synthesis of sphingolipids in RPE-1 cells. (c) Representative immunofluorescence images of RPE-1 cells upon knockdown of scramble sequence (Control), SPTLC1, or SPTLC2. Green, phalloidin staining of f-actin; purple, Hoechst 33342 (DNA); and red anti-lamin B1.