A, B. Immunocytochemistry using HEK293T cells expressing the MAM marker SigmaR1-GFP and antibodies against Hsd17b4 (red, A) and ceramide (blue, B). Arrows in B point at Hsd17B4 associated with MAMs, a portion of which are ceramide-enriched (CEMAMs). C, D. Proximity ligation assay (PLA, red) using anti-ceramide and Hsd17b4 antibodies in SigmR1-GFP (green) expressing HEK293T cells. DAPI staining is not shown in left panel to better visualize juxtaposition of PLA signals to MAMs. In D, ceramide depletion by incubation with FB1 obliterates PLA signals for the putative ceramide-Hsd17b4 complex.