Keratinocyte processes interact with melanocyte dendrites. (A) Keratinocyte processes (yellow arrowheads) wrap around melanocyte dendrites in the optimized co-culture system. Representative image from bottom layer of co-culture. Z, XY images are from lines draw through the keratinocyte process marked by the closed arrowhead. (B) Keratinocyte process remains in contact with melanocyte dendrite during changes in morphology and location. Time lapse imaging of a keratinocyte projection interacting with a melanocyte dendrite. (C) Melanocyte dendrite displacement relative to the keratinocyte cell body during interaction with the keratinocyte process. Distance (d) was measured between the melanocyte dendrite (short yellow line) and the closest edge of the keratinocyte cell body (long yellow line). (D–H) Keratinocyte processes wrap around melanocyte dendrites in intact human skin. (D) TEM cross-section of intact neonatal foreskin. Melanocyte dendrites (magenta) are surrounded by keratinocyte (k1, teal; k2, green) processes (filled arrowheads); dashed yellow line, basement membrane; d, dermis; m, melanosome. (E) Left: Keratinocyte processes physically separate adjacent melanocyte dendrites. Right: Pool of small vesicles (arrowhead) within the keratinocyte (k) adjacent to melanocyte dendrite. Yellow arrowhead, vesicles fused with the keratinocyte plasma membrane. (F) 3D reconstruction of a melanocyte (magenta) and keratinocyte (cyan) processes (boxed region) from intact neonatal foreskin using 30-nm serial FIB-SEM. Yellow line demarcates epidermal–dermal junction. (G) Representative FIB-SEM image from the reconstruction in F. Inset: melanocyte dendrite surrounded by adjacent keratinocyte with two processes (blue, green). (H) Multiple angles from the 3D reconstruction in F with the two keratinocyte processes (blue, green) that overlap each other (marked by asterisk in box) from G. Scale bars, (A) 25 µm, inset, 10 µm, z-xy, 1.5 µm; (B) 2 µm; (C) 2 µm; (D) 0.6 µm; (E) left, 0.6 µm, inset, 0.25 µm; (G) 2 µm, inset, 0.5 µm.