Electron microscopy of hESC primary cilia. (A) Confocal microscopy of hESCs grown on matrigel in a monolayer viewed from the side (a) and the top (b), showing primary cilia (arrows) on undifferentiated hESCs but not on dividing cells (arrowhead). (B) SEM of H1 cells grown for 7 d on matrigel in N2/B27-supplemented medium and starved in DME:F12 without serum replacement for the last 24 h of growth. See Online supplemental material for details. Primary cilia (arrows) are seen on two adjacent cells among numerous smaller microvilli. (C and D) Enlarged images of primary cilia. Note paddle tips. (E) TEM cross sections of primary cilia of H1 and 9 hESCs grown for 7 d on matrigel in N2/B27-supplemented medium and starved in DME:F12 without serum replacement for the last 24 h before fixation. The first panel shows the 9 + 0 arrangement, which becomes disorganized along the ciliary length as shown on the rest of the panels. (F) TEM longitudinal section of a primary cilium (arrowhead) emerging from one of a pair of centrioles/basal bodies. The perpendicular orientation of the basal bodies suggests that the cilium arises from the mother centriole (arrow). A lamellar vesicle (asterisk) is seen budding from the cell surface. (G) TEM of lamellar-type bodies secreted by hESCs.