Fig. 3

Expression of dkk1 in different stages of development of first- and second-generation teeth. (A) 60 hpf: weak mesenchymal expression in tooth 4V¹, epithelial expression starts to be upregulated in 3V¹; (B) 72 hpf: strong epithelial expression in 3V¹ and 5V¹, but loss of signal in 4V¹; (C) 80 hpf: start of formation of 4V² showing no signal yet; epithelial signal is weakening in 3V¹ and 5V¹; (D,E) 100 hpf; dkk1 is now downregulated in all first-generation teeth [3V¹ and 4V¹ in (D), 5V¹ in (E)], whilst the gene is upregulated in the first replacement tooth (4V²); (F) 144 hpf: expression in the two next second-generation teeth, 3V² and 5V². Dark-colored arrowheads indicate specific first-generation teeth and point downwards: dark green, 4V¹, red, 3V¹, dark blue, 5V¹; light-colored arrowheads indicate second-generation teeth and point upwards: light green, 4V², pink, 3V², light blue, 5V². Note that epithelium and mesenchyme of a tooth germ are not necessarily visible on a single section through the germ. Sections may also be slightly oblique and different sets of teeth may be visible on either body side. Insets show higher magnification of the teeth on the left side in each micrograph. Scale bars = 50 µm.