Fig. 3. Serrate1 is not regulated by lateral inhibition in the inner ear. (A,B) Whole-mount view of dissected ears from stage HH12 embryos cultured for 24 hours. In the control (A), Serrate1 is most strongly expressed in two patches of cells located in the anterior (a) and posterior (p) regions of the otic cup. After 24 hours of DAPT treatment (B), Serrate1 expression is absent or greatly reduced in the anterior region, but persists in the posterior region. (C-D') Transverse sections of the neural tube and inner ear of stage HH12 embryos cultured for 24 hours in control (C) or DAPT-supplemented (D) medium; double in situ hybridisation for Serrate1 (red) and Delta1 (green) and immunostaining for Serrate1 protein (blue, and monochrome in C',D'). Delta1 expression is upregulated in both the inner ear and neural tube of DAPT-treated embryos (compare C and D). By contrast, in DAPT-treated embryos, both the intensity and the extent of Serrate1 expression are reduced in the inner ear (compare bracketed regions in C,C' with arrowed regions in D,D'), although they are increased in the neural tube (asterisks in C',D'). (E,F) Stage HH12 embryos cultured for 4 hours in control (E) or DAPT-supplemented (F) medium. After this brief DAPT treatment, Serrate1 expression is upregulated in the neural tube (asterisks), but not in the posterior rim of the otic cup (arrowheads), where its levels of expression appear unchanged as compared to control specimens. (G) Dorsal view of a stage HH10 embryo processed for Serrate1 whole-mount in situ hybridisation; anterior is to the left. Serrate1 expression is not detected in the presumptive otic placode field (ot, arrows), which is located anterior to the first somite (asterisk). Notice the expression of Serrate1 in scattered neurons within the neural tube (arrowheads) and in a region of the cephalic ectoderm (ce). (H,I) Whole-mount view of dissected ears from stage HH10 embryos cultured for 24 hours. In control otocysts (H), the anterior (a) and posterior (p) patches of Serrate1 expression are present. In DAPT-treated specimens (I), Serrate1 expression is absent or reduced in the anterior region, where abnormal extrusion of neuroblasts in the otocyst lumen can be seen (arrowhead; see also Fig. 2E). However, the posterior patch of Serrate1 expression persists. A, anterior; a, anterior region; ce, cephalic ectoderm; D, dorsal; ot, presumptive otic placode field; p, posterior region.