Fig. 3. Loss-of-function of hoxb1 duplicate genes causes alterations in segmental organization of the posterior hindbrain. (A-C) In situ hybridization with krox20 (a marker for r3 and r5) and hoxb4 (expressed in r7 and posterior) at 20 hours, anterior towards the top, rhombomeres r3-r6 and their AP extent are indicated (red double-headed arrows). (A) Wild-type control; (B) embryo injected with 4 mg/ml MOb1b, note reduction in AP extent of r4, r5 and r6 and expansion of r3; (C) Embryo co-injected with 1 mg/ml MOb1a + 4 mg/ml MOb1b, note exacerbation of reduced size of r4 and r6, and further expansion of r3 towards the posterior. (D-F) Bright-field lateral views of live embryos at the 24-hour stage, anterior towards the left. The AP extent of the otic vesicles is indicated by white bars. (D) Wild-type embryo; (E) MOb1b-injected embryo; (F) MOb1a+MOb1b-injected embryo. Arrows indicate otoliths.