Hoxb1 regulates Lrrn2 expression. (A-A") Overlay to show co-expression of ectopic Shh and Hoxb1 and their effect on Lrrn2 expression in a flatmounted hindbrain, using an anti-GFP antibody to localise the region of misexpression. Widespread overexpression is seen throughout the hindbrain, but Lrrn2 is upregulated in r1, r2 and r4 only. (A) Brightfield view of Lrrn2 expression and (A') fluorescence of anti-GFP antibody. (B-C) Coronal sections through an embryo electroporated with RCASBP(B)-mHoxb1 at HH10 and processed 2 days later for Lrrn2 (dark purple) and mouse Hoxb1 (red) expression by in situ hybridisation. (B) Section taken through ventral r4 show endogenous expression of Lrrn2 in r4 (black arrowheads) and ectopic expression of mouse Hoxb1 (black arrows). (C) Corresponding section taken more ventrally through the branchial arches of the same embryo shows upregulation of Lrrn2 expression in BA1 mesoderm (red arrow) and endogenous expression in BA2 (red arrowheads). Scale bar: 100 μm.