Expression of the otic anterior marker genes hmx3a, hmx2 and pax5 after early fgf3 mis-expression.
In situ hybridisation of otic expression patterns in Tg(hsp70:fgf3) embryos following a 30-minute heat shock (HS) at the 10-somite stage (14 hpf). Controls (left-hand panels of each pair of images) were sibling non-transgenic embryos subjected to the same heat shock. Numbers in the dorsal view panels indicate the number of embryos with the phenotype shown and total number (e.g. 13/25) from a mixed batch of transgenic and non-transgenic embryos in each pair of panels; 50% of the batch was expected to be transgenic. (A–F) Two hours after heat shock (16 hpf), expression of hmx3a expanded to cover the entire otic region (B), but there was only a trace of expression of hmx2 or pax5 in the otic placode at this stage. Weak expression of pax5 in the hindbrain after heat shock (F) did not persist (L). (G–L) At 22.5 hpf (8.5 hours after HS), expression of all three genes had now expanded to cover the entire anteroposterior axis of the otic vesicle on the medial side. (M–R’) At 36 hpf (22 hours after HS), expression of hmx3a remained expanded across the otic anteroposterior axis (N,N’); expression of hmx2 was strong at the anterior and posterior poles, and weaker in central regions (P,P’), whereas expression of pax5 resolved into two discrete domains at the anterior and posterior poles of the otic vesicle, and was lost from central regions (R,R’). White arrowheads indicate regions that are normally free of expression in controls; black arrowheads mark ectopic expression in transgenic embryos. A–R are dorsal views showing both otic vesicles, with anterior to the top; M’–R’ are lateral views with anterior to the left. Scale bars, 50 μm (scale bar in A applies to A–L; in M applies to M–R; in M’ applies to M’–R’). For additional examples and time points for hmx2, see S4 Fig; for pax5, see S5 Fig.