Fig. 3. him expression is controlled by Pax2.1 and Fgf8 during the MH maintenance loop. (A,B) him (blue) and pax2.1 (red) expression in ace mutants (B) and WT siblings (A) at the 21-somite stage (all embryos deyolked, lateral view, anterior left). Note that both genes are coincidentally switched off at the MHB, except for a common dorsal patch (arrows), while him expression in the presomitic mesoderm is intact (A',B', insets). (C,D) him expression (blue) in noi mutants (D) and WT siblings (C) at the 17-somite stage (C,D: deyolked embryos, lateral views, anterior left; C'-D'': dorsal views of flat-mounted heads (C',D') and tails (C'',D''). him expression at the MHB is restricted to a ventral patch in noi (arrow), while presomitic expression is unaffected (C'',D'').