Mesodermal and fin defects in nls mutant embryos. (A,B) Lateral views of living 17-somite stage wildtype (A) and nls mutant (B) embryos, photographed with Nomarski optics, showing a kink at the head-trunk boundary in nls. (C,D) Higher magnification view of the posterior head, showing proximity of the first somite to the otic vesicle in nls (D). (E,F) Dorsal views of living 4-day-old wild-type (E) and nls mutant (F) larvae showing absence of pectoral fins (arrow) in nls. (G-N) Dorsal views of embryos labelled with in situ hybridisation and flat-mounted to show reduction in the distance between the krox20 and myoD expression domains (brackets) between nls mutants (I,J,M,N) and wild types (G,H,K,L). (G-J) Immunohistochemical colocalisation of the No tail protein (brown) with krox20, myoD and the presomitic marker her-1 in nls mutants. At the five-somite stage (G,I), expression of krox20 is slightly delayed in rhombomere (r) 5 (arrows). At the 10-somite stage (H,J), posterior head defects in nls are more pronounced and krox20 expression in r5 has recovered. Arrowheads denote migrating neural crest cells from r5 that appear normal in nls. (K,M) Co-localisation of the pronephric marker pax2 reveals that its anteriormost extension in the lateral mesoderm is located lateral to somite 3 in both wild type and nls (arrows). (L,N) Co-localisation of hoxc6 (purple) with krox20 and myoD (brown) at the ten-somite stage reveals an anterior limit of hoxc6 expression at the somite 4/5 boundary in both wild type and nls (arrowheads). Note the loss of clear separation between the first two somites in nls (N). Ot, otic vesicle; s1, somite 1. Anterior is towards the left. Scale bar: 500 μm in A,B.