Fig. 2. mont blanc encodes tfap2a. (A) mob^m610 maps on linkage group 24, between markers Z23011 and Z65547. No recombinants were found between mob^m610 and a SSCP marker in the 3'UTR of tfap2a. (B) Genomic sequence of wild-type and mob^m610 embryonic DNA reveals an AG transition (arrow) at the 3'splice site preceding exon 7 in the mutant. (C) Mutation in the XbaI site (underlined in B and D) is tightly linked to the mob^m610 phenotype. Upper panel shows a sample of map cross animals genotyped with SSLP marker Z65547. In lower panel, DNA from the same animals is amplified and digested by the XbaI enzyme. PCR products spanning the mob^m610 lesion are not cut. (D) Sequence of wild-type and mutant tfap2a cDNA (in capital letters) reveals a 14 bp deletion (in red) that corresponds to the beginning of exon 7. Part of intron 6 is also depicted (in small letters). The XbaI site destroyed by the mutation is underlined and the arrow indicates the mutated base pair. (E) Genomic structure of the tfap2a gene. Exon 1a corresponds to isoform tfap2a1, exon 1b to tfap2a2 and exon 1c to tfap2a3. The arrow indicates the mutation site at the 3'splice site of intron 6. Sequence homology alignment between the C-terminal part of the protein in mob^m610 mutants, wild-type zebrafish and mouse Tcfap2a that shares 86% homology with the zebrafish tfap2a. The usage of the cryptic 3'splice site within exon 7 produces a reading frame shift and disrupts the C-terminal part of the protein. The predicted missense peptide (in red) shares little sequence similarity with the wild-type sequence that is responsible for dimerization and DNA binding of tfap2a.