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Fig. 3. Embryonic expression of tfap2a. (A,E,G,I,K) Lateral and
(B,D,F,H,J) dorsal views of embryos stained with a tfap2a riboprobe
(B,D-K, anterior is towards the left). (A) Expression at 50% epiboly is spread
throughout the blastoderm with a slightly stronger expression at the most
dorsal aspect of the embryo. (B,C) tfap2a expression in neural crest
progenitors at the two-somite stage. Arrowhead in B indicates the level where
the optical section was taken in C. (D,E) Cranial premigratory neural crest
cells express tfap2a at the 10-somite stage. (F,G) Expression extends
to migratory neural crest cells (arrowheads), intermediate mesoderm, brain and
spinal cord neurons. (H,I) tfap2a message is found in brain and
spinal cord neurons, neural crest streams in the head (arrowhead), in the
epidermis and the paired pronephric ducts. (J,K) At 24 hpf, the expression in
the brain is confined to the two anterior domains and the hindbrain
rhombomeres. At this time, increasing numbers of spinal cord neurons and the
migrating lateral line primordium (arrow) express tfap2a. Arrowheads
indicate the craniofacial primordia. (L) Dorsolateral view of the head at 36
hpf. The expression in the primordia of the epibranchial ganglia is visible as
a stripe of cells (arrowheads) between the otic vesicle and the pharyngeal
arches. e, eye; ep, epidermis; hb, hindbrain rhombomeres; im, intermediate
mesoderm; llp, lateral line primordium; nc, neural crest; np, neural plate;
ov, otic vesicle; pnd, pronephric ducts; sc, spinal cord neurons.
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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 mobm610 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 mobm610 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
mobm610 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.
