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Fig. 1. FGF8 expression. (A) Alignment of Xenopus FGF8a and FGF8b amino acid sequences (ClustalW). The signal sequence cleavage position is predicted to be after the 22nd amino acid residue (alanine) (arrowhead), determined by using the SignalP 3.0 program (Bendtsen et al., 2004). Underlining indicates the N-linked glycosylation site (NFT) (reviewed by Dempski and Imperiali, 2002). (B) Xenopus FGF8a and FGF8b result from alternative splicing of the third exon; FGF8a uses an alternative splice acceptor (3′) site. The ATG indicates the translational start; black arrows indicate primers used for PCR amplification in the RTPCR panel in C,D. (C) X. laevis and (D) X. tropicalis RTPCR analysis of whole embryos using primers to amplify both FGF8a and FGF8b simultaneously. The FGF8a product is 253 bp; FGF8b is 286 bp. (E-N) In situ hybridization profile for FGF8 in X. tropicalis at the indicated stages. (E,G,I,L,N) Dorsal views with anterior towards the left; (F) a blastorporal view; (H,J) frontal views, dorsal upwards; (K,M) lateral views, anterior towards the left. FGF8 is expressed circumferentially around the blastopore (E,F) but is restricted to the dorsal posterior mesoderm as gastrulation proceeds; expression in the posterior mesoderm strengthens during neurulation and MHB expression begins (G,H). DM, dorsal mesoderm; MHB, midbrain-hindbrain boundary; ANR, anterior neural ridge; P, placode region; FB, forebrain; PA, pharyngeal arches; S, somite; OV, otic vesicle; Pr, pronephric anlage; TB, tail bud. |
