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Fig. 2 Phylogenetic analysis of the distribution of Gcm-2 and its expression in teleost (zebrafish) and chondrichthyan (dogfish) species. (A) A phylogenetic tree of vertebrate Gcm genes based on CLUSTAL analysis. Dr, zebrafish (Danio rerio); Gg, chicken (Gallus gallus); Hs, human (Homo sapiens); Mm, mouse (Mus musculus); Nf, Australian lungfish (Neoceratodus forsteri); Om, rainbow trout (Oncorhynchus mykiss); Sc, dogfish (Scyliorhinus canicula); Xl, Xenopus (Xenopus laevis). Branch lengths are in units of number of amino acid substitutions per site. (B) Schematic depicting the conserved linkage between Gcm2 and Elovl2 in humans on chromosome 6p24.2, in chickens on chromosome 2 ctg20.4, and in zebrafish on chromosome 24 ctg254791. (C–F) Gcm-2 expression in zebrafish embryos. In these micrographs, anterior is to the left and ventral is to the bottom. Gcm-2 initiates expression in the second pharyngeal pouch in early 3-day-old larval fish (indicated by arrowhead in C). Subsequently, Gcm-2 is expressed sequentially in the more posterior pouches (D), and, by day 4, Gcm-2 is expressed in all of the pouches (E). It is also apparent by day 4 that Gcm-2 is expressed in the developing internal gill buds emerging from the pharyngeal pouches (F). (G and H) Gcm-2 expression in dogfish embryos. This gene is expressed in the internal gill buds protruding from the pharyngeal pouches in stage-27 dogfish embryos (17). The pharyngeal arches are numbered II–VI.