Figure 1.

Evolution of the Mdk/Ptn family and divergence of zebrafish mdka and mdkb after gene duplication. (A) mdk and ptn arose from a gene duplication that occurred before the separation from tetrapods and teleost fish (duplication 1). The two zebrafish mdk co-orthologs arose from a teleost specific genome duplication (duplication 2). There is only one Ptn gene known in zebrafish, but it is possible that duplicated Ptn genes are present in other teleost fish; arrow lengths are not drawn to scale. (B, C) Expression of mdka and mdkb in the developing zebrafish brain at 24 hours post fertilization (hpf), as analysed by RNA whole-mount in situ hybridization. Note expression differences in telencephalon (tc), diencephalon (dc), midbrain (mb) and hindbrain (hb). (D, E) Expression of the putative Mdk receptor rptpz in the developing zebrafish brain at 24 hpf. rptpz is expressed in domains directly adjacent to or overlapping with those expressing mdka or mdkb. B, C, D are dorsal views with anterior to the left, E is a lateral view.