Figure 4.

Divergence of the primordial EMP gene. The phylogeny of Ca-sensitive CSNs (milk), STATH/HTN (saliva), and EMP genes (enamel) was based on the two phylogenetic trees in Fig. 3. The primordial EMP gene appeared early in vertebrate evolution, perhaps in conodont (parenthesized). Immunohistochemical studies suggested the possibility that AMEL and ENAM emerged before the divergence of shark (parenthesized). AMBN diverged before caiman (reptiles). The primordial Ca-sensitive CSN diverged from one of the EMP genes, probably either from ENAM or AMBN before the emergence of monotremes. STATH then diverged from CSN1S2 before the divergence of rodents. Except for AMEL, genes are arranged in this order on chromosome 4.