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Fig. 8 | BMC Evolutionary Biology

Fig. 8

From: Evolutionary origin of type IV classical cadherins in arthropods

Fig. 8

Reconstruction of the evolution of the various forms of classical cadherin in arthropods. a. Schematic representation of a proposed stepwise reduction model that explains the derivation of insect type IV cadherin from the ancestral type III cadherin. Possible homologous regions between different cadherins are placed at the same positions. To avoid confusion, the domains of the derived cadherins are specified according to the type III cadherin organization (top). Changes A-C preceded the last common precursor of type IVa and IVb cadherins (orange circle). The four EC domains that were putatively reduced to a single EC domain (by Change A) are indicated by slanted stripes. Conserved exon-intron insertion sites identified between the type IVb cadherin genes and some type III cadherin genes are indicated by vertical lines (see Fig. 5). The two extra EC domains of type IVb cadherin, which are missing in the type IVa cadherin, were characterized as part of a stretch of EC domains that had been inherited from the ancestral type III cadherin. This indicates that the last common type IVa/IVb cadherin precursor possessed, in addition to the seven EC domains, two EC domains corresponding to the type III cadherin EC6 and EC7 domains. The type IVa cadherin is likely to have arisen through the loss of these two EC domains (Change D), followed by Change E in the insect lineage. b. Schematic cladogram of the proposed phylogenetic relationships among pancrustacean subgroups. Changes A-E define three clades, Clades 1–3

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