Fig. 12

Pax2/5/8 expression domains during ontogeny of various metazoan representatives. A comparison among metazoan animals suggests that the ancestral role of Pax2/5/8 was probably restricted to ectodermal domains while chordates and onychophorans recruited orthologs into the development of mesodermal organ systems. The few data on Lophotrochozoa suggest that Pax2/5/8 expression adheres to the ancestral state, i.e. patterning of certain ectodermal domains. In addition, they show that among mollusks Pax2/5/8 apparently lost its role in the formation of the nervous system (Acanthochitona crinita, Nucula tumidula, Haliotis asinina) with exception of the cephalopods, while the mantle including shell gland strongly express Pax2/5/8. Data on Pax2/5/8, Pax2, Pax5, Pax8, PaxB-expression: [42] (Cnidaria: Nematostella vectensis); [43] (Hemichordata: Saccoglossus kowalevskii); [44] (Echinodermata: Paracentrotus lividus); [10, 13, 14, 20, 45, 46] (Chordata: Oikopleura dioica; Mus musculus, Xenopus laevis, Brachiostoma floridae); present study (Aculiferan mollusks: Acanthochitona crinita); [9], present study (conchiferan mollusks: Haliotis asinina, Nucula tumidula, Idiosepius notoides); [34] (study on the regenerating adult animal, Annelida: Platynereis dumerilii); [47] (Nematoda: Caenorhabditis elegans); [48] (Onychophora: Euperipatoides rowelli); [14, 49] (Insecta: Drosophila melanogaster). Cladogram simplified after [50]