Is the evolution of Cnox-2 Hox/ParaHox genes "multicolored" and "polygenealogical?"

Abstract

Understanding the evolution of metazoan bauplans is linked to understanding the evolution of Hox and ParaHox genes. At the base of metazoan radiation we see in both cases a quite confusing picture yet. Here Cnox-2 is one of the best studied diploblast Hox genes. Homologs of this gene are known from Placozoa and several Cnidaria. In those cases where full length gene sequences, or at least full length homeobox sequences, are available the relationship to Hox genes from triploblastic animals as well as the classification to Hox or ParaHox genes can be controversially discussed. The existing data on possible gene functions also reveal a quite heterogeneous picture. It seems conceivable that part of the "multicolored" picture relates to a "polygenealogical" origin of the Cnox-2 gene.