page 13, col 2, §3:
In the same spirit, recent analyses in terms of gene regulatory networks have raised some surprise, since the same genes regulatory networks seem already present 570 My ago in cnidarians (jellyfish, etc. ); therefore if the same genetic networks are present, either some minor molecular subtleties, downstream of the main genetic kernels, make the difference between animal bauplan (say hydra and rabbit), or it is a matter of spatio-temporal organization (different symmetry breaking) of the same genes with non-chemical boundary effects and wavelength locking.
Where : Minimal ProtoHox cluster inferred from bilaterian and cnidarian Hox complements, D. Chourrout, F. Delsuc, P. Chourrout, R. B. Edvardsen, F. Rentzsch, E. Renfer, M. F. Jensen, B. Zhu, P. deJong, R. E. Steele & U. Technau, Nature 2006, doi:10.1038/nature04863 [abstract below the fold]
Chourrout et al. discuss the evolution of the Hox genes cluster, showing the evolution of complexity from an inferred ancestral ProtoHox cluster. They don’t address any issue concerning gene regultory networks.
Our physicist inappropriately report the content of this paper, misrepresenting the subject, inferring “minor molecular subtleties” where genes’ and clusters’ duplications are discussed, and reach nonsensical conclusions on the base of imaginary data.
The reviewers of the paper, as well as the editor, failed to spot this error. Too bad.
Bilaterian animals have a Hox gene cluster essential for patterning the main body axis, and a ParaHox gene cluster. Comparison of Hox and ParaHox genes has led workers to postulate that both clusters originated from the duplication of an ancient cluster named ProtoHox, which contained up to four genes with at least the precursors of anterior and posterior Hox/ParaHox genes. However, the way in which genes diversified within the ProtoHox, Hox and ParaHox clusters remains unclear because no systematic study of non-bilaterian animals exists. Here we characterize the full Hox/ParaHox gene complements and genomic organization in two cnidarian species (Nematostella vectensis and Hydra magnipapillata), and suggest a ProtoHox cluster simpler than originally thought on the basis of three arguments. First, both species possess bilaterian-like anterior Hox genes, but their non-anterior genes do not appear as counterparts of either bilaterian central or posterior genes; second, two clustered ParaHox genes, Gsx and a gene related to Xlox and Cdx, are found in Nematostella vectensis; and third, we do not find clear phylogenetic support for a common origin of bilaterian Cdx and posterior genes, which might therefore have appeared after the ProtoHox cluster duplication. Consequently, the ProtoHox cluster might have consisted of only two anterior genes. Non-anterior genes could have appeared independently in the Hox and ParaHox clusters, possibly after the separation of bilaterians and cnidarians.
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