Data from: Minimal ProtoHox cluster inferred from bilaterian and cnidarian Hox complements

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.两侧对称动物（Bilaterian animals）拥有用于塑造躯体主轴发育模式的Hox基因簇（Hox gene cluster），以及ParaHox基因簇（ParaHox gene cluster）。通过对Hox与ParaHox基因的比较分析，研究者提出假说：两类基因簇均起源于一个被命名为ProtoHox的古老基因簇（ProtoHox cluster）的复制事件，该古老基因簇最多包含4个基因，至少包含前部与后部Hox/ParaHox基因的前体。然而，由于目前尚无针对非两侧对称动物的系统性研究，ProtoHox、Hox及ParaHox基因簇内的基因分化路径仍未明确。本研究表征了两种刺胞动物（cnidarian species）——韦氏丝海葵（Nematostella vectensis）与大乳头水螅（Hydra magnipapillata）的完整Hox/ParaHox基因全集及基因组组织模式，并基于三项论据提出，ProtoHox基因簇的结构比此前认知的更为简化：其一，两种刺胞动物均拥有类两侧对称动物的前部Hox基因，但其非前部基因并不对应两侧对称动物的中部或后部Hox基因；其二，韦氏丝海葵中存在两个成簇的ParaHox基因：Gsx以及一个与Xlox和Cdx同源的基因；其三，本研究未发现明确的系统发育证据，可支持两侧对称动物的Cdx基因与后部Hox基因拥有共同起源，因此二者可能是在ProtoHox基因簇复制事件之后才演化出现的。据此推测，ProtoHox基因簇可能仅由两个前部基因构成。非前部基因或可独立起源于Hox与ParaHox基因簇，这一过程大概率发生在两侧对称动物与刺胞动物演化分支分离之后。