Dataset Information

Are Hox genes ancestrally involved in axial patterning? Evidence from the hydrozoan Clytia hemisphaerica (Cnidaria).

ABSTRACT:

Background

The early evolution and diversification of Hox-related genes in eumetazoans has been the subject of conflicting hypotheses concerning the evolutionary conservation of their role in axial patterning and the pre-bilaterian origin of the Hox and ParaHox clusters. The diversification of Hox/ParaHox genes clearly predates the origin of bilaterians. However, the existence of a "Hox code" predating the cnidarian-bilaterian ancestor and supporting the deep homology of axes is more controversial. This assumption was mainly based on the interpretation of Hox expression data from the sea anemone, but growing evidence from other cnidarian taxa puts into question this hypothesis.

Methodology/principal findings

Hox, ParaHox and Hox-related genes have been investigated here by phylogenetic analysis and in situ hybridisation in Clytia hemisphaerica, an hydrozoan species with medusa and polyp stages alternating in the life cycle. Our phylogenetic analyses do not support an origin of ParaHox and Hox genes by duplication of an ancestral ProtoHox cluster, and reveal a diversification of the cnidarian HOX9-14 genes into three groups called A, B, C. Among the 7 examined genes, only those belonging to the HOX9-14 and the CDX groups exhibit a restricted expression along the oral-aboral axis during development and in the planula larva, while the others are expressed in very specialised areas at the medusa stage.

Conclusions/significance

Cross species comparison reveals a strong variability of gene expression along the oral-aboral axis and during the life cycle among cnidarian lineages. The most parsimonious interpretation is that the Hox code, collinearity and conservative role along the antero-posterior axis are bilaterian innovations.

SUBMITTER: Chiori R

PROVIDER: S-EPMC2626245 | biostudies-literature | 2009

REPOSITORIES: biostudies-literature

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Publications

Are Hox genes ancestrally involved in axial patterning? Evidence from the hydrozoan Clytia hemisphaerica (Cnidaria).

Chiori Roxane R Jager Muriel M Denker Elsa E Wincker Patrick P Da Silva Corinne C Le Guyader Hervé H Manuel Michaël M Quéinnec Eric E

PloS one 20090121 1

<h4>Background</h4>The early evolution and diversification of Hox-related genes in eumetazoans has been the subject of conflicting hypotheses concerning the evolutionary conservation of their role in axial patterning and the pre-bilaterian origin of the Hox and ParaHox clusters. The diversification of Hox/ParaHox genes clearly predates the origin of bilaterians. However, the existence of a "Hox code" predating the cnidarian-bilaterian ancestor and supporting the deep homology of axes is more con ...[more]

PMID: 19156208

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Project description:BackgroundThe Sox genes are important regulators of animal development belonging to the HMG domain-containing class of transcription factors. Studies in bilaterian models have notably highlighted their pivotal role in controlling progression along cell lineages, various Sox family members being involved at one side or the other of the critical balance between self-renewing stem cells/proliferating progenitors, and cells undergoing differentiation.ResultsWe have investigated the expression of 10 Sox genes in the cnidarian Clytia hemisphaerica. Our phylogenetic analyses allocated most of these Clytia genes to previously-identified Sox groups: SoxB (CheSox2, CheSox3, CheSox10, CheSox13, CheSox14), SoxC (CheSox12), SoxE (CheSox1, CheSox5) and SoxF (CheSox11), one gene (CheSox15) remaining unclassified. In the planula larva and in the medusa, the SoxF orthologue was expressed throughout the endoderm. The other genes were expressed either in stem cells/undifferentiated progenitors, or in differentiating (-ed) cells with a neuro-sensory identity (nematocytes or neurons). In addition, most of them were expressed in the female germline, with their maternal transcripts either localised to the animal region of the egg, or homogeneously distributed.ConclusionsComparison with other cnidarians, ctenophores and bilaterians suggest ancient evolutionary conservation of some aspects of gene expression/function at the Sox family level: (i) many Sox genes are expressed in stem cells and/or undifferentiated progenitors; (ii) other genes, or the same under different contexts, are associated with neuro-sensory cell differentiation; (iii) Sox genes are commonly expressed in the germline; (iv) SoxF group genes are associated with endodermal derivatives. Strikingly, total lack of correlation between a given Sox orthology group and expression/function in stem cells/progenitors vs. in differentiating cells implies that Sox genes can easily switch from one side to the other of the balance between these fundamental cellular states in the course of evolution.

Dataset Information

Are Hox genes ancestrally involved in axial patterning? Evidence from the hydrozoan Clytia hemisphaerica (Cnidaria).

Background

Methodology/principal findings

Conclusions/significance

Publications

Are Hox genes ancestrally involved in axial patterning? Evidence from the hydrozoan Clytia hemisphaerica (Cnidaria).

Similar Datasets

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