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Open Access Research article

The origin and evolution of ARGFX homeobox loci in mammalian radiation

Guang Li12 and Peter WH Holland1*

Author Affiliations

1 Department of Zoology, University of Oxford, South Parks Road, Oxford, OX1 3PS, UK

2 Key Laboratory of the Ministry of Education for Cell Biology and Tumor Cell Engineering, School of Life Sciences, Xiamen University, Xiamen, 361005, China

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BMC Evolutionary Biology 2010, 10:182  doi:10.1186/1471-2148-10-182

Published: 17 June 2010

Abstract

Background

Many homeobox genes show remarkable conservation between divergent animal phyla. In contrast, the ARGFX (Arginine-fifty homeobox) homeobox locus was identified in the human genome but is not present in mouse or invertebrates. Here we ask when and how this locus originated and examine its pattern of molecular evolution.

Results

Phylogenetic and phylogenomic analyses suggest that ARGFX originated by gene duplication from Otx1, Otx2 or Crx during early mammalian evolution, most likely on the stem lineage of the eutherians. ARGFX diverged extensively from its progenitor homeobox gene and its exons have been functional and subject to purifying selection through much of placental mammal radiation. Surprisingly, the coding region is disrupted in most mammalian genomes analysed, with human being the only mammal identified in which the full open reading frame is retained. Indeed, we describe a transcript from human testis that has the potential to encode the full deduced protein.

Conclusions

The unusual pattern of evolution suggests that the ARGFX gene may encode a functional RNA or alternatively it may have 'flickered' between functional and non-functional states in the evolutionary history of mammals, particularly in the period when many mammalian lineages diverged within a relatively short time span.