Isolation of Hox and ParaHox genes in the bivalve Pecten maximus

doi:10.1016/j.gene.2004.12.039

Gene

Volume 348, 28 March 2005, Pages 83-88

https://doi.org/10.1016/j.gene.2004.12.039 Get rights and content

Abstract

The Hox cluster genes encode a set of transcription factors that have been shown to control spatial patterning mechanisms in bilaterian organism development. The ParaHox cluster is the evolutionary sister of the Hox cluster. The two are believed to descend from an ancestral ProtoHox cluster of four genes from which the three ParaHox genes (Gsx, Xlox, and Cdx) and the four Hox gene classes are believed to have originated.

Although molluscs are among the most successful lophotrochozoan groups, very little work has been devoted to the characteristics of their homeotic genes. Using polymerase chain reaction-based approaches, we isolated 13 different Pecten maximus (Bivalvia: Pteriomorphia) sequences corresponding to all the genes of the four Hox cluster classes and to genes Xlox and Cdx of the ParaHox cluster.

Comparison of results with those obtained in other lophotrochozoans seems to confirm the considerable homogeneity of the Hox and ParaHox genes in these taxa both as regards the presence of nearly all the genes of the two clusters and the marked sequence resemblance among orthologous genes.

Introduction

The Hox genes are transcription factors with a 180 bp homeobox encoding a 60 amino acid homeodomain characterised by a helix-turn-helix motif (Gehring et al., 1994).

This gene family is involved in the formation of the antero–posterior axis of bilaterian metazoa during embryo development and is organised into clusters made up of multiple Hox genes.

The Hox genes are generally subdivided into four classes (Kourakis and Martindale, 2001): (1) anterior, which in protostomes includes two genes (lab/Hox1, pb/Hox2); (2) paralog group 3 (PG-3), which in lophotrochozoans consists of a single gene (Hox3) and in Drosophila of three different sequences (zen1, zen2, bcd); (3) central, encompassing five–six genes in lophotrochozoans (Dfd/Hox4, Scr/Hox5, Lox5, Antp, Lox4, Lox2); and (4) posterior, consisting of two genes (Post-1, Post-2) (de Rosa et al., 1999, Balavoine et al., 2002). The gene composition of each class varies broadly across taxa due to duplication, inversion, or gene loss events intervened in the course of evolution (Arthur, 1997).

The ParaHox cluster is the evolutionary sister of the Hox cluster (Brooke et al., 1998). The two are believed to descend from an ancestral four-gene ProtoHox cluster from which the three ParaHox genes (Gsx, Xlox, and Cdx) and the four Hox gene classes are believed to have originated (Brooke et al., 1998, Finnerty and Martindale, 1999, Kourakis and Martindale, 2000).

Existing studies of the presence and characteristics of the homeotic genes in protostomes are not very informative, and the full clusters of Hox and ParaHox genes have only been detected in some groups of Ecdysozoa and Lophotrochozoa (de Rosa et al., 1999, Kourakis and Martindale, 2001, Ferrier and Holland, 2001, Balavoine et al., 2002, Hinman et al., 2003, Lee et al., 2003). In addition, data regarding the correspondence between the Hox genes in different phyla are few and sparse, especially for the posterior class, again also due to duplication and/or gene divergence/loss events that took place during the evolution of each group (de Rosa et al., 1999, Kourakis and Martindale, 2001, Balavoine et al., 2002).

Studies of molluscan Hox and ParaHox genes are scarce. A single gene of the anterior class, the group 3 gene, all the genes of the central class but Lox2, and both posterior class genes have been identified in the cephalopod Euprymna scolopes (Callaerts et al., 2002). The putative Hox genes of all classes but the posterior class have been identified in three gastropods, Patella vulgata (de Rosa et al., 1999), Haliotis rufescens (Degnan and Morse, 1993), and Haliotis asinina (Giusti et al., 2000, Hinman et al., 2003). The Hox genes of group 3 and some genes of the central class have been isolated in various bivalve species (Barucca et al., 2003).

Investigations of the ParaHox genes are even sparser: indeed, the sole gene Cdx has been isolated in E. scolopes (Callaerts et al., 2002) and in H. rufescens (Degnan and Morse, 1993), while genes Cdx and Xlox have been identified in some bivalves (Barucca et al., 2003).

The present study of the presence and characteristics of Hox and ParaHox genes in the pteriomorph Pecten maximus was undertaken to gain further insights into these bivalve genes.

Section snippets

Materials and methods

The specimens of P. maximum came from the Atlantic Ocean (France). Only adult specimens were analysed.

Total DNA was extracted from gonads and abductor muscle according to Jeffreys and Flavell (1977) and then PCR-amplified using degenerate primers published elsewhere (Murtha et al., 1991, Pendleton et al., 1993); the primers for the Post-1 and Post-2 homeobox fragments were those designed by Callaerts et al. (2002).

For the amplification of the labial gene, we used the specific forward primer:

Results and discussion

Twelve unique gene fragments measuring ca. 80 bp (without the primers), corresponding to amino acid sequences of variable length lying between positions 13 and 45 of the homeodomain, were isolated using the degenerate primers. Amino acid sequence analysis allowed to attribute 11 of these genes to the Hox gene cluster and two to the ParaHox cluster (Fig. 1, Fig. 2).

Acknowledgements

Financed by MIUR (Ministero dell'Istruzione dell'Università e della Ricerca) and Università Politecnica delle Marche.

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Isolation of Hox and ParaHox genes in the bivalve Pecten maximus

Abstract

Introduction

Section snippets

Materials and methods

Results and discussion

Acknowledgements

Mol. Phylogenet. Evol.

Gene

Mol. Phylogenet. Evol.

FEBS Lett.

Dev. Biol.

Curr. Biol.

Mol. Phylogenet. Evol.

Cell

Mol. Phylogenet. Evol.

Curr. Biol.

The molecular basis for metameric pattern in the Drosophila embryo

Development

The origin of animal body plans: a study in evolutionary developmental biology

Identification of members of several homeobox genes in a planarian using a ligation-mediated polymerase chain reaction technique

Nucleic Acids Res.

The ParaHox gene cluster is an evolutionary sister of the Hox gene cluster

Nature

Hox genes in the sepiolid squid Euprymna scolopes: implications for the evolution of complex body plans

Proc. Natl. Acad. Sci. U. S. A.

Hox genes in brachiopods and priapulids and protostome evolution

Nature