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. 2002 Feb 19;99(4):2088-93.
doi: 10.1073/pnas.042683899. Epub 2002 Feb 12.

HOX Genes in the Sepiolid Squid Euprymna Scolopes: Implications for the Evolution of Complex Body Plans

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Free PMC article

HOX Genes in the Sepiolid Squid Euprymna Scolopes: Implications for the Evolution of Complex Body Plans

Patrick Callaerts et al. Proc Natl Acad Sci U S A. .
Free PMC article

Abstract

Molluscs display a rich diversity of body plans ranging from the wormlike appearance of aplacophorans to the complex body plan of the cephalopods with highly developed sensory organs, a complex central nervous system, and cognitive abilities unrivaled among the invertebrates. The aim of the current study is to define molecular parameters relevant to the developmental evolution of cephalopods by using the sepiolid squid Euprymna scolopes as a model system. Using PCR-based approaches, we identified one anterior, one paralog group 3, five central, and two posterior group Hox genes. The deduced homeodomain sequences of the E. scolopes Hox cluster genes are most similar to known annelid, brachiopod, and nemertean Hox gene homeodomain sequences. Our results are consistent with the presence of a single Hox gene cluster in cephalopods. Our data also corroborate the proposed existence of a differentiated Hox gene cluster in the last common ancestor of Bilaterians. Furthermore, our phylogenetic analysis and in particular the identification of Post-1 and Post-2 homologs support the Lophotrochozoan clade.

Figures

Figure 1
Figure 1
Dorsal and ventral views of E. scolopes ), subadult specimen.
Figure 2
Figure 2
Comparisons of known Hox orthologs and homeobox-containing genes with predicted E. scolopes homeodomains. Only representative homeodomains and short flanking sequences from individual classes or phyla are shown to simplify the diagrams and to highlight phyletic distances. Emphasis was placed on organisms for which an array of Hox sequences are known to facilitate the orthology comparisons. The Drosophila Antennapedia homeodomain sequence is shown at the top of the alignments. Nonidentical amino acids are shown, and dashes in the subject sequences indicate identity. Paralog-specific amino acids (light gray) and paralog-specific signature motifs (dark gray) are shaded. See Table 1 for abbreviations.
Figure 3
Figure 3
Phylogram analysis of E. scolopes Post-1 and Post-2 homeodomain fragments and other known posterior homeodomain sequences, as revealed by neighbor-joining analysis. Existing representative sequences from Lophotrochozoa, Ecdysozoa, and deuterostomes were selected for the comparison. The Drosophila Hox genes were used as an outgroup. One thousand replicate data sets were generated. Internal edge labels refer to the number of bootstraps supporting the partition. Bootstrap values below 300 were not included in the phylogram. High support is found for the Lophotrochozoan Post-1 and Post-2, and Ecdysozoan Abd-B genes. The scale shows the number of amino acid substitutions per site.

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