Fig. 1.

Genomic organization of Hox genes in Brachiopoda. (A) Images of adult T. transversa and N. anomala, and phylogenetic position of these species within Brachiopoda and Lophotrochozoa. (B) The 10 Hox genes of T. transversa are ordered along three genomic scaffolds and are flanked by external genes (vertical lines); gene orthology is based on best blast hit. Thus, T. transversa has a split Hox cluster composed of three subclusters. No predicted ORFs were identified between the Hox genes in scaffolds A and B. A colored box represents each Hox gene, and below each box are the direction of transcription and the exon-intron composition. The genomic regions containing Hox genes are represented in scale. (C) The genomic organization of brachiopod Hox genes in a phylogenetic context. Adapted with permission from ref. 22. The genomic order of Hox genes in T. transversa is similar to that observed in other spiralians (e.g., C. teleta, L. gigantea), suggesting that the translocation of the Antp gene upstream to lab is a lineage-specific feature of L. anatina. (In T. transversa and L. anatina, the arrows below the genes show the direction of transcription.) A degenerate-primer screening for Hox genes reported the presence of Lox2 and Lox4 in L. anatina (15). Blastn searches against the sequenced L. anatina genome only confirmed the presence of Lox4, in the same scaffold as Post1 and Post2, although genome annotation pipelines failed to predict this gene (69). The low contiguity of the draft genome assembly of N. anomala hampered the recovery of genomic linkages between the identified Hox genes. Each ortholog group is represented by a specific color.