Fig. 3: Reconstruction of the Hox complement of an ancestral cyclostome.

Schematic representations of Hox clusters and syntenic genes of the inshore hagfish (E. burgeri, middle), the sea lamprey (P. marinus, bottom) and a reconstruction of the complement of the last common ancestor of hagfishes and lampreys (top). Genes are represented by colour-coded arrows whose direction marks the sense of transcription: Hox genes in red, non-Hox genes coloured by homology (legend at right). The block between Evx-ζ and Creb2/5/7-ζ is assembled downstream of the Hox-ζ cluster, separated by 7 genes. This might be a misassembly, and their ‘natural’ upstream position is marked by a dashed line. The sea lamprey genome scaffolds and hagfish Hi-C clusters in which Hox clusters are located are indicated to the right of each cluster, with cluster 3 separated into 3L (0–107.78 Mb) and 3R (107.78–194 Mb). Black asterisks mark genes placed at opposite sides of a cluster in the hagfish and the lamprey, but placed at one side of the ancestrally reconstructed cluster on the basis of comparisons with gnathostomes (Supplementary Fig. 9); hashes denote genes present in lampreys in the same chromosome but at a long distance (see Supplementary Fig. 8); white asterisk denotes Nfe2-ζ inferred due to its presence in the Arctic lamprey. Animal illustrations kindly provided by Tamara de Dios Fernández; lamprey and hagfish illustrations reproduced with permission from ref. ¹³³.