Regulatory Genes in Ancestral Chordates


The phylum ‘Chordate’ includes amphioxus, tunicate and vertebrate. The three groups evolved from a common ancestor. The evolution of chordates is a fascinating subject for biologists, who have long pondered which changes in the genome and genes were critical to the evolution, with no real resolution to this issue. Recent genome projects in the chordates have revealed a repertoire of so‐called regulatory genes, and comparison of these essential genes for development has provided insights into chordate evolution. The ancestral chordate is estimated to have had approximately 80% of the genes in the extant chordate genomes. Some regulatory genes are specific to specific lineages, which may have led to the separation of amphioxus, tunicates and vertebrates.

Key concepts

  • Small subsets of genes encoding transcription factors and signal transductions play roles as conductors during development. These genes are called regulatory genes. Genetic changes in regulatory genes served as major driving forces for the evolution of chordates. The regulatory genes present in the ancestral chordate can be deduced by comparing the extant chordate genomes. This information is crucial to understand the evolution of chordates.

Keywords: amphioxus; tunicate; vertebrate; Ciona intestinalis; evolution

Figure 1.

(a) An adult amphioxus Branchiostoma belcheri. (b) A swimming larva of an ascidian Ciona intestinalis. Ascidian larvae have a notochord in the tail. The anterior part of the central nervous system is developed to form a brain vesicle. The brain vesicle contains two pigmented organs, the otolith and ocellus. (c) An adult Ciona intestinalis. After metamorphosis, ascidians lose their tails and start a sessile lifestyle. (d) A schematic phylogenetic tree of deuterostomes showing the relationships between amphioxus, tunicates and vertebrates.

Figure 2.

Wnt clusters. Wnt clusters found in the human, amphioxus and Drosophila genomes are shown in green, pink and blue, respectively. A box represents a Wnt gene, and the position of the box with respect to the horizontal bar indicates the direction of the transcription. The located chromosome or scaffold numbers are described on the right. DrosophilaDWnt4 is orthologous to Wnt9/14/15, and wg an orthologue of Wnt1.



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How to Cite close
Sasakura, Yasunori(Sep 2009) Regulatory Genes in Ancestral Chordates. In: eLS. John Wiley & Sons Ltd, Chichester. [doi: 10.1002/9780470015902.a0021774]