The amphioxus Hairy family: differential fate after duplication.
Vertebrate Hairy genes are highly pleiotropic and have been implicated in numerous functions, such as somitogenesis, neurogenesis and endocrine tissue development. In order to gain insight into the timing of acquisition of these roles by the Hairy subfamily, we have cloned and studied the expression pattern of the Hairy gene(s) in amphioxus. The cephalochordate amphioxus is widely believed to be the living invertebrate more closely related to vertebrates, the genome of which has not undergone the massive gene duplications that took place early during vertebrate evolution. Surprisingly, we have isolated eight Hairy genes from the 'pre-duplicative' amphioxus genome. In situ hybridisation on amphioxus embryos showed that Hairy genes had experienced a process of subfunctionalisation that is predicted in the DDC model (for duplication-degeneration-complementation). Only the summation of four out of the eight Amphi-Hairy genes expression resembles the expression pattern of vertebrate Hairy genes, i.e. in the central nervous system, presomitic mesoderm, somites, notochord and gut. In addition, Amphi-Hairy genes expression suggest that amphioxus early somites are molecularly prefigured in an anteroposterior sequence in the dorsolateral wall of the archenteron, and the presence of a midbrain/hindbrain boundary. The expansion of the amphioxus Hairy subfamily request for caution when deducing the evolutionary history of a gene family in chordates based in the singularity of the amphioxus genome. Amphioxus may resemble the ancestor of the vertebrates, but it is not the ancestor, only its closest living relative, a privileged position that should not assume the freezing of its genome.
Minguillón
Carolina
C
Departament de Genètica, Facultat de Biologia, Universitat de Barcelona, Avenida Diagonal 645, E-08028 Barcelona, Spain.
Jiménez-Delgado
Senda
S
Panopoulou
Georgia
G
Garcia-Fernàndez
Jordi
J
D000595:Amino Acid Sequence; D000818:Animals; D002816:Chordata, Nonvertebrate / Q000196:embryology / Q000235:genetics*; D019143:Evolution, Molecular; D005260:Female; D020440:Gene Duplication; D018507:Gene Expression Regulation, Developmental; D005801:Genes, Homeobox; D018398:Homeodomain Proteins / Q000145:classification / Q000235:genetics; D006801:Humans; D017403:In Situ Hybridization; D008297:Male; D008969:Molecular Sequence Data; D009024:Morphogenesis; D005810:Multigene Family; D010802:Phylogeny; D016415:Sequence Alignment
D018398:Homeodomain Proteins