title: Sequence and developmental expression of AmphiDll, an amphioxus Distal-less gene transcribed in the ectoderm, epidermis and nervous system: insights into evolution of craniate forebrain and neural crest.
abstract: The dynamic expression patterns of the single amphioxus Distal-less homolog (AmphiDll) during development are consistent with successive roles of this gene in global regionalization of the ectoderm, establishment of the dorsoventral axis, specification of migratory epidermal cells early in neurulation and the specification of forebrain. Such a multiplicity of Distal-less functions probably represents an ancestral chordate condition and, during craniate evolution, when this gene diversified into a family of six or so members, the original functions evidently tended to be parcelled out among the descendant genes. In the amphioxus gastrula, AmphiDll is expressed throughout the animal hemisphere (presumptive ectoderm), but is soon downregulated dorsally (in the presumptive neural plate). During early neurulation, AmphiDll-expressing epidermal cells flanking the neural plate extend lamellipodia, appear to migrate over it and meet mid-dorsally. Midway in neurulation, cells near the anterior end of the neural plate begin expressing AmphiDll and, as neurulation terminates, these cells are incorporated into the dorsal part of the neural tube, which forms by a curling of the neural plate. This group of AmphiDll-expressing neural cells and a second group expressing the gene a little later and even more anteriorly in the neural tube demarcate a region that comprises the anterior three/fourths of the cerebral vesicle; this region of the amphioxus neural tube, as judged by neural expression domains of craniate Distal-less-related genes, is evidently homologous to the craniate forebrain. Our results suggest that craniates evolved from an amphioxus-like creature that had the beginnings of a forebrain and possibly a precursor of neural crest - namely, the cell population leading the epidermal overgrowth of the neural plate during early neurulation.
authors.affiliation: Marine Biology Research Division, Scripps Institute of Oceanography, La Jolla, CA 92093-0202, USA.
authors.forename: N D
authors.initials: ND
authors.lastname: Holland
authors.forename: G
authors.initials: G
authors.lastname: Panganiban
authors.forename: E L
authors.initials: EL
authors.lastname: Henyey
authors.forename: L Z
authors.initials: LZ
authors.lastname: Holland
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D005075:Biological Evolution; D015139:Blotting, Southern; D002490:Central Nervous System / Q000196:embryology*; D002816:Chordata, Nonvertebrate / Q000196:embryology; D003001:Cloning, Molecular; D004268:DNA-Binding Proteins; D004475:Ectoderm / Q000378:metabolism; D004817:Epidermis / Q000196:embryology / Q000378:metabolism; D018507:Gene Expression Regulation, Developmental; D005796:Genes; D006651:Histocytochemistry; D017403:In Situ Hybridization; D008855:Microscopy, Electron, Scanning; D008969:Molecular Sequence Data; D009024:Morphogenesis; D009419:Nerve Tissue Proteins / Q000737:chemistry / Q000235:genetics*; D009432:Neural Crest / Q000196:embryology*; D009687:Nuclear Proteins; D016548:Prosencephalon / Q000196:embryology*; D017386:Sequence Homology, Amino Acid
chemical_list: C101540:DLL protein, Branchiostoma floridae; D004268:DNA-Binding Proteins; D009419:Nerve Tissue Proteins; D009687:Nuclear Proteins