Nuclear beta-catenin promotes non-neural ectoderm and posterior cell fates in amphioxus embryos.
In vertebrate development, Wnt/beta-catenin signaling has an early role in specification of dorsal/anterior identity and a late one in posterior specification. To understand the evolution of these roles, we cloned beta-catenin from the invertebrate chordate amphioxus. The exon/intron organization of beta-catenin is highly conserved between amphioxus and other animals including a cnidarian, but not Drosophila. In development, amphioxus beta-catenin is concentrated in all nuclei from the 16-cell stage until the onset of gastrulation when it becomes undetectable in presumptive mesendoderm. Li(+), which up-regulates Wnt/beta-catenin signaling, had no detectable effect on axial patterning when applied before the late blastula stage, suggesting that a role for beta-catenin in specification of dorsal/anterior identity may be a vertebrate innovation. From the mid-gastrula through the neurula stage, the highest levels of nuclear beta-catenin are around the blastopore. In the early neurula, beta-catenin is down-regulated in the neural plate, but remains high in adjacent non-neural ectoderm. Embryos treated with Li(+) at the late blastula stage are markedly posteriorized and lack a neural plate. These results suggest that in amphioxus, as in vertebrates, down-regulation of Wnt/beta-catenin signaling in the neural plate is necessary for maintenance of the neuroectoderm and that a major evolutionarily conserved role of Wnt/beta-catenin signaling is to specify posterior identity and pattern the anterior/posterior axis.
Marine Biology Research Division, Scripps Institution of Oceanography, University of California San Diego, La Jolla, California 92093-0202, USA. lzholland@ucsd.edu
Linda Z
LZ
Holland
Kristen A
KA
Panfilio
Roger
R
Chastain
Michael
M
Schubert
Nicholas D
ND
Holland
D000818:Animals; D019070:Cell Lineage / Q000502:physiology*; D002816:Chordata, Nonvertebrate / Q000196:embryology*; D003001:Cloning, Molecular; D004475:Ectoderm / Q000187:drug effects / Q000502:physiology* / Q000648:ultrastructure; D005091:Exons; D005775:Gastrula / Q000502:physiology; D007438:Introns; D008094:Lithium / Q000494:pharmacology; D008854:Microscopy, Electron; D008969:Molecular Sequence Data; D009687:Nuclear Proteins / Q000502:physiology*; D015398:Signal Transduction / Q000502:physiology
D009687:Nuclear Proteins; D008094:Lithium