The sea urchin animal pole domain is a Six3-dependent neurogenic patterning center.
Two major signaling centers have been shown to control patterning of sea urchin embryos. Canonical Wnt signaling in vegetal blastomeres and Nodal signaling in presumptive oral ectoderm are necessary and sufficient to initiate patterning along the primary and secondary axes, respectively. Here we define and characterize a third patterning center, the animal pole domain (APD), which contains neurogenic ectoderm, and can oppose Wnt and Nodal signaling. The regulatory influence of the APD is normally restricted to the animal pole region, but can operate in most cells of the embryo because, in the absence of Wnt and Nodal, the APD expands throughout the embryo. We have identified many constituent APD regulatory genes expressed in the early blastula and have shown that expression of most of them requires Six3 function. Furthermore, Six3 is necessary for the differentiation of diverse cell types in the APD, including the neurogenic animal plate and immediately flanking ectoderm, indicating that it functions at or near the top of several APD gene regulatory networks. Remarkably, it is also sufficient to respecify the fates of cells in the rest of the embryo, generating an embryo consisting of a greatly expanded, but correctly patterned, APD. A fraction of the large group of Six3-dependent regulatory proteins are orthologous to those expressed in the vertebrate forebrain, suggesting that they controlled formation of the early neurogenic domain in the common deuterostome ancestor of echinoderms and vertebrates.
Wei
Zheng
Z
National Institute for Dental and Craniofacial Research, National Institutes of Health, Bethesda, MD 20892, USA.
Yaguchi
Junko
J
Yaguchi
Shunsuke
S
Angerer
Robert C
RC
Angerer
Lynne M
LM
D000818:Animals; D001483:Base Sequence; D019521:Body Patterning / Q000235:genetics / Q000502:physiology; D002454:Cell Differentiation / Q000235:genetics / Q000502:physiology; D005136:Eye Proteins / Q000235:genetics / Q000378:metabolism*; D020869:Gene Expression Profiling; D018507:Gene Expression Regulation, Developmental; D005809:Genes, Regulator; D018398:Homeodomain Proteins / Q000235:genetics / Q000378:metabolism*; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000378:metabolism*; D055495:Neurogenesis / Q000235:genetics / Q000502:physiology*; D009474:Neurons / Q000166:cytology / Q000378:metabolism; D055457:Nodal Protein / Q000235:genetics / Q000378:metabolism; D020411:Oligonucleotide Array Sequence Analysis; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction; D047270:Strongylocentrotus purpuratus / Q000196:embryology* / Q000235:genetics / Q000378:metabolism*; D016212:Transforming Growth Factor beta / Q000235:genetics / Q000378:metabolism; D051153:Wnt Proteins / Q000235:genetics / Q000378:metabolism; D000097607:Homeobox Protein SIX3
D005136:Eye Proteins; D018398:Homeodomain Proteins; D009419:Nerve Tissue Proteins; D055457:Nodal Protein; D012333:RNA, Messenger; D016212:Transforming Growth Factor beta; D051153:Wnt Proteins; D000097607:Homeobox Protein SIX3