The BMP/CHORDIN antagonism controls sensory pigment cell specification and differentiation in the ascidian embryo.
We have investigated the role of the bone morphogenetic protein (BMP) pathway during neural tissue formation in the ascidian embryo. The orthologue of the BMP antagonist, chordin, was isolated from the ascidian Halocynthia roretzi. While both the expression pattern and the phenotype observed by overexpressing chordin or BMPb (the dpp-subclass BMP) do not suggest a role for these factors in neural induction, BMP/CHORDIN antagonism was found to affect neural patterning. Overexpression of BMPb induced ectopic sensory pigment cells in the brain lineages that do not normally form pigment cells and suppressed pressure organ formation within the brain. Reciprocally, overexpressing chordin suppressed pigment cell formation and induced ectopic pressure organ. We show that pigment cell formation occurs in three steps. (1) During cleavage stages ectodermal cells are neuralized by a vegetal signal that can be substituted by bFGF. (2) At the early gastrula stage, BMPb secreted from the lateral nerve cord blastomeres induces those neuralized blastomeres in close proximity to adopt a pigment cell fate. (3) At the tailbud stage, among these pigment cell precursors, BMPb induces the differentiation of specifically the anterior type of pigment cell, the otolith; while posteriorly, CHORDIN suppresses BMP activity and allows ocellus differentiation.
Darras
S
S
Department of Biological Sciences, Tokyo Institute of Technology, Nagatsuta, Midori-ku, Yokohama, 226-8501, Japan. darras@ibdm.univ-mrs.fr
Nishida
H
H
D000818:Animals; D001757:Blastomeres / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D019521:Body Patterning / Q000187:drug effects; D019485:Bone Morphogenetic Proteins / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism; D001921:Brain / Q000166:cytology* / Q000187:drug effects / Q000196:embryology* / Q000378:metabolism; D002454:Cell Differentiation / Q000187:drug effects; D019070:Cell Lineage / Q000187:drug effects; D003001:Cloning, Molecular; D004475:Ectoderm / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D004625:Embryo, Nonmammalian / Q000166:cytology / Q000187:drug effects / Q000196:embryology / Q000378:metabolism; D004627:Embryonic Induction; D016222:Fibroblast Growth Factor 2 / Q000494:pharmacology; D005775:Gastrula / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D020869:Gene Expression Profiling; D018507:Gene Expression Regulation, Developmental; D006023:Glycoproteins / Q000235:genetics / Q000378:metabolism*; D007150:Immunohistochemistry; D017403:In Situ Hybridization; D036341:Intercellular Signaling Peptides and Proteins; D018878:Limb Buds / Q000166:cytology / Q000187:drug effects / Q000196:embryology / Q000378:metabolism; D008969:Molecular Sequence Data; D009432:Neural Crest / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D010860:Pigments, Biological / Q000378:metabolism*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D013234:Stem Cells / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D013623:Tail / Q000166:cytology / Q000187:drug effects / Q000196:embryology / Q000378:metabolism; D014561:Urochordata / Q000166:cytology / Q000187:drug effects / Q000196:embryology* / Q000378:metabolism
D019485:Bone Morphogenetic Proteins; D006023:Glycoproteins; D036341:Intercellular Signaling Peptides and Proteins; D010860:Pigments, Biological; D012333:RNA, Messenger; D016222:Fibroblast Growth Factor 2; C054234:chordin