title: Blastopore formation and dorsal mesoderm induction are independent events in early Cynops embryogenesis.
abstract: The independent roles of blastopore formation and dorsal mesoderm induction in dorsal axis formation of the Cynops pyrrhogaster embryo were attempted to be clarified. The blastopore-forming (bottle) cells originated mainly from the progeny of the mid-dorsal C and/or D blastomeres of the 32-cell embryo, but were not defined to a fixed blastomere. It was confirmed that the isolated dorsal C and D blastomeres autonomously formed a blastopore. Ultraviolet-irradiated eggs formed an abnormal blastopore and then did not form a dorsal axis, although the lower dorsal marginal zone (LDMZ) still had dorsal mesoderm-inducing activity. Involution of the dorsal marginal zone was disturbed by the abnormal blastopore. These embryos were rescued by artificially facilitating involution of the dorsal marginal zone. Suramin-injected and nocodazole-treated blastulae did not have involution of the dorsal marginal zone, although the blastopore was formed. Neither embryos formed the dorsal axis. The dorsal mesoderm-inducing activity of the LDMZ in the nocodazole-treated gastrulae was still active. In contrast, the LDMZ of the suramin-injected embryos lost its dorsal mesoderm-inducing activity. bra expression was activated in the nocodazole-treated embryos but not in the suramin-injected embryos. The present study suggested that (i) the dorsal determinants consist of blastopore-forming and dorsal mesoderm-inducing factors, which are not always mutually dependent; (ii) both factors are activated during the late blastula stage; (iii) the dorsal marginal zone cannot specify to an organized notochord and muscle without the involution that blastopore formation leads to; and (iv) the localization of both factors in the same place is prerequisite for dorsal axis formation.
authors.affiliation: Department of Biological Science, Faculty of Science, Graduate School of Science and Technology, Kumamoto University, Kumamoto 860-8555, Japan. hanarie@symphony.plala.or.jp
authors.forename: Akio S
authors.initials: AS
authors.lastname: Suzuki
authors.forename: Koji
authors.initials: K
authors.lastname: Sakaguchi
authors.forename: Mineko
authors.initials: M
authors.lastname: Katagiri
authors.forename: Megumi
authors.initials: M
authors.lastname: Ueki
authors.forename: Teruo
authors.initials: T
authors.lastname: Kaneda
mesh_terms: D000663:Amphibians / Q000196:embryology*; D000818:Animals; D000970:Antineoplastic Agents / Q000008:administration & dosage / Q000494:pharmacology; D001757:Blastomeres / Q000502:physiology; D005775:Gastrula / Q000187:drug effects / Q000502:physiology* / Q000528:radiation effects; D051956:Goosecoid Protein; D018398:Homeodomain Proteins / Q000096:biosynthesis / Q000235:genetics; D008648:Mesoderm / Q000502:physiology*; D015739:Nocodazole / Q000494:pharmacology; D012097:Repressor Proteins; D013498:Suramin / Q000008:administration & dosage / Q000494:pharmacology; D014157:Transcription Factors; D014466:Ultraviolet Rays / Q000009:adverse effects
chemical_list: D000970:Antineoplastic Agents; D051956:Goosecoid Protein; D018398:Homeodomain Proteins; D012097:Repressor Proteins; D014157:Transcription Factors; D013498:Suramin; D015739:Nocodazole