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In Xenopus development, during meiosis and cleavage, the extent of polyadenylation plays a central role in regulating the expression of transcripts and this is mediated by cis regulatory cytoplasmic polyadenylation elements (CPE) in the 3'-UTRs. We have identified a palindromic CPE in the mRNA of Xenopus Id3 which is conserved in the Id genes from other vertebrates. It promotes cytoplasmic polyadenylation and is negatively regulated by sequences further upstream in the 3'-UTR. This palindromic CPE promotes polyadenylation in both the epithelial and sensorial layers of the dorsal ectoderm in early embryos, but association with the upstream negative element blocks this effect in the epithelial layer. The asymmetric polyadenylation may be important for establishing a prepattern of transcriptional regulators.
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10525185
???displayArticle.link???Mech Dev
Fig. 7. Localized expression of Gal-Glob mRNA microinjected into fertilized eggs. Gal-Glob RNA was synthesized in vitro and microinjected into embryos of one to two cell stage. Embryos were incubated at 218C until bastula (A), gastrula (B) and neurula (C) stage, stained for b-galactosidase and observed after making them transparent (A1) or as that in (B1, C1). Selected embryos were embedded in paraffin and observed in sections (A2, B2±B4, C2). A2 represents a lateral section cut in the blastocoel area. B2 and B3 represent transversal sections from the blastopore area and from the central part of the embryo respectively. B4 represents a transversal section obtained from a more advanced embryo in which neurulation had already been initiated. C2 represents a transversal section from the central part of the neurula. Animal cap (AC), blastocoel (Bc), epithelial layer (EL), sensorial layer (SL), involuting dorsal mesoderm (IDM), neural tube (NT), notochord (No) and somites (So) are indicated.
Fig. 8. Localized expression of Gal-CPWS mRNA microinjected into fertilized eggs. Gal-CPWS RNA was synthesized in vitro and microinjected into fertilized eggs of one to two cell stage. Embryos were incubated at 218C until blastula (A), gastrula (B) and neurula (C) stage, stained for b-galactosidase and observed after making them transparent (A1) or as that (B1, C1). Selected embryos were embedded in paraf®n and observed in sections (A2, B2±B4, C2). A2 represents a lateral section cut in the blastocoel area. B2 and B3 represent transversal sections from the blastopore area and from the region opposite to it, respectively. B4 is a sagittal section through the blastopore and the line shown represent the cut used to obtain sections as the one represented in B2. C2 represents a transverse section from the anterior half of the neurula. Animal cap (AC), blastocoel (Bc), epithelial layer (EL), sensorial layer (SL), involuting dorsal mesoderm (IDM), neural tube (NT), notochord (No) and somites (So) are indicated.
Fig. 9. Localized expression of GAL-PARS mRNA microinjected into fertilized eggs. Gal-PARS RNA was synthesized in vitro and microinjected into fertilized eggs of one to two cell stage. Embryos were incubated at 218C until blastula (A), gastrula (B) and neurula (C) stage, stained for b-galactosidase and observed after making them transparent (A1) or as that (B1, C1). Selected embryos were embedded in paraf®n and observed in sections (A2, B2-B4, C2). A2 represents a lateral section cut in the blastocoel area. B2, B3 and B4 represent sections from the blastopore area, from the central part of the embryo and from the area opposite to the blastopore respectively. C2 represents a transversal section through the central part of a neurula. Animal cap (AC), blastocoel (Bc), epithelial layer (EL), sensorial layer (SL), involuting dorsal mesoderm (IDM), neural tube (NT), notochord (No) and somites (So) are indicated.
Fig. 10. Localization of mRNA microinjected into fertilized eggs determined by in situ hybridization. Gal-Glob-, Gal-CPWS- and Gal-PARS-mRNA (A,B and C, respectively) were microinjected into fertilized eggs of 1-2 cell stage. Embryos were incubated at 218C and processed for whole mount in situ hybridization as described by Harland (1991). To prepare an RNA antisense probe, the central BamHI fragment from the Gal-Glob construct was first subcloned into the pVZ vector and then in vitro transcribed. Embryos were fixed at blastula (1) or gastrula stage (2). Removal of vitelline envelope was skipped. The control panel D1 and D2 show the pattern obtained with uninjected embryos hybridized with the same Gal-Glob probe. The blastocoel, below the animal cap, is indicated (Bc).
