XB-ART-45709Mech Dev 2012 Jan 01;1299-12:263-74. doi: 10.1016/j.mod.2012.07.001.
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High mobility group B proteins regulate mesoderm formation and dorsoventral patterning during zebrafish and Xenopus early development.
The high mobility group (HMG) proteins constitute a superfamily of nuclear proteins that regulate the expression of a wide range of genes through architectural remodeling of the chromatin structure, and the formation of multiple protein complexes on promoter/enhancer regions, but their function in germ layer specification during early development is not clear. Here we show that hmgb genes regulate mesoderm formation and dorsoventral patterning both in zebrafish and Xenopus early embryos. Overexpression of hmgb3 blocks the expression of the pan-mesoderm gene no tail/Xbra and other ventrolateral mesoderm genes, and results in embryos with shortened anteroposterior axis, while overexpression of hmgb3EnR, which contains the engrailed repressor domain, most potently repressed no tail expression and mesoderm formation. However, hmgb3VP16, which contains the transcriptional activation domain of VP16, had an opposite effect, indicating that hmgb3 may function as a repressor during mesoderm induction and patterning. In addition, we show that hmgb3 inhibits target gene expression downstream of mesoderm-inducing factors. Furthermore, using reporter gene assays in Xenopus whole embryos, we show that hmgb3 differentially regulates the activation of various mesendoderm reporter genes. In particular, it up-regulates the goosecoid, but inhibits the Xbra reporter gene activation. Therefore, our results suggest that hmgb genes may function to fine-tune the specification and/or dorsoventral patterning of mesoderm during zebrafish and Xenopus development.
PubMed ID: 22820002
Article link: Mech Dev
Species referenced: Xenopus
Genes referenced: fn1 foxi1 gsc hmgb3 krt12.4 sox2 sox3 tbxt wnt8a
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|Fig. 6 – Wild-type HMGB3 and HMGB3 mutants inhibit the mesoderm-inducing activity of exogenous factors in zebrafish and Xenopus embryos. (A–K) Animal pole view of ntl (A–G) and gsc (H–K) expression at the 50% epiboly stage of zebrafish embryos previously injected with the mRNAs as indicated on the top. (L) RT-PCR analysis of Xbra and wnt8 gene expression in Xenopus ectoderm explants previously injected with the indicated mRNAs. Fibronectin (FN) was used as an input control. (M) Quantification of Xbra and wnt8 expression level in L. The intensity of Xbra and wnt8 was normalized to that of FN.|
|Fig. 7 – HMGB3 and HMGB3DC inhibit mesoderm gene expression and mesoderm formation in Xenopus whole embryo. Synthetic mRNA was injected along with the Lac Z mRNA as a cell lineage tracer at the 4-cell stage and in situ hybridization was performed using the markers as indicated on the top at the early gastrula (A–I), late gastrula (J–Q) or tail-bud (P–R) stage in control or injected embryos as indicated on the left. (A–C) Vegetal view of Xbra expression. (D–F) Dorso-vegetal view of type II cytokeratin expression. (G–I) Dorso-vegetal view of Xema expression. (J–L) Dorso-vegetal view of sox2 expression. (M–O) Dorsal view of sox3 expression. (P–R) Lateral view of myosin light chain (MLC) expression. Arrows indicate the dorsal lip of blastopore.|