Click here to close
Hello! We notice that you are using Internet Explorer, which is not supported by Xenbase and may cause the site to display incorrectly.
We suggest using a current version of Chrome,
FireFox, or Safari.
Nat Cell Biol
2008 May 01;105:567-74. doi: 10.1038/ncb1719.
Show Gene links
Show Anatomy links
A crucial role of a high mobility group protein HMGA2 in cardiogenesis.
Monzen K
,
Ito Y
,
Naito AT
,
Kasai H
,
Hiroi Y
,
Hayashi D
,
Shiojima I
,
Yamazaki T
,
Miyazono K
,
Asashima M
,
Nagai R
,
Komuro I
.
???displayArticle.abstract???
The high mobility group (HMG) of nuclear proteins regulates expression of many genes through architectural remodelling of the chromatin structure, and formation of multiprotein complexes on promoter/enhancer regions. This leads to the active transcription of their target genes. Here we show that HMGA2, a member of the HMGA sub-family of HMG proteins, has a critical function in cardiogenesis. Overexpression of HMGA2 enhanced, whereas siRNA-mediated knockdown of HMGA2 blocked, cardiomyocyte differentiation of the embryonal carcinoma cell line P19CL6. Moreover, overexpression of a dominant-negative HMGA2 or morpholino-mediated knockdown of HMGA2 expression blocked normal heart formation in Xenopus laevis embryos, suggesting that HMGA2 has an important role in cardiogenesis both in vitro and in vivo. Mechanistically, HMGA2 associated with Smad1/4 and showed synergistic trans-activation of the gene for a cardiac transcription factor Nkx2.5; a conserved HMGA2 binding site was required for the promoter activity of Nkx2.5 gene, both in P19CL6 cells and in transgenic Xenopus embryos. Thus, HMGA2 is a positive regulator of Nkx2.5 gene expression and is essential for normal cardiac development.
Figure 2. (a) Amino-acid sequences of XHMGA2 protein were compared with those of human (NM_001094371), mouse (NM_010441), rat (NM_032070), chicken (NM_205001) and zebrafish (NM_212680) HMGA2. Dots indicate identities and dashed lines are introduced to maximize the alignment. Boxes represent the three AT-hooks. (b) Expression of XHMGA2 mRNA during embryogenesis analysed by RT-PCR. Ornithine decarboxylase (ODC) represents internal controls. (c–h) Expression of XHMGA2 mRNA during embryogenesis analysed by in situ hybridization. Lateral (c) and ventral (d) view of stage-15 embryo. XHMGA2 expression was detected in neural crest (NC) and weakly in precardiac region (arrowhead). Lateral (e) and ventral (f) view of stage-23 embryo. XHMGA2 was expressed in anterior neural tissue (AN), tailbud (TB) and weakly in precardiac region (arrowhead). Lateral (g) and ventral (h) view of stage-32 embryo. XHMGA2 was detected in brain (BR), spinal cord (SC), eye anlage (EA), otic vesicle (OV), branchial arch (BA), pronephric duct (PD) and heart anlage (arrowhead). Anterior is left and dorsal is top for c, e, g, and anterior is left for d, f, h.
Figure 3. (a–d) Overexpression of a dominant-negative XHMGA2 mutant in Xenopus embryos blocked XNkx2.5 expression. Ventral view of stage-23 (a, b) and lateral view of stage-34 (c, d) embryos. Expression of XNkx2.5 mRNA was decreased in XHMGA2–EnR mRNA-injected embryos (b, d, arrowheads), compared with that of control embryos (a, c, arrowheads). (e–p) MO-mediated XHMGA2 knockdown results in impaired cardiogenesis. Whole-mount in situ hybridization analysis was performed sequentially for Xenopus embryos at stage 15 (e–g), stage 23 (h–j) and stage 34 (k–m) for XNkx2.5, and at stage 41 for cardiac troponin I (cTnI) (n–p). Expression of XNkx2.5 mRNA was detected in uninjected control embryos (e, h, k, arrows), whereas it was attenuated in both XHMGA2–MO1 (f, i, l) and XHMGA2–MO2 (g, j, m)-injected embryos (arrowheads). In situ hybridization analysis for cardiac troponin I revealed that the heart size in MO-injected embryos (o, p, arrowheads) was smaller than that of control embryos (n, arrows).
hmga2 (high mobility group AT-hook 2) gene expression in Xenopus laevis embryo, assayed via in situ hybridization, NF stage 15, lateral view, anteriorleft, dorsal up.
hmga2 (high mobility group AT-hook 2) gene expression in Xenopus laevis embryo, assayed via in situ hybridization, NF stage 15, ventral view, anteriorleft.
hmga2 (high mobility group AT-hook 2) gene expression in Xenopus laevis embryo, assayed via in situ hybridization, NF stage 23, ventral view, anterior left
hmga2 (high mobility group AT-hook 2) gene expression in Xenopus laevis embryo, assayed via in situ hybridization, NF stage 23, lateral view, anteriorleft, dorsal up.
hmga2 (high mobility group AT-hook 2) gene expression in Xenopus laevis embryo, assayed via in situ hybridization, NF stage 32, lateral view, anteriorleft, dorsal up.
hmga2 (high mobility group AT-hook 2) gene expression in Xenopus laevis embryo, assayed via in situ hybridization, NF stage 32, lateral view, anteriorleft, dorsal up.
Figure S5 Effects of XHMGA2 knockdown on cardiac, liver/thyroid, and endothelial marker gene expression. Whole-mount in situ hybridizations was performed at stage 34. a-c. XNkx2.5 expression in uninjected (a), MO1-injected (b), and MO2-injected embryos (c). XNkx2.5 expression was downregulated by XHMGA2 knockdown. d-f. Liver and thyroid gland development was verified by the expression of XHex in uninjected (d),
MO1-injected (e), and MO2-injected embryos (f). Expression of the XHex mRNA was attenuated in liver (arrowhead) and lost in thyroid gland (asterisk) by XHMGA2 knockdown. g-i. Vascular formation was verified by the expression of Xmsr in uninjected (g), MO1-injected (h), and MO2- injected embryos (i). Vascular patterning was perturbed (asterisks) by XHMGA2 knockdown.
