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The level of BMP4 signaling is critical for the regulation of distinct T-box gene expression domains and growth along the dorso-ventral axis of the optic cup.

Behesti H, Holt JK, Sowden JC - BMC Dev. Biol. (2006)

Bottom Line: Increased levels of BMP4 signaling caused decreased proliferation, reduced retinal volume and altered the shape of the optic cup.Our findings suggest the existence of a dorsal-high, ventral-low BMP4 signaling gradient across which distinct domains of Tbx2, Tbx3, Tbx5 and Vax2 transcription factor gene expression are set up.Furthermore we show that the correct level of BMP4 signaling is critical for normal growth of the mammalian embryonic eye.

View Article: PubMed Central - HTML - PubMed

Affiliation: Developmental Biology Unit, Institute of Child Health, University College London, 30 Guilford Street, London, WC1N 1EH, UK. h.behesti@ich.ucl.ac.uk <h.behesti@ich.ucl.ac.uk>

ABSTRACT

Background: Polarised gene expression is thought to lead to the graded distribution of signaling molecules providing a patterning mechanism across the embryonic eye. Bone morphogenetic protein 4 (Bmp4) is expressed in the dorsal optic vesicle as it transforms into the optic cup. Bmp4 deletions in human and mouse result in failure of eye development, but little attempt has been made to investigate mammalian targets of BMP4 signaling. In chick, retroviral gene overexpression studies indicate that Bmp4 activates the dorsally expressed Tbx5 gene, which represses ventrally expressed cVax. It is not known whether the Tbx5 related genes, Tbx2 and Tbx3, are BMP4 targets in the mammalian retina and whether BMP4 acts at a distance from its site of expression. Although it is established that Drosophila Dpp (homologue of vertebrate Bmp4) acts as a morphogen, there is little evidence that BMP4 gradients are interpreted to create domains of BMP4 target gene expression in the mouse.

Results: Our data show that the level of BMP4 signaling is critical for the regulation of distinct Tbx2, Tbx3, Tbx5 and Vax2 gene expression domains along the dorso-ventral axis of the mouse optic cup. BMP4 signaling gradients were manipulated in whole mouse embryo cultures during optic cup development, by implantation of beads soaked in BMP4, or the BMP antagonist Noggin, to provide a local signaling source. Tbx2, Tbx3 and Tbx5, showed a differential response to alterations in the level of BMP4 along the entire dorso-ventral axis of the optic cup, suggesting that BMP4 acts across a distance. Increased levels of BMP4 caused expansion of Tbx2 and Tbx3, but not Tbx5, into the ventral retina and repression of the ventral marker Vax2. Conversely, Noggin abolished Tbx5 expression but only shifted Tbx2 expression dorsally. Increased levels of BMP4 signaling caused decreased proliferation, reduced retinal volume and altered the shape of the optic cup.

Conclusion: Our findings suggest the existence of a dorsal-high, ventral-low BMP4 signaling gradient across which distinct domains of Tbx2, Tbx3, Tbx5 and Vax2 transcription factor gene expression are set up. Furthermore we show that the correct level of BMP4 signaling is critical for normal growth of the mammalian embryonic eye.

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Effect of BMP4 treatment on eye size and shape. (A) Retinal volume in BMP4-treated and contralateral BSA-treated eyes estimated from four post-culture embryos and represented by bar charts as mean ± 1 S.D. p = 0.033 by the paired t-test indicates a significant reduction in retinal volume in BMP4-treated eyes. (B, C) Coronal sections of control (B) and contralateral BMP4-treated (C) eyes stained with H&E and showing a reduction in eye size and retinal thickness upon BMP4-treatment. Scale bars: 0.05 mm.
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Figure 6: Effect of BMP4 treatment on eye size and shape. (A) Retinal volume in BMP4-treated and contralateral BSA-treated eyes estimated from four post-culture embryos and represented by bar charts as mean ± 1 S.D. p = 0.033 by the paired t-test indicates a significant reduction in retinal volume in BMP4-treated eyes. (B, C) Coronal sections of control (B) and contralateral BMP4-treated (C) eyes stained with H&E and showing a reduction in eye size and retinal thickness upon BMP4-treatment. Scale bars: 0.05 mm.

Mentions: BMP4-treated eyes of E11.5 embryos, displaying a ventral shift in Tbx2 subfamily gene expression domains, were examined for morphological abnormalities. These eyes appeared smaller in size and this difference was analysed by estimating retinal volumes. Retina from BMP4-treated eyes were consistently smaller than those of contralateral eyes treated with BSA control beads (n = 4 embryos; mean volume ± 1 S.D., BMP4-treated retina = 7.35 × 10-3 mm3 ± 2.3 × 10-3; mean volume ± 1 S.D., BSA-treated retina = 10.90 × 10-3 mm3 ± 1.95 × 10-3; p = 0.033; Fig. 6A).


The level of BMP4 signaling is critical for the regulation of distinct T-box gene expression domains and growth along the dorso-ventral axis of the optic cup.

Behesti H, Holt JK, Sowden JC - BMC Dev. Biol. (2006)

Effect of BMP4 treatment on eye size and shape. (A) Retinal volume in BMP4-treated and contralateral BSA-treated eyes estimated from four post-culture embryos and represented by bar charts as mean ± 1 S.D. p = 0.033 by the paired t-test indicates a significant reduction in retinal volume in BMP4-treated eyes. (B, C) Coronal sections of control (B) and contralateral BMP4-treated (C) eyes stained with H&E and showing a reduction in eye size and retinal thickness upon BMP4-treatment. Scale bars: 0.05 mm.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC1764729&req=5

Figure 6: Effect of BMP4 treatment on eye size and shape. (A) Retinal volume in BMP4-treated and contralateral BSA-treated eyes estimated from four post-culture embryos and represented by bar charts as mean ± 1 S.D. p = 0.033 by the paired t-test indicates a significant reduction in retinal volume in BMP4-treated eyes. (B, C) Coronal sections of control (B) and contralateral BMP4-treated (C) eyes stained with H&E and showing a reduction in eye size and retinal thickness upon BMP4-treatment. Scale bars: 0.05 mm.
Mentions: BMP4-treated eyes of E11.5 embryos, displaying a ventral shift in Tbx2 subfamily gene expression domains, were examined for morphological abnormalities. These eyes appeared smaller in size and this difference was analysed by estimating retinal volumes. Retina from BMP4-treated eyes were consistently smaller than those of contralateral eyes treated with BSA control beads (n = 4 embryos; mean volume ± 1 S.D., BMP4-treated retina = 7.35 × 10-3 mm3 ± 2.3 × 10-3; mean volume ± 1 S.D., BSA-treated retina = 10.90 × 10-3 mm3 ± 1.95 × 10-3; p = 0.033; Fig. 6A).

Bottom Line: Increased levels of BMP4 signaling caused decreased proliferation, reduced retinal volume and altered the shape of the optic cup.Our findings suggest the existence of a dorsal-high, ventral-low BMP4 signaling gradient across which distinct domains of Tbx2, Tbx3, Tbx5 and Vax2 transcription factor gene expression are set up.Furthermore we show that the correct level of BMP4 signaling is critical for normal growth of the mammalian embryonic eye.

View Article: PubMed Central - HTML - PubMed

Affiliation: Developmental Biology Unit, Institute of Child Health, University College London, 30 Guilford Street, London, WC1N 1EH, UK. h.behesti@ich.ucl.ac.uk <h.behesti@ich.ucl.ac.uk>

ABSTRACT

Background: Polarised gene expression is thought to lead to the graded distribution of signaling molecules providing a patterning mechanism across the embryonic eye. Bone morphogenetic protein 4 (Bmp4) is expressed in the dorsal optic vesicle as it transforms into the optic cup. Bmp4 deletions in human and mouse result in failure of eye development, but little attempt has been made to investigate mammalian targets of BMP4 signaling. In chick, retroviral gene overexpression studies indicate that Bmp4 activates the dorsally expressed Tbx5 gene, which represses ventrally expressed cVax. It is not known whether the Tbx5 related genes, Tbx2 and Tbx3, are BMP4 targets in the mammalian retina and whether BMP4 acts at a distance from its site of expression. Although it is established that Drosophila Dpp (homologue of vertebrate Bmp4) acts as a morphogen, there is little evidence that BMP4 gradients are interpreted to create domains of BMP4 target gene expression in the mouse.

Results: Our data show that the level of BMP4 signaling is critical for the regulation of distinct Tbx2, Tbx3, Tbx5 and Vax2 gene expression domains along the dorso-ventral axis of the mouse optic cup. BMP4 signaling gradients were manipulated in whole mouse embryo cultures during optic cup development, by implantation of beads soaked in BMP4, or the BMP antagonist Noggin, to provide a local signaling source. Tbx2, Tbx3 and Tbx5, showed a differential response to alterations in the level of BMP4 along the entire dorso-ventral axis of the optic cup, suggesting that BMP4 acts across a distance. Increased levels of BMP4 caused expansion of Tbx2 and Tbx3, but not Tbx5, into the ventral retina and repression of the ventral marker Vax2. Conversely, Noggin abolished Tbx5 expression but only shifted Tbx2 expression dorsally. Increased levels of BMP4 signaling caused decreased proliferation, reduced retinal volume and altered the shape of the optic cup.

Conclusion: Our findings suggest the existence of a dorsal-high, ventral-low BMP4 signaling gradient across which distinct domains of Tbx2, Tbx3, Tbx5 and Vax2 transcription factor gene expression are set up. Furthermore we show that the correct level of BMP4 signaling is critical for normal growth of the mammalian embryonic eye.

Show MeSH
Related in: MedlinePlus