Limits...
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.

Show MeSH

Related in: MedlinePlus

Induction of Tbx2 and Tbx5 expression by exogenous BMP4. (A, B) Dorsal views of post-culture embryos showing ectopic expression of Tbx2 (A) and Tbx5 (B) in the proximal optic vesicle (arrowheads) after implantation of a BMP4-soaked bead in the peri-ocular mesenchyme (asterisks). Expression is extended into the presumptive RPE on the treated side but restricted to the presumptive neural retina on the contralateral non-treated side shown by transverse sections through the optic vesicle (arrowheads,C-F). (G, H) Lateral views of a post-culture embryo showing normal Tbx5 expression in the non-treated eye (G) and increased Tbx5 expression after implantation of a BMP4-soaked bead in the periocular mesenchyme (H). Arrows demarcate the Tbx5 expression domain. (I-J) Transverse sections of the non-treated and BMP4-treated contralateral eyes showing the extended Tbx5 expression into the presumptive RPE next to the BMP4-soaked bead (arrow). (K-N) Serial transverse sections showing normal Tbx2 expression in a control eye (K, M) and the extension of Tbx2 expression ventrally after implantation of a BMP4-soaked bead in the treated eye (L, N). Sections M and N are immediately ventral to sections K and L. Scale bars: A, B, 0.1 mm; C-F, 0.05 mm; G, H, 0.5 mm; I-N, 0.1 mm. Abbreviations: L, lens vesicle; MN, mandibular region of the first branchial arch; MX, maxillary region of the first branchial arch; N, nasal; NR, neural retina; P-NR, presumptive neural retina; OS, optic stalk; P-RPE, presumptive retinal pigmented epithelium; T, temporal.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC1764729&req=5

Figure 3: Induction of Tbx2 and Tbx5 expression by exogenous BMP4. (A, B) Dorsal views of post-culture embryos showing ectopic expression of Tbx2 (A) and Tbx5 (B) in the proximal optic vesicle (arrowheads) after implantation of a BMP4-soaked bead in the peri-ocular mesenchyme (asterisks). Expression is extended into the presumptive RPE on the treated side but restricted to the presumptive neural retina on the contralateral non-treated side shown by transverse sections through the optic vesicle (arrowheads,C-F). (G, H) Lateral views of a post-culture embryo showing normal Tbx5 expression in the non-treated eye (G) and increased Tbx5 expression after implantation of a BMP4-soaked bead in the periocular mesenchyme (H). Arrows demarcate the Tbx5 expression domain. (I-J) Transverse sections of the non-treated and BMP4-treated contralateral eyes showing the extended Tbx5 expression into the presumptive RPE next to the BMP4-soaked bead (arrow). (K-N) Serial transverse sections showing normal Tbx2 expression in a control eye (K, M) and the extension of Tbx2 expression ventrally after implantation of a BMP4-soaked bead in the treated eye (L, N). Sections M and N are immediately ventral to sections K and L. Scale bars: A, B, 0.1 mm; C-F, 0.05 mm; G, H, 0.5 mm; I-N, 0.1 mm. Abbreviations: L, lens vesicle; MN, mandibular region of the first branchial arch; MX, maxillary region of the first branchial arch; N, nasal; NR, neural retina; P-NR, presumptive neural retina; OS, optic stalk; P-RPE, presumptive retinal pigmented epithelium; T, temporal.

Mentions: Exogenous BMP4 induced ectopic Tbx2 and Tbx5 expression in the proximal optic vesicle, the presumptive RPE (Table 1; Fig. 3A–F). The extension of the normal expression domain is visible in dorsal views of the embryos (Fig. 3A,B). Transverse sections showed Tbx2 and Tbx5 up-regulation in the presumptive RPE that normally does not express the T-box genes, with Tbx2 showing the most marked response (Fig. 3C,D). On the non-treated side, as well as in control embryos implanted with BSA-soaked beads, T-box gene expression was restricted to the dorso-distal optic vesicle (Fig. 3A,B,E,F and data not shown).


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)

Induction of Tbx2 and Tbx5 expression by exogenous BMP4. (A, B) Dorsal views of post-culture embryos showing ectopic expression of Tbx2 (A) and Tbx5 (B) in the proximal optic vesicle (arrowheads) after implantation of a BMP4-soaked bead in the peri-ocular mesenchyme (asterisks). Expression is extended into the presumptive RPE on the treated side but restricted to the presumptive neural retina on the contralateral non-treated side shown by transverse sections through the optic vesicle (arrowheads,C-F). (G, H) Lateral views of a post-culture embryo showing normal Tbx5 expression in the non-treated eye (G) and increased Tbx5 expression after implantation of a BMP4-soaked bead in the periocular mesenchyme (H). Arrows demarcate the Tbx5 expression domain. (I-J) Transverse sections of the non-treated and BMP4-treated contralateral eyes showing the extended Tbx5 expression into the presumptive RPE next to the BMP4-soaked bead (arrow). (K-N) Serial transverse sections showing normal Tbx2 expression in a control eye (K, M) and the extension of Tbx2 expression ventrally after implantation of a BMP4-soaked bead in the treated eye (L, N). Sections M and N are immediately ventral to sections K and L. Scale bars: A, B, 0.1 mm; C-F, 0.05 mm; G, H, 0.5 mm; I-N, 0.1 mm. Abbreviations: L, lens vesicle; MN, mandibular region of the first branchial arch; MX, maxillary region of the first branchial arch; N, nasal; NR, neural retina; P-NR, presumptive neural retina; OS, optic stalk; P-RPE, presumptive retinal pigmented epithelium; T, temporal.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 3: Induction of Tbx2 and Tbx5 expression by exogenous BMP4. (A, B) Dorsal views of post-culture embryos showing ectopic expression of Tbx2 (A) and Tbx5 (B) in the proximal optic vesicle (arrowheads) after implantation of a BMP4-soaked bead in the peri-ocular mesenchyme (asterisks). Expression is extended into the presumptive RPE on the treated side but restricted to the presumptive neural retina on the contralateral non-treated side shown by transverse sections through the optic vesicle (arrowheads,C-F). (G, H) Lateral views of a post-culture embryo showing normal Tbx5 expression in the non-treated eye (G) and increased Tbx5 expression after implantation of a BMP4-soaked bead in the periocular mesenchyme (H). Arrows demarcate the Tbx5 expression domain. (I-J) Transverse sections of the non-treated and BMP4-treated contralateral eyes showing the extended Tbx5 expression into the presumptive RPE next to the BMP4-soaked bead (arrow). (K-N) Serial transverse sections showing normal Tbx2 expression in a control eye (K, M) and the extension of Tbx2 expression ventrally after implantation of a BMP4-soaked bead in the treated eye (L, N). Sections M and N are immediately ventral to sections K and L. Scale bars: A, B, 0.1 mm; C-F, 0.05 mm; G, H, 0.5 mm; I-N, 0.1 mm. Abbreviations: L, lens vesicle; MN, mandibular region of the first branchial arch; MX, maxillary region of the first branchial arch; N, nasal; NR, neural retina; P-NR, presumptive neural retina; OS, optic stalk; P-RPE, presumptive retinal pigmented epithelium; T, temporal.
Mentions: Exogenous BMP4 induced ectopic Tbx2 and Tbx5 expression in the proximal optic vesicle, the presumptive RPE (Table 1; Fig. 3A–F). The extension of the normal expression domain is visible in dorsal views of the embryos (Fig. 3A,B). Transverse sections showed Tbx2 and Tbx5 up-regulation in the presumptive RPE that normally does not express the T-box genes, with Tbx2 showing the most marked response (Fig. 3C,D). On the non-treated side, as well as in control embryos implanted with BSA-soaked beads, T-box gene expression was restricted to the dorso-distal optic vesicle (Fig. 3A,B,E,F and data not shown).

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