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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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Expression of Bmp4, Tbx2, Tbx3, Tbx5, and Vax2 during optic cup formation. (A-C) Bmp4 co-expressed with Tbx5 and Tbx2 in the optic vesicle at E9.5 (arrows; 15 somite stage). Black arrowhead in A indicates Bmp4 expression in the surface ectoderm. White arrowheads indicate expression in mesenchyme ventral to the developing eye. (D-F) Bmp4, Tbx5 and Tbx2 expression in the invaginating optic vesicle at E10.5 (24–29 somite stage). (G, H) Bmp4 and Tbx5 expression at E11.5 in the optic cup in dorsal domain 1, shown schematically in I. (J) Tbx5 expression in dorsal domain 1 in an E11.5 dissected optic cup. (K) Tbx3 expression in dorsal domain 1 and its extension into dorsal domain 2 in the temporal neural retina. (L) Tbx2 expression in domains 1 and 2, shown schematically in M. (N) Tbx3 expression in an E11.5 dissected optic cup. (O) Vax2 expression at E11.5 in the ventral optic cup in domain 4. (P) Double labeling of Tbx2 (red) and Vax2 (blue) shows a domain in between domain 2 and domain 4, which does not express either marker, and is designated domain 3, shown schematically in Q. (R) Tbx2 (red) and Vax2 (blue) expression in an E11.5 dissected optic cup, revealing domain 3 in white. Arrows in G-R indicate the boundaries of gene expression domains. Dashed circles in J, N, R demarcate the lens vesicle. A-F are coronal sections. Scale bars: A-F, 0.05 mm; G, H, K, L, O, P, 0.5 mm; J, N, R, 0.1 mm. Abbreviations: L, lens placode; MN, mandibular process of the first branchial arch; NR, neural retina; P-NR, presumptive neural retina; D-V indicates the dorso-ventral axis, N-T indicates the naso-temporal axis.
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Figure 1: Expression of Bmp4, Tbx2, Tbx3, Tbx5, and Vax2 during optic cup formation. (A-C) Bmp4 co-expressed with Tbx5 and Tbx2 in the optic vesicle at E9.5 (arrows; 15 somite stage). Black arrowhead in A indicates Bmp4 expression in the surface ectoderm. White arrowheads indicate expression in mesenchyme ventral to the developing eye. (D-F) Bmp4, Tbx5 and Tbx2 expression in the invaginating optic vesicle at E10.5 (24–29 somite stage). (G, H) Bmp4 and Tbx5 expression at E11.5 in the optic cup in dorsal domain 1, shown schematically in I. (J) Tbx5 expression in dorsal domain 1 in an E11.5 dissected optic cup. (K) Tbx3 expression in dorsal domain 1 and its extension into dorsal domain 2 in the temporal neural retina. (L) Tbx2 expression in domains 1 and 2, shown schematically in M. (N) Tbx3 expression in an E11.5 dissected optic cup. (O) Vax2 expression at E11.5 in the ventral optic cup in domain 4. (P) Double labeling of Tbx2 (red) and Vax2 (blue) shows a domain in between domain 2 and domain 4, which does not express either marker, and is designated domain 3, shown schematically in Q. (R) Tbx2 (red) and Vax2 (blue) expression in an E11.5 dissected optic cup, revealing domain 3 in white. Arrows in G-R indicate the boundaries of gene expression domains. Dashed circles in J, N, R demarcate the lens vesicle. A-F are coronal sections. Scale bars: A-F, 0.05 mm; G, H, K, L, O, P, 0.5 mm; J, N, R, 0.1 mm. Abbreviations: L, lens placode; MN, mandibular process of the first branchial arch; NR, neural retina; P-NR, presumptive neural retina; D-V indicates the dorso-ventral axis, N-T indicates the naso-temporal axis.

Mentions: The expression pattern of Bmp4 and members of the Tbx2 subfamily were compared during development of the optic cup in mouse embryos. Bmp4 expression was detected in the dorso-distal optic vesicle from E9.5 (Fig. 1A, somite stage 15) in the region of neuroepithelium contacting the surface ectoderm. The distal optic vesicle is the presumptive neural retina. Tbx5 and Tbx2 were expressed in a similar region of the presumptive neural retina as Bmp4 at this stage (Fig. 1B,C). Bmp4 and Tbx2, but not Tbx5 were expressed in the mesenchyme ventral to the optic vesicle (white arrowheads in Fig. 1A and 1C). Bmp4 was also expressed in the surface ectoderm (Fig. 1A, black arrowhead), as previously reported [26].


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)

Expression of Bmp4, Tbx2, Tbx3, Tbx5, and Vax2 during optic cup formation. (A-C) Bmp4 co-expressed with Tbx5 and Tbx2 in the optic vesicle at E9.5 (arrows; 15 somite stage). Black arrowhead in A indicates Bmp4 expression in the surface ectoderm. White arrowheads indicate expression in mesenchyme ventral to the developing eye. (D-F) Bmp4, Tbx5 and Tbx2 expression in the invaginating optic vesicle at E10.5 (24–29 somite stage). (G, H) Bmp4 and Tbx5 expression at E11.5 in the optic cup in dorsal domain 1, shown schematically in I. (J) Tbx5 expression in dorsal domain 1 in an E11.5 dissected optic cup. (K) Tbx3 expression in dorsal domain 1 and its extension into dorsal domain 2 in the temporal neural retina. (L) Tbx2 expression in domains 1 and 2, shown schematically in M. (N) Tbx3 expression in an E11.5 dissected optic cup. (O) Vax2 expression at E11.5 in the ventral optic cup in domain 4. (P) Double labeling of Tbx2 (red) and Vax2 (blue) shows a domain in between domain 2 and domain 4, which does not express either marker, and is designated domain 3, shown schematically in Q. (R) Tbx2 (red) and Vax2 (blue) expression in an E11.5 dissected optic cup, revealing domain 3 in white. Arrows in G-R indicate the boundaries of gene expression domains. Dashed circles in J, N, R demarcate the lens vesicle. A-F are coronal sections. Scale bars: A-F, 0.05 mm; G, H, K, L, O, P, 0.5 mm; J, N, R, 0.1 mm. Abbreviations: L, lens placode; MN, mandibular process of the first branchial arch; NR, neural retina; P-NR, presumptive neural retina; D-V indicates the dorso-ventral axis, N-T indicates the naso-temporal axis.
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Related In: Results  -  Collection

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Figure 1: Expression of Bmp4, Tbx2, Tbx3, Tbx5, and Vax2 during optic cup formation. (A-C) Bmp4 co-expressed with Tbx5 and Tbx2 in the optic vesicle at E9.5 (arrows; 15 somite stage). Black arrowhead in A indicates Bmp4 expression in the surface ectoderm. White arrowheads indicate expression in mesenchyme ventral to the developing eye. (D-F) Bmp4, Tbx5 and Tbx2 expression in the invaginating optic vesicle at E10.5 (24–29 somite stage). (G, H) Bmp4 and Tbx5 expression at E11.5 in the optic cup in dorsal domain 1, shown schematically in I. (J) Tbx5 expression in dorsal domain 1 in an E11.5 dissected optic cup. (K) Tbx3 expression in dorsal domain 1 and its extension into dorsal domain 2 in the temporal neural retina. (L) Tbx2 expression in domains 1 and 2, shown schematically in M. (N) Tbx3 expression in an E11.5 dissected optic cup. (O) Vax2 expression at E11.5 in the ventral optic cup in domain 4. (P) Double labeling of Tbx2 (red) and Vax2 (blue) shows a domain in between domain 2 and domain 4, which does not express either marker, and is designated domain 3, shown schematically in Q. (R) Tbx2 (red) and Vax2 (blue) expression in an E11.5 dissected optic cup, revealing domain 3 in white. Arrows in G-R indicate the boundaries of gene expression domains. Dashed circles in J, N, R demarcate the lens vesicle. A-F are coronal sections. Scale bars: A-F, 0.05 mm; G, H, K, L, O, P, 0.5 mm; J, N, R, 0.1 mm. Abbreviations: L, lens placode; MN, mandibular process of the first branchial arch; NR, neural retina; P-NR, presumptive neural retina; D-V indicates the dorso-ventral axis, N-T indicates the naso-temporal axis.
Mentions: The expression pattern of Bmp4 and members of the Tbx2 subfamily were compared during development of the optic cup in mouse embryos. Bmp4 expression was detected in the dorso-distal optic vesicle from E9.5 (Fig. 1A, somite stage 15) in the region of neuroepithelium contacting the surface ectoderm. The distal optic vesicle is the presumptive neural retina. Tbx5 and Tbx2 were expressed in a similar region of the presumptive neural retina as Bmp4 at this stage (Fig. 1B,C). Bmp4 and Tbx2, but not Tbx5 were expressed in the mesenchyme ventral to the optic vesicle (white arrowheads in Fig. 1A and 1C). Bmp4 was also expressed in the surface ectoderm (Fig. 1A, black arrowhead), as previously reported [26].

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