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First published online 19 July 2006
doi: 10.1242/dev.02493

Development 133, 3179-3190 (2006)
Published by The Company of Biologists 2006
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Proper patterning of the optic fissure requires the sequential activity of BMP7 and SHH

Julian Morcillo1, Juan Ramon Martínez-Morales1,*, Françoise Trousse1,{dagger}, Yasmin Fermin1, Jane C. Sowden2 and Paola Bovolenta1,{ddagger}

1 Departamento de Neurobiología del Desarrollo, Instituto Cajal, CSIC, Dr Arce 37, Madrid 28002, Spain.
2 Developmental Biology Unit, Institute of Child Health, 30 Guilford Street, University College London, London WC1N 1EH, UK.

{ddagger} Author for correspondence (e-mail: bovolenta{at}cajal.csic.es)

Accepted 14 June 2006

The optic disc develops at the interface between optic stalk and retina, and enables both the exit of visual fibres and the entrance of mesenchymal cells that will form the hyaloid artery. In spite of the importance of the optic disc for eye function, little is known about the mechanisms that control its development. Here, we show that in mouse embryos, retinal fissure precursors can be recognised by the expression of netrin 1 and the overlapping distribution of both optic stalk (Pax2, Vax1) and ventral neural retina markers (Vax2, Raldh3). We also show that in the absence of Bmp7, fissure formation is not initiated. This absence is associated with a reduced cell proliferation and apoptosis in the proximoventral quadrant of the optic cup, lack of the hyaloid artery, optic nerve aplasia, and intra-retinal misrouting of RGC axons. BMP7 addition to organotypic cultures of optic vesicles from Bmp7-/- embryos rescues Pax2 expression in the ventral region, while follistatin, a BMP7 antagonist, prevents it in early, but not in late, optic vesicle cultures from wild-type embryos. The presence of Pax2-positive cells in late optic cup is instead abolished by interfering with Shh signalling. Furthermore, SHH addition re-establishes Pax2 expression in late optic cups derived from ocular retardation (or) embryos, where optic disc development is impaired owing to the near absence of SHH-producing RGC. Collectively, these data indicate that BMP7 is required for retinal fissure formation and that its activity is needed, before SHH signalling, for the generation of PAX2-positive cells at the optic disc.

Key words: Mouse, Optic fissure, BMP, SHH


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