Research

Vertebrate eye development

The vertebrate eye develops from precisely aligned tissues including the future retina (red) and lens (green). These tissues develop in a coordinated fashion, controlled by the interactive exchange of molecular signals.

Genes to geometry

The eye develops as a system of three-dimensional tissues. To learn how they take shape we must relate multi-scale regulatory information with the emergent geometry.

We developed software tools that align 3-D imaging data from multiple embryos in order to map molecular, genetic and cellular processes onto the developing anatomy.

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Aligning the lens and retina

Classical experiments suggested that the optic vesicle (future retina) instructs the lens to develop at the correct time and place, but the molecular nature of that instruction has remained elusive.

More recent work from the Streit lab showed that the optic vesicle's role is more permissive than instructive, because it shelters the future lens from the inhibitory influence of near-by neural crest cells - removing the neural crest cells causes ectopic lens development.

Building on previous work, we were able to determine the nature of this lens inhibition, establishing a molecular mechanism for the alignment of lens and retina.

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Controlling a 'master control gene'

The transcription factor-coding gene Pax6 has been called a 'master control gene' for eye development. Not only is it required for healthy eye development, it is also a potent activator of eye development: inappropriate activation of the Pax6 gene can cause eyes to develop ectopically.

It is therefore important to have a means of inhibiting Pax6 gene activity. We were able to identify one such mechanism - the TGF-beta signalling pathway is able to suppress activity of the Pax6 gene product.

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MH1 domain of Smad3 interacts with Pax6 and represses autoregulation of the Pax6 P1 promoter | Nucleic Acids Research | Oxford AcademicPax6 transcription is under the control of two main promoters (P0 and P1), and these are autoregulated by Pax6. Additionally, Pax6 expression is under the control of the TGFβ superfamily, although the precise mechanisms of such regulation are not understood. The effect of TGFβ on Pax6 expression was studied in the FHL124 lens epithelial cell line and was found to cause up to a 50% reduction in Pax6 mRNA levels within 24 h. Analysis of luciferase reporters showed that Pax6 autoregulation of the P1 promoter, and its induction of a synthetic promoter encoding six paired domain-binding sites, were significantly repressed by both an activated TGFβ receptor and TGFβ ligand stimulation. Subsequently, a novel Pax6 binding site in P1 was shown to be necessary for autoregulation, indicating a direct influence of Pax6 protein on P1. In transfected cells, and endogenously in FHL124 cells, Pax6 co-immunoprecipitated with Smad3 following TGFβ receptor activation, while in GST pull-down experiments, the MH1 domain of Smad3 was observed binding the RED sub-domain of the Pax6 paired domain. Finally, in DNA adsorption assays, activated Smad3 inhibited Pax6 from binding the consensus paired domain recognition sequence. We hypothesize that the Pax6 autoregulatory loop is targeted for repression by the TGFβ/Smad pathway, and conclude that this involves diminished paired domain DNA-binding function resulting from a ligand-dependant interaction between Pax6 and Smad3.