Sonic hedgehog expression is disrupted following in ovo ethanol exposure during early chick eye development

- Molecular analysis showed that ethanol had no effect on Shh transcription in our chick embryo model of ethanol-induced microphthalmia.
- However, ethanol exposure did significantly impair Shh-N protein production.
- Surprisingly, downstream Shh pathway members (Ptc, Gli1 and Gli3) were not altered by ethanol exposure.
- Ethanol's disruption of Shh may be mediated through an alternative mechanism independent of the classical signalling pathway.
- Other Shh-related pathways such as Bmp4 and Pax6, which are critical to eye development, clearly need further exploration.

The eye is particularly sensitive to ethanol's teratogenic effects. Our previous work, using a chick embryo model system, has shown that ethanol acts rapidly to perturb vital processes of early eye development producing defects of the lens and retina. Ethanol-induced disruption of the midline ventral telencephalon, a key site for expression of ocular morphogens such as sonic hedgehog (Shh), was further established. Consequently, in this study we have examined the effects of ethanol on the Shh pathway during the period of optic vesicle/optic cup formation. Chick embryos were injected in ovo with 125 μL of a 20% ethanol solution directly into the yolk-sac at HH-stage 7, resulting in peak ethanol uptake of 0.294 g/dL. Subsequent molecular analysis at 12, 24 and 48 h post-treatment revealed that ethanol had no affect on Shh transcription, while, a significant reduction in the expression of the active signalling Shh protein was found. Surprisingly, none of the downstream Shh pathway members (Ptc, Gli1 and Gli3) were significantly altered by ethanol exposure. Overall, our results indicate that ethanol's disruption of Shh may be mediated through some alternative mechanism independent of the classical signalling pathway. However, the precise role of Shh in relation to ethanol teratogenicity continues to be debated. Thus, in conclusion, our findings are discussed in relation to the varied and often conflicting reports of ethanol-induced Shh perturbation found in the literature.