Ethanol induces craniofacial defects in Bmp mutants independent of nkx2.3 by elevating cranial neural crest cell apoptosis.

BACKGROUND

Fetal Alcohol Spectrum Disorders (FASD) describes a wide range of neurological defects and craniofacial malformations associated with prenatal ethanol exposure. While there is growing evidence for a genetic component to FASD, little is known of the cellular mechanisms underlying these ethanol-sensitive loci in facial development. Endoderm morphogenesis to form lateral protrusions called pouches is one key mechanism in facial development. We have previously shown that multiple members of the Bone Morphogenetic Pathway (Bmp) signaling pathway, a key regulator of pouch formation, interacts with ethanol disrupting facial development. However, ethanol does not directly impact Bmp signaling suggesting that downstream effectors, like nkx2.3 may mediate the impact of ethanol on Bmp mutants.

METHODS

Here we use an ethanol exposure paradigm with nkx2.3 knockdown approaches to test if loss of nkx2.3 sensitizes Bmp mutants to ethanol induced facial defects. We then combine a morphometric approach with Hybridization Chain Reaction and immunofluorescence to examine the cellular mechanisms underlying Bmp-ethanol interactions.

RESULTS

We show that Bmp-ethanol interactions alter morphology of the endodermal pouches, independent of nkx2.3 gene expression. Morpholino knock down of nkx2.3 does not sensitize wild type or bmp4 mutant larvae to ethanol-induced facial defects. However, we did observe a significant increase CNCC apoptosis in ethanol-treated Bmp mutants.

CONCLUSIONS

Collectively, our results suggest that ethanol's mode of action is independent of downstream Bmp effectors, converging on CNCC cell survival. Ultimately, our work provides a mechanistic paradigm of ethanol-induced facial defects and connects ethanol exposure with concrete cellular events.