Genetic vulnerabilities to prenatal alcohol exposure: Limb defects in sonic hedgehog and GLI2 heterozygous mice.

BACKGROUND: Genetic factors influence the physical and neurobehavioral manifestations of prenatal alcohol exposure (PAE). Animal models allow the investigation of specific genes that confer vulnerability to, or protection from, birth defects associated with fetal alcohol spectrum disorders (FASDs). The objective of the present experiments was to determine if genetic alterations in the Sonic Hedgehog (Shh) signaling pathways affect the vulnerability to PAE-induced skeletal defects involving the forelimbs and/or hindlimbs. METHOD: Wild-type C57BL/6J female mice were bred with males in which one copy of the Shh or Gli2 genes had been knocked out, to produce litters with both wild-type (+/+) and heterozygous (+/-) embryos. Alcohol doses (two injections of 2.9 g/kg, 4 hours apart) or vehicles were administered starting at gestational day (GD) 9.25, 9.5, or 9.75, a critical exposure time for inducing limb defects. Limb defects were examined at GD 17 using a dysmorphology scale based on abnormalities ranging from increased interdigital spacing to the deletion of multiple fingers and the ulna. RESULTS: Alcohol treatment caused a high incidence of forelimb defects, particularly on the right side, that was higher in Shh+/- and Gli2+/- fetuses compared to wild-type fetuses. Dysmorphology scores were also significantly higher in the Shh+/- and Gli2+/- mice. CONCLUSIONS: These results extend previous findings demonstrating enhanced sensitivity to PAE-induced craniofacial dysmorphology and support the hypothesis that genetic alterations in the Shh signaling pathway influences the vulnerability to alcohol-induced birth defects. Moreover, these results emphasize the importance of understanding the interactions between genes and prenatal exposure to alcohol or other teratogens. Birth Defects Research 109:860-865, 2017. © 2017 Wiley Periodicals, Inc.

Preaxial polydactyly following early gestational exposure to the smoothened agonist, SAG, in C57BL/6J mice.

BACKGROUND: While pharmacological activation of the Hedgehog (HH) signaling pathway may have therapeutic benefits for developmental and adult diseases, its teratogenic potential is of concern. The membrane molecule Smoothened (SMO) transduces HH signaling and can be acutely modulated by antagonists and agonists. The objective of the current experiments was to determine how maternal treatment with the Smo agonist, SAG, affects the developing limb. METHODS: Pregnant C57BL/6J mice received a single injection of SAG (15, 17, or 20 mg/kg, i.p.) or its vehicle on gestational day (GD) 9.25, the time of limb bud induction. Embryos were examined on GD 15 for gross dysmorphology and skeletal staining was performed to visualize the number and type of digits on the fore- and hindlimbs. Additionally, in situ hybridization was performed 4 hr after GD 9.25 SAG administration to determine SAG's effects on Gli1 and Gli2 mRNA expression. RESULTS: The most prevalent effect of SAG was the dose-dependent induction of pre-axial polydactyly; defects ranged from a broad thumb to the duplication of two finger-like digits on the preaxial side of the thumb. The highest SAG dose was effective in ca. 80% of the embryos and increased Gli1 and Gli2 mRNA expression in the limb bud, with Gli1 mRNA being the most upregulated. CONCLUSION: Preaxial polydactyly can be caused in the developing embryo by acute maternal administration of a Smo agonist that activates HH signaling. These results are consistent with the preaxial polydactyly induced in developmental disorders associated with mutations in HH signaling genes.Birth Defects Research 109:49-54, 2017. © 2016 Wiley Periodicals, Inc.