Teratogenic effects of retinoic acid are modulated in mice lacking expression of epidermal growth factor and transforming growth factor-alpha.
BACKGROUND
Epidermal growth factor (EGF) and transforming growth factor-alpha (TGFalpha) regulate cell proliferation and differentiation in the embryo. The induction of cleft palate (CP) by all trans-retinoic acid (RA) was associated with altered expression of TGFalpha, EGF receptor, and binding of EGF. This study uses knockout (KO) mice to examine the roles of EGF and TGFalpha in teratogenic responses of embryos exposed to RA.


METHODS
Pregnant wild-type (WT) mice of mixed genetic background, EGF KO, C57BL/6J, and TGFalpha KO mice were given a single oral dose of RA (100 mg/kg, 10 ml/kg) or corn oil on GD 10 at 12 PM, GD 11 at 12 PM or 4 PM, or GD 12 at 8 AM or 12 PM (plug day = GD 0). GD 18 fetuses were examined for external, visceral, and skeletal effects.


RESULTS
After exposure to RA on GD 12, the incidence of CP in EGF KO was significantly reduced relative to WT. In TGFalpha KO fetuses, RA exposure on GD 10 increased the incidence of CP versus C57BL/6J. The incidence of skeletal defects in the limbs, vertebrae, sternebrae, and ribs were also affected by lack of expression of EGF or TGFalpha with region-specific amelioration or exacerbation of the effects of RA. In TGFalpha KO fetuses, incidences of forelimb long bone and digit defects increased relative to C57BL/6J. In EGF KO fetuses, relative to WT, the incidence of hindlimb oligodactyly was increased. In EGF KO, but not WT, RA produced short, bent radius, humerus, and ulna. Both TGFalpha and EGF KO mice had increased incidences of dilation of the renal pelvis and this was reduced by RA.


CONCLUSIONS
RA exposure produced skeletal and visceral defects in all genotypes; however, EGF or TGFalpha KO influenced the incidence and severity of defects. This study supports a role for EGF and TGFalpha in the response to RA.
Abbott
Barbara D
BD
Reproductive Toxicology Division, National Health and Environmental Effects Research Laboratory, Office of Research and Development, U.S. Environmental Protection Agency, 2525 East Highway 54, Durham, NC 27713, USA. Abbott.barbara@epa.gov
Best
Deborah S
DS
Narotsky
Michael G
MG
D000014:Abnormalities, Drug-Induced / Q000209:etiology*; D000818:Animals; D001842:Bone and Bones / Q000002:abnormalities; D002972:Cleft Palate / Q000139:chemically induced* / Q000235:genetics; D004815:Epidermal Growth Factor / Q000235:genetics / Q000502:physiology*; D005260:Female; D005333:Fetus / Q000002:abnormalities / Q000187:drug effects*; D007682:Kidney Pelvis / Q000002:abnormalities; D051379:Mice; D018345:Mice, Knockout; D010641:Phenotype; D011247:Pregnancy; D049188:Prenatal Injuries; D016211:Transforming Growth Factor alpha / Q000235:genetics / Q000502:physiology*; D014212:Tretinoin / Q000633:toxicity*
D016211:Transforming Growth Factor alpha; D014212:Tretinoin; D004815:Epidermal Growth Factor