Phenytoin-induced alterations in craniofacial gene expression

Abstract

In utero exposure to the anticonvulsant drug phenytoin has been shown to alter normal embryonic development, leading to a pattern of dysmorphogenesis known as the Fetal Hydantoin Syndrome. This embryopathy is characterized by growth retardation, microcephaly, mental deficiency, and craniofacial malformations, although the precise mechanism(s) by which phenytoin alters normal developmental pathways remains unknown. To better understand the molecular events involved in the pathogenesis of phenytoin‐induced congenital defects, alterations in gene expression were examined during critical periods of craniofacial development. Pregnant SWV mice were administered phenytoin (60 mg/kg/day) from gestational day 6.5 until they were sacrificed at selected developmental time points. Tissue from the craniofacial region of control and exposed embryos was isolated, and samples were subjected to in situ transcription, antisense RNA amplification, and hybridization on reverse Northern blots to quantitatively assess expression of 36 candidate genes. Chronic phenytoin exposure significantly altered expression of several genes at distinct times during morphogenesis. Results of these studies show that expression of the retinoic acid receptors (RAR) α, β, and γ were significantly increased by phenytoin exposure. Elevations in gene expression of lamininβ1, and the growth factors IGF‐2, TGFα, and TGFβ1, were also demonstrated in the craniofacial region of phenytoin‐exposed embryos. As several of these genes are transcriptionally regulated by retinoic‐acid‐responsive elements in their promoter regions, phenytoin‐induced alterations in expression of the RAR isoforms may have severe downstream consequences in the regulation of events necessary for normal craniofacial development. Such alterations occurring coordinately at critical times during craniofacial development may account for the dysmorphogenesis often associated with phenytoin exposure. Teratology 59:23–34, 1999. © 1999 Wiley‐Liss, Inc.

TGFβ2 in Embryos with Inborn Anomalies: Effect of Maternal Immunopotentiation

“…7 TGFb2 and other isoforms, TGFb1 and TGFb3 expressed by embryonic cells were also implicated in cardiogenesis, 31 palatogenesis, 32 digit formation 33 as well as in the formation of teratogeninduced cleft palate and limb anomalies. [12][13][14][15][16][17] Based on these findings we suggest that TGFb2 may act as a mediator whereby the maternal immune system may influence the teratogenic response of the embryo. This study was designed to validate such a suggestion.…”

“…It is obvious that distortion of any of these cell activities during organogenesis may lead to the formation of structural anomalies. By now, studies with various teratogens [12][13][14][15][16][17] have led to the claim that an elevated level of TGFbs in teratogen-targeted embryonic structures may, at least partly, contribute to the formation of structural anomalies by altering (inhibiting) cell proliferation.…”

Developmental neurotoxicology

“…However, it is generally not known whether their adverse effects on neurogenesis are related to untoward consequences of actions at such primary loci or are due to events provoked at undefined secondary foci. Phenytoin‐induced deficits have been found to involve altered gene expression at crucial times of neural development (Gelineau‐van Waes et al, 1999). Neural tube disorders, resulting from failure of the neural tube to close during the fourth week of embryogenesis, are among the most common severely disabling birth defects in the United States, with a frequency of approximately 1 in every 2,000 births (Northrup and Vlocik, 2000).…”

Developmental Neurotoxicology

“…However, it is generally not known whether their adverse effects on neurogenesis are related to untoward consequences of actions at such primary loci or are due to events provoked at undefined secondary foci. Phenytoininduced deficits have been found to involve altered gene expression at crucial times of neural development (Gelineau-van Waes et al, 1999). Neural tube disorders, resulting from failure of the neural tube to close during the fourth week of embryogenesis, are among the most common severely disabling birth defects in the United States, with a frequency of approximately 1 in every 2,000 births (Northrup and Vlocik, 2000).…”