Interactions between Shh pathway regulators and fetal alcohol exposure in mice

前脑无裂畸形（HPE）是一种常见的前脑和面中部的出生缺陷， 遗传原因。环境因素之一是母亲在怀孕早期饮酒。在 此外，已在人HPE中鉴定了Sonic hedgehog（Shh）信号传导途径中的突变。的 突变携带者的HPE表型是高度可变的，其影响范围从 前脑和面中部严重缺损至无临床表现。这种变化的原因是不- 已知，但可能还需要的因素包括额外的遗传影响或环境暴露 在胎儿发育期间。基因与环境的相互作用很可能与一种复杂的疾病有关， HPE;但是，很少有这种型号。Cdo和Boc是细胞表面蛋白，其结合Shh并调节 在发育中的胚胎的特定区域中的通路信号强度。Cdo突变小鼠显示HPE， 菌株特异性严重程度：129/Sv背景下的突变体显示出非常轻微的HPE，频率较低，而 C57 BL/6背景上的突变体在高频率下显示更严重的形式。Boc突变小鼠没有 显性效应，但129/Sv Cdo;Boc双突变体显示严重的颅面HPE特征。我们报告 129/Sv小鼠对乙醇诱导的HPE具有抗性;然而，在暴露于129/Sv Cdo突变体的小鼠中， 子宫对乙醇的反应显示出强烈的颅面HPE，并与Cdo;Boc双突变体具有惊人的相似性。 此外，乙醇处理的Cdo突变体前脑中Shh表达强烈减少， 胚胎因此，Cdo的丧失和胎儿乙醇暴露协同产生HPE;这一事实，加上 乙醇处理的Cdo突变胚胎与Cdo非常相似;Boc双突变体，认为Cdo和 乙醇暴露对Shh信号传导具有协同效应。肢体和手指缺陷也与 人胎儿酒精暴露和C57 BL/6胚胎宫内酒精暴露导致畸形， 四肢和手指的后面。Shh是四肢和手指的所有后部图案所必需的。损失 Boc，而不是Cdo，在遗传致敏背景下导致严重的手指缺陷。据推测， 类似于129/Sv Cdo突变小鼠和HPE，129/Sv Boc突变小鼠将对乙醇诱导的HPE致敏。 肢体/手指异常关于乙醇如何破坏已知的调节剂的信息相对较少 对乙醇处理的C57 BL/6和129/Sv小鼠进行的肢体/手指图案化和发育遗传分析将 揭示了这一过程。本研究的目的是：1）分析129/Sv Cdo中乙醇诱导的HPE 突变小鼠; 2）确定乙醇诱导的前脑Shh表达下调的机制 的129/Sv Cdo突变小鼠;和3）分析Shh途径在乙醇诱导的缺陷中的作用， 肢体/手指模式这些研究包括分析一个新开发的基因-环境模型 在一个常见的出生缺陷中，明确的发育突变和乙醇之间的相互作用。此类信息 可能会对公共卫生产生重要影响，并最终有助于对突变携带者的咨询。

Holoprosencephaly (HPE) is a common birth defect of the forebrain and midface with both environmental and genetic causes. Among the environmental factors is maternal alcohol consumption during early pregnancy. In addition, mutations in the Sonic hedgehog (Shh) signaling pathway have been identified in human HPE. The HPE phenotype of mutation carriers is highly variable, with the spectrum of effects ranging in a continuum from severe defects in the forebrain and midface to no clinical manifestation. The reason for this variability is un- known, but factors that may also be required include additional genetic influences or environmental exposures during fetal development. Gene-environment interactions are likely to be involved in a complex malady like HPE; however, there are few models for this. Cdo and Boc are cell surface proteins that bind Shh and regulate pathway signaling strength in specific regions of the developing embryo. Cdo mutant mice display HPE with strain-specific severity: mutants on the 129/Sv background show very mild HPE with low frequency, while mutants on the C57BL/6 background show more severe forms at high frequency. Boc mutant mice are without overt effect, but 129/Sv Cdo;Boc double-mutants display severe craniofacial HPE features. We report that 129/Sv mice are resistant to ethanol-induced HPE; however, 80% of 129/Sv Cdo mutant embryos exposed in utero to ethanol display strong craniofacial HPE and bear a striking resemblance to Cdo;Boc double mutants. Furthermore, there is a strong reduction of Shh expression in the forebrain of ethanol-treated Cdo mutant embryos. Loss of Cdo and fetal ethanol exposure therefore synergize to produce HPE; this fact, plus that ethanol-treated Cdo mutant embryos are so similar to Cdo;Boc double-mutants, argues that loss of Cdo and ethanol exposure have a synergistic effect on Shh signaling. Limb and digit defects are also associated with human fetal alcohol exposure, and in utero ethanol exposure of C57BL/6 embryos results in malformations of the posterior aspects of limbs and digits. Shh is required for all posterior patterning of limbs and digits. Loss of Boc, but not Cdo, results in severe digit defects on a genetically-sensitized background. It is hypothesized that, similar to 129/Sv Cdo mutant mice and HPE, 129/Sv Boc mutant mice will be sensitized to ethanol-induced limb/digit anomalies. There is relatively little information available on how ethanol disrupts the known regulators of limb/digit patterning, and developmental genetic analyses of ethanol-treated C57BL/6 and 129/Sv mice will shed light on this process. The aims of this proposal are: 1) to analyze ethanol-induced HPE in 129/Sv Cdo mutant mice; 2) to identify mechanisms of ethanol-induced down-regulation of Shh expression in the forebrains of 129/Sv Cdo mutant mice; and 3) to analyze the role of the Shh pathway in ethanol-induced defects in limb/digit patterning. These studies involve analysis of a newly developed model of gene-environment interaction between a defined developmental mutation and ethanol in a common birth defect. Such information may have important public health impact and could ultimately aid in the counseling of mutation carriers.