Function of LIM homeodomain protein Lhx2 in odorant receptor gene regulation

气味受体基因可分为两类：类鱼类气味受体基因和类陆地气味受体基因。我们以前已经表明，Lhx2，一个LIM同源结构域蛋白，结合到小鼠M71，II类OR的启动子区中的同源结构域位点，并且Lhx2中的敲除突变排除了所有测试的II类OR基因（包括M71）的表达。在这里，我们报告说，大多数I类OR基因，这是在嗅上皮的背侧区域表达，仍然在Lhx2缺陷的胚胎中表达。有两个例外：两个I类OR基因，通常在更腹侧的区域表达，在Lhx2突变小鼠中不再表达。Lhx2在嗅觉感觉神经元中转录，与I类或II类OR基因的表达无关。因此，Lhx2的缺乏对I类和II类OR基因表达具有不同的影响，表明小鼠中OR基因表达的两种不同途径。

Odorant receptor (OR) genes can be classified into two types: fish-like class I OR genes and terrestrial-specific class II OR genes. We have previously shown that Lhx2, a LIM-homeodomain protein, binds to the homeodomain site in the promoter region of mouse M71, a class II OR, and that a knockout mutation in Lhx2 precludes expression of all tested class II OR genes including M71. Here, we report that most class I OR genes, which are expressed in a dorsal region of the olfactory epithelium, are still expressed in Lhx2-deficient embryos. There are two exceptions: two class I OR genes, which are normally expressed in a more ventral region, are no longer expressed in Lhx2 mutant mice. Lhx2 is transcribed in olfactory sensory neurons irrespective of expression of class I or class II OR genes. Thus, a deficiency of Lhx2has a differential impact on class I and class II OR gene expression, suggesting that two distinct pathways underlie OR gene expression in mouse.