Department of Molecular Genetics, University of Toronto, Toronto, Ontario, Canada.
PLoS One. 2011;6(8):e23868. doi: 10.1371/journal.pone.0023868. Epub 2011 Aug 31.
Williams-Beuren Syndrome (WBS) is a neurodevelopmental disorder caused by a hemizygous deletion of a 1.5 Mb region on chromosome 7q11.23 encompassing 26 genes. One of these genes, GTF2IRD1, codes for a putative transcription factor that is expressed throughout the brain during development. Genotype-phenotype studies in patients with atypical deletions of 7q11.23 implicate this gene in the neurological features of WBS, and Gtf2ird1 knockout mice show reduced innate fear and increased sociability, consistent with features of WBS. Multiple studies have identified in vitro target genes of GTF2IRD1, but we sought to identify in vivo targets in the mouse brain.
METHODOLOGY/PRINCIPAL FINDINGS: We performed the first in vivo microarray screen for transcriptional targets of Gtf2ird1 in brain tissue from Gtf2ird1 knockout and wildtype mice at embryonic day 15.5 and at birth. Changes in gene expression in the mutant mice were moderate (0.5 to 2.5 fold) and of candidate genes with altered expression verified using real-time PCR, most were located on chromosome 5, within 10 Mb of Gtf2ird1. siRNA knock-down of Gtf2ird1 in two mouse neuronal cell lines failed to identify changes in expression of any of the genes identified from the microarray and subsequent analysis showed that differences in expression of genes on chromosome 5 were the result of retention of that chromosome region from the targeted embryonic stem cell line, and so were dependent upon strain rather than Gtf2ird1 genotype. In addition, specific analysis of genes previously identified as direct in vitro targets of GTF2IRD1 failed to show altered expression.
CONCLUSIONS/SIGNIFICANCE: We have been unable to identify any in vivo neuronal targets of GTF2IRD1 through genome-wide expression analysis, despite widespread and robust expression of this protein in the developing rodent brain.
威廉姆斯-比伦综合征（WBS）是一种神经发育障碍，由 7 号染色体 q11.23 上的一个 1.5Mb 区域的单倍体缺失引起，该区域包含 26 个基因。其中一个基因 GTF2IRD1 编码一种假定的转录因子，在发育过程中在整个大脑中表达。7q11.23 非典型缺失患者的基因型-表型研究表明，该基因与 WBS 的神经特征有关，而 Gtf2ird1 基因敲除小鼠表现出先天恐惧减少和社交能力增强，与 WBS 的特征一致。多项研究已经确定了 GTF2IRD1 的体外靶基因，但我们试图在小鼠大脑中确定体内靶基因。
方法/主要发现：我们在胚胎 15.5 天和出生时的 Gtf2ird1 基因敲除和野生型小鼠的脑组织中进行了首次体内 Gtf2ird1 转录靶基因的微阵列筛选。突变小鼠中的基因表达变化适中（0.5 至 2.5 倍），用实时 PCR 验证候选基因表达改变，大多数基因位于染色体 5 上，距离 Gtf2ird1 不到 10Mb。在两种小鼠神经元细胞系中用 siRNA 敲低 Gtf2ird1 未能鉴定出微阵列鉴定的基因表达变化，随后的分析表明，染色体 5 上基因表达的差异是由于靶向胚胎干细胞系保留了该染色体区域所致，因此取决于品系而不是 Gtf2ird1 基因型。此外，对先前鉴定为 GTF2IRD1 体外直接靶基因的基因进行专门分析，未能显示表达改变。
结论/意义：尽管这种蛋白在发育中的啮齿动物大脑中广泛而强烈地表达，但我们通过全基因组表达分析未能鉴定出 GTF2IRD1 的任何体内神经元靶基因。
