<em>In Vivo</em> Functional Requirement of the Mouse <em>Ifitm1</em> Gene for Germ Cell Development, Interferon Mediated Immune Response and Somitogenesis

The mammalian Interferon induced transmembrane protein 1 (Ifitm1) gene was originally identified as a member of a gene family highly inducible by type I and type II interferons. Based on expression analyses, it was suggested to be required for normal primordial germ cell migration. The knockdown of Ifitm1 in mouse embryos provided evidence for a role in somitogenesis. We generated the first targeted knockin allele of the Ifitm1 gene to systematically reassess all inferred functions. Sperm motility and the fertility of male and female mutant mice are as in wild type littermates. Embryonic somites and the adult vertebral column appear normal in homozygous Ifitm1 knockout mice, demonstrating that Ifitm1 is not essential for normal segmentation of the paraxial mesoderm. Proportions of leucocyte subsets, including granulocytes, monocytes, B-cells, T-cells, NK-cells, and NKT-cells, are unchanged in mutant mice. Based on a normal immune response to Listeria monocytogenes infection, there is no evidence for a dysfunction in downstream IFNγ signaling in Ifitm1 mutant mice. Expression from the Ifitm1 locus from E8.5 to E14.5 is highly dynamic. In contrast, in adult mice, Ifitm1 expression is highly restricted and strong in the bronchial epithelium. Intriguingly, IFITM1 is highly overexpressed in tumor epithelia cells of human squamous cell carcinomas and in adenocarcinomas of NSCLC patients. These analyses underline the general importance of targeted in vivo studies for the functional annotation of the mammalian genome. The first comprehensive description of the Ifitm1 expression pattern provides a rational basis for the further examination of Ifitm1 gene functions. Based on our data, the fact that IFITM1 can function as a negative regulator of cell proliferation, and because the gene maps to chromosome band 11p15.5, previously associated with NSCLC, it is likely that IFITM1 in man has a key role in tumor formation.哺乳动物干扰素诱导跨膜蛋白1（Interferon induced transmembrane protein 1，Ifitm1）基因最初被鉴定为一类可被I型和II型干扰素强力诱导的基因家族成员。基于表达分析，有研究推测该基因对正常原始生殖细胞迁移不可或缺。在小鼠胚胎中敲低Ifitm1的实验，为其在体节发生中的作用提供了直接证据。我们首次构建了Ifitm1基因的靶向敲入等位基因，以系统地重新评估所有已被推测的基因功能。雄性和雌性突变小鼠的精子活力与生育能力，均与野生型同窝小鼠无显著差异。纯合子Ifitm1敲除小鼠的胚胎体节及成年个体的脊柱均表现正常，这表明Ifitm1并非体节中胚层正常分节所必需的基因。突变小鼠的白细胞亚群比例（包括粒细胞、单核细胞、B细胞、T细胞、自然杀伤细胞（NK细胞）及自然杀伤T细胞（NKT细胞））未发生明显改变。通过对单核细胞增多性李斯特菌（Listeria monocytogenes）感染的正常免疫应答实验，未发现Ifitm1突变小鼠存在γ干扰素（IFNγ）下游信号通路功能异常的证据。Ifitm1基因座在胚胎发育第8.5天至第14.5天（E8.5至E14.5）的表达模式具有高度动态性。与之形成鲜明对比的是，在成年小鼠体内，Ifitm1的表达具有极强的组织限制性，且在支气管上皮细胞中呈高表达水平。值得注意的是，IFITM1在人类鳞状细胞癌的肿瘤上皮细胞以及非小细胞肺癌（Non-Small Cell Lung Cancer，NSCLC）患者的腺癌组织中呈现高度过表达。本研究分析凸显了靶向体内功能研究对于哺乳动物基因组功能注释的普遍重要性。首次对Ifitm1基因表达模式的全面系统描述，为进一步探究Ifitm1的基因功能提供了科学合理的研究基础。结合本研究数据、IFITM1可作为细胞增殖负调控因子的特性，以及该基因定位于此前与非小细胞肺癌相关的11p15.5染色体带区，我们推测人类IFITM1很可能在肿瘤发生过程中发挥关键作用。