ANALYSIS OF INSERTIONAL MUTATIONS IN TRANSGENIC MICE

小眼畸形（mi）基因突变纯合子小鼠， 皮肤、眼睛和耳朵中不同程度的黑素细胞缺乏，以及 肥大细胞、NK细胞和破骨细胞的各种缺陷。 取决 在突变等位基因上，这样的小鼠是白色的，小眼的， 听力受损。 杂合子要么没有可见的表型，要么 轻度黑素细胞缺乏 某些mi的杂合组合 等位基因显示等位基因间的相互作用，有些加重，有些加重。 减轻了相应表型的严重程度， 纯合子 使用mi基因座的转基因插入突变， 我们已经分离出一个基因，其表达在转基因小鼠中被破坏， 小鼠 该基因编码一种新的 DNA结合的碱性螺旋环螺旋拉链（bHLH~Zip）家族 转录因子，并在野生型小鼠中表达， 视网膜、耳朵和皮肤的黑色素细胞，以及肥大细胞。 基因 在六个不同的，独立的mi等位基因中发生突变，这表明它 确实是多效性突变表型的唯一原因。 这类基因的成员在基因表达中具有广泛的作用。 调节、细胞增殖和发育在物种中是不同的 酵母和人类。 在体外，bHLH~Zip蛋白作为同源二聚体， 异二聚体，这一事实提供了一个理论基础的现象， 等位基因间的相互作用，并表明这些因素的二聚化， 也在体内起作用。 mi处的突变已被提议作为 某些形式的人类Waardenburg综合征和人类白癜风。 的 最近分离的人Mi cDNA将使我们能够研究潜在的 这些疾病的突变。 我们选择分析的第二个插入突变的特征是 脊椎异常，类似于那些在突变中看到的， pax~1转录因子基因位于2号染色体上。 这次插入 而与pax~1不等位，提示该基因可能与pax~1基因无关 被插入中断的基因可能代表pax~1的靶基因。 我们 分析已经进行到隔离的一个地区侧翼的 插入和相关基因组缺失的表征。 目前正在分析来自该基因座的mRNA。 的 突变让人想起某些人类脊椎疾病， 对负责表型的小鼠基因的分子分析可以 导致相应的人类基因的分离。

Mice homozygous for mutations at the microphthalmia (mi) locus have varying degrees of melanocyte deficiencies in skin, eye and ear, and varying deficiencies in mast cells, NK cells, and osteoclasts. Depending on the mutant allele, such mice are white, microphthalmic, and hearing~impaired. Heterozygotes either have no visible phenotype, or a mild melanocyte deficiency. Heterozygous combinations of certain mi alleles show interallelic~interactions, some aggravating and some lessening the severity of the phenotypes seen in corresponding homozygotes. Using a transgenic insertional mutation at the mi locus, we have isolated a gene whose expression is disrupted in the transgenic mice. This gene encodes a novel member of the basic~helix~loop~helix~zipper (bHLH~Zip) family of DNA~binding transcription factors, and is expressed in wild type mice in the melanocytes of the retina, ear and skin, and in mast cells. The gene is mutated in six different, independent mi alleles, suggesting that it is indeed the only one responsible for the pleiotropic mutant phenotype. Members of this class of genes have wide ranging roles in gene regulation, cell proliferation and development in species as divergent as yeast and humans. In vitro, bHLH~Zip proteins act as homodimers and heterodimers, a fact that provides a rationale for the phenomenon of interallelic interactions and suggests that dimerization of these factors also operates in vivo. Mutations at mi have been proposed as models for certain forms of human Waardenburg syndrome and for human vitiligo. The recent isolation of the human Mi cDNA will enable us to study potential mutations in these diseases. A second insertional mutation we have chosen to analyze is characterized by vertebral abnormalities similar to those seen in mutations in the pax~1 transcription factor gene on chromosome 2. This insertion, however, is not allelic with pax~1, which suggests that the gene interrupted by insertion may represent a target gene of pax~1. Our analysis has proceeded to the isolation of a region flanking the insertion and the characterization of an associated genomic deletion. An mRNA derived from this locus is currently being analyzed. The mutation is reminiscent of certain human vertebral diseases, and the molecular analysis of the mouse gene responsible for the phenotype may lead to the isolation of the corresponding human gene.