Manipulating the zebrafish genome through modulation of conserved helicases

描述（由申请人提供）：尽管斑马鱼作为遗传系统具有许多优点，但目前还没有通过靶向诱变来操纵其基因组的技术。我们的目标是通过操纵生殖系中RecQ解旋酶的活性来克服斑马鱼中的这一障碍。在人类、小鼠和鸡中有证据表明，Bloom综合征（BLM）和RECQL 5基因编码的酶在DNA损伤修复过程中通常起调节同源重组的作用。它们正常活性的降低导致自发姐妹染色单体交换和同源重组的增加，并且还与染色体外同源重组的频率增加相关。我们建议在斑马鱼胚胎中瞬时抑制BLM和RECQL 5功能，以允许基因组的操作，包括在种系中的靶向诱变。我们已经鉴定了BLM和RECQL 5的斑马鱼直系同源物，并验证了它们在早期胚胎中的表达。首先，我们将测量blm和recqIS的推定显性阴性（dn）突变抑制内源基因功能的能力。我们已经表明，注射dnblm RNA到胚胎杂合子的色素突变金诱导同源物之间的重组，可检测到的突变细胞的克隆在视网膜色素上皮细胞在3天的发展。我们将使用该试验来确定注射RNA的最佳组合，以瞬时抑制解旋酶功能，同时仍允许正常发育。然后，我们提出通过添加nanosl 3 'UTR将dnRNA靶向原始生殖细胞，将它们的活性限制在注射胚胎的种系。生殖系中解旋酶功能被暂时抑制的鱼将被饲养并筛选生殖细胞存活、生育力降低和诱导的染色体重排或其他突变。这将确立在下一代中恢复靶向突变的可行性。最后，我们已经制备了靶向构建体以在2个基因座中引入突变。第一个将GFP插入到死端基因座中，其编码生殖细胞中特异性表达的推定RNA解旋酶;阳性靶向事件可以在注射的幼虫中作为荧光生殖细胞进行评分。第二种方法将在somitobun基因中引入显性点突变;来自携带突变的卵母细胞的胚胎将显示出特征性的图案缺陷。这些试验将用于优化基因靶向方案。一旦建立，这些用于抑制RecQ解旋酶功能的技术可以促进对斑马鱼基因组的许多操作，例如创建遗传嵌合体;产生对于母体效应突变纯合的生殖细胞，以及最终的种系同源重组。

DESCRIPTION (provided by applicant): Despite the many advantages of zebrafish as a genetic system, there is currently no technology to manipulate its genome through targeted mutagenesis. We aim to overcome this barrier in zebrafish, through manipulation of the activity of RecQ helicases in the germline. There is evidence in human, mouse, and chicken that the enzymes encoded by the Bloom syndrome (BLM) and RECQL5 genes normally function to regulate homologous recombination during DNA damage repair. Reduction of their normal activities leads to an increase in spontaneous sister chromatid exchange and homologue recombination, and also correlates with increased frequency of extrachromosomal homologous recombination. We propose to transiently repress BLM and RECQL5 functions in the zebrafish embryo to allow manipulations of the genome, including targeted mutagenesis in the germline. We have identified the zebrafish orthologues of BLM and RECQL5 and verified their expression in the early embryo. First, we will measure the ability of putative dominant negative (dn) mutations of blm and recqIS to repress endogenous gene function. We have shown that injection of dnblm RNA into embryos heterozygous for the pigment mutation golden induces recombination between homologues, detectable as clones of mutant cells in the retinal pigment epithelium at 3 days of development. We will use this assay to determine the best combination of injected RNAs to transiently repress helicase function while still allowing normal development. We then propose to target dnRNAs to primordial germ cells through the addition of the nanosl 3'UTR, confining their activity to the germline of injected embryos. Fish in which helicase function in the germline has been transiently suppressed will be raised and screened for germ cell survival, reduced fertility, and induced chromosomal rearrangements or other mutations. This will establish the feasibility of recovering targeted mutations in the next generation. Finally, we have made targeting constructs to introduce mutations in 2 loci. The first will insert GFP into the dead end locus, which encodes a putative RNA helicase expressed specifically in germ cells; positive targeting events can be scored as fluorescent germ cells in injected larvae. The second will introduce a dominant point mutation into the somitobun gene; embryos derived from oocytes carrying the mutation will display a characteristic patterning defect. These assays will be used to optimize the protocol for gene targeting. Once established, these techniques for repressing function of RecQ helicases could facilitate many manipulations of the zebrafish genome, such as creation of genetic mosaics; generation of germ cells homozygous for maternal effect mutations, and ultimately germline homologous recombination.