Site‐specific transgenesis of the Drosophila melanogaster Y‐chromosome using CRISPR/Cas9

Despite the importance of Y‐chromosomes in evolution and sex determination, their heterochromatic, repeat‐rich nature makes them difficult to sequence (due, in part, to ambiguities in sequence alignment and assembly) and to genetically manipulate. Therefore, they generally remain poorly understood. For example, the Drosophila melanogaster Y‐chromosome, one of the most extensively studied Y‐chromosomes, is widely heterochromatic and composed mainly of highly repetitive sequences, with only a handful of expressed genes scattered throughout its length. Efforts to insert transgenes on this chromosome have thus far relied on either random insertion of transposons (sometimes harbouring ‘landing sites’ for subsequent integrations) with limited success or on chromosomal translocations, thereby limiting the types of Y‐chromosome‐related questions that could be explored. Here, we describe a versatile approach to site‐specifically insert transgenes on the Y‐chromosome in D. melanogaster via CRISPR/Cas9‐mediated homology‐directed repair. We demonstrate the ability to insert, and detect expression from, fluorescently marked transgenes at two specific locations on the Y‐chromosome, and we utilize these marked Y‐chromosomes to detect and quantify rare chromosomal nondisjunction effects. Finally, we discuss how this Y‐docking technique could be adapted to other insects to aid in the development of genetic control technologies for the management of insect disease vectors and pests.     

Transgenesis and neuronal ablation in parasitic nematodes: revolutionary new tools to dissect host-parasite interactions

Ease of experimental gene transfer into viral and prokaryotic pathogens has made transgenesis a powerful tool for investigating the interactions of these pathogens with the host immune system. Recent advances have made this approach feasible for more complex protozoan parasites. By contrast, the lack of a system for heritable transgenesis in parasitic nematodes has hampered progress toward understanding the development of nematode-specific cellular responses. Recently, however, significant strides towards such a system have been made in several parasitic nematodes, and the possible applications of these in immunological research should now be contemplated. In addition, methods for targeted cell ablation have been successfully adapted from Caenorhabditis elegans methodology and applied to studies of neurobiology and behaviour in Strongyloides stercoralis. Together, these new technical developments offer exciting new tools to interrogate multiple aspects of the host-parasite interaction following nematode infection.     

Reverse genetics and the study of the immune response to schistosomes

The sequencing of the schistosome genome and the establishment of techniques for RNAi and transient transfection in these parasites have opened the door for a reverse genetics approach to studying schistosomes. One of the most intriguing aspects of schistosome biology is the interaction of these parasites with the immune system. The immune response underlies the ability of the host to survive while infected and to eventually develop resistance to further infection. However, it is also instrumental in the development of disease due to its role orchestrating granuloma formation around tissue-trapped parasite eggs. While schistosomes have clearly evolved mechanisms for evading host immune responses, their normal development is, paradoxically, also dependent upon the presence of a normal immune system. This article will review recent advances in the development of tools for studying gene function in schistosomes, and discuss how these new tools may be exploited to investigate issues of key importance in the interaction of schistosomes with the host immune system.     

Site‐directed zebrafish transgenesis into single landing sites with the phiC31 integrase system

Background: Linear DNA‐based and Tol2‐mediated transgenesis are powerful tools for the generation of transgenic zebrafish. However, the integration of multiple copies or transgenes at random genomic locations complicates comparative transgene analysis and makes long‐term transgene stability unpredictable with variable expression. Targeted, site‐directed transgene integration into pre‐determined genomic loci can circumvent these issues. The phiC31 integrase catalyzes the unidirectional recombination reaction between heterotypic attP and attB sites and is an efficient platform for site‐directed transgenesis. Results: We report the implementation of the phiC31 integrase‐mediated attP/attB recombination for site‐directed zebrafish transgenics of attB‐containing transgene vectors into single genomic attP landing sites. We generated Tol2‐based single‐insertion attP transgenic lines and established their performance in phiC31 integrase‐catalyzed integration of an attB‐containing transgene vector. We found stable germline transmission into the next generation of an attB reporter transgene in 34% of all tested animals. We further characterized two functional attP landing site lines and determined their genomic location. Our experiments also demonstrate tissue‐specific transgene applications as well as long‐term stability of phiC31‐mediated transgenes. Conclusions: Our results establish phiC31 integrase‐controlled site‐directed transgenesis into single, genomic attP sites as space‐, time‐, and labor‐efficient zebrafish transgenesis technique. The described reagents are available for distribution to the zebrafish community. Developmental Dynamics 242:949–963, 2013. © 2013 Wiley Periodicals, Inc.     

The Prx1 limb enhancers: Targeted gene expression in developing zebrafish pectoral fins

Limbs represent an excellent model to study the induction, growth, and patterning of several organs. A breakthrough to study gene function in various tissues has been the characterization of regulatory elements that allow tissue‐specific interference of gene function. The mouse Prx1 promoter has been used to generate limb‐specific mutants and overexpress genes in tetrapod limbs. Although zebrafish possess advantages that favor their use to study limb morphogenesis, there is no driver described suitable for specifically interfering with gene function in developing fins. We report the generation of zebrafish lines that express enhanced green fluorescent protein (EGFP) driven by the mouse Prx1 enhancer in developing pectoral fins. We also describe the expression pattern of the zebrafish prrx1 genes and identify three c onserved n on‐coding e lements (CNEs) that we use to generate fin‐specific EGFP reporter lines. Finally, we show that the mouse and zebrafish regulatory elements may be used to modify gene function in pectoral fins. Developmental Dynamics 240:1977–1988, 2011. © 2011 Wiley‐Liss, Inc.     

条件性血管瘤转基因小鼠模型的建立

目的：采用条件性转基因策略构建小鼠血管瘤动物模型,并对其表型进行鉴定。方法：构建血管内皮细胞特异性表达启动子Tie2驱动的鼠多瘤病毒中间T基因（ PyMT）表达质粒（ pTie2?PyMT）,采用DNA显微注射方法,将血管内皮特异性表达的PyMT目的基因导入供体C57BL／6J小鼠的雄原核中,再移植到假孕鼠的输卵管中,产生转基因首建鼠。 PCR方法检测目的基因整合情况,检查转基因鼠基因型,观察转基因鼠表型,对于转基因鼠出现的新生物进行组织学及免疫组织化学检测。采用GraphPad Prism 5．0软件包对实验数据进行统计学分析。结果：经测序分析证实,pTie2?PyMT质粒中PyMT、Tie2启动子和Tie2增强子序列等组成元件被正确克隆、连接,且阅读框正确。出生小鼠基因型经PCR鉴定证实,阳性的转基因小鼠均出现血管瘤样新生物表型。血管瘤样新生物主要表达部位在小鼠的耳、舌、皮肤、黏膜、肝等部位,组织学检查证实为血管瘤样病变,免疫组织化学方法证实新生物的内皮细胞表达PyMT蛋白及血管内皮标志物CD31。结论：Tie2启动子驱动下的PyMT基因可以在小鼠体内诱发血管瘤,该模型鼠可用于血管瘤发病机制的研究。条件控制下的转基因技术是一种有效的建立血管瘤动物模型的方法。     

Transgene‐mediated suppression of dengue viruses in the salivary glands of the yellow fever mosquito,Aedes aegypti

Controlled sex‐, stage‐ and tissue‐specific expression of antipathogen effector molecules is important for genetic engineering strategies to control mosquito‐borne diseases. Adult female salivary glands are involved in pathogen transmission to human hosts and are target sites for expression of antipathogen effector molecules. The Aedes aegypti 30K a and 30K b genes are expressed exclusively in adult female salivary glands and are transcribed divergently from start sites separated by 263 nucleotides. The intergenic, 5′‐ and 3′‐end untranslated regions of both genes are sufficient to express simultaneously two different transgene products in the distal‐lateral lobes of the female salivary glands. An antidengue effector gene, membranes no protein (Mnp), driven by the 30K b promoter, expresses an inverted‐repeat RNA with sequences derived from the premembrane protein‐encoding region of the dengue virus serotype 2 genome and reduces significantly the prevalence and mean intensities of viral infection in mosquito salivary glands and saliva.     

Transgenic rhesus monkeys produced by gene transfer into early-cleavage–stage embryos using a simian immunodeficiency virus-based vector

The development of transgenic technologies in monkeys is important for creating valuable animal models of human physiology so that the etiology of diseases can be studied and potential therapies for their amelioration may be developed. However, the efficiency of producing transgenic primate animals is presently very low, and there are few reports of success. We have developed an improved methodology for the production of transgenic rhesus monkeys, making use of a simian immunodeficiency virus (SIV)-based vector that encodes EGFP and a protocol for infection of early-cleavage–stage embryos. We show that infection does not alter embryo development. Moreover, the timing of infection, either before or during embryonic genome activation, has no observable effect on the level and stability of transgene expression. Of 70 embryos injected with concentrated virus at the one- to two-cell stage or the four- to eight-cell stage and showing fluorescence, 30 were transferred to surrogate mothers. One transgenic fetus was obtained from a fraternal triple pregnancy. Four infant monkeys were produced from four singleton pregnancies, of which two expressed EGFP throughout the whole body. These results demonstrate the usefulness of SIV-based lentiviral vectors for the generation of transgenic monkeys and improve the efficiency of transgenic technology in nonhuman primates.     

Mobility assays confirm the broad host-range activity of the Minos transposable element and validate new transformation tools

Fast and reliable methods for assessing the mobility of the transposable element Minos have been developed. These methods are based on the detection of excision and insertion of Minos transposons from and into plasmids which are co-introduced into cells. Excision is detected by polymerase chain reaction (PCR) with appropriate primers. Transposition is assayed by marker rescue in Escherichia coli, using a transposon plasmid that carries a tetracycline resistance gene and a target plasmid carrying a gene that can be selected against in E. coli. Using both assays, Minos was shown to transpose in Drosophila melanogaster cells and embryos, and in cultured cells of a mosquito, Aedes aegypti, and a lepidopteran, Spodoptera frugiperda. In all cases, mobility was dependent on the presence of exogenously supplied transposase, and both excision and transposition were precise. The results indicate that Minos can transpose in heterologous insect species with comparable efficiencies and therefore has the potential to be used as a transgenesis vector for diverse species.