High efficiency transformation by direct microinjection of DNA into cultured mammalian cells.

Journal ArticleDirect microinjection of DNA by glass micropipettes was used to introduce the Herpes simplex virus thymidine kinase gene into cultured mammalian cells. When DNA was delivered directly into the nuclei of LMTK-, a mouse cell line deficient in thymidine kinase activity, 50--100% of the cells expressed TK enzymatic activity. In contrast, no TK activity could be detected when the DNA was injected into the cytoplasm. The number of injected LMTK- cells capable of indefinite growth in a TK+ selective medium (that is, transformants) depended on the nature of the plasmid DNA into which the HSV-TK gene was inserted. One cell in 500-1000 cells which received nuclear injections with pBR322/TK DNA gave rise to a viable colony when grown in HAT medium (that is, a TK+ selective medium). The transformation frequency increased to one in five injected cells when specific SV40 DNA sequences were also introduced into the HSV-TK plasmid. With the microinjection procedure transformation frequency was relatively insensitive to DNA concentration and did not depend on co-injecting with a carrier DNA. Most of the transformants were stable in nonselective medium as soon as they could be tested

Site-directed mutagenesis by gene targeting in mouse embryo-derived stem cells

Journal ArticleWe mutated, by gene targeting, the endogenous hypoxanthine phosphorlbosyl transferase (HPFlT) gene in mouse embryo-derived stem (ES) cells. A specialized construct of the neomycin resistance (NO') gene was introduced into an exon of a cloned fragment of the Hprf gene and used to transfect ES cells. Among the G418' colonies, l/l000 were also resistant to the base analog &thioguanine (&TG). The G418', 8-TGr cells were all shown to be Hprt- as the result of homologous recombination with the exogenous, neo'-containing, Hprf sequences

Introduction: the molecular genetic analysis of mouse development

Journal ArticleThis paper is an introduction of seven different papers presented in "Seminars in developmental biology" on Molecular Genetic Analysis of Mouse Development . The first paper, by Janet Rossant, describes very early mouse development. The second paper, by Frank Conlon and Rosa Beddington provide an intriguing and insightful comparison of gastrulation in Xenopus and mouse. In the third paper, Brigid Hogan reviews the roles of members of the TGF-β super family in mouse development. In the fourth paper, McMahon and his colleagues provide us with a clear overview of the role of the Wnt family members in mouse development. The fifth paper by Mark, Rijli and Chambon, expertly summarized The role of Hox genes in patterning the branchial region of the head. The sixth paper, by St-Onge, Tuello and Gruss, reviews the role of Pax genes in mouse development. The last paper by Elizabeth Robertson in a fascinating report that provides a description of how two growth factors, IGFI and IGFII and their receptor IGF1R interact to control the growth of the embryo and extraembryonic tissues

Hox genes and mammalian development

presentationWe have examined the interactions of Hox genes in forming a cervical vertebrae, hindbrain, and limbs. In each case, it is apparent that individual Hox genes are performing individual functions but that more profound roles are apparent when they act in combination with others Hox genes. The observed interactions suggest that multiple Hox genes function in concert to regulate overlapping sets of target genes. This suggesting is particularly strong in the interactions observed among the group-3 analogous genes in formation of the cervical vertebrae and among Hoxd11, Hoxd12, and Hoxd13 in formation of the autopod. In each case, the cumulative effect of combining multiple mutations is the deletions of structure, resulting from either lack of specification or lack of specification or lack of proliferation of the precursor cells needed to from the structures. Similarly, the combination of HoxaI and HoxbI mutations results in more extensive deletions of anterior structures than is apparent in mice homozygous for either individual mutation. All the results, both of single and combined mutations, are compatible with a role of Hox genes in the early regionalization of the embryo. In the absence of Hox gene functions, formation of the axes and germ cell layers of the embryo still occurs. At this point, the Hox genes are activated to initiate the formation of the embryo by conferring positional value along the major axes of the embryo. Perhaps the most primitive function of Hox genes is the innate ability, through their chromosomal organization, to covet a series of temporal signals into morphological direction, a conversion of time's arrow into a spatial vector

Gene targeting: an historical perspective

Journal ArticleOur entry into what was going to become the field of gene targeting began in 1977. I was experimenting with the use of extremely small glass needles to inject DNA directly into the nuclei of living cells. The needles were controlled by hydraulically driven micro-manipulators and were directed into nuclei with the aid of a microscope. Using this experimental paradigm, I asked myself whether I could introduce a functional gene into cells by injecting the DNA directly into their nuclei. This procedure turned out to be extremely efficient. One in three cells received the DNA in functional form and went on to divide and stably pass the gene onto its daughter cells (Capecchi, 1980). The high efficiency of micro-injection meant that it was now practical to use this technology to generate transgenic mice by the injection of DNA into one-cell zygotes. The embryos were then allowed to come to term by surgical transfer of the zygote to foster mothers. Indeed, this has become a cottage industry in many laboratories throughout the world (Gordon et al, 1980; Costantini and Lacy, 1981; Brinster et al, 1981; Wagner, E.F. et al, 1981; Wagner, T.C. et al, 1981) . However, generation of transgenic animals in this way involves the introduction of exogenous DNA segments at unpredictable locations in the recipient genome, and not targeted genetic alterations at defined sites

Personal view of gene targeting

Book ChapterGene targeting provides the means for creating strains of mice with mutations in virtually any gene.1 First, the desired mutation is introduced into a cloned copy of the chosen gene by standard recombinant DNA technology. The mutation is then transferred to the genome of a pluripotent mouse embryo-derived stem (ES) cell by means of homologous recombination between the exogenous, mutated DNA sequence and the cognate DNA sequence in the ES cell chromosome. By microinjection of ES cells containing the transferred mutation into blastocysts and by allowing the embryos to come to term in foster mothers, we can generate chimeric mice capable of transmitting the mutation to their offspring (germline chimeras). Finally, interbreeding of heterozygous siblings yields animals homozygous for the desired mutation. Figure 1 outlines the steps, from cultured ES cells to chimeric mouse, used to generate mice with targeted mutations

Disruption of the proto-oncogene int-2 in mouse embryo-derived stem cells: a general strategy for targeting mutations to non-selectable genes.

Journal ArticleGene targeting--homologous recombination of DNA sequences residing in the chromosome with newly introduced DNA sequences--in mouse embryo-derived stem cells promises to provide a means to generate mice of any desired genotype. We describe a positive nd negative selection procedure that enriches 2,000-fold for those cells that contain a targeted mutation. The procedure was applied to the isolation of hprt- and int-2- mutants, but it should be applicable to any gene

Sepp1UF forms are N-terminal selenoprotein P truncations that have peroxidase activity when coupled with thioredoxin reductase-1

pre-printMouse selenoprotein P (Sepp1) consists of an N-terminal domain (residues 1-239) that contains 1 selenocysteine (U) as residue 40 in a proposed redox-active motif (-UYLC-) and a Cterminal domain (residues 240-361) that contains 9 selenocysteines. Sepp1 transports selenium from the liver to other tissues by receptor-mediated endocytosis. It also reduces oxidative stress in vivo by an unknown mechanism. A previously uncharacterized plasma form of Sepp1 is filtered in the glomerulus and taken up by renal proximal convoluted tubule (PCT) cells via megalin-mediated endocytosis. We purified Sepp1 forms from the urine of megalin-/- mice using a monoclonal antibody to the N-terminal domain. Mass spectrometry revealed that the purified Urinary Sepp1 consisted of N-terminal Fragments terminating at 11 sites between residues 183 and 208. It was therefore designated Sepp1UF. Because the N-terminal domain of Sepp1 has a thioredoxin fold, Sepp1UF was compared with full-length Sepp1, Sepp1Δ240-361, and Sepp1U40S as a substrate of thioredoxin reductase-1 (TrxR1). All forms of Sepp1 except Sepp1U40S, which contains serine in place of the selenocysteine, were TrxR1 substrates, catalyzing NADPH oxidation when coupled with H2O2 or tert-butyl hydroperoxide as the terminal electron acceptor. These results are compatible with proteolytic cleavage freeing Sepp1UF from full-length Sepp1, the form that has the role of selenium transport, allowing Sepp1UF to function by itself as a peroxidase. Ultimately, plasma Sepp1UF and small selenium-containing proteins are filtered by the glomerulus and taken up by PCT cells via megalin-mediated endocytosis, preventing loss of selenium in the urine and providing selenium for the synthesis of glutathione peroxidase-3

Selective degradation of abnormal proteins in mammalian tissue culture cells.

Journal ArticleThe degradation rates of several missense mutants of hypoxanthine-guanine phosphoribosyltransferase (EC 2.4.2.8) in mouse L cells are compared to those of the wild-type enzyme. Although the rates of total protein breakdown in the mutant cell lines are identical to that of the parental L cell line, defective molecules of hypoxanthine-guanine phosphoribosyltransferase present in the mutant cell lines are degraded much faster than the wild-type enzyme. The level of defective phosphoribosyltransferase molecules present in the mutant cell lines is inversely proportional to the breakdown rate. This observation indicates that the major factor determining the concentrations of the defective phosphoribosyltransferases is their specific degradation rate. These results strongly support the hypothesis that abnormal proteins are selectively degraded in mammalian cells

Targeted mutations in hoxa-9 and hoxb-9 reveal synergistic interactions.

Journal ArticleMice were generated with a targeted disruption of the homeobox-containing gene hoxb-9. Mice homozygous for this mutation show defects in the development of the first and second ribs. In most cases the first and second ribs are fused near the point at which the first and second pairs of ribs normally attach to the sternum. Abnormalities of the sternum accompany the rib fusions. These include abnormal attachment of the ribs to the sternum, a reduction in the number of intercostal segments of the sternum, and abnormal growth of the intercostal segments. Over half of the homozygous mutants, as well as some heterozygotes, also have an eighth rib attached to the sternum. These results show that hoxb-9 plays a significant role in the specification of thoracic skeletal elements. To reveal potential interactions between the paralogous Hox genes hoxa-9 and hoxb-9, mice heterozygous for both mutations were intercrossed. Mice homozygous for both mutations show more severe phenotypes than predicted by the addition of the individual mutant phenotypes. Both the penetrance and the expressivity of the rib and sternal defects are increased, suggesting synergistic interactions between these genes. In particular, the sternum defects are greatly exacerbated. Interestingly, the defects in hoxb-9 and hoxa-9/ hoxb-9 mutant mice are concentrated along the axial column at points of transition between vertebral types