Macrophage binding of cells resistant and sensitive to contact-dependent cytotoxicity

Efficient generation of myostatin (MSTN) biallelic mutations in cattle using zinc finger nucleases

Genetically engineered zinc-finger nucleases (ZFNs) are useful for marker-free gene targeting using a one-step approach. We used ZFNs to efficiently disrupt bovine myostatin (MSTN), which was identified previously as the gene responsible for double muscling in cattle. The mutation efficiency of bovine somatic cells was approximately 20%, and the biallelic mutation efficiency was 8.3%. To evaluate the function of the mutated MSTN locus before somatic cell nuclear transfer, MSTN mRNA and protein expression was examined in four mutant cell colonies. We generated marker-gene-free cloned cattle, in which the MSTN biallelic mutations consisted of a 6-bp deletion in one of the alleles and a 117-bp deletion and 9-bp insertion in the other allele, resulting in at least four distinct mRNA splice variants. In the MSTN mutant cattle, the total amount of MSTN protein with the C-terminal domain was reduced by approximately 50%, and hypertrophied muscle fibers of the quadriceps and the double-muscled phenotype appeared at one month of age. Our proof-of-concept study is the first to produce MSTN mutations in cattle, and may allow the development of genetically modified strains of double-muscled cattle.

A novel promoterless gene targeting vector to efficiently disrupt PRNP gene in cattle

The PRNP gene encodes a cellular protein named prion, whose misfolded form has been implicated in a number of neuropathic diseases in mammals such as the Bovine Spongiform Encephalopathy (BSE) in cattle. BSE has brought devastating impact on the world economy and human health. Recently, several groups have performed the gene targeting strategy to disrupt the PRNP gene in bovine fibroblast cells and produce BSE-resistant cattle by somatic cell nuclear transfer (SCNT). However, the enrichment efficiency of the gene targeting vector was low. Here, we constructed a novel promoterless gene targeting vector to sequentially disrupt the PRNP gene in bovine fibroblast cells and generate gene targeted cattle by SCNT. The enrichment efficiency of the novel vector was 100% and 60%, respectively. After nuclear transfer, no significant difference was found in the rate of cleavage and blastocyst formation between the knockout and wild type cloned embryos. One PRNP⁺/⁻ calf was born with no obvious abnormal development by now. Fusion RT-PCR and real-time PCR showed one allele of the PRNP gene was functionally disrupted, and the mRNA expression reduced dramatically in the PRNP⁺/⁻ cattle. The reconstituted PRNP⁻/⁻ embryos showed double alleles disruption, and no difference in the rate of cleavage and blastocyst formation.

Removal of selectable marker gene from fibroblast cells in transgenic cloned cattle by transient expression of Cre recombinase and subsequent effects on recloned embryo development

Introduction of selectable marker genes to transgenic animals could create an inconvenience to further research and may exaggerate public concerns regarding biological safety. The objective of the current study was to excise loxP flanked neo(R) in transgenic cloned cattle by transient expression of Cre recombinase. Green fluorescent protein gene (GFP) was incorporated to monitor Cre expression; therefore, Cre-expressed cells could be selected indirectly by fluorescence-activated cell sorting (FACS). The neo(R) was removed and Cre expressed transiently in GFP-positive colonies; excision of neo(R) was confirmed by single-blastocyst PCR in recloned blastocysts, with neo(R)-free fibroblast cells as donors. There was no difference (P>0.05) in rates of cleavage (76.0% vs. 68.8%) or blastocyst formation (56.6% vs. 52.9%) between recloned embryos with neo(R)-free or neo(R)-included donors. The differential staining of recloned blastocysts were similar (P >0.05) in terms of total cell number (124 vs. 122) and the ratio of ICM (Inner Cell Mass) to the total cell number (38.1% vs. 38.2%). Furthermore, pregnancy and calving rates were not different (P>0.05) from those of the control. In conclusion, we successfully excised neo(R) from transgenic cloned cattle; the manipulation did not affect the developmental competence of recloned preimplantation embryos. This approach should benefit bioreactor and transgenic research in livestock.

Macrophage cell lines derived from major histocompatibility complex II-negative mice

Two bone-marrow-derived macrophage cell lines, C2D and C2Dt, were isolated from major histocompatibility class II negative knock-out mice. The C2D cell line was stabilized by continuous culture in colony-stimulating factor-1 and the C2Dt cell line was transformed with SV40 virus large T antigen. These cells exhibited phenotypic properties of macrophages including morphology and expression of Mac 1 and Mac 2 cell surface molecules. These cells also had comparable growth to the bone-marrow-derived macrophage cell line B6MP102. These new cell lines were not spontaneously cytotoxic and were only capable of modest killing of F5b tumor cells when stimulated with LPS and interferon-gamma, but not when stimulated with LPS alone or with staphylococcal exotoxin. C2D and C2Dt cells phagocytosed labeled Staphylococcus aureus similarly to B6MP102 cells but less well than C2D peritoneal macrophages. These cell lines secreted interleukin-6, but not tumor necrosis factor or nitric oxide in response to LPS or staphlococcal enterotoxins A or B C2D(t) cells were tumorigenic in C2D and C57BL/6J mice but C2D cells were not. These data suggest that macrophage cell lines can be established from bone marrow cells of major histocompatibility complex II-negative mice.

Triggering effects of BCG vaccine on antitumor and interleukin-1 secretory activity of T cell lymphokine-primed macrophages

By using an in vitro model, this work demonstrates that BCG (Bacillus Calmette-Guerin) vaccine is able to trigger activation of T cell lymphokine-primed murine macrophages (Mo) for both tumoricidal cytotoxicity and interleukin-1 (IL-1) secretion. The results presented support the view that BCG vaccine may essentially activate primed, but not intact Mo; and that macrophage-mediated both antitumor and immunostimulatory effects of BCG vaccine observed in the body may be largely defined by functional activity of T-lymphocytes responsible for antigen-induced production of macrophage-activating lymphokines.

Murine macrophage activation by staphylococcal exotoxins

We investigated the ability of staphylococcal enterotoxins A and B, exfoliative toxins A and B, and toxic shock syndrome toxin 1 to activate macrophages. All of the toxins tested had the potential to stimulate tumoricidal activity in peritoneal macrophages from lipopolysaccharide-responsive C3HeB/FeJ mice. In contrast, none of the toxins activated cytotoxicity in lipopolysaccharide-unresponsive macrophages from C3H/HeJ mice. We also studied toxin stimulation of monokine secretion. Staphylococcal enterotoxin A, toxic shock syndrome toxin 1, and both exfoliative toxins triggered C3HeB/FeJ macrophages to secrete tumor necrosis factor alpha, but enterotoxin B induced only marginal amounts of tumor necrosis factor. All of the toxins used stimulated interleukin-6 production by macrophages from both strains of mice. Nitric oxide is produced in response to the exfoliative toxins only by the lipopolysaccharide-responsive macrophages. These results suggest that macrophages respond differently to several staphylococcal exotoxins.