Properties of reticulum cell sarcomas in SJL/J mice. III. Promotion of tumor growth in irradiated mice by normal lymphoid cells.

Experiments were performed to elucidate the mechanisms by which lymphocytes obtained from an M-antigen-incompatible strain reduce the specific mixed lymphocyte culture (MLC) response of lymphoid cell populations after injection into allogeneic recipients. Mice of strain CBA were injected with spleen cells from hybrids of the H-2-compatible, M-antigen-incompatible strain C3H. Normal C3H × CBA spleen cells increased the MLC reactivity of the host's lymphocytes during the first 1–3 days, and thereafter the response against C3H was drastically reduced. Mitomycin-treated or antibody-coated C3H × CBA cells rather enhanced the MLC responsiveness. Roughly similar results were obtained by injecting untreated H-2-incompatible C3H hybrid lymphocytes. Lymph node or spleen cell populations from CBA mice, injected with C3H × CBA cells up to 2 weeks earlier, were found to depress the MLC reactivity against C3H when transferred to new CBA hosts. The results indicate that injected cells had survived for 2 weeks in the host. On the other hand, H-2-incompatible C3H hybrid cells could not be detected even at day 3 after injection into CBA mice. The results also indicate that C3H hybrid lymphocytes have to be functionally intact and able to survive in the host for a relatively long period of time to be able to reduce the specific MLC response of the host's lymphocytes.     

Control of rDNA replication in Tetrahymena involves a cis-acting upstream repeat of a promoter element

A novel genetic scheme was used to isolate mutants altered in the formation or maintenance of amplified rDNA in the Tetrahymena macronucleus. One such mutant had a cis-acting rDNA mutation that affected the ability of mutant rDNA molecules to replicate in macronuclei in the presence of a wild-type (B strain) rDNA. The mutant rDNA was lost from these heterozygous macronuclei during vegetative cell divisions, although it was maintained normally in the homozygous or hemizygous state. In contrast, wild-type macronuclear rDNA of the C3 strain used to obtain the mutant outreplicated B strain rDNA in B/C3 heterozygote macronuclei. Sequence differences were found between wild-type B and C3 and mutant C3 rDNAs in the replication origin region, changing an upstream repeat of a highly conserved rRNA promoter element. We propose that the various rDNA alleles differentially compete for limiting amounts of trans-acting factors that bind to these enhancer-like repeats and positively regulate rDNA replication.     

High-level production and secretion of recombinant proteins by the dimorphic yeast Arxula adeninivorans

The non-conventional dimorphic thermo- and salt-resistant yeast Arxula adeninivorans has been developed as a host for heterologous gene expression. For assessment of the system two model genes have been selected: the GFP gene encoding the intracellular green fluorescent protein, and the HSA gene encoding the secreted human serum albumin. The expression system includes two host strains, namely A. adeninivorans LS3, which forms budding cells at 30 degrees C and mycelia at >42 degrees C, and the strain A. adeninivorans 135, which forms mycelia at temperatures as low as 30 degrees C. For expression control the constitutive A. adeninivorans-derived TEF1-promoter and S. cerevisiae-derived PHO5-terminator were selected. The basic A. adeninivorans transformation/expression vector pAL-HPH1 is further equipped with the Escherichia coli-derived hph gene conferring hygromycin B resistance and the 25S rDNA from A. adeninivorans for rDNA targeting. Transformants were obtained for both budding cells and mycelia. In both cell types similar expression levels were achieved and the GFP was localised in the cytoplasm while more than 95% of the HSA accumulated in the culture medium. In initial fermentation trials on a 200-ml shake flask scale maximal HSA product levels were observed after 96 h of cultivation.     

Single-step co-integration of multiple expressible heterologous genes into the ribosomal DNA of the methylotrophic yeast Hansenula polymorpha

We have investigated the methylotrophic yeast Hansenula polymorpha as a host for the co-integration and expression of multiple heterologous genes using an rDNA integration approach. The ribosomal DNA (rDNA) of H. polymorpha was found to consist of a single rDNA cluster of about 50-60 repeats of an 8-kb unit located on chromosome II. A 2.4-kb segment of H. polymorpha rDNA encompassing parts of the 25S, the complete 5S and the non-transcribed spacer region between 25S and 18S rDNA was isolated and inserted into conventional integrative H. polymorpha plasmids harboring the Saccharomyces- cerevisiae-derived URA3 gene for selection. These rDNA plasmids integrated homologously into the rDNA repeats of a H. polymorpha (odc1) host as several independent clusters. Anticipating that this mode of multiple-cluster integration could be used for the simultaneous integration of several distinct rDNA plasmids, the host strain was co-transformed with a mixture of up to three different plasmids, all bearing the same URA3 selection marker. Transformations indeed resulted in mitotically stable strains harboring one, two, or all three plasmids integrated into the rDNA. The overall copy number of the plasmids integrated did not exceed the number of rDNA repeats present in the untransformed host strain, irrespective of the number of different plasmids involved. Strains harboring different plasmids co-expressed the introduced genes, resulting in functional proteins. Thus, this approach provides a new and attractive tool for the rapid generation of recombinant strains that simultaneously co-produce several proteins in desired stoichiometric ratios.     

一株拮抗番茄叶霉病菌的放线菌筛选、鉴定及发酵条件研究

菌株xjy是一株从新疆棉田土壤中筛选出的对番茄叶霉病菌(Fulviafulva)有较强拮抗作用的放线菌,其对23种常见植物病原真菌和6种细菌有较好的抑制效果,抗菌谱广。其形态特征、培养特性、生理生化特性、细胞壁组分与放线菌中的淡紫灰链霉菌(Streptomyces lavendulae)相同,16SrDNA序列同源性达99.6%。研究发现该菌的摇瓶发酵配方和培养条件为:大豆粉2%、葡萄糖2%、NaCl0.8%、CaCO30.2%、(NH4)2SO40.32%,起始pH7.0、28℃、180r/mim、摇瓶培养6d,这些结果为该菌株今后的应用、抗生素的分离提纯和产业化提供了实验依据。     

Replacement of the macronuclear ribosomal RNA genes of a mutant Tetrahymena using electroporation

The macronucleus of the ciliate Tetrahymena contains approx. 10⁴ ribosomal RNA gene molecules (rDNA) in the form of linear, autonomously replicating palindromes. Previous studies have shown that macronuclear rDNA molecules derived from wild-type (wt) inbred strain C3 out-replicate those derived from wt inbred strain B, in macronuclei initially heterozygous for both, leading to the complete loss of the B rDNA. However, rmm-1, a cis-acting laboratory-induced mutation obtained previously by mutagenesis of inbred strain C3, causes the mutant rmm-1 rDNA to be completely out-replicated by B rDNA. These findings suggest the following hierarchy of replication potential: wt C3 > wt B > C3-rmm-1. We used electroporation to test whether cells containing only rmm-1 macronuclear rDNA are favorable recipients for transformation with either wt B or C3 donor rDNA molecules. The donor rDNA molecules carried the selectable marker Pmr (paromomycin resistance) located in the coding region of the 17S rRNA. Transformants were obtained, at a frequency > 1 in 10⁵, by electroporation under a wide range of electrical discharge parameters. The fraction of cells surviving electroporation varied between 2 and > 95% in successful experiments. Replacement (‘transplacement’) of the recipient rDNA was observed, consistent with the prediction that B and C3 rDNA should out-replicate rmm-l rDNA. These findings are also consistent with the previous conclusion that the differential replication determinants reside in the 5'-nontranscribed spacer of the rDNA.     

Thermodesulfobacterium hveragerdense sp. nov., and Thermodesulfovibrio islandicus sp. nov., two thermophilic sulfate reducing bacteria isolated from a Icelandic hot spring

Two thermophilic non-sporeforming sulfate-reducing bacteria (SRB) were isolated from microbial mats collected from an Icelandic hot spring. Strain JSP was a gram negative rod, with an average cell size of 2.8 x 0.5 microm. No flagella were found. Growth occurred between 55 and 74 degrees C with an optimum between 70 and 74 degrees C at pH 7.0. The G+C content was 40 mol%. Strain R1Ha3 was a gram negative vibrio-shaped rod with an average cell size of 1.7 x 0.4 microm. Motility was observed mediated by one polar flagellum. The growth optimum at pH 7.0 was 65 degrees C, and growth occurred between 45 and 70 degrees C. The G+C content was 38 mol%. In the presence of sulfate, both strains used lactate, pyruvate and H2 as electron donors. In addition, strain R1Ha3 used formate. Pyruvate was the only substrate supporting fermentative growth of both strains. Growth occurred with sulfate as well as thiosulfate as electron acceptors. Furthermore, strain R1Ha3 reduced nitrate and strain JSP reduced sulfite. Neither of the strains were able to oxidize lactate completely to CO2 and neither of the strains contained desulfoviridin. 16S rDNA sequencing placed strain JSP in the genus Thermodesulfobacterium and strain R1Ha3 in the genus Thermodesulfovibrio. Based on the DNA-DNA hybridization studies and differences in morphology and physiology to their closest relatives the two new isolates were considered as new species. Strain JSP is named Thermodesulfobacterium hveragerdense and strain R1Ha3 Thermodesulfovibrio islandicus.     

The replication advantage of a free linear rRNA gene is restored by somatic recombination in Tetrahymena thermophila.

The autonomously replicating rRNA genes (rDNA) in the somatic nucleus of Tetrahymena thermophila are maintained at a copy number of approximately 10(4) per nucleus. A mutant in which the replication properties of this molecule were altered was isolated and characterized. This mutation of inbred strain C3, named rmm4, was shown to have the same effect on rDNA replication and to be associated with the same 1-base-pair (bp) deletion as the previously reported, independently derived rmm1 mutation (D. L. Larson, E. H. Blackburn, P. C. Yaeger, and E. Orias, Cell 47:229-240, 1986). The rDNA of inbred strain B, which is at a replicational disadvantage compared with wild-type C3 rDNA, has a 42-bp deletion. This deletion is separated by 25 bp from the 1-bp deletion of rmm4 or rmm1. Southern blot analysis and DNA sequencing revealed that during prolonged vegetative divisions of C3-rmm4/B-rmm heterozygotes, somatic recombination produced rDNAs lacking both the rmm4-associated deletion and the 42-bp deletion. In somatic nuclei in which this rare recombinational event had occurred, all 10(4) copies of nonrecombinant rDNA were eventually replaced by the recombinant rDNA. The results prove that each of the two deletions is the genetic determinant of the observed replication disadvantage. We propose that the analysis of somatically recombinant rDNAs can be used as a general method in locating other mutations which affect rDNA propagation in T. thermophilia.     

彭泽鲫卵源致病性水霉的鉴定及其生物学特性

从患病的彭泽鲫卵上分离3株丝状真菌,经人工感染试验证实其中1株丝状真菌JL1对彭泽鲫卵具有致病性,并进一步研究了其形态与生长特性,开展了ITS rDNA序列分析。实验结果表明,菌株JL1菌丝为透明管状结构,中间无横隔,分枝较少;游动孢子囊多数呈棒状,游动孢子呈多排排列,发育成熟后从孢子囊中释放出来,并迅速游离;藏卵器呈球形,与雄器同枝或异枝。菌株JL1的ITS rDNA序列与GenBank基因库中水霉属菌株自然聚类,同源性高达99%,与Saprolegnia sp.H(登录号:EF460351)的亲缘关系最近。结合形态特征与ITS序列鉴定的结果,判定菌株JL1为水霉菌(Saprolegnia sp.)。此外,菌株JL1在5°C-30°C、pH 4-11范围内均能生长,最适生长温度和pH范围分别为25°C-30°C和6-9。同时菌株JL1对NaCl敏感,质量分数为2%的NaCl即可抑制其生长,可以作为该病防治的依据。     

Functional analysis of T lymphocyte subsets in antiviral host defense

The role of different T cell subsets in antiviral host defense was investigated by treating thymectomized C57BL/6 and CBA/J mice with monoclonal rat anti-Lyt-2 or anti-L3/T4 IgG 2b antibodies 14 and 10 days before infection. This treatment depleted the respective T cell subsets to undetectable levels in peripheral blood when assayed by immunofluorescence. In mice treated with anti-Lyt-2, induction of cytotoxic T cells was reduced to less than 1 to 2% after intravenous infection with Armstrong strain of lymphocytic choriomeningitis virus (LCMV). In addition, no primary swelling of the footpad could be detected following local inoculation of the virus. In animals treated with anti-L3/T4, antiviral cytotoxic T lymphocyte responses were reduced by a factor of 10. These L3/T4+ cell-depleted mice showed delayed footpad swelling after local injection of LCMV Armstrong. After intracerebral infection with LCMV, anti-Lyt-2-treated mice were resistant and those injected with anti-L3/T4 were totally susceptible to LCMV Armstrong-triggered immunopathologic disease. Virus could be detected in the blood of antibody-treated mice 7 days after inoculation; however, no virus could be measured in the blood of surviving anti-Lyt-2-treated animals 15 days after intracerebral infection. Serum titers of interferon-alpha,beta induced by viral infection remained unaffected by depletion of T cell subsets. Anti-L3/T4 antibody-treated C57BL/6 mice failed to generate IgG antibodies against the New Jersey strain of vesicular stomatitis virus, whereas Lyt-2+ cell-depleted mice had normal antivesicular stomatitis virus (New Jersey strain) IgG antibody titers.     

一株甲烷利用菌的分离及其在甲烷气体测定中的应用

从山西太原晋阳湖水样中分离得到一株能以甲烷为唯一碳源生长的菌株ME16.气相色谱分析表明ME16菌株能利用甲烷.ME16菌株的16S rDNA 序列与铜绿假单胞菌(Pseudomonasaeruginosa,ATCC 10145,AF094713)相似性为99%.该菌株最适培养条件为30℃、2%接种量、25%甲烷含量和培养基pH为6.0.用电化学法研究了ME16固定化细胞体系中不同含量甲烷对溶氧的响应时间以及溶氧变化与甲烷含量的关系.结果表明,加入固定化细胞后.溶氧变化在100s内达到平衡,溶氧消耗量与通入甲烷气体含量在0～16%呈线性关系,相关系数为0.9954.对样品气体8次测量,RSD为3.34%,表明该反应体系重现性良好,为该菌株进一步研究甲烷传感器奠定基础.     

Novel bacterial endosymbionts of Acanthamoeba spp. related to the Paramecium caudatum symbiont Caedibacter caryophilus

Acanthamoebae are increasingly being recognized as hosts for obligate bacterial endosymbionts, most of which are presently uncharacterized. In this study, the phylogeny of three Gram-negative, rod-shaped endosymbionts and their Acanthamoeba host cells was analysed by the rRNA approach. Comparative analyses of 16S rDNA sequences retrieved from amoebic cell lysates revealed that the endosymbionts of Acanthamoeba polyphaga HN-3, Acanthamoeba sp. UWC9 and Acanthamoeba sp. UWE39 are related to the Paramecium caudatum endosymbionts Caedibacter caryophilus, Holospora elegans a n d Holospora obtusa . With overall 16S rRNA sequence similarities to their closest relative, C. caryophilus , of between 87% and 93%, these endosymbionts represent three distinct new species. In situ hybridization with fluorescently labelled endosymbiont-specific 16S rRNA-targeted probes demonstrated that the retrieved 16S rDNA sequences originated from the endosymbionts and confirmed their intracellular localization. We propose to classify provisionally the endosymbiont of Acanthamoeba polyphaga HN-3 as ' Candidatus Caedibacter acanthamoebae', the endosymbiont of Acanthamoeba sp. strain UWC9 as ' Candidatus Paracaedibacter acanthamoebae' and the endosymbiont of Acanthamoeba sp. strain UWE39 as ' Candidatus Paracaedibacter symbiosus'. The phylogeny of the Acanthamoeba host cells was analysed by comparative sequence analyses of their 18S rRNA. Although Acanthamoeba polyphaga HN-3 clearly groups together with most of the known Acanthamoeba isolates (18S rRNA sequence type 4), Acanthamoeba sp. UWC9 and UWE39 exhibit < 92% 18S rRNA sequence similarity to each other and to other Acanthamoeba isolates. Therefore, we propose two new sequence types (T13 and T14) within the genus Acanthamoeba containing, respectively, Acanthamoeba sp. UWC9 and Acanthamoeba sp. UWE39.     

黄颡鱼卵水霉病病原的分离鉴定及其无性繁殖特性

【目的】对黄颡鱼卵水霉病病原进行分离鉴定,并对其无性繁殖特性进行研究。【方法】采用传统方法从患水霉病的黄颡鱼卵上进行丝状真菌的分离,然后通过人工感染实验证实分离菌株的致病性,通过形态学观察和ITS rDNA序列分析对致病菌株进行鉴定,并进一步通过单因子法研究其无性繁殖特性。【结果】从患水霉病的黄颡鱼卵上分离了4株丝状真菌,经人工感染试验证实其中一株丝状真菌HP对黄颡鱼卵具有致病性,并进一步研究了其形态与无性繁殖特性,开展了ITS rDNA序列分析。实验结果表明,菌株HP菌丝为透明管状结构,中间无横隔,分枝较少;游动孢子囊多数呈棒状,游动孢子发育成熟后从孢子囊中释放出来,并迅速游离;能够产生第二孢孢子;新孢子囊以内层出的方式产生;藏卵器呈球形,与雄器同枝或异枝。菌株HP的ITS rDNA序列与GenBank基因库中水霉属菌株自然聚类,同源性高达99%,与多子水霉菌株Arg4S(GenBank登录号GQ119935)的亲缘关系最近。结合形态特征与ITS序列鉴定的结果,判定菌株HP为多子水霉(Saprolegnia ferax)。此外,菌株HP在5°C-35°C、pH 4-10范围内均能产生游动孢子,产生游动孢子的最适温度和pH分别为20°C和7,而且5-25 mg/L福尔马林和0.25 1.25 mg/L二硫氰基甲烷对菌株HP产生游动孢子具有明显的抑制作用。【结论】分离鉴定了黄颡鱼卵水霉病病原,并确定了其无性繁殖特性,可以作为该病防治用药的依据。     

Keratinocytes synthesize Ia antigen in acute cutaneous graft-vs-host disease

Keratinocytes express la antigen (Ia) during cutaneous graft-vs-host disease (GVHD); it is, however, unclear whether this Ia is adsorbed from alloactivated donor lymphocytes or from Ia-bearing host Langerhans cells (LC), or whether it is actively synthesized by host keratinocytes. We therefore sought to determine the origin of keratinocyte Ia in a murine model of GVHD. Lethally irradiated C3H/He (H-2k) mice developed characteristic histopathologic changes of acute cutaneous GVHD 7 days after injection of BALB/c (H-2d) bone marrow and spleen cells, and expressed keratinocyte Ia of host (Iak) but not donor (Iad) origin in immunofluorescence studies. To determine whether the Ia was synthesized by keratinocytes or adsorbed from host LC, we investigated GVHD that was induced in chimeric mice. Parental strain A mice were made chimeric by lethal irradiation and reconstitution with (A X B)F1 bone marrow cells as follows: (BALB/c X C3H/He)F1 (H-2d,k) leads to C3H/He (H-2k), B6C3F1 (H-2b,k) leads to C57BL/6 (H-2b), and B6C3F1 (H-2b,k) leads to C3H/He (H-2k). After 3 mo, the LC in the skin of these chimeric mice were mainly of F1 haplotype. The chimeric mice were again lethally irradiated and injected with marrow and spleen cells from a third strain of mouse (C57BL/6, H-2b or BALB/c, H-2d) histoincompatible with both F1 parental strains. In the ensuing GVHD, the chimeric recipients only expressed keratinocyte Ia syngeneic to the original haplotype of the animal (strain A), despite the fact that the majority of their LC were derived from F1 marrow and expressed Ia of both F1 parental strain haplotypes (strains A and B). Together, these findings indicate that keratinocyte Ia in GVHD is synthesized by keratinocytes and is not derived from donor lymphocytes or adsorbed from host LC.     

一株抗水稻纹枯病菌的解淀粉芽胞杆菌分离与鉴定

【目的】筛选对水稻纹枯病菌(Rhizoctonia solani)具有强拮抗作用的细菌菌株。【方法】用指示菌法筛选拮抗菌株;通过形态观察、生理生化实验、Biolog及16S rDNA序列分析鉴定目标菌株;利用平板双向培养法和滤纸片扩散法测定抑菌谱及拮抗性质。【结果】分离到一株高活力的水稻纹枯病菌拮抗菌株YB-3,该菌株属于解淀粉芽胞杆菌(Bacillus amyloliquefaciens);菌株YB-3对常见的14株病原真菌和7株细菌具有较强的拮抗作用,并发现其对亲缘关系较近的芽孢菌属有较强的拮抗作用;该菌株的抑制活性具有温度稳定、耐酸、但对蛋白酶敏感的特点。【结论】通过指示菌法筛选到一株对水稻纹枯病菌有强拮抗作用的解淀粉芽胞杆菌(B.amyloliquefaciens)YB-3,它具有广谱、高效的植物病原菌拮抗活性。     

春兰菌根真菌CL-3菌株的鉴定及共生体系的构建

采用分离自野生春兰(Cymbidium goeringii)根部的真菌CL-3菌株, 进行了春兰内生菌根真菌的人工接种、再分离及其共生培养研究。通过对CL-3菌株形态学观察和ITS序列同源性分析, 发现该菌株ITS序列与Acremonium strictum的亲缘关系最为接近, 序列同源性为100%。用CL-3菌株接种春兰组培苗, 接种后2个月可从组培苗中再分离获得该菌株, 且CL-3菌株处理苗的鲜重增长率达80.5%, 经方差分析, 与对照相比有显著差异。通过石蜡切片和染色, 在已接种的组培苗的根部组织中可观察到CL-3菌株存在。表明CL-3菌株能与组培幼苗成功建立共生培养体系。     

Differences in the fitness of two diverse wild-type human immunodeficiency virus type 1 isolates are related to the efficiency of cell binding and entry

The ability of one primary human immunodeficiency virus type 1 (HIV-1) isolate to outcompete another in primary CD4+ human lymphoid cells appears to be mediated by the efficiency of host cell entry. This study was designed to test the role of entry on fitness of wild-type HIV-1 isolates (e.g., replicative capacity) and to examine the mechanism(s) involved in differential entry efficiency. The gp120 coding regions of two diverse HIV-1 isolates (the more-fit subtype B strain, B5-91US056, and less-fit C strain, C5-97ZA003) were cloned into a neutral HIV-1 backbone by using a recently described yeast cloning technique. The fitness of the primary B5 HIV-1 isolates and its env gene cloned into the NL4-3 laboratory strain had similar fitness, and both were more fit than the C5 primary isolate and its env/NL4-3 chimeric counterpart. Increased fitness of the B5 over C5 virus was mediated by the gp120 coding region of the env gene. An increase in binding/fusion, as well as decreased sensitivity to entry inhibitors (PSC-RANTES and T-20), was observed in cell fusion assays mediated by B5 gp120 compared to C5 gp120. Competitive binding assays using a novel whole virus-cell system indicate that the primary or chimeric B5 had a higher avidity for CD4/CCR5 on host cells than the C5 counterpart. This increased avidity of an HIV-1 isolate for its cell receptors may be a significant factor influencing overall replicative capacity or fitness.     

沙坡头地区根瘤菌DNA同源性及16SrDNA全序列

数值分类和多位点酶电泳分析表明,分离自宁夏沙坡头 地区的12株根瘤菌构成一个独立的表观群。对这一菌群进行了DNA同源性和群内中心菌株1 6SrDNA全序列分析。12个菌株的G+C mol%在56.4～62.2范围内;群内DNA同源性为72.3% ～9.5%,大于70%,属种内水平;中心株N220的16SrDNA全序列与参比菌株的序列比较,从 模拟系统发育树看出,它与三株土壤杆菌、三株根瘤菌的16SrDNA序列同源性在94.8%～99 .2%的相似性水平上构成一个分支,看来沙坡头地区这群根瘤菌是一个独立的新种群。     

DEFECT OF ERYTHROPOIESIS IN NON-LEUKAEMIC AKR MICE

The kinetics of the CFU population and of erythropoiesis were investigated in the AKR strain mouse prior to the onset of thymic leukaemias: haemopoiesis was compared in syngeneic AKR, semi-allogenic C3H and (C3H x AKR) F, mice injected with AKR stem cells. These experiments demonstrate that the reduction in the number of spleen colonies previously described by Perkins et al. (1971) in syngeneic hosts, as compared to semi-allogenic C3H hosts, is actually related to defective erythropoiesis resulting from a dysfunction of the AKR haemopoietic inductive microenvironment (HIM). Erythropoietin secretion is normal in AKR mice. the early haemopoietic events related to the stem cell: lodgement of the CFU (‘f’ factor) and doubling time, are not disturbed, but the onset of CFU proliferation is markedly delayed in the AKR strain. the main expression of the AKR HIM dysfunction is a significant reduction in the number of erythroid (E) colonies and an impaired output of red blood cells per E-colony in the syngeneic host as compared to the allogenic one. In addition, data indicate that a weakly histo-incompatible system, such as that in C3H and hybrid hosts, does not interfere with the stages of haemopoiesis except by lengthening the doubling time of the CFU. the results, on the whole, emphasize the prevalent influence of HIM.     

Use of coisogenic host blastocysts for efficient establishment of germline chimeras with C57BL/6J ES cell lines.

Gene targeting in embryonic stem (ES) cells allows the production of mice with specified genetic mutations. Currently, germline-competent ES cell lines are available from only a limited number of mouse strains, and inappropriate ES cell/host blastocyst combinations often restrict the efficient production of gene-targeted mice. Here, we describe the derivation of C57BL/6J (B6) ES lines and compare the effectiveness of two host blastocyst donors, FVB/NJ (FVB) and the coisogenic strain C57BL/6-Tyr(c)-2J (c2J), for the production of germline chimeras. We found that when B6 ES cells were injected into c2J host blastocysts, a high rate of coat-color chimerism was detected, and germline transmission could be obtained with few blastocyst injections. In all but one case, highly chimeric mice transmitted to 100% of their offspring. The injection of B6 ES cells into FVB blastocysts produced some chimeric mice. However; the proportion of coat-color chimerism was low, with many more blastocyst injections required to generate chimeras capable of germline transmission. Our data support the use of the coisogenic albino host strain, c2J, for the generation of germline-competent chimeric mice when using B6 ES cells.