Neonatal death in mice lacking cardiotrophin-like cytokine is associated with multifocal neuronal hypoplasia

Mice with null mutations of ciliary neurotrophic factor (Cntf) receptor alpha (Cntf-Ralpha), or cytokine-like factor 1 (Clf), one component of Cntf-II (a heterodimeric Cntf-Ralpha ligand), die as neonates from motor neuron loss affecting the facial nucleus and ventral horn of the lumbar spinal cord. Exposure to cardiotrophin-like cytokine (Clc), the other putative Cntf-II element, supports motor neuron survival in vitro and in ovo. Confirmation that Clc ablation induces an equivalent phenotype to Clf deletion would support a role for Clc in the functional Cntf-II complex. In this study, Clc knockout mice had decreased facial motility, did not suckle, died within 24 hours, and had 32% and 29% fewer motor neurons in the facial nucleus and lumbar ventral horn, respectively; thus, Clc is essential for motor neuron survival during development. The concordance of the Clc knockout phenotype with those of mice lacking Cntf-Ralpha or Clf bolsters the hypothesis that Clc participates in Cntf-II.

Repair-deficient 3-methyladenine DNA glycosylase homozygous mutant mouse cells have increased sensitivity to alkylation-induced chromosome damage and cell killing

In Escherichia coli, the repair of 3-methyladenine (3MeA) DNA lesions prevents alkylation-induced cell death because unrepaired 3MeA blocks DNA replication. Whether this lesion is cytotoxic to mammalian cells has been difficult to establish in the absence of 3MeA repair-deficient cell lines. We previously isolated and characterized a mouse 3MeA DNA glycosylase cDNA (Aag) that provides resistance to killing by alkylating agents in E. coli. To determine the in vivo role of Aag, we cloned a large fragment of the Aag gene and used it to create Aag-deficient mouse cells by targeted homologous recombination. Aag null cells have no detectable Aag transcripts or 3MeA DNA glycosylase activity. The loss of Aag renders cells significantly more sensitive to methyl methanesulfonate-induced chromosome damage, and to cell killing induced by two methylating agents, one of which produces almost exclusively 3MeAs. Aag null embryonic stem cells become sensitive to two cancer chemotherapeutic alkylating agents, namely 1,3-bis(2-chloroethyl)-1-nitrosourea and mitomycin C, indicating that Aag status is an important determinant of cellular resistance to these agents. We conclude that this mammalian 3MeA DNA glycosylase plays a pivotal role in preventing alkylation-induced chromosome damage and cytotoxicity.

Abnormal T cell development in CD3-zeta-/- mutant mice and identification of a novel T cell population in the intestine

The T cell antigen receptor (TCR)-associated invariable membrane proteins (CD3-gamma, -delta, -epsilon and -zeta) are critical to the assembly and cell surface expression of the TCR/CD3 complex and to signal transduction upon engagement of TCR with antigen. Disruption of the CD3-zeta gene by homologous recombination resulted in a structurally abnormal thymus which primarily contained CD4- CD8- and TCR/CD3very lowCD4+CD8+ cells. Spleen and lymph nodes of CD3-zeta-/- mutant mice contained a normal number and ratio of CD4+ and CD8+ single positive cells that were TCR/CD3very low. These splenocytes did not respond to antibody cross-linking or mitogenic triggering. The V beta genes of CD4-CD8- and CD4+CD8+ thymocytes and splenic T cells were productively rearranged. These data demonstrated that (i) in the absence of the CD3-zeta chain, the CD4- CD8- thymocytes could differentiate to CD4+CD8+ TCR/CD3very low thymocytes, (ii) that thymic selection might have occurred, (iii) but that the transition to CD4+CD8- and CD4-CD8+ cells took place at a very low rate. Most strikingly, intraepithelial lymphocytes (IELs) isolated from the small intestine or the colon expressed normal levels of TCR/CD3 complexes on their surface which contained Fc epsilon RI gamma homodimers. In contrast to CD3-zeta containing IELs, these cells failed to proliferate after triggering with antibody cross-linking or mitogen. In comparison to thymus-derived peripheral T cells in the spleen and lymph nodes, the preferential expression of normal levels of TCR/CD3 in intestinal IELs suggested they mature via an independent extrathymic pathway.

Immunoglobulin gene rearrangement in B cell deficient mice generated by targeted deletion of the JH locus

B lymphocyte differentiation is characterized by an ordered series of Ig gene assembly and expression events. In the majority of normal B cells, assembly and expression of Ig heavy (H) chain genes precedes that of light (L) chain genes. To determine the role of the Ig heavy chain protein in B cell development and L chain gene rearrangement, we have generated mice that cannot assemble Ig H chain genes as a result of targeted deletion of the JH gene segments in embryonic stem cells. Mice homozygous for this deletion are devoid of slg+ B cells in the bone marrow and periphery. B cell differentiation in these mice is blocked at the large, CD43+ precursor stage. However, these precursor B cells do assemble kappa L chain genes at a low level in the absence of mu H chain proteins. These data demonstrate that rearrangement and expression of the mu H chain gene is not absolutely required for kappa L chain gene rearrangement in vivo. Expression of mu chains may facilitate either efficient L chain gene rearrangement or the survival of cells that have rearranged light chain genes by promoting the differentiation of large, CD43+ to small, CD43- pre-B cells.

B cell development in mice that lack one or both immunoglobulin kappa light chain genes

We have generated mice that lack the ability to produce immunoglobulin (Ig) kappa light chains by targeted deletion of J kappa and C kappa gene segments and the intervening sequences in mouse embryonic stem cells. In wild type mice, approximately 95% of B cells express kappa light chains and only approximately 5% express lambda light chains. Mice heterozygous for the J kappa C kappa deletion have approximately 2-fold more lambda+ B cells than wild-type littermates. Compared with normal mice, homozygous mutants for the J kappa C kappa deletion have about half the number of B cells in both the newly generated and the peripheral B cell compartments, and all of these B cells express lambda light chains in their Ig. Therefore, homozygous mutant mice appear to produce lambda-expressing cells at nearly 10 times the rate observed in normal mice. These findings demonstrate that kappa gene assembly and/or expression is not a prerequisite for lambda gene assembly and expression. Furthermore, there is no detectable rearrangement of 3' kappa RS sequences in lambda+ B cells of the homozygous mutant mice, thus rearrangements of these sequences, per se, is not required for lambda light chain gene assembly. We discuss these findings in the context of their implications for the control of Ig light chain gene rearrangement and potential applications of the mutant animals.

A defect in cell-mediated immune function in insulin-resistant diabetic and obese subjects

In this study, we have evaluated one aspect of the cellular immune process--in vitro release of MIF by lymphocytes obtained from controls; well-controlled, ketosis-prone, insulin-dependent diabetic patients; nonketotic diabetic patients; and nonhyperglycemic obese patients. The results showed that MIF release by cells from well-controlled, insulin-dependent diabetic, nonketotic diabetic, and nonhyperglycemic obese subjects was 100% +/- 8, 48% +/- 17, and 36% +/- 17 of control values, respectively. Thus insulin-sensitive, ketosis-prone diabetic patients have normal MIf release while well-controlled on insulin therapy, whereas insulin-resistant, nonketotic diabetic and nonhyperglycemic obese patients have impaired MIF release. It is possible that this in vitro defect in a cellular immune process is related to the insulin-resistant state and that it may play a role in enhanced susceptibility to infection in insulin-resistant diabetic patients.

Rauscher virus-induced reticulum-cell sarcomas: Their growth in vitro and erythropoietic differentiation

A transplantable reticulum-cell sarcoma induced by Rauscher virus (RV) in (C57BL/6 X DBA/2)F1 (BDF1) mice was grown in tissue culture. Four separate cell lines were established, all of which grew predominantly in suspension. The doubling time of the cells from these cultures ranged from 17 to 32 h. Each culture continued to replicate RV, as indicated by the infectivity in newborn mice of all fluids tested up to the 75th passage. Since the morphological appearance of the cells in vitro was consistent with that of proerythroblasts, all cultures were tested for their ability to differentiate along the erythrocytic line under the influence of dimethylsulphoxide (DMSO). One of the cultures produced small quantities of haemoglobin independently of DMSO. Another was shown to produce haemoglobin, as well as to take up 59Fe and incorporate it into haem, only in the presence of DMSO. The 2 remaining cultures failed to produce haemoglobin, either spontaneously or in the presence of DMSO. Cells from each of the RV-induced cultures, when inoculated back into BDF1 mice, induced typical reticulum-cell sarcomas, without in vivo evidence of erythroid differentiation. In contrast, 2 morphologically identical but non-infectious cell lines derived from Friend virus-induced reticulum-cell sarcomas did not show erythroid differentiation in vivo or in vitro, either in the absence or presence of DMSO.

Unusually high incidence of spontaneous mammary carcinomata in a colony of BALB/c mice

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Helper specificity for retrieval of defective friend virus

A Friend virus-induced reticulum-cell sarcoma from BALB/c mice has been cultivated in vitro in our laboratory for more than 11 years and contains no detectable evidence of virus. However, Friend virus could be retrieved readily from the tissue cultures by any of several lymphatic leukemia viruses belonging to the Friend-Moloney-Rauscher (FMR) group, as long as the helper viruses were actively replicating in a culture. Helper activity appeared to be highly specific and limited to the FMR group including the B-tropic Tennant leukemia virus which produced a B-tropic Friend virus pseudotype. The naturally occurring type AKR murine leukemia viruses and the related Gross passage A virus failed both in vivo and in vitro to retrieve the Friend virus genome from the virus-free tumor cells.