The mouse CD3-gamma, -delta, and -epsilon genes reside within 50 kilobases on chromosome 9, whereas CD3-zeta maps to chromosome 1, band H

Both TCR alpha and TCR delta chain diversity are regulated during thymic ontogeny

TCRalpha and TCRdelta chains are coded by a common genetic locus using a single set of V gene segments (ADV segments). This article addresses the question of regulation of the use of the ADV segments by the TCRalpha and TCRdelta chains. Using both qualitative and quantitative analyses we have studied the use of 23 ADV gene families as part of TCRalpha and TCRdelta transcripts. A number of previously undetected rearrangement and transcription events are described, indicating that the intrathymic TCRdelta repertoire is much more diverse than previously supposed. Repertoire analysis at several developmental time points allowed the description of regulated waves of ADV gene use, not only for TCRdelta chains, but also for TCRalpha chains, during thymic ontogeny. Control of these waves appears to be linked directly to the ADV segments and their local chromatin environment, which may change over the course of T cell differentiation.

Specific requirement for CD3epsilon in T cell development

T cell antigen receptor (TCR) and pre-TCR complexes are composed of clonotypic heterodimers in association with dimers of signal transducing invariant subunits (CD3gamma, -delta, -epsilon, and zeta). The role of individual invariant subunits in T cell development has been investigated by generating gene-specific mutations in mice. Mutation of CD3gamma, -delta, or zeta results in an incomplete block in development, characterized by reduced numbers of mature T cells that express low levels of TCR. In contrast, mature T cells are absent from CD3epsilon-/- mice, and thymocyte development is arrested at the early CD4(-)CD8(-) stage. Although these results suggest that CD3epsilon is essential for pre-TCR and TCR expression/function, their interpretation is complicated by the fact that expression of the CD3gamma and CD3delta genes also is reduced in CD3epsilon-/- mice. Thus, it is unclear whether the phenotype of CD3epsilon-/- mice reflects the collective effects of CD3gamma, -delta, and -epsilon deficiency. By removing the selectable marker (PGK-NEO) from the targeted CD3epsilon gene via Cre/loxP-mediated recombination, we generated mice that lack CD3epsilon yet retain normal expression of the closely linked CD3gamma and CD3delta genes. These (CD3epsilonDelta/Delta) mice exhibited an early arrest in T cell development, similar to that of CD3epsilon-/- mice. Moreover, the developmental defect could be rescued by expression of a CD3epsilon transgene. These results identify an essential role for CD3epsilon in T cell development not shared by the CD3gamma, CD3delta, or zeta-family proteins and provide further evidence that PGK-NEO can influence the expression of genes in its proximity.

TCR-associated zeta-Fc epsilon RI gamma heterodimers on CD4-CD8- NK1.1+ T cells selected by specific class I MHC antigen

The origin of autoreactive CD4-CD8- T cells is largely unknown. In TCR transgenic (Tg) mice expressing the cognate class I MHC antigen, CD4-CD8- T cells differed depending on characteristics of Tg-TCR/antigen interaction. Tg-TCR/CD3lo CD4-CD8- T cells expressing the NK1.1 marker were observed only for a Tg-TCR whose stimulation by antigen was independent of CD8. Unlike normal T cells, which have essentially TCR-associated zeta homodimers, these cells had a high proportion of TCR-associated zeta-Fc epsilon RI gamma heterodimers. They were also characterized by an unusually high content of Fc epsilon RI gamma mRNA and low content of mRNA encoding CD3 epsilon, CD3 gamma, CD3 delta, and zeta. Based on their phenotype and selection requirements, it is proposed that CD4-CD8- thymic precursor cells can be driven along the CD4-CD8-NK1.1+ pathway following coreceptor-independent TCR signaling at an intrathymic stage when Fc epsilon RI gamma and CD3 components are coexpressed.

T cell development in CD3-zeta mutant mice

Increasing evidence points to multiple pathways of T lymphocyte development. The well characterized thymus-dependent pathway gives rise to T cells bearing TCR alpha beta heterodimers and either CD4 or CD8 alpha beta co-receptors. T cells of this lineage populate peripheral lymphoid compartments including lymph nodes, spleen, skin, and Peyer's patches. By comparison, factors which govern extrathymic T cell development are poorly understood. A variety of experiments have shown that intestinal intraepithelial lymphocytes (IELs) develop outside of the thymic environment, e.g., in the gut of nude, SCID, and beta 2m-/- mutant mice, and after transplanting bone marrow or fetal liver cells into irradiated thymectomized adult mice. This review focuses on the role of the CD3-zeta subunit in the development of both thymically and extrathymically derived T cells as determined by gene-targeting experiments in mice. Data from these and other T cell-related mutations continue to define crucial stages in thymocyte differentiation. Most interestingly, CD3-zeta mutant mice contain a unique population of intestinal IELs that develops independently of thymic selective processes and expresses a novel TCR/CD3 complex.

Mouse homologues of human hereditary disease

Details are given of 214 loci known to be associated with human hereditary disease, which have been mapped on both human and mouse chromosomes. Forty two of these have pathological variants in both species; in general the mouse variants are similar in their effects to the corresponding human ones, but exceptions include the Dmd/DMD and Hprt/HPRT mutations which cause little, if any, harm in mice. Possible reasons for phenotypic differences are discussed. In most pathological variants the gene product seems to be absent or greatly reduced in both species. The extensive data on conserved segments between human and mouse chromosomes are used to predict locations in the mouse of over 50 loci of medical interest which are mapped so far only on human chromosomes. In about 80% of these a fairly confident prediction can be made. Some likely homologies between mapped mouse loci and unmapped human ones are also given. Sixty six human and mouse proto-oncogene and growth factor gene homologies are also listed; those of confirmed location are all in known conserved segments. A survey of 18 mapped human disease loci and chromosome regions in which the manifestation or severity of pathological effects is thought to be the result of genomic imprinting shows that most of the homologous regions in the mouse are also associated with imprinting, especially those with homologues on human chromosomes 11p and 15q. Useful methods of accelerating the production of mouse models of human hereditary disease include (1) use of a supermutagen, such as ethylnitrosourea (ENU), (2) targeted mutagenesis involving ES cells, and (3) use of gene transfer techniques, with production of 'knockout mutations'.

The gamma-zeta dimers of Fc receptors as connectors to signal transduction

The gamma-chain of the high affinity receptor for IgE and the zeta-chain of the T-cell antigen receptor associate with various receptors. These chains play a major role in assembly of these receptors and are critical for signal transduction.

The T cell receptor/CD3 complex is composed of at least two autonomous transduction modules

Recent studies have demonstrated that the CD3-zeta subunit of the T cell antigen receptor (TCR) complex is involved in signal transduction. However, the function of the remaining invariant subunits, CD3-gamma, -delta, and epsilon, is still poorly understood. To examine their role in TCR function, we have constructed TCR/CD3 complexes devoid of functional zeta subunit and showed that they are still able to trigger the production of interleukin-2 in response to antigen or superantigen. These data, together with previous results, indicate that the TCR/CD3 complex is composed of at least two parallel transducing units, made of the gamma delta epsilon and zeta chains, respectively. Furthermore, the analysis of partially truncated zeta chains has led us to individualize a functional domain that may have constituted the building block of most of the transducing subunits associated with antigen receptors and some Fc receptors.

Structure of the T cell antigen receptor (TCR): two CD3 epsilon subunits in a functional TCR/CD3 complex

Transgenic mice carrying and expressing the human CD3 epsilon gene incorporate the corresponding protein product into T cell receptor (TCR)/CD3 complexes on thymocyte and T cell surfaces. The chimeric antigen receptors allow normal T cell development and selection of repertoires in vivo and are able to transduce activation signals in vitro. We have exploited the ability to distinguish mouse (m) and human (h)CD3 epsilon chains to analyze the stoichiometry of CD3 epsilon in transgenic mouse TCRs. Immunoprecipitation and fluorescence resonance energy transfer experiments demonstrate that such TCRs can contain both h- and mCD3 epsilon chains, implying that more than one CD3 epsilon subunit occurs per TCR. Antigen comodulation studies are consistent with a stochastic use of h- or mCD3 epsilon during receptor assembly, and further suggest a structure for the TCR/CD3 complex with two CD3 epsilon chains. The determination of CD3 epsilon subunit stoichiometry, together with existing biochemical data, allows the generation of a minimal model for the structure of the TCR and illustrates the potential value of the transgenic approach to the analysis of complex receptors.

Characterization of the CD3 gamma and delta invariant subunits of the sheep T cell antigen receptor

The CD3 gamma and delta chains of the sheep T cell antigen receptor have been characterized by cDNA cloning. In comparison to human and mouse protein sequences, short oligopeptide stretches have been deleted from both the gamma and delta chains. However, apart from further variability in the number and position of potential N-linked glycosylation sites, the general structure of the CD3 gamma and delta proteins is markedly conserved. Particularly remarkable are two motifs consisting of 8 and 32 amino acids, respectively, which locate in the C-terminal half of each protein and which have been precisely conserved in both the CD3 gamma and delta chains of all three species. These motifs probably contribute structural properties essential for the function of the CD3/T cell receptor complex. mRNA of the sheep CD3 gamma (1.5 and 1.2 kb) and CD3 delta (1.5 kb) chains are transcribed from closely linked, single-copy genes, suggesting that common mechanisms for the regulation of CD3 genes are also preserved between species.

DNase I-defined chromatin configuration of the human CD3 gene cluster

The three CD3 genes on human chromosome 11q23 encode proteins (gamma, delta and epsilon) which form part of the antigen receptor on T lymphocytes. All three genes are clustered within 50 kb and are activated approximately contemporaneously during the early stages of T cell ontogeny. In order to pinpoint potential regulatory sequences important for locus activation and tissue-specific gene expression, the chromatin structure of almost 90 kb of this region has been probed in five cell lines using the endonuclease pancreatic DNase I. A set of DNase I hypersensitive (HS) sites has been defined in T cell chromatin, five of which were strong and not found in non-T cells, with the exception of the erythroleukaemia cell line K562, in which three sites were weakly expressed, correlating with a low level of delta mRNA. The subset of five HS sites map close to the CD3 genes and lie in regions which contain elements of defined function: the gamma promoter; the delta promoter and its 3' enhancer; and the epsilon promoter and its 3' enhancer. Since no further major T cell-restricted HS sites lie within the 90kb of the CD3 locus analysed, these five regions may contain all the sequences important for CD3 gene expression.