Faculty Bibliography

Spinal interneurons help to coordinate motor behavior. During spinal cord development, distinct classes of interneurons are generated from progenitor cells located at different positions within the ventral neural tube. V0 and V1 interneurons derive from adjacent progenitor domains that are distinguished by expression of the homeodomain proteins Dbx1 and Dbx2. The spatially restricted expression of Dbx1 has a critical role in establishing the distinction in V0 and V1 neuronal fate. In Dbx1 mutant mice, neural progenitors fail to generate V0 neurons and instead give rise to interneurons that express many characteristics of V1 neurons-their transcription factor profile, neurotransmitter phenotype, migratory pattern, and aspects of their axonal trajectory. Thus, a single progenitor homeodomain transcription factor coordinates many of the differentiated properties of one class of interneurons generated in the ventral spinal cord

The human immunodeficiency virus has evolved various mechanisms to exploit its host cells, including the interruption and augmentation of signal transduction pathways. Recently, two DNA microarray studies have illustrated a remarkably broad-based perturbation in host transcriptional responses, which is in part mediated by the HIV-encoded Nef protein. HIV therefore seems to function as a 'master regulator' of cellular gene expression

The cytoplasmic protein tyrosine kinase Tec has been proposed to have important functions in hematopoiesis and lymphocyte signal transduction. Here we show that Tec-deficient mice developed normally and had no major phenotypic alterations of the immune system. To reveal potential compensatory roles of other Tec kinases such as Bruton's tyrosine kinase (Btk), Tec/Btk double-deficient mice were generated. These mice exhibited a block at the B220(+)CD43(+) stage of B cell development and displayed a severe reduction of peripheral B cell numbers, particularly immunoglobulin (Ig)M(lo)IgD(hi) B cells. Although Tec/Btk(null) mice were able to form germinal centers, the response to T cell-dependent antigens was impaired. Thus, Tec and Btk together have an important role both during B cell development and in the generation and/or function of the peripheral B cell pool. The ability of Tec to compensate for Btk may also explain phenotypic differences in X-linked immunodeficiency (xid) mice compared with human X-linked agammaglobulinemia (XLA) patients

Chemokines play necessary and important roles in regulating the trafficking of lymphocytes to intra- or interlymphoid tissues as well as to sites of inflammation. The complex migratory patterns of lymphoid lineage cells is governed by subset-specific expression of chemokine receptors and their access to specific ligands. Several chemokine receptors and chemokine receptor-like orphan receptors also serve, in conjunction with CD4, as coreceptors for infection by human and simian immunodeficiency viruses (HIV and SIV). Here we show that the expression pattern of Bonzo/STRL33, an orphan SIV/HIV coreceptor, is highly restricted to the memory subset of T cells and is up-regulated upon stimulation of these cells with IL-2 or IL-15. Both the pattern and the regulation of Bonzo expression closely paralleled that of CC family chemokine receptors CCR5 or CCR6 and inversely correlated with CXCR4 expression. However, in striking contrast to CCR5, Bonzo expression was not down-modulated by PMA or mitogen stimulation of T cells. Targeted replacement of the Bonzo gene with a gene encoding green fluorescent protein in mice revealed that the expression and cytokine regulation of mouse Bonzo are comparable to those of its human counterpart. The similar expression and regulation patterns of Bonzo and the HIV coreceptor CCR5 may have implications for understanding the role of HIV/SIV receptors in viral evolution and pathogenesis

Stimulation of beta-adrenergic receptor normally results in signaling by the heterotrimeric G protein G(s), leading to the activation of adenylyl cyclase, production of cAMP, and activation of cAMP-dependent protein kinase (PKA). Here we report that cell death of thymocytes can be induced after stimulation of beta-adrenergic receptor, or by addition of exogenous cAMP. Apoptotic cell death in both cases was observed with the appearance of terminal deoxynucleotidyl transferase-mediated UTP end labeling reactivity and the activation of caspase-3 in S49 T cells. Using thymocytes deficient in either Galpha(s) or PKA, we find that engagement of beta-adrenergic receptors initiated a Galpha(s)-dependent, PKA-independent pathway leading to apoptosis. This alternative pathway involves Src family tyrosine kinase Lck. Furthermore, we show that Lck protein kinase activity can be directly stimulated by purified Galpha(s). Our data reveal a new signaling pathway for Galpha(s), distinct from the classical PKA pathway, that accounts for the apoptotic action of beta-adrenergic receptors

Most developing thymocytes undergo apoptosis because they cannot interact productively with molecules encoded by the major histocompatibility complex. Here, we show that mice lacking the orphan nuclear hormone receptor RORgamma lose thymic expression of the anti-apoptotic factor Bcl-xL. RORgamma thus regulates the survival of CD4+8+ thymocytes and may control the temporal window during which thymocytes can undergo positive selection. RORgamma was also required for development of lymph nodes and Peyer's patches, but not splenic follicles. In its absence, there was loss of a population of CD3-CD4+CD45+ cells that normally express RORgamma and that are likely early progenitors of lymphoid organs. Hence, RORgamma has critical functions in T cell repertoire selection and lymphoid organogenesis

The seven-transmembrane receptor CX(3)CR1 is a specific receptor for the novel CX(3)C chemokine fractalkine (FKN) (neurotactin). In vitro data suggest that membrane anchoring of FKN, and the existence of a shed, soluble FKN isoform allow for both adhesive and chemoattractive properties. Expression on activated endothelium and neurons defines FKN as a potential target for therapeutic intervention in inflammatory conditions, particularly central nervous system diseases. To investigate the physiological function of CX(3)CR1-FKN interactions, we generated a mouse strain in which the CX(3)CR1 gene was replaced by a green fluorescent protein (GFP) reporter gene. In addition to the creation of a mutant CX(3)CR1 locus, this approach enabled us to assign murine CX(3)CR1 expression to monocytes, subsets of NK and dendritic cells, and the brain microglia. Analysis of CX(3)CR1-deficient mice indicates that CX(3)CR1 is the only murine FKN receptor. Yet, defying anticipated FKN functions, absence of CX(3)CR1 interferes neither with monocyte extravasation in a peritonitis model nor with DC migration and differentiation in response to microbial antigens or contact sensitizers. Furthermore, a prominent response of CX(3)CR1-deficient microglia to peripheral nerve injury indicates unimpaired neuronal-glial cross talk in the absence of CX(3)CR1

Productive interaction of a T lymphocyte with an antigen-presenting cell results in the clustering of the T-cell antigen receptor (TCR) and the recruitment of a large signalling complex to the site of cell-cell contact. Subsequent signal transduction resulting in cytokine gene expression requires the activation of one or more of the multiple isoenzymes of serine/threonine-specific protein kinase C (PKC). Among the several PKC isoenzymes expressed in T cells, PKC-theta is unique in being rapidly recruited to the site of TCR clustering. Here we show that PKC-theta is essential for TCR-mediated T-cell activation, but is dispensable during TCR-dependent thymocyte development. TCR-initiated NF-kappaB activation was absent from PKC-theta(-/-) mature T lymphocytes, but was intact in thymocytes. Activation of NF-kappaB by tumour-necrosis factor alpha and interleukin-1 was unaffected in the mutant mice. Although studies in T-cell lines had suggested that PKC-theta regulates activation of the JNK signalling pathway, induction of JNK was normal in T cells from mutant mice. These results indicate that PKC-theta functions in a unique pathway that links the TCR signalling complex to the activation of NF-kappaB in mature T lymphocytes