Identification of regulatory regions that determine expression of murine CD8 locus

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Identification of regulatory regions that determine expression of the murine CD8 locus

The coreceptors CD4 and CD8 play a crucial role during thymocyte development and T cell effector function and their expression is developmentally regulated. To determine the molecular mechanisms underlying the regulation of CD8 gene expression, the murine CDS gene locus was cloned and analysed for deoxyribonuclease (DNaseI) hypersensitivity. Such analysis revealed three thymocyte specific DNaseI hypersensitive regions (cluster II, III and IV). To characterise the role of different clusters of hypersensitive sites in CD8 gene regulation in the context of the endogenous chromosomal location, we deleted selected regions from the mouse genome by homologous recombination. Deletion of cluster III (either all three sites or just sites 1 and 2), which is located in the intergenic region between the CD8α and β genes and directs expression of a reporter transgene in mature CD8 T cells only, affected expression of CD8αα homodimers on intraepithelial (IEL) T cells, both on γδTCR and αβTCR subsets. Surprisingly, none of the thymocyte or peripheral αβTCR CD8αβ T cell subsets were affected by this mutation, which indicated differential activation of these elements within the various T cell subsets. Deletion of cluster II, which is located immediately upstream of the CD8α gene, had two main effects: it affected the levels of expression of the CD8 gene and caused an abnormal subset distribution in the thymus with fewer DP and CDS SP cells and an increase in cells with a CD4 SP phenotype. Staining with several maturation markers, showed that the increased numbers of thymocytes falling within the CD4 SP gate were immature cells. It is concluded that removal of regulatory sequences present in cluster II disturbs the normal developmental chromatin remodelling of the CD8 locus and as a consequence the expression of the CD8α gene

Maturation-Promoting Activity of SATB1 in MGE-Derived Cortical Interneurons

The generation of cortical interneuron subtypes is controlled by genetic programs that are activated in the ventral forebrain and unfold during the prolonged period of inhibitory neuron development. The LIM-homeodomain protein LHX6 is critical for the development of all cortical interneurons originating in the medial ganglionic eminence, but the molecular mechanisms that operate downstream of LHX6 to control the terminal differentiation of somatostatin- and parvalbumin-expressing interneurons within the cortex remain unknown. Here, we provide evidence that the nuclear matrix and genome organizer protein SATB1 is induced by neuronal activity and functions downstream of Lhx6 to control the transition of tangentially migrating immature interneurons into the terminally differentiated Somatostatin (SST)-expressing subtype. Our experiments provide a molecular framework for understanding the genetic and epigenetic mechanisms by which specified but immature cortical interneurons acquire the subtype-defining molecular and morphophysiological characteristics that allow them to integrate and function within cortical circuits

Differential RET signaling pathways drive development of the enteric lymphoid and nervous systems

© 2008 by the American Association for the Advancement of Science; all rights reserved.During the early development of the gastrointestinal tract, signaling through the receptor tyrosine kinase RET is required for initiation of lymphoid organ (Peyer’s patch) formation and for intestinal innervation by enteric neurons. RET signaling occurs through glial cell line–derived neurotrophic factor (GDNF) family receptor α co-receptors present in the same cell (signaling in cis). It is unclear whether RET signaling in trans, which occurs in vitro through co-receptors from other cells, has a biological role. We showed that the initial aggregation of hematopoietic cells to form lymphoid clusters occurred in a RET-dependent, chemokine-independent manner through adhesion-mediated arrest of lymphoid tissue initiator (LTin) cells. Lymphoid tissue inducer cells were not necessary for this initiation phase. LTin cells responded to all RET ligands in trans, requiring factors from other cells, whereas RET was activated in enteric neurons exclusively by GDNF in cis. Furthermore, genetic and molecular approaches revealed that the versatile RET responses in LTin cells were determined by distinct patterns of expression of the genes encoding RET and its co-receptors. Our study shows that a trans RET response in LTin cells determines the initial phase of enteric lymphoid organ morphogenesis, and suggests that differential co-expression of Ret and Gfra can control the specificity of RET signaling