General method for the modification of different BAC types and the rapid generation of BAC transgenic mice

Brain endothelial CXCL12 attracts protective natural killer cells during ischemic stroke

BACKGROUND

The innate lymphoid cell (ILC) family consists of NK cells, ILC type 1, 2, 3 and lymphoid tissue inducer cells. They have been shown to play important roles in homeostasis and immune responses and are generally considered tissue resident. Not much is known about the presence of ILC members within the central nervous system and whether they are tissue resident in this organ too. Therefore, we studied the presence of all ILC members within the central nervous system and after ischemic brain insult.

METHODS

We used the photothrombotic ischemic lesion method to induce ischemic lesions within the mouse brain. Using whole-mount immunofluorescence imaging, we established that the ILCs were present at the rim of the lesion. We quantified the increase of all ILC members at different time-points after the ischemic lesion induction by flow cytometry. Their migration route via chemokine CXCL12 was studied by using different genetic mouse models, in which we induced deletion of Cxcl12 within the blood-brain barrier endothelium, or its receptor, Cxcr4, in the ILCs. The functional role of the ILCs was subsequently established using the beam-walk sensorimotor test.

RESULTS

Here, we report that ILCs are not resident within the mouse brain parenchyma during steady-state conditions, but are attracted towards the ischemic stroke. Specifically, we identify NK cells, ILC1s, ILC2s and ILC3s within the lesion, the highest influx being observed for NK cells and ILC1s. We further show that CXCL12 expressed at the blood-brain barrier is essential for NK cells and NKp46⁺ ILC3s to migrate toward the lesion. Complementary, Cxcr4-deficiency in NK cells prevents NK cells from entering the infarct area. Lack of NK cell migration results in a higher neurological deficit in the beam-walk sensorimotor test.

CONCLUSIONS

This study establishes the lack of ILCs in the mouse central nervous system at steady-state and their migration towards an ischemic brain lesion. Our data show a role for blood-brain barrier-derived CXCL12 in attracting protective NK cells to ischemic brain lesions and identifies a new CXCL12/CXCR4-mediated component of the innate immune response to stroke.

PDGFRα-induced stromal maturation is required to restrain postnatal intestinal epithelial stemness and promote defense mechanisms

After birth, the intestine undergoes major changes to shift from an immature proliferative state to a functional intestinal barrier. By combining inducible lineage tracing and transcriptomics in mouse models, we identify a prodifferentiation PDGFRα^High intestinal stromal lineage originating from postnatal LTβR⁺ perivascular stromal progenitors. The genetic blockage of this lineage increased the intestinal stem cell pool while decreasing epithelial and immune maturation at weaning age, leading to reduced postnatal growth and dysregulated repair responses. Ablating PDGFRα in the LTBR stromal lineage demonstrates that PDGFRα has a major impact on the lineage fate and function, inducing a transcriptomic switch from prostemness genes, such as Rspo3 and Grem1, to prodifferentiation factors, including BMPs, retinoic acid, and laminins, and on spatial organization within the crypt-villus and repair responses. Our results show that the PDGFRα-induced transcriptomic switch in intestinal stromal cells is required in the first weeks after birth to coordinate postnatal intestinal maturation and function.

Distinct Waves from the Hemogenic Endothelium Give Rise to Layered Lymphoid Tissue Inducer Cell Ontogeny

During embryogenesis, lymphoid tissue inducer (LTi) cells are essential for lymph node organogenesis. These cells are part of the innate lymphoid cell (ILC) family. Although their earliest embryonic hematopoietic origin is unclear, other innate immune cells have been shown to be derived from early hemogenic endothelium in the yolk sac as well as the aorta-gonad-mesonephros. A proper model to discriminate between these locations was unavailable. In this study, using a Cxcr4-CreERT2 lineage tracing model, we identify a major contribution from embryonic hemogenic endothelium, but not the yolk sac, toward LTi progenitors. Conversely, embryonic LTi cells are replaced by hematopoietic stem cell-derived cells in adults. We further show that, in the fetal liver, common lymphoid progenitors differentiate into highly dynamic alpha-lymphoid precursor cells that, at this embryonic stage, preferentially mature into LTi precursors and establish their functional LTi cell identity only after reaching the periphery.

Expression of the human isoform of glutamate dehydrogenase, hGDH2, augments TCA cycle capacity and oxidative metabolism of glutamate during glucose deprivation in astrocytes

A key enzyme in brain glutamate homeostasis is glutamate dehydrogenase (GDH) which links carbohydrate and amino acid metabolism mediating glutamate degradation to CO₂ and expanding tricarboxylic acid (TCA) cycle capacity with intermediates, i.e. anaplerosis. Humans express two GDH isoforms, GDH1 and 2, whereas most other mammals express only GDH1. hGDH1 is widely expressed in human brain while hGDH2 is confined to astrocytes. The two isoforms display different enzymatic properties and the nature of these supports that hGDH2 expression in astrocytes potentially increases glutamate oxidation and supports the TCA cycle during energy-demanding processes such as high intensity glutamatergic signaling. However, little is known about how expression of hGDH2 affects the handling of glutamate and TCA cycle metabolism in astrocytes. Therefore, we cultured astrocytes from cerebral cortical tissue of hGDH2-expressing transgenic mice. We measured glutamate uptake and metabolism using [³ H]glutamate, while the effect on metabolic pathways of glutamate and glucose was evaluated by use of ¹³ C and ¹⁴ C substrates and analysis by mass spectrometry and determination of radioactively labeled metabolites including CO₂ , respectively. We conclude that hGDH2 expression increases capacity for uptake and oxidative metabolism of glutamate, particularly during increased workload and aglycemia. Additionally, hGDH2 expression increased utilization of branched-chain amino acids (BCAA) during aglycemia and caused a general decrease in oxidative glucose metabolism. We speculate, that expression of hGDH2 allows astrocytes to spare glucose and utilize BCAAs during substrate shortages. These findings support the proposed role of hGDH2 in astrocytes as an important fail-safe during situations of intense glutamatergic activity. GLIA 2017;65:474-488.

Fundamentals of vitamin D hormone-regulated gene expression

Initial research focused upon several known genetic targets provided early insight into the mechanism of action of the vitamin D hormone (1,25-dihydroxyvitamin D3 (1,25(OH)2D3)). Recently, however, a series of technical advances involving the coupling of chromatin immunoprecipitation (ChIP) to unbiased methodologies that initially involved tiled DNA microarrays (ChIP-chip analysis) and now Next Generation DNA Sequencing techniques (ChIP-seq analysis) has opened new avenues of research into the mechanisms through which 1,25(OH)2D3 regulates gene expression. In this review, we summarize briefly the results of this early work and then focus on more recent studies in which ChIP-chip and ChIP-seq analyses have been used to explore the mechanisms of 1,25(OH)2D3 action on a genome-wide scale providing specific target genes as examples. The results of this work have advanced our understanding of the mechanisms involved at both genetic and epigenetic levels and have revealed a series of new principles through which the vitamin D hormone functions to control the expression of genes. This article is part of a Special Issue entitled '16th Vitamin D Workshop'.

Conditional deletion of p53 and Rb in the renin-expressing compartment of the pancreas leads to a highly penetrant metastatic pancreatic neuroendocrine carcinoma

Efforts to model human pancreatic neuroendocrine tumors (PanNETs) in animals have been moderately successful, with minimal evidence for glucagonomas or metastatic spread. The renin gene, although classically associated with expression in the kidney, is also expressed in many other extrarenal tissues including the pancreas. To induce tumorigenesis within rennin-specific tissues, floxed alleles of p53 and Rb were selectively abrogated using Cre-recombinase driven by the renin promoter. The primary neoplasm generated is a highly metastatic islet cell carcinoma of the pancreas. Lineage tracing identifies descendants of renin-expressing cells as pancreatic alpha cells despite a lack of active renin expression in the mature pancreas. Both primary and metastatic tumors express high levels of glucagon; furthermore, an increased level of glucagon is found in the serum, identifying the pancreatic cancer as a functional glucagonoma. This new model is highly penetrant and exhibits robust frequency of metastases to the lymph nodes and the liver, mimicking human disease, and provides a useful platform for better understanding pancreatic endocrine differentiation and development, as well as islet cell carcinogenesis. The use of fluorescent reporters for lineage tracing of the cells contributing to disease initiation and progression provides an unique opportunity to dissect the timeline of disease, examining mechanisms of the metastatic process, as well as recovering primary and metastatic cells for identifying cooperating mutations that are necessary for progression of disease.

Transgenic mouse models--a seminal breakthrough in oncogene research

Transgenic mouse models are an integral part of modern cancer research, providing a versatile and powerful means of studying tumor initiation and progression, metastasis, and therapy. The present repertoire of these models is very diverse, with a wide range of strategies used to induce tumorigenesis by expressing dominant-acting oncogenes or disrupting the function of tumor-suppressor genes, often in a highly tissue-specific manner. Much of the current technology used in the creation and characterization of transgenic mouse models of cancer will be discussed in depth elsewhere. However, to gain a complete appreciation and understanding of these complex models, it is important to review the history of the field. Transgenic mouse models of cancer evolved as a new and, compared with the early cell-culture-based techniques, more physiologically relevant approach for studying the properties and transforming capacities of oncogenes. Here, we will describe early transgenic mouse models of cancer based on tissue-specific expression of oncogenes and discuss their impact on the development of this still rapidly growing field.

Absence of Siglec-H in MCMV infection elevates interferon alpha production but does not enhance viral clearance

Plasmacytoid dendritic cells (pDCs) express the I-type lectin receptor Siglec-H and produce interferon α (IFNα), a critical anti-viral cytokine during the acute phase of murine cytomegalovirus (MCMV) infection. The ligands and biological functions of Siglec-H still remain incompletely defined in vivo. Thus, we generated a novel bacterial artificial chromosome (BAC)-transgenic “pDCre” mouse which expresses Cre recombinase under the control of the Siglec-H promoter. By crossing these mice with a Rosa26 reporter strain, a representative fraction of Siglec-H⁺ pDCs is terminally labeled with red fluorescent protein (RFP). Interestingly, systemic MCMV infection of these mice causes the downregulation of Siglec-H surface expression. This decline occurs in a TLR9- and MyD88-dependent manner. To elucidate the functional role of Siglec-H during MCMV infection, we utilized a novel Siglec-H deficient mouse strain. In the absence of Siglec-H, the low infection rate of pDCs with MCMV remained unchanged, and pDC activation was still intact. Strikingly, Siglec-H deficiency induced a significant increase in serum IFNα levels following systemic MCMV infection. Although Siglec-H modulates anti-viral IFNα production, the control of viral replication was unchanged in vivo. The novel mouse models will be valuable to shed further light on pDC biology in future studies.

Plasmacytoid dendritic cells (pDCs) represent a minor but functionally important subset of dendritic cells. Siglec-H, a surface receptor expressed on these cells, was shown to modulate IFNα production, which in turn could influence anti-viral functions in vivo. A potential role for Siglec-H as a pathogen uptake receptor has also been postulated. Yet, the precise in vivo function of this molecule in viral replication remained unresolved. In this study, we adopt two novel genetic mouse models to investigate Siglec-H properties and ensuing function in vivo during murine cytomegalovirus (MCMV) infection. By using novel reporter mice which harbour permanently labeled Siglec-H⁺ pDCs, we show that pDCs downregulate Siglec-H upon infection. In an additional experimental system, in which pDCs lack Siglec-H function, we demonstrate that this molecule is not important for the regulation of MCMV pathogenicity. In contrast, in the absence of Siglec-H more IFNα was detectable in the serum. Importantly, this in vivo increase in IFNα production does not influence viral replication. The biological function of Siglec-H downregulation, also in the context of other infections, requires further investigation.

Cells of renin lineage are progenitors of podocytes and parietal epithelial cells in experimental glomerular disease

Glomerular injury leads to podocyte loss, a process directly underlying progressive glomerular scarring and decline of kidney function. The inherent repair process is limited by the inability of podocytes to regenerate. Cells of renin lineage residing alongside glomerular capillaries are reported to have progenitor capacity. We investigated whether cells of renin lineage can repopulate the glomerulus after podocyte injury and serve as glomerular epithelial cell progenitors. Kidney cells expressing renin were genetically fate-mapped in adult Ren1cCreER×Rs-tdTomato-R, Ren1cCre×Rs-ZsGreen-R, and Ren1dCre×Z/EG reporter mice. Podocyte depletion was induced in all three cell-specific reporter mice by cytotoxic anti-podocyte antibodies. After a decrease in podocyte number, a significant increase in the number of labeled cells of renin lineage was observed in glomeruli in a focal distribution along Bowman's capsule, within the glomerular tuft, or in both locations. A subset of cells lining Bowman's capsule activated expression of the glomerular parietal epithelial cell markers paired box protein PAX2 and claudin-1. A subset of labeled cells within the glomerular tuft expressed the podocyte markers Wilms tumor protein 1, nephrin, podocin, and synaptopodin. Neither renin mRNA nor renin protein was detected de novo in diseased glomeruli. These findings provide initial evidence that cells of renin lineage may enhance glomerular regeneration by serving as progenitors for glomerular epithelial cells in glomerular disease characterized by podocyte depletion.

Interleukin-22 reduces lung inflammation during influenza A virus infection and protects against secondary bacterial infection

Interleukin-22 (IL-22) has redundant, protective, or pathogenic functions during autoimmune, inflammatory, and infectious diseases. Here, we addressed the potential role of IL-22 in host defense and pathogenesis during lethal and sublethal respiratory H3N2 influenza A virus (IAV) infection. We show that IL-22, as well as factors associated with its production, are expressed in the lung tissue during the early phases of IAV infection. Our data indicate that retinoic acid receptor-related orphan receptor-γt (RORγt)-positive αβ and γδ T cells, as well as innate lymphoid cells, expressed enhanced Il22 transcripts as early as 2 days postinfection. During lethal or sublethal IAV infections, endogenous IL-22 played no role in the control of IAV replication and in the development of the IAV-specific CD8(+) T cell response. During lethal infection, where wild-type (WT) mice succumbed to severe pneumonia, the lack of IL-22 did not accelerate or delay IAV-associated pathogenesis and animal death. In stark contrast, during sublethal IAV infection, IL-22-deficient animals had enhanced lung injuries and showed a lower airway epithelial integrity relative to WT littermates. Of importance, the protective effect of endogenous IL-22 in pulmonary damages was associated with a more controlled secondary bacterial infection. Indeed, after challenge with Streptococcus pneumoniae, IAV-experienced Il22(-/-) animals were more susceptible than WT controls in terms of survival rate and bacterial burden in the lungs. Together, IL-22 plays no major role during lethal influenza but is beneficial during sublethal H3N2 IAV infection, where it limits lung inflammation and subsequent bacterial superinfections.

piggyBac as a high-capacity transgenesis and gene-therapy vector in human cells and mice

The stable genomic integration and expression of a large transgene is a major hurdle in gene therapy. We show that the modified piggyBac (PB) transposon system can be used to introduce a 207 kb genomic DNA fragment containing the RORγ/γt locus into human cells and mice. PB-mediated transgenesis results in a single copy of a stably inherited and expressed transgene. These results indicate that PB could serve as an effective high-capacity vector for functional analysis of the mammalian genome and for gene therapy in human cells.

Unraveling chemokine and chemokine receptor expression patterns using genetically engineered mice

Over the past 25 years, genetically engineered mouse models have become an integral and invaluable research tool to develop our understanding of mammalian physiology and pathology. This unit describes methods for generating transgenic mice, focusing on reporter animals relevant to chemokine receptor and ligand expression. Specifically, we describe the use of bacterial artificial chromosome (BAC) engineering and embryonic stem cell manipulation to generate "knock in" and transgenic mice.

Transfer of CD8+ T cell memory using Bcl-2 as a marker

The processes that regulate T cell memory generation are important for therapeutic design and the immune response to disease. However, what allows a subset of effector T cells to survive the contraction period to become memory cells is incompletely understood. The Bcl-2 family is critical for T cell survival, and Bcl-2 has been proposed to be important for the survival of memory cells. However, previous studies have relied on double-knockout models, potentially skewing the role of Bcl-2, and the use of Bcl-2 as a marker in adoptive transfer experiments, a method required to confirm the memory potential of cell subsets, has not been possible because of the intracellular localization of the protein. In this study, we present a novel Bcl-2 reporter mouse model and, to our knowledge, show for the first time that a distinct subset of effector T cells, and also a subset within the CD127(hi)KLRG1(lo) memory precursor effector cell population, retains high Bcl-2 expression at the peak of the CD8(+) T cell response to Listeria monocytogenes. Furthermore, we show that Bcl-2 correlates with memory potential in adoptive transfer experiments using both total responding CD8(+) T cells and memory precursor effector cells. These results show that even within the memory precursor effector cell population, Bcl-2 confers a survival advantage in a subset of effector CD8(+) T cells that allows differentiation into memory cells and cement Bcl-2 as a critical factor for T cell memory.

Lineage tracing and genetic ablation of ADAM12(+) perivascular cells identify a major source of profibrotic cells during acute tissue injury

Profibrotic cells that develop upon injury generate permanent scar tissue and impair organ recovery, though their origin and fate are unclear. Here we show that transient expression of ADAM12 (a disintegrin and metalloprotease 12) identifies a distinct proinflammatory subset of platelet-derived growth factor receptor-α-positive stromal cells that are activated upon acute injury in the muscle and dermis. By inducible genetic fate mapping, we demonstrate in vivo that injury-induced ADAM12(+) cells are specific progenitors of a major fraction of collagen-overproducing cells generated during scarring, which are progressively eliminated during healing. Genetic ablation of ADAM12(+) cells, or knockdown of ADAM12, is sufficient to limit generation of profibrotic cells and interstitial collagen accumulation. ADAM12(+) cells induced upon injury are developmentally distinct from muscle and skin lineage cells and are derived from fetal ADAM12(+) cells programmed during vascular wall development. Thus, our data identify injury-activated profibrotic progenitors residing in the perivascular space that can be targeted through ADAM12 to limit tissue scarring.

A humanized pattern of aromatase expression is associated with mammary hyperplasia in mice

Aromatase is essential for estrogen production and is the target of aromatase inhibitors, the most effective endocrine treatment for postmenopausal breast cancer. Peripheral tissues in women, including the breast, express aromatase via alternative promoters. Female mice lack the promoters that drive aromatase expression in peripheral tissues; thus, we generated a transgenic humanized aromatase (Arom(hum)) mouse line containing a single copy of the human aromatase gene to study the link between aromatase expression in mammary adipose tissue and breast pathology. Arom(hum) mice expressed human aromatase, driven by the proximal human promoters II and I.3 and the distal promoter I.4, in breast adipose fibroblasts and myoepithelial cells. Estrogen levels in the breast tissue of Arom(hum) mice were higher than in wild-type mice, whereas circulating levels were similar. Arom(hum) mice exhibited accelerated mammary duct elongation at puberty and an increased incidence of lobuloalveolar breast hyperplasia associated with increased signal transducer and activator of transcription-5 phosphorylation at 24 and 64 wk. Hyperplastic epithelial cells showed remarkably increased proliferative activity. Thus, we demonstrated that the human aromatase gene can be expressed via its native promoters in a wide variety of mouse tissues and in a distribution pattern nearly identical to that of humans. Locally increased tissue levels, but not circulating levels, of estrogen appeared to exert hyperplastic effects on the mammary gland. This novel mouse model will be valuable for developing tissue-specific aromatase inhibition strategies.

Recombinant protein expression in milk of livestock species

Producing complex recombinant proteins in the milk of transgenic animals offers several advantages: large amounts of proteins can be obtained, and in most cases, these proteins are properly folded, assembled, cleaved, and glycosylated. The level of expression of foreign genes in the mammalian gland cannot be predicted in all cases, and appropriate vectors must be used. The main elements of these vectors are as follows: a well-characterized specific promoter, the coding region of the gene of interest, preferably with a homologous or heterologous intron, to improve transcription efficiency, and an insulator or boundary element to counteract the chromosomal position effects at the integration site. Once high expression levels are achieved, and the recombinant protein is purified, an essential step in the analysis of the final product is determining its degree of glycosylation. This is an important readout because it can affect among other parameters the stability and immunogenicity of the recombinant protein.

Visualization of mucosal homeostasis via single- and multiphoton intravital fluorescence microscopy

FIVM has provided many insights into the regulation of immunity. We report the validation of an approach for visualizing murine small bowel via single- and multiphoton FIVM. Tissue damage is limited to ∼200 μm, immediately adjacent to the incision, as confirmed by intravital PI staining. Treatment with 10 KDa dextran-FITC and 70 KDa dextran-TR confirms that perfusion is intact. Selective filtration of 10 KDa but not 70 KDa dextran from the blood indicated that kidney function is also intact. Interestingly, lamina propria vasculature is semipermeable to 10 KDa dextran. Next, reporter mice expressing egfp from the CX3CR1 locus, egfp from the FoxP3 locus, or RFP from the IL-17F locus were used to track DC subsets, FoxP3(+) Tregs, or Th17f cells, respectively. Resident cx3cr1(+/egfp) cells were sessile but actively probed the surrounding microenvironment. Both T cell populations patrol the lamina propria, but the Th17f cells migrate more rapidly than Tregs. Together, these data demonstrate intact vascular perfusion, while intravitally visualizing the mucosal surface of the small bowel. Lastly, the cx3cr1(+) DCs and T cells display activity similar to that found in steady-state, secondary lymphoid organs.

On the emerging role of rabbit as human disease model and the instrumental role of novel transgenic tools

The laboratory rabbit (Oryctolagus cuniculus) is widely used as a model for human diseases, because of its size, which permits non-lethal monitoring of physiological changes and similar disease characteristics. Novel transgenic tools such as, the zinc finger nuclease method and the sleeping beauty transposon mediated or BAC transgenesis were recently adapted to the laboratory rabbit and opened new opportunities in precise tissue and developmental stage specific gene expression/silencing, coupled with increased transgenic efficiencies. Many facets of human development and diseases cannot be investigated in rodents. This is especially true for early prenatal development, its long-lasting effects on health and complex disorders, and some economically important diseases such as atherosclerosis or cardiovascular diseases. The first transgenic rabbits models of arrhythmogenesis mimic human cardiac diseases much better than transgenic mice and hereby underline the importance of non-mouse models. Another emerging field is epigenetic reprogramming and pathogenic mechanisms in diabetic pregnancy, where rabbit models are indispensable. Beyond that rabbit is used for decades as major source of polyclonal antibodies and recently in monoclonal antibody production. Alteration of its genome to increase the efficiency and value of the antibodies by humanization of the immunoglobulin genes, or by increasing the expression of a special receptor (Fc receptor) that augments humoral immune response is a current demand.

Purification of BAC DNA for high-efficiency transgenesis

An unresolved bottleneck in bacterial artificial chromosome (BAC) transgenesis is low efficiency generation of founder mice because of suboptimal quality of the manipulated BAC DNA. Using mini-gel electrophoresis and electro-elution that circumvents CsCl(2) centrifugation, column chromatography, and resin purifications, we have used RECOCHIP, a commercially available dialysis cassette for the purification of BAC DNA that generates transgenic founders with up to 80% efficiency.

A novel bacterial artificial chromosome-transgenic podoplanin-cre mouse targets lymphoid organ stromal cells in vivo

Stromal cells provide the structural foundation of secondary lymphoid organs (SLOs), and regulate leukocyte access and cell migration within the different compartments of spleen and lymph nodes (LNs). Furthermore, several stromal cell subsets have been implied in shaping of T cell responses through direct presentation of antigen. Despite significant gain of knowledge on the biology of different SLO-resident stromal cell subsets, their molecular and functional characterization has remained incomplete. To address this need, we have generated a bacterial artificial chromosome-transgenic mouse model that utilizes the podoplanin (pdpn) promoter to express the Cre-recombinase exclusively in stromal cells of SLOs. The characterization of the Pdpn–Cre mouse revealed transgene expression in subsets of fibroblastic reticular cells and lymphatic endothelial cells in LNs. Furthermore, the transgene facilitated the identification of a novel splenic perivascular stromal cell subpopulation that forms web-like structures around central arterioles. Assessment of the in vivo antigen expression in the genetically tagged stromal cells in Pdpn–Cre mice revealed activation of both MHC I and II-restricted TCR transgenic T cells. Taken together, stromal pdpn–Cre expression is well-suited to characterize the phenotype and to dissect the function of lymphoid organ stromal cells.

In vivo structure/function and expression analysis of the CX3C chemokine fractalkine

The CX3C chemokine family is composed of only one member, CX3CL1, also known as fractalkine, which in mice is the sole ligand of the G protein-coupled, 7-transmembrane receptor CX3CR1. Unlike classic small peptide chemokines, CX3CL1 is synthesized as a membrane-anchored protein that can promote integrin-independent adhesion. Subsequent cleavage by metalloproteases, either constitutive or induced, can generate shed CX3CL1 entities that potentially have chemoattractive activity. To study the CX3C interface in tissues of live animals, we generated transgenic mice (CX3CL1cherry:CX3CR1gfp), which express red and green fluorescent reporter genes under the respective control of the CX3CL1 and CX3CR1 promoters. Furthermore, we performed a structure/function analysis to differentiate the in vivo functions of membrane-tethered versus shed CX3CL1 moieties by comparing their respective ability to correct established defects in macrophage function and leukocyte survival in CX3CL1-deficient mice. Specifically, expression of CX3CL1(105Δ), an obligatory soluble CX3CL1 isoform, reconstituted the formation of transepithelial dendrites by intestinal macrophages but did not rescue circulating Ly6Clo CX3CR1hi blood monocytes in CX3CR1gfp/gfp mice. Instead, monocyte survival required the full-length membrane-anchored CX3CL1, suggesting differential activities of tethered and shed CX3CL1 entities.

IL-1 and IL-23 mediate early IL-17A production in pulmonary inflammation leading to late fibrosis

Background

Idiopathic pulmonary fibrosis is a devastating as yet untreatable disease. We demonstrated recently the predominant role of the NLRP3 inflammasome activation and IL-1β expression in the establishment of pulmonary inflammation and fibrosis in mice.

Methods

The contribution of IL-23 or IL-17 in pulmonary inflammation and fibrosis was assessed using the bleomycin model in deficient mice.

Results

We show that bleomycin or IL-1β-induced lung injury leads to increased expression of early IL-23p19, and IL-17A or IL-17F expression. Early IL-23p19 and IL-17A, but not IL-17F, and IL-17RA signaling are required for inflammatory response to BLM as shown with gene deficient mice or mice treated with neutralizing antibodies. Using FACS analysis, we show a very early IL-17A and IL-17F expression by RORγt⁺ γδ T cells and to a lesser extent by CD4αβ⁺ T cells, but not by iNKT cells, 24 hrs after BLM administration. Moreover, IL-23p19 and IL-17A expressions or IL-17RA signaling are necessary to pulmonary TGF-β1 production, collagen deposition and evolution to fibrosis.

Conclusions

Our findings demonstrate the existence of an early IL-1β-IL-23-IL-17A axis leading to pulmonary inflammation and fibrosis and identify innate IL-23 and IL-17A as interesting drug targets for IL-1β driven lung pathology.

Engineering BAC reporter gene constructs for mouse transgenesis

A culmination of large-scale ideas and efforts has truly allowed for the use of large genomic DNA clones housed in Bacterial Artificial Chromosome (BAC) vectors for biological research. Fundamental advances that have allowed this to happen include (1) the completion of genome sequencing projects and the establishment of highly annotated web-accessible databases allowing for the rapid identity and purchase of BAC clones containing genes of interest. (2) The generation of methodologies to modify BACs genetically, allowing for the rapid creation of gene targeting constructs or transgenic reporter gene constructs using homologous recombination in bacteria.Recent efforts on our part have capitalized on these advances by using BACs and bacterial recombination methods to generate fluorescent protein reporter transgenic mice to study skeletal biology. The rationale for using BAC genomic DNA clones to engineer reporter gene constructs is based on their much larger size, thus increasing the likelihood that most, if not all, of a gene's respective cis regulator elements are present, giving a truer representation of the endogenous gene's expression. In a relatively short amount of time, we have become extremely proficient at generating BAC reporters. Contrary to the widely perceived notion that working with BACs is complex and difficult, we decided to write this chapter to encourage laboratories that are currently using traditional molecular cloning methods to engineer transgenic DNA constructs to strongly consider learning BAC methodologies. As an example, we walk through the steps we took to generate the transgenic reporter mouse line, Tenascin C (TNC)-mCherry.

In vivo depletion of FoxP3+ Tregs using the DEREG mouse model

In recent years, researchers have increasingly focused on the modulation of regulatory T cell (Treg) function to interfere with the outcome of virtually every type of immune response. For a long time, specific in vivo targeting of Tregs was precluded due to the lack of appropriate markers. Only after the discovery of Foxp3 as a Treg-specific transcription factor, was the development of Treg-specific mouse models feasible. We generated DEREG mice (DEpletion of REGulatory T cells), a BAC (bacterial artificial chromosome) transgenic mouse line, which allows direct in vivo analysis and depletion of this exceedingly important cell type. Our DEREG mice carry a DTR-eGFP transgene under the control of an additional Foxp3 promoter, thereby allowing specific depletion of Treg by application of diphtheria toxin at any desired point of time during an ongoing immune response. This chapter will elaborate the advantages and disadvantages of employing different genetic approaches and discuss further parameters used in the studies focusing on employment of diphtheria toxin and its degree of general toxicity in mice. Additionally, we will address the question: to which extent DEREG mice are suitable for studying the effect of long-term Treg depletion during specific immune responses.

Smarcc1/Baf155 couples self-renewal gene repression with changes in chromatin structure in mouse embryonic stem cells

Little is known about the molecular mechanism(s) governing differentiation decisions in embryonic stem cells (ESCs). To identify factors critical for ESC lineage formation, we carried out a functional genetic screen for factors affecting Nanog promoter activity during mESC differentiation. We report that members of the PBAF chromatin remodeling complex, including Smarca4/Brg1, Smarcb1/Baf47, Smarcc1/Baf155, and Smarce1/Baf57, are required for the repression of Nanog and other self-renewal gene expression upon mouse ESC (mESC) differentiation. Knockdown of Smarcc1 or Smarce1 suppressed loss of Nanog expression in multiple forms of differentiation. This effect occurred in the absence of self-renewal factors normally required for Nanog expression (e.g., Oct4), possibly indicating that changes in chromatin structure, rather than loss of self-renewal gene transcription per se, trigger differentiation. Consistent with this notion, mechanistic studies demonstrated that expression of Smarcc1 is necessary for heterochromatin formation and chromatin compaction during differentiation. Collectively, our data reveal that Smarcc1 plays important roles in facilitating mESCs differentiation by coupling gene repression with global and local changes in chromatin structure.

Mapping lineage using BAC-Cre reporter lines

As the brain develops, progenitor cells acquire the features of specific neuronal or glial subtypes through dynamic expression of the fate-determining signaling molecules and their targeting transcription factors. An effective and versatile approach for tracing lineage of progenitors into adult cell types is to target the promoter of an interested gene with Cre (a phage DNA recombinase) to achieve simultaneous activation during neurogenesis. The bacterial artificial chromosome (BAC) is an efficient Cre carrier. Not only the targeted gene remains diploidy in BAC-Cre transgenic mice, but also the large portions of the gene's regulatory elements to be incorporated in the BAC allow Cre to sufficiently and reliably reproduce the endogenous gene expression pattern. When the BAC-Cre mouse is crossed to a Cre reporter mouse, even Cre is transiently expressed. Cre-loxP mediated recombination can permanently activate a reporter gene, such as green fluorescent protein (GFP) in all lineage cells of the gene. Experimental designs and procedures for RecA-based BAC DNA modification and preparation for pronuclear injection are highlighted. Suggestions for the use of BAC-Cre transgenic mice in fate-mapping analyses are also provided.

Caspase-8 deficiency in epidermal keratinocytes triggers an inflammatory skin disease

Expression of enzymatically inactive caspase-8, or deletion of caspase-8 from basal epidermal keratinocytes, triggers chronic skin inflammation in mice. Unlike similar inflammation resulting from arrest of nuclear factor kappaB activation in the epidermal cells, the effect induced by caspase-8 deficiency did not depend on TNF, IL-1, dermal macrophage function, or expression of the toll-like receptor adapter proteins MyD88 or TRIF. Both interferon regulatory factor (IRF) 3 and TANK-binding kinase were constitutively phosphorylated in the caspase-8-deficient epidermis, and knockdown of IRF3 in the epidermis-derived cells from these mice abolished the expression of up-regulated genes. Temporal and spatial analyses of the alterations in gene expression that result from caspase-8 deficiency reveal that the changes are initiated before birth, around the time that cornification develops, and occur mainly in the suprabasal layer. Finally, we found that caspase-8-deficient keratinocytes display an enhanced response to gene activation by transfected DNA. Our findings suggest that an enhanced response to endogenous activators of IRF3 in the epidermis, presumably generated in association with keratinocyte differentiation, contributes to the skin inflammatory process triggered by caspase-8 deficiency.

Trim43a, Trim43b, and Trim43c: Novel mouse genes expressed specifically in mouse preimplantation embryos

We describe the identification and characterization of Trim43a, Trim43b, and Trim43c genes, whose expression are restricted to preimplantation stages and peak at the 8-cell to morula stage. We identified a 5kb DNA fragment that covers upstream region of Trim43a as a putative promoter, which can drive the expression of mStrawberry fluorescent protein in a manner similar to endogenous Trim43 genes. Trim43 genes will be useful stage-specific markers for the study of preimplantation embryos.

Generating transgenic mice from bacterial artificial chromosomes: transgenesis efficiency, integration and expression outcomes

Transgenic mice are widely used in biomedical research to study gene expression, developmental biology, and gene therapy models. Bacterial artificial chromosome (BAC) transgenes direct gene expression at physiological levels with the same developmental timing and expression patterns as endogenous genes in transgenic animal models. We generated 707 transgenic founders from 86 BAC transgenes purified by three different methods. Transgenesis efficiency was the same for all BAC DNA purification methods. Polyamine microinjection buffer was essential for successful integration of intact BAC transgenes. There was no correlation between BAC size and transgenic rate, birth rate, or transgenic efficiency. A narrow DNA concentration range generated the best transgenic efficiency. High DNA concentrations reduced birth rates while very low concentrations resulted in higher birth rates and lower transgenic efficiency. Founders with complete BAC integrations were observed in all 47 BACs for which multiple markers were tested. Additional founders with BAC fragment integrations were observed for 65% of these BACs. Expression data was available for 79 BAC transgenes and expression was observed in transgenic founders from 63 BACs (80%). Consistent and reproducible success in BAC transgenesis required the combination of careful DNA purification, the use of polyamine buffer, and sensitive genotyping assays.

Characterization of the thymic IL-7 niche in vivo

The thymus represents the "cradle" for T cell development, with thymic stroma providing multiple soluble and membrane cues to developing thymocytes. Although IL-7 is recognized as an essential factor for thymopoiesis, the "environmental niche" of thymic IL-7 activity remains poorly characterized in vivo. Using bacterial artificial chromosome transgenic mice in which YFP is under control of IL-7 promoter, we identify a subset of thymic epithelial cells (TECs) that co-express YFP and high levels of Il7 transcripts (IL-7(hi) cells). IL-7(hi) TECs arise during early fetal development, persist throughout life, and co-express homeostatic chemokines (Ccl19, Ccl25, Cxcl12) and cytokines (Il15) that are critical for normal thymopoiesis. In the adult thymus, IL-7(hi) cells localize to the cortico-medullary junction and display traits of both cortical and medullary TECs. Interestingly, the frequency of IL-7(hi) cells decreases with age, suggesting a mechanism for the age-related thymic involution that is associated with declining IL-7 levels. Our temporal-spatial analysis of IL-7-producing cells in the thymus in vivo suggests that thymic IL-7 levels are dynamically regulated under distinct physiological conditions. This IL-7 reporter mouse provides a valuable tool to further dissect the mechanisms that govern thymic IL-7 expression in vivo.

T cell-dendritic cell immunological synapses contain TCR-dependent CD28-CD80 clusters that recruit protein kinase C theta

Short-lived TCR microclusters and a longer-lived protein kinase Ctheta-focusing central supramolecular activation cluster (cSMAC) have been defined in model immunological synapses (IS). In different model systems, CD28-mediated costimulatory interactions have been detected in microclusters, the cSMAC, or segregated from the TCR forming multiple distinct foci. The relationship between TCR and costimulatory molecules in the physiological IS of T cell-dendritic cell (DC) is obscure. To study the dynamic relationship of CD28-CD80 and TCR interactions in the T cell-DC IS during Ag-specific T cell activation, we generated CD80-eCFP mice using bacterial artificial chromosome transgenic technology. In splenic DCs, endogenous CD80 and CD80-eCFP localized to plasma membrane and Golgi apparatus, and CD80-eCFP was functional in vivo. In the OT-II T cell-DC IS, multiple segregated TCR, CD80, and LFA-1 clusters were detected. In the T cell-DC synapse CD80 clusters were colocalized with CD28 and PKCtheta, a characteristic of the cSMAC. Acute blockade of TCR signaling with anti-MHC Ab resulted in a rapid reduction in Ca(2+) signaling and the number and size of the CD80 clusters, a characteristic of TCR microclusters. Thus, the T cell-DC interface contains dynamic costimulatory foci that share characteristics of microclusters and cSMACs.

c-FLIP protects mature T lymphocytes from TCR-mediated killing

Although c-FLIP has been identified as an important player in the extrinsic (death receptor-induced) apoptosis pathway, its endogenous function in mature T lymphocytes remains undefined. c-FLIP may inhibit or promote T cell death as previous data demonstrate that the c-FLIP(L) isoform can promote or inhibit caspase 8 activation while the c-FLIP(S) isoform promotes or inhibits T cell death when overexpressed. Although the c-FLIP(R) isoform inhibits cell death in cell lines, its function in T cells remains unknown. To investigate the function of c-FLIP in mature T cells, we have generated several genetic mouse models with c-FLIP or its individual isoforms deleted in mature T cells. Surprisingly, we found that c-FLIP protects mature T cells not only from apoptosis induced by the death receptors Fas and TNFR but also from TCR-mediated and spontaneous apoptosis. Thus, c-FLIP plays an essential role in protecting mature T cells from a death signal induced through the TCR itself and is required for naive T cell survival. Our results demonstrate that c-FLIP functions beyond the extrinsic death pathway.

In vivo analysis of key elements within the renin regulatory region

Renin is responsible for initiating the enzymatic cascade that results in the production of angiotensin II, the major effector molecule of the renin-angiotensin system (RAS). Extensive information on the regulatory region of the renin gene has been derived by transient transfection studies in vitro, particularly using the As4.1 cell line. To verify key factors within the regulatory region of renin in vivo, homologous recombination was used to introduce a green fluorescent protein (GFP) cassette into exon one of the renin gene contained within a 240 kb bacterial artificial chromosome (BAC) to create a construct that has GFP expression controlled by the renin regulatory region (RenGFP BAC). Within the regulatory region of the RenGFP BAC construct we independently deleted the enhancer, as well as mutated the HOX-PBX site within the proximal promoter element. Transgenic lines were generated for each of these BAC constructs and GFP expression was analyzed throughout a spectrum of tissues positive for renin expression including the kidney, adrenal gland, gonadal artery, and submandibular gland. The results described within this manuscript support the interpretation that the renin enhancer is critical for regulating baseline expression where as the Hox/Pbx site is important for the tissue specificity of renin expression.

The long isoform of cellular FLIP is essential for T lymphocyte proliferation through an NF-kappaB-independent pathway

Although the long isoform of cellular FLIP (c-FLIP(L)) has been implicated in TCR-mediated signaling, its role in T cell proliferation remains controversial. Some studies have demonstrated that overexpression of c-FLIP(L) promotes T cell proliferation and NF-kappaB activation, whereas others have reported that c-FLIP(L) overexpression has no effect or even inhibits T cell proliferation. To establish the role of c-FLIP(L) in T lymphocyte proliferation, we have generated a conditional knockout mouse strain specifically lacking c-FLIP(L) in T lymphocytes. c-FLIP(L)(-/-) mice exhibit severely impaired effector T cell development after Listeria monocytogenes infection in vivo and c-FLIP(L)-deficient T cells display defective TCR-mediated proliferation in vitro. However, c-FLIP(L)(-/-) T cells exhibit normal NF-kappaB activity upon TCR stimulation. These results demonstrate that c-FLIP(L) is essential for T lymphocyte proliferation through an NF-kappaB-independent pathway.

In vivo equilibrium of proinflammatory IL-17+ and regulatory IL-10+ Foxp3+ RORgamma t+ T cells

The nuclear hormone receptor retinoic acid receptor–related orphan receptor γt (RORγt) is required for the generation of T helper 17 cells expressing the proinflammatory cytokine interleukin (IL)-17. In vivo, however, less than half of RORγt⁺ T cells express IL-17. We report here that RORγt⁺ Tαβ cells include Foxp3⁺ cells that coexist with IL-17–producing RORγt⁺ Tαβ cells in all tissues examined. The Foxp3⁺ RORγt⁺ Tαβ express IL-10 and CCL20, and function as regulatory T cells. Furthermore, the ratio of Foxp3⁺ to IL-17–producing RORγt⁺ Tαβ cells remains remarkably constant in mice enduring infection and inflammation. This equilibrium is tuned in favor of IL-10 production by Foxp3 and CCL20, and in favor of IL-17 production by IL-6 and IL-23. In the lung and skin, the largest population of RORγt⁺ T cells express the γδ T cell receptor and produce the highest levels of IL-17 independently of IL-6. Thus, potentially antagonistic proinflammatory IL-17–producing and regulatory Foxp3⁺ RORγt⁺ T cells coexist and are tightly controlled, suggesting that a perturbed equilibrium in RORγt⁺ T cells might lead to decreased immunoreactivity or, in contrast, to pathological inflammation.

Conditional transgenic mouse models: from the basics to genome-wide sets of knockouts and current studies of tissue regeneration

Many mouse models are currently available, providing avenues to elucidate gene function and to recapitulate specific pathological conditions. To a large extent, successful translation of clinical evidence or analytical data into appropriate mouse models is possible through progress in transgenic or gene-targeting technology. Beginning with a review of standard mouse transgenics and conventional gene targeting, this article will move on to discussing the basics of conditional gene expression: the tetracycline (tet)-off and tet-on systems based on the transactivators tet-controlled transactivator (Tta) and reverse tet-on transactivator (rtTA) that allow downregulation or induction of gene expression; Cre or Flp recombinase-mediated modifications, including excision, inversion, insertion and interchromosomal translocation; combination of the tet and Cre systems, permitting inducible knockout, reporter gene activation or activation of point mutations; the avian retroviral system based on delivery of rtTA specifically into cells expressing the avian retroviral receptor, which enables cell type-specific, inducible gene expression; the tamoxifen system, one of the most frequently applied steroid receptor-based systems, allows rapid activation of a fusion protein between the gene of interest and a mutant domain of the estrogen receptor, whereby activation does not depend on transcription; and techniques for cell type-specific ablation. The diphtheria toxin receptor system offers the advantage that it can be combined with the ‘zoo’ of Cre recombinase driver mice. Having described the basics we move on to the cutting edge: generation of genome-wide sets of conditional knockout mice. To this end, large ongoing projects apply two strategies: gene trapping based on random integration of trapping vectors into introns leading to truncation of the transcript, and gene targeting, representing the directed approach using homologous recombination. It can be expected that in the near future genome-wide sets of such mice will be available. Finally, the possibilities of conditional expression systems for investigating gene function in tissue regeneration will be illustrated by examples for neurodegenerative disease, liver regeneration and wound healing of the skin.

Mast cell-specific Cre/loxP-mediated recombination in vivo

Mast cells are important effectors of type I allergy but also essential regulators of innate and adaptive immune responses. The aim of this study was to develop a Cre recombinase-expressing mouse line that allows mast cell-specific inactivation of genes in vivo. Following a BAC transgenic approach, Cre was expressed under the control of the mast cell protease (Mcpt) 5 promoter. Mcpt5-Cre transgenic mice were crossed to the ROSA26-EYFP Cre excision reporter strain. Efficient Cre-mediated recombination was observed in mast cells from the peritoneal cavity and the skin while only minimal reporter gene expression was detected outside the mast cell compartment. Our results show that the Mcpt5 promoter can drive Cre expression in a mast cell-specific fashion. We expect that our Mcpt5-Cre mice will be a useful tool for the investigation of mast cell biology.

BAC to immunology--bacterial artificial chromosome-mediated transgenesis for targeting of immune cells

Thirty years after the first transgenic mouse was produced, a plethora of genetic tools has been developed to study immune cells in vivo. A powerful development is the bacterial artificial chromosome (BAC) transgenic approach, combining advantages of both conventional transgenic and knock-in gene-targeting strategies. In immunology the potential of BAC transgenic technology has yet to be fully harvested and, combined with a variety of elegant genetic tools, it will allow the analysis of complex immunological processes in vivo. In this short review, we discuss the applications of BACs in immunology, such as identification of regulatory regions, expression and cell-fate mapping, cell ablation, conditional mutations and the generation of humanized mice.

Selective depletion of Foxp3+ regulatory T cells induces a scurfy-like disease

The scurfy mutant mouse strain suffers from a fatal lymphoproliferative disease leading to early death within 3-4 wk of age. A frame-shift mutation of the forkhead box transcription factor Foxp3 has been identified as the molecular cause of this multiorgan autoimmune disease. Foxp3 is a central control element in the development and function of regulatory T cells (T reg cells), which are necessary for the maintenance of self-tolerance. However, it is unclear whether dysfunction or a lack of T reg cells is etiologically involved in scurfy pathogenesis and its human correlate, the IPEX syndrome. We describe the generation of bacterial artificial chromosome-transgenic mice termed "depletion of regulatory T cell" (DEREG) mice expressing a diphtheria toxin (DT) receptor-enhanced green fluorescent protein fusion protein under the control of the foxp3 gene locus, allowing selective and efficient depletion of Foxp3+ T reg cells by DT injection. Ablation of Foxp3+ T reg cells in newborn DEREG mice led to the development of scurfy-like symptoms with splenomegaly, lymphadenopathy, insulitis, and severe skin inflammation. Thus, these data provide experimental evidence that the absence of Foxp3+ T reg cells is indeed sufficient to induce a scurfy-like phenotype. Furthermore, DEREG mice will allow a more precise definition of the function of Foxp3+ T reg cells in immune reactions in vivo.

BAC transgenic mice express enhanced green fluorescent protein in central and peripheral cholinergic neurons

The peripheral nervous system has complex and intricate ramifications throughout many target organ systems. To date this system has not been effectively labeled by genetic markers, due largely to inadequate transcriptional specification by minimum promoter constructs. Here we describe transgenic mice in which enhanced green fluorescent protein (eGFP) is expressed under the control of endogenous choline acetyltransferase (ChAT) transcriptional regulatory elements, by knock-in of eGFP within a bacterial artificial chromosome (BAC) spanning the ChAT locus and expression of this construct as a transgene. eGFP is expressed in ChAT(BAC)-eGFP mice in central and peripheral cholinergic neurons, including cell bodies and processes of the somatic motor, somatic sensory, and parasympathetic nervous system in gastrointestinal, respiratory, urogenital, cardiovascular, and other peripheral organ systems. Individual epithelial cells and a subset of lymphocytes within the gastrointestinal and airway mucosa are also labeled, indicating genetic evidence of acetylcholine biosynthesis. Central and peripheral neurons were observed as early as 10.5 days postcoitus in the developing mouse embryo. ChAT(BAC)-eGFP mice allow excellent visualization of all cholinergic elements of the peripheral nervous system, including the submucosal enteric plexus, preganglionic autonomic nerves, and skeletal, cardiac, and smooth muscle neuromuscular junctions. These mice should be useful for in vivo studies of cholinergic neurotransmission and neuromuscular coupling. Moreover, this genetic strategy allows the selective expression and conditional inactivation of genes of interest in cholinergic nerves of the central nervous system and peripheral nervous system.

Identification of evolutionarily conserved regulatory elements in the mouse Fgf8 locus

The secreted signaling molecule fibroblast growth factor 8 (Fgf8) is an essential component of certain embryonic signaling centers including the mid-hindbrain (isthmic) organizer, the first branchial arch (BA1), and the apical ectodermal ridge (AER). In these signaling centers Fgf8 transcripts are expressed in a dynamic and transient fashion, but the mechanism by which this highly specific expression pattern is established remains largely unknown. We used DNA sequence comparisons coupled to transgenic approaches to obtain insight into the structure and function of regulatory elements in the Fgf8 locus. First, a bacterial artificial chromosome (BAC) containing the mouse Fgf8 gene partially rescues the embryonic lethality of Fgf8-deficient mice and controls Fgf8-specific gene expression of a coinjected lacZ reporter transgene. Second, sequence comparison of vertebrate Fgf8 loci revealed evolutionarily highly conserved noncoding sequences that were unexpectedly located mainly 3' of the Fgf8 coding region. Third, in transgenic mice some of these elements were sufficient to target expression to the AER, tail bud, and brain, including the isthmic organizer, indicating that they may represent Fgf8 cis-acting elements. Collectively, these data identify novel regulatory elements of the Fgf8 gene sufficient to drive expression to regions of known Fgf8 activity.

Applications of gene targeting technology to mental retardation and developmental disability research

The human and mouse genome projects elucidated the sequence and position map of innumerous genes expressed in the central nervous system (CNS), advancing our ability to manipulate these sequences and create models to investigate regulation of gene expression and function. In this article, we reviewed gene targeting methodologies with emphasis on applications to CNS development and neurodevelopmental disorders.

Thymic origin of intestinal alphabeta T cells revealed by fate mapping of RORgammat+ cells

Intestinal intraepithelial T lymphocytes (IELs) are likely to play a key role in host mucosal immunity and, unlike other T cells, have been proposed to differentiate from local precursors rather than from thymocytes. We show here that IELs expressing the alphabeta T cell receptor are derived from precursors that express RORgammat, an orphan nuclear hormone receptor detected only in immature CD4+CD8+ thymocytes, fetal lymphoid tissue-inducer (LTi) cells, and LTi-like cells in cryptopatches within the adult intestinal lamina propria. Using cell fate mapping, we found that all intestinal alphabeta T cells are progeny of CD4+CD8+ thymocytes, indicating that the adult intestine is not a significant site for alphabeta T cell development. Our results suggest that intestinal RORgammat+ cells are local organizers of mucosal lymphoid tissue.