JAK/STAT pathway inhibition overcomes IL7-induced glucocorticoid resistance in a subset of human T-cell acute lymphoblastic leukemias.

While outcomes for children with T-cell acute lymphoblastic leukemia (T-ALL) have improved dramatically, survival rates for patients with relapsed/refractory disease remain dismal. Prior studies indicate that glucocorticoid (GC) resistance is more common than resistance to other chemotherapies at relapse. In addition, failure to clear peripheral blasts during a prednisone prophase correlates with an elevated risk of relapse in newly diagnosed patients. Here we show that intrinsic GC resistance is present at diagnosis in early thymic precursor (ETP) T-ALLs as well as in a subset of non-ETP T-ALLs. GC-resistant non-ETP T-ALLs are characterized by strong induction of JAK/STAT signaling in response to interleukin-7 (IL7) stimulation. Removing IL7 or inhibiting JAK/STAT signaling sensitizes these T-ALLs, and a subset of ETP T-ALLs, to GCs. The combination of the GC dexamethasone and the JAK1/2 inhibitor ruxolitinib altered the balance between pro- and anti-apoptotic factors in samples with IL7-dependent GC resistance, but not in samples with IL7-independent GC resistance. Together, these data suggest that the addition of ruxolitinib or other inhibitors of IL7 receptor/JAK/STAT signaling may enhance the efficacy of GCs in a biologically defined subset of T-ALL.

Phenotype of mice lacking functional Deleted in colorectal cancer (Dcc) gene.

The DCC (Deleted in colorectal cancer) gene was first identified as a candidate for a tumour-suppressor gene on human chromosome 18q. More recently, in vitro studies in rodents have provided evidence that DCC might function as a receptor for the axonal chemoattractant netrin-1. Inactivation of the murine Dcc gene caused defects in axonal projections that are similar to those observed in netrin-1-deficient mice but did not affect growth, differentiation, morphogenesis or tumorigenesis in mouse intestine. These observations fail to support a tumour-suppressor function for Dcc, but are consistent with the hypothesis that DCC is a component of a receptor for netrin-1.

Forced expression of the tumor suppressor adenomatosis polyposis coli protein induces disordered cell migration in the intestinal epithelium.

Mutations of the human adenomatosis polyposis coli (APC) gene are associated with the development of familial as well as sporadic intestinal neoplasia. To examine the in vivo function of APC, 129/Sv embryonic stem (ES) cells were transfected with DNA encoding the wild-type human protein under the control of a promoter that is active in all four of the small intestine's principal epithelial lineages during their migration-associated differentiation. ES-APC cells were then introduced into C57BL/6-ROSA26 blastocysts. Analyses of adult B6-ROSA26<-->129/Sv-APC chimeric mice revealed that forced expression of APC results in markedly disordered cell migration. When compared with the effects of forced expression of E-cadherin, the data suggest that APC-catenin and E-cadherin-catenin complexes have opposing effects on intestinal epithelial cell movement/adhesiveness; augmentation of E-cadherin-beta-catenin complexes produces a highly ordered, "adhesive" migration, whereas augmentation of APC-beta-catenin complexes produces a disordered, nonadhesive migratory phenotype. We propose that APC mutations may promote tumorigenesis by increasing the relative activity of cadherin-catenin complexes, resulting in enhanced adhesiveness and functional anchorage of initiated cells within the intestinal crypt. Our studies also indicate that chimeric mice generated from B6-ROSA26 blastocysts and genetically manipulated ES cells should be useful for auditing gene function in the gastrointestinal tract and in other tissues.

Forced expression of E-cadherin in the mouse intestinal epithelium slows cell migration and provides evidence for nonautonomous regulation of cell fate in a self-renewing system.

The adult mouse small intestinal epithelium is self-renewing. Its crypt-villus unit provides a model for studying many of the processes that occur during tissue morphogenesis such as control of proliferative status, specification of cell fate, regulation of differentiation, and induction of death. To assess the contributions of cell-cell and cell-substratum interactions to the coordinated control of these processes, 129/Sv embryonic stem (ES) cells, transfected with a recombinant DNA consisting of a fatty acid-binding protein gene (Fabp1) promoter that functions along the entire length of the crypt-villus axis linked to mouse E-cadherin, were introduced into normal C57Bl/6 (B6) blastocysts. Analyses of adult B6 <--> 129/Sv mice indicated that forced expression of E-cadherin suppresses proliferation and induces apoptosis in the crypt, and slows cell movement up the villus. The slowed migration is not accompanied by a change in distribution of terminal differentiation markers along the crypt-villus axis suggesting that differentiation is largely cell nonautonomous. To determine whether the slowed migration was a direct effect of forced expression of E-cadherin or a secondary effect of reduced crypt cell production, another Fabp promoter was used to restrict overproduction of E-cadherin to the villus epithelium of transgenic mice. Enterocytic migration was slowed, although proliferation and apoptosis were not perturbed in crypts. Augmentation of cellular E-cadherin pools was accompanied by an increase in beta-catenin levels. These findings establish that cadherins and their associated proteins modulate cellular migration, proliferation, and death programs in an adult vertebrate organ.

Inflammatory bowel disease and adenomas in mice expressing a dominant negative N-cadherin.

Cadherins mediate cell adhesion and are essential for normal development. Embryonic stem cells were transfected with a dominant negative N-cadherin mutant (NCAD delta) under the control of promoters active in small intestinal epithelial cells and then introduced into C57BL/6 mouse blastocysts. Analysis of adult chimeric mice revealed that expression of NCAD delta along the entire crypt-villus axis, but not in the villus epithelium alone, produced an inflammatory bowel disease resembling Crohn's disease. NCAD delta perturbed proliferation, migration, and death programs in crypts, which lead to adenomas. This model provides insights about cadherin function in an adult organ and the factors underlying inflammatory bowel disease and intestinal neoplasia.

Organization of the crypt-villus axis and evolution of its stem cell hierarchy during intestinal development.

The small intestinal crypt of the adult mouse represents a model system for studying cell renewal. One or more functionally equivalent stem cells located within the crypt fuel a continuous regeneration of the gut's four principal epithelial cell lineages. These lineages differentiate during a geographically well-organized migration along the crypt-villus axis. This axis does not complete its morphogenetic program until the third postnatal week. We examined the organization of the crypt-villus axis and its stem cell hierarchy in postnatal day 1 (P1) to P28 transgenic mice. These mice contained transcriptional regulatory elements from the liver fatty acid binding protein gene linked to a human growth hormone (hGH) reporter. Adult male and female animals exhibit a striped pattern of hGH accumulation in their villus-associated epithelial cells: vertical coherent bands of wholly hGH-positive epithelial cells derived from a monoclonal crypt and vertical coherent stripes of wholly hGH-negative epithelial cells derived from an adjacent crypt extend to the apical extrusion zone of their common villus. Villus striping develops in a proximal-to-distal wave that extends from the duodenum to the jejunum by P7 and to the ileum by P14. Striping occurs as a result of a loss in the ability to support transgene expression. The decision appears to affect all cells within a stripe, irrespective of their position along the basilar-to-apical axis of a villus, suggesting that it is programmed by the nascent crypt's multipotent stem cell(s). Suppression of transgene expression traverses the crypt-villus axis more rapidly than the rate of epithelial cell migration. The boundary between stripes is very sharp and does not contain cells with transitional levels of the hGH reporter, indicating that the epithelial components of the crypt-villus axis have a higher degree of organization at this stage of development than appreciated previously.

In vivo analysis of cadherin function in the mouse intestinal epithelium: essential roles in adhesion, maintenance of differentiation, and regulation of programmed cell death.

A model system is described for defining the physiologic functions of mammalian cadherins in vivo. 129/Sv embryonic stem (ES) cells, stably transfected with a dominant negative N-cadherin mutant (NCAD delta) under the control of a promoter that only functions in postmitotic enterocytes during their rapid, orderly, and continuous migration up small intestinal villi, were introduced into normal C57B1/6 (B6) blastocysts. In adult B6<->129/Sv chimeric mice, each villus receives the cellular output of several surrounding monoclonal crypts. A polyclonal villus located at the boundary of 129/Sv- and B6-derived intestinal epithelium contains vertical coherent bands of NCAD delta-producing enterocytes plus adjacent bands of normal B6-derived enterocytes. A comparison of the biological properties of these cell populations established that NCAD delta disrupts cell-cell and cell-matrix contacts, increases the rate of migration of enterocytes along the crypt-villus axis, results in a loss of their differentiated polarized phenotype, and produces precocious entry into a death program. These data indicate that enterocytic cadherins are critical cell survival factors that actively maintain intestinal epithelial function in vivo.

Differentiation and self-renewal in the mouse gastrointestinal epithelium.

The mouse gut epithelium represents a dynamic, geographically well organized, developmental system for examining self-renewal and differentiation. Reagents are now available for identifying the molecular mechanisms that regulate cell fate in the gut, the migration-associated differentiation programs of its component cell lineages, and its axial patterning. Considerable attention needs to be paid to two variables when studying gastrointestinal epithelial cell biology: space and time. This has necessitated the use of normal, chimeric, and transgenic animals as experimental models.

Chimeric-transgenic mice represent a powerful tool for studying how the proliferation and differentiation programs of intestinal epithelial cell lineages are regulated.

An in vivo system has been developed for examining the effects of wild-type or mutant proteins on cell fate determination in the mouse intestinal epithelium or on the proliferation and differentiation programs of its component epithelial lineages. This system takes advantage of the fact that at the conclusion of gut morphogenesis, each intestinal crypt is composed of a monoclonal population of cells descended from a single active multipotent stem cell, each villus is supplied by several monoclonal crypts, and the four principal cell types of the intestinal epithelium differentiate during a rapid, geographically well-organized migration along the crypt-to-villus axis. Embryonic stem (ES) cells (129/Sv origin) are initially transfected with recombinant DNAs consisting of a reporter of interest linked to transcriptional regulatory elements that control the cell lineage-specific, differentiation-dependent, and axial patterns of expression of fatty acid binding protein genes in the gut. Stably transfected ES cells are subsequently introduced into host C57BL/6 blastocysts to generate chimeric-transgenic mice. At the borders of ES cell-derived and host blastocyst-derived epithelium, intestinal villi are found that are supplied by both ES cell- and host blastocyst-derived crypts. These villi can be rapidly identified in fixed whole-mount preparations of intestine using the alpha-L-fucose-specific Ulex europaeus agglutinin type I (UEA-I) lectin. They appear striped because UEA-I recognizes a cell-surface carbohydrate polymorphism between the inbred strains used to generate the chimeric animals. The strength of this system derives from the fact that two gut epithelial populations can be compared and contrasted that occupy virtually identical positions along the crypt-to-villus and duodenal-to-colonic axes within the same animal and differ only by the presence or absence of a single gene product. The band of blastocyst-derived epithelium in these striped, polyclonal villi can be used as an internal control to assess the biological effect of the transfected gene product produced in the adjacent stripe of ES-derived cells. The system can be used for either gain-of-function or loss-of-function experiments.

Simultaneous localization of six antigens in single sections of transgenic mouse intestine using a combination of light and fluorescence microscopy.

To study the geographic differentiation of the intestinal epithelium and to understand the complex lineage relationships of its cell populations, it is often necessary to visualize the protein products of multiple genes in sections prepared from different positions along the duodenal-to-colonic and/or crypt-to-villus axes. Multilabel fluorescence or brightfield immunohistochemical techniques have previously been used for this purpose. However, the number of antigens that can be identified on single sections is limited in fluorescence microscopy by the number of fluorophores with non-overlapping absorption and emission characteristics, in brightfield microscopy by the number of visually distinguishable chromogens, and in both methods by the availability of primary antisera raised in multiple species. We have now used a combination of light and fluorescence microscopic techniques to increase the number of antigens that can be detected in a single section to six. Sections were sequentially stained using immunogold with silver intensification, peroxidase-antiperoxidase with diaminobenzidine chromogen, and peroxidase-anti-peroxidase with alpha-naphthol/basic dye as chromogen, followed by simultaneous fluorescent detection with fluorescein, 7-amino-4-methylcoumarin-3-acetic acid, and beta-phycoerythrin. This method enables up to four separate antigens to be visualized within a single cell and two additional antigens to be detected in unrelated cells. The technique is illustrated by examining the cellular patterns of expression of liver fatty acid binding protein/human growth hormone fusion genes in the intestinal epithelium of adult transgenic mice. It should be generally applicable to other experimental systems that require localization of multiple antigens in single tissue sections.

Use of transgenic mice to infer the biological properties of small intestinal stem cells and to examine the lineage relationships of their descendants.

Transgenes, composed of elements of the 5' nontranscribed region of the liver fatty acid-binding protein (L-FABP) gene linked to various reporters, have previously been used to explore the cellular, regional, and temporal differentiation of the mouse intestinal epithelium. In this report, we have analyzed a pedigree of L-FABP/human growth hormone (hGH) transgenic mice that display a stable, heritable, mosaic pattern of reporter expression: wholly hGH-positive or hGH-negative populations of differentiating enterocytes arise from hGH-positive or hGH-negative crypts, respectively, and migrate as vertical coherent bands up the villus producing striped (polyclonal) villi. The ability of enteroendocrine cells within a given villus stripe to support hGH expression coincides with the enterocytic reporter phenotype, suggesting that these two terminally differentiated cells arise from a common multipotent stem cell. hGH-negative crypts are nonrandomly distributed around each villus and their frequency increases along the duodenal-to-ileal axis. Statistical analysis of the observed villus striping pattern suggests that transgene expression is not independently determined in individual crypts but rather in multicrypt "patches." The intact endogenous mouse L-FABP gene (Fabpl) exhibits a similar striped villus pattern of expression in a portion of the distal small intestine. These studies indicate that Fabpl and L-FABP/hGH transgenes represent sensitive markers for exploring the biological properties of gut stem cells and how positional information is encoded in this rapidly and continuously renewing epithelium.

Isolation of mutants defective in early steps of meiotic recombination in the yeast Saccharomyces cerevisiae.

Using a selection based upon the ability of early Rec- mutations (e.g., rad50) to rescue the meiotic lethality of a rad52 spo13 strain, we have isolated 177 mutants. Analysis of 56 of these has generated alleles of the known Rec genes SPO11, ME14 and MER1, as well as defining five new genes: REC102, REC104, REC107, REC113 and REC114. Mutations in all of the new genes appear to specifically affect meiosis; they do not have any detectable mitotic phenotype. Mutations in REC102, REC104 and REC107 reduce meiotic recombination several hundred fold. No alleles of RED1 or HOP1 were isolated, consistent with the proposal that these genes may be primarily involved with chromosome pairing and not exchange.