Epithelial cell growth and differentiation. IV. Controlled spatiotemporal expression of transgenes: new tools to study normal and pathological states

The REMOTE-control system: a system for reversible and tunable control of endogenous gene expression in mice

We report here a robust, tunable, and reversible transcription control system for endogenous genes. The REMOTE-control system (Reversible Manipulation of Transcription at Endogenous loci) employs enhanced lac repression and tet activation systems. With this approach, we show in mouse embryonic stem cells that endogenous Dnmt1 gene transcription could be up- or downregulated in a tunable, inducible, and reversible manner across nearly two orders of magnitude. Transcriptional repression of Dnmt1 by REMOTE-control was potent enough to cause embryonic lethality in mice, reminiscent of a genetic knockout of Dnmt1 and could substantially suppress intestinal polyp formation when applied to an Apc^Min model. Binding by the enhanced lac repressor was sufficiently tight to allow strong attenuation of transcriptional elongation, even at operators located many kilobases downstream of the transcription start site and to produce invariably tight repression of all of the strong viral/mammalian promoters tested. Our approach of targeting tet transcriptional activators to the endogenous Dnmt1 promoter resulted in robust upregulation of this highly expressed housekeeping gene. Our system provides exquisite control of the level, timing, and cell-type specificity of endogenous gene expression, and the potency and versatility of the system will enable high resolution in vivo functional analyses.

Keratins regulate colonic epithelial cell differentiation through the Notch1 signalling pathway

Keratins (K) are intermediate filament proteins important in stress protection and mechanical support of epithelial tissues. K8, K18 and K19 are the main colonic keratins, and K8-knockout (K8^−/−) mice display a keratin dose-dependent hyperproliferation of colonic crypts and a colitis-phenotype. However, the impact of the loss of K8 on intestinal cell differentiation has so far been unknown. Here we show that K8 regulates Notch1 signalling activity and differentiation in the epithelium of the large intestine. Proximity ligation and immunoprecipitation assays demonstrate that K8 and Notch1 co-localize and interact in cell cultures, and in vivo in the colonic epithelial cells. K8 with its heteropolymeric partner K18 enhance Notch1 protein levels and activity in a dose dependent manner. The levels of the full-length Notch1 receptor (FLN), the Notch1 intracellular domain (NICD) and expression of Notch1 downstream target genes are reduced in the absence of K8, and the K8-dependent loss of Notch1 activity can be rescued with re-expression of K8/K18 in K8-knockout CRISPR/Cas9 Caco-2 cells protein levels. In vivo, K8 deletion with subsequent Notch1 downregulation leads to a shift in differentiation towards a goblet cell and enteroendocrine phenotype from an enterocyte cell fate. Furthermore, the K8^−/− colonic hyperproliferation results from an increased number of transit amplifying progenitor cells in these mice. K8/K18 thus interact with Notch1 and regulate Notch1 signalling activity during differentiation of the colonic epithelium.

Intestinal stem cell transplantation

Organoid technologies to expand intestinal epithelial cells are gaining increasing attention as a useful tool to investigate many aspects of intestinal epithelial biology and pathology. One important application of organoid systems would be to use intestinal epithelial cells expanded in culture for following transplantation experiments. In this article, we present a brief overview of the studies that have succeeded in generating new epithelial tissues in the surface of native intestines in mice by organoid transplantation. We also discuss possible applications of this experimental approach in basic research on the intestinal epithelium as well as in regenerative medicine for various types of intestinal diseases in humans.

Trans-presentation: a novel mechanism regulating IL-15 delivery and responses

Interleukin (IL)-15 is a cytokine that acts on a wide range of cell types but is most crucial for the development, homeostasis, and function of a specific group of immune cells that includes CD8 T cells, NK cells, NKT cells, and CD8 alpha alpha intraepithelial lymphocytes. IL-15 signals are transmitted through the IL-2/15R beta and common gamma (gamma C) chains; however, it is the delivery of IL-15 to these signaling components that is quite unique. As opposed to other cytokines that are secreted, IL-15 primarily exists bound to the high affinity IL-15R alpha. When IL-15/IL-15R alpha complexes are shuttled to the cell surface, they can stimulate opposing cells through the beta/gamma C receptor complex. This novel mechanism of IL-15 delivery has been called trans-presentation. This review discusses how the theory of trans-presentation came to be, evidence that it is the major mechanism of action, the current understanding of the cell types thought to mediate trans-presentation, and possible alternatives for IL-15 delivery.

Trans-presentation of IL-15 by intestinal epithelial cells drives development of CD8alphaalpha IELs

IL-15 is crucial for the development of intestinal intraepithelial lymphocytes (IEL) and delivery is mediated by a unique mechanism known as trans-presentation. Parenchymal cells have a major role in the trans-presentation of IL-15 to IELs, but the specific identity of this cell type is unknown. To investigate whether the intestinal epithelial cells (IEC) are the parenchymal cell type involved, a mouse model that expresses IL-15Ralpha exclusively by the IECs (Villin/IL-15Ralpha Tg) was generated. Exclusive expression of IL-15Ralpha by the IECs restored all the deficiencies in the CD8alphaalpha(+)TCRalphabeta(+)and CD8alphaalpha(+)TCRgammadelta(+) subsets that exist in the absence of IL-15Ralpha. Interestingly, most of the IEL recovery was due to the preferential increase in Thy1(low) IELs, which compose a majority of the IEL population. The differentiation of Thy1(high)CD4(-)CD8(-) thymocytes into Thy1(-)CD8alphaalpha IELs was found to require IL-15Ralpha expression specifically by IECs and thus, provides evidence that differentiation of Thy1(low) IELs is one function of trans-presentation of IL-15 in the intestines. In addition to effects in IEL differentiation, trans-presentation of IL-15 by IECs also resulted in an increase in IEL numbers that was accompanied by increases in Bcl-2, but not proliferation. Collectively, this study demonstrates that trans-presentation of IL-15 by IECs alone is completely sufficient to direct the IL-15-mediated development of CD8alphaalpha(+) T cell populations within the IEL compartment, which now includes a newly identified role of IL-15 in the differentiation of Thy1(low) IELs.

Aberrant epithelial morphology and persistent epidermal growth factor receptor signaling in a mouse model of renal carcinoma

The epidermal growth factor receptor (EGFR) has frequently been implicated in hyperproliferative diseases of renal tubule epithelia. We have shown that the NF2 tumor suppressor Merlin inhibits EGFR internalization and signaling in a cell contact-dependent manner. Interestingly, despite the paucity of recurring mutations in human renal cell carcinoma (RCC), homozygous mutation of the NF2 gene is found in approximately 2% of RCC patient samples in the Sanger COSMIC database. To examine the roles of Merlin and EGFR in kidney tumorigenesis, we generated mice with a targeted deletion of Nf2 in the proximal convoluted epithelium using a Villin-Cre transgene. All of these mice developed intratubular neoplasia by 3 months, which progressed to invasive carcinoma by 6-10 months. Kidneys from these mice demonstrated marked hyperproliferation and a concomitant increase in label-retaining putative progenitor cells. Early lumen-filling lesions in this model exhibited hyperactivation of EGFR signaling, altered solubility of adherens junctions components, and loss of epithelial polarity. Renal cortical epithelial cells derived from either early or late lesions were dependent on EGF for in vitro proliferation and were arrested by pharmacologic inhibition of EGFR or re-expression of Nf2. These cells formed malignant tumors upon s.c. injection into immunocompromised mice before in vitro passage. Treatment of Vil-Cre;Nf2(lox/lox) mice with the EGFR inhibitor erlotinib halted the proliferation of tumor cells. These studies give added credence to the role of EGFR signaling and perhaps Nf2 deficiency in RCC and describe a rare and valuable mouse model for exploring the molecular basis of this disease.

Inactivation of conditional Rb by Villin-Cre leads to aggressive tumors outside the gastrointestinal tract

We have crossed mice carrying the conditional Rb(tm2Brn) allele with a constitutive Villin-Cre transgenic mouse. The Villin promoter in these animals is highly expressed in adult intestine and kidney proximal tubules and is expressed in the gut and nephros anlagen during embryogenesis. We report here that these mice develop tumors between 12 and 17 months old outside the gastrointestinal (GI) tract. A high penetrance of pituitary tumors and medullar carcinoma of the thyroid is observed with a lower incidence of hyperplasia of pulmonary neuroendocrine cells and aggressive liver, bile duct, stomach, oral cavity tumors, and lipomas. Rb rearrangement due to ectopic Villin promoter activity in neural crest or neural crest stem cells during embryogenesis is most likely responsible for the medullar carcinoma of the thyroid phenotype. The aggressive nature of the medullar carcinoma of the thyroid and its ability to metastasize to unusual sites make the model suitable for the study of tumor progression and mechanism of metastasis. Observed sites of metastasis include the stomach, small intestine, liver, lung, kidney, pancreas, spleen, bone marrow, salivary gland, fat, lymph nodes, and dorsal root ganglion. Because the Villin promoter is highly active throughout the GI and in the nephros anlagen during development, we find that Rb inactivation is not sufficient to initiate tumorigenesis in the GI or kidneys in mice.