Mesenchymal transcription factor Fkh6 is essential for the development and differentiation of parietal cells

Foxl1-expressing mesenchymal cells constitute the intestinal stem cell niche

BACKGROUND & AIMS

Intestinal epithelial stem cells that express Lgr5 and/or Bmi1 continuously replicate and generate differentiated cells throughout life¹. Previously, Paneth cells were suggested to constitute an epithelium-intrinsic niche that regulates the behavior of these stem cells². However, ablating Paneth cells has no effect on maintenance of functional stem cells^3-5. Here, we demonstrate definitively that a small subset of mesenchymal, subepithelial cells expressing the winged-helix transcription factor Foxl1 are a critical component of the intestinal stem cell niche.

METHODS

We genetically ablated Foxl1⁺ mesenchymal cells in adult mice using two separate models by expressing either the human or simian diphtheria toxin receptor (DTR) under Foxl1 promoter control.

CONCLUSIONS

Killing Foxl1⁺ cells by diphtheria toxin administration led to an abrupt cessation of proliferation of both epithelial stem- and transit-amplifying progenitor-cell populations that was associated with a loss of active Wnt signaling to the intestinal epithelium. Therefore, Foxl1-expressing mesenchymal cells constitute the fundamental niche for intestinal stem cells.

Bmi1 confers resistance to oxidative stress on hematopoietic stem cells

Background

The polycomb-group (PcG) proteins function as general regulators of stem cells. We previously reported that retrovirus-mediated overexpression of Bmi1, a gene encoding a core component of polycomb repressive complex (PRC) 1, maintained self-renewing hematopoietic stem cells (HSCs) during long-term culture. However, the effects of overexpression of Bmi1 on HSCs in vivo remained to be precisely addressed.

Methodology/Principal findings

In this study, we generated a mouse line where Bmi1 can be conditionally overexpressed under the control of the endogenous Rosa26 promoter in a hematopoietic cell-specific fashion (Tie2-Cre;R26Stop^FLBmi1). Although overexpression of Bmi1 did not significantly affect steady state hematopoiesis, it promoted expansion of functional HSCs during ex vivo culture and efficiently protected HSCs against loss of self-renewal capacity during serial transplantation. Overexpression of Bmi1 had no effect on DNA damage response triggered by ionizing radiation. In contrast, Tie2-Cre;R26Stop^FLBmi1 HSCs under oxidative stress maintained a multipotent state and generally tolerated oxidative stress better than the control. Unexpectedly, overexpression of Bmi1 had no impact on the level of intracellular reactive oxygen species (ROS).

Conclusions/Significance

Our findings demonstrate that overexpression of Bmi1 confers resistance to stresses, particularly oxidative stress, onto HSCs. This thereby enhances their regenerative capacity and suggests that Bmi1 is located downstream of ROS signaling and negatively regulated by it.

Loss of Runx3 is a key event in inducing precancerous state of the stomach

BACKGROUND & AIMS

RUNX3 is a tumor suppressor originally identified in gastric cancer. The mutation R122C in RUNX3 promotes gastric carcinogenesis by unclear mechanisms. We investigated how Runx3-deficiency contributes to distinct changes in the gastric epithelium that precede neoplasia.

METHODS

Runx3-deficient (Runx3(-/-)) and wild-type BALB/c adult mice were subjected to histological analyses. Gastric cancer formation after administration of N-methyl-N-nitrosourea was evaluated. Runx3(+/+) and Runx3(-/-) gastric epithelial cell lines were used to investigate the molecular basis underlying Runx3 function.

RESULTS

The gastric epithelia in Runx3(-)/(-) adult mice was hyperplastic, with loss of chief cells and development of mucin 6- and trefoil factor-2-expressing metaplasia. The gastric epithelium of Runx3(-)/(-) mice had an intestinal phenotype that expressed Cdx2. After addition of N-methyl-N-nitrosourea, Runx3- mice, unlike wild-type mice, consistently developed adenocarcinomas, indicating that Runx3-deficiency leads to premalignant changes in the gastric epithelia. RUNX3, but not the RUNX3 mutant R122C, repressed Cdx2 expression by attenuation of oncogenic beta(symbol)-catenin and Tcfs.

CONCLUSIONS

Runx3-deficiency leads to a precancerous state in the gastric epithelia of mice, characterized by loss of chief cells but not parietal cells; inflammation did not appear to be involved.

A novel zinc finger protein Zfp277 mediates transcriptional repression of the Ink4a/arf locus through polycomb repressive complex 1

Background

Polycomb group (PcG) proteins play a crucial role in cellular senescence as key transcriptional regulators of the Ink4a/Arf tumor suppressor gene locus. However, how PcG complexes target and contribute to stable gene silencing of the Ink4a/Arf locus remains little understood.

Methodology/Principal Findings

We examined the function of Zinc finger domain-containing protein 277 (Zfp277), a novel zinc finger protein that interacts with the PcG protein Bmi1. Zfp277 binds to the Ink4a/Arf locus in a Bmi1-independent manner and interacts with polycomb repressor complex (PRC) 1 through direct interaction with Bmi1. Loss of Zfp277 in mouse embryonic fibroblasts (MEFs) caused dissociation of PcG proteins from the Ink4a/Arf locus, resulting in premature senescence associated with derepressed p16^Ink4a and p19^Arf expression. Levels of both Zfp277 and PcG proteins inversely correlated with those of reactive oxygen species (ROS) in senescing MEFs, but the treatment of Zfp277^−/− MEFs with an antioxidant restored the binding of PRC2 but not PRC1 to the Ink4a/Arf locus. Notably, forced expression of Bmi1 in Zfp277^−/− MEFs did not restore the binding of Bmi1 to the Ink4a/Arf locus and failed to bypass cellular senescence. A Zfp277 mutant that could not bind Bmi1 did not rescue Zfp277^−/− MEFs from premature senescence.

Conclusions/Significance

Our findings implicate Zfp277 in the transcriptional regulation of the Ink4a/Arf locus and suggest that the interaction of Zfp277 with Bmi1 is essential for the recruitment of PRC1 to the Ink4a/Arf locus. Our findings also highlight dynamic regulation of both Zfp277 and PcG proteins by the oxidative stress pathways.

The gastric mucosa development and differentiation

The development and differentiation of the gastric mucosa are controlled by a complex interplay of signaling proteins and transcriptional regulators. This process is complicated by the fact that the stomach is derived from two germ layers, the endoderm and the mesoderm, with the first giving rise to the mature epithelium and the latter contributing the smooth muscle required for peristalsis. Reciprocal epithelial-mesenchymal interactions dictate the formation of the stomach during fetal development, and also contribute to its continuous regeneration and differentiation throughout adult life. In this chapter, we discuss the discoveries that have been made in different model systems, from zebrafish to human, which show that the Hedgehog, Wnt, Notch, bone morphogenetic protein, and fibroblast growth factor (FGF) signaling systems play essential roles during various stages of stomach development.

Genomic and genic deletions of the FOX gene cluster on 16q24.1 and inactivating mutations of FOXF1 cause alveolar capillary dysplasia and other malformations

Alveolar capillary dysplasia with misalignment of pulmonary veins (ACD/MPV) is a rare, neonatally lethal developmental disorder of the lung with defining histologic abnormalities typically associated with multiple congenital anomalies (MCA). Using array CGH analysis, we have identified six overlapping microdeletions encompassing the FOX transcription factor gene cluster in chromosome 16q24.1q24.2 in patients with ACD/MPV and MCA. Subsequently, we have identified four different heterozygous mutations (frameshift, nonsense, and no-stop) in the candidate FOXF1 gene in unrelated patients with sporadic ACD/MPV and MCA. Custom-designed, high-resolution microarray analysis of additional ACD/MPV samples revealed one microdeletion harboring FOXF1 and two distinct microdeletions upstream of FOXF1, implicating a position effect. DNA sequence analysis revealed that in six of nine deletions, both breakpoints occurred in the portions of Alu elements showing eight to 43 base pairs of perfect microhomology, suggesting replication error Microhomology-Mediated Break-Induced Replication (MMBIR)/Fork Stalling and Template Switching (FoSTeS) as a mechanism of their formation. In contrast to the association of point mutations in FOXF1 with bowel malrotation, microdeletions of FOXF1 were associated with hypoplastic left heart syndrome and gastrointestinal atresias, probably due to haploinsufficiency for the neighboring FOXC2 and FOXL1 genes. These differences reveal the phenotypic consequences of gene alterations in cis.

Foxl1-Cre BAC transgenic mice: a new tool for gene ablation in the gastrointestinal mesenchyme

The use of Cre-loxP technology for the purpose of cell type-specific gene ablation has revolutionized developmental biology and biomedicine. Several transgenic mouse lines have been developed for the analysis of gene function in the gastrointestinal tract, but in all of these the expression of Cre is limited to the epithelial cell layer. No Cre- expressing transgenic mouse lines ("Cre lines") exist for the deletion of loxP-flanked genes specifically in gut mesoderm. To address this deficiency, we have derived a bacterial artificial chromosome based transgenic mouse line in which the Cre gene is controlled by the Foxl1 promoter and enhancer elements. X-Gal staining of Foxl1-Cre; Rosa26R bi-transgenic lines confirm that Foxl1-Cre results in recombination specifically in the gastrointestinal mesenchyme. The Foxl1-Cre line will facilitate the dissection of mesenchymal to epithelial signaling that is known to play a major role in the patterning and function of the gastrointestinal tract.

Foxl1-deficient mice exhibit aberrant epithelial cell positioning resulting from dysregulated EphB/EphrinB expression in the small intestine

The winged helix transcription factor Foxl1, expressed in the gut mesenchyme, regulates epithelial cell proliferation and differentiation through the Wnt/beta-catenin pathway. To better understand the role of Foxl1 in epithelial morphogenesis, we examined the tissue structure and positioning of epithelial cells in the small intestine of Foxl1-deficient mice. The small intestine of Foxl1-deficient mice manifested aberrant crypt structure, including widely distributed Paneth cells, which coincided with the ectopic and increased expression of EphB2 and EphB3, which are key regulators of epithelial cell positioning. Furthermore, real-time quantitative PCR indicated that a subset of Wnt family genes was highly expressed in the gut mesenchyme of Foxl1-deficient mice compared with that of wild-type mice. Such an increase in Wnt expression was remarkable in the mesenchyme, where the aberrant Paneth cell positioning was observed by in situ hybridization. Foxl1 plays an important role in the maintenance of crypt architecture and epithelial cell positioning through the mesenchymal-epithelial interaction in the small intestine. This interaction is essential for the normal regulation of the Wnt/beta-catenin pathway and the subsequent EphB/EphrinB expression.

Runx3 controls growth and differentiation of gastric epithelial cells in mammals

Runx3 is a transcription factor expressed by gastric epithelial cells. In the Runx3(-/-) mouse, gastric epithelia exhibited hyperplasia, and epithelial apoptosis was suppressed. By analyzing growth of the epithelial cells in primary culture, we found that Runx3(-/-) gastric epithelial cells are less sensitive to the growth-inhibitory and apoptosis-inducing activities of TGF-beta, suggesting that Runx3 is a major growth regulator of gastric epithelial cells by regulating their response to TGF-beta. We also found that Runx3 plays an important role in the control of gastric epithelial differentiation. When subcutaneously implanted into nude mice, Runx3(-/-) gastric epithelial cells formed tumors in which some cells differentiated into intestinal-type cells. Clonal analysis showed that gastric epithelial cells transdifferentiate into intestinal-type cells in the tumor. Considering that gastric epithelial differentiation is very stable, and that intestinal-type cells never differentiate in the mouse stomach, it is remarkable that gastric epithelial cells transdifferentiate into intestinal-type cells. We conclude that Runx3 is deeply involved in the control of both growth and differentiation of gastric epithelial cells. The role of Runx3 in the specification of gastric epithelial cells is discussed.

Reduction of SNAP25 in acid secretion defect of Foxl1-/- gastric parietal cells

Foxl1 is a winged helix transcription factor expressed in the mesenchyme of the gastrointestinal tract. In the absence of Foxl1, parietal cells fail to secrete gastric acid in response to various secretagogue stimuli including cAMP. A marked decrease in H+,K(+)-ATPase expression was observed even though a substantial number of parietal cells still existed in Foxl1-deficient mice. Ultrastructural analysis suggested that the gastric acid secretion defect in Foxl1-deficient mice is mainly due to impairment in the fusion of cytoplasmic tubulovesicular structures to the apical canalicular plasma membrane. Among the molecules involved in the membrane fusion event, only SNAP25 showed a significant decrease in mRNA expression, which likely caused the impairment in acid secretion from parietal cells in Foxl1-deficient mice, with the reduction in H+,K(+)-ATPase expression contributing to additional effect.

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Mesenchymal expression of Foxl1, a winged helix transcriptional factor, regulates generation and maintenance of gut-associated lymphoid organs

The Foxl1 gene, which encodes a winged helix transcriptional regulator, is expressed in the mesenchymal layer of developing and mature gastrointestinal tract. Foxl1-deficient mice exhibit various defects not only in the epithelial layer of the gastrointestinal tract but also in gut-associated lymphoid tissues. In the small intestine of Foxl1-deficient mice, the formation of Peyer's patches is affected, particularly in the caudal region. This alteration is shown to be due to the delayed formation of Peyer's patches organizing centers as revealed by the expressions of VCAM1 and IL-7 receptor alpha-chain at 17.5 days postcoitus. Peyer's patch defects are concordant with the significantly decreased expression of Lymphotoxin beta-receptor in the caudal region of fetal intestine. Foxl1 is suggested to regulate the responsiveness of fetal intestinal mesenchymal cells to inductive signals mediated by Lymphotoxins during Peyer's patch organogenesis. In addition, constitutive outgrowth of colonic patches due to defects in radioresistant stromal components of colonic patches are seen in Foxl1-deficient mice. Because of the functional similarities of hypertrophic colonic patches to those seen in hapten-induced experimental colitis, this hypertrophy is suggested to involve Lymphotoxin beta-receptor signaling. Together, the data suggest that Foxl1 might be involved in cellular responses of gut-associated lymphoid tissues dependent upon the Lymphotoxins/Lymphotoxin beta-receptor axis.

Gastric hyperplasia in mice with targeted disruption of the carbonic anhydrase gene Car9

BACKGROUND & AIMS

Carbonic anhydrase (CA) IX is a highly active enzyme with adhesion capacity that is functionally implicated in acid-base balance and intercellular communication. It is normally present in basolateral membranes of gastrointestinal epithelial cells and ectopically expressed in various carcinomas. To show its physiologic relevance, we have cloned the Car9 gene and generated CA IX-deficient mice.

METHODS

The mice with null mutation of the Car9 gene were obtained by targeted gene disruption. Tissue architecture and expression of markers were determined by histochemical and immunohistochemical techniques.

RESULTS

Mice homozygous for the mutation developed gastric hyperplasia of the glandular epithelium with numerous cysts. The first changes were observed in the newborn animals, and the hyperplasia became prominent at the end of gastric morphogenesis in 4-week-old mice. Loss of CA IX led to overproduction of mucus-secreting pit cells and depletion of pepsinogen-positive chief cells. The proportion of H(+)/K(+)-adenosine triphosphatase-positive parietal cells significantly decreased, but their absolute number was not reduced. Correspondingly, CA IX-deficient mice had normal gastric pH, acid secretion, and serum gastrin levels.

CONCLUSIONS

Phenotypic consequences of the Car9 null mutation show the important role of CA IX in morphogenesis and homeostasis of the glandular gastric epithelium via the control of cell proliferation and differentiation.

Antisecretory effect of somatostatin on gastric acid via inhibition of histamine release in isolated mouse stomach

Somatostatin is known to inhibit gastric acid secretion via both inhibition of histamine release from gastric enterochromaffin-like cells and direct inhibition of parietal cell function. We tried to clarify which of these two mechanisms plays a more important role in the inhibition of gastric acid section by somatostatin using isolated mouse stomach preparations. The gastric acid secretion stimulated by histamine was not inhibited by pretreatment with somatostatin (1 micro M), but somatostatin abolished acid secretion induced by 4-[[[(3-chlorophenyl)amino]carbonyl]oxy]-N,N,N,-trimethyl-2-butynyl-1-aminium chloride (McN-A-343), a muscarinic M(1) receptor agonist. In addition, the histamine-H(2) receptor antagonist famotidine also completely inhibited the secretion stimulated by McN-A-343. Similarly, pretreatment with both somatostatin and famotidine completely abolished pentagastrin-induced acid secretion. Somatostatin partially inhibited the acid secretion stimulated by bethanechol. The late sustained acid secretion induced by bethanechol was reduced more strongly by somatostatin than the initial peak secretion. In addition, somatostatin had no effect on the transient increase in bethanechol-induced acid secretion in famotidine-pretreated preparations. Somatostatin had no effect on basal histamine secretion in isolated mouse stomach preparations, but markedly reduced histamine release induced by McN-A-343 and bethanechol. The present study showed that the acid secretory response via the endogenous histamine-mediated pathway was inhibited by somatostatin, but the response to a direct activation of gastric parietal cells was not. These results suggest that the inhibition of histamine release from enterochromaffin-like cells plays a more important role in the inhibition of gastric acid secretion by somatostatin than the direct inhibition of parietal cells. In addition, somatostatin inhibited the sustained acid secretion more strongly than the initial peak secretion after the cholinergic stimulation.