The small intestine epithelium undergoes rapid and continuous regeneration supported by crypt intestinal stem cells (ISCs). Bmi1 and Lgr5 have been independently identified to mark long-lived multipotent ISCs by lineage tracing in mice; however, the functional distinctions between these two populations remain undefined. Here, we demonstrate that Bmi1 and Lgr5 mark two functionally distinct ISCs in vivo. Lgr5 marks mitotically active ISCs that exhibit exquisite sensitivity to canonical Wnt modulation, contribute robustly to homeostatic regeneration, and are quantitatively ablated by irradiation. In contrast, Bmi1 marks quiescent ISCs that are insensitive to Wnt perturbations, contribute weakly to homeostatic regeneration, and are resistant to high-dose radiation injury. After irradiation, however, the normally quiescent Bmi1 + ISCs dramatically proliferate to clonally repopulate multiple contiguous crypts and villi. Clonogenic culture of isolated single Bmi1 + ISCs yields long-lived self-renewing spheroids of intestinal epithelium that produce Lgr5-expressing cells, thereby establishing a lineage relationship between these two populations in vitro. Taken together, these data provide direct evidence that Bmi1 marks quiescent, injury-inducible reserve ISCs that exhibit striking functional distinctions from Lgr5 + ISCs and support a model whereby distinct ISC populations facilitate homeostatic vs. injury-induced regeneration.R-spondin | Dickkopf-1 | intestinal regeneration T he G protein-coupled receptor Lgr5 and the Polycomb group protein Bmi1 are two recently described molecular markers of self-renewing and multipotent adult stem cell populations residing in the crypt of the small intestine, capable of supporting regeneration of the intestinal epithelium (1, 2). Despite their similar ability to functionally repopulate the intestinal epithelium as demonstrated by independent in vivo lineage tracing experiments in reporter mice, the intestinal stem cells (ISCs) identified by these two molecular markers are spatially distinct. Whereas Lgr5 + ISCs are crypt base columnar (CBC) cells (1, 3) interspersed between Paneth cells and expressed throughout the intestine, Bmi1 + ISCs are mostly restricted to the "+4" cell position abutting the uppermost Paneth cell in proximal small intestine crypts (2). Lgr5 + ISCs are actively cycling (1), equipotent, and contribute to intestinal homeostasis by neutral drift competition (4-6). By comparison, Bmi1 + ISCs are less well characterized, and because of the lack of direct evidence, their cell cycle status is variably ascribed to be rapidly (7) vs. slowly cycling (8). It has been suggested that Bmi1 and Lgr5 mark an overlapping and possibly identical or redundant population of ISCs (5, 7, 9); however, no direct exploration of their functional similarities and differences has been performed. Further, it is unknown how Bmi1 + and Lgr5 + ISCs relate to a proposed model in which the intestine differentially uses an actively cycling ISC population during homeostasis and a distinct quiesce...

Background and Aims-Chronic infection with the bacterial pathogen Helicobacter pylori

Gastric adenocarcinoma is strongly associated with Helicobacter pylori infection; however, most infected persons never develop this malignancy. H. pylori strains harboring the cag pathogenicity island (cag + ), which encodes CagA and a type IV secretion system (T4SS), induce more severe disease outcomes. H. pylori infection is also associated with iron deficiency, which similarly augments gastric cancer risk. To define the influence of iron deficiency on microbial virulence in gastric carcinogenesis, Mongolian gerbils were maintained on iron-depleted diets and infected with an oncogenic H. pylori cag + strain. Iron depletion accelerated the development of H. pylori-induced premalignant and malignant lesions in a cagA-dependent manner. H. pylori strains harvested from iron-depleted gerbils or grown under iron-limiting conditions exhibited enhanced virulence and induction of inflammatory factors. Further, in a human population at high risk for gastric cancer, H. pylori strains isolated from patients with the lowest ferritin levels induced more robust proinflammatory responses compared with strains isolated from patients with the highest ferritin levels, irrespective of histologic status. These data demonstrate that iron deficiency enhances H. pylori virulence and represents a measurable biomarker to identify populations of infected persons at high risk for gastric cancer.

No abstract

Microbes use directed motility to colonize harsh and dynamic environments. We discovered that Helicobacter pylori strains establish bacterial colonies deep in the gastric glands and identified a novel protein, ChePep, necessary to colonize this niche. ChePep is preferentially localized to the flagellar pole. Although mutants lacking ChePep have normal flagellar ultrastructure and are motile, they have a slight defect in swarming ability. By tracking the movement of single bacteria, we found that ∆ChePep mutants cannot control the rotation of their flagella and swim with abnormally frequent reversals. These mutants even sustain bursts of movement backwards with the flagella pulling the bacteria. Genetic analysis of the chemotaxis signaling pathway shows that ChePep regulates flagellar rotation through the chemotaxis system. By examining H. pylori within a microscopic pH gradient, we determined that ChePep is critical for regulating chemotactic behavior. The chePep gene is unique to the Epsilonproteobacteria but is found throughout this diverse group. We expressed ChePep from other members of the Epsilonproteobacteria, including the zoonotic pathogen Campylobacter jejuni and the deep sea hydrothermal vent inhabitant Caminibacter mediatlanticus, in H. pylori and found that ChePep is functionally conserved across this class. ChePep represents a new family of chemotaxis regulators unique to the Epsilonproteobacteria and illustrates the different strategies that microbes have evolved to control motility.