Exocrine-to-endocrine differentiation is detectable only prior to birth in the uninjured mouse pancreas

<p>Abstract</p> <p>Background</p> <p>Histological evidence suggests that insulin-producing beta (β)-cells arise in utero from duct-like structures of the fetal exocrine pancreas, and genetic lineage tracing studies indicate that they are maintained in the adult by self-renewal. These studies have not addressed the origin of the new β-cells that arise in large numbers shortly after birth, and contradictory lineage tracing results have been published regarding the differentiation potential of duct cells in this period. We established an independent approach to address this question directly.</p> <p>Results</p> <p>We generated mice in which duct and acinar cells, comprising the exocrine pancreas, can be genetically marked by virtue of their expressing the mucin gene <it>Muc1</it>. Using these mice, we performed time-specific lineage tracing to determine if these cells undergo endocrine transdifferentiation in vivo. We find that <it>Muc1</it>⁺cells do give rise to β-cells and other islet cells in utero, providing formal proof that mature islets arise from embryonic duct structures. From birth onwards, <it>Muc1 </it>lineage-labeled cells are confined to the exocrine compartment, with no detectable contribution to islet cells.</p> <p>Conclusions</p> <p>These results argue against a significant contribution by exocrine transdifferentiation to the normal postnatal expansion and maintenance of β-cell mass. Exocrine transdifferentiation has been proposed to occur during injury and regeneration, and our experimental model is suited to test this hypothesis in vivo.</p

Distinct requirements for beta-catenin in pancreatic epithelial growth and patterning

AbstractPancreatic exocrine and endocrine lineages arise from multipotent pancreatic progenitor cells (MPCs). Exploiting the mechanisms that govern expansion and differentiation of these cells could enhance efforts to generate β-cells from stem cells. Although our prior work indicates that the canonical Wnt signaling component β-catenin is required qualitatively for exocrine acinar but not endocrine development, precisely how this requirement plays out at the level of MPCs and their lineage-restricted progeny is unknown. In addition, the contribution of β-catenin function to β-cell development remains controversial. To resolve the potential roles of β-catenin in development of MPCs and β-cells, we generated pancreas- and pre-endocrine-specific β-catenin knockout mice. Pancreas-specific loss of β-catenin produced not only a dramatic reduction in acinar cell numbers, but also a significant reduction in β-cell mass. The loss of β-cells is due not to a defect in the differentiation of endocrine precursors, but instead correlates with an early and specific loss of MPCs. In turn, this reflects a novel role for β-catenin in maintaining proximal–distal patterning of the early epithelium, such that distal MPCs resort to a proximal, endocrine-competent “trunk” fate when β-catenin is deleted. Moreover, β-catenin maintains proximal–distal patterning, in part, by inhibiting Notch signaling. Subsequently, β-catenin is required for proliferation of both distal and proximal cells, driving overall organ growth. In distinguishing two distinct roles for β-catenin along the route of β-cell development, we suggest that temporally appropriate positive and negative manipulation of this molecule could enhance expansion and differentiation of stem cell-derived MPCs

Wnt Secretion from Epithelial Cells and Subepithelial Myofibroblasts Is Not Required in the Mouse Intestinal Stem Cell Niche In Vivo

Summary Wnt signaling is a crucial aspect of the intestinal stem cell niche required for crypt cell proliferation and differentiation. Paneth cells or subepithelial myofibroblasts are leading candidate sources of the required Wnt ligands, but this has not been tested in vivo. To abolish Wnt-ligand secretion, we used Porcupine (Porcn) conditional-null mice crossed to strains expressing inducible Cre recombinase in the epithelium, including Paneth cells (Villin-CreERT2); in smooth muscle, including subepithelial myofibroblasts (Myh11-CreERT2); and simultaneously in both compartments. Elimination of Wnt secretion from any of these compartments did not disrupt tissue morphology, cell proliferation, differentiation, or Wnt pathway activity. Thus, Wnt-ligand secretion from these cell populations is dispensable for intestinal homeostasis, revealing that a minor cell type or significant and unexpected redundancy is responsible for physiologic Wnt signaling in vivo

Changing population characteristics, effect-measure modification, and cancer risk factor identification

Epidemiologic studies have identified a number of lifestyle factors, e.g. diet, obesity, and use of certain medications, which affect risk of colon cancer. However, the magnitude and significance of risk factor-disease associations differ among studies. We propose that population trends of changing prevalence of risk factors explains some of the variability between studies when factors that change prevalence also modify the effect of other risk factors. We used data collected from population-based control who were selected as study participants for two time periods, 1991–1994 and 1997–2000, along with data from the literature, to examine changes in the population prevalence of aspirin and non-steroidal anti-inflammatory medication (NSAID) use, obesity, and hormone replacement therapy (HRT) over time. Data from a population-based colon cancer case-control study were used to estimate effect-measurement modification among these factors. Sizeable changes in aspirin use, HRT use, and the proportion of the population that is obese were observed between the 1980s and 2000. Use of NSAIDs interacted with BMI and HRT; HRT use interacted with body mass index (BMI). We estimate that as the prevalence of NSAIDs use changed from 10% to almost 50%, the colon cancer relative risk associated with BMI >30 would change from 1.3 to 1.9 because of the modifying effect of NSAIDs. Similarly, the relative risk estimated for BMI would increase as the prevalence of use of HRT among post-menopausal women increased. In conclusion, as population characteristics change over time, these changes may have an influence on relative risk estimates for colon cancer for other exposures because of effect-measure modification. The impact of population changes on comparability between epidemiologic studies can be kept to a minimum if investigators assess exposure-disease associations within strata of other exposures, and present results in a manner that allows comparisons across studies. Effect-measure modification is an important component of data analysis that should be evaluated to obtain a complete understanding of disease etiology

Structural and functional annotation of the porcine immunome

Background: The domestic pig is known as an excellent model for human immunology and the two species share many pathogens. Susceptibility to infectious disease is one of the major constraints on swine performance, yet the structure and function of genes comprising the pig immunome are not well-characterized. The completion of the pig genome provides the opportunity to annotate the pig immunome, and compare and contrast pig and human immune systems.[br/] Results: The Immune Response Annotation Group (IRAG) used computational curation and manual annotation of the swine genome assembly 10.2 (Sscrofa10.2) to refine the currently available automated annotation of 1,369 immunity-related genes through sequence-based comparison to genes in other species. Within these genes, we annotated 3,472 transcripts. Annotation provided evidence for gene expansions in several immune response families, and identified artiodactyl-specific expansions in the cathelicidin and type 1 Interferon families. We found gene duplications for 18 genes, including 13 immune response genes and five non-immune response genes discovered in the annotation process. Manual annotation provided evidence for many new alternative splice variants and 8 gene duplications. Over 1,100 transcripts without porcine sequence evidence were detected using cross-species annotation. We used a functional approach to discover and accurately annotate porcine immune response genes. A co-expression clustering analysis of transcriptomic data from selected experimental infections or immune stimulations of blood, macrophages or lymph nodes identified a large cluster of genes that exhibited a correlated positive response upon infection across multiple pathogens or immune stimuli. Interestingly, this gene cluster (cluster 4) is enriched for known general human immune response genes, yet contains many un-annotated porcine genes. A phylogenetic analysis of the encoded proteins of cluster 4 genes showed that 15% exhibited an accelerated evolution as compared to 4.1% across the entire genome.[br/] Conclusions: This extensive annotation dramatically extends the genome-based knowledge of the molecular genetics and structure of a major portion of the porcine immunome. Our complementary functional approach using co-expression during immune response has provided new putative immune response annotation for over 500 porcine genes. Our phylogenetic analysis of this core immunome cluster confirms rapid evolutionary change in this set of genes, and that, as in other species, such genes are important components of the pig’s adaptation to pathogen challenge over evolutionary time. These comprehensive and integrated analyses increase the value of the porcine genome sequence and provide important tools for global analyses and data-mining of the porcine immune response

Stem Cells and β Cells: The Same, but Different?

Researchers have long debated whether new pancreatic β cells derive from stem cells or from pre-existing β cells. A new study in this issue of Cell Stem Cell (Smukler et al., 2011) suggests that both sides may be right

Table of Contents

2. The normal pancreas: embryonic development and adult homeostasis...............................2 3. Pancreatic regeneration: re-growth or re-differentiation?..........................................5 4. The exception that proves the rule: pancreatic duct ligation.......................................