Inhibition of TGF-β Signaling Promotes Human Pancreatic β-Cell Replication.

Diabetes is associated with loss of functional pancreatic β-cells, and restoration of β-cells is a major goal for regenerative therapies. Endogenous regeneration of β-cells via β-cell replication has the potential to restore cellular mass; however, pharmacological agents that promote regeneration or expansion of endogenous β-cells have been elusive. The regenerative capacity of β-cells declines rapidly with age, due to accumulation of p16(INK4a), resulting in limited capacity for adult endocrine pancreas regeneration. Here, we show that transforming growth factor-β (TGF-β) signaling via Smad3 integrates with the trithorax complex to activate and maintain Ink4a expression to prevent β-cell replication. Importantly, inhibition of TGF-β signaling can result in repression of the Ink4a/Arf locus, resulting in increased β-cell replication in adult mice. Furthermore, small molecule inhibitors of the TGF-β pathway promote β-cell replication in human islets transplanted into NOD-scid IL-2Rg(null) mice. These data reveal a novel role for TGF-β signaling in the regulation of the Ink4a/Arf locus and highlight the potential of using small molecule inhibitors of TGF-β signaling to promote human β-cell replication

Age-dependent decline in beta-cell proliferation restricts the capacity of beta-cell regeneration in mice.

ObjectiveThe aim of this study was to elucidate whether age plays a role in the expansion or regeneration of beta-cell mass.Research design and methodsWe analyzed the capacity of beta-cell expansion in 1.5- and 8-month-old mice in response to a high-fat diet, after short-term treatment with the glucagon-like peptide 1 (GLP-1) analog exendin-4, or after streptozotocin (STZ) administration.ResultsYoung mice responded to high-fat diet by increasing beta-cell mass and beta-cell proliferation and maintaining normoglycemia. Old mice, by contrast, did not display any increases in beta-cell mass or beta-cell proliferation in response to high-fat diet and became diabetic. To further assess the plasticity of beta-cell mass with respect to age, young and old mice were injected with a single dose of STZ, and beta-cell proliferation was analyzed to assess the regeneration of beta-cells. We observed a fourfold increase in beta-cell proliferation in young mice after STZ administration, whereas no changes in beta-cell proliferation were observed in older mice. The capacity to expand beta-cell mass in response to short-term treatment with the GLP-1 analog exendin-4 also declined with age. The ability of beta-cell mass to expand was correlated with higher levels of Bmi1, a polycomb group protein that is known to regulate the Ink4a locus, and decreased levels of p16(Ink4a)expression in the beta-cells. Young Bmi1(-/-) mice that prematurely upregulate p16(Ink4a)failed to expand beta-cell mass in response to exendin-4, indicating that p16(Ink4a)levels are a critical determinant of beta-cell mass expansion.Conclusionsbeta-Cell proliferation and the capacity of beta-cells to regenerate declines with age and is regulated by the Bmi1/p16(Ink4a)pathway

Cyclin D2 is sufficient to drive β cell self-renewal and regeneration

Diabetes results from an inadequate mass of functional β cells, due to either β cell loss caused by autoimmune destruction (type I diabetes) or β cell failure in response to insulin resistance (type II diabetes). Elucidating the mechanisms that regulate β cell mass may be key to developing new techniques that foster β cell regeneration as a cellular therapy to treat diabetes. While previous studies concluded that cyclin D2 is required for postnatal β cell self-renewal in mice, it is not clear if cyclin D2 is sufficient to drive β cell self-renewal. Using transgenic mice that overexpress cyclin D2 specifically in β cells, we show that cyclin D2 overexpression increases β cell self-renewal post-weaning and results in increased β cell mass. β cells that overexpress cyclin D2 are responsive to glucose stimulation, suggesting they are functionally mature. β cells that overexpress cyclin D2 demonstrate an enhanced regenerative capacity after injury induced by streptozotocin toxicity. To understand if cyclin D2 overexpression is sufficient to drive β cell self-renewal, we generated a novel mouse model where cyclin D2 is only expressed in β cells of cyclin D2−/− mice. Transgenic overexpression of cyclin D2 in cyclin D2−/− β cells was sufficient to restore β cell mass, maintain normoglycaemia, and improve regenerative capacity when compared with cyclin D2−/− littermates. Taken together, our results indicate that cyclin D2 is sufficient to regulate β cell self-renewal and that manipulation of its expression could be used to enhance β cell regeneration

Characterization of Non-hormone Expressing Endocrine Cells in Fetal and Infant Human Pancreas

Context: Previously, we identified chromograninA positive hormone-negative (CPHN) cells in high frequency in human fetal and neonatal pancreas, likely representing nascent endocrine precursor cells. Here, we characterize the putative endocrine fate and replicative status of these newly formed cells.Objective: To establish the replicative frequency and transcriptional identity of CPHN cells, extending our observation on CPHN cell frequency to a larger cohort of fetal and infant pancreas.Design, Setting, and Participants: 8 fetal, 19 infant autopsy pancreata were evaluated for CPHN cell frequency; 12 fetal, 24 infant/child pancreata were evaluated for CPHN replication and identity.Results: CPHN cell frequency decreased 84% (islets) and 42% (clusters) from fetal to infant life. Unlike the beta-cells at this stage, CPHN cells were rarely observed to replicate (0.2 ± 0.1 vs. 4.7 ± 1.0%, CPHN vs. islet hormone positive cell replication, p < 0.001), indicated by the lack of Ki67 expression in CPHN cells whether located in the islets or in small clusters, and with no detectable difference between fetal and infant groups. While the majority of CPHN cells express (in overall compartments of pancreas) the pan-endocrine transcription factor NKX2.2 and beta-cell specific NKX6.1 in comparable frequency in fetal and infant/child cases (81.9 ± 6.3 vs. 82.8 ± 3.8% NKX6.1+-CPHN cells of total CPHN cells, fetal vs. infant/child, p = 0.9; 88.0 ± 4.7 vs. 82.1 ± 5.3% NKX2.2+-CPHN cells of total CPHN cells, fetal vs. infant/child, p = 0.4), the frequency of clustered CPHN cells expressing NKX6.1 or NKX2.2 is lower in infant/child vs. fetal cases (1.2 ± 0.3 vs. 16.7 ± 4.7 clustered NKX6.1+-CPHN cells/mm2, infant/child vs. fetal, p < 0.01; 2.7 ± 1.0 vs. 16.0 ± 4.0 clustered NKX2.2+-CPHN cells/mm2, infant/child vs. fetal, p < 0.01).Conclusions: The frequency of CPHN cells declines steeply from fetal to infant life, presumably as they differentiate to hormone-expressing cells. CPHN cells represent a non-replicative pool of endocrine precursor cells, a proportion of which are likely fated to become beta-cells.Precis: CPHN cell frequency declines steeply from fetal to infant life, as they mature to hormone expression. CPHN cells represent a non-replicative pool of endocrine precursor cells, a proportion of which are likely fated to become beta-cells

Molecular cloning and expression pattern of a Cubitus interruptus homologue from the mulberry silkworm Bombyx mori

A homologue of the segment polarity gene Cubitus interruptus from Bombyx Mori, (BmCi) has been cloned and characterized. This region harbouring Zn2+ finger motif is highly conserved across species. In B. Mori, BmCi RNA expression was first detected at stage 6 of embryogenesis, which reached maximum levels at stage 21C and was maintained until larval hatching. The segmentally reiterated striped pattern of transcript distribution in stage 21C embryos was in conformity with its predicted segment polarity nature. BmCi was expressed in the fore- and hind-wing discs, ovaries, testes and gut during fifth larval intermolt, reminiscent of its expression domains in Drosophila. Besides, BmCi expression was seen in the. anterior part of the middle silkglands in late embryonic stages, and this pattern was maintained during larval development. The transition from third to fourth and fifth larval intermolts was accompanied by an increase in the transcript levels in the middle silkglands. Our results demonstrate the presence of a novel expression domain for Ci in Bombyx. (C) 2002 Elsevier Science Ireland Ltd. All rights reserved

Phylogeny of the Insect Homeobox Gene (Hox) Cluster

The homeobox (Hox) genes form an evolutionarily conserved family encoding transcription factors that play major roles in segmental identity and organ specification across species. The canonical grouping of Hox genes present in the HOM-C cluster of Drosophila or related clusters in other organisms includes eight "typical" genes, which are localized in the order labial (lab), proboscipedia (pb), Deformed (Dfd), Sex combs reduced (Scr), Antennapedia (Antp), Ultrabithorax (Ubx), abdominalA (abdA), and AbdominalB (AbdB). The members of Hox cluster are expressed in a distinct anterior to posterior order in the embryo. Analysis of the relatedness of different members of the Hox gene cluster to each other in four evolutionarily diverse insect taxa revealed that the loci pb/Dfd and AbdB, which are farthest apart in linkage, had a high degree of evolutionary relatedness, indicating that pb/Dfd type anterior genes and AbdB are closest to the ancestral anterior and posterior Hox genes, respectively. The greater relatedness of other posterior genes Ubx and abdA to the more anterior genes such as Antp and Scr suggested that they arose by gene duplications in the more anterior members rather than the posterior AbdB

Molecular cloning and expression pattern of an armadillo homologue from the mulberry silkworm Bombyx mori

Armadillo/β-catenin, encoded by the segment polarity gene armadillo functions as a downstream effector of canonical Wnt signals. The expression patterns of Bm wnt-1, -Ci and -engrailed, suggested the presence of Wnt-1 network in the middle silkglands of Bombyx mori. To test this, a homologue of armadillo from B. mori (Bm arm) was cloned by PCR using degenerate primers, designed based on the conserved regions of the protein, and characterized. The cloned region harboured one complete and two incomplete Armadillo (Arm) repeat motifs and was highly conserved across species. Genomic Southern analysis suggested Bm arm to be a multi-copy gene. The expression of Bm arm RNA was first detected at stage 6 of embryogenesis, which reached maximum levels at stage 21C and was maintained until larval hatching. The RNA was expressed uniformly in the embryos, whereas the Arm protein was localized in a segmentally reiterated striped pattern, in conformity with its predicted segment polarity nature. Bm arm was also expressed in the entire silkgland and the transition from third to fourth and fifth larval intermoults was accompanied by an increase in the transcript levels. However, the Arm protein was predominantly localized to the middle silkglands, especially the middle and posterior sub-compartments. The silkglands represented a novel expression domain for arm in Bombyx, and the results were consistent with the existence of a canonical Wnt network in the middle silkglands

Cell cycle events during the development of the silk glands in the mulberry silkworm Bombyx mori

Silk glands of the mulberry silkworm Bombyx mori are long and paired structures originating from the labial region and are anatomically and physiologically divided into three major compartments, the anterior, middle and posterior silk glands. The silk gland morphogenesis is complete by 8 days post egg laying. Extensive growth of silk glands during the larval stages is due to increase in tissue mass and not cell number. The cells in a completely formed silk gland pursue an endoreplicative cell cycle, and the genome undergoes multiple rounds of replication without mitosis or nuclear division. The expression patterns of cyclin B (mitotic cyclin) and cyclin E (G1 cyclin, essential for G1/S transition in both mitotic and endoreplicative cell cycles) in the course of silk gland development revealed that mitotic cell divisions take place only in the apex of the growing silk gland. However, the persistence of another mitotic focus in the middle silk gland even when the growing apex has moved well past this zone suggested the continued operation of mitosis for a while in this restricted region. The lack of cyclin B expression and abundance of cyclin E in the rest of the areas confirmed an alternation of the G1 and S phases of the cell cycle without an intervening mitotic phase. No expression of cyclin B was noticed anywhere in the silk glands after stage 25 of embryogenesis, indicating a complete switch over to the endomitotic mode of the cell cycle. The onset of expression of various genes encoding different silk proteins correlated with the onset of endomitotic events