Pax4 and Arx Represent Crucial Regulators of the Development of the Endocrine Pancreas

The development of the endocrine pancreas is under the control of highly orchestrated, cross-interacting transcription factors. Pancreas genesis is initiated by the emergence of a Pdx1/Ptf1a marked territory at the foregut/midgut junction. A small fraction of pancreatic fated cells activates the expression of the bHLH transcription factor Ngn3 triggering the endocrine cell program, thus giving rise to beta-, alpha-, delta-, PP-, and epsilon-cells, producing insulin, glucagon, somatostatin, pancreatic polypeptide, and ghrelin, respectively. Two transcription factors, Pax4 and Arx, play a crucial role in differential endocrine cell subtype specification. They were shown to be necessary and sufficient to endow endocrine progenitors with either a beta- or alpha-cell destiny. Interestingly, whereas the forced expression of Arx in beta-cells converts these into cells exhibiting alpha- and PP-cell characteristics, the sole expression of Pax4 in alpha-cells promotes alpha-cell-neogenesis and the acquisition of beta-cell features, the resulting beta-like cells being capable of counteracting chemically induced diabetes. Gaining new insights into the molecular mechanisms controlling Pax4 and Arx expression in the endocrine pancreas may therefore pave new avenues for the therapy of diabetes.

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Present status and expectation of aristaless-related homeobox (ARX) in endocrine pancreas

The International Journal of Developmental Biology ◽

10.1387/ijdb.190242sx ◽

2019 ◽

Vol 63 (11-12) ◽

pp. 579-587 ◽

Cited By ~ 2

Author(s):

Sai Xu ◽

Ji-Ping Xu

Keyword(s):

Transcription Factors ◽

Cell Fate ◽

Endocrine Pancreas ◽

Theoretical Foundation ◽

Alpha Cell ◽

Alpha Cells ◽

Proliferation And Differentiation ◽

Direct Target ◽

Vertebrate Central Nervous System

The aristaless-related homeobox (ARX) gene has become one of most frequently mutated genes which is closely linked with development of the vertebrate central nervous system; however, the molecular and clinical bases of its function in the proliferation and differentiation of the endocrine pancreas have not, to date, been systematically characterized. ARX is considered as a regulator which determines endocrine cell fate and a bio-marker of the pancreatic α-cell. Disruption and mutation of ARX are found to lead to the deletion and reduction of α-cells both in mice models and in humans. Furthermore, expression of ARX is regulated by multiple transcription factors involved in development of the pancreas, such as Ngn3, Isl1, Nkx2.2 and Nkx6.1. Taken together, given the vital importance of glucagon in diabetes treatment, it is possible that ARX may down-regulate exorbitant glucagon levels by reducing the number of α-cells as a direct target; thus, the role of ARX in the maintenance of α-cell identity and quantity should be investigated and summarized. This article mainly focuses on the role of ARX in the endocrine pancreas, introduces the ARX-related animal model and transcription factors, and highlights the latest advances in our understanding in order to provide a clearer theoretical foundation for future scientific research.

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Abstract 20492: Mlf1 Regulates Myocyte Proliferation in Postnatal Hearts

Circulation ◽

10.1161/circ.130.suppl_2.20492 ◽

2014 ◽

Vol 130 (suppl_2) ◽

Author(s):

Shalini Muralidhar ◽

Feng Xiao ◽

Suwannee Thet ◽

Hesham Sadek

Keyword(s):

Cell Cycle ◽

Transcription Factors ◽

Cell Cycle Arrest ◽

Molecular Mechanisms ◽

Gene Array ◽

Bhlh Transcription Factor ◽

Cardiomyocyte Proliferation ◽

Regenerative Capacity ◽

Cycle Arrest ◽

Endogenous Expression

Lower vertebrates, such as newt and zebrafish, retain a robust cardiac regenerative capacity following injury. Although adult mammals lack this cardiac regenerative potential, there is ample interest in understanding how heart regeneration occurs, and to reawaken this process in adult humans. Recently, we showed that mice are capable of regenerating their hearts shortly after birth following injury. This regenerative response is associated with robust proliferation of cardiomyocytes without significant hypertrophy or fibrosis. However, this regenerative capacity is lost by 7 days postnatally, coinciding with cell cycle arrest. In an effort to determine the mechanism of cardiomyocytes cell cycle arrest after the first week of life, we performed a gene array after cardiac injury at multiple post-natal time points. This enabled us to identify a number of transcription factors that are differentially expressed during this postnatal window. We recently reported that one of these transcription factors Meis1 regulates postnatal cell cycle arrest of cardiomyocytes. Furthermore, Myeloid leukemia factor 1 (Mlf1), a bhlh transcription factor that has not been previously studied in the heart has similar dysregulated pattern following injury. Our preliminary data with in-vitro knockdown of Mlf1 in cardiomyocyte resulted in 2-fold increase in cardiomyocyte proliferation. Furthermore, immunohistochemistry results indicated that the endogenous expression and nuclear localization of Mlf1 in the post-natal cardiomyocytes coincides with cell cycle arrest. To explore this pattern, we generated a cardiomyocyte-specific Mlf1 knockout mouse, and showed that loss of Mlf1 results in robust cardiomyocyte proliferation in postnatal hearts (P14). Additionally, we confirmed previous reports that Mlf1 regulates p53 and induces cell cycle arrest by induction of CDK inhibitors like p21 and p57 in these Mlf1 KO mice. This suggests a role of Mlf1 in promoting reactivation of injured myocardium through induction of cardiomyocyte proliferation. These findings will further provide evidences of molecular mechanisms involved in the dormant regenerative capacity in adult mammals that can be a potential target of therapeutic approaches.

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POU domain transcription factor brain 4 confers pancreatic alpha-cell-specific expression of the proglucagon gene through interaction with a novel proximal promoter G1 element.

Molecular and Cellular Biology ◽

10.1128/mcb.17.12.7186 ◽

1997 ◽

Vol 17 (12) ◽

pp. 7186-7194 ◽

Cited By ~ 66

Author(s):

M A Hussain ◽

J Lee ◽

C P Miller ◽

J F Habener

Keyword(s):

Gene Expression ◽

Transcription Factor ◽

Transcription Factors ◽

Alpha Cell ◽

Proximal Promoter ◽

Major Constituent ◽

Alpha Cells ◽

Specific Expression ◽

Pou Domain ◽

Pancreatic Alpha Cell

The proglucagon gene is expressed in a highly restricted tissue-specific manner in the alpha cells of the pancreatic islet, the hypothalamus, and the small and large intestines. Proglucagon is processed to glucagon and glucagon-like peptides GLP-1 and -2. Glucagon is expressed in alpha cells and regulates glucose homeostasis. GLP-1 is implicated in the control of insulin secretion, food intake, and satiety signaling, and GLP-2 is implicated in regulating small-bowel growth. Cell-specific expression of the proglucagon gene is mediated by proteins that interact with the proximal G1 promoter element which contains several AT-rich domains with binding sites for homeodomain transcription factors. In an attempt to identify major homeodomain proteins involved in pancreatic alpha-cell-specific proglucagon expression, we found that the POU domain transcription factor brain 4 is abundantly expressed in proglucagon-producing islet cell lines and rat pancreatic islets. In the latter, brain 4 and glucagon immunoreactivity colocalize in the outer mantle of islets. Electrophoretic mobility shift assays with specific antisera identify brain 4 as a major constituent of nuclear proteins of glucagon-producing cells that bind to the G1 element of the proglucagon gene proximal promoter. Transcriptional transactivation experiments reveal that brain 4 is a major regulator of proglucagon gene expression by its interaction with the G1 element. The finding that a neuronal transcription factor is involved in glucagon gene transcription may explain the presence of proglucagon in certain areas of the brain as well as in pancreatic alpha cells. Further, this finding supports the idea that the neuronal properties of endodermis-derived endocrine pancreatic cells may find their basis in regulation of gene expression by neuronal transcription factors.

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Extensive NEUROG3 occupancy in the human pancreatic endocrine gene regulatory network

10.1101/2021.04.14.439685 ◽

2021 ◽

Author(s):

Valérie Schreiber ◽

Reuben Mercier ◽

Sara Jímenez ◽

Tao Ye ◽

Emmanuel García-Sánchez ◽

...

Keyword(s):

Transcription Factors ◽

Gene Regulatory Network ◽

Beta Cells ◽

Regulatory Network ◽

Islet Cell ◽

Regulatory Elements ◽

Cell Development ◽

Bhlh Transcription Factor ◽

Gene Regulatory ◽

Endocrine Progenitors

Objective: Mice lacking the bHLH transcription factor (TF) Neurog3 do not form pancreatic islet cells, including insulin secreting beta cells, causing diabetes. In human, homozygous mutations of NEUROG3 manifest with neonatal or childhood diabetes. Despite this critical role in islet cell development, the precise function and downstream genetic programs regulated directly by NEUROG3 remain elusive. We therefore mapped genome-wide NEUROG3 occupancy in human induced pluripotent stem cell (iPSC)-derived endocrine progenitors and determined NEUROG3 dependency of associated genes to uncover direct targets. Methods: We generated a novel hiPSC line (NEUROG3-HA-P2A-Venus), where NEUROG3 is HA-tagged and fused to a self-cleaving fluorescent VENUS reporter. We used the CUT&RUN technique to map NEUROG3 occupancy and epigenetic marks in pancreatic endocrine progenitors (PEP) differentiated from this hiPSC line. We integrated NEUROG3 occupancy data with chromatin status and gene expression in PEPs and their NEUROG3-dependence. In addition, we searched whether NEUROG3 binds type 2 diabetes mellitus (T2DM)-associated variants at the PEP stage. Results: CUT&RUN revealed a total of 863 NEUROG3 binding sites assigned to 1268 unique genes. NEUROG3 occupancy was found at promoters as well as at distant cis-regulatory elements frequently overlapping within PEP active enhancers. De novo motif analyses defined a NEUROG3 consensus binding motif and suggested potential co-regulation of NEUROG3 target genes by FOXA, RFX or PBX transcription factors. Moreover, we found that 22% of the genes downregulated in NEUROG3−/− hESC-derived PEPs are bound by NEUROG3 and thus likely to be directly regulated. NEUROG3 targets include transcription factors known to have important roles in islet cell development or function, such as NEUROD1, PAX4, NKX2-2, SOX4, MLXIPL, LMX1B, RFX3, and NEUROG3 itself. Remarkably, we uncovered that NEUROG3 binds transcriptional regulator genes with enriched expression in human fetal pancreatic alpha (e.g., IRX1, IRX2), beta (e.g., NKX6-1, SMAD9, ISX, TFCP2L1) and delta cells (ERBB4) suggesting that NEUROG3 could control islets subtype programs. Moreover, NEUROG3 targets genes critical for insulin secretion in beta cells (e.g., GCK, ABCC8/KCNJ11, CACNA1A, CHGA, SCG2, SLC30A8 and PCSK1). In addition, we unveiled a panel of ncRNA potentially regulated by NEUROG3. Lastly, we identified several T2DM risk SNPs within NEUROG3 peaks suggesting a possible developmental role of NEUROG3 in T2DM susceptibility. Conclusion: Mapping of NEUROG3 genome occupancy in PEPs uncovers an unexpectedly broad, direct control of the endocrine gene regulatory network (GRN) and raises novel hypotheses on how this master regulator controls islet and beta cell differentiation.

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Alpha cell regulation of beta cell function

Diabetologia ◽

10.1007/s00125-020-05196-3 ◽

2020 ◽

Vol 63 (10) ◽

pp. 2064-2075

Author(s):

Tilo Moede ◽

Ingo B. Leibiger ◽

Per-Olof Berggren

Keyword(s):

Blood Glucose ◽

Beta Cell ◽

Beta Cells ◽

Endocrine Cell ◽

Beta Cell Function ◽

Cell Function ◽

Cell Types ◽

Alpha Cell ◽

Alpha Cells

Abstract The islet of Langerhans is a complex endocrine micro-organ consisting of a multitude of endocrine and non-endocrine cell types. The two most abundant and prominent endocrine cell types, the beta and the alpha cells, are essential for the maintenance of blood glucose homeostasis. While the beta cell produces insulin, the only blood glucose-lowering hormone of the body, the alpha cell releases glucagon, which elevates blood glucose. Under physiological conditions, these two cell types affect each other in a paracrine manner. While the release products of the beta cell inhibit alpha cell function, the alpha cell releases factors that are stimulatory for beta cell function and increase glucose-stimulated insulin secretion. The aim of this review is to provide a comprehensive overview of recent research into the regulation of beta cell function by alpha cells, focusing on the effect of alpha cell-secreted factors, such as glucagon and acetylcholine. The consequences of differences in islet architecture between species on the interplay between alpha and beta cells is also discussed. Finally, we give a perspective on the possibility of using an in vivo imaging approach to study the interactions between human alpha and beta cells under in vivo conditions.

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Transcriptomic Analysis of Short-Term Salt-Stress Response in Mega Hybrid Rice Seedlings

Agronomy ◽

10.3390/agronomy11071328 ◽

2021 ◽

Vol 11 (7) ◽

pp. 1328

Author(s):

Noushin Jahan ◽

Yang Lv ◽

Mengqiu Song ◽

Yu Zhang ◽

Liangguang Shang ◽

...

Keyword(s):

Salt Stress ◽

Molecular Mechanisms ◽

Oryza Sativa L ◽

Transcriptome Profiling ◽

Bhlh Transcription Factor ◽

F1 Hybrid ◽

Salt Stress Response ◽

Productivity Losses ◽

Expression Of Genes ◽

Trait Locus

Salinity is a major abiotic stressor that leads to productivity losses in rice (Oryza sativa L.). In this study, transcriptome profiling and heterosis-related genes were analyzed by ribonucleic acid sequencing (RNA-Seq) in seedlings of a mega rice hybrid, Liang-You-Pei-Jiu (LYP9), and its two parents 93–11 and Pei-ai64s (PA64s), under control and two different salinity levels, where we found 8292, 8037, and 631 salt-induced differentially expressed genes (DEGs), respectively. Heterosis-related DEGs were obtained higher after 14 days of salt treatment than after 7 days. There were 631 and 4237 salt-induced DEGs related to heterosis under 7-day and 14-day salt stresses, respectively. Gene functional classification showed the expression of genes involved in photosynthesis activity after 7-day stress treatment, and in metabolic and catabolic activity after 14 days. In addition, we correlated the concurrence of an expression of DEGs for the bHLH transcription factor and a shoot length/salinity-related quantitative trait locus qSL7 that we fine-mapped previously, providing a confirmed case of heterosis-related genes. This experiment reveals the transcriptomic divergence of the rice F1 hybrid and its parental lines under control and salt stress state, and enlightens about the significant molecular mechanisms developed over time in response to salt stress.

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High Energy Intake Induced Overexpression of Transcription Factors and Its Regulatory Genes Involved in Acceleration of Hepatic Lipogenesis: A Rat Model for Type 2 Diabetes

Biomedicines ◽

10.3390/biomedicines7040076 ◽

2019 ◽

Vol 7 (4) ◽

pp. 76 ◽

Cited By ~ 3

Author(s):

Suresh P. Khadke ◽

Aniket A. Kuvalekar ◽

Abhay M. Harsulkar ◽

Nitin Mantri

Keyword(s):

Type 2 Diabetes ◽

Transcription Factors ◽

Glucose Tolerance ◽

Molecular Mechanisms ◽

Target Genes ◽

High Energy ◽

Tolerance Test ◽

Diabetic Control ◽

Ppar Γ

Type 2 diabetes mellitus (T2DM) is a metabolic disorder characterized by impaired insulin action and its secretion. The objectives of the present study were to establish an economical and efficient animal model, mimicking pathophysiology of human T2DM to understand probable molecular mechanisms in context with lipid metabolism. In the present study, male Wistar rats were randomly divided into three groups. Animals were fed with high fat diet (HFD) except healthy control (HC) for 12 weeks. After eight weeks, intra peritoneal glucose tolerance test was performed. After confirmation of glucose intolerance, diabetic control (DC) group was injected with streptozotocin (STZ) (35 mg/kg b.w., i.p.). HFD fed rats showed increase (p ≤ 0.001) in glucose tolerance and HOMA-IR as compared to HC. Diabetes rats showed abnormal (p ≤ 0.001) lipid profile as compared to HC. The hepatocyte expression of transcription factors SREBP-1c and NFκβ, and their target genes were found to be upregulated, while PPAR-γ, CPT1A and FABP expressions were downregulated as compared to the HC. A number of animal models have been raised for studying T2DM, but the study has been restricted to only the biochemical level. The model is validated at biochemical, molecular and histopathological levels, which can be used for screening new therapeutics for the effective management of T2DM.

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