Akihisa Fukuda

Ptf1a, a bHLH transcriptional gene, defines GABAergic neuronal fates in cerebellum

The molecular machinery governing glutamatergic-GABAergic neuronal subtype specification is unclear. Here we describe a cerebellar mutant, cerebelless, which lacks the entire cerebellar cortex in adults. The primary defect of the mutant brains was a specific inhibition of GABAergic neuron production from the cerebellar ventricular zone (VZ), resulting in secondary and complete loss of external germinal layer, pontine, and olivary nuclei during development. We identified the responsible gene, Ptf1a, whose expression was lost in the cerebellar VZ but was maintained in the pancreas in cerebelless. Lineage tracing revealed that two types of neural precursors exist in the cerebellar VZ: Ptf1a-expressing and -nonexpressing precursors, which generate GABAergic and glutamatergic neurons, respectively. Introduction of Ptf1a into glutamatergic neuron precursors in the dorsal telencephalon generated GABAergic neurons with representative morphological and migratory features. Our results suggest that Ptf1a is involved in driving neural precursors to differentiate into GABAergic neurons in the cerebellum.

Stat3 and MMP7 Contribute to Pancreatic Ductal Adenocarcinoma Initiation and Progression

Chronic pancreatitis is a well-known risk factor for pancreatic ductal adenocarcinoma (PDA) development in humans, and inflammation promotes PDA initiation and progression in mouse models of the disease. However, the mechanistic link between inflammatory damage and PDA initiation is unclear. Using a Kras-driven mouse model of PDA, we establish that the inflammatory mediator Stat3 is a critical component of spontaneous and pancreatitis-accelerated PDA precursor formation and supports cell proliferation, metaplasia-associated inflammation, and MMP7 expression during neoplastic development. Furthermore, we show that Stat3 signaling enforces MMP7 expression in PDA cells and that MMP7 deletion limits tumor size and metastasis in mice. Finally, we demonstrate that serum MMP7 level in human patients with PDA correlated with metastatic disease and survival.

Ectopic pancreas formation in Hes1 -knockout mice reveals plasticity of endodermal progenitors of the gut, bile duct, and pancreas

Ectopic pancreas is a developmental anomaly occasionally found in humans. Hes1, a main effector of Notch signaling, regulates the fate and differentiation of many cell types during development. To gain insights into the role of the Notch pathway in pancreatic fate determination, we combined the use of Hes1-knockout mice and lineage tracing employing the Cre/loxP system to specifically mark pancreatic precursor cells and their progeny in Ptf1a-cre and Rosa26 reporter mice. We show that inactivation of Hes1 induces misexpression of Ptf1a in discrete regions of the primitive stomach and duodenum and throughout the common bile duct. All ectopic Ptf1a-expressing cells were reprogrammed, or transcommitted, to multipotent pancreatic progenitor status and subsequently differentiated into mature pancreatic exocrine, endocrine, and duct cells. This process recapitulated normal pancreatogenesis in terms of morphological and genetic features. Furthermore, analysis of Hes1/Ptf1a double mutants revealed that ectopic Ptf1a-cre lineage-labeled cells adopted the fate of region-appropriate gut epithelium or endocrine cells similarly to Ptf1a-inactivated cells in the native pancreatic buds. Our data demonstrate that the Hes1-mediated Notch pathway is required for region-appropriate specification of pancreas in the developing foregut endoderm through regulation of Ptf1a expression, providing novel insight into the pathogenesis of ectopic pancreas development in a mouse model.

Growth arrest‐specific gene 6 and Axl signaling enhances gastric cancer cell survival via Akt pathway

Activation of tyrosine kinases is an important factor during cancer development. Axl, one of the receptor tyrosine kinases, binds to the specific ligand growth arrest‐specific gene 6 (Gas6), which encodes a vitamin K‐dependent γ‐carboxyglutamyl protein. Although many receptor tyrosine kinases and their ligands are involved in gastric carcinogenesis, whether Gas6‐Axl signaling is involved in gastric carcinogenesis has not been elucidated. The aim of this study was to investigate the expression of Gas6 and Axl in gastric cancer and also their roles during gastric carcinogenesis. mRNA and protein of Gas6 and Axl were highly expressed in a substantial proportion of human gastric cancer tissue and cell lines, and Gas6 expression was significantly associated with lymph node metastasis. With recombinant Gas6 and a decoy‐receptor of Axl in vitro, we demonstrated that Gas6‐Axl signaling pathway enhanced cellular survival and invasion and suppressed apoptosis via Akt pathway. Our results suggests that Gas6‐Axl signaling plays a role during gastric carcinogenesis, and that targeting Gas6‐Axl signaling could be a novel therapeutic for gastric cancer.

The chromatin regulator Brg1 suppresses formation of intraductal papillary mucinous neoplasm and pancreatic ductal adenocarcinoma

Pancreatic ductal adenocarcinoma (PDA) develops through distinct precursor lesions, including pancreatic intraepithelial neoplasia (PanIN) and intraductal papillary mucinous neoplasia (IPMN). However, genetic features resulting in IPMN-associated PDA (IPMN–PDA) versus PanIN-associated PDA (PanIN-PDA) are largely unknown. Here we find that loss of Brg1, a core subunit of SWI/SNF chromatin remodelling complexes, cooperates with oncogenic Kras to form cystic neoplastic lesions that resemble human IPMN and progress to PDA. Although Brg1-null IPMN–PDA develops rapidly, it possesses a distinct transcriptional profile compared with PanIN-PDA driven by mutant Kras and hemizygous p53 deletion. IPMN–PDA also is less lethal, mirroring prognostic trends in PDA patients. In addition, Brg1 deletion inhibits Kras-dependent PanIN development from adult acinar cells, but promotes Kras-driven preneoplastic transformation in adult duct cells. Therefore, this study implicates Brg1 as a determinant of context-dependent Kras-driven pancreatic tumorigenesis and suggests that chromatin remodelling may underlie the development of distinct PDA subsets.

Reduction of Ptf1a Gene Dosage Causes Pancreatic Hypoplasia and Diabetes in Mice

OBJECTIVE—Most pancreatic endocrine cells derive from Ptf1a-expressing progenitor cells. In humans, nonsense mutations in Ptf1a have recently been identified as a cause of permanent neonatal diabetes associated with pancreatic agenesis. The death of Ptf1a-null mice soon after birth has not allowed further insight into the pathogenesis of the disease; it is therefore unclear how much pancreatic endocrine function is dependent on Ptf1a in mammals. This study aims to investigate gene-dosage effects of Ptf1a on pancreas development and function in mice. RESEARCH DESIGN AND METHODS—Combining hypomorphic and null alleles of Ptf1a and Cre-mediated lineage tracing, we followed the cell fate of reduced Ptf1a-expressing progenitors and analyzed pancreas development and function in mice. RESULTS—Reduced Ptf1a dosage resulted in pancreatic hypoplasia and glucose intolerance with insufficient insulin secretion in a dosage-dependent manner. In hypomorphic mutant mice, pancreatic bud size was small and substantial proportions of pancreatic progenitors were misspecified to the common bile duct and duodenal cells. Growth with branching morphogenesis and subsequent exocrine cytodifferentiation was reduced and delayed. Total β-cell number was decreased, proportion of non-β islet cells was increased, and α-cells were abnormally intermingled with β-cells. Interestingly, Pdx1 expression was decreased in early pancreatic progenitors but elevated to normal level at the mid-to-late stages of pancreatogenesis. CONCLUSIONS—The dosage of Ptf1a is crucial for pancreas specification, growth, total β-cell number, islet morphogenesis, and endocrine function. Some neonatal diabetes may be caused by mutation or single nucleotide polymorphisms in the Ptf1a gene that reduce gene expression levels.

Rbp‐j regulates expansion of pancreatic epithelial cells and their differentiation into exocrine cells during mouse development

Notch signaling regulates cell fate determination in various tissues. We have reported the generation of mice with a pancreas‐specific knockout of Rbp‐j using Pdx.cre mice. Those mice exhibited premature endocrine and ductal differentiation. We now generated mice in which the Rbp‐j gene was inactivated in Ptf1a‐expressing cells using Ptf1a.cre mice. The timing of the Cre‐mediated deletion in Rbp‐jf/f Ptf1a.cre mice is 1 day later than that in Rbp‐jf/f Pdx.cre mice. In Rbp‐jf/f Ptf1a.cre mouse pancreases, at E13.5, the reduced Hes1 expression was accompanied by reduced epithelial growth, but premature endocrine cell differentiation was minimal. At E15.5, Pdx1 expression was repressed and acinar cell differentiation was reduced, but an increase in acinar cell proliferation was observed during the perinatal period. Our study indicates that, in addition to its role in preventing premature differentiation of early endocrine cells, Rbp‐j regulates epithelial growth, Pdx1 expression, and acinar cell differentiation during mid‐pancreatic development. Developmental Dynamics 236:2779–2791, 2007.

Bmi1 Is Required for Regeneration of the Exocrine Pancreas in Mice

BACKGROUND & AIMS Bmi1 is a member of the Polycomb protein family and represses transcription by modifying chromatin organization at specific promoters. Bmi1 is implicated in the control of stem cell self-renewal and has been shown to regulate cell proliferation, tissue homeostasis, and differentiation. Bmi1 is present in a subpopulation of self-renewing pancreatic acinar cells and is expressed in response to pancreatic damage. We investigated the role of Bmi1 in regeneration of exocrine pancreas. METHODS Acute pancreatitis was induced in Bmi1(-/-) mice with cerulein; pancreatic cell regeneration, differentiation, and apoptosis were assessed. Cultured Bmi1(-/-) and wild-type primary acini were analyzed in vitro to determine acinar-specific consequences of Bmi1 deletion. To investigate cell autonomous versus non-cell autonomous roles for Bmi1 in vivo, pancreatitis was induced in Bmi1(-/-) mice reconstituted with a wild-type hematopoietic system. RESULTS Bmi1 expression was up-regulated in the exocrine pancreas during regeneration after cerulein-induced pancreatitis. Exocrine regeneration was impaired following administration of cerulein to Bmi1(-/-) mice. Pancreata of Bmi1(-/-) mice were hypoplastic, and the exocrine pancreas was replaced with ductal metaplasia that had increased apoptosis and decreased cell proliferation compared with that of wild-type mice. Expression of Cdkn2a and p53-dependent apoptotic genes was markedly up-regulated in Bmi1(-/-) pancreas compared with wild-type mice after injury. Furthermore, after transplantation of bone marrow from wild-type to Bmi1(-/-) mice, the chimeric mice had intermediate levels of pancreatic hypoplasia and significant but incomplete rescue of impaired exocrine regeneration after cerulein injury. CONCLUSIONS Bmi1 contributes to regeneration of the exocrine pancreas after cerulein-induced injury through cell autonomous mechanisms, in part by regulating Cdkn2a expression, and non-cell autonomous mechanisms.

Retroflexed endoscopic multiple band ligation of symptomatic internal hemorrhoids

Abstract Background Elastic band ligation is a well-established nonoperative method for treatment of internal hemorrhoids that give rise to symptoms. This study assessed the efficacy and safety of retroflexed endoscopic multiple band ligation, a procedure that involves extensive ligation of internal hemorrhoids, and the immediately proximal normal rectal mucosa, by means of a retroflexed endoscope. Methods Eighty-two patients with symptoms caused by internal hemorrhoids (15, stage I; 19, stage II; 47, stage III; 1, stage IV) were treated by retroflexed endoscopic multiple band ligation. Symptoms (prolapse, bleeding, pain with defecation) were graded from 0 to 3. Range and form of the internal hemorrhoids were evaluated endoscopically. Retroflexed endoscopic multiple band ligation was performed by using a flexible endoscope with an attached band ligation device in the retroflexed position. Results A mean of 8 bands (range 4-14) were placed per treatment session. Seventy-six patients were treated in a single session, 5 in two sessions, and one in 3 sessions. Symptom and endoscopic scores improved at 4 weeks after the retroflexed endoscopic multiple band ligation: bleeding, from 1.26 to 0.53 ( p p p =0.67); Goligher classification, from 2.41 to 1.09 ( p p p Conclusions Retroflexed endoscopic multiple band ligation is a safe and effective method for treatment for patients with symptoms caused by internal hemorrhoids.

Colonoscopic classification of internal hemorrhoids: usefulness in endoscopic band ligation.

Background:  Bleeding is one of the main symptoms of internal hemorrhoids. However, the conventional Golighers classification of internal hemorrhoids does not consider the severity of bleeding. We intended to establish a useful method for evaluating internal hemorrhoids using a colonoscope that reflected the severity of the symptoms.