Common single-base insertions in the VNTR of the carboxyl ester lipase (CEL) gene are benign and also likely to arise somatically in the exocrine pancreas.

The CEL gene encodes carboxyl ester lipase, a pancreatic digestive enzyme. CEL is extremely polymorphic due to a variable number tandem repeat (VNTR) located in the last exon. Single-base deletions within this VNTR cause the inherited disorder MODY8, whereas little is known about VNTR single-base insertions in pancreatic disease. We therefore mapped CEL insertion variants (CEL-INS) in 200 Norwegian patients with pancreatic neoplastic disorders. Twenty-eight samples (14.0%) carried CEL-INS alleles. Most common were insertions in repeat 9 (9.5%), which always associated with a VNTR length of 13 repeats. The combined INS allele frequency (0.078) was similar to that observed in a control material of 416 subjects (0.075). We performed functional testing in HEK293T cells of a set of CEL-INS variants, in which the insertion site varied from the first to the 12th VNTR repeat. Lipase activity showed little difference among the variants. However, CEL-INS variants with insertions occurring in the most proximal repeats led to protein aggregation and endoplasmic reticulum stress, which upregulated the unfolded protein response. Moreover, by using a CEL-INS-specific antibody, we observed patchy signals in pancreatic tissue from humans without any CEL-INS variant in the germline. Similar pancreatic staining was seen in knock-in mice expressing the most common human CEL VNTR with 16 repeats. CEL-INS proteins may therefore be constantly produced from somatic events in the normal pancreatic parenchyma. This observation along with the high population frequency of CEL-INS alleles strongly suggests that these variants are benign, with a possible exception for insertions in VNTR repeats 1-4.

Exocrine pancreas proteases regulate ß-cell proliferation in zebrafish ciliopathy models and in murine systems.

Pancreatic ß-cells are a critical cell type in the pathology of diabetes. Models of genetic syndromes featuring diabetes can provide novel mechanistic insights into regulation of ß-cells in the context of disease. We previously examined ß-cell mass in models of two ciliopathies, Alström Syndrome (AS) and Bardet-Biedl Syndrome (BBS), which are similar in the presence of metabolic phenotypes, including obesity, but exhibit strikingly different rates of diabetes. Zebrafish models of these disorders show deficient ß-cells with diabetes in AS models and an increased ß-cells absent diabetes in BBS models, indicating ß-cell generation or maintenance that correlates with disease prevalence. Using transcriptome analyses, differential expression of several exocrine pancreas proteases with directionality that was consistent with ß-cell numbers were identified. Based on these lines of evidence, we hypothesized that pancreatic proteases directly impact ß-cells. In the present study, we examined this possibility and found that pancreatic protease genes contribute to proper maintenance of normal ß-cell numbers, proliferation in larval zebrafish, and regulation of AS and BBS ß-cell phenotypes. Our data suggest that these proteins can be taken up directly by cultured ß-cells and ex vivo murine islets, inducing proliferation in both. Endogenous uptake of pancreatic proteases by ß-cells was confirmed in vivo using transgenic zebrafish and in intact murine pancreata. Taken together, these findings support a novel proliferative signaling role for exocrine pancreas proteases through interaction with endocrine ß-cells.

MiR-204-5p Performs a Protective Effect on Cerulein-Induced Rat Pancreatic Acinar Cell AR42J Cell Damage by Targeting Tyrosine 3-Monooxygenase/Tryptophan 5-Monooxygenase Activation Protein Gamma and Regulating PI3K/Hippo Pathways.

OBJECTIVE: This research plans to address the function of miR-204-5p/tyrosine 3-monooxygenase/tryptophan 5-monooxygenase activation protein gamma (YWHAG) in cerulein-induced acute pancreatitis (AP). METHODS: Rat pancreatic acinar cell AR42J was stimulated by 100 nmol/L of cerulein to mimic the situation in AP. Gene Expression Omnibus database was used to select differentially expressed genes. StarBase database and Kyoto Encyclopedia of Genes and Genomes enrichment analysis were used to select the target genes of miR-204-5p, which were further affirmed by dual luciferase assay. The biological behaviors of AR42J cells were measured by cell proliferation and flow cytometry assays. Quantitative real-time polymerase chain reaction and western blot assays were executed to assess YWHAG expression. The secretion of C-C Motif Chemokine Ligand 2/Timp metallopeptidase inhibitor 1 in AR42J cells was evaluated by enzyme-linked immunosorbent assay. The protein expression of YAP1/p-YAP1/PI3K/p-PI3K was measured by western blot. RESULTS: miR-204-5p expression was profoundly reduced in cerulein-induced AP model. YWHAG was upregulated in cerulein-induced AP model and related to C-C Motif Chemokine Ligand 2/Timp1. In addition to the negative association between miR-204-5p and YWHAG, the alleviation impact of miR-204-5p mimic on cerulein-induced AR42J cell damage was blocked by YWHAG overexpression and PI3K/Hippo signaling pathways activation. CONCLUSIONS: These observations indicated that the alleviation impact of miR-204-5p on cerulein-induced AR42J cell damage was mediated via YWHAG and PI3K/Hippo signaling pathways.

Gut microbiome as a response marker for pancreatic enzyme replacement therapy in a porcine model of exocrine pancreas insufficiency.

BACKGROUND: Exocrine pancreatic insufficiency (EPI) is characterized by the loss of active pancreatic enzymes and a resulting severely reduced food digestion. EPI therapy requires orally applied pancreatic enzyme replacement. The gut microbiome is a known mediator of intestinal diseases and may influence the outcome of EPI and the effects of a pancreatic enzyme replacement therapy (PERT). Here, we analyzed the effects of EPI and PERT on the gut microbiome in the model of pancreatic duct ligated minipigs. RESULTS: The microbial community composition in pig feces was analyzed by next generation sequencing of 16S rRNA amplicons. The data were evaluated for α- and ß-diversity changes and changes at the different Operational Taxonomic Unit (OTU) levels by Shannon-Wiener and inverse Simpson index calculation as well as by Principal Coordinates Analysis based on Bray-Curtis dissimilarity. Microbial α-diversity was reduced after EPI induction and reverted to nearly healthy state after PERT. Analysis of microbial composition and ß-diversity showed distinctive clusters of the three study groups and a change towards a composition comparable to healthy animals upon PERT. The relative abundance of possible pathobionts like Escherichia/Shigella, Acinetobacter or Stenotrophomonas was reduced by PERT. CONCLUSION: These data demonstrate that EPI-induced dysbiosis could be reverted by PERT to a nearly healthy state. Elevated α-diversity and the reduction of bacterial overgrowth after PERT promises benefits for EPI patients. Non-invasive microbiome studies may be useful for EPI therapy monitoring and as marker for response to PERT.

Involvement of the exocrine pancreas during COVID-19 infection and possible pathogenetic hypothesis: a concise review.

The gastrointestinal system may be affected by COVID-19 infection with an incidence variable from 3% up to 79%. Several works show that the pancreas, both in its exocrine and endocrine function, can be affected by this viral infection, although this organ has been poorly analyzed in this current epidemic context. This mini-review aims to provide a summary of available studies on exocrine pancreas involvement during COVID-19 infection. A search through MEDLINE/PubMed was conducted on the topic in hand. With regard to exocrine function, some studies highlight the presence of an associated hyperenzymemia (hyperamylasemia, hyperlipasemia), while others describe isolated and rare cases of acute pancreatitis. More attention should be paid to pancreatic impairment in subjects with COVID-19, as this may prove to be one of the elements aggravating its clinical course. Indeed, acute pancreatitis, especially when presenting in severe forms with hyperstimulation of the pro-inflammatory response, may represent a crucial factor in the progression of COVID-19, entailing both an increase in hospitalization days and in mortality rate.

Report on the Short Endoscopic Exocrine Pancreatic Function Test in Children and Young Adults.

OBJECTIVES: Endoscopic pancreatic function test (ePFT) has been in use for exocrine function testing since the 1990s. In patients, short ePFT assesses acinar function, unlike the longer version for ductal function in adults. The present study summarizes characteristics of 1913 short ePFTs (S-ePFT) performed at 2 centers since 2001. METHODS: The main indications in patients presenting at ages infancy to 24.3 years, for the S-ePFT were failure to thrive, weight loss, diarrhea, and abdominal pain with bloating. Secretin was administered as bolus, and 4 aliquots of fluid were collected between 4 and 10 minutes after administration. Amylase, lipase, trypsin, and chymotrypsin activities were measured in the laboratory. RESULTS: The pH of consecutive samples increased by 0.3 to 0.7. Overall, 36.7% had abnormal S-ePFT with selective amylase deficiency (9.5%) and generalized enzyme deficiency (8.9%) being the most frequent. Retest reproducibility, repeatability, and clinical validity were high. By adding S-ePFT to endoscopy for the suspicion of malabsorption, the abnormal findings increased by 36.9%. CONCLUSIONS: Short ePFT assesses pancreatic acinar function in a reliable and clinically meaningful way in patients. Diagnostic yield of endoscopy increased substantially albeit with increased sedation time. By S-ePFT ductal function, cytokines and proteomics can also be assessed.

Leucine improves α-amylase secretion through the general secretory signaling pathway in pancreatic acinar cells of dairy calves.

The present study aimed to elucidate the mechanisms by which leucine impacts the secretion of pancreatic enzymes, especially amylase, by studying the proteomics profiles of pancreatic acinar (PA) cells from dairy cows. PA cells, the experimental model, were treated with four concentrations of leucine (0, 0.23, 0.45, and 0.90 mM). The abundance of different proteins in the four leucine treatment groups was detected. Label-free proteomic analysis enabled the identification of 1,906 proteins in all four treatment groups, and 1,350 of these proteins showed common expression across the groups. The primary effects of leucine supplementation were increased (P < 0.05) citrate synthase and ATPase activity, which enlarged the cytosolic ATP pool, and the upregulation of secretory protein 61 (Sec61) expression, which promoted protein secretion. In summary, these results suggest that leucine increases citrate synthase in the TCA cycle and ATPase activity and promotes the Sec signaling pathway to increase the exocrine function of PA cells.

Carboxyl ester lipase is highly conserved in utilizing maternal supplied lipids during early development of zebrafish and human.

Carboxyl ester lipase (Cel), is a lipolytic enzyme secreted by the pancreas, which hydrolyzes various species of lipids in the gut. Cel is also secreted by mammary gland during lactation and exists in breast milk. It facilitates dietary fat digestion and absorption, thus contributing to normal infant development. This study aimed to examine whether the Cel in zebrafish embryos has a similar role of maternal lipid utilization as in human infants, and how Cel contributes to the utilization of yolk lipids in zebrafish. The cel1 and cel2 genes were expressed ubiquitously in the blastodisc and yolk syncytial layer before 24 hpf, and in the exocrine pancreas after 72 hpf. The cel1 and cel2 morphants exhibited developmental retardation and yolk sac retention. The total cholesterol, cholesterol ester, free cholesterol, and triglyceride were reduced in the morphants' body while accumulated in the yolk (except triglyceride). The FFA content of whole embryos was much lower in morphants than in standard controls. Moreover, the delayed development in cel (cel1/cel2) double morphants was partially rescued by FFA and cholesterol supplementation. Delayed and weakened cholesterol ester transport to the brain and eyes was observed in cel morphants. Correspondingly, shrunken midbrain tectum, microphthalmia, pigmentation-delayed eyes as well as down-regulated Shh target genes were observed in the CNS of double morphants. Interestingly, cholesterol injections reversed these CNS alterations. Our findings suggested that cel genes participate in the lipid releasing from yolk sac to developing body, thereby contributing to the normal growth rate and CNS development in zebrafish.

Group II p21-activated kinase, PAK4, is needed for activation of focal adhesion kinases, MAPK, GSK3, and ß-catenin in rat pancreatic acinar cells.

PAK4 is the only member of the Group II p21-activated kinases (PAKs) present in rat pancreatic acinar cells and is activated by gastrointestinal hormones/neurotransmitters stimulating PLC/cAMP and by various pancreatic growth factors. However, little is known of the role of PAK4 activation in cellular signaling cascades in pancreatic acinar cells. In the present study, we examined the role of PAK4's participation in five different cholecystokinin-8 (CCK-8)-stimulated signaling pathways (PI3K/Akt, MAPK, focal adhesion kinase, GSK3, and ß-catenin), which mediate many of its physiological acinar-cell effects, as well as effects in pathophysiological conditions. To define PAK4's role, the effect of two different PAK4 inhibitors, PF-3758309 and LCH-7749944, was examined under experimental conditions that only inhibited PAK4 activation and not activation of the other pancreatic PAK, Group I PAK2. The inhibitors' effects on activation of these five signaling cascades by both physiological and pathophysiological concentrations of CCK, as well as by 12-O-tetradecanoylphobol-13-acetate (TPA), a PKC-activator, were examined. CCK/TPA activation of focal adhesion kinases(PYK2/p125FAK) and the accompanying adapter proteins (paxillin/p130CAS), Mek1/2, and p44/42, but not c-Raf or other MAPKs (JNK/p38), were mediated by PAK4. Activation of PI3K/Akt/p70s6K was independent of PAK4, whereas GSK3 and ß-catenin stimulation was PAK4-dependent. These results, coupled with recent studies showing PAK4 is important in pancreatic fluid/electrolyte/enzyme secretion and acinar cell growth, show that PAK4 plays an important role in different cellular signaling cascades, which have been shown to mediate numerous physiological and pathophysiological processes in pancreatic acinar cells.NEW & NOTEWORTHY In pancreatic acinar cells, cholecystokinin (CCK) or 12-O-tetradecanoylphobol-13-acetate (TPA) activation of focal adhesion kinases (p125FAK,PYK2) and its accompanying adapter proteins, p130CAS/paxillin; Mek1/2, p44/42, GSK3, and ß-catenin are mediated by PAK4. PI3K/Akt/p70s6K, c-Raf, JNK, or p38 pathways are independent of PAK4 activation.

Akt1 signalling supports acinar proliferation and limits acinar-to-ductal metaplasia formation upon induction of acute pancreatitis.

Molecular signalling mediated by the phosphatidylinositol-3-kinase (PI3K)-Akt axis is a key regulator of cellular functions. Importantly, alteration of the PI3K-Akt signalling underlies the development of different human diseases, thus prompting the investigation of the pathway as a molecular target for pharmacologic intervention. In this regard, recent studies showed that small molecule inhibitors of PI3K, the upstream regulator of the pathway, reduced the development of inflammation during acute pancreatitis, a highly debilitating and potentially lethal disease. Here we investigated whether a specific reduction of Akt activity, by using either pharmacologic Akt inhibition, or genetic inactivation of the Akt1 isoform selectively in pancreatic acinar cells, is effective in ameliorating the onset and progression of the disease. We discovered that systemic reduction of Akt activity did not protect the pancreas from initial damage and only transiently delayed leukocyte recruitment. However, reduction of Akt activity decreased acinar proliferation and exacerbated acinar-to-ductal metaplasia (ADM) formation, two critical events in the progression of pancreatitis. These phenotypes were recapitulated upon conditional inactivation of Akt1 in acinar cells, which resulted in reduced expression of 4E-BP1, a multifunctional protein of key importance in cell proliferation and metaplasia formation. Collectively, our results highlight the critical role played by Akt1 during the development of acute pancreatitis in the control of acinar cell proliferation and ADM formation. In addition, these results harbour important translational implications as they raise the concern that inhibitors of PI3K-Akt signalling pathways may negatively affect the regeneration of the pancreas. Finally, this work provides the basis for further investigating the potential of Akt1 activators to boost pancreatic regeneration following inflammatory insults. © 2019 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Which factors determine exocrine pancreatic dysfunction in diabetes mellitus?

The exocrine structure is significantly affected by diabetes because of endocrine structure-function disorder within the pancreas. Exocrine pancreatic dysfunction (EPD) is the general name of the malabsorption process resulting from inadequate production, release, decreased activation, and/or insufficient degradation of enzymes required for digestion from pancreatic acinar cells. It is important to diagnose patients early and correctly, since there may be both macro- and micro-nutrient deficiency in EPD. In this paper, EPD, the diabetes-EPD relationship, and the predictive, effective factors affecting the emergence of EPD are briefly explained and summarized with contemporary literature and our experienced based on clinical, lab, and radiological findings.

Delivery of pancreatic digestive enzymes into the gastrointestinal tract by pancreatic exocrine tissue transplant.

Exocrine pancreatic insufficiency, caused by disease-induced loss of pancreatic exocrine cells, may be treated through regenerative stem cell technologies that facilitate the production of pancreatic exocrine cells from induced pluripotent stem cells (iPSCs). However, delivering the digestive enzymes produced in the transplanted cells to the gastrointestinal tract remains a challenge. To generate an allogenic transplantation rat model, minced pancreas was transplanted into the gastric submucosal space with ablation of muscularis mucosa. In the allogenic transplantation, transplanted pancreatic cells were engrafted. Elevated amylase was detected in gastric juice, while transplanted cells disappeared through auto-digestion when the muscularis mucosa was not eliminated. Human iPSCs were differentiated into pancreatic exocrine cells by stage-specific treatment with growth factors and chemical compounds, and the differentiated pancreatic cells were implanted into the gastric submucosal space of nude rats. The transplanted cells were engrafted, and amylase was detected in the gastric juice in some cases. These findings suggest that transplantation of pancreatic exocrine cells into the gastric submucosal space with muscularis mucosa elimination will contribute to a regenerative approach for pancreatic exocrine insufficiency.

Early Intra-Acinar Events in Pathogenesis of Pancreatitis.

Premature activation of digestive enzymes in the pancreas has been linked to development of pancreatitis for more than a century. Recent development of novel models to study the role of pathologic enzyme activation has led to advances in our understanding of the mechanisms of pancreatic injury. Colocalization of zymogen and lysosomal fraction occurs early after pancreatitis-causing stimulus. Cathepsin B activates trypsinogen in these colocalized organelles. Active trypsin increases permeability of these organelles resulting in leakage of cathepsin B into the cytosol leading to acinar cell death. Although trypsin-mediated cell death leads to pancreatic injury in early stages of pancreatitis, multiple parallel mechanisms, including activation of inflammatory cascades, endoplasmic reticulum stress, autophagy, and mitochondrial dysfunction in the acinar cells are now recognized to be important in driving the profound systemic inflammatory response and extensive pancreatic injury seen in acute pancreatitis. Chymotrypsin, another acinar protease, has recently been shown be play critical role in clearance of pathologically activated trypsin protecting against pancreatic injury. Mutations in trypsin and other genes thought to be associated with pathologic enzyme activation (such as serine protease inhibitor 1) have been found in familial forms of pancreatitis. Sustained intra-acinar activation of nuclear factor κB pathway seems to be key pathogenic mechanism in chronic pancreatitis. Better understanding of these mechanisms will hopefully allow us to improve treatment strategies in acute and chronic pancreatitis.

Can pancreatic steatosis affect exocrine functions of pancreas?

BACKGROUND/AIMS: Pancreatic steatosis (PS) is a generally used term to define accumulation of fat in the pancreas. In theory PS may be able to affect the exocrine function of pancreas. In this study we aimed to determine the effect of PS on exocrine pancreas function. MATERIALS AND METHODS: Forty-three patients with PS determined by 3 tesla magnetic resonance imaging (MRI) and 48 patients without PS were included in this study. Patients with PS were classified as group 1 and control patients were classified as group 2. Fecal elastase-1 levels were determined. Fecal elastase-1 levels <200 µg/g were defined as exocrine pancreatic insufficiency (EPI). Patients with PS were further grouped according to severity and anatomic distribution of steatosis based on findings of 3 tesla MRI. RESULTS: Fecal elastase-1 levels was significantly lower in group 1 compared to group 2 (319.76±45.7 vs 549.31±69.4, respectively, p=0.003). Proportion of patients with EPI was significantly higher in group 1 than group 2 (35.5% vs 12% p=0.042). There were no significant differences in terms of severity or the anatomic distribution of PS in patients with PS with EPI based on MRI (p=0.052, p=0.198, p=0.405) Conclusion: Current study demonstrates that PS can cause EPI.

Glycogen synthase kinase-3ß ablation limits pancreatitis-induced acinar-to-ductal metaplasia.

Acinar-to-ductal metaplasia (ADM) is a reversible epithelial transdifferentiation process that occurs in the pancreas in response to acute inflammation. ADM can rapidly progress towards pre-malignant pancreatic intraepithelial neoplasia (PanIN) lesions in the presence of mutant KRas and ultimately pancreatic adenocarcinoma (PDAC). In the present work, we elucidate the role and related mechanism of glycogen synthase kinase-3beta (GSK-3ß) in ADM development using in vitro 3D cultures and genetically engineered mouse models. We show that GSK-3ß promotes TGF-α-induced ADM in 3D cultured primary acinar cells, whereas deletion of GSK-3ß attenuates caerulein-induced ADM formation and PanIN progression in KrasG12D transgenic mice. Furthermore, we demonstrate that GSK-3ß ablation influences ADM formation and PanIN progression by suppressing oncogenic KRas-driven cell proliferation. Mechanistically, we show that GSK-3ß regulates proliferation by increasing the activation of S6 kinase. Taken together, these results indicate that GSK-3ß participates in early pancreatitis-induced ADM and thus could be a target for the treatment of chronic pancreatitis and the prevention of PDAC progression. Copyright © 2017 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

FGF21 Is an Exocrine Pancreas Secretagogue.

The metabolic stress hormone FGF21 is highly expressed in exocrine pancreas, where its levels are increased by refeeding and chemically induced pancreatitis. However, its function in the exocrine pancreas remains unknown. Here, we show that FGF21 stimulates digestive enzyme secretion from pancreatic acinar cells through an autocrine/paracrine mechanism that requires signaling through a tyrosine kinase receptor complex composed of an FGF receptor and ß-Klotho. Mice lacking FGF21 accumulate zymogen granules and are susceptible to pancreatic ER stress, an effect that is reversed by administration of recombinant FGF21. Mice carrying an acinar cell-specific deletion of ß-Klotho also accumulate zymogen granules but are refractory to FGF21-stimulated secretion. Like the classical post-prandial secretagogue, cholecystokinin (CCK), FGF21 triggers intracellular calcium release via PLC-IP3R signaling. However, unlike CCK, FGF21 does not induce protein synthesis, thereby preventing protein accumulation. Thus, pancreatic FGF21 is a digestive enzyme secretagogue whose physiologic function is to maintain acinar cell proteostasis.

A Carboxyl Ester Lipase (CEL) Mutant Causes Chronic Pancreatitis by Forming Intracellular Aggregates That Activate Apoptosis.

Patients with chronic pancreatitis (CP) frequently have genetic risk factors for disease. Many of the identified genes have been connected to trypsinogen activation or trypsin inactivation. The description of CP in patients with mutations in the variable number of tandem repeat (VNTR) domain of carboxyl ester lipase (CEL) presents an opportunity to study the pathogenesis of CP independently of trypsin pathways. We tested the hypothesis that a deletion and frameshift mutation (C563fsX673) in the CEL VNTR causes CP through proteotoxic gain-of-function activation of maladaptive cell signaling pathways including cell death pathways. HEK293 or AR42J cells were transfected with constructs expressing CEL with 14 repeats in the VNTR (CEL14R) or C563fsX673 CEL (CEL maturity onset diabetes of youth with a deletion mutation in the VNTR (MODY)). In both cell types, CEL MODY formed intracellular aggregates. Secretion of CEL MODY was decreased compared with that of CEL14R. Expression of CEL MODY increased endoplasmic reticulum stress, activated the unfolded protein response, and caused cell death by apoptosis. Our results demonstrate that disorders of protein homeostasis can lead to CP and suggest that novel therapies to decrease the intracellular accumulation of misfolded protein may be successful in some patients with CP.

Genetic deletion of Rab27B in pancreatic acinar cells affects granules size and has inhibitory effects on amylase secretion.

Small G protein Rab27B is expressed in various secretory cell types and plays a role in mediating secretion. In pancreatic acinar cells, Rab27B was found to be expressed on the zymogen granule membrane and by overexpression to regulate the secretion of zymogen granules. However, the effect of Rab27B deletion on the physiology of pancreatic acinar cells is unknown. In the current study, we utilized the Rab27B KO mouse model to better understand the role of Rab27B in the secretion of pancreatic acinar cells. Our data show that Rab27B deficiency had no obvious effects on the expression of major digestive enzymes and other closely related proteins, e.g. similar small G proteins, such as Rab3D and Rab27A, and putative downstream effectors. The overall morphology of acinar cells was not changed in the knockout pancreas. However, the size of zymogen granules was decreased in KO acinar cells, suggesting a role of Rab27B in regulating the maturation of secretory granules. The secretion of digestive enzymes was moderately decreased in KO acini, compared with the WT control. These data indicate that Rab27B is involved at a different steps of zymogen granule maturation and secretion, which is distinct from that of Rab3D.

Digestive enzymatic activity during ontogenetic development in zebrafish (Danio rerio).

Despite the growing importance of zebrafish (Danio rerio) as an experimental model in biomedical research, some aspect of physiological and related morphological age dependent changes in digestive system during larval development are still unknown. In this paper, a biochemical and morphological study of the digestive tract of zebrafish was undertaken to record the functional changes occurring in this species during its ontogenetic development, particularly from 24 hr to 47 days post fertilization (dpf). Endo- and exo-proteases, as well as α-amylase enzymes, were quantified in zebrafish larvae before first feeding (7 dpf). The most morphologically significant events during the ontogenesis of the gut occurred between 3 dpf (mouth opening) and 7 dpf (end of exocrine pancreas differentiation). The presence of a wide range of digestive enzymes, already active at earlier zebrafish larval stages, closely related with the omnivorous diet of this species. Increasing enzyme activities were found with increasing age, probably in relation with intestinal mucosa folding and consequent absorption surface increase. J. Exp. Zool. (Mol. Dev. Evol.) 324B: 699-706, 2015. © 2015 Wiley Periodicals, Inc.