Pancreatic duct secretion: experimental methods, ion transport mechanisms and regulation

Identification and characterization of mRNAs and lncRNAs in the uterus of polytocous and monotocous Small Tail Han sheep (Ovis aries)

Background

Long non-coding RNAs (lncRNAs) regulate endometrial secretion and uterine volume. However, there is little research on the role of lncRNAs in the uterus of Small Tail Han sheep (FecB++). Herein, RNA-seq was used to comparatively analyze gene expression profiles of uterine tissue between polytocous and monotocous sheep (FecB++) in follicular and luteal phases.

Methods

To identify lncRNA and mRNA expressed in the uterus, the expression of lncRNA and mRNA in the uterus of Small Tail Han sheep (FecB++) from the polytocous group (n = 6) and the monotocous group (n = 6) using RNA-sequencing and real-time polymerase chain reaction (RT-PCR). Identification of differentially expressed lncRNAs and mRNAs were performed between the two groups and two phases . Gene ontology (GO) and pathway enrichment analyses were performed to analyze the biological functions and pathways for the differentially expressed mRNAs. LncRNA-mRNA co-expression network was constructed to further analyses the function of related genes.

Results

In the follicular phase, 473 lncRNAs and 166 mRNAs were differentially expressed in polytocous and monotocous sheep; in the luteal phase, 967 lncRNAs and 505 mRNAs were differentially expressed in polytocous and monotocous sheep. GO and KEGG enrichment analysis showed that the differentially expressed lncRNAs and their target genes are mainly involved in ovarian steroidogenesis, retinol metabolism, the oxytocin signaling pathway, steroid hormone biosynthesis, and the Foxo signaling pathway. Key lncRNAs may regulate reproduction by regulating genes involved in these signaling pathways and biological processes. Specifically, UGT1A1, LHB, TGFB1, TAB1, and RHOA, which are targeted by MSTRG.134747, MSTRG.82376, MSTRG.134749, MSTRG.134751, and MSTRG.134746, may play key regulatory roles. These results offer insight into molecular mechanisms underlying sheep prolificacy.

Sex-independent expression of chloride/formate exchanger Cfex (Slc26a6) in rat pancreas, small intestine, and liver, and male-dominant expression in kidneys

Chloride/formate exchanger (CFEX; SLC26A6) mediates oxalate transport in various mammalian organs. Studies in Cfex knockout mice indicated its possible role in development of male-dominant hyperoxaluria and oxalate urolithiasis. Rats provide an important model for studying this pathophysiological condition, but data on Cfex (rCfex) localisation and regulation in their organs are limited. Here we applied the RT-PCR and immunochemical methods to investigate rCfex mRNA and protein expression and regulation by sex hormones in the pancreas, small intestine, liver, and kidneys from intact prepubertal and adult as well as gonadectomised adult rats treated with sex hormones. rCfex cDNA-transfected HEK293 cells were used to confirm the specificity of the commercial anti-CFEX antibody. Various biochemical parameters were measured in 24-h urine collected in metabolic cages. rCfex mRNA and related protein expression varied in all tested organs. Sex-independent expression of the rCfex protein was detected in pancreatic intercalated ducts (apical domain), small intestinal enterocytes (brush-border membrane; duodenum > jejunum > ileum), and hepatocytes (canalicular membrane). In kidneys, the rCfex protein was immunolocalised to the proximal tubule brush-border with segment-specific pattern (S1=S2<S3), and both rCfex mRNA and protein expression exhibited male-dominant sex differences driven by stimulatory effects of androgens after puberty. However, urinary oxalate excretion was unrelated to renal rCfex protein expression. While the effect of male-dominant expression of rCfex in renal proximal tubules on urine oxalate excretion remains unknown, its expression in the hepatocyte canalicular membrane may be a pathway of oxalate elimination via bile.

Intraluminal volume homeostasis: A common sertonergic mechanism among diverse epithelia

Volume homeostasis is a common physiological phenomenon for fluid secreting organs, such as exocrine and endocrine glands. It is a manifestation of a finite intraluminal space and an ever changing demand for secretory fluids. Volume homeostasis addresses issues of fluid secretion, storage and clearance for efficient functioning. Here we discuss the evidence gathered over the past 2-3 decades on serotonin's role as a feedback inhibitor of secretion in the mammary gland, salivary gland, liver, pancreas, lung, thyroid gland and prostate gland. We propose that serotonin action is a common mechanism of regulating intraductal volume homeostasis.

Molecular and cellular regulation of pancreatic duct cell function

PURPOSE OF REVIEW

The pancreatic duct epithelium is remarkable for its capacity to secrete HCO(3)(-) ions at concentrations as high as 140 mmol/l. The properties of the key transporters involved in this process and the central role played by cystic fibrosis transmembrane conductance regulator (CFTR) are the main focus of this review.

RECENT FINDINGS

The Cl(-)/HCO(3)(-) exchanger at the apical membrane of pancreatic duct cells is now known to be SLC26A6. The 1: 2 stoichiometry and electrogenicity of this exchanger enable it to contribute to the secretion of HCO(3)(-) at high concentrations. The apical CFTR channels also appear to have sufficient HCO(3)(-) permeability to contribute directly to HCO(3)(-) secretion. There is a strong possibility that the Ca(2+)-activated Cl(-) channels at the apical membrane are members of the bestrophin family which, like CFTR, are also permeable to HCO(3)(-). More has been learned about the complex interactions between CFTR and other transporters within macromolecular complexes coordinated at the apical membrane by scaffolding proteins. Further details are also emerging of the protective paracrine roles of nucleotides, nucleosides, bile acids and trypsin in the regulation of ductal secretion.

SUMMARY

Most of the key transporters involved in Cl(-) and HCO(3)(-) secretion have now been identified and characterized. Current research focuses on the molecular interactions between these transporters and the ways in which they are regulated by extracellular signals.