Dietary fiber intake links to decreased risk of colorectal cancers. The underlying mechanisms remain unclear. Recently, we found that butyrate, a short-chain fatty acid produced in gut by bacterial fermentation of dietary fiber, enhances TGF-β signaling in rat intestinal epithelial cells (RIE-1). Furthermore, TGF-β represses inhibitors of differentiation (Ids), leading to apoptosis. We hypothesized that dietary fiber enhances TGF-β's growth inhibitory effects on gut epithelium via inhibition of Id2. In this study, Balb/c and DBA/2N mice were fed with a regular rodent chow or supplemented with a dietary fiber (20% pectin) and Smad3 level in gut epithelium was measured. In vitro, RIE-1 cells were treated with butyrate and TGF-β1, and cell functions were evaluated. Furthermore, the role of Ids in butyrate- and TGF-β-induced growth inhibition was investigated. We found that pectin feeding increased Smad3 protein levels in the jejunum (1.47 ± 0.26-fold, P = 0.045, in Balb/c mice; 1.49 ± 0.19-fold, P = 0.016, in DBA/2N mice), and phospho-Smad3 levels (1.92 ± 0.27-fold, P = 0.009, in Balb/c mice; 1.83 ± 0.28-fold, P = 0.022, in DBA/2N mice). Butyrate or TGF-β alone inhibited cell growth and induced cell cycle arrest. The combined treatment of butyrate and TGF-β synergistically induced cell cycle arrest and apoptosis in RIE-1 cells and repressed Id2 and Id3 levels. Furthermore, knockdown of Id2 gene expression by use of small interfering RNA caused cell cycle arrest and apoptosis. We conclude that dietary fiber pectin enhanced Smad3 expression and activation in the gut. Butyrate and TGF-β induced cell cycle arrest and apoptosis, which may be mediated by repression of Id2. Our results implicate a novel mechanism of dietary fiber in reducing the risk of colorectal cancer development.

The zebrafish species Danio rerio has become one of the major vertebrate model organisms used in biomedical research. However, there are aspects of the model that need to be improved. One of these is the ability to identify individual fish and fish lines by DNA profiling. Although many dinucleotide short tandem repeat (diSTR) markers are available for this and similar purposes, they have certain disadvantages such as an excessive polymerase slippage ("stutter") that causes difficulties in automated genotyping and cross-laboratory comparisons. Here we report on the development of a 13-plex of tetranucleotide and pentanucleotide STRs (tetraSTRs and pentaSTRs, respectively) that have low stutter. The system uses an inexpensive universal primer labelling system, which can easily be converted to a direct labeling system if desired. This 13-plex was examined in three zebrafish lines (NHGRI-1, kca33Tg, and kca66Tg, originally obtained from ZIRC). The average observed heterozygosity (Ho) and expected heterozygosity (He) in these highly inbred lines were 0.291 and 0.359, respectively, which is very similar to what has been found with diSTRs. The probability of identity (PI) for all fish tested was 2.1 × 10 −5 and the PI for siblings (PIsib) was 6.4 × 10 −3 , as calculated by the Genalex package. Ninety percent of the fish tested were correctly identified with their respective strains. It is also demonstrated that this panel can be used to confirm doubled-haploid cell lines. This multiplex should find multiple uses for improving the accuracy and reproducibility of studies using the zebrafish model. Zebrafish (Danio rerio) is the vertebrate animal model most rapidly adopted in biomedical research. The zebrafish genome is 70% similar to the human, and 80% percent of the genes responsible for human diseases have an orthologue in zebrafish 1. It is relatively easy to generate mutant animals, and the cost of zebrafish maintenance is low. Applications of this animal model include, among the many, toxicology, developmental biology, genetics and degenerative diseases, psychiatric conditions, cancer, and metabolic disorders. Researchers can choose from a variety of wild-type and mutant zebrafish lines for their studies. All available from the Zebrafish International Resource Center (ZIRC), wild-type zebrafish lines include Tübingen, AB, NHGRI-1, Sanger AB Tübingen (SAT), WIK, Tüpfel long fin (TL), Nadia, and Cooch Behar. Also available, are more than forty thousand mutant lines. Despite previous reports of the derivation of the IM inbred zebrafish line in 2011, homozygous zebrafish lines for all loci are lacking 2,3. Some initiatives are in progress that may fulfill the need for fish lines that have an identical genetic identity. We are currently working on a strategy to generate homozygous diploid fish using the method developed by Streisinger and colleagues in 1981, followed by somatic cell nuclear transfer (SCNT) 4-9. Once a gynogenetic embryo is developed, we isolate cells from them, and subsequently, after testing for normal k...