Role of Mucin 2 Glycoprotein and L-Fucose in Interaction of Immunity and Microbiome within the Experimental Model of Inflammatory Bowel Disease

Many factors underlie the development of inflammatory bowel disease (IBD) in humans. In particular, imbalance of microbiota and thinning of the mucosal layer in the large intestine play a huge role. Pathogenic microorganisms also exacerbate the course of diseases. In this research the role of mucin 2 deficiency in the formation of intestinal microflora in the experimental model using the Muc2 gene knockout mice in the presence of Helicobacter spp. was investigated. Also, restorative and anti-inflammatory effect of the dietary L-fucose in the Muc2^-/- mice on microflora and immunity was evaluated. For this purpose, bacterial diversity in feces was studied in the animals before and after antibiotic therapy and role of the dietary L-fucose in their recovery was assessed. To determine the effect of bacterial imbalance and fucose on the immune system, mRNA levels of the genes encoding pro-inflammatory cytokines (Tnf, Il1a, Il1b, Il6) and transcription factors of T cells (Foxp3 - Treg, Rorc - Th17, Tbx21 - Th1) were determined in the colon tissue of the Muc2^-/- mice. Significant elimination of bacteria due to antibiotic therapy caused decrease of the fucose levels in the intestine and facilitated reduction of the regulatory T cell transcription factor (Foxp3). When the dietary L-fucose was added to antibiotics, the level of bacterial DNA of Bacteroides spp. in the feces of the Muc2^-/- mice was partially restored. T regulatory cells are involved in the regulation of inflammation in the Muc2^-/- mice. Antibiotics reduced the number of regulatory T cell but did not decrease the inflammatory response to infection. Fucose, as a component of mucin 2, helped to maintain the level of Bacteroides spp. during antibiotic therapy of the Muc2^-/- mice and restored biochemical parameters, but did not affect the inflammatory response.

Fine gene expression regulation by minor sequence variations downstream of the polyadenylation signal

The termination of transcription is a complex process that substantially contributes to gene regulation in eukaryotes. Previously, it was noted that a single cytosine deletion at the position + 32 bp relative to the single polyadenylation signal AAUAAA (hereafter the dC mutation) causes a 2-fold increase in the transcription level of the upstream eGFP reporter in mouse embryonic stem cells. Here, we analyzed the conservation of this phenomenon in immortalized mouse, human and drosophila cell lines and the influence of the dC mutation on the choice of the pre-mRNA cleavage sites. We have constructed dual-reporter plasmids to accurately measure the effect of the dC and other nearby located mutations on eGFP mRNA level by RT-qPCR. In this way, we found that the dC mutation leads to a 2-fold increase in the expression level of the upstream eGFP reporter gene in cultured mouse and human, but not in drosophila cells. In addition, 3' RACE analysis demonstrated that eGFP pre-mRNAs are cut at multiple positions between + 14 to + 31, and that the most proximal cleavage site becomes almost exclusively utilized in the presence of the dC mutation. We also identified new short sequence variations located within positions + 25.. + 40 and + 33.. + 48 that increase eGFP expression up to ~2-4-fold. Altogether, the positive effect of the dC mutation seems to be conserved in mouse embryonic stem cells, mouse embryonic 3T3 fibroblasts and human HEK293T cells. In the latter cells, the dC mutation appears to be involved in regulating pre-mRNA cleavage site selection. Finally, a multiplexed approach is proposed to identify motifs located downstream of cleavage site(s) that are essential for transcription termination.