Nature of bacterial colonization influences transcription of mucin genes in mice during the first week of life

Abstract

Background: Postnatal regulation of the small intestinal mucus layer is potentially important in the development of adult gut functionality. We hypothesized that the nature of bacterial colonization affects mucus gene regulation in early life.We thus analyzed the influence of the presence of a conventional microbiota as well as two selected monocolonizing bacterial strains on the transcription of murine genes involved in mucus layer development during the first week of life.Mouse pups (N = 8/group) from differently colonized dams: Germ-free (GF), conventional specific pathogen free (SPF), monocolonized with either Lactobacillus acidophilus NCFM (Lb) or Escherichia coli Nissle (Ec) were analyzed by qPCR on isolated ileal tissue sections from postnatal days 1 and 6 (PND1, PND6) after birth with respect to: (i) transcription of specific genes involved in mucus production (Muc1-4, Tff3) and (ii) amounts of 16S rRNA of Lactobacillus and E. coli. Quantification of 16S rRNA genes was performed to obtain a measure for amounts of colonized bacteria.

Results: We found a microbiota-independent transcriptional increase of all five mucus genes from PND1 to PND6. Furthermore, the relative level of transcription of certain mucus genes on PND1 was increased by the presence of bacteria. This was observed for Tff3 in the SPF, Ec, and Lb groups; for Muc2 in SPF; and for Muc3 and Muc4 in Ec and Lb, respectively.Detection of bacterial 16S rRNA genes levels above the qPCR detection level occurred only on PND6 and only for some of the colonized animals. On PND6, we found significantly lower levels of Muc1, Muc2 and Muc4 gene transcription for Lb animals with detectable Lactobacillus levels as compared to animals with Lactobacillus levels below the detection limit.

Conclusions: In summary, our data show that development of the expression of genes encoding secreted (Muc2/Tff3) and membrane-bound (Muc1/Muc3/Muc4) mucus regulatory proteins, respectively, is distinct and that the onset of this development may be accelerated by specific groups of bacteria present or absent at the mucosal site.

Figure 1

Comparison of mucin gene expression between the four animal groups on PND1 and PND6. Transcription of Muc1, Muc2, Muc3, Muc4 and Tff3 on postnatal days (PND) 1 and 6 for pups in groups: GF, SPF, Lb and Ec. Each column represents the average relative abundance (Ra) (See Methods) of 8 animals. Error bars show SEM values. ^* p < 0.05, ^** p < 0.01, ^*** p < 0.001 relative to PND1 (for the same group) ⁺ p < 0.05, ⁺⁺ p < 0.01, ⁺⁺⁺ p < 0.001 relative to GF (for the same day).

Figure 2

Difference in mucin gene expression between pups with detectable and undetectable Lactobacillus 16S in Lb. Comparison of Muc1, Muc2, Muc3, Muc4 and Tff3 transcription on PND6 between pups in the Lb group, where Lactobacillus 16S could be detected and could not be detected, respectively. Each column represents the average relative abundance (Ra) of 5/8 (above DL) or 3/8 (below DL) animals. Error bars show SEM values. DL = Detection Limit. ^* p < 0.05, denotes significant difference between detectably colonized and not colonized.