Absence of gut microbiota impairs depletion of Paneth cells but not goblet cells in germ-free VilCreER mice.

Mouse atonal homolog 1 () is a basic helix-loop-helix transcription factor important for the differentiation of secretory cells within the intestinal epithelium. The analysis of Paneth depletion efficiency on () mice treatment with tamoxifen in the presence or absence of intestinal microbiota showed a failure on Paneth cell depletion in germ-free mice as compared with specific pathogen-free (SPF) mice. However, goblet cells were efficiently depleted in germ-free mice. The gene expression of was significantly reduced in the ileum of germ-free mice 5 days after tamoxifen injection as compared with germ-free control, but its protein expression was still detectable in the nuclei of epithelial cells in the crypts. Germ-free mice showed low proliferative ileal crypts and apoptotic cells that were mainly detected in the tip of the villus, consistent with a slow turnover rate of epithelial cells. Although Paneth cells were not depleted in germ-free mice for the first 7 wk after the last tamoxifen injection, far already from the 5 days time-laps observed in SPF conditions, an incomplete depletion of Paneth cells was observed 14 wk after the last tamoxifen injection. Colonization of germ-free mice restored the phenotype observed in SPF mice, highlighting the regulatory role of gut microbes in our model. We conclude that absence of intestinal microbiota in mice is associated with reduced epithelial cell renewal and delays the depletion of preexisting Paneth cells. Cre-lox system is a powerful and widely used research tool developed to understand the specific role of genes. It allows to control the spatial and temporal expression of genes in experimental models. Several limitations including toxicity of Cre recombinase or incomplete excision of floxed loci have been reported in the past. To date, this is the first research study reporting that gut microbes also influence the expected phenotype of Paneth cell depletion in the genetically modified mouse model.