Mist1 Expression Is Required for Paneth Cell Maturation

Paneth cells are professional secretory cells found within the small intestinal crypt epithelium. Although their role as part of the innate immune complex providing antimicrobial secretory products is well-known, the mechanisms that control secretory capacity are not well-understood. MIST1 is a scaling factor that is thought to control secretory capacity of exocrine cells.

Mist1^+/+ and Mist1^-/- mice were used to evaluate the function of MIST1 in small intestinal Paneth cells. We used histologic and immunofluorescence staining to evaluate small intestinal tissue for proliferation and lineage allocation. Total RNA was isolated to evaluate gene expression. Enteroid culture was used to evaluate the impact of the absence of MIST1 expression on intestinal stem cell function.

Absence of MIST1 resulted in increased numbers of Paneth cells exhibiting an intermediate cell phenotype but otherwise did not alter overall epithelial cell lineage allocation. Muc2 and lysozyme staining confirmed the presence of intermediate cells at the crypt base of Mist1^-/- mice. These changes were not associated with changes in mRNA expression of transcription factors associated with lineage allocation, and they were not abrogated by inhibition of Notch signaling. However, the absence of MIST1 expression was associated with alterations in Paneth cell morphology including decreased granule size and distended rough endoplasmic reticulum. Absence of MIST1 was associated with increased budding of enteroid cultures; however, there was no evidence of increased intestinal stem cell numbers in vivo.

MIST1 plays an important role in organization of the Paneth cell secretory apparatus and managing endoplasmic reticulum stress. This role occurs downstream of Paneth cell lineage allocation.