An approach to intersectionally target mature enteroendocrine cells in the small intestine of mice
Enteroendocrine cells (EECs) constitute only a small proportion of Villin-1 (Vil1)-expressing intestinal epithelial cells (IECs) of the gastrointestinal tract; yet, in sum, they build the largest endocrine organ of the body, with each of them storing and releasing a distinct set of peptides for the control of feeding behavior, glucose metabolism, and gastrointestinal motility. Like all IEC types, EECs are continuously renewed from intestinal stem cells in the crypt base and terminally differentiate into mature subtypes while moving up the crypt-villus axis. Interestingly, EECs adjust their hormonal secretion according to their migration statues as EECs receive altering differentiation signals along the crypt-villus axis and thus undergo functional readaptation. Cell-specific targeting of mature EEC subtypes by specific promoters is challenging because the expression of EEC-derived peptides and their precursors are not limited to EECs but are also found in other organs, such as the brain (e.g. Cck and Sst) as well as in the pancreas (e.g. Sst and Gcg). Here, we describe an intersectional genetic approach that enables cell type-specific targeting of functionally distinct EEC subtypes by combining a newly-generated Dre-recombinase expressing mouse line (Vil1-2A-DD-Dre) with multiple existing Cre-recombinase mice, and mouse strains with rox and loxP sites flanked stop cassettes for transgene expression. We found that transgene expression in triple-transgenic mice is highly specific in I, but not D and L cells in the apical villi of the small intestine. The targeting of EECs only in villi is likely caused by the intrinsic Vil1 expression, limiting our Vil1-2A-DD-Dre mouse line and the intersectional genetic approach described here for the investigation of mature EECs. Overall design: Single-cell RNA sequencing of the murine intestinal epithelium was performed by isolating intestinal epithelial cells of male C57BL/6N wildtype mice from the duodenum, jejunum and ileum. Isolated cells from three 12-week-old male mice that were pooled in order to minimize artefacts originating from individual mice.