A minimal promoter region of Kit gene recapitulates mast cell differentiation in development, aging and inflammation.

To follow mast cells (MCs) distribution during aging and inflammation, we characterized two transgenic mouse models in which the EGFP expression is controlled by 9kb or 12kb of Kit gene promoter, defined as p18 and p70, respectively. We detected EGFP-positive cells in the serosal surfaces of the peritoneum, pleuras and pericardium, mucosal cavities, and connective tissue of almost all organs including gonads of p70, but not of p18 mice. By FACS and immunofluorescence for FcεR1, Kit and β7-integrin, we found that these EGFP positive cells were MCs. In non-inflammatory conditions, a higher percentage of EGFP positive cells was found in juvenile with respect to adult serosal surfaces, but no differences between males and females at both developmental ages. We found, however, a striking difference in developing gonads, with low numbers of EGFP positive cells in foetal ovaries compared to age matched testes. Under inflammatory conditions caused by high fat diet (HFD), mice showed an increase in serosal EGFP positve cells. Altogether our results identify a regulatory region of the Kit gene, activated in MCs and that directing EGFP expression, can be employed to trace this immune cell type throughout the organism and in different animal conditions.