Meflin (Islr) expression has gained attention as a marker for mesenchymal stem cells, but its function remains largely unexplored. Here, we report the generation of Meflin-CreER.sup.T2 mice with CreER.sup.T2 inserted under the Meflin gene promoter to label Meflin-expressing cells genetically, thereby enabling their lineages to be traced. We found that in adult mice, Meflin-expressing lineage cells were present in adipose tissue stroma and had differentiated into mature adipocytes. These cells constituted Crown-like structures in the adipose tissue of mice after high-fat diet loading. Cold stimulation led to the differentiation of Meflin-expressing lineage cells into beige adipocytes. Thus, the Meflin-CreER.sup.T2 mouse line is a useful new tool for visualizing and tracking the lineage of Meflin-expressing cells.