Unintended targeting of Dmp1-Cre reveals a critical role for Bmpr1a signaling in the gastrointestinal mesenchyme of adult mice

Abstract

Cre/loxP technology has been widely used to study cell type-specific functions of genes. Proper interpretation of such data critically depends on a clear understanding of the tissue specificity of Cre expression. The Dmp1-Cre mouse, expressing Cre from a 14-kb DNA fragment of the mouse Dmp1 gene, has become a common tool for studying gene function in osteocytes, but the presumed cell specificity is yet to be fully established. By using the Ai9 reporter line that expresses a red fluorescent protein upon Cre recombination, we find that in 2-month-old mice, Dmp1-Cre targets not only osteocytes within the bone matrix but also osteoblasts on the bone surface and preosteoblasts at the metaphyseal chondro-osseous junction. In the bone marrow, Cre activity is evident in certain stromal cells adjacent to the blood vessels, but not in adipocytes. Outside the skeleton, Dmp1-Cre marks not only the skeletal muscle fibers, certain cells in the cerebellum and the hindbrain but also gastric and intestinal mesenchymal cells that express Pdgfra. Confirming the utility of Dmp1-Cre in the gastrointestinal mesenchyme, deletion of Bmpr1a with Dmp1-Cre causes numerous large polyps along the gastrointestinal tract, consistent with prior work involving inhibition of BMP signaling. Thus, caution needs to be exercised when using Dmp1-Cre because it targets not only the osteoblast lineage at an earlier stage than previously appreciated, but also a number of non-skeletal cell types.

Genetics: Caution concerning specificity of gene deletion system

A gene deletion system designed to target bone cells has been shown to have more widespread effects than originally thought. This research tool was designed to target osteocytes, the bone cells entombed in bone matrix. Some evidence has suggested, however, that it can also affect other cells involved in bone development, and cells in bone marrow, muscle and the brain. To investigate further, Fanxin Long from Washington University School of Medicine, USA, and colleagues created mice in which activity of the gene deletion system led to fluorescent labeling of affected cells. They not only confirmed the more widespread effects that had previously been suggested, but revealed previously unseen effects on cells in the gut, highlighting the need for caution when interpreting the effects of gene deletions made with this system.

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