DMP1-targeted Cre Expression in Odontoblasts and Osteocytes

Abstract

Odontoblasts in dentin and osteocytes in bone contain dendritic processes. To test if their dendrites share a common feature, we compared their cellular morphology as visualized using scanning electron microscopy. Analysis of our data showed that both cells share an identical dendritic canalicular system and express extensive processes forming a complex network within the mineralized matrix. Because dentin matrix protein 1 (DMP1), an extracellular matrix protein, is highly expressed in both types of cells, we next tested, using a transgenic approach, whether a 9.6-kb Dmp1 promoter-4-kb 1st intron would be able to target Cre cDNA in these cells for expression/deletion of other genes in odontoblasts and osteocytes. We determined the specificity and efficiency of Cre activity by crossing Dmp1-Cre mice with ROSA26 reporter mice. Results showed that odontoblasts and osteocytes were specifically targeted, suggesting that this animal model will be useful for the preferential study of gene functions in both types of cells.

Androgen receptor (AR) in osteocytes is important for the maintenance of male skeletal integrity: Evidence from targeted AR disruption in mouse osteocytes

“…DMP1-Cre mice were used to drive expression of Cre recombinase specifically to mature osteocytes because DMP1 is a matrix protein, which is highly expressed only in odontoblasts and osteocyte cells. (18) Our finding of a significant decrease of AR expression in the quadriceps muscle can be attributed to DMP1 expression in muscle, however with no significant changes in skeletal muscle weight. (29) Interestingly, although age-related trabecular bone loss in mice affects both genders, males appear to be less affected than females, (30) suggesting that androgens may protect male mice against age-related bone loss.…”

“…(18) Male offsprings were weaned at 3 weeks of age and genotyped by PCR as described previously. (19) Presence of DMP1Cre (534 bp) was determined via PCR with reverse primer 5 0 -CCCGCAGAACCT-GAAGATG-3 0 and forward primer 5 0 -GACCCGGCAAAACAGGTAG-3 0 .…”

“…(16) Moreover, osteocytes express a number of potentially important genes such as receptor activator of NF-kB ligand (RANKL), which are involved in bone remodeling and which might be androgen regulated. (17) Because the impact of inactivation of androgen action through the AR in osteocytes in vivo has not been determined, we generated and characterized a mouse model in which the AR is deleted specifically in terminally differentiated osteocytes using the dentin matrix protein 1 (DMP1) Cre mouse line (18) and the Cre/LoxP system (ocy-ARKO). This ocy-ARKO mouse line targets AR action in a more differentiated population of osteocytes than in a previously described osteoblast ARKO model.…”

Disruption of Lrp4 function by genetic deletion or pharmacological blockade increases bone mass and serum sclerostin levels

“…These phenotypes provide functional validity of the Lrp4 flox/flox line in creating an Lrp4-null mutation after Cre-mediated homologous recombination. Lrp4 flox/flox mice were subsequently crossed with Cre lines driven either by the osteocalcin (Oc) promoter (33) or the dentin matrix protein 1 (Dmp1) promoter (34) to generate osteoblast/osteocyte-specific (Oc-cre) or osteocyte-specific (Dmp1-cre) Lrp4 loss-of-function mice (Fig. 1C).…”

“…The Lrp4-targeting construct, in which exon 1 was flanked by loxP sites, was electroporated into C57BL/6 ES cells followed by subsequent removal of the neomycin-resistance cassette using flip recombinase to generate mice with a targeted Lrp4 gene (Lrp4 flox/flox ). Osteocalcin-cre (Oc-cre) transgenic mice, which express Cre under the control of the human promoter of the osteoblast/osteocyte marker gene Oc and Dmp1-cre transgenic animals, which express Cre under the control of the 9.6-kb promoter fragment of the osteocyte marker gene Dmp1, as well as P Bi-2 -cre expressing Cre recombinase ubiquitously, have been described previously (32)(33)(34) and were maintained on the C57BL/6J genetic background. Lrp4 flox/flox mice were crossed with Cre driver mouse lines, and the offspring from each line were analyzed.…”