Produdion of transgenic mice and functional analysis ofosteaytesusingcis-regulatory regions

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Osteocytes are the most abundant cells in bone. There are approximately 10 times as many osteocytes as osteoblasts in mature bone. Previous studies suggested that osteocytes may be involved in mechanosensing and Ca^<2+> metabolism. However, inside of bone is a network of numerous osteocytes, whose specific function has remained an enigma. DMP1 is highly expressed in the osteocyte and therefore a good marker for the osteocyte lineage and is specifically expressed along and in the canaliculi of osteocytes within the bone matrix. The hypothesis is that the cis-regulatory region of the DMP1 gene contains an osteocyte-specific control module that will activate the endogenous DMP1 gene. Therefore, we identified the 12Kbp cis-regulatory region, which contained osteocyte-specific control module. Then, we made the constructs of cis-regulatory regions of DMP1-GFP, to generation of the transgenic mice that express GFP specifically in the osteocyte.Recent study using DMP1-null mice demonstrated that absence of DMP1 results in defective osteocyte maturation and increased FGF23 expression, leading to renal phosphate-wasting associated hypophosphatamia. Based on this result, we hypothesize that DMP1-overexpression will result in decreased FGF23 expression, leading to hyperphosphatemia. Then we evaluate the phosphate homeostasis and serum FGF-23 in DMP1-overexpressed transgenic mice (DMP1-Tg). There is no significance of TmP/GFR and serum FGF23 values between DMP1-Tg and wild mice. Our findings indicated that DMP1 did not directly induced FGF-23 expression in bony tissue and that loss of DMP1 inducing osteomalacia may lead to increased FGF-23 in bony tissue.