Our previous studies have demonstrated that nuclear factor I-C (NFI-C) null mice developed short molar roots that contain aberrant odontoblasts and abnormal dentin formation. Based on these findings, we performed studies to elucidate the function of NFI-C in odontoblasts. Initial studies demonstrated that aberrant odontoblasts become dissociated and trapped in an osteodentin-like mineralized tissue. Abnormal odontoblasts exhibit strong bone sialoprotein expression but a decreased level of dentin sialophosphoprotein expression when compared with wild type odontoblasts. Loss of Nfic results in an increase in p-Smad2/3 expression in aberrant odontoblasts and pulp cells in the subodontoblastic layer in vivo and primary pulp cells from Nfic-deficient mice in vitro. Cell proliferation analysis of both cervical loop and ectomesenchymal cells of the Nfic-deficient mice revealed significantly decreased proliferative activity compared with wild type mice. In addition, Nfic-deficient primary pulp cells showed increased expression of p21 and p16 but decreased expression of cyclin D1 and cyclin B1, strongly suggesting cell growth arrest caused by a lack of Nfic activity. Analysis of the pulp and abnormal dentin in Nfic-deficient mice revealed an increase in apoptotic activity. Further, Nfic-deficient primary pulp cells exhibited an increase in caspase-8 and -3 activation, whereas the cleaved form of Bid was hardly detected. These results indicate that the loss of Nfic leads to the suppression of odontogenic cell proliferation and differentiation and induces apoptosis of aberrant odontoblasts during root formation, thereby contributing to the formation of short roots.Tooth development is a complex and well coordinated developmental process that is achieved through a series of reciprocal interactions between dental epithelium and neural crest-derived ectomesenchyme (EM).2 The dental epithelium gives rise to the outer and inner enamel epithelium from which ameloblasts differentiate, whereas EM cells differentiate into odontoblasts. The critical roles of several transcription factors and growth factors in crown formation have been well documented (1, 2). After completion of crown formation, the inner and outer enamel epithelial cells proliferate and form Hertwig's epithelial root sheath that plays a key role in root formation. It is believed, based on information derived from crown development, that Hertwig's epithelial root sheath induces the differentiation of EM cells from the radicular pulp area into odontoblasts that are responsible for root dentin formation. However, the molecular mechanisms responsible for root development are not well understood (3-5).The nuclear factor I (NFI) family of transcription/replication factors was first discovered as a family of proteins required for the replication of adenovirus DNA in vitro (6). The NFI gene family encodes site-specific transcription factors essential for the development of a number of organ systems (7). There are four NFI gene family members in vertebrates (Nfia, Nfib, Nfic...

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We have previously reported that the odontogenic ameloblast-associated protein (ODAM) plays important roles in enamel mineralization through the regulation of matrix metalloproteinase-20 (MMP-20). However, the precise function of ODAM in MMP-20 regulation remains largely unknown. The aim of the present study was to uncover the molecular mechanisms responsible for MMP-20 regulation. The subcellular localization of ODAM varies in a stage-specific fashion during ameloblast differentiation. During the secretory stage of amelogenesis ODAM was localized to both the nucleus and cytoplasm of ameloblasts. However, during the maturation stage of amelogenesis, ODAM was observed in the cytoplasm and at the interface between ameloblasts and the enamel layer, but not in the nucleus. Secreted ODAM was detected in the conditioned medium of ameloblast-lineage cell line (ALC) from days 14 to 21, which coincided with the maturation stage of amelogenesis. Interestingly, the expression of Runx2 and nuclear ODAM correlated with MMP-20 expression in ALC. We therefore examined whether ODAM cooperates with Runx2 to regulate MMP-20 and modulate enamel mineralization. Increased expression of ODAM and Runx2 augmented MMP-20 expression, and Runx2 expression enhanced expression of ODAM, although overexpression of ODAM did not influence Runx2 expression. Conversely, loss of Runx2 in ALC decreased ODAM expression, resulting in down-regulation of MMP-20 expression. Increased MMP-20 expression accelerated amelogenin processing during enamel mineralization. Our data suggest that Runx2 regulates the expression of ODAM and that nuclear ODAM serves an important regulatory function in the mineralization of enamel through the regulation of MMP-20 apart from a different, currently unidentified, function of extracellular ODAM.

In bone marrow, bone marrow stromal cells (BMSCs) have the capacity to differentiate into osteoblasts and adipocytes. Age-related osteoporosis is associated with a reciprocal decrease of osteogenesis and an increase of adipogenesis in bone marrow. In this study, we demonstrate that disruption of nuclear factor I-C (NFI-C) impairs osteoblast differentiation and bone formation, and increases bone marrow adipocytes. Interestingly, NFI-C controls postnatal bone formation but does not influence prenatal bone development. We also found decreased NFI-C expression in osteogenic cells from human osteoporotic patients. Notably, transplantation of Nfic-overexpressing BMSCs stimulates osteoblast differentiation and new bone formation, but inhibits adipocyte differentiation by suppressing peroxisome proliferator-activated receptor gamma expression in Nfic 2/2 mice showing an age-related osteoporosis-like phenotype. Finally, NFI-C directly regulates Osterix expression but acts downstream of the bone morphogenetic protein-2-Runx2 pathway. These results suggest that NFI-C acts as a transcriptional switch in cell fate determination between osteoblast and adipocyte differentiation in BMSCs. Therefore, regulation of NFI-C expression in BMSCs could be a novel therapeutic approach for treating agerelated osteoporosis.