Reciprocal Temporospatial Patterns of Msx2 and Osteocalcin Gene Expression During Murine Odontogenesis

Abstract

Msx2 is a homeodomain transcription factor that regulates craniofacial development in vivo and osteocalcin (Osc) promoter activity in vitro. Msx2 is expressed in many craniofacial structures prior to embryonic day (E) E14 but is expressed at later stages in a restricted pattern, primarily in developing teeth and the calvarium. We examine Osc expression by in situ hybridization during murine development, detailing temporospatial relationships with Msx2 expression during preappositional and appositional odontogenesis and calvarial osteogenesis. Osc expression at E14 -14.5 is very low, limited to a few perichondrial osteoblasts in the dorsal aspect of developing ribs. At E16.5 and E18.5, Osc expression is much higher, widely expressed in skeletal osteoblasts, including calvarial osteoblasts that do not express Msx2. No Osc is detected in early preappositional teeth that express Msx2. In incisors studied at an early appositional phase, Msx2 is widely expressed in the tooth, primarily in ovoid preodontoblasts and subjacent dental papilla cells. Osc is detected only in a small number of maturing odontoblasts that also express ␣ 1 (I) collagen (Col1a1) and that are postproliferative (do not express histone H4). Msx2 expression greatly overlaps both histone H4 and Col1a1 expression in ovoid preodontoblasts and dental papilla cells. By the late appositional phases of E18.5 and neonatal teeth, Osc mRNA is highly expressed in mature columnar odontoblasts adjacent to accumulating dentin. In appositional bell-stage molars, reciprocal patterns of Msx2 and Osc are observed in adjacent preodontoblasts and odontoblasts within the same tooth. Osc is expressed in mature columnar odontoblasts, while Msx2 is expressed in adjacent immature ovoid preodontoblasts. In less mature teeth populated only by immature ovoid preodontoblasts, only Msx2 is expressed--no Osc is detected. Thus, Msx2 and Osc are expressed in reciprocal patterns during craniofacial development in vivo, and Msx2 expression in preodontoblasts clearly preceeds Osc expression in odontoblasts. In functional studies using MC3T3-E1 calvarial osteoblasts, Msx2 suppresses endogeneous Osc, but not osteopontin, mRNA accumulation. In toto, these data suggest that Msx2 suppresses Osc expression in the craniofacial skeleton at stages immediately preceeding odontoblast and osteoblast terminal differentiation. (J Bone Miner Res 1998;13:609-619)

MINT, the Msx2 Interacting Nuclear Matrix Target, Enhances Runx2-dependent Activation of the Osteocalcin Fibroblast Growth Factor Response Element

“…During odontogenesis, where stage-specific gene expression programs are spatially resolved, Msx2 and OC are reciprocally expressed (14). Consistent with this, stable expression of Msx2 in MC3T3E1 calvarial osteoblasts suppresses OC, but not osteopontin (OPN), gene expression (14). Unlike recent observations demonstrating that activation of early osteogenic differentiation (e.g.…”

“…PCR primers used for OC ChIP were 5Ј-TAT GAG AGT TGG AGC CCA GTT TAT C-3Ј and 5Ј-CCC TAG AGA CAA GAA CCC TAT GCA T-3Ј directed to the mouse OC (OG2) proximal promoter (GenBank accession number U66848). As a control, the osteopontin promoter gene was amplified because it is not affected by Msx2 (14). Osteopontin genomic PCR primers were 5Ј-CAC AAA ACC AGA GGA GGA AGT GT-3Ј and 5Ј-GGT CCA GAC AGT CTC CAC CAA-3Ј directed against the murine OPN proximal promoter (GenBank™ accession number AY220127.1).…”

“…This is best exemplified by Msx2-dependent suppression of the os-teocalcin (OC) 1 gene in teeth and calvarial osteoblasts (13)(14)(15)(16). During odontogenesis, where stage-specific gene expression programs are spatially resolved, Msx2 and OC are reciprocally expressed (14). Consistent with this, stable expression of Msx2 in MC3T3E1 calvarial osteoblasts suppresses OC, but not osteopontin (OPN), gene expression (14).…”

“…However, Msx2 also clearly functions to delay the timing of osteoblast terminal differentiation. This is best exemplified by Msx2-dependent suppression of the os-teocalcin (OC) 1 gene in teeth and calvarial osteoblasts (13)(14)(15)(16). During odontogenesis, where stage-specific gene expression programs are spatially resolved, Msx2 and OC are reciprocally expressed (14).…”

The Wnt antagonist secreted frizzled‐related protein‐1 controls osteoblast and osteocyte apoptosis

“…In addition, transcription factors like Twist [Lee et al, 1999], Msx-2 [Bidder et al, 1998], and Osterix [Nakashima et al, 2002] are also known to play important roles in regulating osteogenesis [Marie, 2001;Yang and Karsenty, 2002]. Many studies have documented the differential expression of these and other genes during OB differentiation using a variety of in vitro models [Harris and Harris, 2002;Stains and Civitelli, 2003].…”