|
|
||||||||
RAPID COMMUNICATION |
School of Dentistry, Dept. of Oral Biology, University of Missouri-Kansas City, 650 E. 25th St., Kansas City, MO 64108;
* corresponding author, fengj{at}umkc.edu
| ABSTRACT |
|---|
|
|
|---|
KEY WORDS: Bmp4 transgenic mice tooth development promoter
| INTRODUCTION |
|---|
|
|
|---|
Bone morphogenetic protein 4 (Bmp4) is an essential growth factor for embryo development, because it plays a significant role in a large number of developmental systems, such as branching morphogenesis of the lung, lens development, neuroepithelial cell differentiation, primordial germ cell formation, and hair, whisker, and feather formation (Hogan, 1996, 1999; Furuta and Hogan, 1998; Jung et al., 1998; Noramly and Morgan, 1998; Oro and Scott, 1998; Lawson et al., 1999). Recent evidence also suggests that Bmp4 is crucial for tooth formation. First, Bmp4 is expressed in dental epithelium during the initiation of tooth development. Shortly afterward, in the early bud stage, the expression shifts to the dental mesenchyme (Chen and Maas, 1998). This shift of the Bmp4 expression pattern is consistent with the known pattern of sequential and reciprocal epithelial-mesenchymal interactions (Thesleff and Sharpe, 1997). Second, in vitro application of recombinant Bmp4 to the dental mesenchyme mimics the action of dental epithelium during the induction of tooth development. This includes both the morphological changes and the expression of several genes such as Msx1, Msx2, Lef1, and Bmp4 itself (Vainio et al., 1993; Chen et al., 1996; Kratochwil et al., 1996; Thesleff and Sahlberg, 1996). Third, exogenous Bmp4 can partially rescue arrested tooth development in Msx1 mutant mice. These mice display an early arrest of tooth formation and a marked reduction of Bmp4 in the molar mesenchyme (Satokata and Maas, 1994; Chen et al., 1996). Finally, Bmp4 has been linked to determining the sites of tooth development, as well as the type of tooth formed (Neubüser et al., 1997; Tucker et al., 1998).
Understanding the mechanisms underlying the pattern of the temporal and spatial expression of Bmp4 is essential for the identification of the transcriptional factors that are involved in Bmp4 regulation during development. Therefore, we cloned the murine Bmp4 gene, partially characterized its promoter region (Feng et al., 1995), and demonstrated that the domains controlling Bmp4 expression in primordial hair tissues differed from those of mature hair follicles (Feng et al., unpublished observation). Also, the domains controlling Bmp4 expression in hair shaft, hair matrix, and dermal papilla are located in different regions of the Bmp4 gene. The purpose of this study was to determine the extent to which the promoter domains controlling Bmp4 expression in primordial murine teeth were the same as those controlling Bmp4 expression in mature tooth tissues. In addition, we sought to determine if the domains controlling Bmp4 expression during tooth morphogenesis were specific for particular cell types such as odontoblasts or ameloblasts, or for specific types of teeth such as incisors or molars. Using transgenic mice carrying a ß-galactosidase (lacZ) reporter gene driven by different promoter fragments, we have identified a promoter region between -0.26 kb and -1.1 kb of the murine Bmp4 gene that controls its expression in epithelium-derived ameloblasts. We have also demonstrated that regions controlling Bmp4 expression in primordial tooth tissues are different from those controlling its expression in mature teeth.
| METHODS & MATERIALS |
|---|
|
|
|---|
|
|
|
ß-Galactosidase Expression Assay and Immunostaining
b-galactosidase staining was assessed in embryos and newborns according to the method described by Lawson et al. (1999). Briefly, embryos or newborns were fixed with 4% paraformaldehyde for 30 min on ice, and then washed 3 times with PBS for 5 min each. The specimens were then stained overnight in freshly made X-Gal solution (1 mg/mL) at 32°C. ß-galactosidase immunostaining of sections was based on the method described by Liu et al. (1999). Both rabbit anti-lacZ antibody and goat anti-rabbit secondary antibody were obtained from Molecular Probes (Eugene, OR, USA).
Tail PCR Assay
The genotypes of pups were determined by PCR analysis of genomic DNA extracted from tail DNA. Primer 1 (5'-TCTGCTTCAATCAGCGTGCC-3') and anti-sense primer 2 (5'-GCCGTCTGAA TTTGACCTGA-3') were used to identify the lacZ gene.
| RESULTS |
|---|
|
|
|---|
Specifically, the Bmp4 LacZ signal was observed in oral ectoderm at E12.5 (Fig. 1B
), followed by the neural-crest-derived mesenchyme at E13.5 (Fig. 1C
). By stage E15.5 (Fig. 1D
), Bmp4 LacZ signals are highly active in dental follicles, dental organs, dental papilla, and enamel knots. At later differentiation stages, Bmp4 LacZ is expressed in both epithelium-derived ameloblasts, mesenchyme-derived tissues such as odontoblasts, and pulp cells (Figs. 2A, 3A![]()
). It is noteworthy that Bmp4 expression in pulp cells has not been reported before. This is probably due to the fact that the ß-galactosidase inserted into the Bmp4 gene is a highly sensitive expression system. The weak Bmp4 signals in tooth pulp were not detected by in situ hybridization. Bmp4 expression in pulp cells, the odontoblast precursor cells, suggests potential roles of Bmp4 in dentin repair during post-natal life. In addition, Bmp4 expression patterns are very similar in both maxilla and mandible, as well as incisors and molars (Figs. 2, 3![]()
). Analysis of the data suggests that Bmp4 is actively involved in the entire process of tooth morphogenesis, first in the epithelial layer, then in the mesenchyme, and later in all mature tooth tissues, including ameloblasts, odontoblasts, and pulp cells.
The 2.4-kb Murine Bmp4 Promoter is Active in Epithelium-derived Ameloblasts, But Not in Mesenchyme-derived Odontoblasts or Primordial Tooth Tissues
To identify promoter regions controlling Bmp4 expression at different developmental stages and anatomical regions during tooth development, we analyzed LacZ expression in transgenic mice harboring the 2.4-kb Bmp4 promoter LacZ (Bmp4 LacZ2.4p) construct. LacZ expression in these mice was compared with LacZ expression in Bmp4lacZneo knock-in mice at the same developmental stages. As shown in Figs. 2-4![]()
![]()
, LacZ staining is apparent only in the epithelium-derived ameloblast (Figs. 2, 3![]()
), there is no LacZ expression in the mesenchyme-derived odontoblasts or pulp cells, and the pattern of Bmp4 expression is similar in both incisors and molars (Figs. 2, 3![]()
). It is critical to note that while the LacZ signals in somites are similar in Bmp4lacZneo knock-in and Bmp4 LacZ2.4p mouse embryos, there is little LacZ expression during the early stages of tooth morphogenesis (Fig. 1
). This suggests that the domains controlling Bmp4 expression in somites, the primordial tissues for vertebral bone formation, differ from those controlling Bmp4 expression in primordial tooth tissues. Last, Bmp4LacZ signals are detected in tissues such as the tongue, nasal cartilages, bone, and small salivary glands (Figs. 2D, 2G![]()
), while the expression of the LacZ transgene driven by the 2.4-kb promoter fragment is absent in these tissues. This difference may be due to missing control domains or enhancers in the truncated promoter fragment.
|
| DISCUSSION |
|---|
|
|
|---|
Also, we demonstrate that the Bmp4 domains controlling Bmp4 expression in primordial tooth tissues are different from those controlling its expression in mature tooth tissues. While there is strong LacZ expression in Bmp4lacZneo knock-in mice in both primordial tissues. such as the epithelium and the mesenchyme, and the mature tissues, including pulp cells, odontoblasts, and ameloblasts, there is little LacZ expression in primordial tissues from Bmp4LacZ2.4p mice (Fig. 1
). Thus, we propose that domains controlling Bmp4 expression in primordial tooth buds and mature tooth tissues are different (see Fig. 4
for detail). However, we do not have evidence to support a global model to fit other organ morphogenesis such as lungs, kidneys, and buds, because the activity of both the 1.1-kb and the 2.4-kb promoter fragments are too low for analysis of the transgene expression patterns in other organs. Last, the 2.4-kb promoter is active in somites while silent in primordial tooth tissues. This observation suggests that early transcriptional factors for controlling Bmp4 expression in somites are likely different from those for Bmp4 expression in primordial tooth tissues.
In summary, the current working hypothesis for Bmp4 control of tooth morphogenesis may aid in the understanding of the mechanics of epithelial-mesenchymal interactions that are initial steps in the development of many organ systems.
| ACKNOWLEDGMENTS |
|---|
| FOOTNOTES |
|---|
Received May 18, 2001; Last revision November 16, 2001; Accepted November 27, 2001
| REFERENCES |
|---|
|
|
|---|
Chen YP, Bei M, Woo I, Satokata I, Maas R (1996). Msx1 controls reciprocal inductive signaling in mammalian tooth morphogenesis. Development 122:30353044.[Abstract]
Cheng TC, Wallace MC, Merlie JP, Olson EN (1993). Separable regulatory elements governing myogenin transcription in mouse embryogenesis. Science 261:215218.
DiLeone RJ, Russell LB, Kingsley DM (1998). An extensive 3' regulatory region controls expression of Bmp5 in specific anatomical structures of the mouse embryo. Genetics 48:401408.
DiLeone RJ, Marcus GA, Johnson MD, Kingsley DM (2000). Efficient studies of long-distance Bmp5 gene regulation using bacterial artificial chromosomes. Proc Natl Acad Sci USA 97:16121617.
Feng JQ, Chen D, Cooney A, Tsai MJ, Harris MA, Dallas SJ, et al. (1995). The mouse bone morphogenetic protein 4 gene: analysis of promoter utilization in fetal rat calvarial osteoblasts. J Biol Chem 270:2836428373.
Furuta Y, Hogan BLM (1998). BMP4 is essential for lens induction in the mouse embryo. Genes Dev 12(23):37643775.
Hogan BLM (1996). Bone morphogenetic proteins: multifunctional regulators of vertebrate development. Genes Dev 10:15801594.
Hogan BLM (1999). Morphogenesis. Cell 96:225233.[Medline]
Jung HS, Francis-West PH, Widelitz RB, Jiang TX, Ting-Berreth S, Tickle C, et al. (1998). Local inhibitory action of BMPs and their relationship with activation in feather formation: implications for periodic patterning. Dev Biol 196:1123.[Medline]
Kratochwil K, Dull M, Farinas I, Galceran J, Grosschedl R (1996). Lef1 expression is activated by BMP-4 and regulates inductive tissue interactions in tooth and hair development. Genes Dev 10:13821394.
Lawson KA, Dunn NR, Roelen BAJ, Zeinstra LM, Davis AM, Wright CVE, et al. (1999). BMP4 is required for the generation of primordial germ cells in the mouse embryo. Genes Dev 13:424436.
Liu Z, Xie T, Steward R (1999). Lis1, the Drosophila homolog of a human lissencephaly disease gene, is required for germline cell division and oocyte differentiation. Development 126:44774488.[Abstract]
Neubüser A, Peters H, Balling R, Martin GR (1997). Antagonistic interactions between FGF and BMP signaling pathways: a mechanism for positioning the sites of tooth formation. Cell 90:247255.[Medline]
Noramly S, Morgan BA (1998). BMPs mediate lateral inhibition at successive stages in feather tract development. Development 125:37753787.[Abstract]
Oro AE, Scott MP (1998). Splitting hairs: dissecting roles of signaling systems in epidermal development. Cell 95:575578.[Medline]
Satokata I, Maas R (1994). Msx1 deficient mice exhibit cleft palate and abnormalities of craniofacial and tooth development. Nature Genet 6:348356.[Medline]
Thesleff I, Sahlberg C (1996). Growth factors as inductive signals regulating tooth morphogenesis. Semin Cell Dev Biol 7:185193.
Thesleff I, Sharpe P (1997). Signaling networks regulating dental development. Mech Dev 67:111123.[Medline]
Tucker AS, Matthews KL, Sharpe PT (1998). Transformation of tooth type induced by inhibition of BMP signaling. Science 282:11361138.
Vainio S, Karavanova I, Jowett A, Thesleff I (1993). Identification of BMP-4 as a signal mediating secondary induction between epithelial and mesenchymal tissues during early tooth development. Cell 75:4558.[Medline]
This article has been cited by other articles:
![]() |
S. Ruiz, C. Segrelles, A. Bravo, M. Santos, P. Perez, H. Leis, J. L. Jorcano, and J. M. Paramio Abnormal epidermal differentiation and impaired epithelial-mesenchymal tissue interactions in mice lacking the retinoblastoma relatives p107 and p130 Development, June 1, 2003; 130(11): 2341 - 2353. [Abstract] [Full Text] [PDF] |
||||
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
| IADR Journals | Advances in Dental Research ® |
| Journal of Dental Research ® | Critical Reviews (1990-2004) |