Absence of a Transcription Factor Halts Tooth Development in Mid-Stride

Source: University of Alabama at Birmingham

Summary: Researchers have found a key role in tooth development for the transcription factor Specificity protein 7, or Sp7. Lack of Sp7 interrupts the maturation of two types of specialized cells that help create teeth.

Transcription factors are proteins that interact with DNA to turn genes on or off. In embryos, they guide differentiation from the single fertilized egg into all cells that form the different tissues and structures of the body. One of those complex structures is the tooth. It was previously known that Sp7 is required for bone development. Embryos with a double mutation in Sp7 completely lack mineralized bone. In humans, mutation of the Sp7 gene causes osteogenesis imperfecta, a condition that affects the development of bones and craniofacial structures. However, the role of Sp7 in embryonic tooth development was unknown. Researchers from the University of Alabama at Birmingham have found that lack of Sp7 interrupts the maturation of two types of specialized cells that help create teeth. The study findings were published in the journal Journal of Bone and Mineral Research.

Transcription Factor

From left: Amjad Javed, Ph.D., and Haiyan Chen. Credit: University of Alabama at Birmingham

Through the study of mice lacking Sp7, the team found that initial tooth morphogenesis was normal, even though the animals lacked mineralized tooth sockets. However, tooth development did not continue the animals failed to produce normal dentin, the hard tissue that forms the bulk of the tooth, and they failed to produce normal enamel, the super-hard matrix layer that covers the tooth. This was due to reduced proliferation, maturation and polarization of the tooth-forming cells called odontoblasts and ameloblasts. Without Sp7, the animals had small, misshapen teeth, and the odontoblasts and ameloblasts failed to mature beyond the pre-odontoblast and pre-ameloblast stage, as measured by the absence of mature cell markers for those two types of cells. The odontoblasts and ameloblasts were fewer in number and showed disorganized alignments.

Such basic knowledge about the development of teeth or bones adds to the understanding of craniofacial abnormalities, which are among the most common birth defects in humans.

More Information: Ji-Myung Bae et al, “Specificity Protein 7 Is Required for Proliferation and Differentiation of Ameloblasts and Odontoblasts”, Journal of Bone and Mineral Research (2018). DOI: 10.1002/jbmr.3401 

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