Many genes that interact in a complex and interdependent manner participate in the development of the craniofacial complex. One of them, the Msxl homeobox gene, a transcription factor, is expressed from early developmental stages to adulthood in accordance with specific spatio-temporal patterns. When it is suppressed, transgenic mice exhibit craniofacial abnormalities that demonstrate what is its function in normal growth, just as it has been shown that certain Msxl mutations in humans are commonly associated with tooth agenesis.