Genexpression während der Zahnentwicklung der Maus (Mus musculus)

Gene expression in the tooth development of mice (Mus musculus) The
development of teeth and jaw bones are lead by mechanisms that
determine cells to become, teeth, bones or cartilages. The
ectomesenchymal cells of the lower jaw receives signals from
overlying epithelium to differentiate into odontoblasts,
osteoblasts and chondrocytes. Cells from the neural crest are
influenced by ectodermal signals. An early signal (Fgf8) comes from
the oral epithelium and induces the development of the lower jaw.
Molar morphogenesis in the maxillary starts from the mesenchyme,
influenced by genes like Barx1, Dlx2 and Dlx2. At the same time the
absence of genes like Msx1 and genes from the Alx-family is
necessary for a normal development (McCollum and Sharpe, 2001). The
expression of Msx1 and Alx-genes causes the development of
incisors. Mice with null mutation of Dlx1 and Dlx2 fail to develop
maxillary molars. Also additional abnormalities appear in the upper
jaw. All other teeth are regularly developed (Qiu et al., 1997;
Thomas et al., 1997). Dlx5 and Dlx6 are believed to be involved in
the development of the lower molar teeth. Ectopic expression of
Barx1 in the distal mandibular mesenchym, accompanied by loss of
Msx1, results in a transformation of incisors into molars (Tucker
et al., 1998). Msx1 mutant mice have defects in the distal jaw
skeletal tissue. In conclusion, genes that determine the expression
of molar teeth also control the development of the proximal jaw and
genes that regulate incisor morphogenesis also regulate distal jaw
development (McCollum and Sharpe, 2001). Generation of canine and
premolar teeth is caused by overlapping domains of homeobox genes
like Msx1, Dlx1 and Dlx2. In mice, the development of teeth in the
maxilla seems to be different compared to the mandibula. Activin ßA
null mutant mice shows no incisor and molar teeth in the lower jaw.
Growth of teeth stops at bud stage in the mandibula while tooth
development in the upper jaw in unaffected (Matzuk et al., 1995b).
Most of the basic genetic mechanisms during the development of the
teeth in the upper and lower jaw are identical. Only some of them
lead into a different developmental pattern. This could be due to
the different origin of mesenchymal cells (McCollum and Sharpe,
2001). The lower jaw is formed by ectomesenchymal cells originating
from the neural crest from the cranial rostral hindbrain and the
caudal middlebrain while neural crest cells from the caudal
forebrain and middlebrain contribute to the fronto-nasal region
(Osumi-Yamashita et al., 1994).