POHYBOVÉ ÚSTROJÍ - Společnost pro pojivové tkáně

molecules of 26 KDa and below, contact is, at functional roles over the course of its rather
the very least, likely to be associated with the unique life cycle.
N-terminal since this is the only domain that The organic matrix of enamel consists of
contains amine groups. Once processing two major classes of matrix proteins, the
reduces amelogenin to below 18 KDa, amelogenins and nonamelogenins.
amelogenins become soluble prior to their Amelogenins are enriched throughout the
removal from the tissue. Such an arrangement forming enamel layer but are present in
would preserve matrix micro-architecture lowest abundance near the plasma
during processing and maintain the regular membranes of ameloblasts at enamel growth
disposition of crystals while accommodating sites. These proteins apparently form
and perhaps controlling their growth. "supramolecular aggregates" a short distance
away from the cell which may play a role in
regulating mineral deposition. While
M A T R I X - M E D I A T E D amelogenins are present in forming mantle
MINERALIZATION 1N ENAMEL AND predentin before terminal differentiation of
COLLAGEN-BASED HARD TISSUES odontoblasts, nonamelogenins such
A. Nanci and C.E. Smith ameloblastin are only found extracellularly
Faculty of Dentistry, Université de when the "real" enamel layer starts to grow
Montréal, P.O. Box 6128, Station Centre- and mineralize. Nonamelogenins generally
Ville, Montreal, QC, Canada H3C 3J7 and show a reverse distribution compared to
Faculty of Dentistry, McGill University, amelogenins - they accumulate at enamel
Montreal, QC, Canada growth sites where crystallites are actively
Enamel is widely considered to be forming and elongating. Studies with protein
different from other hard tissues because it synthesis inhibitors and region-specific
has a unique structure and chemical antibodies suggest these proteins rapidly
composition, there are no cells or "live" cell fragment and partially degrade soon after they
processes embedded in it, and it does not are secreted. Thus, some enamel matrix
show a mineralization front delineating proteins appear to promote development and
unmineralized and mineralized areas as it elongation of crystallites while others seem
develops. The ends of forming enamel more supportive. The absence of a thick,
crystallites instead abut directly against the unmineralized pre-enamel layer therefore
apical membrane of ameloblasts at sites may not necessarily denote a major difference
where matrix proteins are secreted during the in mineralization mechanisms, but rather a
appositional growth phase. These differences variation in the rate at which analogous events
relate in part to the basic origin of enamel as a take place. For example, the relatively high
secretory product of epithelial cells and to the proline content and insoluble nature of
distinct nature of the matrix proteins they amelogenins suggest similarities to collagen
express. Like other hard tissues, enamel which functions mainly to provide physical
undergoes major chemical and physical support and an environment conductive to
changes as it ages. In the case of bone, deposition of an organized mineral phase.
modelling and remodelling result from the Amelogenins could have the same role as well
activity of cells derived from different as an additional one related to influencing rate
lineages. In enamel, there are only of growth in the width and thickness of
ameloblasts applied directly to the forming enamel crystallites dependant on their
surface and, thus, this cell assumes many removal during maturation. In this context,
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