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How do mineralized tissues form?
Mineralized tissues form in extracellular spaces, the
contents of which are determined by specialized cells that
line the space. Collagen-based extracellular matrices are
extremely ancient, and are associated with the emergence
of multicellularity. Sponges, for instance, which diverged
from the line leading to vertebrates perhaps a billion years
ago express fibrillar collagen. SPARC , the ancestor of the
SCPP gene family, encodes a basement membrane protein.
Collagen-based extracellular matrices must have
evolved for many millions of years prior to the onset of
biomineralization. Interestingly, the SCPPs share only a
small region of similarity with SPARC . This region includes
the signal peptide, the signal peptide cleavage site,
and a Golgi casein kinase phosphorylation site (SXE)
near the amino-terminus of the secreted protein. Therefore
the fundamental features shared by the SCPP family
are the targeting system for secretion into the extracellular
environment where mineralization occurs and a
near N-terminal phosphoserine that might be involved in
calcium binding.
Source:
- Molecular Evolution and Genetic Defects of Teeth, Cells Tissues Organs, 2007