
M. Raspanti / J. Biomedical Science and Engineering 3 (2010) 1169-1174 1173
find its way into histology textbooks. We must take care
not to repeat the original sin of studying only tendons,
and then ascribe what we found here to all other tissues.
Fibrils with helical subfibrils are the most common
among our different tissues. Our data indicate that the
current knowledge on the fibrillogenesis process, all
gained on tendons, does not apply to these fibrils, and
that new research is required.
The next primary objective will be the identification
of the molecular switch controlling the initiation of one
or the other subfibrillar architecture, and which has so
far eluded detection. Fibrillogenesis is a delicate process
which can be influenced by myriad causes, some of
which do not even remain to make up the final product.
Perhaps the most promising candidate appears now
type V collagen. Almost since its discovery the type V
has associated with the control of fibril diameter [28],
and more recently it seems to be essential for fibril for-
mation in vivo: homozygote engineered organisms lack-
ing type V die at embryonic day 10 of cardiovascular
failure, while heterozygotes are viable but lack about
half their collagen fibrils [29].
It seems therefore not unreasonable to hypothesize
that type V collagen is involved in the formation of
slender, uniform fibrils in cornea, blood vessels and
sheaths, but obviously not in tendon and ligaments
where it appears only in traces. Further research is un-
derway.
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