Journal of Dental Research, Vol 69, 1508-1511, Copyright © 1990 by International & American Associations for Dental Research Online Journals
Evidence for uptake of basement membrane by differentiating ameloblasts in the rat incisor enamel organ
T. Sawada, T. Yamamoto, T. Yanagisawa, S. Takuma, H. Hasegawa and K. Watanabe
Department of Oral Pathology, Tokyo Dental College, Chiba, Japan.
Demonstration of type-IV collagen and acid phosphatase (ACPase) was carried
out in the rat incisor enamel organ after the animals were fixed by
perfusion with periodate-lysine-paraformaldehyde. Their incisors were
dissected out, demineralized with EDTA, and prepared into 6-microns-thick
frozen sections. The sections, which had been treated by means of antibody
incubation for type-IV collagen, were washed with a Trismaleate buffer,
incubated in Novikoff's medium for acid phosphatase (ACPase), and then
incubated in a 3, 3'-diaminobenzidine solution. After osmification, the
sections were embedded in epoxy resin for electron microscopy. The plasma
membranes of the distal ends of the inner-enamel-epithelial cells were
relatively even and were lined with a basement membrane. Type-IV collagen
was localized both in the lamina densa and in the filaments attached to the
lamina densa. In differentiating ameloblasts, the remarkably undulating
distal plasma membranes formed irregular shallow and deep invaginations,
and small cytoplasmic processes that penetrated the basement membrane.
Coated pits occurred in various parts of these undulating plasma membranes.
Positive reaction to type-IV collagen was observed in the invaginations and
coated pits. ACPase-positive granules, present in inner-enamel-epithelial
cells, increased in number and sometimes appeared close to both shallow and
deep invaginations of differentiating ameloblasts. These results indicate
that type-IV collagen in the basement membrane of the enamel organ is
removed and degraded by differentiating ameloblasts by means of their
engulfing system.
