Characterization of a mouse amelogenin [A−4]/M59 cell surface receptor

Identification of the functional activity of the [A-4] amelogenin gene splice product in newborn mouse ameloblasts

“…Furthermore, we demonstrated that in tooth organ cultures, the M59/ [A−4] isoform, secreted by maturing mouse odontoblasts before the onset of dentin mineralization, had a direct affect on ameloblast terminal differentiation (14). The present study was undertaken to examine whether r[A−4] binding and uptake in newborn ameloblasts involves LAMP1, as previously observed by us in an in vitro model of fibroblasts (15) In fibroblasts, r[A−4] was shown to bind to cell surface LAMP1 (15). The conventional RT-PCR data demonstrated that untreated LS8 cells constitutively express abundant LAMP1 message (Figure 1), and subsequent examination by immunocytochemistry demonstratetd that the LS8 cells express abundant cell surface ( Figure 3A) and vesicular endosomal/lysosomal LAMP1 ( Figure 4A, D).…”

“…However, as maturation proceeds, cell specific factors, that is factors uniquely produced by the cells themselves, come into play. We demonstrated that particular amelogenin isoforms, which are translated from distinct amelogenin gene splice products, do have signaling properties in fibroblasts and tooth germs in culture (12,13,14,15). Furthermore, we demonstrated that in tooth organ cultures, the M59/ [A−4] isoform, secreted by maturing mouse odontoblasts before the onset of dentin mineralization, had a direct affect on ameloblast terminal differentiation (14).…”

“…Recently, we demonstrated that both r[A−4] and r[A+4] can be taken up from the medium and internalized by fibroblasts and intact tooth germs in culture. In particular, [A−4] bound LAMP1, a member of the lysosomal-associated membrane proteins (15). Mouse LAMP3 (CD63), has been identified in the yeast 2-hybrid (Y2H) system as a binding partner for amelogenin (M180), but not for M59/[A−4] (16).…”

“…The developmentally-restricted expression of alternatively spliced transcripts translates into proteins with dissimilar function, regulated by discrete signaling pathways. The M59/[A−4] peptide demonstrated signaling properties exclusive to ameloblast differentiation in embryonic mouse molars (14,15). In contrast, in the postnatal mouse molar, [A−4] changed the expression of molecules important for matrix biomineralization (22).…”

“…Selective co-expression of [A−4] and M180 in newborn mouse ameloblasts, committed toward terminal differentiation, suggests reciprocal regulation (10). Binding of [A−4] to LAMP1 has been identified in fibroblasts in vitro (15) …”