Differential expression of laminin α chains during murine tooth development

Abstract

Basement membranes of the developing tooth have been previously shown to contain laminins, but the nature of the laminins have not been described. We here studied the distribution of five different laminin α chains during tooth development. We show that both epithelial and mesenchymal cells produce laminin α chains. The mRNAs of three laminin α chains, α1, α2, and α4, were expressed in the tooth mesenchyme, whereas two, the α3 and α5 chain mRNAs, were found in epithelium. Drastic changes in the expression patterns of the two epithelial chains were found during development. The α5 mRNA was widely expressed in tooth epithelia, and the corresponding protein was evenly distributed along the tooth basement membrane throughout embryonic development. This suggests a role for α5 as a major laminin α chain in tooth basement membrane during embryonic stages. The subsequent disappearance of α5 and the drastic increase in α3A mRNA expression during terminal ameloblast differentiation and enamel secretion suggest that α3A acts as an important chain in the enamel matrix after degradation of tooth basement membrane. These studies show that laminin networks in tooth epithelia form as a result of epithelial–mesenchymal interactions and that the molecular composition of the laminin networks varies drastically during development of tooth. Dev. Dyn. 1997;210:206–215. © 1997 Wiley‐Liss, Inc.

Review: Extracellular Matrix Regulates Tooth Morphogenesis

“…Laminin α1 mRNA expression can be detected in the dental mesenchyme, dental papilla, and dental sac throughout embryonic tooth development ( Figure 1) [17], whereas adjacent nondental mesenchyme shows a weaker expression. On postnatal day (P) 1, this expression is lost from the dental papilla, including that form functional odontoblasts that secrete dentin matrix and becomes localized in the polarized odontoblasts below the secretory odontoblasts.…”

“…Laminin α1 protein expression has been detected in the dental papilla as well as in the dental basement membrane [17]. Laminin α2 is expressed in the preameloblast and preodontoblast interfaces and also is localized in odontoblasts, the outer side of the dental epithelium including the papillary cell layer, capillaries, and the muscle basement membrane ( Figure 1) [18].…”

Laminins 2 (α2β1γ1, Lm-211) and 8 (α4β1γ1, Lm-411) are synthesized and secreted by tooth pulp fibroblasts and differentially promote neurite outgrowth from trigeminal ganglion sensory neurons

“…On the other hand, detection of LNa1 chain, most likely as LN-1, in the nerves was unexpected, since expression of this chain is known to be highly restricted to some epithelia in adult stages and not to be associated with nerves under normal conditions [18,20]. Whether this finding relates to the reported LNa1 mRNA expression in developing tooth mesenchyme and the immunohistochemical detection of LNa1 chain in tooth dentin is presently unknown [13,18]. However, LNa1 expression by the nerve bundles may relate to the strong neurite promoting activity of LN-1 originally reported over 20 years ago [36], and now reproduced with TG neurons.…”

“…As demonstrated by in situ hybridization, mesenchymal cells produce transcripts for LNa1, a2 and a4, while a3 and a5 are found in dental epithelium [13]. The LNg2 chain is expressed in dental epithelium and ameloblasts [14,15] and, together with LNa3 and h3 chains, forms LN-5 (a3h3g2, Lm-332), which has a key function in tooth morphogenesis [14,16,17].…”

Putative role of basement membrane for dentinogenesis in the mesenchyme of murine dental papillae in vitro

“…Furthermore, since small amounts of nidogen would lead to very small amounts of affinity complex with the γ1 chain, BM may not be formed. Overall, each of the BM components seems to be derived from the mesenchyme, although very little α1 chain is probably secreted compared with the other chains (Martin and Timpl 1987;Ekblom et al 1990;Salmivirta et al 1997). The present results are similar to findings regarding the formation of BM-like structures at the periphery of mesenchymal cells (Sawada 1995;Vanderberg and Hay 1997) and to reports that BM is not formed in the absence of the polymerisation of laminin (DeArcangelis et al 1996;Smyth et al 1999).…”