Expression profile of active genes in human periodontal ligament and isolation of PLAP-1, a novel SLRP family gene

Periodontal ligament (PDL) is one of the most important tissues in maintain ing the homeostasis of tooth and tooth-supporting tissue, periodontium. In this study, we investigated the expression profile of active genes in the h uman PDL obtained by collecting sequences with a 3'-directed cDNA library, which faithfully represents the composition of the mRNA population. We succ eeded in obtaining a total of 1752 cDNA sequences by sequencing randomly se lected clones and identified a total of 1318 different species as gene sign atures (GS) by their sequence identity, 344 of which were known genes in th e GenBank, and 974 of which were new genes. The resulting expression profil e showed that collagen type land type III were the most abundant genes and that osteogenesis-related proteins, such as SPARC/osteonectin and osteoblas t specific factor 2, were highly expressed. By comparing the expression pro file of PDL with 44 profiles similarly obtained with unrelated human cell/t issue, nine novel genes, which are probably expressed specifically in PDL, were discovered. Among them, we cloned a full-length cDNA of GS5096, which is frequently expressed in freshly-isolated periodontal tissue. We found th at it encodes a novel protein, which is a new member of the class I small l eucine-rich repeat proteoglycan family, and designated it PLAP-1 (periodont al ligament associated protein-1). PLAP-1 mRNA expression was confirmed in in vitro-maintained PDL cells and was enhanced during the course of the cyt odifferentiation of the PDL cells into mineralized tissue-forming cells suc h as osteoblasts and cementoblasts. These findings suggest the involvement of PLAP-1 in the mineralized matrix formation in PDL tissues. (C) 2001 Else vier Science B.V. All rights reserved.