EXPRESSION OF AN EMBRYONIC FIBRONECTIN SPLICING VARIANT IN HUMAN MASSETER MUSCLE

Fibronectin is an extracellular matrix protein that is a key constitue nt of all skeletal muscles. Its deposition increases in a number of pa thological conditions, including some muscular dystrophies in which a progressive increase in lower-face height is often noted. It has been shown in other organ systems that increased deposition of fibronectin is associated with changes in the expression of differentially spliced isoforms of the molecule. This investigation documents the expression of mRNA coding for fibronectin and its splicing variants, EIIIA and E IIIB, in biopsies of masseter muscle from normal and long-face patient s, using reverse transcriptase-polymerase chain reaction. Expression w as compared with that occurring in anatomically and embryologically di ffering somatic skeletal muscle. Masseter expressed fibronectin mRNA c ontaining the EIIIA but not the EIIIB splicing variant. Conversely, so matic skeletal muscle expressed neither the EIIIA nor EIIIB variants. There were no differences between expression of fibronectin containing the EIIIA splicing variants in masseter from normal and long faces. T hese results suggest that variations in fibronectin expression reflect the differing functional demands of muscles from different anatomical locations and indicate that jaw and somatic muscle belong to differen t allotypes. (C) 1998 Elsevier Science Ltd. All rights reserved.