Alternative splicing of ED-A and ED-B sequences of fibronectin pre-mRNA differs in chondrocytes from different cartilaginous tissues and can be modulated by biological factors.

The alternative splicing of the ED-A and ED-B segments of fibronectin pre-mRNA was examined in epiphyseal, costal, and meniscal cartilage from 3-week-old beagles and in nasal, tracheal, articular, and meniscal cartilage from 1- and 2-year-old Labrador retrievers. In contrast to the 100% expression of ED-B(+) mRNA that has been reported for embryonic chick cartilage (Bennett, V.D., Pallante, K.M., and Adams, S.K. (1991) J. Biol. Chem. 266, 5918-5924), all cartilages studied expressed both the ED-B(+) and ED-B(-) forms of fibronectin mRNA with the exception of the trachea, in which expression was 100% ED-B(-). Of all cartilages studied, only the meniscus had detectable levels of ED-A(+) mRNA. Placing articular cartilage chondrocytes in primary monolayer culture dramatically up-regulated the expression of ED-A(+) mRNA to 25% of the total, and this expression was further increased by the addition of transforming growth factor beta 1 or fucoidan to the culture medium. The expression of ED-B(+) mRNA remained at about 18% in the cultured chondrocytes and was not further affected by either transforming growth factor beta 1 or fucoidan. In contrast, dibutyryl cyclic adenosine monophosphate decreased the relative expression of both the ED-A(+) and ED-B(+) forms of fibronectin pre-mRNA. We concluded that the expression of ED-B(+) fibronectin remains relatively high in chondrocytes from cartilaginous canine tissues (15-35%) with the exception of the trachea, in contrast to the less than 10% expression of ED-B(+) fibronectin reported for other non-fetal tissues.