Fig. 7.

A model of adhesion mediated by SP4 and SP1. CADM1 monomers, shown as grey molecules, are inactive in adhesion. When cells adhere, CADM1 forms dimers, shown as red molecules, which are actively involved in adhesion. a Two cells express only SP4, which forms active dimers involved in cell adhesion. b Two cells express both SP4 and SP1 (molecule with additional protein sequence encoded by exon 9, shown as a blue box in SP1 stalk near cell membrane) with the same density along cell membrane (orange line). Because SP4 and SP1 extracellular domains have different lengths, they cannot align properly and form dimers. The total number of CADM1 dimers, involved in cell adhesion, is reduced on the cell surface. However, over time, most of the CADM1 molecules would be able to find a matching partner to dimerise with and cells would be able to adhere as strongly as cells expressing only one CADM1 isoform