Four paralog gelsolin genes are differentially expressed in the earthworm Lumbricus terrestris

We have identified and characterized four distinct variants of the gelsolin-related protein (EWAM P1-P4) in the earthworm L. terrestris. All of these proteins biochemically qualify as gelsolins since they sever actin filaments in a calcium dependent manner. P1, P2 and P3 are present in the Lumbricus body wall muscle whereas in the gizzard muscle P3 and P4 were found. P1-P4 are encoded by four paralog genes and are differentially expressed in various muscle cell tissues. While the genes for P1 and P2 contain one intron, there was no intron in both P3 and P4 genes. The coding sequences consist of 1104bp (368 amino acids) for P1/P4 and 1101bp (367 amino acids) for P2/P3. Corresponding genes were confirmed by northern blot analysis which revealed three (calculated lengths: 3100, 2300 and 2100 nucleotides) and two (calculated lengths: 2300 and 1700 nucleotides) mRNA transcripts in the body wall and the gizzard, respectively. EWAM mRNA was localized by fluorescence in situ hybridization in the body wall and the gizzard muscle. P1 mRNA was detected in the inner proximal layers of both the circular and longitudinal muscle of the body wall whereas in the gizzard no significant staining was observed for P1. P2-P4 mRNAs were abundant in the outer distal layers of both the circular and the longitudinal muscles of both body wall and gizzard. The differential expression of four paralog gelsolin genes suggests a functional adaptation of different muscle cells with respect to actin filament turnover and modulation of its polymer state.