ABSTRACT
BACKGROUND: Previously we have reported on the development of a new mouse anti-titin monoclonal antibody, named MAb Titl 5 H1.1, using the synthetic peptide N-AVNKYGIGEPLESDSVVAK-C which corresponds to an amino acid sequence in the A-region of the titin molecule as immunogen. In the human skeletal muscles, MAb Titl 5 H1.1 reacts specifically with titin in the A-band of the sarcomere and in different non-muscle cell types with nucleus and cytoplasm, including centrioles. In this report we have studied the evolutionary aspects of the binding of MAb Tit1 5 H1.1 with its target antigen (titin). RESULTS: We have specified the epitope area of MAb Tit1 5 H1.1 by subpeptide mapping to the hexapeptide N-AVNKYG-C. According to protein databases this amino acid sequence is located in the COOH-terminus of several different Fn3 domains of the A-region of titin molecule in many organisms, such as human being, mouse, rabbit, zebrafish (Danio rerio), and even in sea squirt (Ciona intestinalis). Our immunohisto- and cytochemical studies with MAb Tit1 5 H1.1 in human, mouse and zebrafish tissues and cell cultures showed a striated staining pattern in muscle cells and also staining of centrioles, cytoplasm and nuclei in non-muscle cells. CONCLUSIONS: The data confirm that titin can play, in addition to the known roles in striated muscle cells also an important role in non-muscle cells as a centriole associated protein. This phenomenon is highly conserved in the evolution and is related to Fn3 domains of the titin molecule. Using titin A-band-specific monoclonal antibody MAb Tit1 5 H1.1 it was possible to locate titin in the sarcomeres of skeletal muscle cells and in the centrioles, cytoplasm and nuclei of non-muscle cells in phylogenetically so distant organisms as Homo sapiens, Mus musculus and zebrafish (Danio rerio).
ABSTRACT
We report the development of a new mouse anti-titin monoclonal antibody, named MAb Tit1 5H1.1, using the synthetic peptide corresponding to an amino acid sequence in the A-band of the titin molecule as immunogen. In the human skeletal muscle, MAb Tit1 5H1.1 reveals a clearly striated staining pattern, reacting with the A-band of the sarcomere. Electrophoretic, immunoblotting, and amino acid sequence analyses with ESI-MS/MS of human skeletal muscle tissue proved the target antigen of MAb Tit1 5H1.1 to be titin. The antibody reacts with titin also in non-muscle cells, producing a punctate pattern in cytoplasm and the nucleus. The most striking finding was a clear reaction of MAb Tit1 5H1.1 with centrioles in all cell types investigated so far. Immunocytochemical co-localization study with ninein-specific antibodies confirmed that the target antigen of MAb Tit1 5H1.1 is a centriole-associated protein. Experiments of the inhibition of synthesis of titin using titin siRNA duplex for the destruction of titin mRNA have shown a decreased staining of centrioles by MAb Tit1 5H1.1 in non-muscle cells and support the proposal that the target antigen of MAb is indeed titin. We suggest this anti-titin monoclonal antibody could be a valuable tool in the study of titin function and its subcellular location, both in muscle and non-muscle cells.
