title: Diphosphorylated but not monophosphorylated myosin II regulatory light chain localizes to the midzone without its heavy chain during cytokinesis.
abstract: Myosin II is activated by the monophosphorylation of its regulatory light chain (MRLC) at Ser19 (1P-MRLC). Its ATPase activity is further enhanced by MRLC diphosphorylation at Thr18/Ser19 (2P-MRLC). As these phosphorylated MRLCs are colocalized with their heavy chains at the contractile ring in dividing cells, we believe that the phosphorylated MRLC acts as a subunit of the activated myosin II during cytokinesis. However, the distinct role(s) of 1P- and 2P-MRLC during cytokinesis has not been elucidated. In this study, a monoclonal antibody (4F12) specific for 2P-MRLC was raised and used to examine the roles of 2P-MRLC in cultured mammalian cells. Our confocal microscopic observations using 4F12 revealed that 2P-MRLC localized to the contractile ring, and, unexpectedly, to the midzone also. Interestingly, 2P-MRLC did not colocalize with 1P-MRLC, myosin II heavy chain, and F-actin at the midzone. These results suggest that 2P-MRLC has a role different from that of 1P-MRLC at the midzone, and is not a subunit of myosin II.
authors.affiliation: Department of Biological Science, Graduate School of Science, Hiroshima University, Higashi-Hiroshima 739-8526, Japan.
authors.forename: Tomo
authors.initials: T
authors.lastname: Kondo
authors.forename: Rieko
authors.initials: R
authors.lastname: Isoda
authors.forename: Takashi
authors.initials: T
authors.lastname: Uchimura
authors.forename: Mutsumi
authors.initials: M
authors.lastname: Sugiyama
authors.forename: Kozue
authors.initials: K
authors.lastname: Hamao
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Hosoya
mesh_terms: D000911:Antibodies, Monoclonal; D048749:Cytokinesis; D006367:HeLa Cells; D006801:Humans; D018994:Myosin Light Chains / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation
chemical_list: D000911:Antibodies, Monoclonal; C466107:MRLC2 protein, human; D018994:Myosin Light Chains