Localization of type I myosin and F-actin to the leading edge region of the forespore membrane in Schizosaccharomyces pombe.
Myo1, a heavy chain of type I myosin of the fission yeast Schizosaccharomyces pombe, is essential for sporulation. Here we have analyzed the expression, localization and cellular function of the type I myosin light chain calmodulin, Cam2, encoded by cam2(+). Transcription of cam2(+) was constitutive and markedly enhanced in meiosis. The cam2 null mutant was viable and completed sporulation normally at 28 degrees C, but formed four-spored asci poorly at 34 degrees C. In those sporulation-defective cells, the forespore membrane was formed abnormally. A Cam2-GFP fusion protein accumulated at the cell poles in interphase cells and at the medial septation site in postmitotic cells, colocalizing with Myo1 and F-actin patches. During the mating process, a single Cam2-GFP dot was detected at the tip of the mating projection. During meiosis-I, the Cam2-GFP dots dispersed into the cell periphery and the cytoplasm. At metaphase-II, intense Cam2-GFP signals appeared near Meu14 rings which were formed at the leading edge of expanding forespore membranes. This localization of Cam2 was dependent upon Myo1; and sporulation defect of cam2Delta at 34 degrees C was alleviated by overexpressing Myo1DeltaIQ. These results suggest a close relationship between Cam2 and Myo1. In addition, both F-actin and Myo1 localized with Cam2 in the leading edge region. In summary, type I myosin and F-actin accumulate at the leading edge area of the forespore membrane and may play a pivotal role in its assembly.
Itadani
Akiko
A
Department of Biology, Graduate School of Science, Osaka City University, Sumiyoshi-ku, Osaka 558-8585, Japan.
Nakamura
Taro
T
Shimoda
Chikashi
C
D000199:Actins / Q000235:genetics / Q000378:metabolism*; D000595:Amino Acid Sequence; D002147:Calmodulin / Q000032:analysis / Q000235:genetics / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism*; D015966:Gene Expression Regulation, Fungal; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics; D024461:Myosin Type I / Q000235:genetics / Q000378:metabolism*; D010641:Phenotype; D012333:RNA, Messenger / Q000378:metabolism; D012568:Schizosaccharomyces / Q000378:metabolism*; D029702:Schizosaccharomyces pombe Proteins / Q000032:analysis / Q000378:metabolism*; D013172:Spores, Fungal / Q000737:chemistry / Q000378:metabolism*
D000199:Actins; D002147:Calmodulin; C518784:Cam2 protein, S pombe; D012333:RNA, Messenger; D029702:Schizosaccharomyces pombe Proteins; D024461:Myosin Type I