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Eukaryotic Cell doi:10.1128/EC.00464-07
Copyright (c) 2008, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Overlapping functions of the two talin homologues in Dictyostelium

National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba Central 4, 1-1-1 Higashi, Tsukuba, Ibaraki 305-8562, Japan; RIKEN, Center for Developmental Biology, 2-2-3 Minatojima-minamimachi, Chuo-ku, Kobe 650-0047, Japan; Department of Botany, Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan; Institute for Cell Biology (ABI), Ludwig Maximilians University, Schillerstr. 42, 80336 Munich, Germany

^* To whom correspondence should be addressed. Email: mas-tsujioka{at}cdb.riken.jp.

	Abstract

Talin is a cytoskeletal protein involved in constructing and regulating focal adhesions in animal cells. The cellular slime mould Dictyostelium discoideum has two talin homologues, talA and talB, and earlier studies have characterized the single knock-out mutants. TalA^- cells show reduced adhesion to the substrates and slightly impaired cytokinesis leading to a high proportion of multinucleated cells in the vegetative stage while the development is normal. In contrast, talB^- cells are characterized by reduced motility in the developmental stage, and are arrested at the tight mound stage. Here, we created and analyzed a double mutant disrupting both talA and talB. Defects in adhesion to the substrates, cytokinesis, and development were severer in talA^-/talB^- cells. TalA^-/talB^- cells failed to attach to the substrates in the vegetative stage, exhibited a higher proportion of multinucleated cells than talA^- cells, and showed more reduced motility during the development and an earlier developmental arrest than talB^- cells at the loose mound stage. Moreover, overexpressions of either talA or talB compensated the loss of the other talin, respectively. The analysis of talA^-/talB^- cells also revealed that talin was required for the formation of paxillin-rich adhesion sites and that there was another adhesion mechanism which is independent of talin in the developmental stage. This is the first study demonstrating overlapping functions of two talin homologues, and our data further indicate the importance of talin.