Mechanical signals transmitted through the cytoplasmic actin cytoskeleton must be relayed to the nucleus to control gene expression. LIM domains are protein-protein interaction modules found in cytoskeletal proteins and transcriptional regulators. Here, we identify three LIM protein families (zyxin, paxillin, and FHL) whose members preferentially localize to the actin cytoskeleton in mechanically stimulated cells through their tandem LIM domains. A minimal actin-myosin reconstitution system reveals that representatives of all three families directly bind F-actin only in the presence of mechanical force. Point mutations at a site conserved in each LIM domain of these proteins disrupt tensed F-actin binding in vitro and cytoskeletal localization in cells, demonstrating a common, avidity-based mechanism. Finally, we find that binding to tensed F-actin in the cytoplasm excludes the cancer-associated transcriptional co-activator FHL2 from the nucleus in stiff microenvironments. This establishes direct force-activated F-actin binding as a mechanosensing mechanism by which cytoskeletal tension can govern nuclear localization.
tensed
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Many options have been envisaged to avoid these undesirable consequences. One option is denying that future-tensed statements are bivalent (Broad 1923, Markosian 1995). However, this view is subject to criticism too since (i) it conflicts with retrospective evaluations of future-tensed statements (Besson & Hattiangadi 2013, MacFarlane 2003, 2008), and (ii) it is not clear what semantics one ought to assume when modeling truth-value gaps. A second option is to argue that the bivalence of past- and future-tensed statements is compatible with non-eternalist ontologies and/or with an open future. This option comes in various flavors: Todd (2016) argues that future-tensed statements are all false; Barnes & Cameron (2009, 2011) say that although future-tensed statements are bivalent, the truth-value of some of these is unsettled; Correia & Rosenkranz (2018) assert that the grounding requirement on tensed truths must be weakened, so that it allows the present truth-values of some future-tensed statements to be grounded in how, at some future time, things will be; etc. Thus, the problem of finding an appropriate way of formally representing arguments involving tensed truths is still a source of intense debate.
In this book and the companion volume The Tenseless Theory of Time: A Critical Examination, Craig undertakes the first thorough appraisal of the arguments for and against the tensed and tenseless theories of time. The discussions range widely over issues in the philosophy of language, phenomenology, relativity theory, philosophy of space and time, metaphysics, and philosophy of religion.
The Tensed Theory of Time sets out to discover whether the ineliminability of tense from language and our experience of tense warrants a belief in its objective ontological status, or whether the defeaters raised by McTaggart's paradox and the Myth of Passage serve to undermine any warrant that the tensed theory of time may be supposed to enjoy.
A difficulty for a view of divine eternity as timelessness is that if time is tensed, then God, in virtue of His omniscience, must know tensed facts. But tensed facts, such as It is now t, can only be known by a temporally located being.Defenders of divine atemporality may attempt to escape the force of this argument by contending either that a timeless being can know tensed facts or else that ignorance of tensed facts is compatible with divine omniscience. Kvanvig, Wierenga, and Leftow adopt both of these strategies in their various defenses of divine timelessness. Their respective solutions are analyzed in detail and shown to be untenable.Thus, if the theist holds to a tensed view of time, he should construe divine eternity in terms of omnitemporality.
Some atemporalists have attempted to argue that God does know tensed facts, thus denying the truth of (5). For example, Jonathan Kvanvig holds both to the objective reality of tensed facts and to God's timeless knowledge of all facts, which together imply that God has timeless knowledge of tensed facts. Kvanvig's defense of this position relies upon his analysis of propositions expressed by sentences containing personal indexicals. [2] In lieu of positing privately accessible propositions, he analyzes belief in terms of a triadic relation between an intentional attitude, a proposition, and a particular manner of accessing, or grasping, the proposition. Personal indexicals express individual essences, which are part of the propositional content of the sentence containing such indexical words. But this propositional content is differently accessed by different persons. When Kvanvig says, "I'm Kvanvig," he expresses the same proposition as I do when I say to him, "You're Kvanvig," but this propositional content is directly grasped by Kvanvig and indirectly grasped by me. Kvanvig suggests that the proposition is grasped through the meanings of the sentences involved; since these are different, [3] the propositional content is differently accessed by Kvanvig and me. Thus, an omniscient God has the same knowledge of the facts as we do with respect to the propositions we express through sentences containing personal indexicals, but we directly access those propositions involving our respective individual essences, while God accesses this same propositional content indirectly.
At face value, Kvanvig's analysis would not seem to be a defense of God's timeless knowledge of tensed facts, but the claim that tense in some way derives from the manner of accessing propositional content, which itself is tenseless. For the essences of the times picked out by temporal indexicals do not include their tensed properties (for example, presentness), or it becomes inexplicable how indexical expressions like "today" and "yesterday" could refer to the same individual essence and how God could timelessly grasp propositional content involving such essences. But Kvanvig denies that there is any temporal element expressed by tensed sentences which is not part of their propositional content. Referring to what he calls the "proposition"
Wierenga's analysis fails to explain how God can grasp propositions involving haecceities which include the property of presentness without His being temporal. It therefore also fails as a defense of a timeless God's knowledge of tensed facts.
Finally, consider Brian Leftow's defense of God's timeless knowledge of tensed facts. The key to Leftow's solution is his distinction, inspired by the Special Theory of Relativity, between events' occurrence relative to various temporal reference frames and their occurrence relative to God's "reference frame" of eternity. Relative to eternity, all events are eternally present, even though relative to various temporal reference frames they may be past, present, or future respectively. Thus, relative to eternity there simply are no temporally tensed facts to be known. Leftow explains,
A factually omniscient being can only be required to grasp directly such facts as are genuinely facts within that being's framework of reference. Thus the fact that a timeless being grasps directly only the essentially tensed facts of eternity does not count against His strict factual omniscience, provided that He has some other access to the essentially tensed facts of other reference frames. But . . . a timeless God can know all the facts of simultaneity that obtain in other reference frames. Thus He can know what the essentially tensed facts of these other frames are, though He cannot be directly presented with these facts: it is just not true that the only way God can know facts is by some sort of direct presentation. [20]
Leftow's appeal to the distinction between direct and indirect grasping will not serve to provide God with a knowledge of tensed facts, however. At best God can know what are the simultaneity classes of events relative to any arbitrarily specified reference frame or hypothetical observer, but He cannot know what point on the world line of that observer or which simultaneity class of events is present in that frame. [21] When we realize that the "eternal present" is just a metaphorical description of a tenseless state of existence, then it is evident that on Leftow's account God knows no tensed facts. At the very least He knows no temporally tensed facts, which is what was to be proved.
Indeed, Leftow's account of what he calls "factual omniscience" implies that there really are no tensed facts. [22] According to Leftow a fact is either the existing of a subject or a subject's exemplifying of an attribute. The same fact can render a number of distinct propositions true. In Leftow's view the same fact that renders It is then (i.e., at 3 P.M.) 3 P.M. true also renders true what is expressed by the sentence token "It is now 3 P.M." These are distinct truths, different propositions, rendered true by the same fact. That fact is accessible at all times in varying ways and the various modes of access one can have to this fact generate distinctive truths that can only be known at various times. So even if God cannot be propositionally omniscient concerning events in time, He can still be factually omniscient in regard to them.
Moreover, Leftow's account of God's factual omniscience seems untenable. For Leftow does not think that the propositional context expressed by tensed sentences is tenseless and that tense results from the mode of presentation to or access by language users. Rather he holds that there are tensed propositions which can be known only at certain times. But unless Leftow is prepared to reject a view of truth as correspondence, there must be facts corresponding to true tensed propositions, for example, that 3 P.M. is present. If this proposition is true, then it states a fact about the world. Even if we agree with Leftow that there are facts which are stated by no proposition, he has not given us any reason to doubt that every true proposition states a fact. Indeed, a view of truth as correspondence seems to require it. It follows, therefore, that a timeless God is not only not propositionally omniscient, but not even factually omniscient. 2ff7e9595c
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