Cytoskeletal Signaling: Is Memory Encoded in Microtubule Lattices by CaMKII Phosphorylation?

Memory is attributed to strengthened synaptic connections among particular brain neurons, yet synaptic membrane components are transient, whereas memories can endure. This suggests synaptic information is encoded and ‘hard-wired’ elsewhere, e.g. at molecular levels within the post-synaptic neuron. In long-term potentiation (LTP), a cellular and molecular model for memory, post-synaptic calcium ion (Ca2+) flux activates the hexagonal Ca2+-calmodulin dependent kinase II (CaMKII), a dodacameric holoenzyme containing 2 hexagonal sets of 6 kinase domains. Each kinase domain can either phosphorylate substrate proteins, or not (i.e. encoding one bit). Thus each set of extended CaMKII kinases can potentially encode synaptic Ca2+ information via phosphorylation as ordered arrays of binary ‘bits’. Candidate sites for CaMKII phosphorylation-encoded molecular memory include microtubules (MTs), cylindrical organelles whose surfaces represent a regular lattice with a pattern of hexagonal polymers of the protein tubulin. Using molecular mechanics modeling and electrostatic profiling, we find that spatial dimensions and geometry of the extended CaMKII kinase domains precisely match those of MT hexagonal lattices. This suggests sets of six CaMKII kinase domains phosphorylate hexagonal MT lattice neighborhoods collectively, e.g. conveying synaptic information as ordered arrays of six “bits”, and thus “bytes”, with 64 to 5,281 possible bit states per CaMKII-MT byte. Signaling and encoding in MTs and other cytoskeletal structures offer rapid, robust solid-state information processing which may reflect a general code for MT-based memory and information processing within neurons and other eukaryotic cells

Fission-track thermochronology, vertical kinematics, and tectonic development along the western extension of the North Anatolian Fault zone

We have investigated the low-temperature history of pre-Neogene basement areas adjacent to the western extension of the North Anatolian Fault zone (NAFZ) by apatite fission track thermochronology of 33 samples taken from Marmara island, Kapidag peninsula (both in the Sea of Marmara), Samothrake island, and Chalkidike peninsula (both in the North Aegean region). Together with already published apatite fission track data from 30 other sampling localities of the region, these data (63 in total) have been evaluated mainly with regard to the transitional period from the Mesohellenic orogeny (Eocene-Oligocene) to the plate-tectonical individualization of the Aegean-Antolian microplate, to gain a better understanding of the tectonical chronology that has led to modern east Mediterranean plate tectonics. Apatite fission track investigations of the area under discussion reveal two major events of cooling and exhumation of pre-Neogene rocks. A first frequency maximum of cooling ages between 35 and 25 Ma (late Eocene to early Oligocene) is due to postorogenic regional erosion after the climax of the Mesohellenic orogeny, which was caused by continental collision of the Pelagonian platform and the Rila-Rhodope zone after the final closure of the Axios-Vardar Ocean. A second frequency maximum of cooling ages between 17 and 11.5 Ma (early to middle Miocene) depicts more localized uplift and exhumation in consequence of transpressive and/or transtensive movements along early structural discontinuities that gave rise to the later fault systems in the western extension of the NAFZ. The earliest fault structures of this system have developed shortly after the orogenic collapse and crustal extension of the Rila-Rhodope area but quasi simultaneously with the onset of subduction along the modern Hellenic trench. The regional distribution of fission track ages of the Miocene age group (17 to 11.5 Ma), and corresponding thermochronological calculations based on frequency distributions of confined track lengths suggest that an early fault propagation has occurred from east to west during the Miocene. The onset of subduction along the Hellenic trench and subsequent gravitational retreat of the subducting oceanic slab are considered as a major cause for transtension of the Aegean crust, especially with regard to the development of north Aegean pull-apart basins. Such early fault structures have facilitated the westward propagation of a continuous NAFZ that took place during the Pliocene from the easternmost Marmara region to the Gallipoli peninsula and to the North Aegean trough. Copyright 2010 by the American Geophysical Union