Testing Simulation Theory with Cross-Modal Multivariate Classification of fMRI Data

The discovery of mirror neurons has suggested a potential neural basis for simulation and common coding theories of action perception, theories which propose that we understand other people's actions because perceiving their actions activates some of our neurons in much the same way as when we perform the actions. We propose testing this model directly in humans with functional magnetic resonance imaging (fMRI) by means of cross-modal classification. Cross-modal classification evaluates whether a classifier that has learned to separate stimuli in the sensory domain can also separate the stimuli in the motor domain. Successful classification provides support for simulation theories because it means that the fMRI signal, and presumably brain activity, is similar when perceiving and performing actions. In this paper we demonstrate the feasibility of the technique by showing that classifiers which have learned to discriminate whether a participant heard a hand or a mouth action, based on the activity patterns in the premotor cortex, can also determine, without additional training, whether the participant executed a hand or mouth action. This provides direct evidence that, while perceiving others' actions, (1) the pattern of activity in premotor voxels with sensory properties is a significant source of information regarding the nature of these actions, and (2) that this information shares a common code with motor execution

The Non-Linear Path from Gene Dysfunction to Genetic Disease: Lessons from the MICPCH Mouse Model

Most human disease manifests as a result of tissue pathology, due to an underlying disease process (pathogenesis), rather than the acute loss of specific molecular function(s). Successful therapeutic strategies thus may either target the correction of a specific molecular function or halt the disease process. For the vast majority of brain diseases, clear etiologic and pathogenic mechanisms are still elusive, impeding the discovery or design of effective disease-modifying drugs. The development of valid animal models and their proper characterization is thus critical for uncovering the molecular basis of the underlying pathobiological processes of brain disorders. MICPCH (microcephaly and pontocerebellar hypoplasia) is a monogenic condition that results from variants of an X-linked gene, CASK (calcium/calmodulin-dependent serine protein kinase). CASK variants are associated with a wide range of clinical presentations, from lethality and epileptic encephalopathies to intellectual disabilities, microcephaly, and autistic traits. We have examined CASK loss-of-function mutations in model organisms to simultaneously understand the pathogenesis of MICPCH and the molecular function/s of CASK. Our studies point to a highly complex relationship between the potential molecular function/s of CASK and the phenotypes observed in model organisms and humans. Here we discuss the implications of our observations from the pathogenesis of MICPCH as a cautionary narrative against oversimplifying molecular interpretations of data obtained from genetically modified animal models of human diseases

Subcellular localization of GFP-hCASK and GFP-hCASK mutants in HEK-393 cells.

<p>Images were obtained with a 63X Plan-apochromat 1.4 N.A oil lens. White arrows indicate representative intracellular aggregates. Insert shows higher magnification.</p

Mechanochemical Coupling in Spin-Labeled, Active, Isometric Muscle

ABSTRACT Observed effects of inorganic phosphate (P i) on active isometric muscle may provide the answer to one of the fundamental questions in muscle biophysics: how are the free energies of the chemical species in the myosin-catalyzed ATP hydrolysis (ATPase) reaction coupled to muscle force? Pate and Cooke (1989. Pflugers Arch. 414:73–81) showed that active, isometric muscle force varies logarithmically with [P i]. Here, by simultaneously measuring electron paramagnetic resonance and the force of spin-labeled muscle fibers, we show that, in active, isometric muscle, the fraction of myosin heads in any given biochemical state is independent of both [P i] and force. These direct observations of mechanochemical coupling in muscle are immediately described by a muscle equation of state containing muscle force as a state variable. These results challenge the conventional assumption mechanochemical coupling is localized to individual myosin heads in muscle

Structural modeling of four CASK mutations.

<p>Dotted lines indicate contacts. <i>A.</i> CAMK domain of CASK (3c0i.pdb) showing R28 and Y268. <i>B.</i> Native (Arg, cyan) and mutant (Leu, magenta) side-chains at position 28. <i>C.</i> Native (Tyr, cyan) and mutant (His, magenta) side-chains at position 268. <i>D.</i> SH3-GuK domain homology model showing Y728 and W919. SH3 region, yellow. GuK region, pink. <i>E.</i> Native (Tyr, cyan) and mutant (Cys, magenta) side-chains at position 728. <i>F.</i> Native (Trp, cyan) and mutant (Arg, magenta) side-chains at position 919.</p

Glycerol treatment eliminates intracellular aggregates.

<p>Six hours after transfection, media was exchanged for either fresh media alone or containing 10% glycerol. <i>A.</i> Images, 40X. Insert shows higher magnification. <i>B.</i> Using five representative 20X images (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0088276#pone.0088276.s007" target="_blank">Figure S7</a>) for each condition, individual cells were classified as free of or containing aggregates in Image J. Bars and error bars represent the average and standard deviation of three independent analyses. * and # indicate statistically significant differences from the wild-type images.</p

Domain location and conservation of five CASK mutations.

<p><i>A.</i> Five CASK XLMR mutations are shown in reference to CASK’s domain structure. <i>B.</i> A comparison of the five mutation sites in CASK orthologs from nine species. Conserved residues, white. Residues identical to the mutation, black. Residues that differ from the wild-type and mutant hCASK sequence are gradiently shaded to indicate their similarity to the native hCASK residue.</p

Characterization of aggregates.

<p>Images of HEK cells transfected with <i>A)</i> GFP-CASK-Y728C or <i>B)</i> GFP-CASK-W919R were obtained with a 63X Plan-apochromat 1.4 N.A oil lens. First column shows aggregated GFP-CASK protein. Panels labeled “mCherry” show cells that were co-transfected with GFP-CASK and mCherry, which remains cytosolic. Panels labeled “Thioflavin T” represent coverslips that were fixed and then stained with Thioflavin T, which shows enhanced fluorescence in the presence of amyloid fibrils. Panels labeled “Golgi-RFP” represent coverslips that were treated with CellLight® Golgi-RFP which labels the Golgi network. Third column shows an overlay, demonstrating that aggregates are cytosolic (mCherry, Golgi-RFP) but not amyloid in nature (Thioflavin T).</p