Assessment of Rhodopseudomonas sphaeroides chromatophore membrane asymmetry through bilateral antiserum adsorption studies.

The asymmetric structure of the Rhodopseudomonas sphaeroides chromatophore membrane was examined in detail by crossed immunoelectrophoresis techniques. Because these methods are quantitative and allow increased resolution and sensitivity, it was possible to analyze simultaneously the relative transmembrane distribution of a number of previously identified antigenic components. This was demonstrated by analysis of immunoglobulin samples that were adsorbed by preincubation with either isolated chromatophores or osmotically protected spheroplasts. The photochemical reaction center, the light-harvesting bacteriochlorophyll a-protein complex, the L-lactate dehydrogenase, and reduced nicotinamide adenine dinucleotide dehydrogenase (EC 1.6.99.3) were found to be exposed on the chromatophore surface (cytoplasmic aspect of the membrane within the cell). Other antigenic components were found to be exposed on the surface of spheroplasts (periplasmic aspect of the in vivo chromatophore membrane). Antigens with determinants expressed on both sides of the chromatophore membrane were also identified. Charge shift crossed immunoelectrophoresis confirmed the suggested amphiphilic character of the pigment-protein complexes and identified several additional amphiphilic membrane components.     

Broca's area and the hierarchical organization of human behavior

The prefrontal cortex subserves executive control, i.e., the organization of action or thought in relation to internal goals. This brain region hosts a system of executive processes extending from premotor to the most anterior prefrontal regions that governs the temporal organization of behavior. Little is known, however, about the prefrontal executive system involved in the hierarchical organization of behavior. Here, we show using magnetic resonance imaging in humans that the posterior portion of the prefrontal cortex, including Broca's area and its homolog in the right hemisphere, contains a system of executive processes that control start and end states and the nesting of functional segments that combine in hierarchically organized action plans. Our results indicate that Broca's area and its right homolog process hierarchically structured behaviors regardless of their temporal organization, suggesting a fundamental segregation between prefrontal executive systems involved in the hierarchical and temporal organization of goal-directed behaviors.     

A twin study of dental dimension. I. Discordance,asymmetry, and mirror imagery

Bilateral tooth measurements in twins were partitioned into three orthogonal contrasts, each associated with one degree of freedom, to estimate three parameters: discordance, asymmetry, and mirror imagery. The probability levels of the within-pair variance ratios were used to test for significance of these estimates. The results provided strong evidences for the existence of significant genetic determinants of almost all of the individual tooth dimensions, but little or no evidence for a genetic basis of asymmetry. The analysis gave no indication that monozygotic twinning was associated with an increased degree of either fluctuating asymmetry or mirror imagery, when compared to dizygotic twins. The data on monozygotic twins further suggested that for most variables examined, the increment of environmental discordance resulting from the twinning phenomena was greater than the developmental noise that caused asymmetry within individual cotwins.     

Signal transduction through the T cell antigen receptor. Activation of phospholipase C through a G protein-independent coupling mechanism.

The T cell Ag (Ti-CD3) receptor complex has been proposed to regulate phosphoinositide-specific phospholipase C (PLC) through a cholera toxin (CTX)-sensitive guanine nucleotide-binding (G) protein. In this study, we have used CTX and staurosporine as pharmacologic probes to further define the linkage between the Ti-CD3 receptor and PLC activity in the human T cell line, Jurkat. CTX pretreatment inhibited Ti-CD3 receptor-dependent phosphoinositide hydrolysis and, concomitantly, protein tyrosine kinase activation in intact cells. Studies with electrically permeabilized Jurkat cells revealed that guanosine 5'-(3-O-thio) triphosphate stimulated an increase in PLC activity, that unlike the response to Ti-CD3 receptor ligation, was not affected by cellular pretreatment with CTX. In contrast, the phosphotyrosine phosphatase inhibitors, orthovanadate and molybdate anions, stimulated phosphoinositide hydrolysis in permeabilized cells through a CTX-sensitive mechanism of PLC activation. Additional studies with a known PTK inhibitor, staurosporine, supported the results obtained with CTX. Staurosporine pretreatment inhibited the phosphoinositide hydrolysis induced by anti-CD3 antibodies or phosphotyrosine phosphatase inhibitors, but failed to alter the G protein-dependent PLC activation response to guanosine 5'-(3-O-thio) triphosphate. The results of this study indicate that PLC activity(s) in Jurkat cells are regulated by both G protein- and PTK-dependent coupling mechanisms. However, the differential inhibitory effects of CTX and staurosporine on these PLC activation pathways strongly suggest that a protein tyrosine kinase activation event, rather than a G protein, mediates the functional linkage between the Ti-CD3 receptor and PLC activity in Jurkat cells.     

Selective priming of syntactic processing by event-related transcranial magnetic stimulation of Broca's area

It remains controversial whether Broca's aphasia is an articulatory deficit, a lexical-access problem, or agrammatism. In spite of recent neuroimaging studies, the causal link between cortical activity and linguistic subcomponents has not been elucidated. Here we report an experiment with event-related transcranial magnetic stimulation (TMS) to clarify the role of Broca's area, more specifically, the left inferior frontal gyrus (F3op/F3t), in syntactic processing. An experimental paradigm contrasted sentences requiring syntactic decisions with those requiring semantic decisions. We found selective priming effects on syntactic decisions when TMS was administered to the left F3op/F3t at a specific timing, but not to the left middle frontal gyrus (F2). Our results provide direct evidence of the involvement of the left F3op/F3t in syntactic processing.     

Left-right asymmetry: actin-myosin through the looking glass

Despite being bilaterally symmetric, most Metazoa exhibit clear, genetically determined left-right differences. In several animals, microtubule-based structures are thought to be the source of chiral information used to establish handedness. Now, two new studies in Drosophila identify a role for unconventional myosin motors in this process.