Possible origins of macroscopic left-right asymmetry in organisms

I consider the microscopic mechanisms by which a particular left-right (L/R) asymmetry is generated at the organism level from the microscopic handedness of cytoskeletal molecules. In light of a fundamental symmetry principle, the typical pattern-formation mechanisms of diffusion plus regulation cannot implement the "right-hand rule"; at the microscopic level, the cell's cytoskeleton of chiral filaments seems always to be involved, usually in collective states driven by polymerization forces or molecular motors. It seems particularly easy for handedness to emerge in a shear or rotation in the background of an effectively two-dimensional system, such as the cell membrane or a layer of cells, as this requires no pre-existing axis apart from the layer normal. I detail a scenario involving actin/myosin layers in snails and in C. elegans, and also one about the microtubule layer in plant cells. I also survey the other examples that I am aware of, such as the emergence of handedness such as the emergence of handedness in neurons, in eukaryote cell motility, and in non-flagellated bacteria.Comment: 42 pages, 6 figures, resubmitted to J. Stat. Phys. special issue. Major rewrite, rearranged sections/subsections, new Fig 3 + 6, new physics in Sec 2.4 and 3.4.1, added Sec 5 and subsections of Sec

STATE LEGISLATORS AND ECONOMIC DEVELOPMENT: UNIVERSITY-INDUSTRY RELATIONSHIPS AND THE ROLE OF GOVERNMENT IN BIOTECHNOLOGY

This article presents a detailed examination of some key political dimen- sions underlying cooperative research in agricultural biotechnology among state land-grant universities, state legislatures, and biotechnology corpora- tions. Factor analysis and path analysis methods are employed to assess differences in the perceptions of university administrators, biotechnology corporation researchers, and state legislators, using national and state survey data. Two attitudinal dimensions, one regarding cooperation among university and corporate researchers, and the other regarding barriers to joint research, are extracted. Generally similar attitudes are shared by university and legislative respondents, who are concerned over the prospects of market-oriented university research. In contrast, corporate respondents are more concerned with reducing barriers to cooperative research and the need for more open communication between academia and industry, and with issues of patent rights. Extensions of this work to other states and to other high-technology industries are considered. Copyright 1990 by The Policy Studies Organization.

A Proton Magnetic Resonance Spectroscopy Study of Age-related Changes in Frontal Lobe Metabolite Concentrations

Ageing is associated with reduction of grey matter volume and it is reported that the frontal lobes are preferentially affected. We have applied quantitative magnetic resonance spectroscopy (MRS), incorporating measurement of brain tissue water content and metabolite T2 relaxation times, to determine absolute concentrations of the putative neuronal marker N-acetylaspartate (NAA), creatine (Cr) and choline (Cho) compounds in the frontal lobe of 50 male subjects aged between 20 and 70 years (10 per decade). The fractional brain water content (βMR) did not change significantly as a function of age (r = 0.07, P = 0.65) and had a mean value of 81% (CV = 2%). The concentration (in millimoles per litre brain tissue) of NAA decreased significantly with age (r = -0.42, P = 0.003), with an overall decrease of 12% between the third and seventh decades. The concentrations of Cr and Cho did not change significantly with age. The interpretation of the age-dependent decrease in NAA concentration as reflecting either a reduction in neuronal volume, number or function is discussed