“The Real Point is Control”: The Reception of Barbara McClintock's Controlling Elements

In the standard narrative of her life, Barbara McClintock discovered genetic transposition in the 1940s but no one believed her. She was ignored until molecular biologists of the 1970s “rediscovered” transposition and vindicated her heretical discovery. New archival documents, as well as interviews and close reading of published papers, belie this narrative. Transposition was accepted immediately by both maize and bacterial geneticists. Maize geneticists confirmed it repeatedly in the early 1950s and by the late 1950s it was considered a classic discovery. But for McClintock, movable elements were part of an elaborate system of genetic control that she hypothesized to explain development and differentiation. This theory was highly speculative and was not widely accepted, even by those who had discovered transposition independently. When Jacob and Monod presented their alternative model for gene regulation, the operon, her controller argument was discarded as incorrect. Transposition, however, was soon discovered in microorganisms and by the late 1970s was recognized as a phenomenon of biomedical importance. For McClintock, the award of the 1983 Nobel Prize to her for the discovery of movable genetic elements, long treated as a legitimation, may well have been bittersweet. This new look at McClintock's experiments and theory has implications for the intellectual history of biology, the social history of American genetics, and McClintock's role in the historiography of women in science. This revised version was published online in July 2006 with corrections to the Cover Date.     

Membrane Permeabilization by Oligomeric α-Synuclein: In Search of the Mechanism

Background

The question of how the aggregation of the neuronal protein α-synuclein contributes to neuronal toxicity in Parkinson''s disease has been the subject of intensive research over the past decade. Recently, attention has shifted from the amyloid fibrils to soluble oligomeric intermediates in the α-synuclein aggregation process. These oligomers are hypothesized to be cytotoxic and to permeabilize cellular membranes, possibly by forming pore-like complexes in the bilayer. Although the subject of α-synuclein oligomer-membrane interactions has attracted much attention, there is only limited evidence that supports the pore formation by α-synuclein oligomers. In addition the existing data are contradictory.

Methodology/Principal Findings

Here we have studied the mechanism of lipid bilayer disruption by a well-characterized α-synuclein oligomer species in detail using a number of in vitro bilayer systems and assays. Dye efflux from vesicles induced by oligomeric α-synuclein was found to be a fast all-or-none process. Individual vesicles swiftly lose their contents but overall vesicle morphology remains unaltered. A newly developed assay based on a dextran-coupled dye showed that non-equilibrium processes dominate the disruption of the vesicles. The membrane is highly permeable to solute influx directly after oligomer addition, after which membrane integrity is partly restored. The permeabilization of the membrane is possibly related to the intrinsic instability of the bilayer. Vesicles composed of negatively charged lipids, which are generally used for measuring α-synuclein-lipid interactions, were unstable to protein adsorption in general.

Conclusions/Significance

The dye efflux from negatively charged vesicles upon addition of α-synuclein has been hypothesized to occur through the formation of oligomeric membrane pores. However, our results show that the dye efflux characteristics are consistent with bilayer defects caused by membrane instability. These data shed new insights into potential mechanisms of toxicity of oligomeric α-synuclein species.     

In search of an “autophagomometer”

Recent years have seen the realization that macroautophagy (which we will call autophagy) is not only important in yeast but is necessary for diverse functions in plants and animals. Importantly, autophagy can have an impact on human pathologies including infectious diseases, cancers, and neurodegenerative conditions.¹ Thus, we need to be able to measure autophagy accurately in order to understand how it can be regulated physiologically and with exogenous agents.     

The “Artificial Artery” as In Vitro Perfusion Model

Metabolic stimuli, pressure, and fluid shear stress (FSS) are major mediators of vascular plasticity. The exposure of the vessel wall to increased laminar FSS is the main trigger of arteriogenesis, the remodelling of pre-existent arterio-arteriolar anastomoses to functional conductance arteries. In this study, we have used an in vitro bioreactor to investigate cell-specific interactions, molecular mechanisms as well as time-dependent effects under laminar FSS conditions. This bioreactor termed “artificial artery” can be used for screening potential arterio-protective substances, pro-arteriogenic factors, and for investigating biomarkers of cardiovascular diseases such as cardiac diseases. The bioreactor is built up out of 14 hollow fiber membranes colonized with endothelial cells (HUVECs) on the inside and smooth muscle cells (HUASMCs) on the outside. By means of Hoechst 33342 staining as well as immunocytochemistry of ß-catenin and α-smooth-muscle-actin, a microporous polypropylene membrane was characterized as being the appropriate polymer for co-colonization. Defined arterial flow conditions (0.1 N/m2 and 3 N/m2), metabolic exchange, and cross-talk of HUVECs and HUASMCs through hollow fibers mimic physiological in vivo conditions of the vasculature. Analysing mono- and co-culture secretomes by MALDI-TOF-TOF mass spectrometry, we could show that HUVECs secreted Up4A upon 3 N/m2. A constant cellular secretion of randomly chosen peptides verified viability of the “artificial artery” for a cultivation period up to five days. qRT-PCR analyses revealed an up-regulation of KLF2 and TIMP1 as mechano-regulated genes and demonstrated arterio-protective, homeostatic FSS conditions by a down-regulation of EDN1. Expression analyses of VWF and EDN1 furthermore confirmed that RNA of both cell types could separately be isolated without cross-contamination. CCND1 mRNA expression in HUVECs did not change upon FSS indicating a quiescent endothelial phenotype. Taken together, the “artificial artery” provides a solid in vitro model to test pharmacological active compounds for their impact on arterio-damaging or arterio-protective properties on vascular response.     

The Teaching of “Adaptation”

The use of the data from various athletic sports for exercises in the interpretation of data is proposed, and accounts are given of two such exercises. The first looks at the relationship between time and distance in world records for men running. When the logarithm of the time is plotted against the logarithm of the distance a straight line is produced. Thefactors that govern the speeds at which various distances are run are discussed and the application of these to other sports and to animals other than man is briefly mentioned. The second exercise looks at anomalous performances by men running in the 1968 Olympic Games which took place at high altitude. It is shown that while the lowered air resistance increased the speeds in sprint events, and the lowered oxygen content slowed down speeds in long distance events, these were not the only factors involved in limiting speeds.

Among the advantages of the use of such data are that they are readily and easily available, that they are the result of a lengthy selection process involving many subjects, that they appeal to students interested in sport and that they can link courses in biology and physical education.