A Possible Inductive Mechanism for Magnetogenetics

Reports of genetically conferred sensitivity to magnetic stimuli have preceded plausible mechanistic explanations. Frequently, these experiments rely on a fusion of ferritin with a transient receptor potential vanniloid channel protein, speculating associated mechanical or thermal cues. However, it has been argued compellingly that the small magnetic moment of ferritin precludes these possibilities. Here, we offer an alternative hypothesis based on stochastic resonance that does not require appreciable interaction of ferritin with the applied field. Rather, we suggest that ferritin might act merely as a localized source of high frequency inductive noise on the membrane. When combined with externally applied time-varying fields, this noise might help surmount the activation threshold of endogenous voltage-gated ion channels. To explore this concept, we use the stochastic Landau-Lifshitz-Gilbert equation to model magnetization dynamics and compare the magnetic field noise resulting from ferritin and from a 15 nm magnetite particle.

Observed Enhancement of Reflectivity and the Electric Field in Long-Lived Florida Anvils

A study of two long-lived Florida anvils showed that reflectivity >20 dBZ increased in area, thickness, and sometimes magnitude at the midlevel well downstream of the convective cores. In these same regions electric fields maintained strengths >10 kV m−1 for many tens of minutes and became quite uniform over tens of kilometers. Millimetric aggregates persisted at 9–10 km for extended times and distances. Aggregation of ice particles enhanced by the strong electric fields might have contributed to reflectivity growth in the early anvil, but is unlikely to explain observations farther out in the anvil. The enhanced reflectivity and existence of small, medium, and large ice particles far out into the anvil suggest that an updraft was acting, perhaps in weak convective cells formed by instability generated from the evaporation and melting of falling ice particles. It is concluded that charge separation must have occurred in these anvils, perhaps at the melting level but also at higher altitudes, in order to maintain fields >10 kV m−1 at 9–10 km for extended periods of time over large distances. The authors speculate that charge separation occurred as a result of ice–ice particle collisions (without supercooled water being present) via either a noninductive or perhaps even an inductive mechanism, given the observed broad ice particle spectra, the strong preexisting electric fields, and the many tens of minutes available for particle interactions. The observations, particularly in the early anvil, show that the charge structure in these anvils was quite complex.

Inducing constraint activity in innovative design

In this paper, a methodology for inducing trends in a first principle reasoning system for design innovation is presented. Dimensional Variable Expansion is used in 1stPRINCE (FIRST PRINciple Computational Evaluator) to create additional design variables and introduce new prototypes. Trends are observed at each generation of the prototype and induction is used to predict optimal constraint activity at the limit of the iterative procedure. The inductive mechanism is applied to a constant-radius beam under flexural load and a tapered beam of varying radius and superior performance is derived. A circular wheel is created from a primitive-prototype consisting of a rectangular, spinning block that is optimized for minimum resistance to spinning. Although presented as a technique to perform innovative design, the inductive methodology can also be utilized as an AI approach to shape optimization.

Epithelial induction of osteogenesis in embryonic chick mandibular mesenchyme studied by transfilter tissue recombinations

The initiation of osteogenesis in the mandibular mesenchyme of the embryonic chick at 7 days is dependent upon an epithelial induction which occurs in the mandible up to the fourth day in ovo. In the present study, transfilter tissue recombinations were used to study this inductive mechanism. The epithelial and mesenchymal components of the mandibles were separated before the completion of the induction and recombined to form transfilter explants which were either cultured for 9 days or grafted onto the chorioallantoic membrane for host embryos for 7 days. Control experiments demonstrated that the tissue separation and recombination techniques did not interfere with the normal epithelial induction, and confirmed that mandibular mesenchyme isolated at this stage was incapable of forming bone. Bone was observed in 86 % of the CAM-grafted intact mandible controls and in 80 % of the cultured intact mandible controls. Bone failed to form in the mesenchyme of transfilter explants when Millipore filters with 0·45 μm pores were used. Bone was observed as frequently as in control explants when the mandibular mesenchyme was separated from its epithelium by 0·8 μm or 0·4 μm porosity Nuclepore filters. Only about 30% of the transfilter explants prepared with 0·1 μm porosity Nuclepore filters formed bone and none of the explants prepared with 0·03 μm porosity Nuclepore filters formed bone. SEM studies demonstrated a distinct correlation between the formation of bone in transfilter explants and the ability of the epithelium and mesenchyme to penetrate the pores of the filters. Thus, the present study provides evidence that the site of the induction is restricted to the epithelial—mesenchymal interface, and that the induction is not mediated by a diffusible substance. The nature of the inductive mechanism is discussed with respect to this and other recent studies which suggest that the induction may be mediated by a non-diffusible epithelial cell product resident in the epithelial basal lamina.

Epithelial induction of osteogenesis in embryonic chick mandibular mesenchyme: a possible role for basal lamina

The initiation of osteogenesis at 7 days in the embryonic chick mandibular mesenchyme depends on an epithelial induction in the mandible to day 4. This article reviews a series of experiments conducted to study the nature of this inductive mechanism. Transfilter tissue recombinations were used to determine whether direct tissue apposition was required for induction. Ultrastructural studies of the epithelial–mesenchymal interface were conducted to see if direct epithelial–mesenchymal cell–cell contacts occurred during the inductive stage in vivo. Epithelial cells were cultured on Millipore filters for 28 days and allowed to deposit extracellular products. These products were tested for inductive activity. Findings from these three sets of experiments were discussed with respect to the inductive mechanism. Our results indicate that the induction is not mediated by a diffusible substance and that direct apposition of the two tissues is required. The mechanism of induction, however, does not require direct epithelial–mesenchymal cell to cell contacts. This suggests that a nondiffusible component of the extracellular matrix may be involved. Epithelial extracellular products are inductively active and have the appearance of basal lamina. The active component of the extracellular product is proteinaceous, perhaps collagen, and appears to be situated in the epithelial basal lamina. The role of basal lamina in epithelial–mesenchymal interactions is discussed.

A marker induction mechanism for the establishment of ordered neural mappings: its application to the retinotectal problem

This paper examines the idea that ordered patterns of nerve connections are set up by means of markers carried by the individual cells. The case of the ordered retinotectal projection in amphibia and fishes is discussed in great detail. It is suggested that retinotectal mappings are the result of two mechanisms acting in concert. One mechanism induces a set of retinal markers into the tectum. By this means, an initially haphazard pattern of synapses is transformed into a continuous or piece-wise continuous projection. The other mechanism places the individual pieces of the map in the correct orientation. The machinery necessary for this inductive scheme has been expressed in terms of a set of differential equations, which have been solved numerically for a number of cases. Straightforward assumptions are made as to how markers are distributed in the retina; how they are induced into the tectum; and how the induced markers bring about alterations in the pattern of synaptic contacts. A detailed physiological interpretation of the model is given. The inductive mechanism has been formulated at the level of the individual synaptic interactions. Therefore, it is possible to specify, in a given situation, not only the nature of the end state of the mapping but also how the mapping develops over time. The role of the modes of growth of retina and tectum in shaping the developing projection becomes clear. Since, on this model, the tectum is initially devoid of markers, there is an important difference between the development and the regeneration of ordered mappings. In the development of duplicate maps from various types of compound-eyes, it is suggested that the tectum, rather than the retina, contains an abnormal distribution of markers. An important parameter in these experiments, and also in the regeneration experiments where part-duplication has been found, is the range of interaction amongst the retinal cells. It is suggested that the results of many of the regeneration experiments (including apparently contradictory ones) are manifestations of a conflict between the two alternative ways of specifying the orientation of the map: through the information carried by the markers previously induced into the tectum and through the orientation mechanism itself.