Labile assembly of a tardigrade protein induces biostasis.

Tardigrades are microscopic animals that survive desiccation by inducing biostasis. To survive drying tardigrades rely on intrinsically disordered CAHS proteins, which also function to prevent perturbations induced by drying in vitro and in heterologous systems. CAHS proteins have been shown to form gels both in vitro and in vivo, which has been speculated to be linked to their protective capacity. However, the sequence features and mechanisms underlying gel formation and the necessity of gelation for protection have not been demonstrated. Here we report a mechanism of fibrillization and gelation for CAHS D similar to that of intermediate filament assembly. We show that in vitro, gelation restricts molecular motion, immobilizing and protecting labile material from the harmful effects of drying. In vivo, we observe that CAHS D forms fibrillar networks during osmotic stress. Fibrillar networking of CAHS D improves survival of osmotically shocked cells. We observe two emergent properties associated with fibrillization; (i) prevention of cell volume change and (ii) reduction of metabolic activity during osmotic shock. We find that there is no significant correlation between maintenance of cell volume and survival, while there is a significant correlation between reduced metabolism and survival. Importantly, CAHS D's fibrillar network formation is reversible and metabolic rates return to control levels after CAHS fibers are resolved. This work provides insights into how tardigrades induce reversible biostasis through the self-assembly of labile CAHS gels.

Effect of veratridine on the release of neurotrophic factors in nerve tissue cultures.

The depolarizing agent veratridine was shown to affect the level of neurotrophic substances in combined cultures of neonatal rat hippocampus and chick embryo spinal ganglia. In this experimental model, the level of neurotrophic factors in rat hippocampus explants increased as a result of increases in neuronal activity mediated by veratridine. The effects of these neurotrophins on neurite growth in the sensitive spinal ganglion neurons in the combined cultures were evaluated using morphometric methods. Neurite-stimulating effects were seen when veratridine was added to the nutritive medium at a concentration of 90 nM. Antibody to nerve growth factor blocked the action of veratridine. These results demonstrate a role for neuron activity as a regulatory mechanism controlling the expression of neurotrophins.

Effect of cerebral neurite-stimulating protein on morphogenesis of organotypical culture of spinal ganglia.

We have extracted a cationic protein with a molecular weight of 15,000 kdalton from the hemispheres of rat and bovine brain. Addition of the protein to the nutrient medium of the organotypical culture of chick embryo spinal ganglia results in a considerable (2-2.5 fold) increase in the growth zone of the explants. The neurite-stimulating effect of the protein is observed at a concentration of 10 ng/ml. We observed an intensive longitudinal growth of neurites, an increase in their amount per unit area, a considerable intensification of ramification, and formation of strong anastomoses, numerous dense plexuses, and arcades. Fasciculi of neurites covered with glia are formed. The cerebral neurite-stimulating protein is evidently one of the neuron-growth factors regulating development of the nervous system in the body.