Comparative Analysis of Muscle Atrophy During Spaceflight, Nutritional Deficiency and Disuse in the Nematode Caenorhabditis elegans.

While spaceflight is becoming more common than before, the hazards spaceflight and space microgravity pose to the human body remain relatively unexplored. Astronauts experience muscle atrophy after spaceflight, but the exact reasons for this and solutions are unknown. Here, we take advantage of the nematode C. elegans to understand the effects of space microgravity on worm body wall muscle. We found that space microgravity induces muscle atrophy in C. elegans from two independent spaceflight missions. As a comparison to spaceflight-induced muscle atrophy, we assessed the effects of acute nutritional deprivation and muscle disuse on C. elegans muscle cells. We found that these two factors also induce muscle atrophy in the nematode. Finally, we identified clp-4, which encodes a calpain protease that promotes muscle atrophy. Mutants of clp-4 suppress starvation-induced muscle atrophy. Such comparative analyses of different factors causing muscle atrophy in C. elegans could provide a way to identify novel genetic factors regulating space microgravity-induced muscle atrophy.

Comparison of Life Traits in Two Bacterivorous Nematodes Suggest Different Ecological Strategies to Exploit Similar Habitats.

Environments can be in states of dynamic change as well as persistent stability. These different states are a result of outside external conditions, but also the constant flux of living organisms in that ecological fauna. Nematodes are tremendously diverse, and many types can reside in the same soil microenvironments at the same time. To examine how so many nematodes can thrive and exploit a single environment, we identified two bacterivorous nematodes, Caenorhabditis elegans and Acrobeloides tricornis, that can inhabit rotting apple and soil environments. We cultured both nematodes in the laboratory and compared their life traits. We found that whereas C. elegans develops and reproduces extremely quickly, A. tricornis reaches sexual maturity much later and lays eggs at a slower rate but remains fertile for a longer time. In addition, A. tricornis displays a slower feeding behavior than C. elegans. Finally, A. tricornis has a significantly longer lifespan than C. elegans. These differences in development, physiology and behavior between the two nematodes hint at different ecological strategies to exploit the same habitat over different time periods, C. elegans as a colonizer-type nematode, and A. tricornis as more of a persister.

Muscle and epidermal contributions of the structural protein ß-spectrin promote hypergravity-induced motor neuron axon defects in C. elegans.

Biology is adapted to Earth's gravity force, and the long-term effects of varying gravity on the development of animals is unclear. Previously, we reported that high gravity, called hypergravity, increases defects in the development of motor neuron axons in the nematode Caenorhabditis elegans. Here, we show that a mutation in the unc-70 gene that encodes the cytoskeletal ß-spectrin protein suppresses hypergravity-induced axon defects. UNC-70 expression is required in both muscle and epidermis to promote the axon defects in high gravity. We reveal that the location of axon defects is correlated to the size of the muscle cell that the axon traverses. We also show that mutations that compromise key proteins of hemidesmosomal structures suppress hypergravity-induced axon defects. These hemidesmosomal structures play a crucial role in coupling mechanical force between the muscle, epidermis and the external cuticle. We speculate a model in which the rigid organization of muscle, epidermal and cuticular layers under high gravity pressure compresses the narrow axon migration pathways in the extracellular matrix hindering proper axon pathfinding of motor neurons.