Hypergravity hinders axonal development of motor neurons inCaenorhabditis elegans

Abstract

As space flight becomes more accessible in the future, humans will be exposed to gravity conditions other than our 1G environment on Earth. Our bodies and physiology, however, are adapted for life at 1G gravity. Altering gravity can have profound effects on the body, particularly the development of muscles, but the reasons and biology behind gravity’s effect are not fully known. We asked whether increasing gravity had effects on the development of motor neurons that innervate and control muscle, a relatively unexplored area of gravity biology. Using the nematode model organism Caenorhabditis elegans, we examined changes in response to hypergravity in the development of the 19 GABAergic DD/VD motor neurons that innervate body muscle. We found that a high gravity force above 10G significantly increases the number of animals with defects in the development of axonal projections from the DD/VD neurons. We showed that a critical period of hypergravity exposure during the embryonic/early larval stage was sufficient to induce defects. While characterizing the nature of the axonal defects, we found that in normal 1G gravity conditions, DD/VD axonal defects occasionally occurred, with the majority of defects occurring on the dorsal side of the animal and in the mid-body region, and a significantly higher rate of error in the 13 VD axons than the 6 DD axons. Hypergravity exposure increased the rate of DD/VD axonal defects, but did not change the distribution or the characteristics of the defects. Our study demonstrates that altering gravity can impact motor neuron development.

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

“…Previously, we showed that hypergravity exposure increases DD/VD motor neuron axon defects 22 . Here, we sought to explain how gravity force can alter the axon development in the worm.…”

“…Hypergravity cultivation chamber was prepared as previously described 22 . For hypergravity experiment, eggs were collected from gravid adult animals by bleaching using standard procedures 25 and then transferred into the cultivation tube around 100–150 in number.…”

“…For hypergravity experiment, eggs were collected from gravid adult animals by bleaching using standard procedures 25 and then transferred into the cultivation tube around 100–150 in number. Developing embryos were exposed to 100G hypergravity by setting a temperature-controlled Sorval Legend Micro 17R centrifuge system to 1200 RPM for 60 h at 20 °C similar to previous protocols 22 . Control tubes (1G condition) were maintained in an incubator at 20 °C.…”

“…VD neuron axon outgrowth occurs similarly during the L1 larval stage to complete the development of the 19 DD/VD motor neurons. Previously, we showed that hypergravity exposure of at least 10G increases defects in axon development in the DD/VD motor neurons in C. elegans 22 . Hypergravity during the L1 larval stage before the VD axons are even born was sufficient to cause an increase in defects, and the increase was consistently observed in all DD/VD axons.…”

microRNAs involved in the control of toxicity on locomotion behavior induced by simulated microgravity stress in Caenorhabditis elegans

“…Nematode hypergravity cultivation tub was prepared according to previous protocols 51 . The 1 ml of NGM was placed into each 1.5 ml centrifuge tube and then transferred to a heat block set to prevent immediate solidification of agar.…”