Planarian regeneration in space: Persistent anatomical, behavioral, and bacteriological changes induced by space travel

Abstract

Regeneration is regulated not only by chemical signals but also by physical processes, such as bioelectric gradients. How these may change in the absence of the normal gravitational and geomagnetic fields is largely unknown. Planarian flatworms were moved to the International Space Station for 5 weeks, immediately after removing their heads and tails. A control group in spring water remained on Earth. No manipulation of the planaria occurred while they were in orbit, and space‐exposed worms were returned to our laboratory for analysis. One animal out of 15 regenerated into a double‐headed phenotype—normally an extremely rare event. Remarkably, amputating this double‐headed worm again, in plain water, resulted again in the double‐headed phenotype. Moreover, even when tested 20 months after return to Earth, the space‐exposed worms displayed significant quantitative differences in behavior and microbiome composition. These observations may have implications for human and animal space travelers, but could also elucidate how microgravity and hypomagnetic environments could be used to trigger desired morphological, neurological, physiological, and bacteriomic changes for various regenerative and bioengineering applications.

Bipolarity in planarians is not induced by space travel

“…Morokuma et al. (2017) conclude that this demonstrates a stable, major body‐plan modification, the persistence of which may not be due to space travel but may be a general feature of such heteromorphoses.…”

“…(2017) that space travel of regenerating pieces of planarian flatworms underlies the induction of bipolar heads and that on Earth the occurrence of such heteromorphoses is extremely rare are unjustified and mostly rest on an eclectic survey of the literature.…”

“…(2017, Fig. 2A) cut off a head fragment and a tail fragment, thus creating a middle portion of the body containing a major organ of the alimentary system, namely the tubular pharynx.…”

“…Morokuma et al. (2017) state that during their extended studies on D. japonica they have never encountered a bipolar animal in their colonies or during their experiments. Therefore, they conclude that the bipolar condition must be an effect of space travel and they speculate on the possible underlying mechanism of induction.…”

“…And not only is this part of the report of Morokuma et al. (2017) based on a single event but also on only one experiment with no repeat. Although logistical limitations may have prevented Morokuma et al.…”