Years ago, my friend Rick Bribiescas and I got into a friendly debate about the cause of muscle atrophy and bone loss during space flight. We both felt that a homeostatic mechanism was thrown out of whack by the circumstances of weightlessness. One of us suggested that zero gravity caused to lose their ability to regulate tissue mass because gravity would be part of the mechanism for measuring this variable. The other of us thought the body was reacting as though it was falling, and transforming ingested material into bodily tissue would be forestalled until some time after hitting the ground, but that never happened. I can’t remember which of us thought which.
But we were probably both wrong. It may be the case that gravity is an expected contextual feature of normal cellular activity, so when there is either not much gravity (as in zero-G of space flight) or even too much gravity, cellular processes to awry more or less randomly, which would ultimately translate into gene expression being up or down regulated, more or less randomly, across the genome.
A recent study placed fertile fruit fly eggs in three different environments: High magnetism and normal gravity, simulated zero G caused by a magnetic field, and double G caused by the same magnetic field but turned upside down.