How important is gravity as a physical “constraint” in shaping the organization of living organisms

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How important is gravity as a physical “constraint” in shaping the organization of living organisms

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How do cells change their shape and functions when exposed to microgravity (either simulated or real, as experienced onboard of the International Space Station)? Since our earlier experiments – showing that bone cells displayed different morphological shapes after few hours of culture in microgravity – we were impressed by the fact that cells underwent a partitioning into two distinct phenotypes (see figure). That trend became even more evident when we focus on normal and cancerous breast cells. Indeed, two different clusters emerged from the native population after 12 hours of microgravity. These two subsets of cells displayed different shapes as well as subtle differences in a number of critical pathways. In the paper just published in NPJ Microgravity, we report that such diversity in phenotypic organization is essentially independent from changes in genome activity, as the gene expression patterns between the two clusters does not significantly change. In a paper we are about to submit, we demonstrate also that even apoptosis behaves in a different manner within the two cluster. The two different clusters emerging in weightlessness are adaptive – reversible - configurations, notwithstanding they are true, stable phenotypes.

To perform our analysis, we wanted to use a method that allowed us to consider the whole cellular system, without the focus on a single pathway or aspect. Therefore, we employed a trigonometry-based method that considers experimental points as trajectories in an angular space, allowing the description of a multidimension phenomenon. We described how the same genotype, lacking the gravitational constrain, can generate different phenotypes thank to the regain of degrees of freedom. Cellular systems occupy different positions (“attractors”) in the space of compatible states according to the new life conditions, demonstrating the strong influence of biophysical factors on cellular phenotype, often underestimated in molecular biology studies.

This kind of finding implies two relevant conclusions: first, phenotypic variability does not require consensual changes in genome activity, as already proposed by those studies highlighting the complexity of the genotype-phenotype relationships. Important changes in the biophysical microenvironment (or in the biophysical properties of the environment) can successfully enact the emergence of “non-canonical” phenotypes. This occurrence could also be true for those conditions, like cancer, in which human tissues show disruption of the morphogenetic field with altered biophysical properties (i.e., increased stiffness). Therefore, such model could help in investigating how the biophysical properties of the microenvironment can contribute in shaping and driving the cell fate commitment toward different ends. Second, the fact that the absence of gravity hinders the “normal” process of phenotypic commitment raises several concerns about the persistence of terrestrial life in the outer space, unless a planet with the same gravitational mass as the earth is discovered in the future.

Figure shows how microgravity enacted the emergence of two distinct morphological phenotypes in bone cells (MC-3T3-E1) CTRL: normal gravity RPM: microgravity. See, F. Testa et al.   Fractal analysis of shape changes in murine osteoblasts cultured under simulated microgravity. Rend. Fis. Acc. Lincei, 2014, 25:39-47.

This post was a collaboration between Mariano Bizzarri and Agnese Po. The complete article can be found here:

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