MaxSynBio - Max Planck Research Network in Synthetic Biology
Genetic exchange between protocells
May 2018
Scientists from the MPI of Biochemistry in Martinsried and the MPI for Colloids and Interfaces in Potsdam investigate how environmental conditions on early earth might have facilitated the evolution of protocells.
It is commonly assumed, that the precursors of modern cells consisted of an amphiphilic membrane enclosing an RNA-based self-replicating genetic system and a primitive metabolism void of protein enzymes. These protocells must have relied on simple physicochemical self-organization processes within and across such vesicular structures. We investigate freeze-thaw cycling as a potential environmental driver for the evolutionary necessary content exchange between vesicles.
Two populations of vesicles are generated, one with vesicles containing DNA labeled with a red fluorescent dye and one containing DNA labeled with a green fluorescent dye. Freezing and subsequent thawing of the vesicles results in mixing of their contents and thus in a variety of different ratios of both fluorescent signals inside the vesicles.
Two populations of vesicles are generated, one with vesicles containing DNA labeled with a red fluorescent dye and one containing DNA labeled with a green fluorescent dye. Freezing and subsequent thawing of the vesicles results in mixing of their contents and thus in a variety of different ratios of both fluorescent signals inside the vesicles.
We generate two populations of vesicles with differently labelled DNA oligonucleotides and freeze-thaw the samples. If fast freezing is followed by slow thawing, we see signs of nucleic acid exchange in all vesicles (see Figure). In contrast, slow freezing and fast thawing both adversely affect content mixing. Using a high throughput procedure, we characterize content mixing between lipid vesicles for a variety of conditions. Surprisingly, and in contrast to previous reports for content mixing between vesicles, we found that the content is not exchanged through vesicle fusion and fission, but that vesicles largely maintain their membrane identity and even large molecules are exchanged via diffusion across the membranes. These results offer an attractive explanation of how intravesicular content, including primitive RNA replicators, could have spread within vesicle populations using transient periods of increased membrane permeability. Our approach supports efficient screening of the vast parameter space of prebiotically plausible molecules and environmental conditions, to yield universal mechanistic insights into how cellular life may have emerged.
