Protoneilla

Protoneilla is a term used in theoretical discussions of early cellular evolution to denote an intermediate, protocell-like lineage that could have bridged RNA-based metabolism and the emergence of robust genetic replication. The concept is not based on a single fossil or molecule, but rather serves as a modeling construct in origin-of-life research.

In common models, protoneilla is imagined as a small, lipid-bound vesicle containing a primitive metabolic network and short, template-directed polymers. The membrane provides compartmentalization, while simple catalysis and uptake of nutrients enable growth and division under fluctuating conditions. Genetic material is envisioned as rudimentary and transient, sufficient to guide replication-like processes but lacking modern proofreading or repair mechanisms.

Protoneilla is hypothesized to have inhabited environments with natural compartments, such as coastal hydrothermal systems or drying ponds, where wet-dry cycles and mineral surfaces could support polymerization and concentration of reactants.

Usage of protoneilla in models helps researchers explore sequencing of key innovations, such as compartmentation, metabolism, replication, and peptide or protein catalysts. It also frames questions about the timing of the RNA world and the transition to protein-mediated biology, as well as the plausibility of stable heredity prior to LUCA.

Critics note that protoneilla is a speculative construct with limited empirical constraints. It remains a heuristic device rather than an established lineage, and some researchers advocate more direct approaches to testing origin-of-life scenarios through experiments and abiogenesis research.

See also protocell, RNA world, origin of life, LUCA.