2015
Volume 15, Number 2, pp. 41–44
Structural dependence above unicellular levels is exploited to evolve multicellularity
Ariel Fernández Stigliano1, 2
1Argentine Institute of Mathematics (I. A. M.), National Research Council (CONICET), 1083 Buenos Aires, Argentina
2Collegium Basilea, Institute for Advanced Study, 4053 Basel, Switzerland
Clues to the evolution of multicellularity are emerging from comparative genomics and functional genetics studies of monophyletic unicellular/multicellular species pairs with recent divergence [1, 2]. Such studies have not revealed significant innovation at the genomic or protein domain level, but have identified a causative plexus in the coöption of unicellular functionalities into genes and pathways responsive to developmental cues [3–6]. We argue that without proteomic innovation, this coöption could only materialize with a degree of functional coöperativity well above unicellular levels. What raw properties of a unicellular proteome are harnessed by such functional exaptations? This work addresses the question by examining the structural dependence of proteins (Q) across species. This parameter differentiates unicellular and multicellular species by globally characterizing their proteome interdependence, and identifies the unicellular volvocine alga Chlamydomonas reinhardtii [3] as the sole outlier, with a level of structural dependence closer to that of a multicellular species. This result is significant since volvocine algae provide a model for the evolution of multicellularity [1–7] and is revealing since structural dependence implies a lack of functional autonomy that enables coöption without the need to innovate at the proteomic level.