My new paper is out now in the journal BIO-Complexity, regarding the origins of the eukaryotic cell division cycle. [1] This is a subject of long-standing interest to me, and I have published several articles over at Evolution News on it, detailing the exquisite engineering and design manifested by the cycle and its control systems. I refer readers to those articles for a survey of how the cell cycle is regulated and its irreducibly complex features:
“The Eukaryotic Cell Cycle: A Masterpiece of Design”
“How the Eukaryotic Cell Cycle is Controlled”
“The Cell’s Surveillance System: Introducing the Cell Cycle Checkpoint Pathways”
“Astounding: The Role of Motor Proteins in Cell Division”
“The Elegant Spindle Assembly Checkpoint”
“Engineered Elegance: Generating the Wait Anaphase Signal”
My paper argues that various features of the eukaryotic cell division cycle exhibit irreducible complexity. Moreover, almost all of the components (which are inferred by previous phylostratigraphic studies to have been present in the last eukaryotic common ancestor) appear to have arisen after the split between archaeal and eukaryotic lineages. Indeed, homologues of the mitotic components could not even be identified among the Asgard archaea, a superphylum believed to represent the closest living relatives to eukaryotes.
Particularly Striking Results
These results are particularly striking given that there is essentially no similarity at all between the mode of cell division employed by eukaryotic cells and that employed by prokaryotic cells, either in terms of the protein components that are involved or the underlying logic. Given the crucial nature of many of the cell division components in both prokaryotes and eukaryotes, it seems highly implausible that there exists a viable stepwise pathway from the prokaryotic to eukaryotic cell division cycle that avoids non-viable intermediates.
In subsequent articles, I will unpack in greater detail the paper and its implications. For now, I want to direct readers to the paper itself. Here is the abstract:
The origin of the eukaryotic cell represents one of the most significant innovations in the history of life. Prokaryotic and eukaryotic cells have distinct modes of cell division both in the mechanisms of cell bifurcation and DNA segregation and in the underlying protein components that drive those processes. Recent phylogenomic analysis shows that most mitotic components were already present in the last eukaryotic common ancestor (LECA), Given the presence of modern-like cell cycle complexity in LECA, it is expected that homologues exist among prokaryotes for at least some of the components involved. This study used the Basic Local Alignment Search Tool (BLAST) to survey the proteomes of prokaryotes (in particular, members of the Asgard superphylum) for potential homologues of components of the anaphase promoting complex / cyclosome (APC/C) and its substrates and the mitotic checkpoint complex (MCC) and kinetochore network. Although the data gathered have failed to definitively show the presence of full homologues for most of the proteins investigated, this analysis reveals that the mitotic machinery is closely associated with eukaryogenesis. While the time window available for the origin of these mechanisms is unclear, even a large window (e.g., 2–3 billion years of time) would be insufficient for blind evolutionary mechanisms to produce such complex systems. This analysis raises significant questions about the feasibility of evolutionary processes to account for such an abrupt transition.
You can download the entire paper, free, here.
Notes
1. McLatchie J (2024) Phylogenetic Challenges to the Evolutionary Origin of the Eukaryotic Cell Cycle. BIO-Complexity 2024 (4):1–19 doi:10.5048/BIO-C.2024.4.
This article was originally published at Evolution News & Science Today, on November 27th, 2024.