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Create AnaColon_summary_Bingham_and_Ratcliff_2024 #28

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17 changes: 17 additions & 0 deletions prompts/2024/english/prompt_2024_01/AnaColon_summary_Bingham_and_Ratcliff_2024
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please move this file to prompts/2024/english/prompt_2024_02/AnaColon_summary_Bingham_and_Ratcliff_2024.md because it is currently in a directory meant for a different paper and prompt.

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Complex multicellularity has evolved five separate times in eukaryotes but has never evolved in prokaryotes. Complex multicellularity has been defined as a large organism composed of many cells that lives for an extensive period of time. Some prokaryotes are multicellular but they do not have the morphologies of complex multicellular organisms.
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To improve this writing for e.g. a blog post or professional summary, you'll want to make sure you don't start two back-to-back sentences the same way ('Complex multicellularity has...'). Or is the first sentence meant to be a title? If so, you should try out markdown formatting. First you'll have to change the filename as I suggested above (adding the '.md' extension tells GitHub to treat your text as if it's markdown instead of plain text). Then, you simply have to put a pound sign at the beginning of a line that's meant to act as a heading. E.g.:

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# Complex multicellularity has evolved...

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Complex multicellularity has evolved...

You can see how it looks when rendered by using the 'preview' button when editing on GitHub

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I would say 'Complex multicellularity has been defined as a large organism composed of many cells that lives for an extensive period of time' is not quite accurate. The article's definition says that organisms with complex multicellularity often live long, but not that that's an essential part of the definition. They do say it's a 'term of art', so you've got some flexibility, but one important aspect missing from your definition is that these organisms don't just have many cells, but many cell types.


This paper proposes a new hypothesis as to why prokaryotes lack complex multicellularity compared to eukaryotes. When bottle neck events causing a reduced efficient population size cells are divided into groups. In response to this eukaryotes will undergo genomic expansion while prokaryotes will undergo genomic deletion. These differences in responses could be an explanation as to why eukaryotes have been able to evolve complex multicellularity and prokaryotes have not.
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'When bottle neck events causing a reduced efficient population size cells are divided into groups.'
->
'When cells are divided into groups, this causes bottleneck events, with reduced effective population sizes.'


Eukaryotic have transposons and introns that facilitate genomic expansion through replication. Prokaryotes tend to have deletion bias where they will delete parts of their genome. These subcellular mechanisms influence their response to bottleneck effects.
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'through replication' is a little vague - do you get the nuances of this? These 'mobile genetic elements' are kind of like viruses, and get replicated and moved around in our genomes within the lifespan of single cells and without reproduction of the organism itself. And importantly, they often take other, nearby pieces of the genome with them - so a transposon that happens to be next to an unrelated gene will get copied to a different part of the genome, and maybe the second copy of the transposon will have a fragment of that other gene next to it. This allows pieces of genes to get mixed around and recombined, as well as duplicated.


With an expanded genome, eukaryotes have more potential for the emergence of new genes. This would facilitate their evolution after experiencing a bottleneck effect with a reduced population size. Prokaryotes would lose genetic material which would cause less genetic diversity as they try to evolve. Less genomic material leads to less opportunity for evolutionary events to occur.
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An important point in the paper is that, perhaps because of these large genomes (or maybe enabling the large genomes), eukaryotes tend to have 'default off' gene expression. So when these random duplications and fragmentations happen, they accumulate as 'junk DNA' that's not automatically 'used'. This makes the copying much less dangerous.


When comparing complex multicellular genomes to unicellular relatives in fungal lineages, the genomes for complex organism are twice as big. This includes protein-encoding regions and non-coding regions that can serve as evolutionary regions for gene regulation.

Cyanobacteria have a large genome, however, they have a high frequency of pseudogenes that would result from gene deletion. This supports the hypothesis that prokaryotes favor gene deletion compared to gene replication.
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'Cyanobacteria have a large genome' - relatively speaking. Large for a bacterium; still not large compared to eukaryotes. For example, the human genome is 6.37 Gbp but the largest cyanobacterial genome in this paper's figure 1A is ~13 Mbp (500 times fewer A's, T's, C's, and G's)


Evolutionarily speaking, there is a strong selection for genome expansion. Despite this, larger multicellular organisms are less capable of evolving larger genomes due to experiencing an increase in genetic drift.
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The strong selection for genome expansion that they mentioned near the end of their results is one that they created in a model - it is not necessarily true in reality or in general.


Further studies need to be performed to determine the validity of the hypothesis. However, this hypothesis does stand the chance of changing the narrative of why complex multicellularity has evolved in eukaryotes and not prokaryotes.
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What is your opinion of their ideas? What do you think about the dueling hypotheses they set up - that multicellularity arises due to drift or that it arises due to selection?


DOI: https://doi.org/10.1073/pnas.2319840121