Need something to blame for having soul-crushing zoom meetings and having to do your taxes?

Let’s talk about eukaryogenesis: how multicellular organisms (that’s us!) came to be, and the crusty lil motherfuckers that started it all and now we’re here :)

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The running theory goes like this: eukaryogenesis was when an archaea (single-celled organism), during the Archean period roughly 3 billion years ago, pretty much ate (and didn’t digest!) a bacteria that was an ancestor to what is now our favorite organelle, the mitochondria.

There’s actually a NEW eukaryogenesis theory that I am pretty partial to, and I’m gonna talk about that at the end of the thread!

I wanna take a pause right here and emphasize that this archaea most likely didn’t have a “Eureka!” moment (prob because it didn’t have a fuckin consciousness but ya know). This process was likely very messy and spanned generations and probably failed a few times, etc etc.

But I don’t wanna make this thread too long so I do apologize for all the over-simplification! Anyway....

The archaea didn’t just take up the bacteria: they ended up forming a syntrophic relationship. The proto-mitochondria provided energy, the archaea provided a place to chill, they both went to baseball games and made friends and had a good ol’ time taking over the world.

^ that’s all way oversimplifying it, but the theory itself explains how complex multicellular life with organelles and DNA and fancy replication and communication and student loans came from simple lil RNA having prokaryotes, or single-celled organisms.

“Ok so who are these stupid archaea that started all this? I just wanna talk.”

So we’re fairly certain now that we’ve found the closest living ancestor to that son of a bitch, but before I get there, there’s 3 different major transitional species: LACA, FECA, and LECA.

The oldest is LACA, which means Last Archaean Common Ancestor. That’s the Hungry Hungry Archaea, which then became FECA: First Eukaryotic Common Ancestor. Then came LECA, the Last Eukaryotic Common Ancestor, the ancestor to all Eukarya, which has extant relatives.

There’s been lots of study as to which of these extant (still living!) organisms are closest to LECA, but recently we’ve locked down the current front runner: Lokiarchaeota.

Yup. *That* Loki. Trickster god himself.

You can find relatives of the lil shits, far as we know, on the sea floor near Greenland. What’s special about these archaea is that they represent a lot of the same features that eukaryotes have. And I mean a *lot*: they share roughly 175 ESPs, or eukaryotic signature proteins,

which includes eukaryote-like cytoskeleton proteins (membrane mobility which help it eat and move and shit) and even information processing proteins!

Also gonna pause right here and state that looking for mechanisms that can take up a mitochondrial-like bacteria is a fraction of the battle when discerning LECA’s qualities and the history of eukaryogenesis.

Eukaryotes are *crazy* complex! Y’all remember the fucking Kreb’s cycle?

Of COURSE NOT, because it’s so fucking complex!!! There’s SO MANY other characteristics that make eukaryotes unique that biologists have to find out how and when these characteristics came to be.

This includes mobility, communication and transport between organelles, membrane manipulation (this one ESPECIALLY), environmental response mechanisms, not to mention the slew of proteins and genetic code and structures that are unique to eukaryotes only!

And the fuckin Loki, y’all... it has a lot of these things.

Anyway, now I wanna talk about the new method of eukaryogenesis that was proposed earlier this year. It’s called Entangle, Engulf, Endogenize, or the E3 method. Hopefully everyone can access it here https://www.biorxiv.org/content/10.1101/726976v1 but if not lmk!

Once upon a time, RIGHT BEFORE the Lokiarchaeota emerged in the literature as the top contender for relative to LECA, Hiruyoki Imachi and their badass colleagues sampled a Loki relative. I love this story because the team really didn’t know they were sitting on a gold mine!

So they studied the hell out of these things and they found some cool stuff: 1. They were incredibly slow to metabolize. That’s because they’re so small for archaea, but also because they live on the goddamn sea floor. Not many grocery stores there, if you didn’t know.

2. It’s a TINY anaerobic coccus (doesn’t use oxygen and is ball-shaped) but relies on two syntrophic organisms: salt-loving bacteria and another methane-loving archaea. So this Loki relative (named MK-D1) lives with 2 BFFs that help it metabolize and reproduce. Hence the presence

of proteins and a certain structure that helps it communicate with its BFFs. This certain structure is 3. It’s arms.

MK-D1 has membrane-based extracellular protrusions that the two BFFs sit on. In fact, they’re wrapped up in MK-D1’s shitty lil arms.

So Imachi and their team did some lookin and found out that, holy shit, these eukarya possess arms that catch their lil friends and help them... live. Become more organized. Rely on each other.

These eukarya are so small and so slow to metabolize, eating them would’ve been hard especially before the Great Oxidation Event. So they thought: what if it wasn’t lunch, but a syntrophic dance instead?

It was around this time that Loki emerged as THE prime candidate for studying eukaryogenesis. I’m not 100% sure on this but I’m p sure Imachi was like holy shit.

So here’s the closest relative to LECA that we know of, it’s so smol and so lazy but it has friends. So they hypothesized this: archaea and bacteria shared a dance, which, over time, led them to grow closer and adapt, then they became one.

Entangle, engulf, endogenize.

Of course this is theory and it’s very hard to know for certain, but regardless of how shitty this (possibly) Loki made life for us... it’s still really cool to be one step closer in knowing where we come from.

Pls hmu with questions and I apologize for not defining every term!! But hope you enjoyed :)

I def meant to say archaea instead of eukarya towards the end there lol my b