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SaintUlvemann t1_isgnvv3 wrote

Reply to comment by goltz20707 in TIL: Sperms were thought to move by wiggling their tails side-to-side, like eels, for 350 years. But research shows that they roll as they move forward like a spinning top. by vect77

Eukaryotic flagella aren't helical, though. There are multiple types of flagella. Description:

>Bacterial flagella are helical filaments, each with a rotary motor at its base which can turn clockwise or counterclockwise. ... > >Archaeal flagella (archaella) are superficially similar to bacterial flagella in that it also has a rotary motor, but are different in many details and considered non-homologous. > >Eukaryotic flagella — those of animal, plant, and protist cells — are complex cellular projections that lash back and forth. Eukaryotic flagella and motile cilia are identical in structure, but have different lengths, waveforms, and functions.

...and diagram.

That's why the rotary motion is a surprise.

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LostFerret t1_isgypue wrote

Rotary motion is not a surprise. See paper from 1901 https://www.jstor.org/stable/pdf/2453750.pdf

More work building on this with self powered nanomachines https://journals.aps.org/rmp/pdf/10.1103/RevModPhys.88.045006

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SaintUlvemann t1_ish61aq wrote

Right, but assuming you are referring to page 370 of the first link, this is the reason they gave for this spiral motion:

"The Flagellata and Ciliata are as a rule asymmetrical in form. One of these organisms, as, for example, Loxodes (Fig. 2), or Paramecium (Fig. 3), when it leaves the bottom and starts to swim freely through the water, cannot go in a straight line, but owing to its lack of symmetry continually swerves toward one side, so that it tends to describe a circle."

This is not a disputation of how the cilia or flagella beat, but rather a description of the effect such beating has on an asymmetrical object. This does not apply to sperm cells since, in terms of their form, they *are* symmetric in shape, apart from the shape deformations caused by the flailing of their flagellum itself.

In contrast, the paper we're talking about purports to have found that sperm cells fundamentally do not even beat back and forth in the first place; they only beat in one direction, and then they continuously rotate the mass of the entire "head" of the sperm, in order to keep themselves moving forward.

That's different than what your paper shows.

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LostFerret t1_ishybgl wrote

Ah, sorry, didn't realize that second paper was paywalled. Fhe first paper focuses on form generating asmety in cilliated swimmers, the second paper extends that to asymmetry in either form or force and classifies swimmers as pushing (posterior flagellum) or pulling (anterior flagellum).

Both papers present the idea that any asymmetry in the swimmingof unicellular swimmers will produce circular or irregular patterns unless balanced by regular rotation linked to those forces. This is further explored in that more recent paper.

We expect EVERY eukaryotic, unicellular swimmer capable of helical / straight lines to follow this behavior, its just the way that the physics of swimming work at low reynolds numbers. Honestly, it would be way more surprising if we found a unicellular swimmer that did NOT spin while swimming.

So while sperm bodies may be somewhat symmetrical (im not sure if this is actually the case? There are a ton of weird fuckin sperm out there..google ostracod sperm for a trip..i dont know the range of human sperm morphology), the force they are producing is definitely not. To counter this asymmetry they rotate the entire cell, not just the head. This creates a helical procession that lets the sperm swim relatively straight.

We've known that euk. Flagellum don't beat in a single plane for a while, so im surprised we hadn't picked up on the asymmetrical beat pattern of human sperm until now. The imaging is pretty cool here though, I'd love to get my cells on that scope though they're tiny compared to sperm.

The title of this post is hot garbage tho, i was so happy to see you post about the prot/euk flagellar difference.

I think this is just a case of silo'd science. I only found those two papers because im working with weird non-animal cells and the modelers im collaborating with had some questions we couldnt answer so i did a very thorough literature search. They do bacterial motility modeling and hadn't seen the paper despite it being directly related to one of their theses. Human research, especially sperm research, is pretty isolated so it's likely the researchers who published the new paper didnt know it exists.

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schizboi t1_isj3d7p wrote

Love the sources, doing the lords work here thank you

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SaintUlvemann t1_isjfsoh wrote

Ah, thanks for that: that second one was paywalled, yeah, and ostensibly my institution doesn't have a subscription. I'd even written something saying so, but, I lost it 'cause of whatever bug it is leads comment text to go missing after copypaste, was too lazy to rewrite.

>I think this is just a case of silo'd science.

Yeah... I'm pretty sure a pretty core chunk of my thesis is essentially just a case of me speaking into the silence of missing knowledge, created by siloed science... a siloed science silence, if that ain't too pretentious.

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