Thibaut Brunet
@thibautbrunet.bsky.social
Evolutionary cell biology / evolution of morphogenesis / animal origins / choanoflagellates @institutpasteur.bsky.social
https://research.pasteur.fr/en/team/evolutionary-cell-biology-and-evolution-of-morphogenesis/
https://research.pasteur.fr/en/team/evolutionary-cell-biology-and-evolution-of-morphogenesis/
The American Library in Paris has quite a few nice scientific biographies - I guess I got my winter reading sorted
November 12, 2025 at 1:23 PM
The American Library in Paris has quite a few nice scientific biographies - I guess I got my winter reading sorted
both are right: the best is marine microbiology
November 2, 2025 at 5:47 PM
both are right: the best is marine microbiology
he is! first one to make many observations and to describe many species... he also wrote "the" book
October 17, 2025 at 3:50 PM
he is! first one to make many observations and to describe many species... he also wrote "the" book
Conservation might extend even further: DJ Pan's lab had shown that YAP helps multicellular colonies resist flattening by gravity in yet another relative of animals (the filopodiated amoeba Capsaspora) by making cells more contractile -a function also present in zebrafish tinyurl.com/323jmdht
October 5, 2025 at 10:35 AM
Conservation might extend even further: DJ Pan's lab had shown that YAP helps multicellular colonies resist flattening by gravity in yet another relative of animals (the filopodiated amoeba Capsaspora) by making cells more contractile -a function also present in zebrafish tinyurl.com/323jmdht
This nicely tied in with the earlier genetic and biophysical evidence that ECM quantity sets choano rosette size and shape. Targets of Warts/Yorkie included collagen, laminin-like proteins, C-type lectins - and couscous, one of the "rosette development genes" from the historical mutant screen.
October 5, 2025 at 10:35 AM
This nicely tied in with the earlier genetic and biophysical evidence that ECM quantity sets choano rosette size and shape. Targets of Warts/Yorkie included collagen, laminin-like proteins, C-type lectins - and couscous, one of the "rosette development genes" from the historical mutant screen.
... but there's a catch: in animals, YAP most canonically acts by controlling cell proliferation. In S. rosetta, we found no evidence that the Warts phenotype would be due to increased cell division. Instead, RNAseq revealed massive upregulation of ECM components in giant rosettes.
October 5, 2025 at 10:35 AM
... but there's a catch: in animals, YAP most canonically acts by controlling cell proliferation. In S. rosetta, we found no evidence that the Warts phenotype would be due to increased cell division. Instead, RNAseq revealed massive upregulation of ECM components in giant rosettes.
Surprisingly, disrupting warts kinases in S. rosetta caused a very animal-like phenotype: giant rosettes colonies!
This suggests the molecular pathways that control multicellular development in animals and choanos might be more conserved than we expected...
This suggests the molecular pathways that control multicellular development in animals and choanos might be more conserved than we expected...
October 5, 2025 at 10:35 AM
Surprisingly, disrupting warts kinases in S. rosetta caused a very animal-like phenotype: giant rosettes colonies!
This suggests the molecular pathways that control multicellular development in animals and choanos might be more conserved than we expected...
This suggests the molecular pathways that control multicellular development in animals and choanos might be more conserved than we expected...
In animals, YAP stimulates tissue growth by enhancing proliferation. This is highly conserved: if you over-activate YAP (by removing the kinases that keep it in check) in a fly eye, you get a giant eye; in a mouse liver, you get a giant liver.
The genes were known to be conserved in choanos...
The genes were known to be conserved in choanos...
October 5, 2025 at 10:35 AM
In animals, YAP stimulates tissue growth by enhancing proliferation. This is highly conserved: if you over-activate YAP (by removing the kinases that keep it in check) in a fly eye, you get a giant eye; in a mouse liver, you get a giant liver.
The genes were known to be conserved in choanos...
The genes were known to be conserved in choanos...
Fast-forward to 2022: having established a selection-based gene knockout method for S. rosetta, we set out to study the Hippo pathway - a star pathway of animal development, in which the kinases Hippo and Warts control organ size via the transcription coactivator YAP.
October 5, 2025 at 10:35 AM
Fast-forward to 2022: having established a selection-based gene knockout method for S. rosetta, we set out to study the Hippo pathway - a star pathway of animal development, in which the kinases Hippo and Warts control organ size via the transcription coactivator YAP.
When rosettes reach a critical size, cells undergo a 'jamming transition', pressure becomes unsustainable - and rosettes split into two. In other words: a limiting quantity of ECM sets rosette size and shape.
October 5, 2025 at 10:35 AM
When rosettes reach a critical size, cells undergo a 'jamming transition', pressure becomes unsustainable - and rosettes split into two. In other words: a limiting quantity of ECM sets rosette size and shape.
@blarson.bsky.social showed that ECM secretion underlies biophysically self-organized morphogenesis: all cells compete for adhesion to a limiting basal patch of central ECM, leading to spherical arrangement of cells around that patch and to rising cell-cell pressure as the rosette grows larger.
October 5, 2025 at 10:35 AM
@blarson.bsky.social showed that ECM secretion underlies biophysically self-organized morphogenesis: all cells compete for adhesion to a limiting basal patch of central ECM, leading to spherical arrangement of cells around that patch and to rising cell-cell pressure as the rosette grows larger.
Over 2013-2018, a mutant screen initiated by @teralevin.bsky.social revealed 3 genes necessary for rosette development. Strikingly, all 3 have to do with ECM secretion: rosetteless (a secreted C-type lectin that's part of ECM), jumble and couscous (2 glycosyltransferases needed for ECM synthesis).
October 5, 2025 at 10:35 AM
Over 2013-2018, a mutant screen initiated by @teralevin.bsky.social revealed 3 genes necessary for rosette development. Strikingly, all 3 have to do with ECM secretion: rosetteless (a secreted C-type lectin that's part of ECM), jumble and couscous (2 glycosyltransferases needed for ECM synthesis).
How do these rosettes develop? When they form rosettes, cells secrete a basal extracellular matrix, to which cells anchor by filopodia. That ECM (akin to a basal lamina) keeps the cells together (together with cytoplasmic bridges).
October 5, 2025 at 10:35 AM
How do these rosettes develop? When they form rosettes, cells secrete a basal extracellular matrix, to which cells anchor by filopodia. That ECM (akin to a basal lamina) keeps the cells together (together with cytoplasmic bridges).
Now for the biological story: when it detects certain bacteria, the choanoflagellate S. rosetta undergoes serial cell division to develop into a swimming sphere of cells aptly named "rosette", which evokes (mutatis mutandis) a morula stage embryo.
October 5, 2025 at 10:35 AM
Now for the biological story: when it detects certain bacteria, the choanoflagellate S. rosetta undergoes serial cell division to develop into a swimming sphere of cells aptly named "rosette", which evokes (mutatis mutandis) a morula stage embryo.
First things first: huge bravos to research technician extraordinaire Chantal Combredet & to PhD student extraordinaire Mylan Ansel, who made this happen.
October 5, 2025 at 10:35 AM
First things first: huge bravos to research technician extraordinaire Chantal Combredet & to PhD student extraordinaire Mylan Ansel, who made this happen.
Latest from ours: www.cell.com/cell-reports...
This is two stories in one: a case study/cautionary tale on developing genetic tools in new organisms, and the first hint at a gene regulatory network for choanoflagellate multicellular development (which turn out to involve a Hippo/YAP/ECM loop!) A 🧵
This is two stories in one: a case study/cautionary tale on developing genetic tools in new organisms, and the first hint at a gene regulatory network for choanoflagellate multicellular development (which turn out to involve a Hippo/YAP/ECM loop!) A 🧵
October 5, 2025 at 10:35 AM
Latest from ours: www.cell.com/cell-reports...
This is two stories in one: a case study/cautionary tale on developing genetic tools in new organisms, and the first hint at a gene regulatory network for choanoflagellate multicellular development (which turn out to involve a Hippo/YAP/ECM loop!) A 🧵
This is two stories in one: a case study/cautionary tale on developing genetic tools in new organisms, and the first hint at a gene regulatory network for choanoflagellate multicellular development (which turn out to involve a Hippo/YAP/ECM loop!) A 🧵
Seems that we have a new reporter strain (pic: @jujumathieu.bsky.social)
October 2, 2025 at 5:06 PM
Seems that we have a new reporter strain (pic: @jujumathieu.bsky.social)
... and might be especially key in confined microenvironments such as the soil, where protists are often trapped in thin liquid layers in pores between grains. (Choanos are commonly found in soil, but their ecology and motility in this environment are pretty much unknown; pic: tinyurl.com/9vh488bk)
September 9, 2025 at 6:12 PM
... and might be especially key in confined microenvironments such as the soil, where protists are often trapped in thin liquid layers in pores between grains. (Choanos are commonly found in soil, but their ecology and motility in this environment are pretty much unknown; pic: tinyurl.com/9vh488bk)
Gliding is conserved in at least 2 choano species we looked at (C. flexa and S. rosetta). We don't know in which natural context it is deployed, but we think it is likely to be involved in interactions with surfaces such as biofilms...
September 9, 2025 at 6:12 PM
Gliding is conserved in at least 2 choano species we looked at (C. flexa and S. rosetta). We don't know in which natural context it is deployed, but we think it is likely to be involved in interactions with surfaces such as biofilms...
Most striking, in some instances of spontaneous flagellar detachment, the flagellum can glide on its own - mercilessly leaving the cell body behind, stabbing it on the way if need be (don't do this at home).
September 9, 2025 at 6:12 PM
Most striking, in some instances of spontaneous flagellar detachment, the flagellum can glide on its own - mercilessly leaving the cell body behind, stabbing it on the way if need be (don't do this at home).
Do choanos defy the laws of physics? Not quite. Multiple pieces of evidence suggest the motor force for gliding resides in the flagellum (like in Chlamydomonas): (1) flagellar ablation prevents gliding (2) inhibition of the molecular motors of intraflagellar transport abolish it too.
September 9, 2025 at 6:12 PM
Do choanos defy the laws of physics? Not quite. Multiple pieces of evidence suggest the motor force for gliding resides in the flagellum (like in Chlamydomonas): (1) flagellar ablation prevents gliding (2) inhibition of the molecular motors of intraflagellar transport abolish it too.
In this new study, @maitefreired.bsky.social has shown that moderate confinement activates *yet another* mode of motility: choanos straighten their flagellum, and start moving over the substrate at pretty high speed (~1 µm/sec) without any visible cell deformation. They glide!
September 9, 2025 at 6:12 PM
In this new study, @maitefreired.bsky.social has shown that moderate confinement activates *yet another* mode of motility: choanos straighten their flagellum, and start moving over the substrate at pretty high speed (~1 µm/sec) without any visible cell deformation. They glide!
What about choanos? They are best-known as flagellar swimmers. In 2021, we showed they are additionally capable of amoeboid motility, crawling via cell protrusions under strong geometric confinement. (elifesciences.org/articles/61037)
September 9, 2025 at 6:12 PM
What about choanos? They are best-known as flagellar swimmers. In 2021, we showed they are additionally capable of amoeboid motility, crawling via cell protrusions under strong geometric confinement. (elifesciences.org/articles/61037)
Gliding in diverse protists involves different parts of the cell - eg, flagella & IFT motors in the alga Chlamydomonas (pic: tinyurl.com/ye2jsbs5) - suggesting multiple evolutionary origins. Interestingly, gliding has also only been described so far in lineages very distant from animals and fungi.
September 9, 2025 at 6:12 PM
Gliding in diverse protists involves different parts of the cell - eg, flagella & IFT motors in the alga Chlamydomonas (pic: tinyurl.com/ye2jsbs5) - suggesting multiple evolutionary origins. Interestingly, gliding has also only been described so far in lineages very distant from animals and fungi.
Do diatoms disprove physics? Not really. They also exert a force on the substrate, but this time, the action occurs at the molecular scale: movement is powered by adhesive transmembrane proteins stuck to the substrate and coupled to intracellular molecular motors. (fig: tinyurl.com/ytd55aw5)
September 9, 2025 at 6:12 PM
Do diatoms disprove physics? Not really. They also exert a force on the substrate, but this time, the action occurs at the molecular scale: movement is powered by adhesive transmembrane proteins stuck to the substrate and coupled to intracellular molecular motors. (fig: tinyurl.com/ytd55aw5)