Lionel Christiaen, PhD (he/him/his)
@lionlchristiaen.bsky.social
Dev cell syst biol, cardiopharyngeal, coll migr, ecodevo. Dir Sars Centre, U Bergen. NIH DEV1 rev. Prof NYU Bio. Postdoc UC Berkeley. PhD CNRS/Paris XI. Agrégé. Archicube. French & American.
https://www.uib.no/en/michaelsarscentre/141681/christiaen-group
https://www.uib.no/en/michaelsarscentre/141681/christiaen-group
Actually, scratch 4x, make it 80x more for Life Sciences
November 30, 2025 at 10:48 AM
Actually, scratch 4x, make it 80x more for Life Sciences
And very excited to pivot to writing up the tour-de-force study by extraordinary co-authors Margaux and Keira. Stay tuned for further insights into cardiopharyngeal morphogenetic networks from high-content image-based profiling of CRISPR/Cas9-induced phenotypes.
November 15, 2025 at 11:52 AM
And very excited to pivot to writing up the tour-de-force study by extraordinary co-authors Margaux and Keira. Stay tuned for further insights into cardiopharyngeal morphogenetic networks from high-content image-based profiling of CRISPR/Cas9-induced phenotypes.
Taken together, we argue that cell cycle progression and forward regulatory interactions promote transcriptome maturation, which fosters multilineage competence in cardiopharyngeal progenitors.
November 15, 2025 at 10:03 AM
Taken together, we argue that cell cycle progression and forward regulatory interactions promote transcriptome maturation, which fosters multilineage competence in cardiopharyngeal progenitors.
Finally, we tested if Depdc1b, which is activated at the G1-S transition and contains E2F motifs in its proximal element, requires both GATA and cell cycle progression for expression. Indeed, misexpression of the G1-S inhibitor Cdkn1 inhibited Depdc1b expression.
November 15, 2025 at 9:58 AM
Finally, we tested if Depdc1b, which is activated at the G1-S transition and contains E2F motifs in its proximal element, requires both GATA and cell cycle progression for expression. Indeed, misexpression of the G1-S inhibitor Cdkn1 inhibited Depdc1b expression.
Notably, motifs for classic cell-cycle transcription factors such as E2F and Myc/Max, were enriched in maturing clusters and the corresponding TFs dynamically expressed in the trajectory suggesting a coupling between maturation and cell cycle progression.
November 15, 2025 at 9:53 AM
Notably, motifs for classic cell-cycle transcription factors such as E2F and Myc/Max, were enriched in maturing clusters and the corresponding TFs dynamically expressed in the trajectory suggesting a coupling between maturation and cell cycle progression.
Depdc1b showed up as one of yhe few genes downregulated by Gata, so we tested this regulatory interaction and found a cardiopharyngeal enhancer for Depdc1b, which contains conserved GATA motifs necessary for expression.
November 15, 2025 at 9:48 AM
Depdc1b showed up as one of yhe few genes downregulated by Gata, so we tested this regulatory interaction and found a cardiopharyngeal enhancer for Depdc1b, which contains conserved GATA motifs necessary for expression.
The usual suspects, Fox and Gata, kept popping up, so we reuse our sample barcoding strategy to profile CRISPR perturbations using FACS and scRNA-seq. This once again showed the massive impact of Foxf on the expression of intermediate and mature gene clusters, and minor effect of Gata4/5/6.
November 15, 2025 at 9:42 AM
The usual suspects, Fox and Gata, kept popping up, so we reuse our sample barcoding strategy to profile CRISPR perturbations using FACS and scRNA-seq. This once again showed the massive impact of Foxf on the expression of intermediate and mature gene clusters, and minor effect of Gata4/5/6.
Considering the importance of transcriptome maturation for multipotent cardiopharyngeal competence, we asked how it is regulated, first by looking for transcription factor motifs enrich in the accessome near cluster-specific genes and signs of (feed)forward subcircuits.
November 15, 2025 at 9:38 AM
Considering the importance of transcriptome maturation for multipotent cardiopharyngeal competence, we asked how it is regulated, first by looking for transcription factor motifs enrich in the accessome near cluster-specific genes and signs of (feed)forward subcircuits.
Focusing on the DEP-domain and (pseudo)RhoGAP domain containing Depdc1b, we showed that division orientation is important to position the daughter cells in contact with or away from the lateral mesenchyme, to produce distinct Tbx1/10+ progenitors and heart precursors.
November 15, 2025 at 9:30 AM
Focusing on the DEP-domain and (pseudo)RhoGAP domain containing Depdc1b, we showed that division orientation is important to position the daughter cells in contact with or away from the lateral mesenchyme, to produce distinct Tbx1/10+ progenitors and heart precursors.
We then turned to CRISPR to probe the importance of mature genes for multipotent progenitors competence, showing a variety of requirements for oriented and/or asymmetric division, and/or Tbx1/10 expression.
November 15, 2025 at 9:24 AM
We then turned to CRISPR to probe the importance of mature genes for multipotent progenitors competence, showing a variety of requirements for oriented and/or asymmetric division, and/or Tbx1/10 expression.
Extended the technical and conceptual proofs of concept, we used our transgene-based barcoding and denoising methods. pubmed.ncbi.nlm.nih.gov/33411784/ to profile whole embryos obtained every hour from 5 to 14 hours post-fertilization in one shot, and recovered evidence for transcriptome maturation
November 15, 2025 at 9:19 AM
Extended the technical and conceptual proofs of concept, we used our transgene-based barcoding and denoising methods. pubmed.ncbi.nlm.nih.gov/33411784/ to profile whole embryos obtained every hour from 5 to 14 hours post-fertilization in one shot, and recovered evidence for transcriptome maturation
Here we show that multilineage priming starts in the intermediate regulatory state (cluster 2 genes) but is completed in the mature state (cluster 5 genes), arguing that transcriptome maturation fosters multilineage competence.
November 15, 2025 at 9:09 AM
Here we show that multilineage priming starts in the intermediate regulatory state (cluster 2 genes) but is completed in the mature state (cluster 5 genes), arguing that transcriptome maturation fosters multilineage competence.
Looking under the hood, we identified candidate “mature” genes, which peak in the mature state and include many development control genes, not only G2 markers, the cells being well into G2 by then.
November 15, 2025 at 9:02 AM
Looking under the hood, we identified candidate “mature” genes, which peak in the mature state and include many development control genes, not only G2 markers, the cells being well into G2 by then.
At the cell level, the Gata4/5/6+ cardiopharyngeal progenitors seems to transition to regulatory states, as suggested by both clustering and RNA velocity, with increasing “speeds” at transitions.
November 15, 2025 at 8:55 AM
At the cell level, the Gata4/5/6+ cardiopharyngeal progenitors seems to transition to regulatory states, as suggested by both clustering and RNA velocity, with increasing “speeds” at transitions.
This worked nicely to recover known trajectories and cell types.
November 15, 2025 at 8:51 AM
This worked nicely to recover known trajectories and cell types.
We developed a transgene-based sample barcoding approach to profile 10 time points in one shot with scRNA-seq, taking advantage of cell-to-cell variability to capture higher resolution (pseudo)temporal dynamics.
November 15, 2025 at 8:50 AM
We developed a transgene-based sample barcoding approach to profile 10 time points in one shot with scRNA-seq, taking advantage of cell-to-cell variability to capture higher resolution (pseudo)temporal dynamics.
So we went back to think about the relatively long interphase of cardiopharyngeal progenitors, during which they migrate collectively before dividing in an oriented and asymmetric manner to produce Tnx1/10+ secondary progenitors and Tbx1/10- first heart precursor cell, future cardiomyocytes.
November 15, 2025 at 8:40 AM
So we went back to think about the relatively long interphase of cardiopharyngeal progenitors, during which they migrate collectively before dividing in an oriented and asymmetric manner to produce Tnx1/10+ secondary progenitors and Tbx1/10- first heart precursor cell, future cardiomyocytes.
Using a PCNA::GFP reporter, we mapped G1, S and G2 in cardiopharyngeal progenitors, noting that Cdc25 could trigger mitosis only once cells had entered G2, as expected.
November 15, 2025 at 8:36 AM
Using a PCNA::GFP reporter, we mapped G1, S and G2 in cardiopharyngeal progenitors, noting that Cdc25 could trigger mitosis only once cells had entered G2, as expected.
Here we found that precocious mitosis, induced by overexpressing the phosphatase Cdc25, is not sufficient to force Tbx1/10 activation, which happened almost on the clock and after division but with a delay from the time of mitosis.
November 15, 2025 at 8:32 AM
Here we found that precocious mitosis, induced by overexpressing the phosphatase Cdc25, is not sufficient to force Tbx1/10 activation, which happened almost on the clock and after division but with a delay from the time of mitosis.
We already knew that Tbx1/10, which is essential for cardiopharyngeal fate choices, needs mitosis to be transcriptionally activated.
November 15, 2025 at 8:26 AM
We already knew that Tbx1/10, which is essential for cardiopharyngeal fate choices, needs mitosis to be transcriptionally activated.
Friday seminar treat with a talk by Prof. De Tomaso on the reproductive and regenerative prowesses of colonial ascidians at @msarscentre.bsky.social in #SunnyBergen
November 7, 2025 at 11:00 AM
Friday seminar treat with a talk by Prof. De Tomaso on the reproductive and regenerative prowesses of colonial ascidians at @msarscentre.bsky.social in #SunnyBergen
Awesome to welcome and host @enricodanielloszn.bsky.social for a seminar and (short) visit at @msarscentre.bsky.social in #SunnyBergen, which - sometimes - is only a state of mind. 😉☀️🇳🇴
November 5, 2025 at 4:44 PM
Awesome to welcome and host @enricodanielloszn.bsky.social for a seminar and (short) visit at @msarscentre.bsky.social in #SunnyBergen, which - sometimes - is only a state of mind. 😉☀️🇳🇴
Late to repost, but it was an absolute treat to host Nico and discuss the biophysics of spindle positioning and more on a very #SunnyBergen day.
October 25, 2025 at 1:19 PM
Late to repost, but it was an absolute treat to host Nico and discuss the biophysics of spindle positioning and more on a very #SunnyBergen day.
Modeling whole ascidian embryos for #forksningdagene 😉🧪🧬🔬#devbio
September 22, 2025 at 6:04 AM
Modeling whole ascidian embryos for #forksningdagene 😉🧪🧬🔬#devbio
