Chloe Girard, PhD
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chloegirard.bsky.social
Chloe Girard, PhD
@chloegirard.bsky.social
1.4K followers 1.1K following 420 posts
Personally done with meiosis I. Professionally in love with it.
Permanent researcher at I2BC 🇫🇷 Arabidopsis 🌱 Sordaria 🍄 Genetics/Genomics 🧬 Fixed and live imaging 🔬.
#meiosis4ever her/she
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chloegirard.bsky.social
This is the work of a tremendous PhD student, Benoit Madec, who did everything in this study (genetics, molecular biology, all the bioinformatics analyses)

He defended his PhD on Monday and is now Dr Madec!

I am very proud of him and all the work he has accomplished!
Benoît during his PhD defense on Monday!
October 1, 2025 at 9:05 AM
chloegirard.bsky.social
Ok but so what do you think is happening?!

We propose a model in which presence of polymorphism is a major driver of recombination in A. thaliana, totally reshaping the crossover landscape, and competing with other rec. drivers that usually favor crossovers in the pericentromeric "HRZ" regions.
Our model: Left: in full hybrids (or fully homozygous lines for that matter, check out Raphaël Mercier's work Lian et al., 2022), most crossovers occur around the centromeres, promoted by unknown recombination drivers (although we have a few hypotheses!!). Right: in cases where recombination has the choice, crossovers are favored in polymorphic regions (purple) at the expense of non-polymorphic ones (yellow). We also discuss the role of crossover interference (dint) in shaping the crossover landscape, whose strength is unchanged in the two situations, but whose effect can amplify the differences cause by the presence of polymorphism.
October 1, 2025 at 8:31 AM
chloegirard.bsky.social
How is this happening ?

Recombination involves the invasion of an intact matrix by a broken DNA molecule. If the sequence of the two DNA molecules differes, this can create mismatches, recognized by the MMR (mismatch repair)/

The MMR protein MSH2 is required for COs to form in polymorphic regions.
Top: Recombination Rate (cM/Mb) on chromosome 3 of A. thaliana, in both WT and msh2 mutant lines. Yellow: non-polymorphic regions, Purple: polymorphic regions. Dashed line: Centromere Bottom: recombination rate across the genome in both WT and msh2, in all polymorphic regions (purple, left) and non-polymorphic ones (yellow, left) of the genome. We observe that the recombination rate is lower in msh2 than in WT in polymorphic regions, but the opposite is true in non-polymorphic ones. This suggests that MSH2 drives recombination to polymorphic regions.
October 1, 2025 at 8:31 AM
chloegirard.bsky.social
What is fantastic about this discovery?

Not only do we turn cold region of the genome hot, but we also turn hot regions cold !

Case and point: the High-Recombination Zone (HRZ) that flanks the centeromeres in A. thaliana can be depleted of crossovers (see also Fig 1 above).
Recombination Rate (cM/Mb) on chromosome 2 of A. thaliana (male meiosis). When non-polymorphic (yellow), the HRZ (high-recombination zone) sees its recombination rate decrease compared to full F1 hybrids (grey, where polymorphism is distributed all along the chromosomes). This is due to the fact that a polymorphic region (purple) is present on the arm of the chromosome, which promotes local recombination, at the expense of the HRZ.
October 1, 2025 at 8:31 AM
chloegirard.bsky.social
And what do we see ?

Always higher recombination in polymorphic regions (heterozygous, purple), than in non-polymorphic ones (homozygous, yellow).

This is true in male and female meiosis, across the genome, independently of other genomic features.
Top: recombination rate (RR) across chromosomes 4 of A. thaliana. Purple: RR when the region is polymorphic (Heterozygous) Yellow: RR when the region is non-polymorphic (Homozygous) Grey: Centromeric region. Pale blue: Pericentromeres, as defined by DNA methylation levels. Bottom: Normalized total number of crossovers per region, the darker the color palette, the more COs. When a region is heterozygous (polymorphic, purple) , the recombination rate is higher than when the same region is homozygous (non polymorphic, yellow).
October 1, 2025 at 8:31 AM
chloegirard.bsky.social
How did we figure this out?

We used Recombinant Inbred Lines, which genomes are a patchwork of two parental genomes. After many generations of inbreeding, these lines are now homozygous.

We backcrossed the RIL to its parents, and measured recombination genome-wide in both crosses.
Experimental design: a Recombinant Inbred Line (RIL, top) is crossed to its original parents (Catania-1 and Columbia-0). This produces two lines (bottom) in which some regions are polymorphic, and some are not. Because we performed both crosses, we can measure crossovers (COs) in each region under its polymorphic (purple) or non-polymorphic state (yellow). We also analyzed male and female meiosis independently for both reciprocal crosses.
October 1, 2025 at 8:31 AM
chloegirard.bsky.social
🚨 First pre-print from my team !!

TL;DR: presence of polymorphism (sequence differences between the homologous chromosomes) can *increase* the local rate of recombination in Arabidopsis thaliana, turning cold regions of the genome hot (purple v. grey) !
The recombination frequency (cM/Mb) along chromosome 4 of A. thaliana (female meiosis). In full hybrids (grey), where polymorphism is distributed all along chromosomes, most crossovers occur in the regions surrounding the Centromere (Cen), and very few at chromosome ends (Tel: telomeres). In lines where polymorphism is restricted to chromosome ends (purple), the local recombination rate increases drastically, at the expense of the non-polymorphic regions (yellow).
October 1, 2025 at 8:31 AM
chloegirard.bsky.social
Congratulations @heidiserra.bsky.social for your @cnrs.fr Bronze Medal !!!

www.insb.cnrs.fr/fr/personne/...

So proud to have such a badass friend and colleague !
#meiosis4ever
July 10, 2025 at 12:52 PM
chloegirard.bsky.social
We’re here for the EMBO meiosis 2025 in Engelberg!

Very nice venue, thank you Kirsten Bomblies and Marinela Dukic for organizing!
The Kursaal hall in Engelberg where the EMBO Meiosis 2025 is held
June 22, 2025 at 3:26 PM
chloegirard.bsky.social
Mon chachat t’envoie un câlin
My big cat on the floor in « please pet me » mode
June 10, 2025 at 10:32 AM
chloegirard.bsky.social
Look at that red nucleus stretching like CRAZY ! Who knew nuclei could do that ! DNA stretching, sure, but what about the nuclear membrane ?! (scale bar 10µm !)

The longest measured nucleus reached 71µm !!
June 10, 2025 at 9:02 AM
chloegirard.bsky.social
Les gnocchi rôtis de @owiowifouettemoi.bsky.social c’est l’invention géniale
Picture of said roasted gnocchi with red onions, cherry tomatoes, and pieces of lard
June 1, 2025 at 5:42 PM
chloegirard.bsky.social
Second Triathlon S done!
Very happy about my time (2h05, 750m swim, 23km bike, 5km run).
Me in my trisuit on the beach, next to my son holding a banner that says “Allez Maman Chloé” (Go Mommy Chloe)
May 18, 2025 at 7:14 PM
chloegirard.bsky.social
Had an absolute blast in Iceland these past two weeks. Away from all the nastiness of the world. Back to science with a clearer head and purpose.
Five pictures of Iceland, first showing me and my kid climbing a snowy slope, second the two of us in a frozen water all, middle one of Snæfellsnes peninsula, fourth one is my kid in the car listening to stories with headphones and looking out through the window, last one is another Snaefellsnes picture with snowy mountain
March 3, 2025 at 5:52 PM
chloegirard.bsky.social
Such great nappers, and I love to nap alongside them!
My black cat sleeping on a yellow blanket. There are four paws in the picture but it’s hard to know which ones are front and which ones are back!
January 24, 2025 at 10:13 PM
chloegirard.bsky.social
Dinner is cooking, best time of the day.
My cat on my lap A glass of bourbon in my hand The Christmas tree is still up There are toys everywhere In the back my messy kitchen
January 8, 2025 at 7:32 PM
chloegirard.bsky.social
Hello #FrenchESR

Qqun a déjà appliqué et/ou obtenu un financement MRSEI de l'ANR pour le Montage de réseaux scientifiques européens ?

Je serais intéressée de discuter de vive voix avec vous !
Page de garde du document détaillant l'appel d'offre "Appel à propositions Montage de réseaux scientifiques européens ou internationaux (MRSEI)"
January 6, 2025 at 2:50 PM
chloegirard.bsky.social
Câlin du matin!
My black cat sleeping on the side, holding a white plush toy (Milou from Tintin) between his front paws
December 11, 2024 at 5:07 PM
chloegirard.bsky.social
My dad (24yo at the time) holding me (a few days old). I am smiling and he is looking at me
November 29, 2024 at 7:47 AM
chloegirard.bsky.social
Hihihi
Word cloud from my Google scholar profile. Prominent words include: meiotic, complex, formation, crossovers.
November 22, 2024 at 9:37 PM
chloegirard.bsky.social
we never get snow in November in Paris, but we did yesterday !!
Picture of the snowy lawn at my workplace
November 22, 2024 at 7:18 PM
chloegirard.bsky.social
Sounds about right!
Word cloud based on my Google scholar profile. Most prominent words are: meiotic, complex, formation, crossovers, crossover (yes, once plural once singular, this is how much I like crossovers).
November 22, 2024 at 7:16 PM
chloegirard.bsky.social
Decided to take my son out school earlier than usual and get some daytime play in the snow! ❄️
Very rudimentary snowman we built with my son. Eyes are made of pine cones, nose with a carrot (obviously !) and mouse of chestnuts. It’s roughly 40cm high, on our outdoor table.
November 21, 2024 at 5:05 PM
chloegirard.bsky.social
Opening of the Bettencourt Foundation ceremony for Impulscience grant announcement.

« Un chercheur est celui qui risque sa vérité et qui se casse la figure » Michel Serres

[a research is someone risking their truth and falls on the wayside]
Françoise Meyer Bettencourt during her speech for the opening of the ceremony
November 19, 2024 at 6:53 PM
chloegirard.bsky.social
Thank you @charleneboumendil.bsky.social for coming to I2BC ! We had fun talking condensates!
Charlene talking through her thank you slide from her talk
November 18, 2024 at 8:41 PM