Eszter Posfai

Postdoctoral Scientist- Lim Lab Primary Work Address: Dept of Molecular Biology, Princeton, NJ, 08544 Current HHMI Employees, click here to apply via your Workday account. The Lim Lab at Princeton University is seeking an energetic,...

LIMmunity is growing! 🤰🤱👶

We are looking for curious & driven postdocs to join us at @princetonmolbio.bsky.social & HHMI to explore the fascinating world of maternal-offspring immune partnerships!

Come be part of our collaborative team!

hhmi.wd1.myworkdayjobs.com/en-US/Extern...

Figure 1 - Live imaging of endogenously tagged YAP-miRFP670, mScarlet-I-SOX2 and CDX2-eGFP during the first fate decision in preimplantation embryos. (A) A developmental timeline of trophectoderm (TE) and inner cell mass (ICM) specification. The first cell differentiation event, between the TE (green) and ICM (purple), initiates at the 16-cell stage, establishing distinct inner, ICM, and outer, TE, cell populations in the 32-cell stage embryo. Embryos in this study are imaged until the 32-cell stage. Days post-fertilization are denoted by embryonic day. (B) Sox2 and Cdx2 expression is regulated by YAP. In ICM cells, YAP is phosphorylated and retained in the cytoplasm, facilitating Sox2 expression. In TE cells, YAP is predominantly localized to the nucleus where it activates expression of Cdx2. (C) Time-lapse images of a representative embryo expressing YAP-miRFP670, mScarlet-I-SOX2 and H2B-miRFP670 from the 8-cell through the late 32-cell stage. A z-stack was acquired every 15 min for YAP and H2B channels, and every 30 min for the SOX2 channel. Maximum intensity projections (MIPs) are shown. Unit of time is hours. Scale bar: 10 µm. (D) Time-lapse images of a representative embryo expressing YAP-miRFP670, CDX2-eGFP and H2B-miRFP670 from the 8-cell stage through the late 32-cell stage. Scale bar: 10 µm.

Mathematical modelling of the first fate decision

This Research Highlight showcases the work from Maria Avdeeva, Madeleine Chalifoux, Bradley Joyce, Stanislav Y. Shvartsman, Eszter Posfai @eposfai.bsky.social :

journals.biologists.com/dev/article/...

Depletion of a neural cell adhesion molecule disrupts both epithelial and germ layer identity in sea anemone embryos Assembly of cells into epithelial layers marks the early steps of tissue organization and embryonic development in most animals. Although several conserved proteins are known to be essential for epith...

our unexpected results on the importance of a neural cell adhesion molecule in sea anemone epithelialization and gastrulation are just posted in the following preprint.

www.biorxiv.org/content/10.1...

The #devbio project that encompassed the majority of my postdoc is finally out! Huge thanks to my coauthors and our collaborators without whom this work would not have been possible, and my adviser Eszter Posfai who let me play with a light sheet microscope and some colorful mice :)

Live imaging endogenous transcription factor dynamics reveals mechanisms of epiblast and primitive endoderm fate segregation Kim-Yip, Denberg, et al. visualize epiblast and primitive endoderm specification by live imaging key transcription factors. They reveal systematic and stochastic features by identifying a primary epib...

Moral of the story: the mouse embryo uses some preplanning as well as some randomness to conduct this important fate decision. Huge thank you to everyone involved + to @currentbiology.bsky.social for the awesome publishing experience! www.cell.com/current-biol...

Whether the trajectory is maintained towards PE or switches to Epi is in part predicted by the level of another TF, NANOG, which in turn seems to behave in a stochastic manner.

We then showed that FGF signaling, with the ligand likely from the primary Epi lineage, sets all other cells on the course towards PE differentiation. This trajectory however switches in some lineages, within a defined developmental window, giving rise to a second wave of Epi cells.

We found the emergence of a founder, termed primary Epi cell lineage as the first symmetry breaking event. Moreover, this primary Epi cell was marked by early expression of SOX2, a TF linked to the segregation of the previous fate decision. Therefore, symmetry breaking is linked to lineage history.

We simultaneously live image endogenously tagged transcription factors (up to 3 of them!) key to this fate decision, which allowed us not only to analyze the lineage history of cells, but also to directly visualize how individual cells choose their fates in developing embryos.

Thrilled to share our work using live imaging to understand how Epiblast (future embryo proper) and Primitive Endoderm (future extraembryonic tissues) cell fates segregate in the preimplantation mouse embryo. Gargantuan effort led by amazing @rpkimyip.bsky.social, David Denberg and Denis Faerberg!

pYtags - our in vivo biosensors for receptor tyrosine kinases - in all their beauty on the cover of Cell Reports! Read more here: www.cell.com/cell-reports...

We’re hiring! Our lab at WashU has an opening for a Senior/Staff Scientist position. If you're passionate about ovarian physiology, oocyte quality, and excited to contribute to a dynamic and growing team, we’d love to hear from you! Reach out to me directly for more information.

Excited to share that our work building in vivo biosensors for receptor tyrosine kinases (pYtags!) is now out www.cell.com/cell-reports...

Intercellular bridges are essential for transposon repression and meiosis in the male germline - Nature Communications A conserved feature of metazoan meiosis is that it occurs in a syncytium. Here, the authors show that intercellular bridges that connect germ cells in a syncytium are critical for ensuring proper meio...

For my first science post here, I’m proud to advertise our latest work exploring why germ cell connectivity is really important for meiosis 🐁

Done with some awesome colleagues @florpratto.bsky.social

www.nature.com/articles/s41...

Epithelial polarization by the planar cell polarity complex is exclusively non–cell autonomous For cells to polarize collectively along a tissue plane, asymmetrically localized planar cell polarity (PCP) complexes must form intercellular contacts between neighboring cells. Yet, it is unknown wh...

How many cells do you need to establish PCP? The magic number is 3! Beautiful work by Lena Basta in Danelle Devenport's lab. Happy to have contributed. www.science.org/doi/10.1126/...

Epithelial polarization by the planar cell polarity complex is exclusively non–cell autonomous For cells to polarize collectively along a tissue plane, asymmetrically localized planar cell polarity (PCP) complexes must form intercellular contacts between neighboring cells. Yet, it is unknown wh...

Interaction between two cells is necessary and sufficient to initiate PCP sorting😀, as shown by Lena P. Basta, Bradley W. Joyce, Dr. Eszter Posfai @eposfai.bsky.social , and Dr. Danelle Devenport. Here is the article. www.science.org/doi/10.1126/...

Generative model for the first cell fate bifurcation in mammalian development The first cell fate bifurcation in mammalian development directs cells toward either the trophectoderm (TE) or inner cell mass (ICM) compartments in preimplantation embryos. This decision is regulated by the subcellular localization of a transcriptional co-activator YAP and takes place over several progressively asyn-chronous cleavage divisions. As a result of this asynchrony and variable arrangement of blastomeres, reconstructing the dynamics of the TE/ICM cell specification from fixed embryos is extremely challenging. To address this, we developed a live imaging approach and applied it to measure pairwise dynamics of nuclear YAP and its direct target genes, CDX2 and SOX2, key transcription factors of TE and ICM, respectively. Using these datasets, we constructed a generative model of the first cell fate bifurcation, which reveals the time-dependent statistics of the TE and ICM cell allocation. In addition to making testable predictions for the joint dynamics of the full YAP/CDX2/SOX2 motif, the model revealed the stochastic nature of the induction timing of the key cell fate determinants and identified the features of YAP dynamics that are necessary or sufficient for this induction. Notably, temporal heterogeneity was particularly prominent for SOX2 expression among ICM cells. As heterogeneities within the ICM have been linked to the initiation of the second cell fate decision in the embryo, understanding the origins of this variability is of key significance. The presented approach reveals the dynamics of the first cell fate choice and lays the groundwork for dissecting the next cell fate bifurcations in mouse development. ### Competing Interest Statement The authors have declared no competing interest.

The second paper, incorporating a probabilistic modeling approach, investigates the relationship between YAP dynamics and two of its downstream transcription factor targets, SOX2 (ICM) and CDX2 (TE).

www.biorxiv.org/content/10.1...

Geometric, cell cycle and maternal-to-zygotic transition-associated YAP dynamics during preimplantation embryo development During the first cell fate decision in mammalian embryos the inner cell mass cells, which will give rise to the embryo proper and other extraembryonic tissues, segregate from the trophectoderm cells, the precursors of the placenta. Cell fate segregation proceeds in a gradual manner encompassing two rounds of cell division, as well as cell positional and morphological changes. While it is known that the activity of the Hippo signaling pathway and the subcellular localization of its downstream effector YAP dictate lineage specific gene expression, the response of YAP to these dynamic cellular changes remains incompletely understood. Here we address these questions by quantitative live imaging of endogenously tagged YAP while simultaneously monitoring geometric cellular features and cell cycle progression throughout cell fate segregation. We apply a probabilistic model to our dynamic data, providing a quantitative characterization of the mutual effects of YAP and cellular relative exposed area, which has previously been shown to correlate with subcellular YAP localization in fixed samples. Additionally, we study how nuclear YAP levels are influenced by other factors, such as the decreasing pool of maternally provided YAP that is partitioned to daughter cells through cleavage divisions, cell cycle-associated nuclear volume changes, and a delay after divisions in adjusting YAP levels to new cell positions. Interestingly, we find that establishing low nuclear YAP levels required for the inner cell mass fate is largely achieved by passive cell cycle-associated mechanisms. Moreover, contrary to expectations, we find that mechanical perturbations that result in cell shape changes do not influence YAP localization in the embryo. Together our work identifies how various inputs are integrated over a dynamic developmental time course to shape the levels of a key molecular determinant of the first cell fate choice. ### Competing Interest Statement The authors have declared no competing interest.

The first paper looks at how different inputs, such as cell position and shape, cell cycle progression and transitioning from maternal to zygotic resources during early development impact the nuclear levels of YAP, a key regulator this fate decision.

www.biorxiv.org/content/10.1...

A duo of preprints on the dynamics of the first cell fate decision in mouse by Madeleine Chalifoux (first grad student in the lab!) and Maria Avdeeva (Flatiron).

We use quantitative live imaging of key cell fate determinants to follow the segregation of inner cell mass and trophectoderm lineages.

Congrats, looking fwd to reading!!

Have you ever wanted to *see* receptor activity in embryos? If so, our new preprint is for you! In it, we showcase a new live-cell biosensor for visualizing receptor tyrosine kinase activity in living embryos – pYtags!

www.biorxiv.org/content/10.1...

An intriguing mechanism of germline cyst formation through innovative live imaging in fetal mice gonads, and computational modeling.

Check out my dispatch in @currentbiology.bsky.social on this beautiful work.

kwnsfk27.r.eu-west-1.awstrack.me/L0/https:%2F%2…

Sensing of extracellular L-Proline availability by the integrated stress response determines the outcome of cell competition. Cell competition is a quality control acting from development to the adult that eliminates cells that are less-fit than their neighbours. How winner cells induce the elimination of losers during this ...

Fascinating & unexpected from the Rodriguez lab on cell competition acting as a nutrient sensor

Winner cells increase L-Proline uptake in losers, repressing their survival pathway (ISR) to kill them

Explains old observations that starvation prevents competition

www.biorxiv.org/content/10.1...

Sharing my latest preprint as a re-introduction to bsky!

biorxiv.org/content/10.1...
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Everyday, cells like this crawl through your body to protect you. While we know that their front 🔴 and back 🔵 polarity programs work together, how exactly do these two processes communicate?

Thank you, John! 😀

Thank you, Andi!

Can I pls be added? Thanks!

Please add me as well, thx! :)

Check out our new paper in @currentbiology.bsky.social by amazing grad students @ezlevy.bsky.social and @isabellaleite.bsky.social “A tug-of-war between germ cell motility and intercellular bridges controls germline cyst formation in mice”
authors.elsevier.com/a/1k7fg3QW8S...