Myriam Hemberger

Myriam Hemberger has located to Canada to take up a Professorship at the University of Calgary. Her new webpage can be found here.

Research Summary

The focus of our work is on the establishment, maintenance and differentiation of trophoblast cells leading to formation of a functional placenta. The placenta is the defining organ of most mammals, providing a nutritive conduit that is crucial for all embryonic development to occur. Trophoblast cells are the major building blocks of the developing placenta. They are the first cell type to arise very early in development when they are set apart from cells giving rise to the embryo itself. The various functions of trophoblast cells early in development are vital for reproductive success, as they lay the foundations for a normal pregnancy and healthy foetus later on. A better understanding of the mechanisms underlying these early events will be critical to develop better screens and therapeutic avenues for pregnancy complications.
 
We are in particular interested in how the early trophoblast niche is regulated by transcription factors and specific epigenetic modifiers to ensure normal development. Leading on from this, we also investigate how susceptible the trophoblast compartment is to perturbations by extrinsic factors that activate specific signalling cascades, including in the context of development in mothers of advanced age. For this we are taking a range of high-throughput epigenomic and transcriptomic approaches to study these early events in placental development.
 
Key among our tools is the use of murine trophoblast stem (TS) cells, which mimic many of the properties of the early placenta. Learning about the self-renewal mechanisms of TS cells, in comparison to embryonic stem (ES) cells, will help us uncover the fundamental principles of how the early placenta develops and is influenced by external factors, which may be predictive for life long physiology and health. These insights will also enable us to better understand the earliest steps in human placentation and to develop novel cellular research tools to study the underlying molecular processes.

Latest Publications

Excessive endoplasmic reticulum stress drives aberrant mouse trophoblast differentiation and placental development leading to pregnancy loss.
Capatina N, Hemberger M, Burton GJ, Watson ED, Yung HW

Endoplasmic reticulum (ER) stress promotes placental dysmorphogenesis and is associated with poor pregnancy outcomes. We show that unfolded protein response signalling pathways located in the ER drive differentiation of mouse trophoblast stem cells into trophoblast subtypes involved in development of the placental labyrinth zone and trophoblast invasion. In a mouse model of chronic ER stress (Eif2s1 ), higher ER stress in homozygous blastocysts is accompanied by reduced trophectoderm cell number, developmental delay, and is associated with an increased incidence of early pregnancy loss. Administration of the chemical chaperone, tauroursodeoxycholic acid, to Eif2s1 heterozygous females during pregnancy alleviated ER stress in the mutant placenta, restored normal trophoblast populations and reduced the frequency of early pregnancy loss. Our results suggest that alleviation of intrauterine ER stress could provide a potential therapeutic target to improve pregnancy outcome in women with pre-gestational metabolic or gynaecologic conditions. ABSTRACT: Women with pre-gestational health conditions (e.g., obesity, diabetes) or gynaecological problems (e.g., endometriosis) are at increased risk of adverse pregnancy outcomes including miscarriage, preeclampsia and fetal growth restriction. Increasing evidence suggests that unfavourable intrauterine conditions leading to poor implantation and/or defective placentation are a possible causative factor. The endoplasmic reticulum (ER) unfolded protein response (UPR ) signalling pathways are a convergence point of various physiological stress stimuli that can be triggered by an unfavourable intrauterine environment. Therefore, we explored the impact of ER stress on mouse trophoblast differentiation in vitro, mouse blastocyst formation and early placenta development in the Eif2s1 mutant mouse model of chronic ER stress. Chemically-manipulated ER stress or activation of UPR pathways in a mouse trophoblast stem cell line promoted lineage-specific differentiation. Co-treatment with specific UPR pathway inhibitors rescued this effect. While the inner cell mass was unaffected, the trophectoderm of homozygous Eif2s1 blastocysts exhibited ER stress associated with a reduced cell number. Furthermore, one-third of Eif2s1 homozygous blastocysts exhibited severe developmental defects. We have previously reported a reduced trophoblast population and premature trophoblast differentiation in Eif2s1 homozygous placentas at mid-gestation. Here, we demonstrate that treatment of Eif2s1 heterozygous pregnant females with the chemical chaperone tauroursodeoxycholic acid alleviated ER stress, restored the trophoblast population, and reduced the frequency of embryonic lethality. Our data suggest that therapeutic targeting of ER stress may improve pregnancy outcome in women with pre-gestational metabolic or gynaecologic conditions. This article is protected by copyright. All rights reserved.

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The Journal of physiology, 1, 1, 16 Jul 2021

PMID: 34269420

BAP1/ASXL complex modulation regulates epithelial-mesenchymal transition during trophoblast differentiation and invasion.
Perez-Garcia V, Lea G, Lopez-Jimenez P, Okkenhaug H, Burton GJ, Moffett A, Turco MY, Hemberger M

Normal function of the placenta depends on the earliest developmental stages when trophoblast cells differentiate and invade into the endometrium to establish the definitive maternal-fetal interface. Previously, we identified the ubiquitously expressed tumour suppressor BRCA1-associated protein 1 (BAP1) as a central factor of a novel molecular node controlling early mouse placentation. However, functional insights into how BAP1 regulates trophoblast biology are still missing. Using CRISPR/Cas9 knockout and overexpression technology in mouse trophoblast stem cells, here we demonstrate that the downregulation of BAP1 protein is essential to trigger epithelial-mesenchymal transition (EMT) during trophoblast differentiation associated with a gain of invasiveness. Moreover, we show that the function of BAP1 in suppressing EMT progression is dependent on the binding of BAP1 to additional sex comb-like (ASXL1/2) proteins to form the polycomb repressive deubiquitinase (PR-DUB) complex. Finally, both endogenous expression patterns and BAP1 overexpression experiments in human trophoblast stem cells suggest that the molecular function of BAP1 in regulating trophoblast differentiation and EMT progression is conserved in mice and humans. Our results reveal that the physiological modulation of BAP1 determines the invasive properties of the trophoblast, delineating a new role of the BAP1 PR-DUB complex in regulating early placentation.

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eLife, 10, 1, 25 Jun 2021

PMID: 34170818

Open Access

Increased transcriptome variation and localised DNA methylation changes in oocytes from aged mice revealed by parallel single-cell analysis.
Castillo-Fernandez J, Herrera-Puerta E, Demond H, Clark SJ, Hanna CW, Hemberger M, Kelsey G

Advancing maternal age causes a progressive reduction in fertility. The decline in developmental competence of the oocyte with age is likely to be a consequence of multiple contributory factors. Loss of epigenetic quality of the oocyte could impair early developmental events or programme adverse outcomes in offspring that manifest only later in life. Here, we undertake joint profiling of the transcriptome and DNA methylome of individual oocytes from reproductively young and old mice undergoing natural ovulation. We find reduced complexity as well as increased variance in the transcriptome of oocytes from aged females. This transcriptome heterogeneity is reflected in the identification of discrete sub-populations. Oocytes with a transcriptome characteristic of immature chromatin configuration (NSN) clustered into two groups: one with reduced developmental competence, as indicated by lower expression of maternal effect genes, and one with a young-like transcriptome. Oocytes from older females had on average reduced CpG methylation, but the characteristic bimodal methylation landscape of the oocyte was preserved. Germline differentially methylated regions of imprinted genes were appropriately methylated irrespective of age. For the majority of differentially expressed transcripts, the absence of correlated methylation changes suggests a post-transcriptional basis for most age-related effects on the transcriptome. However, we did find differences in gene body methylation at which there were corresponding changes in gene expression, indicating age-related effects on transcription that translate into methylation differences. Interestingly, oocytes varied in expression and methylation of these genes, which could contribute to variable competence of oocytes or penetrance of maternal age-related phenotypes in offspring.

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Aging cell, 1, 1, 17 Nov 2020

PMID: 33201571