Co-activators in extravillous trophoblast differentiation

Correct development of the human placenta provides the basis for successful pregnancy and fetal wellbeing. Cells of the placenta, the trophoblasts, specialize into different subtypes. One subtype, the extravillous trophoblast (EVT), originates from placental tissue that is attached to the uterus of the mother and migrates into maternal uterine tissue and vessels. EVTs play a pivotal role in placenta development since they prevent rejection of the foetus by the mothers immune system and modify the maternal spiral arteries thereby regulating fetal blood and oxygen supply. Failures in this remodelling process are associated with severe pregnancy complications such as preeclampsia or intrauterine growth restriction which are among the major causes of maternal and foetal morbidity and mortality in western countries. In contrast, abnormal, tumour-like EVT proliferation and invasion occurs in gestational trophoblastic diseases. Underlying causes could be defects in correct placentation and formation of the EVT lineage at early stages of pregnancy. However, molecular mechanisms controlling development of this particular invasive cell type remain only scarce. Herein, we propose to study the role of Yes-associated protein (YAP) and transcriptional co-activator with PDZ-binding motif (TAZ), two proteins that are known to act at the intersection of different developmental signalling pathways. In the nucleus YAP/TAZ function as co-activators of TGF-beta, Wingless and Hippo-dependent gene transcription thereby controlling cell fate decisions. Our preliminary data show that YAP and TAZ are present in nuclei of EVTs. Therefore, we hypothesize that YAP/TAZ could be critical for physiological and abnormal placenta formation and EVT development. Herein, we will study for the first time the biological effects of YAP/TAZ in EVTs, unravel their target genes and investigate YAP/TAZ-controlled genomic regions. We will utilize different placental model systems as well as innovative molecular techniques such as gene silencing, RNA sequencing and chromatin immunoprecipitation - DNA sequencing to analyse the role of YAP/TAZ in human trophoblasts. Moreover, expression of the co-activators in placental pathologies with aberrant trophoblast invasion will be investigated. To fulfil these tasks a collaborative network will be established involving newly employed PhD students, different experts from the Medical University of Vienna (Obstetrics and Fetal-maternal Medicine, Pathology, Core Unit Genomics) as well as scientists from the Department of Genetics, Stanford. In summary, results of the project will give novel insights into critical steps of EVT development thus providing the basis to a better understanding of pregnancy diseases associated with abnormal placental and trophoblast function.

The aim of this project was to gain better insights into the molecular processes of early human placental development. In particular, development of the two differentiated trophoblast subtypes within the first two weeks of gestation is critical for physiological placental function. On the one hand, syncytiotrophoblasts arise by cell fusion of trophoblast progenitors residing in the placental epithelium which transport nutrients and oxygen to the developing fetus and secrete pregnancy hormones into the maternal circulation. On the other hand, invasive extravillous trophoblasts develop during early gestation invading the maternal uterus and its vessels thereby provoking remodelling of the maternal spiral arteries. The latter is critical for adapted blood flow to the growing placenta. Defects in trophoblast differentiation have been noticed in various pregnancy disorders. For example, severe forms of intrauterine growth restriction and early onset preeclampsia are associated with failures in placentation and remodelling of the uterine spiral arteries thereby provoking oxidative damage of the developing placenta. A better understanding of physiological trophoblast development represents a prerequisite for abnormal placentation in gestational disorders and their diagnosis and treatment long-term. However, molecular processes controlling early human placental development are largely unknown, mostly due to the fact that appropriate model systems recapitulating early placentation were lacking in the past. Herein, we developed for the first time self-renewing 3-dimensional trophoblast organoids consisting of human trophoblast stem cells, progenitors and differentiated subtypes. Whereas the organoids undergo spontaneous cells fusion, formation of the invasive trophoblasts can be specifically generated by changing the culture conditions. Hence, trophoblast organoids represent the first model for precise induction of invasive trophoblast lineage. We used this model as well as primary trophoblast cells to investigate the role of the transcriptional co-activators YAP and TAZ in trophoblast stem cell renewal and invasive trophoblast function, respectively. In addition, we identified the receptor Notch1 as the first factor required for the development of the invasive extravillous trophoblast lineage.