209 Rho signaling-directed regulation of YAP/TAZ in parthenogenetic stem cells

Mammalian oocyte maturation is characterised by asymmetric meiotic division that is regulated by specific cytoskeleton organisation. Similarly, during early embryonic divisions, one of the most important steps is the establishment of polarity that allows cells to adopt distinct developmental fates. All of these events are driven by dynamic changes in actin filaments. It has been demonstrated recently that the Rho signalling pathway plays a key role in the organisation and rearrangement of actin-containing structures, regulating cell polarity and migration. In addition, beside its effect on cell cytoskeleton, Rho directly interacts with the Hippo pathway, influencing both embryonic cell proliferation and differentiation. Because both Rho and Hippo are expressed by the oocyte and maternally inherited (Zhang et al. 2014 Cell Cycle 13, 3390-3403, https://doi.org/10.4161/15384101.2014.952967; Menchero et al. 2017 Dev. Dyn. 246, 245-261, https://doi.org/10.1002/dvdy.24471), we investigated their regulation in parthenogenetic embryonic stem cells (ParthESC) that possess exclusively maternal genetic material, and compared the results with biparental ESCs. Previous results obtained by whole-transcriptome analysis revealed the presence of several differentially expressed genes involved in the Rho pathway and showed no differences for most of the Hippo signalling genes. To better elucidate the molecular mechanisms involved, in the present study, we dissected the expression pattern of the Rho and Hippo regulatory genes in human biparental ESCs and ParthESC. Experiments were performed on 4 biparental ESC and 4 ParthESC lines using cells between passages 5 to 25. The results showed significantly increased transcription of the Rho GTPase family genes (RHOA, RHOB, and RHOC) in ParthESC compared with biparental ESCs. Consistent with this, 12 of 17 Rho activators were significantly upregulated, whereas 8 of 11 Rho inhibitors were significantly decreased in ParthESC. Furthermore, monoparental cells displayed significantly higher expression levels of YAP and TAZ, whereas the upstream genes involved in the Hippo pathway (LATS1/2, MOB1, MST1/2, NF2) were comparable in the two cell types. Interestingly, a significantly higher total YAP protein content was detected in ParthESC, whereas the quantity of the phosphorylated form was comparable in the two cell types. This accounts for the observed upregulation of Rho genes, which stimulate the assembly of contractile actin stress fibres, inhibiting LATS1/2 phosphorylation and preventing subsequent phosphorylation of YAP/TAZ (Yu and Guan 2013 Genes Dev. 27, 355-371; https://doi.org/10.1101/gad.210773.112). Altogether, our results suggest that the Rho pathway may regulate YAP/TAZ behaviour via a LATS/MST/NF2-independent process in ParthESC, similarly to a previous report in oocytes (Posfai and Rossant 2016 Cell Res. 26, 393-394; https://doi.org/10.1038/cr.2016). Although further clarifications are needed, we hypothesise that the regulatory mechanisms detected in ParthESC may be related to their strictly maternal origin, with a possible impact on their plasticity and potency. This study was supported by Carraresi Foundation. Authors are members of the COST Actions CA16119.

212 Increased expression of YAP/TAZ encourages outgrowth establishment and three-dimensional colony formation and boosts plasticity of parthenogenetic stem cells

Cell proliferation, apoptosis, and differentiation are essential processes from the early phases of embryogenesis to adult tissue formation and maintenance. These mechanisms also play a key role in embryonic stem cells (ESCs), which are able to proliferate maintaining pluripotency and, at the same time, give rise to all populations belonging to the three germ layers in response to specific stimuli. ESCs are, therefore, considered a well-established invitro model to study the complexity of these processes. We previously generated porcine and human diploid parthenogenetic embryonic stem cells (ParthESC) that showed many features and regulatory pathways common to biparental ESCs. However, we observed that monoparental cells demonstrated a greater ability to form outgrowths and generate stable three-dimensional (3D) spheroid colonies, which are distinctive signs of high plasticity (Brevini et al. 2010 STCR 6; https://doi.org/10.1007/s12015-010-9153-2). In the present study, we compared porcine and human biparental ESCs and ParthESC. Pluripotency gene expression was analysed and ELISA tests for global DNA methylation and total YAP levels were performed. Our results showed that ParthESCs showed significantly higher expression levels of YAP and TAZ than biparental ESCs. In contrast, the analysis of the upstream genes involved in the Hippo signalling pathway revealed no differences. We demonstrated that YAP remains in a dephosphorylated form, encouraging its nuclear compartmentalization and direct interaction with the nuclear transcription factors TEADs and SMADs, that are also upregulated and maintain pluripotency, repressing differentiation processes (Beyer et al. 2013 Cell Rep. 5, 1611-1624; https://doi.org/10.1016/j.celrep.2013.11.021). These complex regulatory interactions accompanied the overexpression of the pluripotency-related genes OCT4, NANOG, REX1, SOX2, UTF1, and TERT. In parallel, we observed a decrease of DNMT3 and DNMT4 activity that resulted in a global DNA hypomethylation and a chromatin high-permissive state. Altogether, our results demonstrate a significant upregulation of YAP/TAZ activity in monoparental cell lines. This may account for their greater ability to form outgrowths and generate 3D spheroid colonies and increased plasticity compared with biparental counterparts. It is interesting to note that YAP mRNA is supplied and expressed by the oocyte and is maternally inherited (Yu et al. 2016 Cell Res. 26, 275-287; https://doi.org/10.1038/cr.2016.20). Although further clarifications are needed, we hypothesise that its higher expression in ParthESC may be related to the strictly maternal origin of these cells. This study was supported by the Carraresi Foundation. Authors are members of the COST Actions CA16119.

187 Phenotype switch of human fibroblasts into trophoblastic cells

The first differentiation event in mammalian embryos is the formation of the trophectoderm, which is crucial for implantation of the blastocyst and gives rise to specialised populations of trophoblast cells in the definitive placenta. However, our understanding of these early differentiation events is limited, particularly in humans, because of ethical and legal restrictions on the isolation and manipulation of human embryogenesis. Here we describe experiments aimed at converting human fibroblasts into trophoblastic cells, using 5-azacytidine (5-aza-CR) to erase the original phenotype and a cocktail containing bone morphogenic protein 4 (BMP4) and inhibitors of the activin/nodal/ERK signalling pathways, to drive trophoblastic differentiation. The method required 3 main steps: (1) preparation of mouse embryonic fibroblasts (MEF) monolayer, and culture and collection of MEF conditioned medium (CM); (2) culture of human fibroblasts, obtained from a skin biopsy, and epigenetic erasure with 5-aza-CR for 18 h; (3) use of CM, with BMP4 (50 ng mL−1), PD0325901 (1 µM), CHIR99021 (1 µM), and PD173074 (0.1 µM) to differentiate erased human fibroblasts to trophoblast cells. Morphology changes were monitored along the process. In the initial phase of differentiation, a mixture of cell types appeared, including small cells growing in clusters and giant cells possessing very large nuclei. After 2 weeks of culture, cells displayed a distinct trophoblast-like morphology and showed the presence of typical clustering/lacunae monolayer patterning. Cells continued to proliferate and maintained a normal karyotype. BMP4-mediated differentiation was also assessed by quantitative RT-PCR using primers specific for 2 trophoblast markers: keratin 7 (KRT7) and caudal type homeobox 2 (CDX2), that are absent in the original fibroblasts. Their expression appeared by Day 3 of induction and was strong and steady throughout the process, confirming that the acquisition of a trophoblast-like morphology was supported by the activation of trophoblast-specific gene transcription. The results demonstrate the possibility of obtaining trophoblast-like cells through the conversion of human fibroblasts and confirm the involvement of BMP4-together with the inhibition of the activin/nodal/ERK signalling pathway-to activate early trophoblast differentiation in vitro. The challenge for future experiments will be to determine the precise role of BMP signals in human trophoblast definition in vivo, which, to our knowledge, has not been elucidated yet. The method here described is efficient and reproducible and has the advantage of utilising easily accessible cells as a starting population. It can be used for a variety of applications, including drug discovery and stem cell research, as well as to implement studies on the pathogenesis of developmental disorders with trophoblast defects. This research was supported by Carraresi Foundation. Authors are members of the COST Actions CA16119 and CM1406.

[Computerized stabilometry in the monitoring of antiepileptic therapy in children]

Computerized stabilometry is an useful test to monitor postural effects of anticonvulsant therapy in adults. Our study was carried out on 65 epileptic children: 51 were treated with CBZ or PHT or VPA or PB in monotherapy, and 14 were not on therapy, in the aim to observe abnormalities of postural control in pediatric population. Computerized stabilometry has to be considered auxiliary monitoring to evaluate toxic effect of anticonvulsant therapy in children.