(278g) Wnt-YAP Interactions during Neural Tissue Patterning of Human Induced Pluripotent Stem Cells

Julie Bejoy, Liqing Song, Yan Li

Department of Chemical and Biomedical Engineering, FAMU-FSU College of Engineering, Florida Agricultural and Mechanical University, Tallahassee, Florida, USA

Abstract

Human induced pluripotent stem cells (hiPSCs) have special ability to self-assemble into mini-organ like structures (e.g., organoids, mini-brains). In this process, Wnt signaling impacts regional patterning and positional identity of hiPSC-derived neural progenitors. One important function of Wnt signaling is to regulate Yes-associated protein (YAP) expression (nuclear or cytoplasmic), the pivotal regulator of cell proliferation and differentiation during organ growth and tissue generation. However, the crosstalk between Wnt and YAP expression during neural patterning of hiPSCs has not been well investigated. The objective of this study is to reveal the capability of Wnt signaling in the regulation of YAP expression to modulate 3-D neural spheroid formation from hiPSCs. Human iPSK3 cells were induced toward neural lineages through embryoid body formation. Wnt signaling was activated using CHIR99021, which was found to induce nuclear localization of YAP. CHIR99021 treatment upregulated the expression of HOXB4, the marker for hindbrain/spinal cord, while in the absence of Wnt activation, the cells maintained rostral forebrain neural identity (expression of TBR1 and BRN2) (by RT-PCR analysis and immunocytochemistry). Modulation of YAP expression with cytochalasin D also influenced neural cell identity, indicating bi-directional interactions of Wnt signaling and YAP expression. The perturbation of neural patterning was also evaluated by incorporating the neural spheroids with microparticles fabricated with triblock copolymer polycaprolactone-poly(dimethylsiloxane)-polycaprolactone. This study should advance our understanding on the biological processes regulated by Wnt signaling and YAP activity during neural tissue patterning and brain organoid engineering. The results have the significance in neurological disease modeling, drug screening, neural tissue regeneration, as well as studying virus infection.