Robert Wood Johnson Medical School, USA
Posters & Accepted Abstracts: J Stem Cell Res Ther
Aggregates of Embryonic Stem (ES) cells cultured in suspension form spherical Embryoid Bodies (EBs) that compact and differentiate to organize into a tissue consisting of two epithelia enclosing a lumen. During this morphogenetic transformation, outer cells on the EB surface first differentiate into endoderm. The endoderm secretes laminins, collagen IV and other ECM proteins which assemble into an underlying basement membrane. The inner cells adjacent to the basement membrane differentiate and polarize to become the epiblast epithelium. The cells that do not come in contact with the basement membrane die by apoptosis, creating a proamniotic-like cavity. The sequence of events recapitulates peri-implantation embryonic development and provides a tractable model to study epithelial differentiation and self-organization into three-dimensional tissues. By using this model system, we demonstrated that the tumor suppressor PTEN is essential for epithelial differentiation and polarization. Surprisingly, the role of PTEN does not depend upon its well-known lipid phosphatase activity, which converts PIP3 to PIP2 and antagonizes the PI3KAkt pathway. Reconstitution of PTEN-null EBs with PTEN mutants suggests that its protein phosphatase activity is required for the morphogenetic process. Mass spectrometry identified a novel protein substrate of PTEN that controls actin dynamics. Gain- and loss-of-function analyses indicate this new substrate mediates PTEN-dependent epithelial differentiation and formation of the threedimensional tissue architecture.
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