Date Published: November 10, 2009
Publisher: Public Library of Science
Author(s): Kenta Nakamura, Nathan Salomonis, Kiichiro Tomoda, Shinya Yamanaka, Bruce R. Conklin, Catherine M. Verfaillie. http://doi.org/10.1371/journal.pone.0007780
Abstract: Reprogramming adult human somatic cells to create human induced pluripotent stem (hiPS) cell colonies involves a dramatic morphological and organizational transition. These colonies are morphologically indistinguishable from those of pluripotent human embryonic stem (hES) cells. G protein-coupled receptors (GPCRs) are required in diverse developmental processes, but their role in pluripotent colony morphology and organization is unknown. We tested the hypothesis that Gi-coupled GPCR signaling contributes to the characteristic morphology and organization of human pluripotent colonies.
Partial Text: The ability to reprogram somatic cells back to a pluripotent state has revolutionized our understanding of developmental biology . The creation of patient-specific pluripotent stem cells was a seminal advance toward the use of stem cells for cell-based therapies and regenerative medicine . During reprogramming, adult human somatic cells undergo a remarkable transition from dispersed unicellular fibroblasts to well defined multicellular colonies of human induced pluripotent stem (hiPS) cells that are morphologically indistinguishable from human embryonic stem (hES) cells – (Figure 1). Both hiPS cells and hES cells self-renew indefinitely as highly-organized pluripotent colonies that resemble the inner cell mass from which hES cells are primarily derived , . Interestingly, human pluripotent colonies form a flat uniform monolayer, while mouse pluripotent colonies form thicker, multilayered colonies . Since pluripotent colony morphology correlates closely with the maintenance of pluripotency, the mechanisms by which these colonies form and organize may be important for controlling somatic cell reprogramming. Understanding these mechanisms may also allow better control of hiPS cell growth and differentiation ex vivo for therapeutic applications.
This study shows that the colony morphology characteristic of pluripotent hES and hiPS cells is maintained through a pertussis toxin-sensitive mechanism downstream of Gi-coupled GPCRs. Wild-type colonies were discrete and radial with flat, monolayer organization. Absence of this characteristic morphology and organization usually suggests a lack or loss of pluripotency in human pluripotent cell cultures , . Gi signaling may specifically mediate the morphology and organization of pluripotent stem cell colonies by outwardly regulating the density of cells within the colony. We refer to this as the “outward model” of pluripotent stem cell organization (Figure 8).