Human embryonic stem cells (hESCs) are potential therapeutic tools and models of human development. With a growing interest in primary cilia in signal transduction pathways that are crucial for embryological development and tissue differentiation and interest in mechanisms regulating human hESC differentiation, demonstrating the existence of primary cilia and the localization of signaling components in undifferentiated hESCs establishes a mechanistic basis for the regulation of hESC differentiation. Using electron microscopy (EM), immunofluorescence, and confocal microscopies, we show that primary cilia are present in three undifferentiated hESC lines. EM reveals the characteristic 9 + 0 axoneme. The number and length of cilia increase after serum starvation. Important components of the hedgehog (Hh) pathway, including smoothened, patched 1 (Ptc1), and Gli1 and 2, are present in the cilia. Stimulation of the pathway results in the concerted movement of Ptc1 out of, and smoothened into, the primary cilium as well as up-regulation of GLI1 and PTC1. These findings show that hESCs contain primary cilia associated with working Hh machinery.

Historically, the science of medicine has met a great deal of social rejection, if not outright hostility. Through the years physicians have had to maintain a delicate balance between the norms and values established by societies and the dictates of their own conscience of what constitutes the best interest of their patients. Confronted by the dilemma of facing social ostracism or defying their duties as stated in the Hippocratic oath to be “bound by a stipulation and oath according to the law of medicine, but to none others (Information for Research on Euthanasia, 2003)”, physicians have often faced difficult ethic quandaries. It is a hotly debated issue whether the duty of physicians is to assess every individual case and act solely according to their own best judgment or act in line with the rigid norms and social structures imposed by the community. Issues such as euthanasia, abortion and organ transplantation present the very essence of this controversial bioethical debate.