The negative cell cycle regulators, p27(Kip1), p18(Ink4c), and GSK-3, play critical role in maintaining quiescence of adult human pancreatic β-cells and restrict their ability to proliferate.

"Disclosure of Potential Conflicts of Interest No potential conflicts of interest were disclosed."

"For this work, the authors greatly acknowledge the support provided by the grants, NIH-RO1-DK-013914 and NIH-RO1-CA-090764, to Dr Donald F Steiner of the University of Chicago and Dr Nissim Hay of the University of Illinois at Chicago, respectively. The authors gratefully acknowledge the support of Drs Louis H Philipson and Christopher J Rhodes of the University of Chicago who provided adult human pancreatic tissue and immunohistochemistry protocol and also, some of the antibodies (primary and secondary) and reagents required for this work. Isolated adult human islets were obtained primarily form the NIH-sponsored Integrated Islet Distribution Program (IIDP), City of Hope National Medical Center, Duarte, CA. The authors are also thankful to Dr Piotr Witkowski of the University of Chicago for proving isolated adult human islets. Additionally, the authors like to gratefully acknowledge the assistance provided by the integrated microscopy facility and human tissue resource center of the University of Chicago."