Actin Retreats into Nucleus (VIDEO) University of North Carolina Health Care This video is under embargo. Please login to access this video. Caption Left: normal mesenchymal stem cell. Right: with cytochalasin D added, the actin fibers in the cytoplasm break down and reform in the nucleus and kick start the transformation of the stem cell into an osteoblast. Credit UNC School of Medicine Usage Restrictions credit properly License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.