Proteins as They Age (IMAGE) University at Buffalo Caption The images above show key structural proteins (actin and tubulin) as cells age. The top raw shows still dividing, and, the bottom raw shows senescent (cells that no longer divide) cells. Their comparison highlights the difference in shape of these cells. Credit Credit: University at Buffalo. Usage Restrictions None 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.