- Zebrafish lacking Alzheimer presenilin enhancer 2 (Pen-2) demonstrate excessive p53-dependent apoptosis and neuronal loss. Campbell, W.A., Yang, H., Zetterberg, H., Baulac, S., Sears, J.A., Liu, T., Wong, S.T., Zhong, T.P., Xia, W. J. Neurochem. (2006)