pSIVA: Polarity Sensitive Indicator of Viability & Apoptosis

New Apoptosis Monitoring Tool for Microscopy & Flow Cytometry

pSIVA is a novel phosphatidylserine (PS) exposure reporter for monitoring cell death, apoptosis and survival by live-cell imaging. Live-cell imaging is a vital application for studying dynamic biological processes such as apoptosis in real time. However, prior to the advent of pSIVA, there had been a lack of available reporters for studying cell death/survival processes.

pSIVA is conjugated to IANBD, a polarity sensitive dye that fluoresces only when pSIVA is bound to the cell membrane.

First developed by Dr. Ralf Langen and his colleagues at USC in 2010, pSIVA already has several impressive publications (1-3). pSIVA’s most notable live-imaging applications including monitoring the subcellular onset of PS externalization, tracking PS exposure throughout the death process (Movies 1 and 2), and demonstrating reversible PS exposure events associated with rescuable cell death (Movie 3). The demonstration of reversible PS exposure by pSIVA is considered to be among the most significant assay advances in the Cell Death and Apoptosis field today. In addition to live cell imaging, pSIVA can also be used for standard fluorescence microscopy, in vivo analysis of cell death and flow cytometry.

Time-lapse imaging of primary rat dorsal ganglion (DRG) sensory neurons induced to undergo apoptosis by NGF deprivation. Images were taken from 9 hr after NGF withdrawal, and the movies were compiled at 6 frames per second with 20 min intervals between image frames. Movies 1 and 2 are of different neurons. pSIVA-IANBD (detects PS exposure): green. PI (detects loss of membrane integrity): red. Note that pSIVA-IANBD labels the axon prior to the cell body, and that pSIVA-IANBD fluorescence appears prior to PI staining. Time-lapse imaging of rat DRG recovery from the brink of death showing reversibility of apoptosis for the first time. Neurons were deprived of NGF for 10 h to induce apoptosis. After 10 h, NGF was added back to the culture to induce rescue. Images were taken from 7.5 h after NGF withdrawal and the movie was compiled at 4 frames per second with a 30 min interval between image frames. pSIVA-IANBD: green. PI: red. Boxes highlight specific areas where the intensity of pSIVA-IANBD fluorescence reverses.