Aminophospholipid translocase TAT-1 promotes phosphatidylserine exposure during C. elegans apoptosis

Extracellular annexin A5: functions of phosphatidylserine-binding and two-dimensional crystallization

In normal healthy cells phosphatidylserine is located in the inner leaflet of the plasma membrane. However, on activated platelets, dying cells and under specific circumstances also on various types of viable leukocytes phosphatidylserine is actively externalized to the outer leaflet of the plasma membrane. Annexin A5 has the ability to bind in a calcium-dependent manner to phosphatidylserine and to form a membrane-bound two-dimensional crystal lattice. Based on these abilities various functions for extracellular annexin A5 on the phosphatidylserine-expressing plasma membrane have been proposed. In this review we describe possible mechanisms for externalization of annexin A5 and various processes in which extracellular annexin A5 may play a role such as blood coagulation, apoptosis, phagocytosis and formation of plasma membrane-derived microparticles. We further highlight the recent discovery of internalization of extracellular annexin A5 by phosphatidylserine-expressing cells.

Cognate putative nuclear localization signal effects strong nuclear localization of a GFP reporter and facilitates gene expression studies in Caenorhabditis elegans

Targeting a gene expression reporter, usually the green fluorescent protein (GFP), to the nucleus via a translationally fused nuclear localization signal (NLS) greatly facilitates recognition and identification of the reporter-expressing cells in Caenorhabditis elegans. Presently circulating nematode transcriptional gene expression vectors use the viral NLS from simian virus 40 (SV40) large T antigen. This NLS, however fails to ensure sufficient localization of the GFP peptide to the nucleus. We modified the common transcriptional reporter SV40 NLS-GFP by adding to its C terminus a cognate putative NLS from the transcription factor egl-13. The EGL-13 NLS effected clear contrast in fluorescence intensity between the nucleus and the cytoplasm in cells with strong reporter signal and efficiently highlighted the nucleus in tissues with weak reporter expression in a wide range of tested tissues. The SV40 NLS-GFP-EGL-13 NLS vector should become a valuable tool for gene expression studies in C. elegans.

Engulfment of apoptotic cells: signals for a good meal

The clearance of apoptotic cells by phagocytes is an integral component of normal life, and defects in this process can have significant implications for self tolerance and autoimmunity. Recent studies have provided new insights into the engulfment process, including how phagocytes seek apoptotic cells, how they recognize and ingest these targets and how they maintain cellular homeostasis after the 'meal'. Several new factors that regulate engulfment have been identified, whereas the roles of some of the older players require revision. This Review focuses on these recent developments and attempts to highlight some of the important questions in this field.