As apoptosis progresses, the cell begins to condense and the halo becomes more intense (q, arrowhead). YFP::actin halos highlight cells at an early stage of apoptosis, before they begin to condense their DNA (q, arrows t, overlay).
o–t, YFP::actin transgenic animals (o, DIC p, camera lucida) were stained with Hoechst 33342 (s), which measures condensation of DNA, and with SYTO 41 (r), which stains engulfed apoptotic cells. F-actin structures within the syncytial germ line (i, arrows) do not colocalize with YFP::actin, which is expressed only in the somatic sheath cells. i–n, Phalloidin staining (i, l) colocalized with YFP::actin staining (j, m) both around apoptotic cells (k, arrowhead (overlay)) and in filamentous actin structures (n, (overlay)). f, h, Pictures were overexposed so intrusions of the somatic sheath between oocytes became visible (h, white arrowheads). Mutations in the engulfment apparatus (ced-1(e1735) (e, f) and ced-7(n1996) (g, h)) abrogate actin staining around the apoptotic cell corpse. In wild-type worms (a, b), both refractile corpses (arrowheads) and early stage pre-refractile corpses (arrows) are highlighted corpse number increases in gla-1 mutants (c, d). Recruitment of actin halos around apoptotic cells in the hermaphrodite germ line requires CED-1 and CED-7.a–h, Arrows/arrowheads indicate refractile corpses (DIC) or YFP::actin halos. Furthermore, we find that the CED-10(Rac) GTPase acts genetically downstream of these proteins to mediate corpse removal, functionally linking the two engulfment pathways and identifying the CED-1, -6 and -7 signalling module as upstream regulators of Rac activation. Here, we show that CED-1, CED-6 and CED-7 are required for actin reorganization around the apoptotic cell corpse, and that CED-1 and CED-6 colocalize with each other and with actin around the dead cell. Molecular understanding of how the second pathway promotes engulfment of the apoptotic cell is lacking. In the second group, the candidate receptor CED-1 (CD91/LRP/SREC) probably recognizes an unknown ligand on the apoptotic cell and signals via its cytoplasmic tail to the adaptor protein CED-6 (hCED-6/GULP), whereas CED-7 (ABCA1) is thought to play a role in membrane dynamics. In the first pathway, the proteins CED-2, CED-5 and CED-12 (mammalian homologues CrkII, Dock180 and ELMO, respectively) function to activate CED-10 (Rac1). In Caenorhabditis elegans, two conserved, partially redundant genetic pathways regulate this process. The removal of apoptotic cells is essential for the physiological well being of the organism.
0 kommentar(er)
