Figure 1. Apoptosis is coupled to phagocytosis in the young adult SGZ.

(A) Confocal photomicrographs of apoptotic cells in the young adult (1m.o.) SGZ. Apoptotic cells (arrowheads), detected by pyknosis/karyorrhexis (condensed DAPI staining) and act-casp3, are predominantly located in the SGZ (A1), and more sparsely in the granular cell layer (A2) and hilus (A3). Apoptotic cells in A1 and A2 are engulfed by microglia visualized in fms-EGFP mice.

(B) Quantification of the location of apoptotic cells, identified by pyknosis and act-casp3 expression, in the hippocampus. The vast majority of apoptotic cells is located strictly in the SGZ.

(C) Different stages of phagocytosis in the SGZ. The microglial engulfment of apoptotic cells (pyknotic, act-casp3 immunopositive) was assessed in orthogonal projections of confocal z-stacks. Apoptotic cells are either not phagocytosed (C1); undergoing early phagocytosis (loose microglial pouch, conspicuous act-casp3 immunolabeling; C2); or late phagocytosis (tight microglial pouch, dim act-casp3 immunolabeling; C3).

(D) Quantification of the phagocytic index (Ph-index), i.e., the percentage of SGZ apoptotic cells that are engulfed by microglia (early and late phagocytosis together), in three independent experiments. A large percentage (> 90%) of the apoptotic cells is completely engulfed by microglia.

(E) Confocal photomicrographs of the SGZ showing Iba+ microglial processes and somas intermingled with the SGZ NPCs (nestin-GFP+) and NBs (PSA-NCAM+). DAPI staining indicates cell nuclei. The arrowhead points to an apoptotic (pyknotic) cell, identified by condensed DAPI staining, that expresses PSA-NCAM and is engulfed by the microglial process.

Scale bars: A, C, 10μm; E, 20μm; See also Fig. S1. Bars represent mean ± SEM