Figure 3. Unequal proteasomal segregation as a mechanism for asymmetric cell division.

(A)Undivided P14 CD8⁺ TCR transgenic T cells were harvested as in Figure 1A and stained for the α1 chain of the proteasome 20S subunit (green), β-tubulin (red), and DNA (blue). Asymmetry of proteasome localization was observed in 62% (n=74) of cells. (B) CD4⁺ T cells were activated in vitro for 28h and stained as in (A). Asymmetry of proteasome localization was observed in 74% (n=125) of cells. (C) CD4⁺ T cells were activated in vitro for 28h, treated with the proteasome activity probe MVB003 for 2h, and stained for β-tubulin (red), and DNA (blue). Asymmetry of degradative activity was observed in 65% (n=22) of cells. (D) Undivided P14 CD8⁺ TCR transgenic T cells were harvested as in Figure 1A, and stained for the proteasome 20S α1 subunit (green), PKCζ (red), β-tubulin (blue), and DNA (grayscale). In co-staining experiments where both molecules were asymmetrically inherited, proteasome and PKCζ were inherited by the same daughter cell in 95% of cells (n=34). (E) Undivided P14 CD8⁺ TCR transgenic T cells were harvested as in Figure 1A, and stained for T-bet (green), proteasome 20S α1 subunit (red), β-tubulin (blue), and DNA (grayscale). In co-staining experiments where both molecules were asymmetrically inherited, proteasome and T-bet were inherited by opposite daughter cells in 90% of cells (n=29). (F) CD4⁺ T cells were activated as in (B) and stained as in (E). In co-staining experiments where both molecules were asymmetrically inherited, proteasome and T-bet were inherited by opposite daughter cells in 90% of cells (n=14). Results are representative of three separate experiments.