Fig. 5.

Degron reporters label phagocytosed cell debris and enable tracking. a–c The histone reporter mCh::H2B labels chromosomes in embryonic nuclei and two polar bodies (n = 13). The first polar body (arrowhead) is trapped in the eggshell (dashed oval). Scale bar: 10 µm. a The second polar body (2PB, arrow) neighbours the anterior blastomere (AB cell) in a two-cell embryo. b The 2PB is engulfed in a phagosome in a 15-cell embryo. Due to H2B fluorescence from surrounding embryonic nuclei, it is hard to track the 2PB. c Automated tracking of the 2PB (yellow) results in crossing tracks from nearby nuclei (white), increasing the potential need for manual correction. d–f Embryos labelled with ZF1-tagged mCh::H2B (n = 12). d The released 2PB neighbours a two-cell embryo. e After engulfment, the 2PB is easily trackable due to degradation of ZF1::mCh::H2B in somatic cell nuclei. See also Supplementary Movie 3. f Automated tracking of the 2PB (yellow) is simplified by removing the label of nearby nuclei (white). g Degron reporters released in cells or other debris prior to expression of the ZIF-1 ubiquitin ligase adaptor are protected from ZF1-mediated degradation. After engulfment in a second layer of membrane, they are still protected from proteasomal degradation. As degron reporters are degraded in the cytosol, only the reporters within the phagosome remain fluorescent, improving the signal-to-noise ratio