Figure 6

Chromatin in micronuclei is degraded by autophagy. Transmission electron microscopy analysis of autophagosome formation around micronuclei and invasion of tubular membranes inside the chromatin territory. Micronuclei were found in diploid hybrid males (a) and females (b–d) during the premetamorphosis stage of somatic development according to Gosner (1960), (a–d) stages 37, 41, 31, 36 respectively. (a) Sequestration of the cytoplasm by lipid double membranes (arrowheads) surrounding large heterochromatinized, intact micronucleus. (b) Micronucleus accompanied by two membranes assembling on the surface (arrowheads): cap-shaped (at the bottom) and linear (upper part), inside the chromatin the invading membranes are visible. Arrows point the disruptions of nuclear envelope in micronucleus (c) Autophagosome membranes (arrowheads) encapsulating micronucleus are partially double- or single layered. Vacuolar spaces are signs of degeneration (white spaces) and vesicles similar to lysosomes are visible. (d) Micronucleus with tubular membranes invading chromatin. n – nucleus, m – mitochondria, mn – micronucleus. Scale bars 2 µm.