Figure S5.

Topology of AL-Insertion, Related to Figure 3

(A) Transmission electron micrograph (TEM) of a Drosophila syncytial blastoderm embryo in interphase, showing the NE and adjacent AL (yellow boxes). AL appear as ribosome decorated (arrowheads) parallel ER stretches containing NPCs that morphologically resemble NPCs at the NE at the given resolution.

(B–B″) Overview (B and B′) and higher magnification (B″) micrographs obtained by correlative light and electron microscopy (CLEM) showing AL-insertion into the NE (see also Figure 3C). RFP::Nup107 fluorescence is concentrated along the NE and at AL-NPCs (arrowhead in B and B′, AL in B″). Light microscopy images and electron micrographs on the same section are correlated by His2A::GFP in the nucleus and the auto-fluorescence of mitochondria in the GFP-channel (B′).

(C–C′) Single slice (C) and isosurface-rendering (C′) of a volume obtained by Focused Ion Beam-Scanning Electron Microscopy (FIB-SEM), showing interconnectivity of stacked, AL membrane sheets (black box in C) that are oriented parallel to the NE (C and C′). AL-membranes connect to the NE adjacent to NE-openings.

(D–F) TEM-sections depicting redundant NE membrane patches that are branched to the nuclear interior (red arrowheads in D–F). Note the redundant NPC containing membrane sheet close to an NE opening in (D). In (F) an inserting NPC containing ER stretch (yellow arrowhead) is close to redundant NE branching to the nucleoplasm (red arrowhead).