Figure 5. Bmb foci mark sites corresponding to pre-, post- and active karyomere fusion.

(A) At time point designated 0 min (mid-anaphase) at the 32- to 64-cell transition, Bmb protein (green) is first seen accumulating at the leading edge of the separating chromosomes (inset, arrowhead) prior to the assembly of nucleoporins (marked by mab414, red). (B) As the chromosomes continue to separate, nuclear membrane (marked by mab414) and Bmb surround individual chromosomes forming karyomeres. Insets in B show a more advanced example from the same time point (1 min). (C) Karyomeres become increasingly more spherical and prominent Bmb foci are more apparent at karyomere-karyomere interfaces (arrowheads). In another example, Bmb foci span a former interface, which now lacks nuclear membrane (inset, arrowheads) and a prominent Bmb aggregate interfaces adjacent karyomeres (inset, arrowhead). (D) At the 3 min time point larger secondary karyomeres are present. (E) Another 2 min example at a 90° view compared to C (an asterisk in C marks reference point). Bmb foci at karyomere-karyomere interfaces, where membrane is still present (arrowheads) or partially/completely absent (arrows). (F) Secondary karyomere formation at a 45° view. ( G) Bmb foci (Bmb, arrowheads) flank presumptive karyomere pre-fusion site (membrane still present- 414, arrowheads) and Bmb foci can be found at presumptive karyomere post-fusion sites (lack of membrane- 414, arrows). Note G–H shows mononucleus formation (5 min) from a lateral side view (G) and another sample from a 90° vantage point (reference point marked with asterisk in G) (H). All panels correspond to individual confocal Z-slices. Scale bar = 5 μm and insets show 2X enlargements. For each time point n ≥ 3. (I) Time-lapse imaging of Bmb-venus. Bmb foci are seen at the karyomere-karyomere interfaces (arrowheads) and are ultimately eliminated (arrows) as the mononucleus is formed. See also Movie S3 and Figure S3 for details.