Figure 2.
Lamin extends from nuclear envelope channels and retracts as acentrics rejoin daughter nuclei.(A and A′) Stills from videos (Video 2) of two mitotic neuroblasts expressing I-CreI, H2Av-RFP (magenta), and Lamin-GFP (green). As acentrics (arrows) approached nuclear envelope channels (arrowheads), lamin extended outward from the channels toward the acentric (brackets). As the acentrics passed through channels to rejoin nuclei, these lamin extensions retracted back. Time is written in seconds after initial acentric poleward movement. Scale bars is 2 µm. Yellow dashed boxes indicate magnified regions. (B) Lengths of lamin extensions (n = 18) at their longest point during acentric segregation (left) and at the time the nuclear envelope has completed reassembly (right). Each dot represents the length of a lamin extension from one nucleus. Lines connect the extension lengths at their longest value and at completed nuclear envelope reassembly for the same nucleus. The lengths of 16 of 18 lamin extensions decreased from their longest value during acentric segregation to complete nuclear envelope reassembly (blue dots). The lengths of 2 of 18 lamin extensions increased from their longest value during acentric segregation to complete nuclear envelope reassembly (red dots). Boxes represent interquartile ranges and lines represent medians of the measured data. Asterisks indicate statistical significance (P = 0.005) determined by a paired two-sided t test. (C) Correlation between the distance of the nearest point on the acentric to the nucleus at the time of channel formation (x axis) and to the longest length of the lamin extension during acentric segregation (y axis). Each dot represents one acentric/nucleus pair (n = 18). Blue dots represent acentric/nucleus pairs whose lamin extensions decreased by the time of complete nuclear envelope reassembly. Red dots represent acentric/nucleus pairs whose lamin extensions increased by the time of complete nuclear envelope reassembly. The black line is the regression line for all data points. (D) Starting at the time of maximum lamin extension, the correlation between the distance an acentric travels (x axis) and the distance the lamin extension retracts during the same time period (y axis). Each dot represents one acentric/nucleus pair (n = 18). Blue dots represent acentric/nucleus pairs whose lamin extensions decreased by the time of complete nuclear envelope reassembly. Red dots represent acentric/nucleus pairs whose lamin extensions increased by the time of complete nuclear envelope reassembly. The black line is the regression line for all data points. (E) 3D reconstructions from videos of mitotic neuroblasts expressing I-CreI, H2Av-RFP (magenta), and Lamin-GFP (green) imaged on a lattice light-sheet microscope (left). Constructed surface models of the nuclear envelope are shown to the right of each image. Images are representative of I-CreI–expressing neuroblasts that had no acentrics (left), had acentrics and nuclear envelope channels (middle), or had acentrics (arrows) and no channels (right). While divisions with no acentrics and divisions with acentrics but no channels formed smooth daughter nuclei, divisions with acentrics and channels had daughter nuclei that were wrinkled and protruded, including at locations far from where the acentric had entered (asterisk). Scale bars are 2 µm. (F) Measurement of the sphericity of the nuclear envelopes of daughter nuclei from neuroblasts expressing I-CreI that had no acentrics (left; n = 6), acentrics and channels (middle; n = 7), or acentrics but no channels (right; n = 3). Divisions with both acentrics and channels had daughter nuclei with relatively lower sphericities than those from divisions with no acentrics and divisions with acentrics but no channels. Boxes represent interquartile ranges and lines represent medians of the measured data. Asterisks indicate statistical significance (P = 0.003) by a two-sided Mann–Whitney–Wilcoxon test. The difference between divisions with channels and divisions with micronuclei was not statistically different (P = 0.07) as was the difference between divisions without acentrics and divisions with micronuclei (P = 0.5), determined by two-sided Mann–Whitney–Wilcoxon tests.

Lamin extends from nuclear envelope channels and retracts as acentrics rejoin daughter nuclei. (A and A′) Stills from videos (Video 2) of two mitotic neuroblasts expressing I-CreI, H2Av-RFP (magenta), and Lamin-GFP (green). As acentrics (arrows) approached nuclear envelope channels (arrowheads), lamin extended outward from the channels toward the acentric (brackets). As the acentrics passed through channels to rejoin nuclei, these lamin extensions retracted back. Time is written in seconds after initial acentric poleward movement. Scale bars is 2 µm. Yellow dashed boxes indicate magnified regions. (B) Lengths of lamin extensions (n = 18) at their longest point during acentric segregation (left) and at the time the nuclear envelope has completed reassembly (right). Each dot represents the length of a lamin extension from one nucleus. Lines connect the extension lengths at their longest value and at completed nuclear envelope reassembly for the same nucleus. The lengths of 16 of 18 lamin extensions decreased from their longest value during acentric segregation to complete nuclear envelope reassembly (blue dots). The lengths of 2 of 18 lamin extensions increased from their longest value during acentric segregation to complete nuclear envelope reassembly (red dots). Boxes represent interquartile ranges and lines represent medians of the measured data. Asterisks indicate statistical significance (P = 0.005) determined by a paired two-sided t test. (C) Correlation between the distance of the nearest point on the acentric to the nucleus at the time of channel formation (x axis) and to the longest length of the lamin extension during acentric segregation (y axis). Each dot represents one acentric/nucleus pair (n = 18). Blue dots represent acentric/nucleus pairs whose lamin extensions decreased by the time of complete nuclear envelope reassembly. Red dots represent acentric/nucleus pairs whose lamin extensions increased by the time of complete nuclear envelope reassembly. The black line is the regression line for all data points. (D) Starting at the time of maximum lamin extension, the correlation between the distance an acentric travels (x axis) and the distance the lamin extension retracts during the same time period (y axis). Each dot represents one acentric/nucleus pair (n = 18). Blue dots represent acentric/nucleus pairs whose lamin extensions decreased by the time of complete nuclear envelope reassembly. Red dots represent acentric/nucleus pairs whose lamin extensions increased by the time of complete nuclear envelope reassembly. The black line is the regression line for all data points. (E) 3D reconstructions from videos of mitotic neuroblasts expressing I-CreI, H2Av-RFP (magenta), and Lamin-GFP (green) imaged on a lattice light-sheet microscope (left). Constructed surface models of the nuclear envelope are shown to the right of each image. Images are representative of I-CreI–expressing neuroblasts that had no acentrics (left), had acentrics and nuclear envelope channels (middle), or had acentrics (arrows) and no channels (right). While divisions with no acentrics and divisions with acentrics but no channels formed smooth daughter nuclei, divisions with acentrics and channels had daughter nuclei that were wrinkled and protruded, including at locations far from where the acentric had entered (asterisk). Scale bars are 2 µm. (F) Measurement of the sphericity of the nuclear envelopes of daughter nuclei from neuroblasts expressing I-CreI that had no acentrics (left; n = 6), acentrics and channels (middle; n = 7), or acentrics but no channels (right; n = 3). Divisions with both acentrics and channels had daughter nuclei with relatively lower sphericities than those from divisions with no acentrics and divisions with acentrics but no channels. Boxes represent interquartile ranges and lines represent medians of the measured data. Asterisks indicate statistical significance (P = 0.003) by a two-sided Mann–Whitney–Wilcoxon test. The difference between divisions with channels and divisions with micronuclei was not statistically different (P = 0.07) as was the difference between divisions without acentrics and divisions with micronuclei (P = 0.5), determined by two-sided Mann–Whitney–Wilcoxon tests.

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