Use of dextran beads for live analysis of the nuclear division and nuclear envelope breakdown/reformation cycles in the Drosophila embryo.

We employ fluorescently labeled dextran beads to follow cycles of nuclear division and nuclear envelope breakdown in living Drosophila embryos. When injected into syncytial Drosophila embryos, 3000 mol wt fluorescently labeled dextran beads concentrate in the interphase nucleus. Through confocal microscopy, undisrupted multiple cycles of nuclear division are readily followed. In contrast, 40,000 mol wt fluorescently labeled dextran beads concentrate in the cytoplasm and enter the nucleus only after nuclear envelope breakdown during prophase. Once the nuclear envelope reforms during telophase, these large dextran beads are again excluded from the nuclei. The complementary behavior of the large and small dextran beads makes them applicable to a broad range of cellular studies. We employ the 40,000 mol wt fluorescein-labeled beads, in combination with rhodamine-labeled histones, to demonstrate that nuclear envelope breakdown occurs about 3.5-4.0 minutes prior to the initiation of anaphase.