Fig. 1: Pericentromeric heterochromatin progressively surrounds the nucleolus during Drosophila embryonic development.
a, Schematic of PCH organization around the multiphasic nucleolus in Drosophila nuclei (left). Maximum intensity projections of live epidermal nuclei from late Drosophila embryos (approximately 14–16 h after egg laying; centre and right). The distribution of GFP–HP1a and RFP–Fib (centre) as well as RFP–HP1a and GFP–Mod is shown (right). Nuclei marked with a white box are shown enlarged in xy and xz projections, and the dashed lines indicate the nuclear boundaries. b, Maximum intensity projections (xy view) of individual live nuclei of GFP–HP1a and RFP–Fib in cycles 13–17 ((i)–(v), respectively) of Drosophila embryogenesis. The numbers on the top left corner of each image indicate the time (min) after mitotic exit. Three-dimensional renders of the nucleus marked with white dashed lines are presented (right). Time-lapse imaging at minute-scale resolution in Supplementary Videos 2–6. c, Levels of HP1a occupancy around the nucleolus during specific developmental cycles; subscript e, early cycle (15–30 min into the specified interphase); l, late cycle (50–70 min). The schematic next to the graph illustrates the analysis approach: a shell was generated around Fib (dark blue circle) and HP1a occupancy was calculated as the fraction of the volume of this shell that intersects with HP1a segments (dark blue crosses). Data are the mean ± s.d. of n = 162 (14l), 179 (15l), 174 (16e), 189 (16l) and 143 (17e) Fib–HP1a pairs in individual nuclei analysed from five embryos imaged at the defined developmental stage. d, Combined immunolabelling and FISH of 1.686 repeats, Fib and DAPI in epidermal cell nuclei from fixed early (cycle 15) and late-stage Drosophila embryos. e, Distance between the centres of geometry of 1.686 loci and Fib in epidermal cell nuclei from early- (cycle 15) and late-stage Drosophila embryos. Data are the mean ± s.d. of n =61 (early) and 62 (late) 1.686–Fib pairs pooled from three fixed embryos at each developmental stage. The P value was calculated using an unpaired two-tailed Student’s t-test. f, Schematic summarizing the dynamic reorganization of nucleoli and PCH during Drosophila development, highlighting the analysed nucleolar and PCH phases, proteins and DNA repeats.
