HLB assembly begins during nuclear cycle 10. (A–C) w¹¹¹⁸ syncytial blastoderm embryos stained with MPM-2 (left), α-Mxc (middle), α-FLASH (right), and DAPI. (D–F) w¹¹¹⁸ syncytial blastoderm embryos stained with MPM-2 (left), α–Mute-LS (middle), α-Mxc (right), and DAPI. Insets show a single nucleus. Interphase of nuclear cycles 9–11 is shown. Yellow arrows indicate a nucleus containing foci of Mxc and FLASH (B) or Mute (E) lacking a MPM-2 focus. Nuclei with one (white arrows) or two (white arrowheads) HLBs are indicated. txn, histone transcription. Bars, 10 µm.