Borr is a chromosomal passenger protein during mitosis but is absent during male meiosis. (A) Expression profiles for borr and aust. borr is expressed in all tissues analyzed and aust is expressed only in testes. (B–F) Fixed tissues stained with antibodies to α-tubulin (green), Borr (red), and with DAPI to visualize DNA (blue). In syncytial embryos (B), larval neuroblasts (C), and testis gonial mitoses (D), Borr shows a chromosomal passenger localization. (E) Part of a testicle containing spermatocytes before meiosis (G2) and cells in meiotic telophase I (arrows). Note that Borr is present in the nuclei of G2 spermatocytes but does not accumulate at the central spindle midzone of meiotic cells (arrows). (F) Borr staining is progressively lost during the extended primary spermatocyte prophase before meiosis I. Bars, 5 μm.