Centromeric protein bodies on avian lampbrush chromosomes contain a protein detectable with an antibody against DNA topoisomerase II
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In the oocyte nuclei (germinal vesicle or GV) of a variety of avian species, prominent spherical entities termed protein bodies (PBs) arise at the centromeric regions of the lampbrush chromosomes (LBCs). In spite of the obvious protein nature of PBs, nothing is known about their composition. We show that an antibody against DNA topoisomerase II (topo II), the DNA unwinding enzyme, recognizes PBs from chaffinch and pigeon oocytes. In later chaffinch oocytes, the PBs fuse to form a karyosphere, which is also labeled by the anti-topo II antibody. Furthermore, we show that proteins characteristic of Cajal bodies and B-snurposomes are not found in PBs, despite morphological similarities among these structures. Using immunoelectron microscopy and immunofluorescent laser scanning microscopy we demonstrated that topo II localizes predominantly in the dense material of PBs. Two antigens of ∼170 kDa (which corresponds to topo II) and ∼100 kDa were revealed with the antibody against topo II on immunoblots of avian GV proteins. We propose that the smaller protein results from oocyte specific topo II cleavage, since it was not detected in nuclei from testis cells. This represents the first report of a defined protein in the centromeric PBs on avian LBCs.
KeywordsTopo Centromeric Region Germinal Vesicle Meiotic Prophase Lampbrush Chromosome
We thank the following people for antibodies: R. Hock (mAb 4A6), X.-D. Fu and T. Maniatis (mAb anti-SC35), U. Scheer (mAb V22), J. Steitz (mAb Y12), E. Chan (R288 serum), M. Pollard (mAbs 72B9 and 17C12) and M. Schmidt-Zachmann (mAbs No114 and No185). We are grateful to J. Gall for critical reading of the manuscript and helpful comments. This work was supported by research grant 02-04-49116 from the Russian Foundation for Basic Research. We used the equipment of the Core Facilities “CHROMAS” (Biological Institute, Saint-Petersburg State University).
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