Click here to close
Hello! We notice that you are using Internet Explorer, which is not supported by Xenbase and may cause the site to display incorrectly.
We suggest using a current version of Chrome,
FireFox, or Safari.
Localization of a high molecular weight form of DNA topoisomerase I in amphibian oocytes.
Gebauer D
,
Mais C
,
Zinger K
,
Hock R
,
Lieb B
,
Scheer U
.
???displayArticle.abstract???
Xenopus oocytes express a 165 kDa variant of DNA topoisomerase I (topo I) as opposed to the canonical 110 kDa form of somatic cells (Richard and Bogenhagen, Dev. Biol. 146: 4-11, 1991). By immunofluorescence microscopy using variant-specific antibodies we show that this high molecular weight form is associated with lampbrush chromosome loops and the inner regions of the amplified nucleoli. Inhibition of topo I-activity by either Camptothecin-treatment or microinjection of neutralizing antibodies resulted in loop retraction and the condensation of chromosomes and amplified nucleoli. These data indicate that the oocyte-specific 165 kDa form of topo I is involved in transcriptional processes mediated by RNA polymerase I and II and is therefore functionally equivalent to the somatic cell 110 kDa counterpart.
Fig.1. Immunofluorescence local.
ization of topo I on spread
Xenopus lampbrush chromosomes
and amplified nucleoli.
Spread nuclear contents of stage iV
OOCVtes were incubared wirh topo I
antiserum (A,C,D) or the corresponding
preimmune serum (B).
After incubation with topo I anti-serum lampbrush chromosomes fluoresce
In controls (AI and after CPTtreatment
(C), but not in
AMD-treated oocytes (D). The inner
regions of the amplified nucleoli (n)
which appear as dense cores in
phase contrast (A'', are intensely
stained by the topo I antiserum (A).
The corresponding Hoechst staining
(A'.D') and phase contrast images
(A"-D") are shown. Bar. 20 pm.
Fig. 2. Immunofluorescence
microscopy of paraffin sections of
freeze-substituted Xenopus
oocytes. Sections of control (AI or
CPT-treared(BI pieces of ovary were
stained with ropo I antiserum. In
both cases the amplified nucleoli (n)
fluoresce after incubation with the
antiserum. Fluorescence of the
lampbrush chromosome portions
included in rhe sections is recognized
only after CPT-treatment (Iin B)
(see text for explanation). Bars, 30
~m.
Fig. 3. Effect of affinity-purified topa I antibodies on lampbrush
chromosomes after microinjection into PleurodeJes oocyte nuclei.
Stage IV oocytes were mlcroinjecred into the nucfei with 40 ng of affinity-
purified topo I antibodies (B.C.DI or the same amount of non-immune
rabbit immunoglobulins (AI. Lampbrush chromosomes were prepared 1
h tBI. 2 h ICI and 4 h IA,DI afrer injection and photographed with an
inverred microscope using phase contrast optics. All micrographs show
the heteromorphic fampbrush chromosome bivalent number IV with the
diagnostic globular loop (arrows). Injection of tapo I antibodies causes
loop retraction and shortening of lampbrush chromosomes. Bar. 20 tlm
