A unique structure, the conjusome, has been identified and initially characterized in Tetrahymena thermophila. The conjusome appears only during a specific phase of conjugation. Immunofluorescence microscopy reveals that the conjusome is strongly labeled by antibodies to the protein Pdd1p. Pdd1p is a chromodomain protein and participates in the formation of chromatin-containing structures in developing macronuclear anlagen. Recent studies suggest that Pdd1p is physically associated with the elimination of specific germ-line sequences from developing macronuclei (anlagen) and may play a role in heterochromatin assembly. The conjusome contains Pdd1p, but it is devoid of any detectable DNA. The conjusome appears before DNA elimination begins in the developing anlagen and after Pdd1p is found in the parental macronucleus. Transmission electron microscopic observations reveal that the conjusome is not a membrane-bounded structure. The conjusome ranges in size from about 1 microm to sizes approaching 7 microm, depending on its maturity. It is composed of a coarse reticulum of a fibrous, electron dense material, interspersed with apparent background cytoplasm. Our initial characterization does suggest a number of possible functions for what may be a new, transient organelle.

Aufderheide
K. J.
(
1986
).
Identification of the basal bodies and kinetodesmal fibers in living cells of Paramecium tetraurelia Sonneborn, 1975 and Paramecium sonneborni Aufderheide, Daggett & Nerad, 1983.
J. Protozool
33
,
77
80
Bruns
P. J.
,
Brussard
T. B.
(
1974
).
Pair formation in Tetrahymena pyriformis: An inducible developmental system.
J. Exp. Zool
183
,
337
343
Chalker
D. L.
,
Yao
M. C.
(
1996
).
Non-Mendelian, heritable blocks to DNA rearrangement are induced by loading the somatic nucleus of Tetrahymena thermophila with germ line-limited DNA.
Mol. Cell Biol
16
,
3658
3667
Coyne
R. S.
,
Chalker
D. L.
,
Yao
M.-C.
(
1996
).
Genome downsizing during ciliate development: nuclear division of labor through chromosome restructuring.
Annu. Rev. Genet
30
,
557
578
Cole
E. S.
,
Soelter
T. A.
(
1997
).
A mutational analysis of conjugation in Tetrahymena thermophila. 2. Phenotypes affecting middle and late development: Third prezygotic nuclear division, pronuclear exchange, pronuclear fusion, and postzygotic development.
Dev. Biol
189
,
233
245
Dryl
S.
(
1959
).
Antigenic transformation in Paramecium aurelia after homologous antiserum treatment during conjugation or autogamy.
J. Protozool
6
,
25
–.
Greider
C. W.
,
Blackburn
E. H.
(
1989
).
A telomeric sequence in the RNA of Tetrahymena telomerase is required for telomeric repeat synthesis.
Nature
337
,
331
337
Heasman
J.
,
Quarmby
J.
,
Wylie
C. C.
(
1984
).
The mitochondrial cloud of Xenopus oocytes: The source of germinal granule material.
Dev. Biol
105
,
458
469
Illmense
K.
,
Mahowald
A. P.
(
1974
).
Transplantation of posterior pole plasm in Drosophila. Induction of germ cells at the anterior of the egg.
Proc. Nat. Acad. Sci. USA
71
,
1016
1020
Kaczanowski
A.
,
Ramel
M.
,
Kaczanoska
J.
,
Wheatley
D.
(
1991
).
Macronuclear differentiation in conjugating pairs of Tetrahymena treated with the antitubuline drug nocodazole.
Exp. Cell Res
195
,
330
337
Klobutcher
L. A.
,
Jahn
C. L.
(
1991
).
Developmentally controlled genomic rearrangements in ciliated protozoa.
Curr. Opin. Genet. Dev
1
,
397
403
Martindale
D. W.
,
Allis
C. D.
,
Bruns
P. J.
(
1982
).
Conjugation in Tetrahymena thermophila (a temporal analysis of cytological stages).
Exp. Cell Res
140
,
227
236
Meyer
E.
,
Duharcourt
S.
(
1996
).
Epigenetic programming of developmental genome rearrangements in ciliates.
Cell
87
,
9
12
Numata
O.
,
Sugai
T.
,
Watanabe
Y.
(
1985
).
Control of germ cell nuclear behavior at fertilization by Tetrahymena intermediate filament protein.
Nature
314
,
192
194
Prescott
D. M.
(
1994
).
The DNA of ciliated protozoa.
Microbiol. Rev.
58
,
233
267
Preer
J. R.
Jr.
(
1997
).
Whatever happened to Paramecium genetics?.
Genetics
145
,
217
225
Smothers
J. F.
,
Mizzen
C. A.
,
Tubbert
M. M.
,
Cook
R. G.
,
Allis
C. D.
(
1997
).
Pdd1p associates with germline-restricted chromatin and asecond novel anlagen-enriched protein in developmentally programmed DNA elimination structures.
Development
124
,
4537
4545
Sonneborn
T. M.
,
Schneller
M. V.
(
1979
).
A genetic system for alternative stable characteristics in genomically identical homozygous clones.
Dev. Genet
1
,
21
46
Wolf
N.
,
Priess
J.
,
Hirsh
D.
(
1983
).
Segregation of germline granules in early embryos of Caenorhabditis elegans: an electron microscopic analysis.
J. Embryol. Exp. Morphol
73
,
297
306
Yao
M.-C.
,
Gall
J. G.
(
1979
).
Alteration of the Tetrahymena genome during nuclear differentiation.
J. Protozool
26
,
10
13
Yao
M.-C.
,
Choi
J.
,
Yokoyaman
S.
,
Austerberry
C. F.
,
Yao
C. H.
(
1984
).
DNA elimination in Tetrahymena: a developmental process involving extensive breakage and rejoining of DNA at defined sites.
Cell
36
,
433
440
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