The Posterior Sex Combs (Psc) gene of Drosophila has been studied at the molecular level both because it is a Polycomb group (Pc-G) gene and hence required for the maintenance of segmental determination, and because it is the Drosophila homolog of the murine bmi-1 oncogene. Although genetic interactions indicated that Psc functioned as a Pc-G gene, the zygotic mutant phenotype of Psc showed little evidence of segmental transformations. We have examined mutant embryos derived from a mutant maternal germ line and found a stronger mutant phenotype, indicating that the weak zygotic phenotype of Psc is due to maternal rescue. We have found that Psc RNA accumulates in developing oocytes and this maternal RNA is presumably responsible for the maternal rescue. We have studied the expression of the Psc gene at both the RNA and protein levels. On northern blots, we find evidence for two Psc mRNAs and, on western blots, we find evidence for two Psc proteins that are altered either in abundance or size in Psc mutants. The Psc protein accumulates in all regions of the embryo and also in many tissues in a variety of developmental stages. In all cases, it is nuclear, as is its mammalian homolog, the bmi-1 protein. On polytene chromosomes, we find Psc at 45 chromosomal loci where two other Pc-G proteins are present.

Adler
P. N.
,
Charlton
J.
,
Brunk
B.
(
1989
)
Genetic interactions of the Suppressor 2 of zeste region genes.
Dev. Genet
10
,
249
260
Adler
P. N.
,
Martin
E. C.
,
Charlton
J.
,
Jones
K.
(
1991
)
Phenotypic consequences and genetic interactions of a null mutation in the Drosophila Posterior Sex Combs gene.
Dev. Genet
12
,
349
361
Benson
M.
,
Pirrotta
V.
(
1987
)
The product of the Drosophila zeste gene binds to specific DNA sequences in white and Ubx.
EMBO J
6
,
1387
1392
Bopp
D.
,
Bell
L. R.
,
Cline
T. W.
,
Schedl
P.
(
1991
)
Developmental distribution of female-specific Sex-lethal proteins in Drosophila melanogaster.
Genes Dev
5
,
403
415
Breen
T. R.
,
Duncan
I. M.
(
1986
)
Maternal expression of genes that regulate the bithorax complex of Drosophila melanogaster.
Dev. Biol
118
,
442
456
Brown
N. H.
,
Kafatos
F. C.
(
1988
)
Functional cDNA libraries from Drosophila embryos.
J. Mol. Biol
203
,
425
437
Brunk
B. P.
,
Adler
P. N.
(
1990
)
Aristapedioid, a gain of function homeotic mutation in Drosophila melanogaster.
Genetics
124
,
145
156
Brunk
B. P.
,
Martin
E. C.
,
Adler
P. N.
(
1991
)
Molecular genetics of the Posterior Sex Combs/Suppressor 2 of zeste region of Drosophila: Aberrant expression of the Suppressor 2 of zeste gene results in abnormal bristle development.
Genetics
128
,
119
132
Brunk
B. P.
,
Martin
E. C.
,
Adler
P. N.
(
1991
)
Drosophila genes Posterior Sex Combs and Suppressor two of zeste encode proteins with homology to the murine bmi-1 oncogene.
Nature
353
,
351
353
Busturia
A.
,
Morata
G.
(
1988
)
Ectopic expression of homeotic genes caused by the elimination of the Polycomb gene in Drosophila imaginal epidermis.
Development
104
,
713
720
Castelli-Gair
J. E.
,
Garcia-Bellido
A.
(
1990
)
Interactions of Polycomb and trithorax with cis regulatory regions of Ultrabithorax during the development of Drosophila melanogaster.
EMBO J
9
,
4267
4275
Celniker
S. E.
,
Keelan
D. J.
,
Lewis
E. B.
(
1990
)
The molecular genetics of the bithorax complex of Drosophila: characterization of the products of the Abdominal-B domain.
Genes Dev
3
,
1424
1436
DeCamillis
M.
,
Cheng
N.
,
Pierre
D.
,
Brock
H. W.
(
1992
)
The polyhomeotic gene of Drosophila encodes a chromatin protein that shares polytene chromosome-binding sites with Polycomb.
Genes Dev
6
,
223
232
Deatrick
J.
,
Daly
M.
,
Randsholt
N. B.
,
Brock
H. W.
(
1991
)
The complex genetic locus polyhomeotic in Drosophila melanogaster potentially encodes two homologous zinc-finger proteins.
Gene
105
,
185
195
Denell
R. E.
,
Frederick
R. D.
(
1983
)
Homeosis in Drosophila: A description of the Polycomb lethal syndrome.
Dev. Biol
97
,
34
47
Delorenzi
M.
,
Bienz
M.
(
1990
)
Expression of Abdominal-B homeoproteins in Drosophila embryos.
Development
108
,
323
329
Dura
J. M.
,
Randsholt
N. B.
,
Deatrick
J.
,
Erk
I.
,
Santamaria
P.
,
Freeman
J. D.
,
Freeman
S. J.
,
Weddell
D.
,
Brock
H. W.
(
1987
)
A complex genetic locus, polyhomeotic, is required for segmental specification and epidermal development in D. melanogaster.
Cell
51
,
829
839
Dura
J. M.
,
Ingham
P.
(
1988
)
Tissue-and stage-specific control of homeotic and segmentation gene expression in Drosophila embryos by the polyhomeotic gene.
Development
103
,
733
741
Franke
A.
,
DeCamillis
M.
,
Zink
D.
,
Cheng
N.
,
Brock
H. W.
,
Paro
R.
(
1992
)
Polycomb and polyhomeotic are constituents of a multimeric protein complex in chromatin of Drosophila melanogaster.
EMBO J
11
,
2941
2950
Gaunt
S. J.
,
Singh
P. B.
(
1990
)
Homeogene expression patterns and chromosomal imprinting.
Trends Genet
6
,
208
212
Germino
J.
,
Gray
J. G.
,
Charbonneau
H.
,
Vanaman
T.
,
Bastia
D.
(
1983
)
Use of fusions and protein-protein interaction in the isolation of a biologically active regulatory protein: The replication initiator protein of plasmid R6K.
Proc. Natl. Acad. Sci. USA
80
,
6848
6852
Ingham
P. W.
(
1984
)
A gene that regulates the Bithorax Complex differentially in larval and adult cells of Drosophila.
Cell
37
,
815
823
Ingham
P. W.
(
1988
)
The molecular genetics of embryonic pattern formation in Drosophila.
Nature
335
,
25
34
Jones
R. S.
,
Gelbart
W. M.
(
1990
)
Genetic analysis of the Enhancer of zeste locus and its role in gene regulation in Drosophila melanogaster.
Genetics
126
,
185
199
Jurgens
G.
(
1985
)
A group of genes controlling the spatial expression of the bithorax complex in Drosophila.
Nature
316
,
153
155
Karch
F.
,
Weiffenbach
B.
,
Peifer
M.
,
Bender
W.
,
Duncan
I.
,
Celniker
S.
,
Crosby
M.
,
Lewis
E. B.
(
1985
)
The abdominal region of the bithorax complex.
Cell
43
,
81
96
Lasko
P. F.
,
Pardue
M. L.
(
1988
)
Studies on the genetic organization of the vestigial microregion of Drosophila melanogaster.
Genetics
120
,
495
502
Lasko
P. F.
,
Ashburner
M.
(
1990
)
Posterior localization of vasa protein correlates with, but is not sufficient for, pole cell development.
Genes Dev
4
,
905
921
Lawrence
P. A.
,
Johnston
P.
,
Struhl
G.
(
1983
)
Different requirements for homeotic genes in the soma and germ line of Drosophila.
Cell
35
,
27
34
Lewis
E. B.
(
1978
)
A gene complex controlling segmentation in Drosophila.
Nature
276
,
565
570
Locke
J.
,
Kotarski
M. A.
,
Tartof
K. D.
(
1988
)
Dosage-dependent modifiers of position effect variegation in Drosophila and a mass action model that explains their effect.
Genetics
120
,
181
198
Messmer
S.
,
Franke
A.
,
Paro
R.
(
1992
)
Analysis of the functional role of the Polycomb chromo domain in Drosophila melanogaster.
Genes Dev
6
,
1241
1254
Paro
R.
(
1990
)
Imprinting the determined state into the chromatin of Drosophila.
Trends Genet
6
,
416
421
Paro
R.
,
Hogness
D. S.
(
1991
)
The Polycomb protein shares a homologous domain with a heterochromatin-associated protein of Drosophila.
Proc. Natl. Acad. Sci. USA
88
,
263
267
Phillips
M. D.
,
Shearn
A.
(
1990
)
Mutations in polycombeotic, a Drosophila Polycomb-group gene, cause a wide range of maternal and zygotic phenotypes.
Genetics
125
,
91
101
Reuter
G.
,
Giarre
M.
,
Farah
J.
,
Gausz
J.
,
Spierer
A.
,
Spierer
P.
(
1990
)
Dependence of position-effect variegation in Drosophila on dose of a gene encoding an unusual zinc-finger protein.
Nature
344
,
219
223
Ruther
U.
,
Muller-Hill
B.
(
1983
)
Easy identification of cDNA clones.
EMBO J
2
,
1791
1794
Singh
P. B.
,
Miller
R.
,
Pearce
J.
,
Kothary
R.
,
Burton
R. D.
,
Paro
R.
,
James
T. C.
,
Gaunt
S. J.
(
1991
)
A sequence motif found in a Drosophila heterochromatin protein is conserved in animals and plants.
Nucl. Acids Res
19
,
789
794
Simon
J.
,
Chiang
A. C.
,
Bender
W.
(
1992
)
Ten different Polycomb-group genes are required for spatial control of the abdA and AbdB homeotic products.
Development
114
,
493
505
Smouse
D.
,
Goodman
C.
,
Mohawald
A.
,
Perrimon
N.
(
1988
)
polyhomeotic: a gene required for the embryonic development of axon pathways in the central nervous system of Drosophila.
Genes Dev
2
,
830
842
Struhl
G.
(
1981
)
A gene product required for correct initiation of segmental determination in Drosophila.
Nature
293
,
36
41
Struhl
G.
(
1983
)
Role of the esc +gene product in ensuring the selective expression of segment-specific homeotic genes in Drosophila.
J. Embryol. Exp. Morph
76
,
297
331
Struhl
G.
,
Akam
M.
(
1985
)
Altered distribution of the Ultrabithorax transcripts in extra sex combs mutant embryos of Drosophila.
EMBO J
4
,
3259
3264
Struhl
G.
,
White
R. A. H.
(
1985
)
Regulation of the Ultrabithorax gene of Drosophila by other bithorax complex genes.
Cell
43
,
507
519
Suter
B.
,
Steward
R.
(
1991
)
Requirement for phosphorylation and localization of the Bicaudal-D protein in Drosophila oocyte differentiation.
Cell
67
,
917
926
Tagawa
M.
,
Sakamoto
T.
,
Shigemoto
K.
,
Matsubara
H.
,
Tamura
Y.
,
Ito
T.
,
Nakamura
I.
,
Okitsu
A.
,
Imai
K.
,
Taniguchi
M.
(
1990
)
Expression of novel DNA-binding protein with zinc finger structure in various tumor cells.
J. Biol. Chem
265
,
20021
20026
Tartof
K. D.
,
Bishop
C.
,
Jones
M.
,
Hobbs
C.
,
Locke
J.
(
1989
)
Towards an understanding of position effect variegation.
Dev. Genet
10
,
162
176
van Lohuizen
M.
,
Frasch
M.
,
Wientjens
E.
,
Berns
A.
(
1991
)
Sequence similarity between the mammalian bmi-1 proto-oncogene and the Drosophila regulatory genes Psc and Su(z)2.
Nature
353
,
353
355
Wedeen
C.
,
Harding
K.
,
Levine
M.
(
1986
)
Spatial regulation of Antennapedia and Bithorax gene expression by the Polycomb locus in Drosophila.
Cell
44
,
739
748
Wu
C.-T.
,
Jones
R. S.
,
Lasko
P. F.
,
Gelbart
W. M.
(
1989
)
Homeosis and the interaction of zeste and white in Drosophila.
Mol. Gen. Genet
218
,
5
–.
Zink
B.
,
Paro
R.
(
1989
)
In vivo binding pattern of a trans-regulator of homeotic genes in Drosophila melanogaster.
Nature
337
,
468
471
Zink
B.
,
Engström
Y.
,
Gehring
W.
,
Paro
R.
(
1991
)
Direct interaction of the Polycomb protein with the Antennapedia regulatory sequences in polytene chromosomes of Drosophila melanogaster.
EMBO J
10
,
153
162
This content is only available via PDF.