At the posterior pole of the Drosophila oocyte, oskar induces a tightly localized assembly of pole plasm. This spatial restriction of oskar activity has been thought to be achieved by the localization of oskar mRNA, since mislocalization of the RNA to the anterior induces anterior pole plasm. However, ectopic pole plasm does not form in mutant ovaries where oskar mRNA is not localized, suggesting that the unlocalized mRNA is inactive. As a first step towards understanding how oskar activity is restricted to the posterior pole, we analyzed oskar translation in wild type and mutants. We show that the targeting of oskar activity to the posterior pole involves two steps of spatial restriction, cytoskeleton-dependent localization of the mRNA and localization-dependent translation. Furthermore, our experiments demonstrate that two isoforms of Oskar protein are produced by alternative start codon usage. The short isoform, which is translated from the second in-frame AUG of the mRNA, has full oskar activity. Finally, we show that when oskar RNA is localized, accumulation of Oskar protein requires the functions of vasa and tudor, as well as oskar itself, suggesting a positive feedback mechanism in the induction of pole plasm by oskar.
Reference
Barker
D. D.
, Wang
C.
, Moore
J.
, Dickinson
L. K.
, Lehmann
R.
(1992
) Pumilio is essential for function but not for distribution of the Drosophila abdominal determinant Nanos.
Genes Dev
6
, 2312
–2326
Boeck
R.
, Kolakofsky
D.
(1994
) Positions +5 and +6 can be major determinants of the efficiency of non-AUG initiation codons for protein synthesis.
EMBO J
13
, 3608
–3617
Boswell
R. E.
, Mahowald
A. P.
(1985
) tudor, a gene required for assembly of the germ plasm in Drosophila melanogaster.
Cell
43
, 97
–104
Boswell
R. E.
, Prout
M. E.
, Steichen
J. C.
(1991
) Mutations in a newly identified Drosophilamelanogaster gene, mago nashi, disrupt germ cell formation and result in the formation of mirror-image symmetrical double abdomen embryos.
Development
113
, 373
–384
Cavener
D.
(1987
) Comparison of the consensus sequences flanking translational start-sites in Drosophila and vertebrates.
Nucl. Acids Res
15
, 1353
–1361
Christerson
L. B.
, McKearin
D. M.
(1994
) orb is required for anteroposterior and dorsoventral patterning during Drosophila oogenesis.
Genes Dev
8
, 614
–628
Clark
I.
, Giniger
E.
, Ruohola-Baker
H.
, Jan
L. Y.
, Jan
Y. N.
(1994
) Transient posterior localization of a kinesin fusion protein reflects anteroposterior polarity of the Drosophila oocyte.
Curr. Biol
4
, 289
–300
Curran
J.
, Kolakofsky
D.
(1989
) Scanning independent ribosomal initiation of the Sendai virus Y proteins in vitro and in vivo.
EMBO J
8
, 521
–526
Driever
W.
, Siegel
V.
, Nusslein-Volhard
C.
(1990
) Autonomous determination of anterior structures in the early Drosophila embryo by the bicoid morphogen.
Development
109
, 811
–820
Driever
W.
, Nusslein-Volhard
C.
(1988
) A gradient of bicoid protein in Drosophila embryos.
Cell
54
, 83
–93
Ephrussi
A.
, Dickinson
L. K.
, Lehmann
R.
(1991
) oskar organizes the germ plasm and directs localization of the posterior determinant nanos.
Cell
66
, 37
–50
Ephrussi
A.
, Lehmann
R.
(1992
) Induction of germ cell formation by oskar.
Nature
358
, 387
–392
Ferrandon
D.
, Elphick
L.
, Nusslein-Volhard
C.
, St Johnston
D.
(1994
) Staufen protein associates with the 3'UTR of bicoid mRNA to form particles that move in a microtubule-dependent manner.
Cell
79
, 1221
–1232
Gavis
E. R.
, Lehmann
R.
(1992
) Localization of nanos RNA controls embryonic polarity.
Cell
71
, 301
–313
Gavis
E. R.
, Lehmann
R.
(1994
) Translational regulation of nanos by RNA localization.
Nature
369
, 315
–318
González-Reyes
A.
, Elliott
H.
, St Johnston
D.
(1995
) Polarization of both major body axes in Drosophila by gurken-torpedo signalling.
Nature
375
, 654
–658
Grunert
S.
, Jackson
R. J.
(1994
) The immediate downstream codon strongly influences the efficiency of utilization of eukaryotic translation initiation codons.
EMBO J
13
, 3618
–3630
Hay
B.
, Ackerman
L.
, Barbel
S.
, Jan
L. Y.
, Jan
Y. N.
(1988
) Identification of a component of Drosophila polar granules.
Development
103
, 625
–640
Illmensee
K.
, Mahowald
A. P.
(1974
). Transplantation of posterior polar plasm in Drosophila. Induction of germ cells at the anterior pole of the egg.
Proc. Natl. Acad. Sci. USA
71
, 1016
–1020
Kim-Ha
J.
, Kerr
K.
, Macdonald
P. M.
(1995
) Translational regulation of oskar mRNA by bruno, an ovarian RNA-binding protein, is essential.
Cell
81
, 403
–412
Kim-Ha
J.
, Smith
J. L.
, Macdonald
P. M.
(1991
) oskar mRNA is localized to the posterior pole of the Drosophila oocyte.
Cell
66
, 23
–35
Kim-Ha
J.
, Webster
P. J.
, Smith
J. L.
, Macdonald
P. M.
(1993
) Multiple RNA regulatory elements mediate distinct steps in localization of oskar mRNA.
Development
119
, 169
–178
Kozak
M.
(1986
) Point mutations define a sequence flanking the AUG initiator codon that modulates translation by eukaryotic ribosomes.
Cell
44
, 283
–292
Kozak
M.
(1987
) An analysis of 5-noncoding sequences from 699 vertebrate messenter RNAs.
Nucl. Acids Res
15
, 8125
–8148
Lasko
P. F.
, Ashburner
M.
(1988
) The product of the Drosophila gene vasa is very similar to eukaryotic initiation factor-4A.
Nature
335
, 611
–617
Lehmann
R.
, Nusslein-Volhard
C.
(1986
) Abdominal segmentation, pole cell formation, and embryonic polarity require the localized activity of oskar, a maternal gene in Drosophila.
Cell
47
, 141
–152
Lehmann
R.
, Nusslein-Volhard
C.
(1991
) The maternal gene nanos hasa central role in pattern formation of the Drosophila embryo.
Development
112
, 679
–691
Mahowald
A. P.
(1968
) Polar granules of Drosophila II. Ultrastructural changes during early embryogenesis.
J. Exp. Zool
167
, 237
–262
Mahowald
A. P.
(1971
) Polar granules of Drosophila IV. Cytochemical studies showing loss of RNA from polar granules during early stages om embryogenesis.
J. Exp. Zool
176
, 345
–352
Manseau
L. J.
, Schupbach
T.
(1989
) cappuccino and spire: Two unique maternal-effect loci required for both the anteroposterior and dorsoventral patterns of the Drosophila embryo.
Genes Dev
3
, 1437
–1452
Mohler
J.
, Wieschaus
E. F.
(1986
) Dominant maternal effect mutations of Drosophila melanogaster causing the production of double-abdomen embryos.
Genetics
112
, 808
–822
Neuman-Silberberg
F. S.
, Schupbach
T.
(1993
) The Drosophila dorsoventral patterning gene gurken produces a dorsally localized RNA and encodes a TGF-like protein.
Cell
75
, 165
–174
Newmark
P. A.
, Boswell
R. E.
(1994
) The mago nashi locus encodes an essential product required for germ plasm assembly in Drosophila.
Development
120
, 1303
–1313
Pokrywka
N. J.
, Stephenson
E. C.
(1995
) Microtubules are a general component of mRNA localization systems in Drosophila oocytes.
Dev. Biol
167
, 363
–370
Reuter
G.
, Szidonya
J.
(1983
) Cytogenetic analysis of variegation suppressors and dominant temperature-sensitive lethals in region 23–26 of chromosome 2L in Drosophilamelanogaster.
Chromosoma
88
, 277
–285
Roth
S.
, Neuman-Silberberg
F. S.
, Barcelo
G.
, Schupbach
T.
(1995
) cornichon and the EGF receptor signaling process are necessary for both anterior-posterior and dorsal-ventral pattern formation in Drosophila.
Cell
81
, 967
–978
Rubin
G. M.
, Spradling
A. C.
(1982
) Genetic transformation of Drosophila with transposable element vectors.
Science
218
, 348
–353
Salles
F. J.
, Lieberfarb
M. E.
, Wreden
C.
, Gergen
J. P.
, Strickland
S.
(1994
) Coordinate initiation of Drosophila development by regulated polyadenylation of maternal messenger RNAs.
Science
266
, 1996
–1999
St Johnston
D.
, Beuchle
D.
, Nusslein-Volhard
C.
(1991
) staufen, a gene required to localize maternal RNAs in the Drosophila egg.
Cell
66
, 51
–63
St Johnston
D.
, Nusslein-Volhard
C.
(1992
) The origin of pattern and polarity in the Drosophila embryo.
Cell
68
, 201
–219
Tam
J. P.
(1988
) Synthetic peptide vaccine design: Synthesis and properties of a high-density multiple antigenic peptide system.
Proc. Natl. Acad. Sci. USA
85
, 5409
–5413
Theurkauf
W. E.
, Baum
H.
, Jieying
B.
, Wensink
P. C.
(1986
) Tissue-specific and constitutive alpha-tubulin genes of Drosophila melanogaster code for structurally distinct proteins.
Proc. Natl. Acad. Sci. USA
83
, 8477
–8481
Wharton
R. P.
, Struhl
G.
(1991
) RNA regulatory elements mediate control of Drosophila body pattern by the posterior morphogen nanos.
Cell
67
, 955
–967
This content is only available via PDF.
© 1995 by Company of Biologists
1995
