The homeotic genes of the bithorax complex are required, among other things, for establishing the patterns of sensory organs in the embryonic peripheral nervous system (PNS). However, the molecular mechanisms by which these genes affect pattern formation in the PNS are not understood and other genes that function in this pathway are not characterized. Here we report the phenotypic and molecular analysis of one such gene, homothorax (hth; also named dorsotonals). Mutations in the hth gene seem to alter the identity of the abdominal chordotonal neurons, which depend on Abd-A for their normal development. However, these mutations do not alter the expression of the abd-A gene, suggesting that hth may be involved in modulating abd-A activity. We have generated multiple mutations in the hth locus and cloned the hth gene. hth encodes a homeodomain-containing protein that is most similar to the murine proto-oncogene meis1. The hth gene is expressed throughout embryonic development in a spatially restricted pattern, which is modulated in abdominal segments by abd-A and Ubx. The spatial distribution of the HTH protein during embryonic development is very similar to the distribution of the Extradenticle (EXD) protein, a known modulator of homeotic gene activity. Here we show that the PNS phenotype of exd mutant embryos is virtually indistinguishable from that of hth mutant embryos and does not simply follow the homeotic transformations observed in the epidermis. We also show that the HTH protein is present in extremely low levels in embryos lacking exd activity as compared to wild-type embryos. In contrast, the EXD protein is present in fairly normal levels in hth mutant embryos, but fails to accumulate in nuclei and remains cytoplasmic. Ectopic expression of hth can drive ectopic nuclear localization of EXD. Based on our observations we propose that the genetic interactions between hth and exd serve as a novel mechanism for regulating homeotic protein activity in embryonic PNS development.

REFERENCES

Aspland
S. E.
,
White
R. A. H.
(
1997
)
Nucleoplasmic localisation of extradenticle protein is spatially regulated throughout development in Drosophila.
Development
124
,
741
747
Blochlinger
K. R.
,
Bodmer
R.
,
Jack
J. W.
,
Jan
L. Y.
,
Jan
Y. N.
(
1988
)
Primary structure and expression of a product from cut, a locus involved in specifying sensory organ identity in Drosophila.
Nature
333
,
629
635
Blochlinger
K.
,
Bodmer
R.
,
Jan
L. Y.
,
Jan
Y. N.
(
1990
)
Patterns of expression of Cut, a protein required for external sensory organ development in wild-type and cut mutant Drosophila embryos.
Genes Dev
4
,
1322
1331
Blochlinger
K.
,
Jan
L. Y.
,
Jan
Y. N.
(
1991
)
Transformation of sensory organ identity by ectopic expression of Cut in Drosophila.
Genes Dev
5
,
1124
1135
Bodmer
R.
,
Barbel
S.
,
Shepherd
S.
,
Jack
J. W.
,
Jan
L. Y.
,
Jan
Y. N.
(
1987
)
Transformation of sensory organs by mutations of the cut locus of D. melanogaster.
Cell
51
,
293
307
Brand
A. H.
,
Perrimon
N.
(
1993
)
Targeted gene expression as a means of altering cell fates and generating dominant phenotypes.
Development
118
,
401
415
Campos-Ortega
J. A.
(
1995
)
Genetic mechanisms of early neurogenesis in Drosophila melanogaster.
Mol. Neurobiol
10
,
75
89
Capovilla
M.
,
Brandt
M.
,
Botas
J.
(
1994
)
Direct regulation of decapentaplegic by Ultrabithorax and its role in Drosophila midgut morphogenesis.
Cell
76
,
461
475
Chan
S.-K.
,
Jaffe
L.
,
Capovilla
M.
,
Botas
J.
,
Mann
R.
(
1994
)
The DNA binding specificity of Ultrabithorax is modulated by cooperative interactions with Extradenticle, another homeoprotein.
Cell
78
,
603
615
Chanut
F.
,
Heberlein
U.
(
1997
)
Role of decapentaplegic in initiation and progression of the morphogenetic furrow in the developing Drosophila retina.
Development
124
,
559
567
Doe
C. Q.
(
1996
)
Asymmetric cell division and neurogenesis.
Curr. Opin. Genet. Dev
6
,
562
566
Flegel
W. A.
,
Singson
A. W.
,
Margolis
J. S.
,
Bang
A. G.
,
Posakony
J.W.
,
Murre
C.
(
1993
)
Dpbx, a new homeobox gene closely related to the human proto-oncogene pbx1 Molecular structure and developmental expression.
Mech. Dev
41
,
155
161
Goodman
C. S.
,
Bastiani
M. J.
,
Doe
C. Q.
,
Du Lac
S.
,
Helfand
S. L.
,
Kuwada
K. Y.
,
Thomas
J. B.
(
1984
)
Cell recognition during neuronal development.
Science
225
,
1271
1279
Hartenstein
V.
(
1987
)
The influence of segmental compartmentalisation on the development of the larval peripheral nervous system in Drosophila melanogaster.
Dev. Biol
196
,
101
112
Hassan
B.
,
Vaessin
H.
(
1996
)
Regulatory interactions during early neurogenesis in Drosophila.
Dev. Genet
18
,
18
27
Heuer
J.
,
Kaufman
T.
(
1992
)
Homeotic genes have specific functional roles in the establishment of the Drosophila embryonic peripheral nervous system.
Development
115
,
35
47
Jarman
A. P.
,
Grell
E. E.
,
Ackerman
L.
,
Jan
L. Y.
,
Jan
Y. N.
(
1994
)
atonal is the proneural gene for Drosophila photoreceptors.
Nature
369
,
398
403
Kania
A.
,
Salzberg
A.
,
Baht
M.
,
D'Evelyn
D.
,
He
Y.
,
Kiss
I.
,
Bellen
H. J.
(
1995
)
: P -element mutations affecting embryonic peripheral nervous system development in Drosophila melanogaster.
Genetics
139
,
1663
1678
Karch
F.
,
Bender
W.
,
Weiffenbach
B.
(
1990
)
Abdominal-A expression in Drosophila embryos.
Genes Dev
4
,
1573
1578
Kellerman
K. A.
,
Mattson
D. M.
,
Duncan
I.
(
1990
)
Mutations affecting the stability of the fushi tarazu protein of Drosopila.
Genes Dev
4
,
1936
1950
Lewis
E. B.
(
1978
)
A gene complex controlling segmentation in Drosophila.
Nature
276
,
565
570
Ma
C.
,
Moses
K.
(
1995
)
Wingless and patched are negative regulators of the morphogenetic furrow and can affect tissue polarity in the developing Drosophila compound eye.
Development
121
,
2279
2289
Manak
J. R.
,
Mathies
L. D.
,
Scott
M. P.
(
1995
)
Regulation of a decapentaplegic midgut enhancer by homeotic proteins.
Development
120
,
3605
3619
Maniatis
T.
,
Hardison
R. C.
,
Lacy
E.
,
Lauer
J.
,
O'Connell
C.
,
Quon
D.
,
Sim
G. K.
,
Efstratiadis
A.
(
1978
)
The isolation of structural genes from libraries of eucaryotic DNA.
Cell
15
,
687
701
Mann
R. S.
,
Abu-Shaar
M.
(
1996
)
Nuclear import of the homeodomain protein Extradenticle in response to Wg and Dpp signalling.
Nature
383
,
630
633
Moskow
J. J.
,
Bullrich
F.
,
Hubener
K.
,
Daar
I. O.
,
Buchberg
A. M.
(
1995
)
Meis1, a PBX1 -related homeobox gene involved in myeloid leukemia in BXH-2 mice.
Mol. Cell. Biol
15
,
5434
5443
Nakamura
T.
,
Jenkins
N. A.
,
Copeland
N. G.
(
1996
)
Identification of a new family of Pbx-related homeobox genes.
Oncogene
13
,
2235
2242
Nakamura
T.
,
Largaespada
D. A.
,
Shaughnessy
J. D.
,
Jenkins
N.
,
Copeland
N. G.
(
1996
)
Cooperative activation of Hoxa and Pbx1 -related genes in murine myeloid leukaemias.
Nature Genetics
12
,
149
153
Okabe
M.
,
Okano
H.
(
1997
)
Two-step induction of chordotonal organ precursors in Drosophila embryogenesis.
Development
124
,
1045
1053
Peifer
M.
,
Wieschaus
E.
(
1990
)
Mutations in the Drosophila gene extradenticle affect the way specific homeodomain proteins regulate segmental identity.
Genes Dev
4
,
1209
1223
Pignoni
F.
,
Zipurski
S. L.
(
1997
)
Induction of Drosophila eye development by Decapentaplegic.
Development
124
,
271
278
Posakony
J. W.
(
1994
)
Nature versus nurture: asymmetric cell divisions in Drosophila bristle development.
Cell
76
,
415
418
Rauskolb
C.
,
Peifer
M.
,
Wieschaus
E.
(
1993
)
extradenticle, a regulator of homeotic gene activity, is a homolog of the homeobox-containing human protooncogene PBX1.
Cell
74
,
1101
1112
Salzberg
A.
,
D'Evelyn
D.
,
Schulze
K. L.
,
Lee
J.-K.
,
Strumpf
D.
,
Tsai
L.
,
Bellen
H. J.
(
1994
)
Mutations affecting the pattern of the PNS in Drosophila reveal novel aspects of neuronal development.
Neuron
13
,
268
287
Salzberg
A.
,
Prokopenko
S. N.
,
He
Y.-C.
,
Tsai
P.
,
Deák
P.
,
Pál
M.
,
Maroy
P.
,
Glover
D. M.
,
Bellen
H. J.
(
1997
)
P Element insertion alleles of essential genes on the third chromosome of Drosophila melanogaster: mutations affecting embryonic PNS development.
Genetics
147
,
1723
1741
Sanchez-Herrero
E.
,
Vernos
I.
,
Marco
R.
,
Morata
G.
(
1985
)
Genetic organization of Drosophia bithorax complex.
Nature
313
,
108
113
Seeger
M.
,
Tear
G.
,
Ferres-Marco
D.
,
Goodman
C. S.
(
1993
)
Mutations affecting growth cone guidance in Drosophila: genes necessary for guidance toward or away from the midline.
Neuron
10
,
409
426
Smith
J. E. J.
,
Bollekens
J. A.
,
Inghirami
G.
,
Takeshita
K.
(
1997
)
Cloning and mapping of the MEIS1 gene, the human homolog of a murine leukomogenic gene.
Genomics
43
,
99
103
Steelman
S.
,
Moskow
J. J.
,
Muzynski
K.
,
North
C.
,
Druck
T.
,
Montgomery
J. C.
,
Huebner
K.
,
Daar
I. O.
,
Buchberg
A. M.
(
1997
)
Identification of a conserved family of Meis1 -related homeobox genes.
Genome Res
7
,
142
156
Sun
Y. H.
,
Tsai
C.-J.
,
Green
M. M.
,
Chao
L.-L.
,
Yu
C.-T.
,
Jaw
T. J.
,
Yeh
J.-Y.
,
Bolshakov
V. N.
(
1995
)
white as a reporter gene to detecttranscriptional silencers specifying position-specific expression during Drosophila melanogaster eye development.
Genetics
141
,
1075
1086
Tautz
D.
,
Pfeifle
C.
(
1989
)
A non-radioactive in situ hybridization method for the localization of specific RNAs in Drosophila embryos reveals translational control of the segmentation gene hunchback.
Chromosoma
98
,
81
85
Treisman
J. E.
,
Rubin
G. M.
(
1995
)
wingless inhibits morphogenetic furrow movement in the Drosophila eye disk.
Development
121
,
3519
3527
van Dijk
M. A.
,
Murre
C.
(
1994
)
extradenticle raises the DNA binding specificity of homeotic selector gene products.
Cell
78
,
617
624
Vincent
S.
,
Ruberte
E.
,
Grieder
N. C.
,
Chen
C.-K.
,
Haerry
T.
,
Schuh
R.
,
Affolter
M.
(
1997
)
DPP controls tracheal cell migration along the dorsoventral body axis of the Drosophila embryo.
Development
124
,
2741
2750
Wakimoto
B. T.
,
Kaufman
T. C.
(
1981
)
Analysis of larval segmentation in lethal genotypes associated with the Antennapedia complex in Drosophila melanogaster.
Dev. Biol
81
,
51
64
Wilson
C.
,
Pearson Kurth
R.
,
Bellen
H. J.
,
O'Kane
C. J.
,
Grossniklaus
U.
,
Gehring
W. J.
(
1989
)
P-element-mediated enhancer detection: an efficient method for isolating and characterizing developmentally regulated genes in Drosophila.
Genes Dev
3
,
1301
1313
Zinn
K.
,
McAllister
L.
,
Goodman
C. S.
(
1988
)
Sequence analysis and neuronal expression of fasciclin I in grasshopper and Drosophila.
Cell
53
,
577
587
Rieckhof
G. E.
,
Casares
F.
,
Don Ryoo
H.
,
Abu-Shaar
M.
,
Mann
R.S.
(
1997
)
Nuclear translocation of extradenticle requires homothorax, whic h encodes an extradenticle-related homeodomain protein.
Cell
91
,
171
183
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