Su(z)12, a novel Drosophila Polycomb group gene that is conserved in vertebrates and plants
Anna Birve1,
Aditya K. Sengupta2,
Dirk Beuchle2,
Jan Larsson1,
James A. Kennison3,
Åsa Rasmuson-Lestander1 and
Jürg Müller2,*
1 Department of Genetics, Umeå University, S-90187 Umeå, Sweden
2 Max Planck Institute for Developmental Biology, Spemannstrasse 35/III, 72076, Tübingen, Germany
3 Laboratory of Molecular Genetics, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892-2785, USA
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Fig. 1. Homeotic transformations in a Su(z)12 mutant pharate adult male. Homeotic transformations are evident in several body segments. Sex combs, a structure normally only present on the first leg, are present on the first tarsal segments of all meso- and metathoracic legs (arrowheads); the antennae are partially transformed into legs (asterisk) and wings are much smaller and partially transformed into haltere-like structures (arrows). These homeotic transformations are consistent with inappropriate activation of several ANTC and BXC genes in the imaginal disc primordia of these structures (see text). The genotype of the animal shown is Su(z)125/Su(z)123 but similar homeotic phenotypes are observed in Su(z)125/Su(z)124 pharate adults; these mutant combinations die as pharate adults and never eclose from the pupal case.
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Fig. 2. Misexpression of homeotic genes and homeotic transformations in Su(z)12 mutant embryos. (A,B) Embryos at stage 16 (A) and stage 11 (B) stained with antibody against Ubx protein. In wild-type (wt) embryos, Ubx is expressed from parasegments (ps) 5 to ps 13 (anterior margin of ps 5 in all cases marked by an arrowhead) and in five midline cells in ps 4 (visible in A). (A) Su(z)124 homozygous embryos (zyg-) show misexpression of Ubx anterior to ps 5 but only in a few cells in the CNS and in the brain (asterisk); more extensive misexpression of Ubx is seen in ps 1-4 of Su(z)121 homozygotes. (B) Su(z)122/Df(3L)kto2 embryos derived from Su(z)122 germline clones show strong expression of Ubx from ps 1 to ps 14 already at this earlier stage owing to the lack of both maternal and zygotic (mat- zyg-) wild-type Su(z)12 protein. (C) Cuticles of a wild-type and a Su(z)12 mutant embryo of the same genotype as in B. In the Su(z)12 mutant embryo all abdominal, thoracic and several head segments (not all visible in this focal plane) are homeotically transformed into copies of the eighth abdominal segment owing to misexpression of the Abd-B gene in every segment (the eighth abdominal segment is marked by an arrow in the wild-type embryo and the first abdominal segment is marked by a white arrowhead). Su(z)125/Df(3L)kto2 embryos derived from Su(z)125germline clones show similar misexpression of Ubx and cuticle phenotypes like the embryos shown in B and C (data not shown).
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Fig. 3. Su(z)12 function is required throughout development to repress HOX genes. Wing imaginal discs with clones of cells that are homozygous for the indicated Su(z)12 allele were stained with antibodies against GFP (green) and Ubx or Abd-B protein (red) as indicated. Neither Ubx nor Abd-B proteins are normally expressed in the wing imaginal disc. In each case, homozygous Su(z)12 mutant cells are marked by the absence of GFP protein (green) and in all experiments the Minute technique was used (see text). (A) Clones were induced 96 hours before analysis. Strong misexpression of Ubx and Abd-B protein is detected in clones that are homozygous for the strong alleles Su(z)121 and Su(z)124; note that both homeotic genes are derepressed in almost all clones, throughout the disc. In clones homozygous for the hypomorphic allele Su(z)122, misexpression of Ubx occurs only in clones in central regions of the wing pouch and in the hinge region; Abd-B is not derepressed in these clones. No derepression of Ubx or Abd-B is detected in Su(z)125 mutant clones, consistent with the genetic data that this allele is a weaker hypomorph than Su(z)122. (B) Kinetics of derepression of Ubx and Abd-B in Su(z)121 and Su(z)124 mutant clones. 48 hours after clone induction Ubx is still repressed in almost all Su(z)124 mutant clones but Su(z)121 mutant clones in the wing pouch already show strong misexpression of Ubx. 72 hours after clone induction, most Su(z)121 mutant clones show strong misexpression of Ubx, whereas only Su(z)124 mutant clones in the pouch show strong Ubx signal and Ubx is apparently still repressed in other regions of the disc.
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Fig. 4. Su(z)12 mutations suppress position-effect variegation. Heads of adult flies that are hemizygous for the wm4 rearrangement. In wild-type flies (left), pigmentation in eyes is drastically reduced owing to silencing of the white (w) gene in most ommatidia. In animals that are heterozygous for any of the Su(z)12 alleles (right), there is a partial release from silencing and the w gene is expressed in most ommatidia; the loss of silencing is stronger in case of the EMS-induced Su(z)12 alleles. In each case, the wild-type (+/+) control flies on the left carry the TM3 balancer chromosome and are the siblings of the corresponding Su(z)12 mutants.
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Fig. 5. Lesions in mutant Su(z)12 alleles and comparison between Su(z)12 and related proteins in humans and in Arabidopsis. (Top) Schematic representation of the Drosophila malnogaster Su(z)12 (Dm Su(z)12), Homo sapiens Su(z)12 (Hs SU(Z)12, KIAA0160) and Arabidopsis thaliana (At) EMF2 (N. Yoshida, personal communication), VRN2 (A. Gendall, personal communication) and FIS2 (Luo et al., 1999) proteins (white rectangles) with zinc finger (black box) and VEFS box (stippled box). The locations of the molecular lesions in four different Su(z)12 alleles are indicated (see text). Alignment of the zinc fingers (top right) and the VEFS box (below). Identical amino acids that are found in all five proteins are boxed in red and listed below the alignments, similarities are boxed in colors using the code listed below. Bottom: alignment of Drosophila Su(z)12 and human SU(Z)12 amino acid sequences. Note that the two proteins are conserved over the whole length of the protein. The conserved Gly mutated in Su(z)122 is indicated by an arrowhead.
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