doi: 10.1242/10.1242/dev.00405
Effects of tethering HP1 to euchromatic regions of the Drosophila genome
Yuhong Li1,
John R. Danzer1,
Pedro Alvarez2,
Andrew S. Belmont2 and
Lori L. Wallrath1,*
1 Department of Biochemistry, University of Iowa, Iowa City, IA 52242, USA
2 Department of Cell and Structural Biology, University of Illinois,
Urbana-Champaign, Urbana, IL 61801, USA
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Fig. 1. lacI-HP1 fusion protein co-localizes with endogenous HP1. Polytene
chromosomes from expressor stock LH2, expressing lacI-HP1,
were squashed and stained with antibodies to HP1 (red) and antibodies to
lacI (green). The chromocenter (C) and telomeres (T) are indicated.
Complete co-localization is observed as yellow in the merged image.
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Fig. 2. Tethered HP1 causes silencing at some, but not all, genomic sites. The left
column shows the eye phenotype observed for stocks 157.1, J3.2 and S9.2 with
and without tethered GFP-lacI. The middle column shows the eye
phenotype with and without tethered lacI-HP1. The right column shows
localization of the lacI-HP1 fusion protein on polytene chromosomes.
The arrow denotes the location of lac repeats. Polytene chromosomes
were stained with antibodies against lacI (green).
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Fig. 3. Tethered lacI-HP1 causes ectopic associations. Third instar larvae
of stocks 157.1, 157.4.112 and P2.5 expressing lacI-HP1 were stained
with antibodies to lacI (green). Arrows indicate the locations of
lac repeats. The percent of nuclei showing ectopic associations, out
of 60 nuclei scored for each cytological position, are shown at the bottom of
each panel. Associations were observed between the tethered site and other
HP1-containing sites (A,B), but were also observed at sites not enriched with
HP1 (C).
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Fig. 4. HP1 functions downstream of SU(VAR)3-9. (A) The lac repeats show a
low level of HP1 and H3 K9 methylation in the absence of lacI-HP1.
Polytene chromosomes from stock 157.1 containing a reporter transgene with 256
copies of lac repeats were stained with antibodies to HP1 (green) and
antibodies to H3 K9 di-methyl (red). Arrows indicate the locations of
lac repeats. (B) Tethered HP1 does not intensify H3 K9 methylation.
Strong staining is observed for the HP1 antibody, but not the H3 K9 di-methyl
antibody, upon expression of lacI-HP1. (C) Expression of a
Su(var)3-9-EGFP transgene leads to recruitment of SU(VAR)3-9-EGFP
(upper row) and increased H3 K9 methylation (bottom row). (D) Silencing by
tethered HP1 (stock 157.1) was unaffected in Su(var)3-906
hetero- and homozygotes as indicated by a white eye phenotype (middle and
bottom rows). The homozygous Su(var)3-906 flies show a
rough eye phenotype due to the roughest mutation used as a marker on
the Su(var)3-906-bearing chromosome (bottom row). By
contrast, Su(var)3-906 heterozygotes show suppression of
white gene in In(1)wm4, a stock carrying an
inversion placing the white gene next to centric heterochromatin, and
118E-10 a stock carrying a hsp70-white P-element inserted within
centric heterochromatin.
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© The Company of Biologists Ltd 2003
