Department of Organismal Biology and Anatomy
Committee on Evolutionary Biology, University of Chicago
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Abstract |
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Introduction |
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Hsp70 gene number/organization is now known for many of these taxa. The primitive condition for the genus Drosophila is two hsp70 genes at one cluster in a characteristic inverted-pair arrangement (fig. 1
). In species groups other than melanogaster, the hsp70-containing cytological locus is single and resides in Muller's E element, according to analyses of heat-induced transcriptional puffing (in repleta, virilis, willistoni, and obscura spp.; see Peters, Lubsen, and Sondermeijer [1980
]; Gubenko and Baricheva [1979
]; Bonorino et al. [1993
]; and Molto et al. [1992
], respectively). Within the melanogaster group, Konstantopoulou, Nikolaidis, and Scouras (1998)
recently characterized the hsp70 genes of Drosophila auraria, a member of the large montium species subgroup. This species retains the ancestral condition, with two hsp70 genes arranged as an inverted pair on the E element. The montium subgroup is basal to an as-yet-unresolved cluster of six species subgroups (see above), including the eight-species melanogaster subgroup (Pelandakis and Solignac 1993
; Russo, Takezaki, and Nei 1995
). Within the melanogaster subgroup, Leigh Brown and Ish-Horowicz (1981)
established that the hsp70 cluster is duplicated in Drosophila yakuba, Drosophila teissieri, Drosophila simulans, Drosophila mauritiana (four genes each), and D. melanogaster (the only species with five genes; see fig. 1
).
At the outset of this research, Drosophila orena and Drosophila erecta, basal members of the subgroup, remained unexamined (fig. 1 ). Thus, the two-to-four hsp70 duplication clearly postdates the origin of the melanogaster group, but could predate, coincide with, or have occurred after the radiation of the melanogaster subgroup. Here, we resolve this uncertainty by determining both the number of hsp70-containing chromosomal loci in representative species from all species subgroups within the melanogaster group and hsp70 endonuclease data for previously unexamined members of the melanogaster subgroup.
How did the two-to-four duplication event occur? Simple duplication via unequal crossing over seems unlikely, given that the two hsp70 clusters are some 500 kb apart and no classical or molecular genetic studies have yet identified additional duplicated genes in either the intervening or the flanking regions. However, unequal crossing over followed by a large-scale chromosomal rearrangement could yield the long distance between the gene clusters. Chromosomal arrangements differ extensively among the ananassae, montium, and melanogaster subgroups (Hinton and Downs 1975
; Lemeunier and Ashburner 1984
; Drosopoulou et al. 1997
). The polytene chromosomes of the other subgroups remain too poorly mapped, however, to determine whether these subgroups share a rearrangement containing both hsp70 clusters. Alternatively, the additional hsp70 cluster could be inserted elsewhere via double crossing over with homologous flanking sequences (e.g., simple or inverted repeats). Finally, the lack of introns in the hsp70 coding sequences, the presence of polyA tails, and numerous simple repetitive sequences within and around the hsp70 clusters are all consistent with a transposition-mediated mechanism (see GenBank accession number X78403; Mason et al. 1982
; Konstantopoulou et al. 1995
).
Apparently, simple tandem duplication gave rise to the fifth hsp70 gene at 87C1 in D. melanogaster (Leigh Brown and Ish-Horowicz 1981
). However, contrasting patterns of 5'- and 3'-flanking sequence homology among the three hsp70 genes at 87C1 suggest a more complex, mosaic history (Torok et al. 1982
; Bettencourt 2001
). Here, we analyze the genomic sequence around and between the hsp70 clusters of D. melanogaster to determine which mechanisms created first four, and then five hsp70 genes.
Finally, the D. melanogaster hsp70 genes were created and are maintained as functional copies by concerted evolution, vary and respond to laboratory and natural selection (Bettencourt 2001)
, and play a critical role in inducible thermotolerance, a phenotype with demonstrable fitness effects in nature (Feder and Krebs 1997
). These facts suggest that this species exploited "preadaptive" duplications for adaptive evolution. Other species possessing duplicate hsp70 genes need not have done the same; accordingly, here we examine hsp70 sequences of D. mauritiana, a closely related species that inhabits a different ecological niche (David et al. 1989
).
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Materials and Methods |
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DNA Probes
Probes for both fixed in situ hybridization (FISH) and genomic Southern blotting were prepared via PCR using the plasmid pDM300 as template (a gift of S. L. Lindquist). pDM300 contains one D. melanogaster hsp70 gene from the 87C1 cluster (McGarry and Lindquist 1986
). For FISH to polytene chromosomes, a biotin-labeled probe of 542 bp (approximately the third quartile of the
2-kb hsp70 coding sequence) was amplified with biotin-labeled dUTP (Boehringer Mannheim) and the primers HSP70-U (5'-AAAGTAAGCCGTGCCAGGTT-3') and D-L (5'-ACTTCTATCTGGGGCACACC-3'). For Southern blotting, a DIG-labeled probe of 1,022 bp (the 3' half of the coding sequence) was amplified with DIG-labeled dUTP (Boehringer Mannheim) and the primers HSP70-U (see above) and A-L (5'-CCAGAGTAGCCGCCAAATCC-3'). This probe is highly specific for hsp70 genes (for details and amplification conditions, see Bettencourt, Feder, and Cavicchi 1999
).
FISH
To obtain larvae for dissection, 515 mated females of each species were allowed to oviposit on a soft banana-based medium for 3 days at 18°C. Adults were then cleared and larvae were allowed to develop at 18°C, with dry yeast added approximately 1 week later. Salivary glands of wandering third-instar larvae were dissected, and polytene chromosomes were prepared according to Ashburner (1989b). After overnight hybridization at 65°C with the biotin-labeled probe, chromosomes were reacted with biotin-specific antibodies (Boehringer Mannheim) and mounted in the presence of FITC-conjugated DAPI. Chromosomes were visualized with a Nikon fluorescence microscope and a digital CCD camera.
Southern Blotting
Genomic DNA was extracted from 75 adult flies of each species with 1:1 phenol-chloroform and resuspended in 50 µl of TE buffer. Ten micrograms of DNA was digested with appropriate restriction enzymes (Promega), electrophoresed on 0.5%1% agarose gels, and transferred to Nytran nylon membranes (Schliecher and Schuell). Hybridization to the DIG-labeled probe was conducted overnight at 65°C according to the Boehringer-Mannheim DIG/Genius User's Guide (http://biochem.boehringer-mannheim.com/). Blots were visualized with CSPD chemiluminescent substrate (Boehringer Mannheim). Exposures to Fuji X-ray film varied from 15 to 45 min. After development, films were scanned on an Agfa flatbed scanner and images were processed in Adobe Photoshop.
Mapping of the D. orena and D. erecta hsp70 genes followed the restriction maps for D. melanogaster, D. simulans, and D. mauritiana generated by Leigh Brown and Ish-Horowicz (1981)
. Figure 2A
summarizes these map data.
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Isolation and Characterization of the D. orena and D. mauritiana hsp70 Genes
Using both the Celera genomic sequence and predicted transcripts, we designed primers specific for exons in the predicted genes most closely flanking both the 87A7 and the 87C1 hsp70 clusters (accession information: 87A7upstream, CG18546, downstream, CG3281; 87C1upstream, CG5608, downstream, CG7078). All four primers87A7-U, 87A7-L, 87C1-U, and 87C1-Lwere used previously, along with the primer START-U (5'-ATGCCTGC(C/T)ATTGGAATCGA-3'), to PCR amplify the hsp70 genes of D. simulans, as described elsewhere (Bettencourt 2001)
. PCR was conducted with the MasterAmp kit (Epicentre), which utilizes a proofreader enzyme for fidelity. PCR products were purified, cloned, and sequenced with internal primers and an ABI automated sequencer as described in Bettencourt (2001)
. Sequences were aligned using CLUSTALX and analyzed with DNASP (J. Rozas) and SITES (J. Hey).
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Results |
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Hsp70 Gene Organization in the melanogaster Subgroup
Southern blots performed as positive controls confirmed the map generated by Leigh Brown and Ish-Horowicz (1981)
(figs. 2 and 5 ). Digestion of D. simulans and D. mauritiana DNA with Xba1 and Bgl2 yielded four hybridization signals (simulans,
9, 4, 3, and 2.5 kb; mauritiana ST strain,
9, 4, 3.5, and 3 kb), each containing one hsp70 gene (fig. 5
). Different strains of D. mauritiana varied in the sizes of the four hsp70-containing fragments; for example, the G105 strain lacked the
3.5-kb band but gained a
6-kb band (data not shown). Beyond this prominent polymorphism, all species display some restriction site polymorphism in the 75-fly genomic preparations and sporadic faint signals. Drosophila sechellia, unmapped by Leigh Brown and Ish-Horowicz (1981)
, displays a banding pattern identical to its sister species D. simulans (fig. 5
). Drosophila yakuba and D. teissieri also possessed four hsp70 genes in the conserved arrangement (fig. 5
; see also Leigh Brown and Ish-Horowicz 1981). Drosophila yakuba displayed significant restriction site polymorphism; the most informative digest was Xba1/Bgl1, which yielded four signals of
10, 3, 2.5, and 2.3 kb (fig. 5
). Digestion of D. teissieri DNA with Xba1/Bgl2 yielded four signals, of
5, 4, 2.8, and 2.6 kb (fig. 5
).
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Unit of Duplication in the Two-to-Four Event
In all four pairwise comparisons (87A7 upstream vs. 87C1 upstream, 87A7 downstream vs. 87C1 downstream, 87A7 upstream vs. 87C1 downstream, 87A7 downstream vs. 87C1 upstream), basic filtered BLAST (http://www.ncbi.nlm.nih.gov/BLAST) failed to reveal any homologous sequences in the 33.5 kb flanking the hsp70 genes. Only one unfiltered BLAST revealed a putatively homologous run of T nucleotides (TTTTTTTTTTTTTTTTTTTGCT)
29.3 kb and
28.3 kb upstream of 87A7 and 87C1, respectively (in reverse orientation, upstream of 87C1).
Using the GeneScene application (http://www.fruitfly.org/annot/genescene-launch-static.html), we identified the four predicted genes that most closely flanked the 87A7 and 87C1 hsp70 clusters. The four genes, listed in order of increasing distance from the centromere and labeled with accession and distance from the nearby hsp70 gene (measured in base pairs between the beginning or end of the closest predicted exon and hsp70 stop codon), were 87A7 (CG18546, 442 bp upstream; CG3281, 165 bp downstream) and 87C1 (CG5608, 333 bp upstream; CG7078, 1,569 bp downstream). All four of the genes are completely nonhomologous with respect to one another. For example, CG3281 encodes a 1,854-bp zinc-finger-containing transcription factor, while CG7078, whose transcript is 2,090 bp, encodes a G protein-linked receptor. Neither is repeated at either 87A7 or 87C1, further suggesting that the sequences flanking both of the hsp70 clusters are novel and completely unrelated. Only the hsp70 genes are duplicated.
The intergenic regions of 87A7 and 87C1 (between the hsp70 genes) were not compared. Previous workers found that these regions were no longer similar: at 87C1, a large (>40 kb) amount of repetitive sequence lay between the proximal and distal hsp70 genes, as compared with the 12 kb at 87A7 (see GenBank entries J01103 and K01293). Both regions were unresolved (N's) in the Celera sequence.
Origin and Molecular Evolution of a Fifth hsp70 Gene at 87C1 in D. melanogaster
The Celera genomic sequence reveals that the hsp70Bb/hsp70Bc region is of mosaic origin, with both gene conversion and duplication likely contributing (fig. 6
). As noted by previous authors, the 3'-flanking region of hsp70Bb is nearly identical to that of hsp70Ba for 350 bp (Torok et al. 1982
; Bettencourt 2001
). In the genomic sequence, this homologous region extends for 545 bp past the polyA addition signal of hsp70Bb and includes 234 bp of CG5608-derived sequence (in reverse orientation, bearing a 39-bp deletion; see fig. 6
). Continuing in the 3' orientation from hsp70Bb, 38 bp of unique sequence precedes 209 bp of hsp70Bbhsp70Bc intergenic sequence that is 93% identical (excluding a 26-bp indel) to that found 5' of hsp70Bb (fig. 6
). The hsp70Bc 5' UTR immediately follows, differing from that of hsp70Bb at only 3 of 330 sites (fig. 6
). Thus, duplicated sequence flanks hsp70Bb on both sides, consistent with tandem duplication. The portion of hsp70Bb's 3' flank that is homologous to hsp70Ba and CG5608 likely arose via gene conversion (fig. 6
). Conversion between hsp70Ba and hsp70Bb also occurs in the coding regions (Bettencourt 2001)
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Discussion |
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The two-to-four duplication event was likely a retrotransposition: no other duplicated sequences flank the 87A7 and 87C1 gene clusters of D. melanogaster. In addition, the hsp70 genes have no introns, are surrounded by simple repetitive DNA (Mason et al. 1982
), and bear polyA tails (at least in the case of the ancestral two-copy hsp70 cluster of D. auraria described in Konstantopoulou et al. [1995
]). Whether the intergenic region at either gene cluster retains any mobile elementderived sequence remains to be investigated. The origin of the fifth hsp70 gene in D. melanogaster was more complex: tandem duplication and remodeling via gene conversion likely formed the mosaic hsp70Bb/hsp70Bc region.
Duplicated genes often either diverge toward new functions or degenerate toward non- or subfunctionality (Nei and Hughes 1992
; Lynch and Force 2000
). Instead, the hsp70 genes of D. melanogaster persist as functional duplicate copies, consistent with one adaptive role of Hsp70 expression, inducible thermotolerance (Feder and Krebs 1997, 1998
). Drosophila melanogaster exploits its five hsp70 genes to achieve efficient, extremely high Hsp70 protein expression (Bettencourt, Feder, and Cavicchi 1999
). The high inducible thermotolerance conferred by this expression affords survival of a wide range of thermal challenges across the species' broad distribution (Feder, Blair, and Figueras 1997
; Roberts and Feder 1999
). Drosophila simulans expresses nearly as much Hsp70 and is often as thermotolerant with its four hsp70s (Krebs 1999
), which are all functional gene copies (Bettencourt 2001)
. Duplication is a relatively simple and effective way to increase expression of a selected gene (Spofford 1972
), and evolution may have used this mechanism (among others) to increase Hsp70 expression in these species. Sequence analysis of D. melanogaster and D. simulans is consistent with this assertion: both species' hsp70 genes display rapid concerted evolution and strong purifying selection on polymorphisms that are shared among genes (Leigh Brown and Ish-Horowicz 1981
; Bettencourt and Feder 1998, 1999
; Bettencourt 2001
).
In contrast, the hsp70 gene family of D. mauritiana is degenerate. Null alleles of three of the four hsp70 genes are at high frequencies; four or five functional hsp70 genes are apparently not necessary for survival. Purifying selection alone is thus perhaps not likely to be responsible for the maintenance of duplicate functional hsp70 gene copies in D. simulans and D. melanogaster; natural selection may favor their function. In the absence of data directly linking the presence of null alleles with reduced exposure to thermal stress and/or functional consequences for Hsp70 expression and thermotolerance in any of these species, this is an untested but exciting hypothesis for future study.
Duplication of the hsp70 cluster may have been a key step in the evolutionary pathway of D. melanogaster and D. simulans toward increased Hsp70 expression, inducible thermotolerance, niche breadth, and geographic range (Krebs and Feder 1997
). This pathway, however, is but one of several available for populations evolving environmental stress tolerance. Additionally, the two-to-four hsp70 duplication is not the only step, considerably predated the escape of D. melanogaster and D. simulans from their ancestral niche and range, and has not conferred a similar ecological/geographic breadth on the other species that share it. Other species in the melanogaster subgroup, all with four hsp70 genes, exhibit narrower Hsp70 "expression curves" sensu Bettencourt, Feder, and Cavicchi (1999)
, are less inducibly thermotolerant, and have far more restricted ranges than D. melanogaster (Stanley et al. 1980
; Lachaise et al. 1988
; Benson 1998
). In some of these species, such as D. mauritiana, selection on the duplicated hsp70 sequences themselves appears to be relaxed due to a reduced functional role, and thus alleles at both 87A and 87C are null. However, D. orena, also restricted in range and thermotolerance, possesses four apparently functional hsp70 genes. Clearly, whether selection acts on the hsp70 genes themselves can vary in a lineage- and gene-specific fashion. Furthermore, while hsp70 duplication does not necessitate an evolutionary increase in Hsp70 expression and thermotolerance, the converse is true: several other drosophilid groups have achieved high Hsp70 expression, thermotolerance, and broad distributions with single hsp70 clusters (Krebs 1999
; Krebs and Bettencourt 1999
). Numerous regulatory mechanisms can increase Hsp70 expression given a constant number of hsp70 copies (Lindquist, DiDomenico, and Bugaisky 1982
; Petersen and Lindquist 1989
; Morimoto et al. 1994
). Analysis of hsp70 sequence in these single-cluster species could elucidate the evolutionary acquisition of high Hsp70 expression and thermotolerance via regulation rather than duplication.
In conclusion, the hsp70 genome of D. melanogaster has undergone amplification during its evolutionary past in a pattern consistent with an adaptive role. This provides further support for the hypothesis that hsp70 is a target of strong natural selection in D. melanogaster, a hypothesis now supported by multiple lines of evidence (e.g., variation in nature [Krebs and Feder 1997
], response to laboratory selection [Bettencourt, Feder, and Cavicchi 1999
], link to fitness in the wild [Roberts and Feder 1999
], and concerted evolution via gene conversion and natural selection [Bettencourt 2001
]). However, in other species, both closely and distantly related, different evolutionary means have been used to achieve similar ends.
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Supplementary Material |
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Acknowledgements |
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Footnotes |
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1 Keywords: Drosophila
hsp70, gene duplication
concerted evolution
2 Address for correspondence and reprints: Brian R. Bettencourt, Department of Organismal Biology and Anatomy, University of Chicago, 1027 East 57th Street, Chicago, Illinois 60637. E-mail: b-bettencourt{at}uchicago.edu
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References |
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---|
Ashburner M., 1989a. Drosophila: a laboratory handbook Cold Spring Harbor Laboratory Press, Cold Spring Harbor, N.Y
. 1989b. Drosophila: a laboratory manual Cold Spring Harbor Laboratory Press, Cold Spring Harbor, N.Y
Benedict M. Q., A. F. Cockburn, J. A. Seawright, 1993 The Hsp70 heat-shock gene family of the mosquito Anopheles albimanus. Insect Mol. Biol 2:93-102[Medline]
Benson D. A., 1998 The evolution of Hsp70-mediated thermotolerance in Drosophila. Undergraduate honors thesis, University of Chicago
Bettencourt B. R., 2001 Molecular and phenotypic adaptation of hsp70 and thermotolerance Ph.D. thesis, University of Chicago
Bettencourt B. R., M. E. Feder, 1998 Molecular evolution of the Drosophila hsp70 gene family Am. Zool 38:159A.
. 1999 Gene conversion and natural selection drive hsp70 molecular evolution in Drosophila. Am. Zool 39:15A.
Bettencourt B. R., M. E. Feder, S. Cavicchi, 1999 Experimental evolution of Hsp70 expression and thermotolerance in Drosophila melanogaster. Evolution 53:484-492[ISI]
Bonorino C. B. C., M. Pereira, C. E. V. Alonso, V. L. S. Valente, E. Abdelhay, 1993 In situ mapping of the hsp70 locus in seven species of the willistoni group of Drosophila. Rev. Bras. Genet 16:561-571[ISI]
Caccone A., E. N. Moriyama, J. M. Gleason, L. Nigro, J. R. Powell, 1996 A molecular phylogeny for the Drosophila melanogaster subgroup and the problem of polymorphism data Mol. Biol. Evol 13:1224-1232[Abstract]
Cariou M. L., 1987 Biochemical phylogeny of the eight species in the Drosophila melanogaster subgroup, including D. sechellia and D. orena. Genet. Res 50:181-186[ISI][Medline]
Clark J. B., W. P. Maddison, M. G. Kidwell, 1994 Phylogenetic analysis supports horizontal transfer of P transposable elements Mol. Biol. Evol 11:40-50[Abstract]
David J. R., S. F. Mcevey, M. Solignac, L. Tsacas, 1989 Drosophila communities on Mauritius and the ecological niche of Drosophila mauritiana Diptera Drosophilidae Rev. Zool. Afr 103:107-116
Drosopoulou E., I. Konstantopoulou, Z. G. Scouras, 1996 The heat shock genes in the Drosophila montium subgroup: chromosomal localization and evolutionary implications Chromosoma 105:104-110[ISI][Medline]
Drosopoulou E., M. Tsiafouli, P. Mavragani-Tsipidou, Z. G. Scouras, 1997 The glutamate dehydrogenase, E74 and putative actin gene loci in the Drosophila montium subgroup. Chromosomal homologies among the montium species and D. melanogaster. Chromosoma 106:20-28[ISI][Medline]
Feder M. E., N. Blair, H. Figueras, 1997 Natural thermal stress and heat-shock protein expression in Drosophila larvae and pupae Funct. Ecol 11:90-100[ISI]
Feder M. E., R. A. Krebs, 1997 Ecological and evolutionary physiology of heat-shock proteins and the stress response in Drosophila: complementary insights from genetic engineering and natural variation Pp. 155173 in R. Bijlsma and V. Loeschcke, eds. Stress, adaptation, and evolution. Birkhäuser Verlag, Basel, Switzerland
. 1998 Natural and genetic engineering of thermotolerance in Drosophila melanogaster. Am. Zool 38:503-517[ISI]
Gubenko I. S., E. M. Baricheva, 1979 Drosophila virilis puffs induced by temperature and other environmental factors Genetika 15:1399-1414[ISI]
Hinton C. W., J. E. Downs, 1975 The mitotic, polytene, and meiotic chromosomes of Drosophila ananassae. J. Hered 66:353-361[ISI][Medline]
Holmgren R., K. Livak, R. Morimoto, R. Freund, M. Meselson, 1979 Studies of cloned sequences from four Drosophila heat shock loci Cell 18:1359-1370[ISI][Medline]
Konstantopoulou I., N. Nikolaidis, Z. G. Scouras, 1998 The hsp70 locus of Drosophila auraria (montium subgroup) is single and contains copies in a conserved arrangement Chromosoma 107:577-586[ISI][Medline]
Konstantopoulou I., C. A. Ouzounis, E. Drosopoulou, M. Yiangou, P. Sideras, C. Sander, Z. G. Scouras, 1995 A Drosophila hsp70 gene contains long, antiparallel, coupled open reading frames (LAC ORFs) conserved in homologous loci J. Mol. Evol 41:414-420[ISI][Medline]
Krebs R. A., 1999 A comparison of Hsp70 expression and thermotolerance in adults and larvae of three Drosophila species Cell Stress Chap 4:243-249[ISI][Medline]
Krebs R. A., B. R. Bettencourt, 1999 Evolution of thermotolerance and variation in the heat shock protein, HSP70 Am. Zool 39:910-919[ISI]
Krebs R. A., M. E. Feder, 1997 Natural variation in the expression of the heat-shock protein Hsp70 in a population of Drosophila melanogaster, and its correlation with tolerance of ecologically relevant thermal stress Evolution 51:173-179[ISI]
Lachaise D., M. L. Cariou, J. R. David, F. Lemeunier, L. Tsacas, M. Ashburner, 1988 Historical biogeography of the Drosophila melanogaster species subgroup Evol. Biol 22:159-225[ISI]
Leigh Brown A. J., D. Ish-Horowicz, 1981 Evolution of the 87A and 87C heat-shock loci in Drosophila. Nature 290:677-682[ISI][Medline]
Lemeunier F., M. Ashburner, 1984 Relationships within the Drosophila melanogaster species subgroup of the genus Drosophila (Sophophora): 4. The chromosomes of 2 new species Chromosoma 89:343-351[ISI]
Lemeunier F., J. R. David, L. Tsacas, 1986 The melanogaster species group Pp. 148256 in M. Ashburner, H. L. Carson, and J. N. Thompson, eds. The genetics and biology of Drosophila. Vol. 3e. Academic Press, London
Lindquist S. L., B. J. DiDomenico, G. Bugaisky, 1982 Regulation of the heat shock response in Drosophila and yeast Pp. 167176 in M. J. Schlesinger, M. Ashburner, and A. Tissieres, eds. Heat shock from bacteria to man. Cold Spring Harbor Laboratory Press, Cold Spring Harbor, N.Y
Lynch M., A. Force, 2000 The probability of duplicate gene preservation by subfunctionalization Genetics 154:459-473
McGarry T. J., S. Lindquist, 1986 Inhibition of heat shock protein synthesis by heat-inducible antisense RNA Proc. Natl. Acad. Sci. USA 83:399-403[Abstract]
Mason P. I., I. Torok, I. Kiss, F. Karch, A. Udvardy, 1982 Evolutionary implications of a complex pattern of DNA sequence homology extending far upstream of the hsp70 genes at loci 87A7 and 87C1 in Drosophila melanogaster. J. Mol. Biol 156:21-35[ISI][Medline]
Molto M. D., L. Pascual, M. J. Martinez-Sebastian, R. De Frutos, 1992 Genetic analysis of heat shock response in three Drosophila species of the obscura group Genome 35:870-880[ISI][Medline]
Morimoto R. I., D. A. Jurivich, P. E. Kroeger, S. K. Mathur, S. P. Murphy, A. Nakai, K. Sarge, K. Abravaya, L. T. Sistonen, 1994 Regulation of heat shock gene transcription by a family of heat shock factors Pp. 417456 in R. I. Morimoto, A. Tissieres, and C. Georgopoulos, eds. The biology of heat shock proteins and molecular chaperones. Cold Spring Harbor Laboratory Press, Cold Spring Harbor, N.Y
Nei M., A. L. Hughes, 1992 Balanced polymorphism and evolution by the birth-and-death process in the MHC loci Pp. 2738 in K. Tsuji, M. Aizawa, and T. Sasazuki, eds. Eleventh Histocompatibility Workshop and Conference. Vol. 2. Oxford University Press, Oxford, England
Pelandakis M., M. Solignac, 1993 Molecular phylogeny of Drosophila based on ribosomal RNA sequences J. Mol. Evol 37:525-543[ISI][Medline]
Perkins L. A., J. S. Doctor, K. Zhang, L. Stinson, N. Perrimon, E. A. Craig, 1990 Molecular and developmental characterization of the heat shock cognate 4 gene of Drosophila melanogaster. Mol. Cell. Biol 10:3232-3238[ISI][Medline]
Peters F. P., N. H. Lubsen, P. J. Sondermeijer, 1980 Rapid sequence divergence in a heat shock locus of Drosophila. Chromosoma 81:271-280[ISI][Medline]
Petersen R. B., S. Lindquist, 1989 Regulation of HSP70 synthesis by messenger RNA degradation Cell. Regul 1:135-149[ISI][Medline]
Roberts S. P., M. E. Feder, 1999 Natural hyperthermia and expression of the heat shock protein Hsp70 affect developmental abnormalities in Drosophila melanogaster. Oecologia 121:323-329[ISI]
Russo C. A. M., N. Takezaki, M. Nei, 1995 Molecular phylogeny and divergence times of drosophilid species Mol. Biol. Evol 12:391-404[Abstract]
Spofford J. B., 1972 A heterotic model for the evolution of duplications Brookhaven Symp. Biol 23:121-143[Medline]
Stanley S. M., P. A. Parsons, G. E. Spence, L. Weber, 1980 Resistance of species of the Drosophila melanogaster subgroup to environmental extremes Aust. J. Zool 28:413-421[ISI]
Torok I., P. J. Mason, F. Karch, I. Kiss, A. Udvardy, 1982 Extensive regions of homology associated with heat-induced genes at loci 87A7 and 87C1 in Drosophila melanogaster. Pp. 1925 in M. J. Schlesinger, M. Ashburner, and A. Tissieres, eds. Heat shock from bacteria to man. Cold Spring Harbor Laboratory Press, New York
Welte M. A., J. M. Tetrault, R. P. Dellavalle, S. L. Lindquist, 1993 A new method for manipulating transgenes: engineering heat tolerance in a complex, multicellular organism Curr. Biol 3:842-853[ISI]