A clustered set of three Sp-family genes is ancestral in the Metazoa: evidence from sequence analysis, protein domain structure, developmental expression patterns and chromosomal location
© Schaeper et al; licensee BioMed Central Ltd. 2010
Received: 13 January 2010
Accepted: 30 March 2010
Published: 30 March 2010
The Sp-family of transcription factors are evolutionarily conserved zinc finger proteins present in many animal species. The orthology of the Sp genes in different animals is unclear and their evolutionary history is therefore controversially discussed. This is especially the case for the Sp gene buttonhead (btd) which plays a key role in head development in Drosophila melanogaster, and has been proposed to have originated by a recent gene duplication. The purpose of the presented study was to trace orthologs of btd in other insects and reconstruct the evolutionary history of the Sp genes within the metazoa.
We isolated Sp genes from representatives of a holometabolous insect (Tribolium castaneum), a hemimetabolous insect (Oncopeltus fasciatus), primitively wingless hexapods (Folsomia candida and Thermobia domestica), and an amphipod crustacean (Parhyale hawaienis). We supplemented this data set with data from fully sequenced animal genomes. We performed phylogenetic sequence analysis with the result that all Sp factors fall into three monophyletic clades. These clades are also supported by protein domain structure, gene expression, and chromosomal location. We show that clear orthologs of the D. melanogaster btd gene are present even in the basal insects, and that the Sp5-related genes in the genome sequence of several deuterostomes and the basal metazoans Trichoplax adhaerens and Nematostella vectensis are also orthologs of btd.
All available data provide strong evidence for an ancestral cluster of three Sp-family genes as well as synteny of this Sp cluster and the Hox cluster. The ancestral Sp gene cluster already contained a Sp5/btd ortholog, which strongly suggests that btd is not the result of a recent gene duplication, but directly traces back to an ancestral gene already present in the metazoan ancestor.
Zinc finger transcription factors are a large and widespread family of DNA binding proteins and play an important role in transcriptional regulation (e.g. ). The general transcription factor Sp1 (named after the original purification method through sephacryl and phosphocellulose columns) was the first identified and cloned binding-specific human transcription factor [2–4]. In the meantime a number of additional genes related to Sp1 have been identified in the human genome, and homologous genes have been isolated from several other animal species as well (e.g. [1, 5]). The members of this Sp-family of transcription factors share three highly conserved Cys2His2-type zinc fingers, which bind to G-rich DNA elements, such as GC-boxes (GGGGCGGGG) and GT/CACC-boxes (GGTGTGGGG) . These binding sites are present in many control regions of both tissue-specific and ubiquitously expressed genes [6, 7] indicating that Sp-family transcription factors potentially regulate a large number of target genes. Indeed, it was shown that Sp-family transcription factors have diverse functions throughout the embryonic development of humans and other animals. For instance, in vertebrates they are involved in cell cycle regulation, the control of morphogenetic pathways, the development of several organ systems, and they also have been linked to the development of cancer (e.g. [5, 8–17]). In the fly Drosophila melanogaster, the gene buttonhead (btd) codes for a member of the Sp-family, which represents an important factor for the formation of several head segments and is also involved in the development of the central and peripheral nervous system [8, 18–20].
The number of Sp-family genes present in the genome varies in the Metazoa. Humans and mice, for example, have nine Sp-family genes , and some teleost fishes have even more (11 in the pufferfish Fugu rubripes , 13 in the zebrafish Danio rerio ). From D. melanogaster two Sp-family genes have been reported, btd and D-Sp1 , but a third one is present in the fully sequenced genome sequence . This variable complement of Sp-family genes and their evolutionary diversification made it difficult to assign orthology between the genes of different species. Therefore, the ancestral number of Sp-family genes and the evolution and orthology of the hitherto identified Sp-family genes was unclear. This situation also led to a considerable confusion in the nomenclature of the Sp-family genes and to several unfortunate designations of not directly homologous Sp-family members with homonymous names thus misleadingly suggesting orthology. For example, D. melanogaster D-Sp1 is not most closely related to human Sp1 but to Sp8  and the gene originally termed mouse mBtd is in fact orthologous to Sp8 .
Especially the origin and orthology of the D. melanogaster head gap gene btd has been debated. Previous studies discovered functional similarities between btd and some vertebrate Sp genes, but could not confidently identify a genuine btd orthologue in vertebrates [13, 15, 25], and it had been proposed that the btd gene might be the result of a recent gene duplication when another Sp-family gene, D-Sp1, in the vicinity of btd was discovered in D. melanogaster [8, 20]. This gene is not only located directly next to btd, but the two genes also have similar postblastodermal expression patterns and partially overlapping developmental functions [8, 20]. All this suggested that btd evolved by a tandem duplication in the phylogenetic lineage leading to D. melanogaster.
In order to reconstruct the evolution of the Sp-family genes, we have first tried to trace homologs of btd in other insects. We have surveyed not only additional dipterans and other holometabolous insects, but we have also searched for Sp-family genes in representatives of hemimetabolous insects (the heteropteran Oncopeltus fasciatus) and the primitively wingless ectognathous and entognathous hexapods (the zygopteran Thermobia domestica and the collembolan Folsomia candida, respectively). We could identify clear orthologs of the D. melanogaster btd gene in these basal hexapods, indicating that the proposed gene duplication did not take place recently within the insects. We have therefore performed a comprehensive study of Sp-family gene evolution based on phylogenetic sequence analysis, protein domain structure characteristics, spatio-temporal mRNA expression analysis, as well as genomic localisation analysis. Our phylogenetic analysis shows that the available Sp-family factors fall into three large clades and that a true btd ortholog is already present in the basal metazoans Trichoplax adhaerens and Nematostella vectensis. The proteins in each clade also display similar structural characteristics and often form a cluster of three genes in the genome. Intriguingly, the available data suggest that this Sp gene cluster has been ancestrally linked to the Hox gene cluster and in the vertebrates appears to have been affected by the multiple duplications of this cluster. This synteny and co-evolution of the Hox and the Sp clusters in the vertebrates also explains the high number of Sp-family genes in this animal group.
Results and Discussion
A search for Sp-family genes in insects and crustaceans
As mentioned in the introduction, previous work had suggested that D. melanogaster possesses two closely related Sp genes, btd and D-Sp1 [8, 19]. However, a search in the fully sequenced D. melanogaster genome revealed the presence of an additional gene, CG5669, with high similarity to btd and D-Sp1. This complement of three Sp-family genes could be the result of a recent gene duplication [8, 20]. In order to identify when such a gene duplication event might have occured, we sought to identify the number of Sp-family genes in additional insect species.
We searched the genome sequence of selected insect species with fully sequenced genomes. In addition we performed PCR-based surveys in specially selected additional species. In the Diptera, a complement of three Sp-family genes seems to be the rule: in the genome sequences of Drosophila pseudobscura and the mosquito Anopheles gambiae we found three different Sp-family genes each. We then searched in the genomes of species outside the Diptera. In the lepidopteran Bombyx mori (silk moth), the hymenopterans Apis mellifera (honeybee) and Nasonia vitripennis (jewel wasp), and the coleopteran Tribolium castaneum (flour beetle) we also detected three Sp-family genes each. This taxon sampling included only holometabolous insects and we have therefore also isolated cDNA fragments of Sp-family genes from representatives of the hemimetabolous and the primitively wingless hexapods. In the higher hemimetabolous heteropteran O. fasciatus (milkweed bug), we were able to isolate two different Sp-family gene fragments. The Zygentoma represent the youngest branch of the primitively wingless insects . We have used the zygentoman T. domestica (firebrat), from which we could isolate three different Sp-family gene fragments. The Collembola are members of the most basal branch of the primitive hexapods (Entognatha) . In the collembolan F. candida (white springtail), we were also able to detect three different fragments of Sp-family genes.
These results show that a complement of three Sp-family genes is present in all studied hexapod species, except for O. fasciatus for which the genome sequence is not available and a third Sp-family member could have been missed in our PCR-based search. We have then tried to establish the number of Sp-family genes in the Crustacea, which phylogenetically is the sister group of the insects according to recent analyses (e.g. [27–30]). The waterflea Daphnia pulex is a member of the Branchiopoda. In the fully sequenced genome of D. pulex we detected the presence of three different Sp-family genes. The Malacostraca (higher crustaceans) are a group of primitively marine species. We have used PCR to isolate Sp-family gene fragments from the malacostracan Parhyale hawaiensis (beachhopper), which yielded two different fragments. However, as with the results for O. fasciatus the PCR survey may have missed an additional Sp-family gene in P. hawaiensis.
Taken together, these results strongly suggest that a complement of three different Sp-family genes is ancestral in the arthropods. Interestingly, three different Sp-family genes are also present in the fully sequenced genomes of the basal chordate lineage Branchiostoma floridae, and the echinoderm Strongylocentrotus purpuratus. Three different Sp-family genes are also present in the fully sequenced genomes of the cnidarian N. vectensis, and the placozoan T. adhaerens - both representing basal branches in the metazoan phylogenetic tree. This could be taken as evidence that the possession of three Sp-family genes is ancestral in the Metazoa. On the other hand, the high number of Sp-family genes in the genomes of vertebrates (e.g. nine Sp-family genes in humans and mice, 7 in the chicken, and more than 10 in fish), indicates that the Sp-genes can be subject to frequent duplications. Thus, the "triplets" in insects, cnidarians, placozoans, echinoderms, and basal chordates might potentially have originated independently.
Phylogenetic analysis of Sp-family genes supports three large clades
We have in addition performed a Bayesian analysis of the same dataset. The resulting unrooted tree is shown in Fig. 1b. The Bayesian tree differs from the quartet puzzling tree in several places, but the only marked differences are Sp5/Btd and Sp1-4 from T. adhaerens, which are not included in the Sp5/Btd and Sp1-4 clade, respectively. The inconsistent placement of these T. adhaerens sequences in the two analyses might be explained by the phylogenetically old age of this lineage. Importantly, the three monophyletic clades Sp1-4, Sp5/Btd, and Sp6-9 are also recovered with this method and all three clades have very high support values. Thus, this additional analysis over all supports the quartet puzzling analysis.
Protein structure supports the existence of two large groups of Sp factors
Embryonic expression patterns of insect and crustacean Sp genes
All available data collectively and consistently suggest that a small Sp gene cluster comprising three Sp genes is ancestral in the Metazoa and that the triplets present in the insects derive from these ancestral three genes, i.e. the genes in the respective clades are orthologous. This argues against the alternative hypothesis that the sets of three Sp genes in the different insect species originated by independent duplication events. As an additional test of the orthologous nature of the three Sp genes in the different insect species we compared their expression patterns during embryogenesis by in situ hybridization. We reasoned that the genes of the same clade should show similar expression patterns in all species if they were true orthologs, but show different patterns if they originated through unrelated duplication events. In the following we compare the expression data from insects, the crustacean P. hawaiensis and published data from vertebrates arranged according to the three Sp-gene clades.
The genes of the Sp1-4 clade
The genes of the Sp5/btd clade
The expression of btd (the D. melanogaster representative of the Sp5/btd clade) has been reported previously [8, 19]. The gene is first expressed in an anterior head stripe (Fig. 3d) and a dorsal spot appears slightly later (Fig. 3e). The head stripe is roughly located in the area of the intercalary and mandibulary segment and later abuts the cephalic furrow (Fig. 3f). Later a metameric (segmentally repeated) pattern emerges that might be correlated with segment formation and peripheral nervous system development (Fig. 3g-i) [8, 20]. Furthermore, Dm btd is expressed in the imaginal discs of legs and antennae [8, 38]. The expression of the T. castaneum btd gene has been published before  and is very similar to the D. melanogaster btd pattern: Tc-btd is expressed in an early head stripe in the area of the intercalary and mandibulary segment (Fig. 4d) and later a metameric pattern emerges (Fig. 4e). In older stages the gene is also expressed in the appendages and in the nervous system (Fig. 4f). The expression pattern of Sp5/btd in T. domestica is very similar to the T. castaneum btd pattern. In the early blastoderm the gene is expressed in an anterior stripe (Fig. 6d), that lies in the intercalary/mandibulary area in slightly more advanced germ band stage embryos (Fig. 6e). Later a metameric pattern emerges (Fig. 6f, g) and in older stages expression in the nervous system and, weakly, in the appendages is detected (Fig. 6 h). In F. candida we were not able to detect an early head stripe for Sp5/btd, because our fixation protocol did not allow us to fix blastoderm stages of this species. The later expression pattern of Sp5/btd in F. candida is very similar to the other insects: there is a metameric expression (Fig. 7c, d), a weak expression in the appendages (Fig. 7d), and expression in the nervous system (Fig. 7e).
There are 3 genes related to Sp5 in the zebrafish genome. Sp5 (also known as bts1) , Sp5-like (also known as spr2)  and similar-to-Sp5. Sp5 in zebrafish is expressed in a head stripe along the midbrain-hindbrain boundary, in the otic vesicles, diencephalon, tail bud, and in the somites . Zebrafish Sp5-like expression is partially overlapping the Sp5 expression in ectodermal and mesodermal tissue, the brain, trunk neural crest cells, and somites . Mouse Sp5 is also expressed in a head stripe at the midbrain-hindbrain boundary, in the primitive streak, and later in the tail bud, otic vesicles, limb buds, the developing central nervous system, somites and pharyngeal region [12, 40]. In summary, the expression of the genes in this clade are highly similar in the insects and clear similarities also exist to the expression in the vertebrates. This again supports the orthology of the genes in this clade.
The genes of the Sp6-8 clade
The expression of D-Sp1 (the D. melanogaster representative of the Sp6-9 clade) has been published previously [8, 20]. The gene is maternally contributed (Fig. 3j), and earliest embryonic expression is seen in the brain (Fig. 3k, l). Later, strong expression is seen in the limb primordia of the antennae and legs (Fig. 3m, n) and in a punctate pattern in the ventral nerve cord (Fig. 3o). The expression of the T. castaneum Sp8 gene has been reported earlier . Like the D. melanogaster D-Sp1 gene, the T. castaneum Sp8 gene is expressed in the brain, ventral nerve cord, and the limb buds (Fig. 4g, h). In the growing legs the gene is expressed in a pattern comprising several rings (Fig. 4h) . The gene Sp8/9 from O. fasciatus has been published recently . Sp8/9 is expressed in the brain, in a punctate pattern in the ventral nerve cord and in the limbs (Fig. 5d). Similar to the legs in older T. castaneum embryos, the O. fasciatus Sp8/9 gene is expressed in several rings in the legs (Fig. 5e). The Sp6-9 gene from T. domestica is expressed in the limb buds (Fig. 6i, j) and later in at least two rings in the legs (Fig. 6k, l). In young segments that have just separated from the growth zone there is a stripe of Sp6-9 expression and in older segments the gene is expressed in a punctate pattern in the ventral nerve cord. There is also an expression domain in the brain. In the springtail F. candida the Sp6-9 gene is expressed in the brain and in a punctate pattern in the ventral nervous system (Fig. 7f-h). The gene is also expressed in the limb buds (Fig. 7f-h) and at later stages in two separate rings in the legs (Fig. 7i). These data show that the embryonic expression pattern of the Sp6-9 representatives is very similar in all studied insect species. These similarities extend to the crustaceans as shown by Sp6-9 expression in P. hawaiensis. In this species the gene is expressed in the limb buds (Fig. 8d, e) and at later stages in the peraeopods and in the two branches of the pleopods and the first two pairs of uropods (Fig. 8f). In addition, there is a punctate expression pattern in the ventral nerve cord (Fig. 8f).
Expression data for the members of this clade are also available from vertebrates. Intitial RT-PCR analysis of mouse Sp6 expression suggested expression in all tissues studied , but later studies showed a specific expression pattern in hair follicles and the apical ectodermal ridge (AER) of the developing limbs [15, 43]. Consequently, Sp6 null mice are nude and show defects in skin, teeth, limbs (syndactyly and oligodactyly), and lung alveols. Sp7 (also known as osterix) is so far only documented to be expressed in the osteoblasts. Bone formation fails in Sp7 deficient mice due to impaired osteoblast differentiation [44–46]. Apart from expression domains in the nervous system (brain) both Sp8 and Sp9 are predominantly expressed in the AER of the limbs in mouse, chick and zebrafish and are essential for limb and fin outgrowth [13, 14, 47, 48]. In summary, the expression patterns of the genes in this clade are strikingly similar in the insects and crustaceans and very similar expression patterns also exist from some vertebrate representatives of this clade, again supporting the orthology of the genes in this clade.
Summarizing the available gene expression data it is evident that the gene expression profiles of the arthropod and vertebrate members within each clade are very similar. This lends further support to our notion that the Sp-family genes in the Metazoa fall into three monophyletic clades that each derives from a single ancestral gene from a cluster comprising three genes. The ubiquitous pattern of the Sp1-4 genes separates them from the Sp5/btd and Sp6-9 genes that display more complex expression patterns frequently comprising at least domains in the nervous system, limbs and segments. This observation fully agrees with our analysis of protein structure that also suggests that the Sp5/btd clade and the Sp6-9 clade form a larger grouping (the Sp5-9 group).
Chromosomal location of Sp genes suggest an ancestral triplet
The eumetazoan ancestor already possessed a triplet cluster of Sp-family genes (Fig. 10, "eumetazoa grade") as evidenced by the three closely linked Sp genes in the genome of the sea anemone N. vectensis. This cnidarian species has eight Hox genes. It is debated whether the Cnidaria represent a grade before or after the formation of a true Hox gene cluster, but recent analyses strongly suggest that the ancestral Cnidarian had indeed a genuine Hox gene cluster comprising at least one anterior and one posterior Hox gene [49, 59]. This cluster apparently has broken apart during cnidarian evolution leading to the dispersed set of 8 Hox genes in N. vectensis . None of these Hox genes in N. vectensis is on the scaffold that contains the Sp genes, but comparative genomics studies suggest that the four clustered Hox genes and the Sp gene cluster are located next to each other on the so called "PAL A" linkage group . Thus, the Eumetazoa ancestor likely possessed a Sp gene cluster linked to the primordial Hox gene cluster (Fig. 10, "eumetazoan grade").
In the Bilateria the Hox cluster underwent further elaboration by gene duplications, whereas the nearby Sp gene cluster preserved the ancestral number of three genes. Nevertheless, the evolution of the Hox cluster also had an impact on the evolution of the Sp cluster in different ways in different bilaterian lineages. In the insects for example, the Sp gene cluster became partially independent from the Hox gene cluster by the relocation of the Sp5/btd and the Sp6-9 genes (Fig. 10, top right). In the dipterans the Sp1-4 gene is still linked to the Hox gene cluster, but in other insects (and in the crustacean D. pulex) the Sp1-4 gene appears to have become detached from the Hox gene cluster as well. In the vertebrates, the Hox gene cluster was duplicated several times leading to a total set of four Hox gene clusters in tetrapods , and the nearby Sp gene cluster evidently was duplicated along with the Hox gene cluster (Fig. 10, top left). Additional partial genome duplications have occurred in the teleost fishes [61, 62] likely accounting for the additional Sp genes (e.g. in D. rerio and F. rubripes). In summary, our results show that the btd gene did not originate from a recent gene duplication, but traces back to an ancient Sp5/Btd gene already present in basal metazoans.
Materials and methods
Arthropod husbandry, embryo collection and fixation
The O. fasciatus (milkweed bug) culture was kept as described in Hughes and Kaufman . Embryos of all stages were fixed as reported previously . Dissections of milkweed bug embryos were performed under a fluorescence stereomicroscope using SYTOX Green nucleic acid stain (Invitrogen) before in situ staining . T. domestica (firebrat) were cultured as described in Rogers et al.  with some modifications: Firebrats were kept in plastic containers in an incubator at 36°C and fed with oatmeal. For better handling especially of very young embryos during the dissection procedure, firebrat eggs were first boiled for 1 min in a waterbath and cooled on ice for 1 min. Afterwards, embryos were fixed for 1 h in fixative (4% formaldehyde in phosphate buffered saline and 0,1% Tween-20). Embryos were stained with SYTOX Green nucleic acid stain and dissected as described for O. fasciatus . F. candida (white springtail) were raised at room temperature in plastic containers with a thin layer of plaster mixed with charcoal. Springtail embryos from 0-5 days were collected with a fine brush and put into a 1,5 ml reaction tube filled with 500 μl water. Embryos were boiled for 1 min in a waterbath, cooled on ice for 1 min, then put into a 50 μm mesh net and treated with 50% bleach for 6 min. Afterwards, embryos were washed with water and put into 100% Methanol. These embryos were then sonicated for 45 sec in Methanol, vortexed several times and stored at -20°C until use. P. hawaiensis (amphipod beachhopper) were cultured in shallow plastic boxes at 26°C filled with a thin layer of crushed coral substrate and artificial seawater (30 g/l of synthetic sea salt) and fed with dry fish flakes twice a week. Membrane pumps ventilated the water. Gravid amphipod females were anaesthesized with clove oil (10 μl per 50 ml seawater) and embryos were collected out of the brood prouch with forceps. Dissection and fixation was performed as described in Browne et al. .
Gene cloning and sequence analysis
D. melanogaster embryos from 0-20 h, T. castaneum embryos from 0-72 h, O. fasciatus embryos from 0-96 h, T. domestica and F. candida embryos from 0-5 days, and P. hawaiensis embryos of all described stages , were used for mRNA isolation using the MicroPoly(A)Purist kit (Ambion). Double-stranded (ds) cDNA and RACE template synthesis was performed using the SMART PCR cDNA Synthesis kit and SMART RACE cDNA Amplification Kit (Clontech). Degenerate primers were designed based on alignments of differerent Sp factor sequences (e.g. D. melanogaster, T. castaneum, mouse). Sp factors of the different arthropod species used in this study were isolated with different combinations of the following degenerate primers: Fw_GRATCDCPNC (GGC MGG GCI ACI TGY GAY TGY CCI AAY TG), Fw_RCRCPNC (MGI TGY MGI TGY CCI AAY TG), Fw_CHV/IPGCGK (TGY CAY RTI CCI GGI TGY GGI AA), Rev_RSDELQRH (TGI CKY TGI ARY TCR TCI SWI C), Rev_KRFMRSDHL (ARR TGR TCI SWI CKC ATR AAI CKY AA). RACE PCR was performed with gene specific primers designed on the basis of the results of the degenerate primers PCR. RACE primer sequences are given in Additional File 3. PCR fragments were cloned into the pCR-II (Invitrogen) and sequenced. All newly isolated sequences have been submitted to the EMBL Nucleotide Database with the following accession numbers: Of_Sp1-4 [EMBL: FN562984], Td_Sp1-4 [EMBL: FN562988], Td_Sp5/btd [EMBL: FN562989], Td_Sp6-9 [EMBL: FN562990], Fc_Sp1-4 [EMBL: FN562985], Fc_Sp5/btd [EMBL: FN562986], Fc_Sp6-9 [EMBL: FN562987], Ph_Sp1-4 [EMBL: FN562991], Ph_Sp6-9 [EMBL: FN562992]. BLAST analysis was used to identify the Sp1-4 homologue of D. melanogaster and T. castaneum. Gene specific primers were made to amplify Tc_btd [GenBank: NM_001114320.1], Tc_Sp8 [GenBank: NM_001039420] and Tc_Sp1-4 [GenBank: XM_967159] from T. castaneum cDNA, as well as Dm_btd [GenBank: NM_078545], Dm_D-Sp1 [GenBank: NM_132351] and Dm_CG5669 (Sp1-4) [GenBank: NM_142975] from D. melanogaster cDNA. The sequences of these primers are given in Additional File 3. We have used the publicly available genome sequencing data for a selection of metazoan species: H. sapiens (Genome Reference Consortium Human Build 37 (GRCh37), Primary_Assembly) [69, 70], M. musculus (Reference assembly (C57BL/6J)) , N. vitripennis , D. melanogaster (release 5.10) , D. pseudobscura (release Dpse_2.0) , A. mellifera (Amel_4.0) , A. gambiae (AgamP3.3) , T. castaneum (Tcas_3.0) , B. mori (version 01 BABH01000000) , D. pulex (JGI-2006-09) , S. purpuratus (Build 1.1) , N. vectensis (Nematostella vectensis v1.0) , G. gallus (Gallus_gallus-2.1) , F. rubripes (Fourth Fugu Genome assembly) , D. rerio , B. floridae (Branchiostoma floridae v1.0) , and T. adhaerens (Trichoplax adhaerens Grell-BS-1999 v1.0) . Phylogenetic analysis of different Sp transcription factor sequences with the Quartet Puzzling method was performed as described in Prpic et al. . Additional Bayesian analysis was performed using MrBayes  and the tree was visualized with PhyloWidget . The accession numbers and the protein sequences alignment are described in Additional File 1.
In situ hybridization
The length of the templates, the clone ID, and the RNA polymerase used for digoxygenin labeled RNA probe synthesis are given in Additional File 3. D. melanogaster and T. castaneum in situ was performed essentially as described in Wohlfrom et al. , O. fasciatus in situ hybridization was done according to Liu and Kaufman , P. hawaiensis in situ was performed as reported in Browne et al. , and in situ hybridizations for F. candida and T. domestica were done essentially as described in Hughes et al. .
- The abbreviations used to denominate the different species are as follows:
Ag Anopheles gambiae:
- Am :
- Bf :
- Bm :
- Dm :
- Dp :
- Dps :
- Dr :
- Fc :
- Fr :
- Gg :
- Hs :
- Mm :
- Nav :
- Nv :
- Of :
- Ph :
- Sp :
- Ta :
- Tc :
- Td :
This work has been funded by the European Community's Marie Curie Research Training Network ZOONET under contract MRTN-CT-2004-005624 (to EAW), and a grant from the Deutsche Forschungsgemeinschaft (PR 1109/1-1 to NMP).
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