Ultrabithorax Research Articles

Transcriptional activation by GAGA factor is through its direct interaction with dmTAF3

The GAGA factor (GAF), encoded by the Trithorax like gene (Trl) is a multifunctional protein involved in gene activation, Polycomb-dependent repression, chromatin remodeling and is a component of chromatin domain boundaries. Although first isolated as transcriptional activator of the Drosophila homeotic gene Ultrabithorax (Ubx), the molecular basis of this GAF activity is unknown. Here we show that dmTAF3 (also known as BIP2 and dTAFII155), a component of TFIID, interacts directly with GAF. We generated mutations in dmTAF3 and show that, in Trl mutant background, they affect transcription of Ubx leading to enhancement of Ubx phenotype. These results reveal that the gene activation pathway involving GAF is through its direct interaction with dmTAF3.

Recruitment ofDrosophilaPolycomb-group proteins by Polycomblike, a component of a novel protein complex in larvae

Polycomb-group (PcG) proteins are highly conserved epigenetic transcriptional repressors that play central roles in numerous examples of developmental gene regulation. Four PcG repressor complexes have been purified from Drosophila embryos: PRC1, PRC2, Pcl-PRC2 and PhoRC. Previous studies described a hierarchical recruitment pathway of PcG proteins at the bxd Polycomb Response Element (PRE) of the Ultrabithorax (Ubx) gene in larval wing imaginal discs. The DNA-binding proteins Pho and/or Phol are required for target site binding by PRC2, which in turn is required for chromosome binding by PRC1. Here, we identify a novel larval complex that contains the PcG protein Polycomblike (Pcl) that is distinct from PRC1 and PRC2 and which is also dependent on Pho and/or Phol for binding to the bxd PRE in wing imaginal discs. RNAi-mediated depletion of Pcl in larvae disrupts chromosome binding by E(z), a core component of PRC2, but Pcl does not require E(z) for chromosome binding. These results place the Pcl complex (PCLC) downstream of Pho and/or Phol and upstream of PRC2 and PRC1 in the recruitment hierarchy.

Functionally distinct regulatory RNAs generated by bidirectional transcription and processing of microRNA loci

Many microRNA (miRNA) loci exhibit compelling hairpin structures on both sense and antisense strands; however, the possibility that a miRNA gene might produce functional species from its antisense strand has not been examined. We report here that antisense transcription of the Hox miRNA locus mir-iab-4 generates the novel pre-miRNA hairpin mir-iab-8, which is then processed into endogenous mature miRNAs. Sense and antisense iab-4/iab-8 miRNAs are functionally distinguished by their distinct domains of expression and targeting capabilities. We find that miR-iab-8-5p, like miR-iab-4-5p, is also relevant to Hox gene regulation. Ectopic mir-iab-8 can strongly repress the Hox genes Ultrabithorax and abdominal-A via extensive arrays of conserved target sites, and can induce a dramatic homeotic transformation of halteres into wings. We generalize the antisense miRNA principle by showing that several other loci in both invertebrates and vertebrates are endogenously processed on their antisense strands into mature miRNAs with distinct seeds. These findings demonstrate that antisense transcription and processing contributes to the functional diversification of miRNA genes.

Ubx regulates differential enlargement and diversification of insect hind legs.

Differential enlargement of hind (T3) legs represents one of the hallmarks of insect evolution. However, the actual mechanism(s) responsible are yet to be determined. To address this issue, we have now studied the molecular basis of T3 leg enlargement in Oncopeltus fasciatus (milkweed bug) and Acheta domesticus (house cricket). In Oncopeltus, the T3 tibia displays a moderate increase in size, whereas in Acheta, the T3 femur, tibia, and tarsus are all greatly enlarged. Here, we show that the hox gene Ultrabithorax (Ubx) is expressed in the enlarged segments of hind legs. Furthermore, we demonstrate that depletion of Ubx during embryogenesis has a primary effect in T3 legs and causes shortening of leg segments that are enlarged in a wild type. This result shows that Ubx is regulating the differential growth and enlargement of T3 legs in both Oncopeltus and Acheta. The emerging view suggests that Ubx was co-opted for a novel role in regulating leg growth and that the transcriptional modification of its expression may be a universal mechanism for the evolutionary diversification of insect hind legs.

The function and regulation of Ultrabithorax in the legs of Drosophila melanogaster

Alterations in Hox gene expression patterns have been implicated in both large and small-scale morphological evolution. An improved understanding of these changes requires a detailed understanding of Hox gene cis-regulatory function and evolution. cis-regulatory evolution of the Hox gene Ultrabithorax ( Ubx) has been shown to contribute to evolution of trichome patterns on the posterior second femur (T2p) of Drosophila species. As a step toward determining how this function of Ubx has evolved, we performed a series of experiments to clarify the role of Ubx in patterning femurs and to identify the cis-regulatory regions of Ubx that drive expression in T2p. We first performed clonal analysis to further define Ubx function in patterning bristle and trichome patterns in the legs. We found that low levels of Ubx expression are sufficient to repress an eighth bristle row on the posterior second and third femurs, whereas higher levels of expression are required to promote the development and migration of other bristles on the third femur and to repress trichomes. We then tested the hypothesis that the evolutionary difference in T2p trichome patterns due to Ubx was caused by a change in the global cis-regulation of Ubx expression. We found no evidence to support this view, suggesting that the evolved difference in Ubx function reflects evolution of a leg-specific enhancer. We then searched for the regulatory regions of the Ubx locus that drive expression in the second and third femur by assaying all existing regulatory mutations of the Ubx locus and new deficiencies in the large intron of Ubx that we generated by P-element-induced male recombination. We found that two enhancer regions previously known to regulate Ubx expression in the legs, abx and pbx, are required for Ubx expression in the third femur, but that they do not contribute to pupal expression of Ubx in the second femur. This analysis allowed us to rule out at least 100 kb of DNA in and around the Ubx locus as containing a T2p-specific enhancer. We then surveyed an additional approximately 30 kb using enhancer constructs. None of these enhancer constructs produced an expression pattern similar to Ubx expression in T2p. Thus, after surveying over 95% of the Ubx locus, we have not been able to localize a T2p-specific enhancer. While the enhancer could reside within the small regions we have not surveyed, it is also possible that the enhancer is structurally complex and/or acts only within its native genomic context.

Duplicated Hox genes in the spider Cupiennius salei

BackgroundHox genes are expressed in specific domains along the anterior posterior body axis and define the regional identity. In most animals these genes are organized in a single cluster in the genome and the order of the genes in the cluster is correlated with the anterior to posterior expression of the genes in the embryo. The conserved order of the various Hox gene orthologs in the cluster among most bilaterians implies that such a Hox cluster was present in their last common ancestor. Vertebrates are the only metazoans so far that have been shown to contain duplicated Hox clusters, while all other bilaterians seem to possess only a single cluster.ResultsWe here show that at least three Hox genes of the spider Cupiennius salei are present as two copies in this spider. In addition to the previously described duplicated Ultrabithorax gene, we here present sequence and expression data of a second Deformed gene, and of two Sex comb reduced genes. In addition, we describe the sequence and expression of the Cupiennius proboscipedia gene. The spider Cupiennius salei is the first chelicerate for which orthologs of all ten classes of arthropod Hox genes have been described. The posterior expression boundary of all anterior Hox genes is at the tagma border of the prosoma and opisthosoma, while the posterior boundary of the posterior Hox genes is at the posterior end of the embryo.ConclusionThe presence of at least three duplicated Hox genes points to a major duplication event in the lineage to this spider, perhaps even of the complete Hox cluster as has taken place in the lineage to the vertebrates. The combined data of all Cupiennius Hox genes reveal the existence of two distinct posterior expression boundaries that correspond to morphological tagmata boundaries.

Hox control of morphogen mobility and organ development through regulation of glypican expression

Animal bodies are composed of structures that vary in size and shape within and between species. Selector genes generate these differences by altering the expression of effector genes whose identities are largely unknown. Prime candidates for such effector genes are components of morphogen signaling pathways, which control growth and patterning during development. Here we show that in Drosophila the Hox selector gene Ultrabithorax (Ubx) modulates morphogen signaling in the haltere through transcriptional regulation of the glypican dally. Ubx, in combination with the posterior selector gene engrailed (en), represses dally expression in the posterior (P) compartment of the haltere. Compared with the serially homologous wing, where Ubx is not expressed, low levels of posterior dally in the haltere contribute to a reduced P compartment size and an overall smaller appendage size. We also show that one molecular consequence of dally repression in the posterior haltere is to reduce Dpp diffusion into and through the P compartment. Our results suggest that Dpp mobility is biased towards cells with higher levels of Dally and that selector genes modulate organ development by regulating glypican levels.

The UBX-regulated network in the haltere imaginal disc of D. melanogaster

Hox proteins have been proposed to act at multiple levels within regulatory hierarchies and to directly control the expression of a plethora of target genes. However, for any specific Hox protein or tissue, very few direct in vivo-regulated target genes have been identified. Here, we have identified target genes of the Hox protein Ultrabithorax (UBX), which modifies the genetic regulatory network of the wing to generate the haltere, a modified hindwing. We used whole-genome microarrays and custom arrays including all predicted transcription factors and signaling molecules in the Drosophila melanogaster genome to identify differentially expressed genes in wing and haltere imaginal discs. To elucidate the regulation of selected genes in more detail, we isolated cis-regulatory elements (CREs) for genes that were specifically expressed in either the wing disc or haltere disc. We demonstrate that UBX binds directly to sites in one element, and these sites are critical for activation in the haltere disc. These results indicate that haltere and metathoracic segment morphology is not achieved merely by turning off the wing and mesothoracic development programs, but rather specific genes must also be activated to form these structures. The evolution of haltere morphology involved changes in UBX-regulated target genes, both positive and negative, throughout the wing genetic regulatory network.

Histone trimethylation and the maintenance of transcriptional ON and OFF states by trxG and PcG proteins.

Polycomb group (PcG) and trithorax group (trxG) proteins act as antagonistic regulators to maintain transcriptional OFF and ON states of HOX and other target genes. To study the molecular basis of PcG/trxG control, we analyzed the chromatin of the HOX gene Ultrabithorax (Ubx) in Ubx(OFF)and Ubx(ON)cells purified from developing Drosophila. We find that PcG protein complexes PhoRC, PRC1, and PRC2 and the Trx protein are all constitutively bound to Polycomb response elements (PREs) in the OFF and ON state. In contrast, the trxG protein Ash1 is only bound in the ON state; not at PREs but downstream of the transcription start site. In the OFF state, we find extensive trimethylation at H3-K27, H3-K9, and H4-K20 across the entire Ubx gene; i.e., throughout the upstream control, promoter, and coding region. In the ON state, the upstream control region is also trimethylated at H3-K27, H3-K9, and H4-K20, but all three modifications are absent in the promoter and 5' coding region. Our analyses of mutants that lack the PcG histone methyltransferase (HMTase) E(z) or the trxG HMTase Ash1 provide strong evidence that differential histone lysine trimethylation at the promoter and in the coding region confers transcriptional ON and OFF states of Ubx. In particular, our results suggest that PRE-tethered PcG protein complexes act over long distances to generate Pc-repressed chromatin that is trimethylated at H3-K27, H3-K9, and H4-K20, but that the trxG HMTase Ash1 selectively prevents this trimethylation in the promoter and coding region in the ON state.

Hyped‐up for Hox in Hyderabad

The EMBO Workshop on Upstream and Downstream of Hox Genes took place in Hyderabad, India, between 14 and 17 December 2005, and was organized by R. Mishra and F. Karch. ![][1] For many years, EMBO workshops dealing with new insights into the regulation and function of Hox genes have been held in Switzerland. However, last year, the EMBO World Programme, together with the Centre for Cellular and Molecular Biology (CCMB), held a workshop entitled Upstream and Downstream of Hox Genes in the CCMB's hometown of Hyderabad, India. Imagine beautiful gardens full of butterflies and palm trees, a delightful guest house neighbouring a state‐of‐the‐art research centre, all in a peaceful oasis surrounded by a pulsating and crowded Indian city. The question at the beginning of the meeting was whether the talks and discussions would match the stunning environment; it was answered rapidly and affirmatively. Hox genes have had an illustrious and curious history. Perhaps one of the most famous images in biology from the past century is the four‐winged mutant of the fruit fly Drosophila melanogaster caused by mutations in the Hox gene Ultrabithorax ( Ubx ). This fascinating mutant fly, discovered and characterized by Edward B. Lewis, has motivated many investigators to join the field to understand how these genes are responsible for such complex changes in morphology. Another highlight of Hox history was Matthew Scott's, William McGinnis's and Walter Gehring's discovery of the homeodomain—a 60‐amino‐acid DNA‐binding motif now known to be a key domain in hundreds of genes throughout the animal, fungal and plant kingdoms. Although a lot has been learned through experiments stemming from these important discoveries, there are still many open questions. Among the questions being debated in the field and at the meeting are: How is the regulation of the Hox genes initiated and maintained? How do Hox proteins … [1]: /embed/graphic-1.gif

Negative regulation of Egfr/Ras pathway by Ultrabithorax during haltere development in Drosophila

In Drosophila, wings and halteres are the dorsal appendages of the second and third thoracic segments, respectively. In the third thoracic segment, homeotic selector gene Ultrabithorax ( Ubx) suppresses wing development to mediate haltere development (E.B. Lewis, 1978. A gene complex controlling segmentation in Drosophila. Nature 276, 565-570). Halteres lack stout sensory bristles of the wing margin and veins that reticulate the wing blade. Furthermore, wing and haltere epithelia differ in the size, shape, spacing and number of cuticular hairs. The differential development of wing and haltere, thus, constitutes a good genetic system to study cell fate determination. Here, we report that down-regulation of Egfr/Ras pathway is critical for haltere fate specification: over-expression of positive components of this pathway causes significant haltere-to-wing transformations. RNA in situ, immunohistochemistry, and epistasis genetic experiments suggest that Ubx negatively regulates the expression of the ligand vein as well as the receptor Egf-r to down-regulate the signaling pathway. Electromobility shift assays further suggest that Egf-r is a potential direct target of Ubx. These results and other recent findings suggest that homeotic genes may regulate cell fate determination by directly regulating few steps at the top of the hierarchy of selected signal transduction pathways.

RETRACTED: Noncoding RNAs of trithorax response elements recruit Drosophila Ash1 to Ultrabithorax.

Homeotic genes contain cis-regulatory trithorax response elements (TREs) that are targeted by epigenetic activators and transcribed in a tissue-specific manner. We show that the transcripts of three TREs located in the Drosophila homeotic gene Ultrabithorax (Ubx) mediate transcription activation by recruiting the epigenetic regulator Ash1 to the template TREs. TRE transcription coincides with Ubx transcription and recruitment of Ash1 to TREs in Drosophila. The SET domain of Ash1 binds all three TRE transcripts, with each TRE transcript hybridizing with and recruiting Ash1 only to the corresponding TRE in chromatin. Transgenic transcription of TRE transcripts restores recruitment of Ash1 to Ubx TREs and restores Ubx expression in Drosophila cells and tissues that lack endogenous TRE transcripts. Small interfering RNA-induced degradation of TRE transcripts attenuates Ash1 recruitment to TREs and Ubx expression, which suggests that noncoding TRE transcripts play an important role in epigenetic activation of gene expression.

Physical and Genetic Interactions Link Hox Function with Diverse Transcription Factors and Cell Signaling Proteins

Positional information provided by Hox homeotic transcription factors is integrated with other transcription factors and cell signaling cascades in specific combinations to dictate context- and gene-specific Hox activity. Protein-protein interactions between these groups have long been hypothesized to modulate Hox functions, yielding a context-specific function. However, difficulties in applying interaction screens to potent transcription factors have limited partner identification. A yeast two-hybrid screen using transcription activation-deficient mutants of the Drosophila melanogaster Hox protein Ultrabithorax IB identified an array of interacting proteins, consisting primarily of transcription factors and components of cell signaling pathways. Interactions were confirmed with wild-type Ultrabithorax (UBX) in phage display experiments and by immunoprecipitation for a subset of partners. In vivo assays demonstrated that two Ultrabithorax IB partners, Armadillo, regulated by Wingless/WNT signaling, and the homeodomain protein Aristaless, inhibit UBX-dependent haltere development from the default wing development pathway. Therefore, transcription factors and cell signaling proteins that subdivide Hox-specified tissues can both alter Hox function in vivo and interact with the corresponding Hox protein in vitro. UBX may also modulate partner function: the pupal death phenotype induced by ectopic expression of the UBX partner Hairy required the presence of UBX. Thus, Hox.transcription factor complexes may integrate a variety of positional cues, generating the specificity and versatility required for context-dependent Hox function.

Modulation of AP and DV signaling pathways by the homeotic gene Ultrabithorax during haltere development in Drosophila

Suppression of wing fate and specification of haltere fate in Drosophila by the homeotic gene Ultrabithorax is a classical example of Hox regulation of serial homology (Lewis, E.B. 1978. Nature 276, 565–570) and has served as a paradigm for understanding homeotic gene function. We have used DNA microarray analyses to identify potential targets of Ultrabithorax function during haltere specification. Expression patterns of 18 validated target genes and functional analyses of a subset of these genes suggest that down-regulation of both anterior–posterior and dorso-ventral signaling is critical for haltere fate specification. This is further confirmed by the observation that combined over-expression of Decapentaplegic and Vestigial is sufficient to override the effect of Ubx and cause dramatic haltere-to-wing transformations. Our results also demonstrate that analysis of the differential development of wing and haltere is a good assay system to identify novel regulators of key signaling pathways.

Steroid-dependent modification of Hox function drives myocyte reprogramming in theDrosophilaheart

In the Drosophila larval cardiac tube, aorta and heart differentiation are controlled by the Hox genes Ultrabithorax (Ubx) and abdominal A (abdA), respectively. There is evidence that the cardiac tube undergoes extensive morphological and functional changes during metamorphosis to form the adult organ, but both the origin of adult cardiac tube myocytes and the underlying genetic control have not been established. Using in vivo time-lapse analysis, we show that the adult fruit fly cardiac tube is formed during metamorphosis by the reprogramming of differentiated and already functional larval cardiomyocytes, without cell proliferation. We characterise the genetic control of the process, which is cell autonomously ensured by the modulation of Ubx expression and AbdA activity. Larval aorta myocytes are remodelled to differentiate into the functional adult heart, in a process that requires the regulation of Ubx expression. Conversely, the shape, polarity, function and molecular characteristics of the surviving larval contractile heart myocytes are profoundly transformed as these cells are reprogrammed to form the adult terminal chamber. This process is mediated by the regulation of AbdA protein function, which is successively required within these persisting myocytes for the acquisition of both larval and adult differentiated states. Importantly, AbdA specificity is switched at metamorphosis to induce a novel genetic program that leads to differentiation of the terminal chamber. Finally, the steroid hormone ecdysone controls cardiac tube remodelling by impinging on both the regulation of Ubx expression and the modification of AbdA function. Our results shed light on the genetic control of one in vivo occurring remodelling process, which involves a steroid-dependent modification of Hox expression and function.

Tarsus determination inDrosophila melanogaster

Arista versus tarsus determination is well investigated in Drosophila, yet it remains unresolved whether Antennapedia (ANTP) cell autonomously or noncell autonomously determines tarsus identity and whether Sex combs reduced (SCR) is the HOX protein required for normal tarsus determination. Three observations rule out a cell autonomous role for ANTP in tarsus determination. (i) Clonal ectopic overexpression of ANTP did not repress the expression of the arista determining protein Homothorax (HTH) in early 3rd stadium antennal imaginal discs. (ii) Clonal ectopic expression of ANTP did not transform the arista to a tarsus. (iii) Ectopic overexpression of ANTP, Labial (LAB), Deformed (DFD), SCR, Ultrabithorax (UBX), Abdominal-A (ABD-A), or Abdominal-B (ABD-B), using the dppGAL4 driver, resulted in arista-to-tarsus transformations, and repressed HTH/Extradenticle (EXD) activity noncell autonomously in early 3rd stadium antennal imaginal discs. SCR may not be the HOX protein required for normal tarsus determination, because co-ectopic expression of Proboscipedia (PB) inhibited the arista-to-tarsus transformations induced by ectopic expression of DFD, SCR, ANTP, UBX, ABD-A, and ABD-B. The proposal that SCR is the HOX protein required for normal tarsus determination is dependent on SCR being the sole target of PB suppression, which is not the case. Therefore, the possibility exists that normal tarsus determination is HOX independent.

The Drosophila RYBP gene functions as a Polycomb-dependent transcriptional repressor

The Polycomb and trithorax groups of genes control the maintenance of homeotic gene expression in a variety of organisms. A putative participant in the regulation of this process is the murine RYBP (Ring and YY1 Binding Protein) gene. Sequence comparison between different species has identified the homologous gene in Drosophila, the dRYBP gene. We have investigated whether dRYBP participates in the mechanisms of silencing of homeotic genes expression. We first studied its expression by RNA in situ hybridisation and detected dRYBP expression ubiquitously and throughout development. Moreover, we generated a polyclonal anti-dRYBP antibody that recognises the dRYBP protein. dRYBP protein is nuclear and expressed maternally and ubiquitously throughout development. To study the transcriptional activity of dRYBP, we generated a fusion protein containing the entire dRYBP protein and the GAL4 DNA binding domain. This fusion protein functions, in vivo, as a transcriptional repressor throughout development. Importantly, this repression is dependent on the function of the Polycomb group genes. Furthermore, using the GAL4/UAS system, we have over expressed dRYBP in the haltere and the wing imaginal discs. In the haltere discs, high levels of dRYBP repress the expression of the homeotic Ultrabithorax gene. This repression is Polycomb dependent. In the wing discs, dRYBP over expression produces a variety of phenotypes suggesting the overall miss regulation of the many putative genes affected by high levels of dRYBP. Taking together, our results indicate that dRYBP is able to interact with PcG proteins to repress transcription suggesting that the dRYBP gene might belong to the Polycomb group of genes in Drosophila.

Localization of the Drosophila protein FL(2)D in somatic cells and female gonads

The Drosophila gene female-lethal(2)d [fl(2)d] has been implicated in the alternative splicing regulation of genes involved in sexual determination, such as Sex-lethal and transformer, and in the alternative splicing of the gene Ultrabithorax. Here, the expression and subcellular localization of the FL(2)D protein is reported. FL(2)D is ubiquitously expressed in embryos, in imaginal discs of larvae and in ovaries. In Schneider cells, the protein is detected throughout the nucleoplasm, excluding the nucleolus, and partially co-localizes with SXL in nuclear speckles. In addition, FL(2)D associates with multiple transcriptionally active loci on salivary gland polytene chromosomes, consistent with the proposal that the protein is involved in the post-transcriptional regulation of a variety of genes. Interestingly, the localization of FL(2)D in nurse cells changes during oogenesis, from a rather diffuse early nuclear pattern in the germarium to a preferential accumulation at the nuclear periphery of nurse cells of developing cysts.

Direct regulation ofknotgene expression by Ultrabithorax and the evolution of cis-regulatory elements inDrosophila

The regulation of development by Hox proteins is important in the evolution of animal morphology, but how the regulatory sequences of Hox-regulated target genes function and evolve is unclear. To understand the regulatory organization and evolution of a Hox target gene, we have identified a wing-specific cis-regulatory element controlling the knot gene, which is expressed in the developing Drosophila wing but not the haltere. This regulatory element contains a single binding site that is crucial for activation by the transcription factor Cubitus interruptus (Ci), and a cluster of binding sites for repression by the Hox protein Ultrabithorax (UBX). The negative and positive control regions are physically separable, demonstrating that UBX does not repress by competing for occupancy of Ci-binding sites. Although knot expression is conserved among Drosophila species, this cluster of UBX binding sites is not. We isolated the knot wing cis-regulatory element from D. pseudoobscura, which contains a cluster of UBX-binding sites that is not homologous to the functionally defined D. melanogaster cluster. It is, however, homologous to a second D. melanogaster region containing a cluster of UBX sites that can also function as a repressor element. Thus, the knot regulatory region in D. melanogaster has two apparently functionally redundant blocks of sequences for repression by UBX, both of which are widely separated from activator sequences. This redundancy suggests that the complete evolutionary unit of regulatory control is larger than the minimal experimentally defined control element. The span of regulatory sequences upon which selection acts may, in general, be more expansive and less modular than functional studies of these elements have previously indicated.

Ultrabithorax is required for membranous wing identity in the beetle Tribolium castaneum

The two pairs of wings that are characteristic of ancestral pterygotes (winged insects) have often undergone evolutionary modification. In the fruitfly, Drosophila melanogaster, differences between the membranous forewings and the modified hindwings (halteres) depend on the Hox gene Ultrabithorax (Ubx). The Drosophila forewings develop without Hox input, while Ubx represses genes that are important for wing development, promoting haltere identity. However, the idea that Hox input is important to the morphologically specialized wing derivatives such as halteres, and not the more ancestral wings, requires examination in other insect orders. In beetles, such as Tribolium castaneum, it is the forewings that are modified (to form elytra), while the hindwings retain a morphologically more ancestral identity. Here we show that in this beetle Ubx 'de-specializes' the hindwings, which are transformed to elytra when the gene is knocked down. We also show evidence that elytra result from a Hox-free state, despite their diverged morphology. Ubx function in the hindwing seems necessary for a change in the expression of spalt, iroquois and achaete-scute homologues from elytron-like to more typical wing-like patterns. This counteracting effect of Ubx in beetle hindwings represents a previously unknown mode of wing diversification in insects.