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Ants are found everywhere from garden to mountaintop. They are at their most diverse in the tropics, but that does not make the 61 species of our part of the world any less fascinating or significant. As social insects, ants have fascinating life histories. Ecologically, they are highly important and influential. From tiny guest ants living in the nests of bigger species to gigantic wood ant mounds with hundreds of thousands of workers, there is a lifetime of possibility for study. This edition of Ants covers the general biology and ecology of species occurring in Britain and Ireland, including the Channel Islands. The book presents photographs and descriptions of workers for all 61 species on the regional list, together with distribution maps. There is also an account of some of the exotic species that may turn up in heated buildings. The extensively illustrated keys deal with workers, queens and males of all the species. These have been specially written and are the first comprehensive keys since those of the first edition 30 years ago. There are also quick-check keys to workers and nests, as well as a detailed list of kit suppliers and an extensive reference list. Ants are among the most familiar of insects and can form a crucial part of their ecosystem, having an impact far greater than their small individual size would lead us to expect. This book is for anyone wanting to learn more about these endlessly interesting insects, by reading and by applying some of the methods discussed to make new discoveries.

Although the lineage-determining ability of transcription factors is often modulated according to cellular context, the mechanisms by which such switching occurs are not well known. Using a transcriptional programming model, we found that Atoh1 is repurposed from a neuronal to an inner ear hair cell (HC) determinant by the combined activities of Gfi1 and Pou4f3. In this process, Atoh1 maintains its regulation of neuronal genes but gains ability to regulate HC genes. Pou4f3 enables Atoh1 access to genomic locations controlling the expression of sensory (including HC) genes, but Atoh1 + Pou4f3 are not sufficient for HC differentiation. Gfi1 is key to the Atoh1-induced lineage switch, but surprisingly does not alter Atoh1’s binding profile. Gfi1 acts in two divergent ways. It represses the induction by Atoh1 of genes that antagonise HC differentiation, a function in keeping with its well-known repressor role in haematopoiesis. Remarkably, we find that Gfi1 also acts as a co-activator: it binds directly to Atoh1 at existing target genes to enhance its activity. These findings highlight the diversity of mechanisms by which one TF can redirect the activity of another to enable combinatorial control of cell identity.

Axonemal dynein motors are large multi-subunit complexes that drive ciliary movement. Cytoplasmic assembly of these motor complexes involves several co-chaperones, some of which are related to the R2TP co-chaperone complex. Mutations of these genes in humans cause the motile ciliopathy, Primary Ciliary Dyskinesia (PCD), but their different roles are not completely known. Two such dynein (axonemal) assembly factors (DNAAFs) that are thought to function together in an R2TP-like complex are DNAAF4 (DYX1C1) and DNAAF6 (PIH1D3). Here we investigate the

Axonemal dynein motors are large multi-subunit complexes that drive ciliary movement. Cytoplasmic assembly of these motor complexes involves several co-chaperones, some of which are related to the R2TP co-chaperone complex. Mutations of these genes in humans cause the motile ciliopathy, Primary Ciliary Dyskinesia (PCD), but their different roles are not completely known. Two such dynein (axonemal) assembly factors (DNAAFs) that are thought to function together in an R2TP-like complex are DNAAF4 (DYX1C1) and DNAAF6 (PIH1D3). Here we investigate the Drosophila homologues, CG14921/Dnaaf4 and CG5048/Dnaaf6. Surprisingly, Drosophila Dnaaf4 is truncated such that it completely lacks a TPR domain, which in human DNAAF4 is likely required to recruit HSP90. Despite this, we provide evidence that Drosophila Dnaaf4 and Dnaaf6 proteins can associate in an R2TP-like complex that has a conserved role in dynein assembly. Both are specifically expressed and required during the development of the two Drosophila cell types with motile cilia: mechanosensory chordotonal neurons and sperm. Flies that lack either gene are viable but with impaired chordotonal neuron function and lack motile sperm. We provide molecular evidence that Dnaaf4 and Dnaaf6 are required for assembly of outer dynein arms (ODAs) and a subset of inner dynein arms (IDAs).

The Drosophila chordotonal neuron cilium is the site of mechanosensory transduction. The cilium has a 9 + 0 axoneme structure and is highly sub-compartmentalised, with proximal and distal zones harbouring different TRP channels and the proximal zone axoneme also being decorated with axonemal dynein motor complexes. The activity of the dynein complexes is essential for mechanotransduction. We investigate the localisation of TRP channels and dynein motor complexes during ciliogenesis. Differences in timing of TRP channel localisation correlate with order of construction of the two ciliary zones. Dynein motor complexes are initially not confined to their target proximal zone, but ectopic complexes beyond the proximal zone are later cleared, perhaps by retrograde transport. Differences in transient distal localisation of outer and inner dynein arm complexes (ODAs and IDAs) are consistent with previous suggestions from unicellular eukaryotes of differences in processivity during intraflagellar transport. Stable localisation depends on the targeting of their docking proteins in the proximal zone. For ODA, we characterise an ODA docking complex (ODA-DC) that is targeted directly to the proximal zone. Interestingly, the subunit composition of the ODA-DC in chordotonal neuron cilia appears to be different from the predicted ODA-DC in Drosophila sperm.

Ciliary motility is powered by a suite of highly conserved axoneme-specific dynein motor complexes. In humans, the impairment of these motors through mutation results in the disease primary ciliary dyskinesia (PCD). Studies in Drosophila have helped to validate several PCD genes whose products are required for cytoplasmic pre-assembly of axonemal dynein motors. Here we report the characterisation of the Drosophila orthologue of the less-known assembly factor DNAAF3. This gene, CG17669 (Dnaaf3), is expressed exclusively in developing mechanosensory chordotonal (Ch) neurons and the cells that generate spermatozoa, The only two Drosophila cell types bearing cilia/flagella containing dynein motors. Mutation of Dnaaf3 results in larvae that are deaf and adults that are uncoordinated, indicating defective Ch neuron function. The mutant Ch neuron cilia of the antenna specifically lack dynein arms, while Ca imaging in larvae reveals a complete loss of Ch neuron response to vibration stimulus, confirming that mechanotransduction relies on ciliary dynein motors. Mutant males are infertile with immotile sperm whose flagella lack dynein arms and show axoneme disruption. Analysis of proteomic changes suggest a reduction in heavy chains of all axonemal dynein forms, consistent with an impairment of dynein pre-assembly., Summary: DNAAF3 function as a dynein assembly factor for motile cilia is conserved in Drosophila.

The interaction of animals with conspecifics, termed social behaviour, has a major impact on the survival of many vertebrate species. Neuropeptide hormones modulate the underlying physiology that governs social interactions, and many findings concerning the neuroendocrine mechanisms of social behaviours have been extrapolated from animal models to humans. Neurones expressing neuropeptides show similar distribution patterns within the hypothalamic nucleus, even when evolutionarily distant species are compared. During evolution, hypothalamic neuropeptides and releasing hormones have retained not only their structures, but also their biological functions, including their effects on behaviour. Here, we review the current understanding of the mechanisms of social behaviours in several classes of animals, such as worms, insects and fish, as well as laboratory, wild and domesticated mammals.

Although the lineage-determining ability of transcription factors is often modulated according to cellular context, the mechanisms by which such switching occurs are not well known. Using a transcriptional programming model, we found that Atoh1 is repurposed from a neuronal to an inner ear hair cell (HC) determinant by the combined activities of Gfi1 and Pou4f3. In this process, Atoh1 maintains its regulation of neuronal genes but gains ability to regulate HC genes. Pou4f3 enables Atoh1 access to genomic locations controlling the expression of sensory (including HC) genes, but Atoh1+Pou4f3 are not sufficient for HC differentiation. Gfi1 is key to the Atoh1-induced lineage switch, but surprisingly does not alter Atoh1’s binding profile. Gfi1 acts in two divergent ways. It represses the induction by Atoh1 of genes that antagonise HC differentiation, a function in keeping with its well-known repressor role in haematopoiesis. Remarkably, we find that Gfi1 also acts as a co-activator: it binds directly to Atoh1 at existing target genes to enhance its activity. These findings highlight the diversity of mechanisms by which one TF can redirect the activity of another to enable combinatorial control of cell identity.

The widespread loss of hearing is one of the major threats to future wellbeing in ageing human societies. Amongst its various forms, age-related hearing loss (ARHL) carries the vast bulk of the global disease burden. The causes for the terminal decline of auditory function, however, are as unknown as the mechanisms that maintain sensitive hearing before its breakdown. We here present an in-depth analysis of maintenance and ageing in the auditory system of the fruit flyDrosophila melanogaster. We show thatDrosophila, just like humans, display ARHL and that their auditory life span is homeostatically supported by a set of evolutionarily conserved transcription factors. The transcription factors Onecut (closest human orthologues: ONECUT2, ONECUT3), Optix (SIX3, SIX6), Worniu (SNAI2) and Amos (ATOH1, ATOH7, NEUROD1) emerged as key regulators acting upstream of core sensory genes, including components of the fly’s molecular machinery for auditory transduction and amplification.

The motile cilium/flagellum is an ancient eukaryotic organelle. The molecular machinery of ciliary motility comprises a variety of cilium-specific dynein motor complexes along with other complexes that regulate their activity. Assembling the motors requires the function of dedicated “assembly factors” and transport processes. In humans, mutation of any one of at least 40 different genes encoding components of the motility apparatus causes Primary Ciliary Dyskinesia (PCD), a disease of defective ciliary motility. Recently, Drosophila has emerged as a model for motile cilia biology and motile ciliopathies. This is somewhat surprising as most Drosophila cells lack cilia, and motile cilia are confined to just two specialized cell types: the sperm flagellum with a 9+2 axoneme and the ciliated dendrite of auditory/proprioceptive (chordotonal, Ch) neurons with a 9+0 axoneme. To determine the utility of Drosophila as a model for motile cilia, we survey the Drosophila genome for ciliary motility gene homologs, and assess their expression and function. We find that the molecules of cilium motility are well conserved in Drosophila. Most are readily characterized by their restricted cell-type specific expression patterns and phenotypes. There are also striking differences between the two motile ciliated cell types. Notably, sperm and Ch neuron cilia express and require entirely different outer dynein arm variants—the first time this has been clearly established in any organism. These differences might reflect the specialized functions for motility in the two cilium types. Moreover, the Ch neuron cilia lack the critical two-headed inner arm dynein (I1/f) but surprisingly retain key regulatory proteins previously associated with it. This may have implications for other motile 9+0 cilia, including vertebrate embryonic nodal cilia required for left-right axis asymmetry. We discuss the possibility that cell-type specificity in ciliary motility machinery might occur in humans, and therefore underlie some of the phenotypic variation observed in PCD caused by different gene mutations. Our work lays the foundation for the increasing use of Drosophila as an excellent model for new motile ciliary gene discovery and validation, for understanding motile cilium function and assembly, as well as understanding the nature of genetic defects underlying human motile ciliopathies.

Molecular chaperones promote the folding and macromolecular assembly of a diverse set of ‘client’ proteins. How ubiquitous chaperone machineries direct their activities towards specific sets of substrates is unclear. Through the use of mouse genetics, imaging and quantitative proteomics we uncover that ZMYND10 is a novel co-chaperone that confers specificity for the FKBP8-HSP90 chaperone complex towards axonemal dynein clients required for cilia motility. Loss of ZMYND10 perturbs the chaperoning of axonemal dynein heavy chains, triggering broader degradation of dynein motor subunits. We show that pharmacological inhibition of FKBP8 phenocopies dynein motor instability associated with the loss of ZMYND10 in airway cells and that human disease-causing variants of ZMYND10 disrupt its ability to act as an FKBP8-HSP90 co-chaperone. Our study indicates that primary ciliary dyskinesia (PCD), caused by mutations in dynein assembly factors disrupting cytoplasmic pre-assembly of axonemal dynein motors, should be considered a cell-type specific protein-misfolding disease.

Molecular chaperones promote the folding and macromolecular assembly of a diverse set of substrate ‘client’ proteins. How the ubiquitous chaperone machinery directs its activities towards a specific set of substrates and whether this selectivity could be targeted for therapeutic intervention is of intense research. Through the use of mouse genetics, imaging and quantitative proteomics we uncover that ZMYND10 is a novel co-chaperone for the FKBP8-HSP90 chaperone complex during the biosynthesis of axonemal dynein heavy chains required for cilia motility. In the absence of ZMYND10, defects in dynein heavy chains trigger broader dynein motor degradation. We show that FKBP8 inhibition phenocopies dynein motor instability in airway cells, and human disease-causing variants of ZMYND10 disrupt its ability to act as FKBP8-HSP90 co-chaperone. Our study indicates that the motile ciliopathy Primary Ciliary Dyskinesia (PCD) should be considered a cell-type specific protein-misfolding disease and opens the potential for rational drug design that could restore specificity to the ubiquitous chaperone apparatus towards dynein subunits.

Mechanosensation is an evolutionarily ancient sensory modality seen in all main animal groups. Mechanosensation can be mediated by sensory neurons or by dedicated receptor cells that form synapses with sensory neurons. Evidence over the last 15-20 years suggests that both classes of mechanosensory cells can be specified by the atonal class of basic helix-loop-helix transcription factors. In this review we discuss recent work addressing how atonal factors specify mechanosensitive cells in vertebrates and invertebrates, and how the redeployment of these factors underlies the regeneration of mechanosensitive cells in some vertebrate groups.

Primary ciliary dyskinesia (PCD) is a ciliopathy characterized by airway disease, infertility, and laterality defects, often caused by dual loss of the inner dynein arms (IDAs) and outer dynein arms (ODAs), which power cilia and flagella beating. Using whole-exome and candidate-gene Sanger resequencing in PCD-affected families afflicted with combined IDA and ODA defects, we found that 6/38 (16%) carried biallelic mutations in the conserved zinc-finger gene BLU (ZMYND10). ZMYND10 mutations conferred dynein-arm loss seen at the ultrastructural and immunofluorescence level and complete cilia immotility, except in hypomorphic p.Val16Gly (c.47T>G) homozygote individuals, whose cilia retained a stiff and slowed beat. In mice, Zmynd10 mRNA is restricted to regions containing motile cilia. In a Drosophila model of PCD, Zmynd10 is exclusively expressed in cells with motile cilia: chordotonal sensory neurons and sperm. In these cells, P-element-mediated gene silencing caused IDA and ODA defects, proprioception deficits, and sterility due to immotile sperm. Drosophila Zmynd10 with an equivalent c.47T>G (p.Val16Gly) missense change rescued mutant male sterility less than the wild-type did. Tagged Drosophila ZMYND10 is localized primarily to the cytoplasm, and human ZMYND10 interacts with LRRC6, another cytoplasmically localized protein altered in PCD. Using a fly model of PCD, we conclude that ZMYND10 is a cytoplasmic protein required for IDA and ODA assembly and that its variants cause ciliary dysmotility and PCD with laterality defects.

During development, proneural transcription factors of the basic helix-loop-helix (bHLH) family are required to commit cells to a neural fate. In Drosophila neurogenesis, a key mechanism promoting sense organ precursor (SOP) fate is the synergy between proneural factors and their coactivator Senseless in transcriptional activation of target genes. Here we present evidence that posttranslational modification by SUMO enhances this synergy via an effect on Senseless protein. We show that Senseless is a direct target for SUMO modification and that mutagenesis of a predicted SUMOylation motif in Senseless reduces Senseless/proneural synergy both in vivo and in cell culture. We propose that SUMOylation of Senseless via lysine 509 promotes its synergy with proneural proteins during transcriptional activation and hence regulates an important step in neurogenesis leading to the formation and maturation of the SOPs.

Summary Cilia have evolved hugely diverse structures and functions to participate in a wide variety of developmental and physiological processes. Ciliary specialization requires differences in gene expression, but few transcription factors are known to regulate this, and their molecular function is unclear. Here, we show that the Drosophila Forkhead box (Fox) gene, fd3F, is required for specialization of the mechanosensory cilium of chordotonal (Ch) neurons. fd3F regulates genes for Ch-specific axonemal dyneins and TRPV ion channels, which are required for sensory transduction, and retrograde transport genes, which are required to differentiate their distinct motile and sensory ciliary zones. fd3F is reminiscent of vertebrate Foxj1, a motile cilia regulator, but fd3F regulates motility genes as part of a broader sensory regulation program. Fd3F cooperates with the pan-ciliary transcription factor, Rfx, to regulate its targets directly. This illuminates pathways involved in ciliary specialization and the molecular mechanism of transcription factors that regulate them., Graphical Abstract Highlights ► Fd3F is a Fox transcription factor for mechanosensory ciliary specialization ► Regulates genes for ciliary motility, compartmentalization, and sensory transduction ► Fd3F modulates the activity of the pan-ciliogenic transcription factor, Rfx ► Fd3F is likely related to Foxj1, the vertebrate regulator of motile ciliated cells, Cilia are highly diverse. The motile sensory cilia of Drosophila mechanosensory neurons provide a good model of ciliary structural and functional specialization. Newton et al. show that Fox and Rfx transcription factors work in concert to activate a gene expression program for ciliary specialization in these neurons.

Much of developmental biology is concerned with the processes by which cells become committed to particular fates in a regulated fashion, whereas cell biology addresses, among other things, the variety of differentiated forms and functions that cells can acquire. One open question is how the regulators of the former process lead to attainment of the latter. 'High-level' regulators of cell fate specification include the proneural factors, which drive cells to commit as precursors in the sensory nervous system. Recent research has concentrated on the gene expression events downstream of proneural factor function. Here we summarise this research and describe our own research that has provided clear links between a proneural factor, atonal, and the cell biological programme of ciliogenesis, which is a central aspect of sensory neuron differentiation.

Crayfish (Astacus astacus) muscle stretch receptors show strong homology to mammalian muscle spindles and bipolar neurons in D. melanogaster. All are typical, non-ciliated, stretch-sensitive, afferent neurons. Such receptors are observed in many species and perform an important sensory role. However, they are poorly characterised. A previous study reported a bio-mechanical and behavioural model of A. astacus stretch receptors, which used the principles of elasticity and tension in a spring to describe the adaptation of a mechano-sensory ending. This model described the changing mechano-sensory currents in the receptor when subjected to a stretch protocol. Here, we re-implement and extend this model. Notably, we introduce additional descriptions of voltage-gated channels that are suggested to contribute to stretch receptor mechano-transduction. Our model presents a more complete picture of the initiation of the mechano-receptor potential in response to a stretching stimulus. The inclusion of voltage-dependent sodium and potassium currents in addition to the initial mechano-sensitive sodium current allowed the model to account for most of the initial stretch response of the receptor. This preliminary model has potential for extension to describe fully the behaviour of non-ciliated mechano-sensors across species and predict the molecular mediators of mechano-transduction.

A significant number of ciliary disease genes have been found to encode proteins that localise to the basal body. By contrast, a large number of basal-body-associated proteins remain to be characterised. Here, we report the identification of a new basal body protein that is required for ciliogenesis in Drosophila. Dilatory (DILA) is a predicted coiled-coil protein homologous to vertebrate AZI1 (also known as CEP131). Mutations in dila specifically exhibit defects in ciliated cells (sensory neurons and sperm). Several features of the neuronal phenotype suggest a defect in intraflagellar transport. In sensory neuron cilia, DILA protein localises to the ciliary base, including the basal body and putative transition zone, and it interacts genetically with the ciliary coiled-coil protein, Uncoordinated. These data implicate DILA in regulating intraflagellar transport at the base of sensory cilia.

The p38 mitogen activated protein kinase (MAPK) signaling pathway has been suggested to play a significant role in the gastric mucosal inflammatory response to chronic Helicobacter pylori (H. pylori) infection. Nuclear translocation is thought to be important for p38 function, but no nuclear translocation signals have been found in the protein and no nuclear carrier proteins have been identified for p38. We have investigated the role of small ubiquitin-related modifier (SUMO) in the nuclear transfer of p38 in response to H. pylori infection. Exposure of human AGS cells to H. pylori induced the activation of p38 and the expression of SUMOs, especially SUMO-2. SUMO knockdown counteracted the effect of H. pylori infection by decreasing the resulting p38 mediated cellular apoptosis through a reduction in the nuclear fraction of phosphorylated p38. We identified a non-covalent interaction between SUMOs and p38 via SUMO interaction motifs (SIMs), and showed that SUMO-dependent nuclear transfer of p38 was decreased upon mutation of its SIMs. This study has identified a new pathway of p38 nuclear translocation, in response to H. pylori infection. We conclude that in the presence of H. pylori SUMO-2 has a major role in regulating nuclear levels of p38, through non-covalent SUMO-p38 interactions, independent of the p38 phosphorylation state.

The question of how proneural bHLH transcription factors recognize and regulate their target genes is still relatively poorly understood. We previously showed that Scute (Sc) and Atonal (Ato) target genes have different cognate E box motifs, suggesting that specific DNA interactions contribute to differences in their target gene specificity. Here we show that Sc and Ato proteins (in combination with Daughterless) can activate reporter gene expression via their cognate E boxes in a non-neuronal cell culture system, suggesting that the proteins have strong intrinsic abilities to recognize different E box motifs in the absence of specialized cofactors. Functional comparison of E boxes from several target genes and site-directed mutagenesis of E box motifs suggests that specificity and activity require further sequence elements flanking both sides of the previously identified E box motifs. Moreover, the proneural cofactor, Senseless, can augment the function of Sc and Ato on their cognate E boxes and therefore may contribute to proneural specificity.

Using the well-characterised paradigm of Drosophila sensory nervous system development, we examine the functional distinctness of the Amos and Atonal (Ato) proneural transcription factors, which have different mutant phenotypes but share very high similarity in their signature bHLH domains. Using misexpression and mutant rescue assays, we show that Ato and Amos proteins have abundantly distinct intrinsic proneural capabilities in much of the ectoderm. The eye, however, is an exception: here both proteins share the capability to direct the R8 photoreceptor fate choice. Therefore, functional distinctness between these closely related transcription factors varies with developmental context, indicating different molecular mechanisms of specificity in different contexts. Consistent with this, the structural basis for their distinctness also varies depending upon the function in question. In previous studies of neural bHLH factors, specificity invariably mapped to the bHLH domain sequence. Similarly, and despite their high similarity, much of the Amos’ specificity relative to Ato maps to Amos-specific residues in its bHLH domain. For Ato-specific functions, however, the Amos bHLH domain can substitute for that of Ato. Consequently, Ato’s specificity relative to Amos requires the non-bHLH portion of the Ato protein. Ato provides a powerful precedence for a role of non-bHLH sequences in modulating bHLH functional specificity. This has implications for structural and functional comparisons of other closely related transcription factors, and for understanding the molecular basis of specificity.

Stretch-activated afferent neurons, such as those of mammalian muscle spindles, are essential for proprioception and motor co-ordination, but the underlying mechanisms of mechanotransduction are poorly understood. The dorsal bipolar dendritic (dbd) sensory neurons are putative stretch receptors in the Drosophila larval body wall. We have developed an in vivo protocol to obtain receptor potential recordings from intact dbd neurons in response to stretch. Receptor potential changes in dbd neurons in response to stretch showed a complex, dynamic profile with similar characteristics to those previously observed for mammalian muscle spindles. These profiles were reproduced by a general in silico model of stretch-activated neurons. This in silico model predicts an essential role for a mechanosensory cation channel (MSC) in all aspects of receptor potential generation. Using pharmacological and genetic techniques, we identified the putative mechanosensory channel, DmPiezo, as a strong candidate for this functional role in dbd neurons, with TRPA1 playing a subsidiary role. We also show that rat muscle spindles exhibit a ruthenium red-sensitive current, but found no expression evidence this corresponds to Piezo activity. In summary, we show that the dbd neuron is a stretch receptor and demonstrate that this neuron is a tractable model for investigating mechanisms of mechanotransduction.

Much attention has been given to mammalian muscle spindles and their role in stretch‐mediated muscle proprioception. Recent studies, particularly, have sought to determine the molecular mediators of stretch‐evoked mechanotransduction, which these endings rely upon for functionality. Nonetheless, much about these endings remains unknown. Opportunities may be presented from consideration of extensive parallel research in stretch receptor mechanisms in arthropods. Such systems may provide a useful source of additional data and powerful tools for dissecting the complex systems of stretch transduction apparatus. At the least, such systems provide tractable exemplars of how organisms solve the problem of converting stretch stimuli to electrical output. Potentially, they may even provide molecular mechanisms and candidate molecular mediators of direct relevance to mammalian muscle spindles. Here we provide a brief overview of research on arthropod stretch receptors.

Background In vertebrates, rootletin is the major structural component of the ciliary rootlet and is also part of the tether linking the centrioles of the centrosome. Various functions have been ascribed to the rootlet, including maintenance of ciliary integrity through anchoring and facilitation of transport to the cilium or at the base of the cilium. In Drosophila, Rootletin function has not been explored. Results In the Drosophila embryo, Rootletin is expressed exclusively in cell lineages of type I sensory neurons, the only somatic cells bearing a cilium. Expression is strongest in mechanosensory chordotonal neurons. Knock-down of Rootletin results in loss of ciliary rootlet in these neurons and severe disruption of their sensory function. However, the sensory cilium appears largely normal in structure and in localisation of proteins suggesting no strong defect in ciliogenesis. No evidence was found for a defect in cell division. Conclusions The role of Rootletin as a component of the ciliary rootlet is conserved in Drosophila. In contrast, lack of a general role in cell division is consistent with lack of centriole tethering during the centrosome cycle in Drosophila. Although our evidence is consistent with an anchoring role for the rootlet, severe loss of mechanosensory function of chordotonal (Ch) neurons upon Rootletin knock-down may suggest a direct role for the rootlet in the mechanotransduction mechanism itself.

For a particular functional family of basic helix-loop-helix (bHLH) transcription factors, there is ample evidence that different factors regulate different target genes but little idea of how these different target genes are distinguished. We investigated the contribution of DNA binding site differences to the specificities of two functionally related proneural bHLH transcription factors required for the genesis of Drosophila sense organ precursors (Atonal and Scute). We show that the proneural target gene, Bearded, is regulated by both Scute and Atonal via distinct E-box consensus binding sites. By comparing with other Ato-dependent enhancer sequences, we define an Ato-specific binding consensus that differs from the previously defined Scute-specific E-box consensus, thereby defining distinct E(Ato) and E(Sc) sites. These E-box variants are crucial for function. First, tandem repeats of 20-bp sequences containing E(Ato) and E(Sc) sites are sufficient to confer Atonal- and Scute-specific expression patterns, respectively, on a reporter gene in vivo. Second, interchanging E(Ato) and E(Sc) sites within enhancers almost abolishes enhancer activity. While the latter finding shows that enhancer context is also important in defining how proneural proteins interact with these sites, it is clear that differential utilization of DNA binding sites underlies proneural protein specificity.

In Drosophila, commitment of a cell to a sense organ precursor (SOP) fate requires bHLH proneural transcription factor upregulation, a process that depends in most cases on the interplay of proneural gene autoregulation and inhibitory Notch signaling. A subset of SOPs are selected by a recruitment pathway involving EGFR signaling to ectodermal cells expressing the proneural gene atonal. We show that EGFR signaling drives recruitment by directly facilitating atonal autoregulation. Pointed, the transcription factor that mediates EGFR signaling, and Atonal protein itself bind cooperatively to adjacent conserved binding sites in an atonal enhancer. Recruitment is therefore contingent on the combined presence of Atonal protein (providing competence) and EGFR signaling (triggering recruitment). Thus, autoregulation is the nodal control point targeted by signaling. This exemplifies a simple and general mechanism for regulating the transition from competence to cell fate commitment whereby a cell signal directly targets the autoregulation of a selector gene.

The Notch intercellular signalling pathway is important throughout development, and its components are modulated by a variety of cellular and molecular mechanisms. Ligand and receptor trafficking are tightly controlled,although context-specific regulation of this is incompletely understood. We show that during sense organ precursor specification in Drosophila,the cell adhesion molecule Echinoid colocalises extensively with the Notch ligand, Delta, at the cell membrane and in early endosomes. Echinoid facilitates efficient Notch pathway signalling. Cultured cell experiments suggest that Echinoid is associated with the cis-endocytosis of Delta, and is therefore linked to the signalling events that have been shown to require such Delta trafficking. Consistent with this, overexpression of Echinoid protein causes a reduction in Delta level at the membrane and in endosomes. In vivo and cell culture studies suggest that homophilic interaction of Echinoid on adjacent cells is necessary for its function.

Proneural genes encode basic-helix-loop-helix (bHLH) transcription factors required for neural precursor specification. Recently amos was identified as a new candidate Drosophila proneural gene related to atonal. Having isolated the first specific amosloss-of-function mutations, we show definitively that amos is required to specify the precursors of two classes of olfactory sensilla. Unlike other known proneural mutations, a novel characteristic of amos loss of function is the appearance of ectopic sensory bristles in addition to loss of olfactory sensilla, owing to the inappropriate function of scute. This supports a model of inhibitory interactions between proneural genes, whereby ato-like genes (amos and ato) must suppress sensory bristle fate as well as promote alternative sense organ subtypes.