EGF receptor and Notch signaling act upstream of Eyeless/Pax6 to control eye specification

Control of fate specification within the dorsal head of Drosophila melanogaster

During development, unique combinations of transcription factors and signaling pathways carve the nascent eye-antennal disc of the fruit fly Drosophila melanogaster into several territories that will eventually develop into the compound eye, ocelli, head epidermis, bristles, antenna and maxillary palpus of the adult head. Juxtaposed patterns of Hedgehog (Hh) and Decapentaplegic (Dpp) initiate compound eye development, while reciprocal domains of Dpp and Wingless (Wg) induce formation of the antennal and maxillary palp fields. Hh and Wg signaling, but not Dpp, contribute to the patterning of the dorsal head vertex. Here, we show that combinatorial reductions of the Pax6 transcription factor Twin of Eyeless and either the Wg pathway or the Mirror (Mirr) transcription factor trigger a transformation of the ocelli into a compound eye and the neighboring head epidermis into an antenna. These changes in fate are accompanied by the ectopic expression of Dpp, which might be expected to trigger these changes in fate. However, the transformation of the field cannot be replicated by increasing Dpp levels alone despite the recreation of adjacent Hh-Dpp and Wg-Dpp domains. As such, the emergence of these ectopic organs occurs through a unique regulatory path.

Two distinct functions of Lim1 in the Drosophila antenna

The Lim1 transcription factor is required in Drosophila for patterning the eye-antennal disk. At the adult stage, Lim1 is strongly expressed in Johnston's Organ (JO) neurons, the antennal auditory organ. Using RNAi-mediated knockdown of Lim1 using a strong neuronal driver, we find a significant reduction in electrophysiological responses to auditory stimuli, recorded from the antennal nerve. This reduction can be accounted for by Lim1 knockdown in the auditory subset of JO neurons, with no effect of knockdown in JO neuron subsets associated with wind or gravity detection. Conversely, Lim1 knockdown in JO sense organ precursors had no effect on hearing. Mosaic animals with antennal clones of the Lim1 E9 null mutation showed morphological defects in the antenna, and significant auditory electrophysiological defects. Our results are consistent with two distinct functions for Lim1 in the antenna, including an early patterning function in the eye-antennal disk, and a later neural differentiation function in the JO neurons.

The emerging regulatory roles of non-coding RNAs associated with glucose metabolism in breast cancer

Altered energy metabolism is one of the hallmarks of tumorigenesis and essential for fulfilling the high demand for metabolic energy in a tumor through accelerating glycolysis and reprogramming the glycolysis metabolism through the Warburg effect. The dysregulated glucose metabolic pathways are coordinated not only by proteins coding genes but also by non-coding RNAs (ncRNAs) during the initiation and cancer progression. The ncRNAs are responsible for regulating numerous cellular processes under developmental and pathological conditions. Recent studies have shown that various ncRNAs such as microRNAs, circular RNAs, and long noncoding RNAs are extensively involved in rewriting glucose metabolism in human cancers. In this review, we demonstrated the role of ncRNAs in the progression of breast cancer with a focus on outlining the aberrant expression of glucose metabolic pathways. Moreover, we have discussed the existing and probable future applications of ncRNAs to regulate energy pathways along with their importance in the prognosis, diagnosis, and future therapeutics for human breast carcinoma.

Polycomb safeguards imaginal disc specification through control of the Vestigial-Scalloped complex

A fundamental goal of developmental biology is to understand how cell and tissue fates are specified. The imaginal discs of Drosophila are excellent model systems for addressing this paradigm as their fate can be redirected when discs regenerate after injury or when key selector genes are misregulated. Here, we show that when Polycomb expression is reduced, the wing selector gene vestigial is ectopically activated. This leads to the inappropriate formation of the Vestigial-Scalloped complex, which forces the eye to transform into a wing. We further demonstrate that disrupting this complex does not simply block wing formation or restore eye development. Instead, immunohistochemistry and high-throughput genomic analysis show that the eye-antennal disc unexpectedly undergoes hyperplastic growth with multiple domains being organized into other imaginal discs and tissues. These findings provide insight into the complex developmental landscape that tissues must navigate before adopting their final fate.

Hippo pathway and Bonus control developmental cell fate decisions in the Drosophila eye

The canonical function of the Hippo signaling pathway is the regulation of organ growth. How this pathway controls cell-fate determination is less well understood. Here, we identify a function of the Hippo pathway in cell-fate decisions in the developing Drosophila eye, exerted through the interaction of Yorkie (Yki) with the transcriptional regulator Bonus (Bon), an ortholog of mammalian transcriptional intermediary factor 1/tripartite motif (TIF1/TRIM) family proteins. Instead of controlling tissue growth, Yki and Bon promote epidermal and antennal fates at the expense of the eye fate. Proteomic, transcriptomic, and genetic analyses reveal that Yki and Bon control these cell-fate decisions by recruiting transcriptional and post-transcriptional co-regulators and by repressing Notch target genes and activating epidermal differentiation genes. Our work expands the range of functions and regulatory mechanisms under Hippo pathway control.

The early history of the eye-antennal disc of Drosophila melanogaster

A pair of eye-antennal imaginal discs give rise to nearly all external structures of the adult Drosophila head including the compound eyes, ocelli, antennae, maxillary palps, head epidermis, and bristles. In the earliest days of Drosophila research, investigators would examine thousands of adult flies in search of viable mutants whose appearance deviated from the norm. The compound eyes are dispensable for viability and perturbations to their structure are easy to detect. As such, the adult compound eye and the developing eye-antennal disc emerged as focal points for studies of genetics and developmental biology. Since few tools were available at the time, early researchers put an enormous amount of thought into models that would explain their experimental observations-many of these hypotheses remain to be tested. However, these "ancient" studies have been lost to time and are no longer read or incorporated into today's literature despite the abundance of field-defining discoveries that are contained therein. In this FlyBook chapter, I will bring these forgotten classics together and draw connections between them and modern studies of tissue specification and patterning. In doing so, I hope to bring a larger appreciation of the contributions that the eye-antennal disc has made to our understanding of development as well as draw the readers' attention to the earliest studies of this important imaginal disc. Armed with the today's toolkit of sophisticated genetic and molecular methods and using the old papers as a guide, we can use the eye-antennal disc to unravel the mysteries of development.

The timing of cell fate decisions is crucial for initiating pattern formation in the Drosophila eye

The eye-antennal disc of Drosophila is composed of three cell layers: a columnar epithelium called the disc proper (DP); an overlying sheet of squamous cells called the peripodial epithelium (PE); and a strip of cuboidal cells that joins the other two cellular sheets to each other and comprises the outer margin (M) of the disc. The M cells play an important role in patterning the eye because it is here that the Hedgehog (Hh), Decapentaplegic (Dpp) and JAK/STAT pathways function to initiate pattern formation. Dpp signaling is lost from the margin of eyes absent (eya) mutant discs and, as a result, the initiation of retinal patterning is blocked. Based on these observations, Eya has been proposed to control the initiation of the morphogenetic furrow via regulation of Dpp signaling within the M. We show that the failure in pattern formation surprisingly results from M cells prematurely adopting a head epidermis fate. This switch in fate normally takes place during pupal development after the eye has been patterned. Our results suggest that the timing of cell fate decisions is essential for correct eye development.

Shaping an optical dome: The size and shape of the insect compound eye

The insect compound eye is the most abundant eye architecture on earth. It comes in a wide variety of shapes and sizes, which are exquisitely adapted to specific ecosystems. Here, we explore the organisational principles and pathways, from molecular to tissular, that underpin the building of this organ and highlight why it is an excellent model system to investigate the relationship between genes and tissue form. The compound eye offers wide fields of view, high sensitivity in motion detection and infinite depth of field. It is made of an array of visual units called ommatidia, which are precisely tiled in 3D to shape the retinal tissue as a dome-like structure. The eye starts off as a 2D epithelium, and it acquires its 3D organisation as ommatidia get into shape. Each ommatidium is made of a complement of retinal cells, including light-detecting photoreceptors and lens-secreting cells. The lens cells generate the typical hexagonal facet lens that lies atop the photoreceptors so that the eye surface consists of a quasi-crystalline array of these hexagonal facet-lenses. This array is curved to various degree, depending on the size and shape of the eye, and on the region of the retina. This curvature sets the resolution and visual field of the eye and is determined by i) the number and size of the facet lens - large ommatidial lenses can be used to generate flat, higher resolution areas, while smaller facets allow for stronger curvature of the eye, and ii) precise control of the inter facet-lens angle, which determines the optical axis of the each ommatidium. In this review we discuss how combinatorial variation in eye primordium shape, ommatidial number, facet lens size and inter facet-lens angle underpins the wide variety of insect eye shapes, and we explore what is known about the mechanisms that might control these parameters.

Cell proliferation control by Notch signalling during imaginal discs development in Drosophila

The Notch signalling pathway is evolutionary conserved and participates in numerous developmental processes, including the control of cell proliferation. However, Notch signalling can promote or restrain cell division depending on the developmental context, as has been observed in human cancer where Notch can function as a tumor suppressor or an oncogene. Thus, the outcome of Notch signalling can be influenced by the cross-talk between Notch and other signalling pathways. The use of model organisms such as Drosophila has been proven to be very valuable to understand the developmental role of the Notch pathway in different tissues and its relationship with other signalling pathways during cell proliferation control. Here we review recent studies in Drosophila that shed light in the developmental control of cell proliferation by the Notch pathway in different contexts such as the eye, wing and leg imaginal discs. We also discuss the autonomous and non-autonomous effects of the Notch pathway on cell proliferation and its interactions with different signalling pathways.

Remodelling of oxygen-transporting tracheoles drives intestinal regeneration and tumorigenesis in Drosophila

The Drosophila trachea, as the functional equivalent of mammalian blood vessels, senses hypoxia and oxygenates the body. Here, we show that the adult intestinal tracheae are dynamic and respond to enteric infection, oxidative agents and tumours with increased terminal branching. Increased tracheation is necessary for efficient damage-induced intestinal stem cell (ISC)-mediated regeneration and is sufficient to drive ISC proliferation in undamaged intestines. Gut damage or tumours induce HIF-1α (Sima in Drosophila), which stimulates tracheole branching via the FGF (Branchless (Bnl))-FGFR (Breathless (Btl)) signalling cascade. Bnl-Btl signalling is required in the intestinal epithelium and the trachea for efficient damage-induced tracheal remodelling and ISC proliferation. Chemical or Pseudomonas-generated reactive oxygen species directly affect the trachea and are necessary for branching and intestinal regeneration. Similarly, tracheole branching and the resulting increase in oxygenation are essential for intestinal tumour growth. We have identified a mechanism of tracheal-intestinal tissue communication, whereby damage and tumours induce neo-tracheogenesis in Drosophila, a process reminiscent of cancer-induced neoangiogenesis in mammals.

A multi-gene knockdown approach reveals a new role for Pax6 in controlling organ number in Drosophila

Genetic screens are designed to target individual genes for the practical reason of establishing a clear association between a mutant phenotype and a single genetic locus. This allows for a developmental or physiological role to be assigned to the wild-type gene. We previously observed that the concurrent loss of Pax6 and Polycomb epigenetic repressors in Drosophila leads the eye to transform into a wing. This fate change is not seen when either factor is disrupted separately. An implication of this finding is that standard screens may miss the roles that combinations of genes play in development. Here, we show that this phenomenon is not limited to Pax6 and Polycomb but rather applies more generally. We demonstrate that in the Drosophila eye-antennal disc, the simultaneous downregulation of Pax6 with either the NURF nucleosome remodeling complex or the Pointed transcription factor transforms the head epidermis into an antenna. This is a previously unidentified fate change that is also not observed with the loss of individual genes. We propose that the use of multi-gene knockdowns is an essential tool for unraveling the complexity of development.

Salt inducible kinases as novel Notch interactors in the developing Drosophila retina

Developmental processes require strict regulation of proliferation, differentiation and patterning for the generation of final organ size. Aberrations in these fundamental events are critically important in tumorigenesis and cancer progression. Salt inducible kinases (Siks) are evolutionarily conserved genes involved in diverse biological processes, including salt sensing, metabolism, muscle, cartilage and bone formation, but their role in development remains largely unknown. Recent findings implicate Siks in mitotic control, and in both tumor suppression and progression. Using a tumor model in the Drosophila eye, we show that perturbation of Sik function exacerbates tumor-like tissue overgrowth and metastasis. Furthermore, we show that both Drosophila Sik genes, Sik2 and Sik3, function in eye development processes. We propose that an important target of Siks may be the Notch signaling pathway, as we demonstrate genetic interaction between Siks and Notch pathway members. Finally, we investigate Sik expression in the developing retina and show that Sik2 is expressed in all photoreceptors, basal to cell junctions, while Sik3 appears to be expressed specifically in R3/R4 cells in the developing eye. Combined, our data suggest that Sik genes are important for eye tissue specification and growth, and that their dysregulation may contribute to tumor formation.

Intimate functional interactions between TGS1 and the Smn complex revealed by an analysis of the Drosophila eye development

Trimethylguanosine synthase 1 (TGS1) is a conserved enzyme that mediates formation of the trimethylguanosine cap on several RNAs, including snRNAs and telomerase RNA. Previous studies have shown that TGS1 binds the Survival Motor Neuron (SMN) protein, whose deficiency causes spinal muscular atrophy (SMA). Here, we analyzed the roles of the Drosophila orthologs of the human TGS1 and SMN genes. We show that the Drosophila TGS1 protein (dTgs1) physically interacts with all subunits of the Drosophila Smn complex (Smn, Gem2, Gem3, Gem4 and Gem5), and that a human TGS1 transgene rescues the mutant phenotype caused by dTgs1 loss. We demonstrate that both dTgs1 and Smn are required for viability of retinal progenitor cells and that downregulation of these genes leads to a reduced eye size. Importantly, overexpression of dTgs1 partially rescues the eye defects caused by Smn depletion, and vice versa. These results suggest that the Drosophila eye model can be exploited for screens aimed at the identification of genes and drugs that modify the phenotypes elicited by Tgs1 and Smn deficiency. These modifiers could help to understand the molecular mechanisms underlying SMA pathogenesis and devise new therapies for this genetic disease.

We explored the functional relationships between TGS1 and SMN using Drosophila as model organism. TGS1 is an enzyme that modifies the structure of the 5’-end of several RNAs, including telomerase RNA and the small nuclear RNAs (snRNAs) that are required for messenger RNA maturation. The SMN protein regulates snRNAs biogenesis and mutations in human SMN cause Spinal Muscular Atrophy (SMA), a devastating disorder characterized by neurodegeneration, progressive paralysis and death. We show that mutations in the Drosophila TGS1 (dTgs1) gene cause lethality, which is rescued by a human TGS1 transgene. We also show that the dTgs1 protein physically interacts with all subunits of the Smn complex, and that downregulation of either dTgs1 or Smn leads to a reduced Drosophila eye size. Notably, overexpression of dTgs1 partially rescues the eye defects caused by Smn knockdown, and vice versa, indicating that these genes cooperate in eye development. These results suggest that the eye model can be exploited for screens aimed at detection of chemical and genetic modifiers of the eye mutant phenotype elicited by dTgs1 and Smn deficiency, providing new clues about SMA pathogenesis and potential therapies.

Selective elimination of cancer cells by the adenovirus E4orf4 protein in a Drosophila cancer model: a new paradigm for cancer therapy

The adenovirus (Ad) E4orf4 protein contributes to efficient progression of virus infection. When expressed alone E4orf4 induces p53- and caspase-independent cell-death, which is more effective in cancer cells than in normal cells in tissue culture. Cancer selectivity of E4orf4-induced cell-death may result from interference with various regulatory pathways that cancer cells are more dependent on, including DNA damage signaling and proliferation control. E4orf4 signaling is conserved in several organisms, including yeast, Drosophila, and mammalian cells, indicating that E4orf4-induced cell-death can be investigated in these model organisms. The Drosophila genetic model system has contributed significantly to the study of cancer and to identification of novel cancer therapeutics. Here, we used the fly model to investigate the ability of E4orf4 to eliminate cancer tissues in a whole organism with minimal damage to normal tissues. We show that E4orf4 dramatically inhibited tumorigenesis and rescued survival of flies carrying a variety of tumors, including highly aggressive and metastatic tumors in the fly brain and eye discs. Moreover, E4orf4 rescued the morphology of adult eyes containing scrib^- cancer clones even when expressed at a much later stage than scrib elimination. The E4orf4 partner protein phosphatase 2A (PP2A) was required for inhibition of tumorigenesis by E4orf4 in the system described here, whereas another E4orf4 partner, Src kinase, provided only minimal contribution to this process. Our results suggest that E4orf4 is an effective anticancer agent and reveal a promising potential for E4orf4-based cancer treatments.

Protein Phosphatases-A Touchy Enemy in the Battle Against Glioblastomas: A Review

Glioblastoma (GBM) is the most common malignant tumor arising from brain parenchyma. Although many efforts have been made to develop therapies for GBM, the prognosis still remains poor, mainly because of the difficulty in total resection of the tumor mass from brain tissue and the resistance of the residual tumor against standard chemoradiotherapy. Therefore, novel adjuvant therapies are urgently needed. Recent genome-wide analyses of GBM cases have clarified molecular signaling mechanisms underlying GBM biology. However, results of clinical trials targeting phosphorylation-mediated signaling have been unsatisfactory to date. Protein phosphatases are enzymes that antagonize phosphorylation signaling by dephosphorylating phosphorylated signaling molecules. Recently, the critical roles of phosphatases in the regulation of oncogenic signaling in malignant tumor cells have been reported, and tumorigenic roles of deregulated phosphatases have been demonstrated in GBM. However, a detailed mechanism underlying phosphatase-mediated signaling transduction in the regulation of GBM has not been elucidated, and such information is necessary to apply phosphatases as a therapeutic target for GBM. This review highlights and summarizes the phosphatases that have crucial roles in the regulation of oncogenic signaling in GBM cells.

EGFR/Notch Antagonists Enhance the Response to Inhibitors of the PI3K-Akt Pathway by Decreasing Tumor-Initiating Cell Frequency

PURPOSE

Both EGFR and PI3K-Akt signaling pathways have been used as therapeutically actionable targets, but resistance is frequently reported. In this report, we show that enrichment of the cancer stem cell (CSC) subsets and dysregulation of Notch signaling underlie the challenges to therapy and describe the development of bispecific antibodies targeting both HER and Notch signaling.

EXPERIMENTAL DESIGN

We utilized cell-based models to study Notch signaling in drug-induced CSC expansion. Both cancer cell line models and patient-derived xenograft tumors were used to evaluate the antitumor effects of bispecific antibodies. Cell assays, flow cytometry, qPCR, and in vivo serial transplantation assays were employed to investigate the mechanisms of action and pharmacodynamic readouts.

RESULTS

We found that EGFR/Notch targeting bispecific antibodies exhibited a notable antistem cell effect in both in vitro and in vivo assays. Bispecific antibodies delayed the occurrence of acquired resistance to EGFR inhibitors in triple-negative breast cancer cell line-based models and showed efficacy in patient-derived xenografts. Moreover, the EGFR/Notch bispecific antibody PTG12 in combination with GDC-0941 exerted a stronger antitumor effect than the combined therapy of PI3K inhibitor with EGFR inhibitors or tarextumab in a broad spectrum of epithelial tumors. Mechanistically, bispecific antibody treatment inhibits the stem cell-like subpopulation, reduces tumor-initiating cell frequency, and downregulates the mesenchymal gene expression.

CONCLUSIONS

These findings suggest that the coblockade of EGFR and Notch signaling has the potential to increase the response to PI3K inhibition, and PTG12 may gain clinical efficacy when combined with PI3K blockage in cancer treatment.

Specification and Patterning of Drosophila Appendages

Appendages are external projections of the body that serve the animal for locomotion, feeding, or environment exploration. The appendages of the fruit fly Drosophilamelanogaster are derived from the imaginal discs, epithelial sac-like structures specified in the embryo that grow and pattern during larva development. In the last decades, genetic and developmental studies in the fruit fly have provided extensive knowledge regarding the mechanisms that direct the formation of the appendages. Importantly, many of the signaling pathways and patterning genes identified and characterized in Drosophila have similar functions during vertebrate appendage development. In this review, we will summarize the genetic and molecular mechanisms that lead to the specification of appendage primordia in the embryo and their posterior patterning during imaginal disc development. The identification of the regulatory logic underlying appendage specification in Drosophila suggests that the evolutionary origin of the insect wing is, in part, related to the development of ventral appendages.

Drosophila Pax6 promotes development of the entire eye-antennal disc, thereby ensuring proper adult head formation

Paired box 6 (Pax6) is considered to be the master control gene for eye development in all seeing animals studied so far. In vertebrates, it is required not only for lens/retina formation but also for the development of the CNS, olfactory system, and pancreas. Although Pax6 plays important roles in cell differentiation, proliferation, and patterning during the development of these systems, the underlying mechanism remains poorly understood. In the fruit fly, Drosophila melanogaster, Pax6 also functions in a range of tissues, including the eye and brain. In this report, we describe the function of Pax6 in Drosophila eye-antennal disc development. Previous studies have suggested that the two fly Pax6 genes, eyeless (ey) and twin of eyeless (toy), initiate eye specification, whereas eyegone (eyg) and the Notch (N) pathway independently regulate cell proliferation. Here, we show that Pax6 controls eye progenitor cell survival and proliferation through the activation of teashirt (tsh) and eyg, thereby indicating that Pax6 initiates both eye specification and proliferation. Although simultaneous loss of ey and toy during early eye-antennal disc development disrupts the development of all head structures derived from the eye-antennal disc, overexpression of N or tsh in the absence of Pax6 rescues only antennal and head epidermis development. Furthermore, overexpression of tsh induces a homeotic transformation of the fly head into thoracic structures. Taking these data together, we demonstrate that Pax6 promotes development of the entire eye-antennal disc and that the retinal determination network works to repress alternative tissue fates, which ensures proper development of adult head structures.

Polycomb group (PcG) proteins and Pax6 cooperate to inhibit in vivo reprogramming of the developing Drosophila eye

How different cells and tissues commit to and determine their fates has been a central question in developmental biology since the seminal embryological experiments conducted by Wilhelm Roux and Hans Driesch in sea urchins and frogs. Here, we demonstrate that Polycomb group (PcG) proteins maintain Drosophila eye specification by suppressing the activation of alternative fate choices. The loss of PcG in the developing eye results in a cellular reprogramming event in which the eye is redirected to a wing fate. This fate transformation occurs with either the individual loss of Polycomb proteins or the simultaneous reduction of the Pleiohomeotic repressive complex and Pax6. Interestingly, the requirement for retinal selector genes is limited to Pax6, as the removal of more downstream members does not lead to the eye-wing transformation. We also show that distinct PcG complexes are required during different developmental windows throughout eye formation. These findings build on earlier observations that the eye can be reprogrammed to initiate head epidermis, antennal and leg development.

Dynamic genome wide expression profiling of Drosophila head development reveals a novel role of Hunchback in retinal glia cell development and blood-brain barrier integrity

Drosophila melanogaster head development represents a valuable process to study the developmental control of various organs, such as the antennae, the dorsal ocelli and the compound eyes from a common precursor, the eye-antennal imaginal disc. While the gene regulatory network underlying compound eye development has been extensively studied, the key transcription factors regulating the formation of other head structures from the same imaginal disc are largely unknown. We obtained the developmental transcriptome of the eye-antennal discs covering late patterning processes at the late 2^nd larval instar stage to the onset and progression of differentiation at the end of larval development. We revealed the expression profiles of all genes expressed during eye-antennal disc development and we determined temporally co-expressed genes by hierarchical clustering. Since co-expressed genes may be regulated by common transcriptional regulators, we combined our transcriptome dataset with publicly available ChIP-seq data to identify central transcription factors that co-regulate genes during head development. Besides the identification of already known and well-described transcription factors, we show that the transcription factor Hunchback (Hb) regulates a significant number of genes that are expressed during late differentiation stages. We confirm that hb is expressed in two polyploid subperineurial glia cells (carpet cells) and a thorough functional analysis shows that loss of Hb function results in a loss of carpet cells in the eye-antennal disc. Additionally, we provide for the first time functional data indicating that carpet cells are an integral part of the blood-brain barrier. Eventually, we combined our expression data with a de novo Hb motif search to reveal stage specific putative target genes of which we find a significant number indeed expressed in carpet cells.

The development of different cell types must be tightly coordinated, and the eye-antennal imaginal discs of Drosophila melanogaster represent an excellent model to study the molecular mechanisms underlying this coordination. These imaginal discs contain the anlagen of nearly all adult head structures, such as the antennae, the head cuticle, the ocelli and the compound eyes. While large scale screens have been performed to unravel the gene regulatory network underlying compound eye development, a comprehensive understanding of genome wide expression dynamics throughout head development is still missing to date. We studied the genome wide gene expression dynamics during eye-antennal disc development in D. melanogaster to identify new central regulators of the underlying gene regulatory network. Expression based gene clustering and transcription factor motif enrichment analyses revealed a central regulatory role of the transcription factor Hunchback (Hb). We confirmed that hb is expressed in two polyploid retinal subperineurial glia cells (carpet cells). Our functional analysis shows that Hb is necessary for carpet cell development and we show for the first time that the carpet cells are an integral part of the blood-brain barrier.

Signalling crosstalk during early tumorigenesis in the absence of Polycomb silencing

In response to stress and injury a coordinated activation of conserved signalling modules, such as JNK and JAK/STAT, is critical to trigger regenerative tissue restoration. While these pathways rebuild homeostasis and promote faithful organ recovery, it is intriguing that they also become activated in various tumour conditions. Therefore, it is crucial to understand how similar pathways can achieve context-dependent functional outputs, likely depending on cellular states. Compromised chromatin regulation, upon removal of the Polycomb group member polyhomeotic, leads to tumour formation with ectopic activation of JNK signalling, mediated by egr/grnd, in addition to JAK/STAT and Notch. Employing quantitative analyses, we show that blocking ectopic signalling impairs ph tumour growth. Furthermore, JAK/STAT functions in parallel to JNK, while Notch relies on JNK. Here, we reveal a signalling hierarchy in ph tumours that is distinct from the regenerative processes regulated by these pathways. Absence of ph renders a permissive state for expression of target genes, but our results suggest that both loss of repression and the presence of activators may collectively regulate gene expression during tumorigenesis. Further dissecting the effect of signalling, developmental or stress-induced factors will thus elucidate the regulation of physiological responses and the contribution of context-specific cellular states.

Allocation of distinct organ fates from a precursor field requires a shift in expression and function of gene regulatory networks

A common occurrence in metazoan development is the rise of multiple tissues/organs from a single uniform precursor field. One example is the anterior forebrain of vertebrates, which produces the eyes, hypothalamus, diencephalon, and telencephalon. Another instance is the Drosophila wing disc, which generates the adult wing blade, the hinge, and the thorax. Gene regulatory networks (GRNs) that are comprised of signaling pathways and batteries of transcription factors parcel the undifferentiated field into discrete territories. This simple model is challenged by two observations. First, many GRN members that are thought to control the fate of one organ are actually expressed throughout the entire precursor field at earlier points in development. Second, each GRN can simultaneously promote one of the possible fates choices while repressing the other alternatives. It is therefore unclear how GRNs function to allocate tissue fates if their members are uniformly expressed and competing with each other within the same populations of cells. We address this paradigm by studying fate specification in the Drosophila eye-antennal disc. The disc, which begins its development as a homogeneous precursor field, produces a number of adult structures including the compound eyes, the ocelli, the antennae, the maxillary palps, and the surrounding head epidermis. Several selector genes that control the fates of the eye and antenna, respectively, are first expressed throughout the entire eye-antennal disc. We show that during early stages, these genes are tasked with promoting the growth of the entire field. Upon segregation to distinct territories within the disc, each GRN continues to promote growth while taking on the additional roles of promoting distinct primary fates and repressing alternate fates. The timing of both expression pattern restriction and expansion of functional duties is an elemental requirement for allocating fates within a single field.

A battery of transcription factors collectively called the retinal determination (RD) network controls the earliest steps in the specification of the fruit fly compound eye. Loss-of-function mutations lead to the loss of the compound eyes while over-expression of RD network members in non-retinal tissues induces the formation of ectopic eyes. These observations suggest that the network governs the growth, specification, and patterning of the eye field. Recent studies have also shown that the RD network represses the fates of the non-ocular tissues that are also derived from the disc such as the antenna, maxillary palp, and head epidermis. One inconsistency in the model for how this network controls eye specification is that many of its members are expressed throughout the entire eye-antennal disc. In this study, we show that early in development, the RD network is expressed throughout and promotes the growth of the entire eye-antennal disc. After the initial growth phase, the expression of these genes is restricted to just the eye field. This temporal and spatial limiting of the RD network to the developing eye is essential so that its role can expand to include promoting eye specification and repressing non-ocular fates.

Artificial selection for odor-guided behavior in Drosophila reveals changes in food consumption

Background

The olfactory system enables organisms to detect chemical cues in the environment and can signal the availability of food or the presence of a predator. Appropriate behavioral responses to these chemical cues are therefore important for organismal survival and can influence traits such as organismal life span and food consumption. However, understanding the genetic mechanisms underlying odor-guided behavior, correlated responses in other traits, and how these constrain or promote their evolution, remain an important challenge. Here, we performed artificial selection for attractive and aversive behavioral responses to four chemical compounds, two aromatics (4-ethylguaiacol and 4-methylphenol) and two esters (methyl hexanoate and ethyl acetate), for thirty generations.

Results

Artificial selection for odor-guided behavior revealed symmetrical responses to selection for each of the four chemical compounds. We then investigated whether selection for odor-guided behavior resulted in correlated responses in life history traits and/or food consumption. We found changes in food consumption upon selection for behavioral responses to aromatics. In many cases, lines selected for increased attraction to aromatics showed an increase in food consumption. We then performed RNA sequencing of lines selected for responses to 4-ethylguaiacol to identify candidate genes associated with odor-guided behavior and its impact on food consumption. We identified 91 genes that were differentially expressed among lines, many of which were associated with metabolic processes. RNAi-mediated knockdown of select candidate genes further supports their role in odor-guided behavior and/or food consumption.

Conclusions

This study identifies novel genes underlying variation in odor-guided behavior and further elucidates the genetic mechanisms underlying the interrelationship between olfaction and feeding.

Electronic supplementary material

The online version of this article (10.1186/s12864-017-4233-1) contains supplementary material, which is available to authorized users.

Eya2 overexpression promotes the invasion of human astrocytoma through the regulation of ERK/MMP9 signaling

The overexpression of eyes absent (Eya) 2 has been found in several human cancers. However, its biological roles and clinical significance in human astrocytoma have not yet been explored. This study investigated the clinical significance and biological roles of Eya2 in human astrocytoma tissues and cell lines. Using immunohistochemistry, we found Eya2 overexpression in 33 out of 90 (36.7%) astrocytoma specimens. The rate of Eya2 overexpression was higher in grade III-IV (48.1%) than in grade Ⅰ+Ⅱ astrocytomas (21.1%). Transfection with an Eya2 expression plasmid was performed in A172 cells with a low endogenous expression of Eya2 and the knockdown of Eya2 was carried out in U251 cells with a high endogenous expression using siRNA. Eya2 overexpression induced A172 cell proliferation and invasion, while the knockdown of Eya2 using siRNA decreased the proliferation and invasion of U251 cells. In addition, we found that transfection with the Eya2 expression plasmid facilitated cell cycle progression, and that the knockdown of Eya2 inhibited cell cycle progression, accompanied by a change in the expression of cell cycle-related proteins, including cyclin D1 and cyclin E. Eya2 also positively regulated extracellular signal-regulated kinase (ERK) activity and matrix metalloproteinase (MMP)9 expression. The blockade of ERK signaling using an inhibitor abolished the effects of Eya2 on A172 cell invasion and MMP9 production. In addition, we found that there was a positive correlation between Eya2 and Six1 in the astrocytoma cell lines. Immunoprecipitation revealed that Eya2 interacted with Six1 protein in the U251 cell line, which exhibited a high expression of both proteins. Eya2 failed to upregulate MMP expression in the A172 cells in which Six1 was silenced. On the whole, our data indicate that Eya2 may serve as a potential oncoprotein in human astrocytoma. Eya2 regulates astrocytoma cell proliferation and invasion, possibly through the regulation of ERK signaling.

The fly eye: Through the looking glass

The developing eye-antennal disc of Drosophila melanogaster has been studied for more than a century, and it has been used as a model system to study diverse processes, such as tissue specification, organ growth, programmed cell death, compartment boundaries, pattern formation, cell fate specification, and planar cell polarity. The findings that have come out of these studies have informed our understanding of basic developmental processes as well as human disease. For example, the isolation of a white-eyed fly ultimately led to a greater appreciation of the role that sex chromosomes play in development, sex determination, and sex linked genetic disorders. Similarly, the discovery of the Sevenless receptor tyrosine kinase pathway not only revealed how the fate of the R7 photoreceptor is selected but it also helped our understanding of how disruptions in similar biochemical pathways result in tumorigenesis and cancer onset. In this article, I will discuss some underappreciated areas of fly eye development that are fertile for investigation and are ripe for producing exciting new breakthroughs. The topics covered here include organ shape, growth control, inductive signaling, and right-left symmetry. Developmental Dynamics 247:111-123, 2018. © 2017 Wiley Periodicals, Inc.

Mechanisms controlling diversification of olfactory sensory neuron classes

Animals survive in harsh and fluctuating environments using sensory neurons to detect and respond to changes in their surroundings. Olfactory sensory neurons are essential for detecting food, identifying danger, and sensing pheromones. The ability to sense a large repertoire of different types of odors is crucial to distinguish between different situations, and is achieved through neuronal diversity within the olfactory system. Here, we review the developmental mechanisms used to establish diversity of olfactory sensory neurons in various model organisms, including Caenorhabditis elegans, Drosophila, and vertebrate models. Understanding and comparing how different olfactory neurons develop within the nervous system of different animals can provide insight into how the olfactory system is shaped in humans.

Antagonism of EGFR and Notch limits resistance to EGFR inhibitors and radiation by decreasing tumor-initiating cell frequency

Epidermal growth factor receptor (EGFR) blockade and radiation are efficacious in the treatment of cancer, but resistance is commonly reported. Studies have suggested that dysregulation of Notch signaling and enrichment of the cancer stem cell population underlie these treatment challenges. Our data show that dual targeting of EGFR and Notch2/3 receptors with antibody CT16 not only inhibited signaling mediated by these receptors but also showed a strong anti-stem cell effect both in vitro and in vivo. Treatment with CT16 prevented acquired resistance to EGFR inhibitors and radiation in non-small cell lung cancer (NSCLC) cell line models and patient-derived xenograft tumors. CT16 also had a superior radiosensitizing impact compared with EGFR inhibitors. CT16 in combination with radiation had a larger antitumor effect than the combination of radiation with EGFR inhibitors or tarextumab. Mechanistically, CT16 treatment inhibits the stem cell-like subpopulation, which has a high mesenchymal gene expression and DNA repair activity, and reduces tumor-initiating cell frequency. This finding highlights the capacity of a combined blockade of EGFR and Notch signaling to augment the response to radiation and suggests that CT16 may achieve clinical efficacy when combined with radiation in NSCLC treatment.

Insect-Like Organization of the Stomatopod Central Complex: Functional and Phylogenetic Implications

One approach to investigating functional attributes of the central complex is to relate its various elaborations to pancrustacean phylogeny, to taxon-specific behavioral repertoires and ecological settings. Here we review morphological similarities between the central complex of stomatopod crustaceans and the central complex of dicondylic insects. We discuss whether their central complexes possess comparable functional properties, despite the phyletic distance separating these taxa, with mantis shrimp (Stomatopoda) belonging to the basal branch of Eumalacostraca. Stomatopods possess the most elaborate visual receptor system in nature and display a fascinating behavioral repertoire, including refined appendicular dexterity such as independently moving eyestalks. They are also unparalleled in their ability to maneuver during both swimming and substrate locomotion. Like other pancrustaceans, stomatopods possess a set of midline neuropils, called the central complex, which in dicondylic insects have been shown to mediate the selection of motor actions for a range of behaviors. As in dicondylic insects, the stomatopod central complex comprises a modular protocerebral bridge (PB) supplying decussating axons to a scalloped fan-shaped body (FB) and its accompanying ellipsoid body (EB), which is linked to a set of paired noduli and other recognized satellite regions. We consider the functional implications of these attributes in the context of stomatopod behaviors, particularly of their eyestalks that can move independently or conjointly depending on the visual scene.

Master regulators in development: Views from the Drosophila retinal determination and mammalian pluripotency gene networks

Among the mechanisms that steer cells to their correct fate during development, master regulatory networks are unique in their sufficiency to trigger a developmental program outside of its normal context. In this review we discuss the key features that underlie master regulatory potency during normal and ectopic development, focusing on two examples, the retinal determination gene network (RDGN) that directs eye development in the fruit fly and the pluripotency gene network (PGN) that maintains cell fate competency in the early mammalian embryo. In addition to the hierarchical transcriptional activation, extensive positive transcriptional feedback, and cooperative protein-protein interactions that enable master regulators to override competing cellular programs, recent evidence suggests that network topology must also be dynamic, with extensive rewiring of the interactions and feedback loops required to navigate the correct sequence of developmental transitions to reach a final fate. By synthesizing the in vivo evidence provided by the RDGN with the extensive mechanistic insight gleaned from the PGN, we highlight the unique regulatory capabilities that continual reorganization into new hierarchies confers on master control networks. We suggest that deeper understanding of such dynamics should be a priority, as accurate spatiotemporal remodeling of network topology will undoubtedly be essential for successful stem cell based therapeutic efforts.

Distal-less homeobox genes of insects and spiders: genomic organization, function, regulation and evolution

The Distal-less (Dll) genes are homeodomain transcription factors that are present in most Metazoa and in representatives of all investigated arthropod groups. In Drosophila, the best studied insect, Dll plays an essential role in forming the proximodistal axis of the legs, antennae and analia, and in specifying antennal identity. The initiation of Dll expression in clusters of cells in mid-lateral regions of the Drosophila embryo represents the earliest genetic marker of limbs. Dll genes are involved in the development of the peripheral nervous system and sensitive organs, and they also function as master regulators of black pigmentation in some insect lineages. Here we analyze the complete genomes of six insects, the nematode Caenorhabditis elegans and Homo sapiens, as well as multiple Dll sequences available in databases in order to examine the structure and protein features of these genes. We also review the function, expression, regulation and evolution of arthropod Dll genes with emphasis on insects and spiders.

Regulatory mechanisms of EGFR signalling during Drosophila eye development

EGFR signalling is a well-conserved signalling pathway playing major roles during development and cancers. This review explores what studying the EGFR pathway during Drosophila eye development has taught us in terms of the diversity of its regulatory mechanisms. This model system has allowed the identification of numerous positive and negative regulators acting at specific time and place, thus participating to the tight control of signalling. EGFR signalling regulation is achieved by a variety of mechanisms, including the control of ligand processing, the availability of the receptor itself and the transduction of the cascade in the cytoplasm. Ultimately, the transcriptional responses contribute to the establishment of positive and negative feedback loops. The combination of these multiple mechanisms employed to regulate the EGFR pathway leads to specific cellular outcomes involved in functions as diverse as the acquisition of cell fate, proliferation, survival, adherens junction remodelling and morphogenesis.

MicroRNA-101 inhibits cell proliferation and induces apoptosis by targeting EYA1 in breast cancer

MicroRNAs (miRNAs or miRs) regulate gene expression by negatively modulating the stability or translational efficiency of their target genes by targeting the 3'-untranslated region (3'-UTR). Aberrant miRNA expression has been reported in various types of cancer; miRNAs can function as either oncogenes or tumor suppressor genes in cancer. In this study, we examined the expression level of miR‑101 in breast cancer tissues and cell lines by RT-qPCR, and found that miR‑101 expression was downregulated in breast cancer tissues and cell lines; indeed, in 6 of the 28 tissue samples, miR‑101 could not be detected. Furthermore, miR‑101, when transfected into SKBR3 cells, inhibited cell proliferation and promoted apoptosis, while miR‑101 inhibitor had the opposite effect. A dual-luciferase reporter assay revealed that miR‑101 targeted the 3'-UTR of eyes absent homolog 1 (Drosophila) (EYA1). Western blot analysis demonstrated a significantly decreased protein level of EYA1 in the SKBR3 cells transfected with miR‑101 mimic, whereas transfection with miR‑101 inhibitor led to an increased level of EYA1. Moreover, an increased expression of EYA1 was also found in breast cancer tissues and cell lines. The silencing of EYA1 using siRNA targeting EYA1 (EYA1‑siRNA) significantly inhibited SKBR3 cell proliferation and promoted apoptosis, and also suppressed the increased proliferation induced by transfection with miR‑101 inhibitor. The protein expression levels of Notch signaling components (jagged1, Hes1 and Hey1) were significantly decreased by transfection with miR‑101 mimic and EYA1-siRNA, and were increased by transfection with miR‑101 inhibitor. Furthermore, the elevated protein expression levels of jagged1, Hes1 and Hey1 induced by transfection with miR‑101 inhibitor in the SKBR3 cells were significantly decreased by transfection with EYA1-siRNA. Taken together, these results suggest that miR‑101 is down-regulated in breast cancer, and can inhibit cell proliferation and promote apoptosis by targeting EYA1 through the Notch signaling pathway.

Arthropod eyes: The early Cambrian fossil record and divergent evolution of visual systems

Four types of eyes serve the visual neuropils of extant arthropods: compound retinas composed of adjacent facets; a visual surface populated by spaced eyelets; a smooth transparent cuticle providing inwardly directed lens cylinders; and single-lens eyes. The first type is a characteristic of pancrustaceans, the eyes of which comprise lenses arranged as hexagonal or rectilinear arrays, each lens crowning 8-9 photoreceptor neurons. Except for Scutigeromorpha, the second type typifies Myriapoda whose relatively large eyelets surmount numerous photoreceptive rhabdoms stacked together as tiers. Scutigeromorph eyes are facetted, each lens crowning some dozen photoreceptor neurons of a modified apposition-type eye. Extant chelicerate eyes are single-lensed except in xiphosurans, whose lateral eyes comprise a cuticle with a smooth outer surface and an inner one providing regular arrays of lens cylinders. This account discusses whether these disparate eye types speak for or against divergence from one ancestral eye type. Previous considerations of eye evolution, focusing on the eyes of trilobites and on facet proliferation in xiphosurans and myriapods, have proposed that the mode of development of eyes in those taxa is distinct from that of pancrustaceans and is the plesiomorphic condition from which facetted eyes have evolved. But the recent discovery of enormous regularly facetted compound eyes belonging to early Cambrian radiodontans suggests that high-resolution facetted eyes with superior optics may be the ground pattern organization for arthropods, predating the evolution of arthrodization and jointed post-protocerebral appendages. Here we provide evidence that compound eye organization in stem-group euarthropods of the Cambrian can be understood in terms of eye morphologies diverging from this ancestral radiodontan-type ground pattern. We show that in certain Cambrian groups apposition eyes relate to fixed or mobile eyestalks, whereas other groups reveal concomitant evolution of sessile eyes equipped with optics typical of extant xiphosurans. Observations of fossil material, including that of trilobites and eurypterids, support the proposition that the ancestral compound eye was the apposition type. Cambrian arthropods include possible precursors of mandibulate eyes. The latter are the modified compound eyes, now sessile, and their underlying optic lobes exemplified by scutigeromorph chilopods, and the mobile stalked compound eyes and more elaborate optic lobes typifying Pancrustacea. Radical divergence from an ancestral apposition type is demonstrated by the evolution of chelicerate eyes, from doublet sessile-eyed stem-group taxa to special apposition eyes of xiphosurans, the compound eyes of eurypterids, and single-lens eyes of arachnids. Different eye types are discussed with respect to possible modes of life of the extinct species that possessed them, comparing these to extant counterparts and the types of visual centers the eyes might have served.

Are there ergodic limits to evolution? Ergodic exploration of genome space and convergence

We examine the analogy between evolutionary dynamics and statistical mechanics to include the fundamental question of ergodicity-the representative exploration of the space of possible states (in the case of evolution this is genome space). Several properties of evolutionary dynamics are identified that allow a generalization of the ergodic dynamics, familiar in dynamical systems theory, to evolution. Two classes of evolved biological structure then arise, differentiated by the qualitative duration of their evolutionary time scales. The first class has an ergodicity time scale (the time required for representative genome exploration) longer than available evolutionary time, and has incompletely explored the genotypic and phenotypic space of its possibilities. This case generates no expectation of convergence to an optimal phenotype or possibility of its prediction. The second, more interesting, class exhibits an evolutionary form of ergodicity-essentially all of the structural space within the constraints of slower evolutionary variables have been sampled; the ergodicity time scale for the system evolution is less than the evolutionary time. In this case, some convergence towards similar optima may be expected for equivalent systems in different species where both possess ergodic evolutionary dynamics. When the fitness maximum is set by physical, rather than co-evolved, constraints, it is additionally possible to make predictions of some properties of the evolved structures and systems. We propose four structures that emerge from evolution within genotypes whose fitness is induced from their phenotypes. Together, these result in an exponential speeding up of evolution, when compared with complete exploration of genomic space. We illustrate a possible case of application and a prediction of convergence together with attaining a physical fitness optimum in the case of invertebrate compound eye resolution.

Notching on Cancer's Door: Notch Signaling in Brain Tumors

Notch receptors play an essential role in the regulation of central cellular processes during embryonic and postnatal development. The mammalian genome encodes for four Notch paralogs (Notch 1–4), which are activated by three Delta-like (Dll1/3/4) and two Serrate-like (Jagged1/2) ligands. Further, non-canonical Notch ligands such as epidermal growth factor like protein 7 (EGFL7) have been identified and serve mostly as antagonists of Notch signaling. The Notch pathway prevents neuronal differentiation in the central nervous system by driving neural stem cell maintenance and commitment of neural progenitor cells into the glial lineage. Notch is therefore often implicated in the development of brain tumors, as tumor cells share various characteristics with neural stem and progenitor cells. Notch receptors are overexpressed in gliomas and their oncogenicity has been confirmed by gain- and loss-of-function studies in vitro and in vivo. To this end, special attention is paid to the impact of Notch signaling on stem-like brain tumor-propagating cells as these cells contribute to growth, survival, invasion, and recurrence of brain tumors. Based on the outcome of ongoing studies in vivo, Notch-directed therapies such as γ-secretase inhibitors and blocking antibodies have entered and completed various clinical trials. This review summarizes the current knowledge on Notch signaling in brain tumor formation and therapy.

Notch-EGFR/HER2 Bidirectional Crosstalk in Breast Cancer

The Notch pathway is a well-established mediator of cell-cell communication that plays a critical role in stem cell survival, self-renewal, cell fate decisions, tumorigenesis, invasion, metastasis, and drug resistance in a variety of cancers. An interesting form of crosstalk exists between the Notch receptor and the Epidermal Growth Factor Receptor Tyrosine Kinase family, which consists of HER-1, -2, -3, and -4. Overexpression of HER and/or Notch occurs in several human cancers including brain, lung, breast, ovary, and skin making them potent oncogenes capable of advancing malignant disease. Continued assessment of interplay between these two critical signaling networks uncovers new insight into mechanisms used by HER-driven cancer cells to exploit Notch as a compensatory pathway. The compensatory Notch pathway maintains HER-induced downstream signals transmitted to pathways such as Mitogen Activated Protein Kinase and Phosphatidylinositol 3-Kinase (PI3K), thereby allowing cancer cells to survive molecular targeted therapies, undergo epithelial to mesenchymal transitioning, and increase cellular invasion. Uncovering the critical crosstalk between the HER and Notch pathways can lead to improved screening for the expression of these oncogenes enabling patients to optimize their personal treatment options and predict potential treatment resistance. This review will focus on the current state of crosstalk between the HER and Notch receptors and the effectiveness of current therapies targeting HER-driven cancers.

Mutation of potential MAPK phosphorylation sites in the Notch antagonist Hairless

Cellular differentiation during eumetazoan development is based on highly conserved signalling pathways. Two of them, the Notch and the EGFR signalling pathways, are closely intertwined. We have identified two potential target sites of the Mitogen activated kinase (MAPK), the downstream effector kinase of EGFR, within Hairless (H), the major antagonist of Notch signalling in Drosophila. Assuming that phosphorylation of these sites modulates H activity, a direct influence of EGFR signalling on Notch pathway regulation might be possible. This hypothesis was tested by generating a phospho-deficient and a phospho-mimetic H isoform and by assaying for their biological activity. We first addressed the binding of known H interaction partners Su(H), Gro, CtBP and Pros26.4 which was similar between mutant and wild type H. Next we assayed eye, wing and bristle development which are strongly affected by the overexpression of H due to the inhibition of Notch signalling. Overexpression of the mutant constructs resulted in phenotypes similar to wildtype H overexpression, yet with subtle differences in phenotypic severity. However, large variations suggest that the mutated residues may be critical for the overall structure or stability of H. Albeit of minor impact, EGFR may fine tune Notch signalling via MAPK dependent phosphorylation of H.

Mef2 interacts with the Notch pathway during adult muscle development in Drosophila melanogaster

Myogenesis of indirect flight muscles (IFMs) in Drosophila melanogaster follows a well-defined cellular developmental scheme. During embryogenesis, a set of cells, the Adult Muscle Precursors (AMPs), are specified. These cells will become proliferating myoblasts during the larval stages which will then give rise to the adult IFMs. Although the cellular aspect of this developmental process is well studied, the molecular biology behind the different stages is still under investigation. In particular, the interactions required during the transition from proliferating myoblasts to differentiated myoblasts ready to fuse to the muscle fiber. It has been previously shown that the Notch pathway is active in proliferating myoblasts, and that this pathway is inhibited in developing muscle fibers. Furthermore, the Myocyte Enhancing Factor 2 (Mef2), Vestigial (Vg) and Scalloped (Sd) transcription factors are necessary for IFM development and that Vg is required for Notch pathway repression in differentiating fibers. Here we examine the interactions between Notch and Mef2 and mechanisms by which the Notch pathway is inhibited during differentiation. We show that Mef2 is capable of inhibiting the Notch pathway in non myogenic cells. A previous screen for Mef2 potential targets identified Delta a component of the Notch pathway. Dl is expressed in Mef2 and Sd-positive developing fibers. Our results show that Mef2 and possibly Sd regulate a Dl enhancer specifically expressed in the developing IFMs and that Mef2 is required for Dl expression in developing IFMs.

Dissection and immunostaining of imaginal discs from Drosophila melanogaster

A significant portion of post-embryonic development in the fruit fly, Drosophila melanogaster, takes place within a set of sac-like structures called imaginal discs. These discs give rise to a high percentage of adult structures that are found within the adult fly. Here we describe a protocol that has been optimized to recover these discs and prepare them for analysis with antibodies, transcriptional reporters and protein traps. This procedure is best suited for thin tissues like imaginal discs, but can be easily modified for use with thicker tissues such as the larval brain and adult ovary. The written protocol and accompanying video will guide the reader/viewer through the dissection of third instar larvae, fixation of tissue, and treatment of imaginal discs with antibodies. The protocol can be used to dissect imaginal discs from younger first and second instar larvae as well. The advantage of this protocol is that it is relatively short and it has been optimized for the high quality preservation of the dissected tissue. Another advantage is that the fixation procedure that is employed works well with the overwhelming number of antibodies that recognize Drosophila proteins. In our experience, there is a very small number of sensitive antibodies that do not work well with this procedure. In these situations, the remedy appears to be to use an alternate fixation cocktail while continuing to follow the guidelines that we have set forth for the dissection steps and antibody incubations.

An intronic microRNA links Rb/E2F and EGFR signaling

The importance of microRNAs in the regulation of various aspects of biology and disease is well recognized. However, what remains largely unappreciated is that a significant number of miRNAs are embedded within and are often co-expressed with protein-coding host genes. Such a configuration raises the possibility of a functional interaction between a miRNA and the gene it resides in. This is exemplified by the Drosophila melanogaster dE2f1 gene that harbors two miRNAs, mir-11 and mir-998, within its last intron. miR-11 was demonstrated to limit the proapoptotic function of dE2F1 by repressing cell death genes that are directly regulated by dE2F1, however the biological role of miR-998 was unknown. Here we show that one of the functions of miR-998 is to suppress dE2F1-dependent cell death specifically in rbf mutants by elevating EGFR signaling. Mechanistically, miR-998 operates by repressing dCbl, a negative regulator of EGFR signaling. Significantly, dCbl is a critical target of miR-998 since dCbl phenocopies the effects of miR-998 on dE2f1-dependent apoptosis in rbf mutants. Importantly, this regulation is conserved, as the miR-998 seed family member miR-29 repressed c-Cbl, and enhanced MAPK activity and wound healing in mammalian cells. Therefore, the two intronic miRNAs embedded in the dE2f1 gene limit the apoptotic function of dE2f1, but operate in different contexts and act through distinct mechanisms. These results also illustrate that examining an intronic miRNA in the context of its host's function can be valuable in elucidating the biological function of the miRNA, and provide new information about the regulation of the host gene itself.

Animal genomes encode hundreds of microRNA genes that impact all areas of biology by limiting the expression of their targets. What remains largely unappreciated is that a significant proportion of microRNA genes are embedded within protein-coding genes, and are often co-expressed with their hosts, which raises the possibility of a functional interaction between them. The mir-998 gene is located within an intron of the gene encoding Drosophila E2F1 transcription factor. E2F1 can induce the expression of cell death genes, and its activity is negatively regulated by the pRB tumour suppressor protein. In certain settings, unrestrained E2F1 activity is sufficient to induce cell death in cells lacking functional pRB. Here, we show that miR-998 limits cell death in Rb-deficient cells by repressing dCbl, a negative regulator of Epidermal Growth Factor Receptor signaling (EGFR). miR-998 also augments EGFR signaling in differentiating photoreceptor cells. Furthermore, we show that the interaction between miR-998 and Cbl is conserved: in human cells, miR-29, a mir-29/998 seed family member, enhances EGFR signaling by targeting c-Cbl. Therefore, by examining the role of an intronic microRNA in the context of its host's function, we identified an important microRNA target and uncovered a biological function of the microRNA.

A vertex specific dorsal selector Dve represses the ventral appendage identity in Drosophila head

Developmental fields are subdivided into lineage-restricted cell populations, known as compartments. In the eye imaginal disc of Drosophila, dorso-ventral (DV) lineage restriction is the primary event, whereas antero-posterior compartment boundary is the first lineage restriction in other imaginal discs. The Iroquois complex (Iro-C) genes function as dorsal selectors and repress the default, ventral, identity in the eye-head primordium. In Iro-C mutant clones, change of the dorsal identity to default ventral fate leads to generation of ectopic DV boundary, which results in dorsal eye enlargement, and duplication of ventral appendages like antenna and maxillary palp. Similar phenotypes were observed in heads with defective proventriculus (dve) mutant clones. Here, we show that the homeobox gene dve is a downstream effector of Iro-C in the dorsal head capsule (vertex) specification and represses the ventral (antennal) identity. Two homeodomain proteins Distal-less (Dll) and Homothorax (Hth) are known to be determinants of the antennal identity. Ectopic antenna formation in heads with dve mutant clones was associated with ectopic Dll expression and endogenous Hth expression in the vertex region. Interestingly, dve Dll double mutant clones could also induce ectopic antennae lacking the distal structures, suggesting that the Dve activity is crucial for repressing inappropriate antenna-forming potential in the vertex region. Our results clearly indicate that not only the activation of effector genes to execute developmental program but also the repression of inappropriate program is crucial for establishment of the organ identity.

Linking pathways in the developing and aging brain with neurodegeneration

The molecular and cellular mechanisms, which coordinate the critical stages of brain development to reach a normal structural organization with appropriate networks, are progressively being elucidated. Experimental and clinical studies provide evidence of the occurrence of developmental alterations induced by genetic or environmental factors leading to the formation of aberrant networks associated with learning disabilities. Moreover, evidence is accumulating that suggests that also late-onset neurological disorders, even Alzheimer's disease, might be considered disorders of aberrant neural development with pathological changes that are set up at early stages of development before the appearance of the symptoms. Thus, evaluating proteins and pathways that are important in age-related neurodegeneration in the developing brain together with the characterization of mechanisms important during brain development with relevance to brain aging are of crucial importance. In the present review we focus on (1) aspects of neurogenesis with relevance to aging; (2) neurodegenerative disease (NDD)-associated proteins/pathways in the developing brain; and (3) further pathways of the developing or neurodegenerating brains that show commonalities. Elucidation of complex pathogenetic routes characterizing the earliest stage of the detrimental processes that result in pathological aging represents an essential first step toward a therapeutic intervention which is able to reverse these pathological processes and prevent the onset of the disease. Based on the shared features between pathways, we conclude that prevention of NDDs of the elderly might begin during the fetal and childhood life by providing the mothers and their children a healthy environment for the fetal and childhood development.

miR-30a suppresses breast cancer cell proliferation and migration by targeting Eya2

Eye absent (Eya) proteins are involved in cell fate determination in a broad spectrum of cells and tissues. Aberrant expression of Eya2 has been documented in a variety of cancers and correlates with clinical outcome. However, whether microRNAs (miRNAs) can regulate Eya2 expression remains unknown. Here, we show that miR-30a represses Eya2 expression by binding to the 3'-untranslated region of Eya2. Overexpression of Eya2 in miR-30a-transfected breast cancer cells effectively rescued the inhibition of cell proliferation and migration caused by miR-30a. Knockdown of Eya2 by small-interfering RNA (siRNA) in breast cancer cells mimicked the effect induced by miR-30a and abolished the ability of miR-30a to regulate breast cancer cell proliferation and migration. The miR-30a/Eya2 axis could regulate G1/S cell cycle progression, accompanied by the modulation of expression of cell cycle-related proteins, including cyclin A, cyclin D1, cyclin E, and c-Myc. Moreover, miR-30a expression was downregulated in breast cancer patients, and negatively correlated with Eya2, which was upregulated in breast cancer patients. These data suggest that the miR-30a/Eya2 axis may play an important role in breast cancer development and progression and that miR-30a activation or Eya2 inhibition may be a useful strategy for cancer treatment.

Eye-specification genes in the bacterial light organ of the bobtail squid Euprymna scolopes, and their expression in response to symbiont cues

The squid Euprymna scolopes has evolved independent sets of tissues capable of light detection, including a complex eye and a photophore or 'light organ', which houses the luminous bacterial symbiont Vibrio fischeri. As the eye and light organ originate from different embryonic tissues, we examined whether the eye-specification genes, pax6, eya, six, and dac, are shared by these two organs, and if so, whether they are regulated in the light organ by symbiosis. We obtained sequences of the four genes with PCR, confirmed orthology with phylogenetic analysis, and determined that each was expressed in the eye and light organ. With in situ hybridization (ISH), we localized the gene transcripts in developing embryos, comparing the patterns of expression in the two organs. The four transcripts localized to similar tissues, including those associated with the visual system ∼1/4 into embryogenesis (Naef stage 18) and the light organ ∼3/4 into embryogenesis (Naef stage 26). We used ISH and quantitative real-time PCR to examine transcript expression and differential regulation in postembryonic light organs in response to the following colonization conditions: wild-type, luminescent V. fischeri; a mutant strain defective in light production; and as a control, no symbiont. In ISH experiments light organs showed down regulation of the pax6, eya, and six transcripts in response to wild-type V. fischeri. Mutant strains also induced down regulation of the pax6 and eya transcripts, but not of the six transcript. Thus, luminescence was required for down regulation of the six transcript. We discuss these results in the context of symbiont-induced light-organ development. Our study indicates that the eye-specification genes are expressed in light-interacting tissues independent of their embryonic origin and are capable of responding to bacterial cues. These results offer evidence for evolutionary tinkering or the recruitment of eye development genes for use in a light-sensing photophore.

Expression of mutant CHMP2B, an ESCRT-III component involved in frontotemporal dementia, causes eye deformities due to Notch misregulation in Drosophila

Endosomal sorting complexes required for transport (ESCRTs) mediate sorting of ubiquitinated membrane proteins into multivesicular bodies en route to lysosomes for degradation. A mutation in CHMP2B (CHMP2B(Intron5), an ESCRT-III component) that is associated with a hereditary form of frontotemporal dementia (FTD3) disrupts the endosomal-lysosomal pathway and causes accumulation of autophagosomes and multilamellar structures. We previously demonstrated that expression of CHMP2B(Intron5) in the Drosophila eye using GMR-Gal4 causes misregulation of the Toll receptor pathway. Here, we show that ectopic expression of CHMP2B(Intron5) using eyeless-Gal4 (ey>CHMP2B(Intron5)), a driver with different spatiotemporal expression attributes than GMR-Gal4 in the Drosophila eye, causes eye deformities when compared to expression of wild-type CHMP2B (CHMP2B(WT)) and the Drosophila homologue of CHMP2B (CG4618). In addition, ey>CHMP2B(Intron5) flies showed defects in photoreceptor cell patterning and phototactic behavior. Furthermore, ey>CHMP2B(Intron5) flies showed accumulation of Notch in enlarged endosomes and up-regulation of Notch activity. Partial loss of Notch activity in ey>CHMP2B(Intron5) flies significantly rescued eye deformities, photoreceptor patterning defect, and phototactic behavior defect, indicating that these defects are primarily due to Notch misregulation. These results demonstrate that CHMP2B(Intron5) preferentially affects different receptor signaling pathways in a cellular and developmental context-dependent manner.

Notch signaling in the brain: in good and bad times

Notch signaling is an evolutionarily conserved pathway, which is fundamental for neuronal development and specification. In the last decade, increasing evidence has pointed out an important role of this pathway beyond embryonic development, indicating that Notch also displays a critical function in the mature brain of vertebrates and invertebrates. This pathway appears to be involved in neural progenitor regulation, neuronal connectivity, synaptic plasticity and learning/memory. In addition, Notch appears to be aberrantly regulated in neurodegenerative diseases, including Alzheimer's disease and ischemic injury. The molecular mechanisms by which Notch displays these functions in the mature brain are not fully understood, but are currently the subject of intense research. In this review, we will discuss old and novel Notch targets and molecular mediators that contribute to Notch function in the mature brain and will summarize recent findings that explore the two facets of Notch signaling in brain physiology and pathology.

Ectopic antenna induction by overexpression of CG17836/Xrp1 encoding an AT-hook DNA binding motif protein in Drosophila

Drosophila imaginal discs are an excellent model system for studies of developmental plasticity. In imaginal discs, most cells adhere strictly to their specific identity, but some cells undergo transdetermination, a process wherein the determined identity switches to another disc-specific identity. In this study, we performed gain-of-function screening and identified a gene, CG17836/Xrp1, that induces ectopic antennae in the eye field upon overexpression at the early eye disc stage. An essential factor in the distalization process, Distalles, and its upstream regulators Wingless, Hedgehog, and Decapentaplegic, are ectopically induced by CG17836/Xrp1 overexpression in eye discs, and this provides molecular evidence of the formation of ectopic antennae. Further, forced expression of CG17836/Xrp1 induced severe cell-proliferation defects. These findings suggest that CG17836/Xrp1 is involved in the regulation of cell proliferation in eye discs and affects disc identity specification.