The Friend of GATA proteins U-shaped, FOG-1, and FOG-2 function as negative regulators of blood, heart, and eye development in Drosophila

GATA factor Serpent promotes phagocytosis in non-professional phagocytes during Drosophila oogenesis

Clearance of dying cells is essential for tissue homeostasis and requires both professional and non-professional phagocytes; however, it is unclear what promotes phagocytosis by non-professional phagocytes. Follicle cells of Drosophila egg chambers function as non-professional phagocytes to clear large germ cell debris in mid and late oogenesis, providing an excellent model for the study of non-professional phagocytes. Here, we demonstrate that GATA factor Serpent (Srp) plays an indispensable role in promoting the phagocytic capacity of follicle cells in both processes. Srp is upregulated in follicle cells of degenerating mid-stage egg chambers, and its knockdown results in incomplete clearance of germ cell debris and premature follicle cell death. In addition, Srp is upregulated in stretch follicle cells and is essential for clearing the nurse cell nuclei in late oogenesis. Genetic analysis reveals that Srp acts downstream of JNK signaling to upregulate the expression of the phagocytic receptor Draper as well as other components in the corpse processing machinery. Our findings highlight the crucial role for Srp in non-professional phagocytes during Drosophila oogenesis, which may also be conserved across species.

Numerous Serine/Threonine Kinases Affect Blood Cell Homeostasis in Drosophila melanogaster

Blood cells in Drosophila serve primarily innate immune responses. Various stressors influence blood cell homeostasis regarding both numbers and the proportion of blood cell types. The principle molecular mechanisms governing hematopoiesis are conserved amongst species and involve major signaling pathways like Notch, Toll, JNK, JAK/Stat or RTK. Albeit signaling pathways generally rely on the activity of protein kinases, their specific contribution to hematopoiesis remains understudied. Here, we assess the role of Serine/Threonine kinases with the potential to phosphorylate the transcription factor Su(H) in crystal cell homeostasis. Su(H) is central to Notch signal transduction, and its inhibition by phosphorylation impedes crystal cell formation. Overall, nearly twenty percent of all Drosophila Serine/Threonine kinases were studied in two assays, global and hemocyte-specific overexpression and downregulation, respectively. Unexpectedly, the majority of kinases influenced crystal cell numbers, albeit only a few were related to hematopoiesis so far. Four kinases appeared essential for crystal cell formation, whereas most kinases restrained crystal cell development. This group comprises all kinase classes, indicative of the complex regulatory network underlying blood cell homeostasis. The rather indiscriminative response we observed opens the possibility that blood cells measure their overall phospho-status as a proxy for stress-signals, and activate an adaptive immune response accordingly.

Transcription factor expression landscape in Drosophila embryonic cell lines

BACKGROUND

Transcription factor (TF) proteins are a key component of the gene regulatory networks that control cellular fates and function. TFs bind DNA regulatory elements in a sequence-specific manner and modulate target gene expression through combinatorial interactions with each other, cofactors, and chromatin-modifying proteins. Large-scale studies over the last two decades have helped shed light on the complex network of TFs that regulate development in Drosophila melanogaster.

RESULTS

Here, we present a detailed characterization of expression of all known and predicted Drosophila TFs in two well-established embryonic cell lines, Kc167 and S2 cells. Using deep coverage RNA sequencing approaches we investigate the transcriptional profile of all 707 TF coding genes in both cell types. Only 103 TFs have no detectable expression in either cell line and 493 TFs have a read count of 5 or greater in at least one of the cell lines. The 493 TFs belong to 54 different DNA-binding domain families, with significant enrichment of those in the zf-C2H2 family. We identified 123 differentially expressed genes, with 57 expressed at significantly higher levels in Kc167 cells than S2 cells, and 66 expressed at significantly lower levels in Kc167 cells than S2 cells. Network mapping reveals that many of these TFs are crucial components of regulatory networks involved in cell proliferation, cell-cell signaling pathways, and eye development.

CONCLUSIONS

We produced a reference TF coding gene expression dataset in the extensively studied Drosophila Kc167 and S2 embryonic cell lines, and gained insight into the TF regulatory networks that control the activity of these cells.

Single-cell RNA sequencing of mid-to-late stage spider embryos: new insights into spider development

BACKGROUND

The common house spider Parasteatoda tepidariorum represents an emerging new model organism of arthropod evolutionary and developmental (EvoDevo) studies. Recent technical advances have resulted in the first single-cell sequencing (SCS) data on this species allowing deeper insights to be gained into its early development, but mid-to-late stage embryos were not included in these pioneering studies.

RESULTS

Therefore, we performed SCS on mid-to-late stage embryos of Parasteatoda and characterized resulting cell clusters by means of in-silico analysis (comparison of key markers of each cluster with previously published information on these genes). In-silico prediction of the nature of each cluster was then tested/verified by means of additional in-situ hybridization experiments with additional markers of each cluster.

CONCLUSIONS

Our data show that SCS data reliably group cells with similar genetic fingerprints into more or less distinct clusters, and thus allows identification of developing cell types on a broader level, such as the distinction of ectodermal, mesodermal and endodermal cell lineages, as well as the identification of distinct developing tissues such as subtypes of nervous tissue cells, the developing heart, or the ventral sulcus (VS). In comparison with recent other SCS studies on the same species, our data represent later developmental stages, and thus provide insights into different stages of developing cell types and tissues such as differentiating neurons and the VS that are only present at these later stages.

Conserved mechanisms of NuRD function in hematopoetic gene expression

The Nucleosome Remodeling and Deacetylating Complex (NuRD) is ubiquitously expressed in all metazoans. It combines nucleosome remodeling and histone deacetylating activities to generate inaccessible chromatin structures and to repress gene transcription. NuRD is involved in the generation and maintenance of a wide variety of lineage-specific gene expression programs during differentiation and in differentiated cells. A close cooperation with a large number of lineage-specific transcription factors is key to allow NuRD to function in many distinct differentiation contexts. The molecular nature of this interplay between transcription factors and NuRD is complex and not well understood. This review uses hematopoiesis as a paradigm to highlight recent advances in our understanding of how transcription factors and NuRD cooperate at the molecular level during differentiation. A comparison of vertebrate and invertebrate systems serves to identify the conserved and fundamental concepts guiding functional interactions between transcription factors and NuRD. We also discuss how the transcription factor-NuRD axis constitutes a potential therapeutic target for the treatment of hemoglobinopathies.

Transcriptome profile in Drosophila Kc and S2 embryonic cell lines

Drosophila melanogaster cell lines are an important resource for a range of studies spanning genomics, molecular genetics, and cell biology. Amongst these valuable lines are Kc167 (Kc) and Schneider 2 (S2) cells, which were originally isolated in the late 1960s from embryonic sources and have been used extensively to investigate a broad spectrum of biological activities including cell-cell signaling and immune system function. Whole-genome tiling microarray analysis of total RNA from these two cell types was performed as part of the modENCODE project over a decade ago and revealed that they share a number of gene expression features. Here, we expand on these earlier studies by using deep-coverage RNA-sequencing approaches to investigate the transcriptional profile in Kc and S2 cells in detail. Comparison of the transcriptomes reveals that ∼75% of the 13,919 annotated genes are expressed at a detectable level in at least one of the cell lines, with the majority of these genes expressed at high levels in both cell lines. Despite the overall similarity of the transcriptional landscape in the two cell types, 2,588 differentially expressed genes are identified. Many of the genes with the largest fold change are known only by their "CG" designations, indicating that the molecular control of Kc and S2 cell identity may be regulated in part by a cohort of relatively uncharacterized genes. Our data also indicate that both cell lines have distinct hemocyte-like identities, but share active signaling pathways and express a number of genes in the network responsible for dorsal-ventral patterning of the early embryo.

Molecular mechanism of hyperactive tooth root formation in oculo-facio-cardio-dental syndrome

Mutations in the B-cell lymphoma 6 (BCL6) interacting corepressor (BCOR) cause oculo-facio-cardio-dental (OFCD) syndrome, a rare X-linked dominant condition that includes dental radiculomegaly among other characteristics. BCOR regulates downstream genes via BCL6 as a transcriptional corepressor. However, the molecular mechanism underlying the occurrence of radiculomegaly is still unknown. Thus, this study was aimed at identifying BCOR-regulated genetic pathways in radiculomegaly. The microarray profile of affected tissues revealed that the gene-specific transcriptional factors group, wherein nucleus factor 1B, distal-less homeobox 5, and zinc finger protein multitype 2 (ZFPM2) were the most upregulated, was significantly expressed in periodontal ligament (PDL) cells of the diseased patient with a frameshift mutation (c.3668delC) in BCOR. Wild-type BCOR overexpression in human periodontal ligament fibroblasts cells significantly hampered cellular proliferation and ZFPM2 mRNA downregulation. Promoter binding assays showed that wild-type BCOR was recruited in the BCL6 binding of the ZFPM2 promoter region after immunoprecipitation, while mutant BCOR, which was the same genotype as of our patient, failed to recruit these promoter regions. Knockdown of ZFPM2 expression in mutant PDL cells significantly reduced cellular proliferation as well as mRNA expression of alkaline phosphatase, an important marker of odontoblasts and cementoblasts. Collectively, our findings suggest that BCOR mutation-induced ZFPM2 regulation via BCL6 possibly contributes to hyperactive root formation in OFCD syndrome. Clinical data from patients with rare genetic diseases may aid in furthering the understanding of the mechanism controlling the final root length.

Bombyx mori U-shaped regulates the melanization cascade and immune response via binding with the Lozenge protein

Zinc finger protein, an important transcription factor, regulates gene expression associated with various physiological and pathological processes. U-shaped, belong to the Friend of GATA (FOG) transcription factor, plays a crucial role in hematopoiesis by interacting with the GATA transcription factor as a co-factor. However, little is known about its functions in insects. In the present study, a U-shaped cDNA was identified and characterized from the silkworm Bombyx mori and its potential roles in innate immunity investigated. The predicted silkworm U-shaped amino acid sequence contained a classical nuclear localization signal (NLS) motif "GESSPKRRRR" at position 450-459, and arginine residues at position 456 and 478 are the critical sites of the NLS. U-shaped mRNA was detected in all tested tissues of the B. mori; however, the highest levels were found in the hemocytes. U-shaped mRNA expression levels were upregulated in the hemocyte after the Escherichia coli and Staphylococcus aureus challenge. Furthermore, U-shaped knockdown significantly reduced the melanization process and suppressed the expression of melanization-associated genes, including PPO1, PPO2, PPAE and BAEE. In addition, U-shaped interacts with Lozenge protein to regulate the innate immune response of the insect. Our results revealed that U-shaped binds directly to Lozenge protein to modulate the melanization process and innate immune responses in silkworm.

A novel Ush transcription factor involving in hematopoiesis of Eriocheir sinensis

The FOG transcriptional factor is a co-regulator that recognizes and binds to the GATA N-terminal zinc-finger domain and participates in hemocyte production and differentiation. In this study, an FOG-like gene, Ush, was characterized from Eriocheir sinensis, which consists of an 897 bp full-length open reading frame, encoding a polypeptide of 298 amino acids with four ZnF_C2H2 domains. The EsUsh mRNA transcripts were mainly expressed in the hematopoietic tissue (HPT) and hemocytes, and were significantly higher in hyalinocytes than semi-granulocytes and granulocytes, which were separated by Percoll gradient centrifugation. The transcription levels of EsUsh were found to be significantly upregulated in HPT, but downregulated in hemocytes after exsanguination. By using flow cytometry to determine the percentage of hemocyte sub-population after exsanguination, the percentage of hyalinocytes was found to significantly downregulated, while the percentage of granulocytes was significantly upregulated. Silencing EsUsh by dsRNA interference significantly decreased the percentage of hyalinocytes and small granulocytes, and increased the percentage of medium granulocytes and large granulocytes. Such findings suggest that EsUsh might be involved in hemocyte production and differentiation, especially in promoting hyalinocyte formation and limiting granulocyte generation and differentiation.

DNA binding protein CgIkaros-like regulates the proliferation of agranulocytes and granulocytes in oyster (Crassostrea gigas)

DNA-binding protein Ikaros is a major determinant of haematopoietic lineage, especially in the development, differentiation and proliferation of lymphocytes. In the present study, a Ikaros homologue (designed as CgIkaros-like) was identified and characterized as a vital determinant in the proliferation of haemocytes during haematopoiesis of Pacific oyster Crassostrea gigas. The complete coding sequence of CgIkaros-like was of 1329 bp encoding a predicted polypeptide of 442 amino acids with four ZnF regions, locating at the C-terminus and N-terminus respectively. The highest expression level of CgIkaros-like mRNA was found in gills, followed by haemocytes and gonad. The mRNA transcripts of CgIkaros-like could be detected in all the haemocytes with higher abundance in semi-granulocytes and agranulocytes. CgIkaros-like protein was localized in both of cytoplasm and nucleus with higher abundance in nucleus of oyster haemocytes. The mRNA and protein expression levels of agranulocyte marker CgCD9, granulocyte marker CgAATase, cell cycle related gene CgCDK2, Notch receptor CgNotch and Notch target gene CgHes1 all increased significantly (p < 0.05) after CgIkaros-like was interfered by siRNAs, which were about 27.33-, 2.63-, 24.34-, 4.45- and 6.08-fold of that in the siRNA-NC control group, respectively. While the transcripts of CgGATA3 and CgRunx did not change significantly after CgIkaros-like was interfered. These results demonstrated that CgIkaros-like functioned as a transcription factor combined with Notch pathway to mediate CgCDK2 and regulate the proliferation of oyster haemocytes.

Involvement of Cis-Acting Elements in Molecular Regulation of JH-Mediated Vitellogenin Gene 2 of Female Periplaneta americana

Vitellogenins (Vgs) are yolk protein precursors that are regulated by juvenile hormone (JH) and/or 20-hydroxyecdysone (20E) in insects. JH acts as the principal gonadotropin that stimulates vitellogenesis in hemimetabolous insects. In this study, we cloned and characterized the Periplaneta americana Vitellogenin 2 (Vg2) promoter. Multiple sites for putative transcription factor binding were predicted for the 1,804 bp Vg2 promoter region, such as the Broad-Complex, ecdysone response element (EcRE), GATA, Hairy, JH response element (JHRE), and Methoprene (Met)-binding motif, among others. Luciferase reporter assay has identified that construct -177 bp is enough to support JH III induction but not 20E suppression. This 38 bp region (from -177 to -139 bp) contains two conserved response element half-sites separated by 2 nucleotides spacer (DR2) and is designated as Vg2RE (^-168GAGTCACGGAGTCGCCGCTG^-149). Mutation assay and luciferase assay data using mutated constructs verified the crucial role of G residues in Vg2RE for binding the isolated fat body nuclear protein. In Sf9 cells, a luciferase reporter placed under the control of a minimal promoter containing Vg2RE was induced by JH III in a dose- and time-dependent manner. Nuclear proteins isolated from previtellogenic female fat body cells bound to Vg2RE, and this binding was outcompeted by a 50-fold excess of cold Drosophila melanogaster DR4 and Galleria mellonella JH binding protein response elements (Chorion factor-I/Ultraspiracle). Affinity pull-down experiment with nuclear extracts of previtellogenic female fat body, using 31-bp probe Vg2RE as bait, yielded a 71 kDa candidate nuclear protein that may mediate the regulatory action of the JH III.

Variation in Pleiotropic Hub Gene Expression Is Associated with Interspecific Differences in Head Shape and Eye Size in Drosophila

Revealing the mechanisms underlying the breathtaking morphological diversity observed in nature is a major challenge in Biology. It has been established that recurrent mutations in hotspot genes cause the repeated evolution of morphological traits, such as body pigmentation or the gain and loss of structures. To date, however, it remains elusive whether hotspot genes contribute to natural variation in the size and shape of organs. As natural variation in head morphology is pervasive in Drosophila, we studied the molecular and developmental basis of differences in compound eye size and head shape in two closely related Drosophila species. We show differences in the progression of retinal differentiation between species and we applied comparative transcriptomics and chromatin accessibility data to identify the GATA transcription factor Pannier (Pnr) as central factor associated with these differences. Although the genetic manipulation of Pnr affected multiple aspects of dorsal head development, the effect of natural variation is restricted to a subset of the phenotypic space. We present data suggesting that this developmental constraint is caused by the coevolution of expression of pnr and its cofactor u-shaped (ush). We propose that natural variation in expression or function of highly connected developmental regulators with pleiotropic functions is a major driver for morphological evolution and we discuss implications on gene regulatory network evolution. In comparison to previous findings, our data strongly suggest that evolutionary hotspots are not the only contributors to the repeated evolution of eye size and head shape in Drosophila.

Ush regulates hemocyte-specific gene expression, fatty acid metabolism and cell cycle progression and cooperates with dNuRD to orchestrate hematopoiesis

The generation of lineage-specific gene expression programmes that alter proliferation capacity, metabolic profile and cell type-specific functions during differentiation from multipotent stem cells to specialised cell types is crucial for development. During differentiation gene expression programmes are dynamically modulated by a complex interplay between sequence-specific transcription factors, associated cofactors and epigenetic regulators. Here, we study U-shaped (Ush), a multi-zinc finger protein that maintains the multipotency of stem cell-like hemocyte progenitors during Drosophila hematopoiesis. Using genomewide approaches we reveal that Ush binds to promoters and enhancers and that it controls the expression of three gene classes that encode proteins relevant to stem cell-like functions and differentiation: cell cycle regulators, key metabolic enzymes and proteins conferring specific functions of differentiated hemocytes. We employ complementary biochemical approaches to characterise the molecular mechanisms of Ush-mediated gene regulation. We uncover distinct Ush isoforms one of which binds the Nucleosome Remodeling and Deacetylation (NuRD) complex using an evolutionary conserved peptide motif. Remarkably, the Ush/NuRD complex specifically contributes to the repression of lineage-specific genes but does not impact the expression of cell cycle regulators or metabolic genes. This reveals a mechanism that enables specific and concerted modulation of functionally related portions of a wider gene expression programme. Finally, we use genetic assays to demonstrate that Ush and NuRD regulate enhancer activity during hemocyte differentiation in vivo and that both cooperate to suppress the differentiation of lamellocytes, a highly specialised blood cell type. Our findings reveal that Ush coordinates proliferation, metabolism and cell type-specific activities by isoform-specific cooperation with an epigenetic regulator.

Drosophila Hox genes induce melanized pseudo-tumors when misexpressed in hemocytes

Hox genes are early determinants of cell identity along the anterior–posterior body axis across bilaterians. Several late non-homeotic functions of Hox genes have emerged in a variety of processes involved in organogenesis in several organisms, including mammals. Several studies have reported the misexpression of Hox genes in a variety of malignancies including acute myeloid leukemia. The Hox genes Dfd, Ubx, abd-A and Abd-B were overexpressed via the UAS-Gal4 system using Cg-Gal4, Lsp2-Gal4, He-Gal4 and HmlD3-Gal4 as specific drivers. Genetic interaction was tested by bringing overexpression lines in heterozygous mutant backgrounds of Polycomb and trithorax group factors. Larvae were visually scored for melanized bodies. Circulating hemocytes were quantified and tested for differentiation. Pupal lethality was assessed. Expression of Dfd, Ubx and abd-A, but not Abd-B in the hematopoietic compartment of Drosophila led to the appearance of circulating melanized bodies, an increase in cell number, cell-autonomous proliferation, and differentiation of hemocytes. Pupal lethality and melanized pseudo-tumors were suppressed in Psc¹ and esc² backgrounds while polycomb group member mutations Pc¹ and Su(z)12³ and trithorax group member mutation TrlR⁸⁵ enhanced the phenotype. Dfd, Ubx and abd-A are leukemogenic. Mutations in Polycomb and trithorax group members modulate the leukemogenic phenotype. Our RNAseq of Cg-Gal4 > UAS-abd-A hemocytes may contain genes important to Hox gene induced leukemias.

A functional genomics screen identifying blood cell development genes in Drosophila by undergraduates participating in a course-based research experience

Undergraduate students participating in the UCLA Undergraduate Research Consortium for Functional Genomics (URCFG) have conducted a two-phased screen using RNA interference (RNAi) in combination with fluorescent reporter proteins to identify genes important for hematopoiesis in Drosophila. This screen disrupted the function of approximately 3500 genes and identified 137 candidate genes for which loss of function leads to observable changes in the hematopoietic development. Targeting RNAi to maturing, progenitor, and regulatory cell types identified key subsets that either limit or promote blood cell maturation. Bioinformatic analysis reveals gene enrichment in several previously uncharacterized areas, including RNA processing and export and vesicular trafficking. Lastly, the participation of students in this course-based undergraduate research experience (CURE) correlated with increased learning gains across several areas, as well as increased STEM retention, indicating that authentic, student-driven research in the form of a CURE represents an impactful and enriching pedagogical approach.

The Role of Lozenge in Drosophila Hematopoiesis

Drosophila hematopoiesis is comparable to mammalian differentiation of myeloid lineages, and therefore, has been a useful model organism in illustrating the molecular and genetic basis for hematopoiesis. Multiple novel regulators and signals have been uncovered using the tools of Drosophila genetics. A Runt domain protein, lozenge, is one of the first players recognized and closely studied in the hematopoietic lineage specification. Here, we explore the role of lozenge in determination of prohemocytes into a special class of hemocyte, namely the crystal cell, and discuss molecules and signals controlling the lozenge function and its implication in immunity and stress response. Given the highly conserved nature of Runt domain in both invertebrates and vertebrates, studies in Drosophila will enlighten our perspectives on Runx-mediated development and pathologies.

Beadex, a homologue of the vertebrate LIM domain only protein, is a novel regulator of crystal cell development in Drosophila melanogaster

Haematopoiesis is a complex process in which the regulatory mechanisms of several implicated transcription factors remain uncertain. Drosophila melanogaster is an excellent model to resolve the unanswered questions about the blood cell development. This study describes the role of Beadex, a Drosophila homologue of LIM domain only 2 (LMO2), in haematopoiesis. Mutants of Beadex were analysed for blood cell abnormalities. Crystal cells, a subset of haemocytes, were significantly more in Beadex hypermorphic flies. Similarly, Beadex misexpression in prohemocytes altered the crystal cell numbers. Stage-specific misexpression analyses demonstrated that Beadex functions after the prohemocytes enter the crystal cell lineage. We also discovered that Pannier-U-shaped complex is a negative regulator of the crystal cell differentiation and is possibly negatively regulated by Beadex through its interaction with Pannier. We, therefore, suggest the mechanism of two novel regulators of crystal cell specification-Beadex and Pannier-during Drosophila haematopoiesis.

microRNA Profiling in Glaucoma Eyes With Varying Degrees of Optic Neuropathy by Using Next-Generation Sequencing

Purpose

To explore the microRNA (miRNA) profile and its putative role in glaucomatous optic neuropathy by using next-generation sequencing.

Methods

Aqueous humor (AH) samples were collected from 19 primary open-angle glaucoma (POAG) eyes and 17 cataract eyes before surgery. Next-generation sequencing was performed for RNA samples extracted from 18 AH samples, and the bioinformatics approach was applied for samples with adequate clean data output. The other 18 samples were used for quantitative PCR validation of sequencing results.

Results

In total, 12 (six POAG and six cataract controls) samples with sufficient clean data output after sequencing were used for further data analysis. Four hundred sixty-six and 480 mature miRNAs were detected in the POAG and cataract control groups, respectively. Among them, 164 miRNAs were detected in all POAG samples, and 96 miRNAs were detected in all cataract control samples. Furthermore, 88 miRNAs were identified as differently expressed between POAG and cataract control eyes. In addition, 16 miRNAs were differently expressed between POAG eyes with severe visual field damage and eyes with moderate visual field damage. This differential expression was predicted to regulate thiamine metabolism, purine metabolism, and transcriptional misregulation. Relative expression patterns of hsa-miR-184, hsa-miR-486-5p, and hsa-miR-93-5p were confirmed by quantitative PCR.

Conclusions

This study comprehensively demonstrated the miRNA expression profile in the AH of POAG eyes, especially the differential expression of miRNA in eyes with varying degrees of visual field damage, which, together with the underlying miRNA-related pathways, indicate new targets for the pathogenesis and progression of POAG.

Drosophila as a Genetic Model for Hematopoiesis

In this FlyBook chapter, we present a survey of the current literature on the development of the hematopoietic system in Drosophila The Drosophila blood system consists entirely of cells that function in innate immunity, tissue integrity, wound healing, and various forms of stress response, and are therefore functionally similar to myeloid cells in mammals. The primary cell types are specialized for phagocytic, melanization, and encapsulation functions. As in mammalian systems, multiple sites of hematopoiesis are evident in Drosophila and the mechanisms involved in this process employ many of the same molecular strategies that exemplify blood development in humans. Drosophila blood progenitors respond to internal and external stress by coopting developmental pathways that involve both local and systemic signals. An important goal of these Drosophila studies is to develop the tools and mechanisms critical to further our understanding of human hematopoiesis during homeostasis and dysfunction.

Hedgehog signaling from the Posterior Signaling Center maintains U-shaped expression and a prohemocyte population in Drosophila

Hematopoietic progenitor choice between multipotency and differentiation is tightly regulated by intrinsic factors and extrinsic signals from the surrounding microenvironment. The Drosophila melanogaster hematopoietic lymph gland has emerged as a powerful tool to investigate mechanisms that regulate hematopoietic progenitor choice in vivo. The lymph gland contains progenitor cells, which share key characteristics with mammalian hematopoietic progenitors such as quiescence, multipotency and niche-dependence. The lymph gland is zonally arranged, with progenitors located in medullary zone, differentiating cells in the cortical zone, and the stem cell niche or Posterior Signaling Center (PSC) residing at the base of the medullary zone (MZ). This arrangement facilitates investigations into how signaling from the microenvironment controls progenitor choice. The Drosophila Friend of GATA transcriptional regulator, U-shaped, is a conserved hematopoietic regulator. To identify additional novel intrinsic and extrinsic regulators that interface with U-shaped to control hematopoiesis, we conducted an in vivo screen for factors that genetically interact with u-shaped. Smoothened, a downstream effector of Hedgehog signaling, was one of the factors identified in the screen. Here we report our studies that characterized the relationship between Smoothened and U-shaped. We showed that the PSC and Hedgehog signaling are required for U-shaped expression and that U-shaped is an important intrinsic progenitor regulator. These observations identify a potential link between the progenitor regulatory machinery and extrinsic signals from the PSC. Furthermore, we showed that both Hedgehog signaling and the PSC are required to maintain a subpopulation of progenitors. This led to a delineation of PSC-dependent versus PSC-independent progenitors and provided further evidence that the MZ progenitor population is heterogeneous. Overall, we have identified a connection between a conserved hematopoietic master regulator and a putative stem cell niche, which adds to our understanding of how signals from the microenvironment regulate progenitor multipotency.

Macrophage Functions in Tissue Patterning and Disease: New Insights from the Fly

Macrophages are multifunctional innate immune cells that seed all tissues within the body and play disparate roles throughout development and in adult tissues, both in health and disease. Their complex developmental origins and many of their functions are being deciphered in mammalian tissues, but opportunities for live imaging and the genetic tractability of Drosophila are offering complementary insights into how these fascinating cells integrate a multitude of guidance cues to fulfill their many tasks and migrate to distant sites to either direct developmental patterning or raise an inflammatory response.

Haploinsufficiency for ANKRD11-flanking genes makes the difference between KBG and 16q24.3 microdeletion syndromes: 12 new cases

16q24 deletion involving the ANKRD11 gene, ranging from 137 kb to 2 Mb, have been associated with a microdeletion syndrome characterized by variable cognitive impairment, autism spectrum disorder, facial dysmorphisms with dental anomalies, brain abnormalities essentially affecting the corpus callosum and short stature. On the other hand, patients carrying either deletions encompassing solely ANKRD11 or its loss-of-function variants were reported in association with the KBG syndrome, characterized by a very similar phenotype, including mild-to-moderate intellectual disability, short stature and macrodontia of upper incisors, with inter and intrafamilial variability. To assess whether the haploinsufficiency of ANKRD11-flanking genes, such as ZFPM1, CDH15 and ZNF778, contributed to either the severity of the neurological impairment or was associated with other clinical features, we collected 12 new cases with a 16q24.2q24.3 deletion (de novo in 11 cases), ranging from 343 kb to 2.3 Mb. In 11 of them, the deletion involved the ANKRD11 gene, whereas in 1 case only flanking genes upstream to it were deleted. By comparing the clinical and genetic features of our patients with those previously reported, we show that the severity of the neurological phenotype and the frequency of congenital heart defects characterize the deletions that, besides ANKRD11, contain ZFPM1, CDH15 and ZNF778 as well. Moreover, the presence of thrombocytopenia and astigmatism should be taken into account to distinguish between 16q24 microdeletion syndrome and KBG syndrome. The single patient not deleted for ANKRD11, whose phenotype is characterized by milder psychomotor delay, cardiac congenital malformation, thrombocytopenia and astigmatism, confirms all this data.

Monocyte/Macrophage: NK Cell Cooperation-Old Tools for New Functions

Monocyte/macrophage and natural killer (NK) cells are partners from a phylogenetic standpoint of innate immune system development and its evolutionary progressive interaction with adaptive immunity. The equally conservative ways of development and differentiation of both invertebrate hemocytes and vertebrate macrophages are reviewed. Evolutionary conserved molecules occurring in macrophage receptors and effectors have been inherited by vertebrates after their common ancestor with invertebrates. Cytolytic functions of mammalian NK cells, which are rooted in immune cells of invertebrates, although certain NK cell receptors (NKRs) are mammalian new events, are characterized. Broad heterogeneity of macrophage and NK cell phenotypes that depends on surrounding microenvironment conditions and expression profiles of specific receptors and activation mechanisms of both cell types are discussed. The particular tissue specificity of macrophages and NK cells, as well as their plasticity and mechanisms of their polarization to different functional subtypes have been underlined. The chapter summarized studies revealing the specific molecular mechanisms and regulation of NK cells and macrophages that enable their highly specific cross-cooperation. Attention is given to the evolving role of human monocyte/macrophage and NK cell interaction in pathogenesis of hypersensitivity reaction-based disorders, including autoimmunity, as well as in cancer surveillance and progression.

The Role of GATA in Mammalian Reproduction

GATA transcription factors are emerging as critical players in mammalian reproductive development and function. GATA-4 contributes to fetal male gonadal development by regulating genes mediating Müllerian duct regression and the onset of testosterone production. GATA-2 expression appears to be sexually dimorphic being transiently expressed in the germ cell lineage of the fetal ovary but not the fetal testis. In the reproductive system, GATA-1 is exclusively expressed in Sertoli cells at specific seminiferous tubule stages. In addition, GATA-4 and GATA-6 are localized primary to ovarian and testicular somatic cells. The majority of cell transfection studies demonstrate that GATA-1 and GATA-4 can stimulate inhibin subunit gene promoter constructs. Other studies provide strong evidence that GATA-4 and GATA-6 can activate genes mediating gonadal cell steroidogenesis. GATA-2 and GATA-3 are found in pituitary and placental cells and can regulate alpha-glycoprotein subunit gene expression. Gonadal expression and activation of GATAs appear to be regulated in part by gonadotropin signaling via the cyclic AMP-protein kinase A pathway. This review will cover the current knowledge regarding GATA expression and function at all levels of the reproductive axis.

Revisiting the role of the Gcm transcription factor, from master regulator to Swiss army knife

Master genes are known to induce the differentiation of a multipotent cell into a specific cell type. These molecules are often transcription factors that switch on the regulatory cascade that triggers cell specification. Gcm was first described as the master gene of the glial fate in Drosophila as it induces the differentiation of neuroblasts into glia in the developing nervous system. Later on, Gcm was also shown to regulate the differentiation of blood, tendon and peritracheal cells as well as that of neuronal subsets. Thus, the glial master gene is used in at least 4 additional systems to promote differentiation. To understand the numerous roles of Gcm, we recently reported a genome-wide screen of Gcm direct targets in the Drosophila embryo. This screen provided new insight into the role and mode of action of this powerful transcription factor, notably on the interactions between Gcm and major differentiation pathways such as the Hedgehog, Notch and JAK/STAT. Here, we discuss the mode of action of Gcm in the different systems, we present new tissues that require Gcm and we revise the concept of 'master gene'.

The Friend of GATA Transcriptional Co-Regulator, U-Shaped, Is a Downstream Antagonist of Dorsal-Driven Prohemocyte Differentiation in Drosophila

Recent studies suggest that mammalian hematopoietic stem and progenitor cells (HSPCs) respond directly to infection and inflammatory signaling. These signaling pathways also regulate HSPCs during steady-state conditions (absence of infection), and dysregulation may lead to cancer or age-related loss of progenitor repopulation capacity. Toll-like receptors (TLRs) are a major class of pathogen recognition receptors, and are expressed on the surface of immune effector cells and HSPCs. TLR/NF-κB activation promotes HSPCs differentiation; however, the mechanisms by which this signaling pathway alters the intrinsic transcriptional landscape are not well understood. Although Drosophila prohemocytes are the functional equivalent of mammalian HSPCs, a prohemocyte-specific function for Toll signaling has not been reported. Using Drosophila transgenics, we identified prohemocyte-specific roles for Toll pathway members, Dorsal and Cactus. We showed that Dorsal is required to limit the size of the progenitor pool. Additionally, we showed that activation of Toll signaling in prohemocytes drives differentiation in a manner that is analogous to TLR/NF-κB-driven HSPC differentiation. This was accomplished by showing that over-expression of Dorsal, or knockdown of Cactus, promotes differentiation. We also investigated whether Dorsal and Cactus control prohemocyte differentiation by regulating a key intrinsic prohemocyte factor, U-shaped (Ush), which is known to promote multipotency and block differentiation. We showed that Dorsal repressed Ush expression levels to promote differentiation, whereas Cactus maintained Ush levels to block differentiation. Additionally, we showed that another Toll antagonist, Lesswright, also maintained the level of Ush to block differentiation and promote proliferative quiescence. Collectively, these results identify a novel role for Ush as a downstream target of Toll signaling.

Macrophages and cellular immunity in Drosophila melanogaster

The invertebrate Drosophila melanogaster has been a powerful model for understanding blood cell development and immunity. Drosophila is a holometabolous insect, which transitions through a series of life stages from embryo, larva and pupa to adulthood. In spite of this, remarkable parallels exist between Drosophila and vertebrate macrophages, both in terms of development and function. More than 90% of Drosophila blood cells (hemocytes) are macrophages (plasmatocytes), making this highly tractable genetic system attractive for studying a variety of questions in macrophage biology. In vertebrates, recent findings revealed that macrophages have two independent origins: self-renewing macrophages, which reside and proliferate in local microenvironments in a variety of tissues, and macrophages of the monocyte lineage, which derive from hematopoietic stem or progenitor cells. Like vertebrates, Drosophila possesses two macrophage lineages with a conserved dual ontogeny. These parallels allow us to take advantage of the Drosophila model when investigating macrophage lineage specification, maintenance and amplification, and the induction of macrophages and their progenitors by local microenvironments and systemic cues. Beyond macrophage development, Drosophila further serves as a paradigm for understanding the mechanisms underlying macrophage function and cellular immunity in infection, tissue homeostasis and cancer, throughout development and adult life.

Functional Conservation of the Glide/Gcm Regulatory Network Controlling Glia, Hemocyte, and Tendon Cell Differentiation in Drosophila

High-throughput screens allow us to understand how transcription factors trigger developmental processes, including cell specification. A major challenge is identification of their binding sites because feedback loops and homeostatic interactions may mask the direct impact of those factors in transcriptome analyses. Moreover, this approach dissects the downstream signaling cascades and facilitates identification of conserved transcriptional programs. Here we show the results and the validation of a DNA adenine methyltransferase identification (DamID) genome-wide screen that identifies the direct targets of Glide/Gcm, a potent transcription factor that controls glia, hemocyte, and tendon cell differentiation in Drosophila. The screen identifies many genes that had not been previously associated with Glide/Gcm and highlights three major signaling pathways interacting with Glide/Gcm: Notch, Hedgehog, and JAK/STAT, which all involve feedback loops. Furthermore, the screen identifies effector molecules that are necessary for cell-cell interactions during late developmental processes and/or in ontogeny. Typically, immunoglobulin (Ig) domain-containing proteins control cell adhesion and axonal navigation. This shows that early and transiently expressed fate determinants not only control other transcription factors that, in turn, implement a specific developmental program but also directly affect late developmental events and cell function. Finally, while the mammalian genome contains two orthologous Gcm genes, their function has been demonstrated in vertebrate-specific tissues, placenta, and parathyroid glands, begging questions on the evolutionary conservation of the Gcm cascade in higher organisms. Here we provide the first evidence for the conservation of Gcm direct targets in humans. In sum, this work uncovers novel aspects of cell specification and sets the basis for further understanding of the role of conserved Gcm gene regulatory cascades.

Whole-Genome Sequencing and Integrative Genomic Analysis Approach on Two 22q11.2 Deletion Syndrome Family Trios for Genotype to Phenotype Correlations

The 22q11.2 deletion syndrome (22q11DS) affects 1:4,000 live births and presents with highly variable phenotype expressivity. In this study, we developed an analytical approach utilizing whole-genome sequencing (WGS) and integrative analysis to discover genetic modifiers. Our pipeline combined available tools in order to prioritize rare, predicted deleterious, coding and noncoding single-nucleotide variants (SNVs), and insertion/deletions from WGS. We sequenced two unrelated probands with 22q11DS, with contrasting clinical findings, and their unaffected parents. Proband P1 had cognitive impairment, psychotic episodes, anxiety, and tetralogy of Fallot (TOF), whereas proband P2 had juvenile rheumatoid arthritis but no other major clinical findings. In P1, we identified common variants in COMT and PRODH on 22q11.2 as well as rare potentially deleterious DNA variants in other behavioral/neurocognitive genes. We also identified a de novo SNV in ADNP2 (NM_014913.3:c.2243G>C), encoding a neuroprotective protein that may be involved in behavioral disorders. In P2, we identified a novel nonsynonymous SNV in ZFPM2 (NM_012082.3:c.1576C>T), a known causative gene for TOF, which may act as a protective variant downstream of TBX1, haploinsufficiency of which is responsible for congenital heart disease in individuals with 22q11DS.

Drosophila blood cells and their role in immune responses

Drosophila melanogaster has been extensively used to study the humoral arm of innate immunity because of the developmental and functional parallels with mammalian innate immunity. However, the fly cellular response to infection is far less understood. Investigative work on Drosophila haemocytes, the immunosurveillance cells of the insect, has revealed that they fulfil roles similar to mammalian monocytes and macrophages. They respond to wound signals and orchestrate the coagulation response. In addition, they phagocytose and encapsulate invading pathogens, and clear up apoptotic bodies controlling inflammation. This review briefly describes the Drosophila haematopoietic system and discusses what is currently known about the contribution of haemocytes to the immune response upon infection and wounding, during all stages of development.

Antioxidants maintain E-cadherin levels to limit Drosophila prohemocyte differentiation

Mitochondrial reactive oxygen species (ROS) regulate a variety of biological processes by networking with signal transduction pathways to maintain homeostasis and support adaptation to stress. In this capacity, ROS have been shown to promote the differentiation of progenitor cells, including mammalian embryonic and hematopoietic stem cells and Drosophila hematopoietic progenitors (prohemocytes). However, many questions remain about how ROS alter the regulatory machinery to promote progenitor differentiation. Here, we provide evidence for the hypothesis that ROS reduce E-cadherin levels to promote Drosophila prohemocyte differentiation. Specifically, we show that knockdown of the antioxidants, Superoxide dismutatase 2 and Catalase reduce E-cadherin protein levels prior to the loss of Odd-skipped-expressing prohemocytes. Additionally, over-expression of E-cadherin limits prohemocyte differentiation resulting from paraquat-induced oxidative stress. Furthermore, two established targets of ROS, Enhancer of Polycomb and FOS, control the level of E-cadherin protein expression. Finally, we show that knockdown of either Superoxide dismutatase 2 or Catalase leads to an increase in the E-cadherin repressor, Serpent. As a result, antioxidants and targets of ROS can control E-cadherin protein levels, and over-expression of E-cadherin can ameliorate the prohemocyte response to oxidative stress. Collectively, these data strongly suggest that ROS promote differentiation by reducing E-cadherin levels. In mammalian systems, ROS promote embryonic stem cell differentiation, whereas E-cadherin blocks differentiation. However, it is not known if elevated ROS reduce E-cadherin to promote embryonic stem cell differentiation. Thus, our findings may have identified an important mechanism by which ROS promote stem/progenitor cell differentiation.

The identification and structure of an N-terminal PR domain show that FOG1 is a member of the PRDM family of proteins

FOG1 is a transcriptional regulator that acts in concert with the hematopoietic master regulator GATA1 to coordinate the differentiation of platelets and erythrocytes. Despite considerable effort, however, the mechanisms through which FOG1 regulates gene expression are only partially understood. Here we report the discovery of a previously unrecognized domain in FOG1: a PR (PRD-BF1 and RIZ) domain that is distantly related in sequence to the SET domains that are found in many histone methyltransferases. We have used NMR spectroscopy to determine the solution structure of this domain, revealing that the domain shares close structural similarity with SET domains. Titration with S-adenosyl-L-homocysteine, the cofactor product synonymous with SET domain methyltransferase activity, indicated that the FOG PR domain is not, however, likely to function as a methyltransferase in the same fashion. We also sought to define the function of this domain using both pulldown experiments and gel shift assays. However, neither pulldowns from mammalian nuclear extracts nor yeast two-hybrid assays reproducibly revealed binding partners, and we were unable to detect nucleic-acid-binding activity in this domain using our high-diversity Pentaprobe oligonucleotides. Overall, our data demonstrate that FOG1 is a member of the PRDM (PR domain containing proteins, with zinc fingers) family of transcriptional regulators. The function of many PR domains, however, remains somewhat enigmatic for the time being.

Drosophila as a model for the two myeloid blood cell systems in vertebrates

Fish, mice, and humans rely on two coexisting myeloid blood cell systems. One is sustained by hematopoietic progenitor cells, which reside in specialized microenvironments (niches) in hematopoietic organs and give rise to cells of the monocyte lineage. The other system corresponds to the independent lineage of self-renewing tissue macrophages, which colonize organs during embryonic development and are maintained during later life by proliferation in local tissue microenvironments. However, little is known about the nature of these microenvironments and their regulation. Moreover, many vertebrate tissues contain a mix of both tissue-resident and monocyte-derived macrophages, posing a challenge to the study of lineage-specific regulatory mechanisms and function. This review highlights how research in the simple model organism Drosophila melanogaster can address many of these outstanding questions in the field. Drawing parallels between hematopoiesis in Drosophila and vertebrates, we illustrate the evolutionary conservation of the two myeloid systems across animal phyla. Much like vertebrates, Drosophila possesses a lineage of self-renewing tissue-resident macrophages, which we refer to as tissue hemocytes, as well as a "definitive" lineage of macrophages that derive from hematopoiesis in the progenitor-based lymph gland. We summarize key findings from Drosophila hematopoiesis that illustrate how local microenvironments, systemic signals, immune challenges, and nervous inputs regulate adaptive responses of tissue-resident macrophages and progenitor-based hematopoiesis to maximize fitness of the animal.

Drosophila as a model to study the role of blood cells in inflammation, innate immunity and cancer

Drosophila has a primitive yet effective blood system with three types of haemocytes which function throughout different developmental stages and environmental stimuli. Haemocytes play essential roles in tissue modeling during embryogenesis and morphogenesis, and also in innate immunity. The open circulatory system of Drosophila makes haemocytes ideal signal mediators to cells and tissues in response to events such as infection and wounding. The application of recently developed and sophisticated genetic tools to the relatively simple genome of Drosophila has made the fly a popular system for modeling human tumorigensis and metastasis. Drosophila is now used for screening and investigation of genes implicated in human leukemia and also in modeling development of solid tumors. This second line of research offers promising opportunities to determine the seemingly conflicting roles of blood cells in tumor progression and invasion. This review provides an overview of the signaling pathways conserved in Drosophila during haematopoiesis, haemostasis, innate immunity, wound healing and inflammation. We also review the most recent progress in the use of Drosophila as a cancer research model with an emphasis on the roles haemocytes can play in various cancer models and in the links between inflammation and cancer.

The cell-mediated immunity of Drosophila melanogaster: hemocyte lineages, immune compartments, microanatomy and regulation

In the animal kingdom, innate immunity is the first line of defense against invading pathogens. The dangers of microbial and parasitic attacks are countered by similar mechanisms, involving the prototypes of the cell-mediated immune responses, the phagocytosis and encapsulation. Work on Drosophila has played an important role in promoting an understanding of the basic mechanisms of phylogenetically conserved modules of innate immunity. The aim of this review is to survey the developments in the identification and functional definition of immune cell types and the immunological compartments of Drosophila melanogaster. We focus on the molecular and developmental aspects of the blood cell types and compartments, as well as the dynamics of blood cell development and the immune response. Further advances in the characterization of the innate immune mechanisms in Drosophila will provide basic clues to the understanding of the importance of the evolutionary conserved mechanisms of innate immune defenses in the animal kingdom.

Drosophila E-cadherin functions in hematopoietic progenitors to maintain multipotency and block differentiation

A fundamental question in stem cell biology concerns the regulatory strategies that control the choice between multipotency and differentiation. Drosophila blood progenitors or prohemocytes exhibit key stem cell characteristics, including multipotency, quiescence, and niche dependence. As a result, studies of Drosophila hematopoiesis have provided important insights into the molecular mechanisms that control these processes. Here, we show that E-cadherin is an important regulator of prohemocyte fate choice, maintaining prohemocyte multipotency and blocking differentiation. These functions are reminiscent of the role of E-cadherin in mammalian embryonic stem cells. We also show that mis-expression of E-cadherin in differentiating hemocytes disrupts the boundary between these cells and undifferentiated prohemocytes. Additionally, upregulation of E-cadherin in differentiating hemocytes increases the number of intermediate cell types expressing the prohemocyte marker, Patched. Furthermore, our studies indicate that the Drosophila GATA transcriptional co-factor, U-shaped, is required for E-cadherin expression. Consequently, E-cadherin is a downstream target of U-shaped in the maintenance of prohemocyte multipotency. In contrast, we showed that forced expression of the U-shaped GATA-binding partner, Serpent, repressed E-cadherin expression and promoted lamellocyte differentiation. Thus, U-shaped may maintain E-cadherin expression by blocking the inhibitory activity of Serpent. Collectively, these observations suggest that GATA:FOG complex formation regulates E-cadherin levels and, thereby, the choice between multipotency and differentiation. The work presented in this report further defines the molecular basis of prohemocyte cell fate choice, which will provide important insights into the mechanisms that govern stem cell biology.

FOG2 protein down-regulation by transforming growth factor-β1-induced microRNA-200b/c leads to Akt kinase activation and glomerular mesangial hypertrophy related to diabetic nephropathy

Glomerular hypertrophy is a hallmark of diabetic nephropathy. Akt kinase activated by transforming growth factor-β1 (TGF-β) plays an important role in glomerular mesangial hypertrophy. However, the mechanisms of Akt activation by TGF-β are not fully understood. Recently, miR-200 and its target FOG2 were reported to regulate the activity of phosphatidylinositol 3-kinase (the upstream activator of Akt) in insulin signaling. Here, we show that TGF-β activates Akt in glomerular mesangial cells by inducing miR-200b and miR-200c, both of which target FOG2, an inhibitor of phosphatidylinositol 3-kinase activation. FOG2 expression was reduced in the glomeruli of diabetic mice as well as TGF-β-treated mouse mesangial cells (MMC). FOG2 knockdown by siRNAs in MMC activated Akt and increased the protein content/cell ratio suggesting hypertrophy. A significant increase of miR-200b/c levels was detected in diabetic mouse glomeruli and TGF-β-treated MMC. Transfection of MMC with miR-200b/c mimics significantly decreased the expression of FOG2. Conversely, miR-200b/c inhibitors attenuated TGF-β-induced decrease in FOG2 expression. Furthermore, miR-200b/c mimics increased the protein content/cell ratio, whereas miR-200b/c inhibitors abrogated the TGF-β-induced increase in protein content/cell. In addition, down-regulation of FOG2 by miR-200b/c could activate not only Akt but also ERK, which was also through PI3K activation. These data suggest a new mechanism for TGF-β-induced Akt activation through FOG2 down-regulation by miR-200b/c, which can lead to glomerular mesangial hypertrophy in the progression of diabetic nephropathy.

Extracellular matrix-modulated Heartless signaling in Drosophila blood progenitors regulates their differentiation via a Ras/ETS/FOG pathway and target of rapamycin function

Maintenance of hematopoietic progenitors ensures a continuous supply of blood cells during the lifespan of an organism. Thus, understanding the molecular basis for progenitor maintenance is a continued focus of investigation. A large pool of undifferentiated blood progenitors are maintained in the Drosophila hematopoietic organ, the larval lymph gland, by a complex network of signaling pathways that are mediated by niche-, progenitor-, or differentiated hemocyte-derived signals. In this study we examined the function of the Drosophila fibroblast growth factor receptor (FGFR), Heartless, a critical regulator of early lymph gland progenitor specification in the late embryo, during larval lymph gland hematopoiesis. Activation of Heartless signaling in hemocyte progenitors by its two ligands, Pyramus and Thisbe, is both required and sufficient to induce progenitor differentiation and formation of the plasmatocyte-rich lymph gland cortical zone. We identify two transcriptional regulators that function downstream of Heartless signaling in lymph gland progenitors, the ETS protein, Pointed, and the Friend-of-GATA (FOG) protein, U-shaped, which are required for this Heartless-induced differentiation response. Furthermore, cross-talk of Heartless and target of rapamycin signaling in hemocyte progenitors is required for lamellocyte differentiation downstream of Thisbe-mediated Heartless activation. Finally, we identify the Drosophila heparan sulfate proteoglycan, Trol, as a critical negative regulator of Heartless ligand signaling in the lymph gland, demonstrating that sequestration of differentiation signals by the extracellular matrix is a unique mechanism employed in blood progenitor maintenance that is of potential relevance to many other stem cell niches.

Notch cooperates with Lozenge/Runx to lock haemocytes into a differentiation programme

The diverse functions of Notch signalling imply that it must elicit context-specific programmes of gene expression. With the aim of investigating how Notch drives cells to differentiate, we have used a genome-wide approach to identify direct Notch targets in Drosophila haemocytes (blood cells), where Notch promotes crystal cell differentiation. Many of the identified Notch-regulated enhancers contain Runx and GATA motifs, and we demonstrate that binding of the Runx protein Lozenge (Lz) is required for enhancers to be competent to respond to Notch. Functional studies of targets, such as klumpfuss (ERG/WT1 family) and pebbled/hindsight (RREB1 homologue), show that Notch acts both to prevent the cells adopting alternate cell fates and to promote morphological characteristics associated with crystal cell differentiation. Inappropriate activity of Klumpfuss perturbs the differentiation programme, resulting in melanotic tumours. Thus, by acting as a master regulator, Lz directs Notch to activate selectively a combination of target genes that correctly locks cells into the differentiation programme.

Combinatorial regulation of tissue specification by GATA and FOG factors

The development of complex organisms requires the formation of diverse cell types from common stem and progenitor cells. GATA family transcriptional regulators and their dedicated co-factors, termed Friend of GATA (FOG) proteins, control cell fate and differentiation in multiple tissue types from Drosophila to man. FOGs can both facilitate and antagonize GATA factor transcriptional regulation depending on the factor, cell, and even the specific gene target. In this review, we highlight recent studies that have elucidated mechanisms by which FOGs regulate GATA factor function and discuss how these factors use these diverse modes of gene regulation to control cell lineage specification throughout metazoans.

Signal transduction pathways, intrinsic regulators, and the control of cell fate choice

BACKGROUND

Information regarding changes in organismal status is transmitted to the stem cell regulatory machinery by a limited number of signal transduction pathways. Consequently, these pathways derive their functional specificity through interactions with stem cell intrinsic master regulators, notably transcription factors. Identifying the molecular underpinnings of these interactions is critical to understanding stem cell function.

SCOPE OF REVIEW

This review focuses on studies in Drosophila that identify the gene regulatory basis for interactions between three different signal transduction pathways and an intrinsic master transcriptional regulator in the context of hematopoietic stem-like cell fate choice. Specifically, the interface between the GATA:FOG regulatory complex and the JAK/STAT, BMP, and Hedgehog pathways is examined.

MAJOR CONCLUSIONS

The GATA:FOG complex coordinates information transmitted by at least three different signal transduction pathways as a means to control stem-like cell fate choice. This illustrates emerging principles concerning regulation of stem cell function and describes a gene regulatory link between changes in organismal status and stem cell response.

GENERAL SIGNIFICANCE

The Drosophila model system offers a powerful approach to identify the molecular basis of how stem cells receive, interpret, and then respond to changes in organismal status. This article is part of a Special Issue entitled: Biochemistry of Stem Cells.

Common variants at 9p21 and 8q22 are associated with increased susceptibility to optic nerve degeneration in glaucoma

Optic nerve degeneration caused by glaucoma is a leading cause of blindness worldwide. Patients affected by the normal-pressure form of glaucoma are more likely to harbor risk alleles for glaucoma-related optic nerve disease. We have performed a meta-analysis of two independent genome-wide association studies for primary open angle glaucoma (POAG) followed by a normal-pressure glaucoma (NPG, defined by intraocular pressure (IOP) less than 22 mmHg) subgroup analysis. The single-nucleotide polymorphisms that showed the most significant associations were tested for association with a second form of glaucoma, exfoliation-syndrome glaucoma. The overall meta-analysis of the GLAUGEN and NEIGHBOR dataset results (3,146 cases and 3,487 controls) identified significant associations between two loci and POAG: the CDKN2BAS region on 9p21 (rs2157719 [G], OR = 0.69 [95%CI 0.63-0.75], p = 1.86×10⁻¹⁸), and the SIX1/SIX6 region on chromosome 14q23 (rs10483727 [A], OR = 1.32 [95%CI 1.21-1.43], p = 3.87×10⁻¹¹). In sub-group analysis two loci were significantly associated with NPG: 9p21 containing the CDKN2BAS gene (rs2157719 [G], OR = 0.58 [95% CI 0.50-0.67], p = 1.17×10⁻¹²) and a probable regulatory region on 8q22 (rs284489 [G], OR = 0.62 [95% CI 0.53-0.72], p = 8.88×10⁻¹⁰). Both NPG loci were also nominally associated with a second type of glaucoma, exfoliation syndrome glaucoma (rs2157719 [G], OR = 0.59 [95% CI 0.41-0.87], p = 0.004 and rs284489 [G], OR = 0.76 [95% CI 0.54-1.06], p = 0.021), suggesting that these loci might contribute more generally to optic nerve degeneration in glaucoma. Because both loci influence transforming growth factor beta (TGF-beta) signaling, we performed a genomic pathway analysis that showed an association between the TGF-beta pathway and NPG (permuted p = 0.009). These results suggest that neuro-protective therapies targeting TGF-beta signaling could be effective for multiple forms of glaucoma.

New gene functions in megakaryopoiesis and platelet formation

Platelets are the second most abundant cell type in blood and are essential for maintaining haemostasis. Their count and volume are tightly controlled within narrow physiological ranges, but there is only limited understanding of the molecular processes controlling both traits. Here we carried out a high-powered meta-analysis of genome-wide association studies (GWAS) in up to 66,867 individuals of European ancestry, followed by extensive biological and functional assessment. We identified 68 genomic loci reliably associated with platelet count and volume mapping to established and putative novel regulators of megakaryopoiesis and platelet formation. These genes show megakaryocyte-specific gene expression patterns and extensive network connectivity. Using gene silencing in Danio rerio and Drosophila melanogaster, we identified 11 of the genes as novel regulators of blood cell formation. Taken together, our findings advance understanding of novel gene functions controlling fate-determining events during megakaryopoiesis and platelet formation, providing a new example of successful translation of GWAS to function.

Drosophila cellular immunity: a story of migration and adhesion

Research during the past 15 years has led to significant breakthroughs, providing evidence of a high degree of similarity between insect and mammalian innate immune responses, both humoural and cellular, and highlighting Drosophila melanogaster as a model system for studying the evolution of innate immunity. In a manner similar to cells of the mammalian monocyte and macrophage lineage, Drosophila immunosurveillance cells (haemocytes) have a number of roles. For example, they respond to wound signals, are involved in wound healing and contribute to the coagulation response. Moreover, they participate in the phagocytosis and encapsulation of invading pathogens, are involved in the removal of apoptotic bodies and produce components of the extracellular matrix. There are several reasons for using the Drosophila cellular immune response as a model to understand cell signalling during adhesion and migration in vivo: many genes involved in the regulation of Drosophila haematopoiesis and cellular immunity have been maintained across taxonomic groups ranging from flies to humans, many aspects of Drosophila and mammalian innate immunity seem to be conserved, and Drosophila is a simplified and well-studied genetic model system. In the present Commentary, we will discuss what is known about cellular adhesion and migration in the Drosophila cellular immune response, during both embryonic and larval development, and where possible compare it with related mechanisms in vertebrates.

Conditional ablation of Gata4 and Fog2 genes in mice reveals their distinct roles in mammalian sexual differentiation

Assembly of functioning testis and ovary requires a GATA4-FOG2 transcriptional complex. To define the separate roles for GATA4 and FOG2 proteins in sexual development of the testis we have ablated the corresponding genes in somatic gonadal cells. We have established that GATA4 is required for testis differentiation, for the expression of Dmrt1 gene, and for testis cord morphogenesis. While Sf1Cre-mediated excision of Gata4 permitted normal expression of most genes associated with embryonic testis development, gonadal loss of Fog2 resulted in an early partial block in male pathway and sex reversal. We have also determined that testis sexual differentiation is sensitive to the timing of GATA4 loss during embryogenesis. Our results now demonstrate that these two genes also have non-overlapping essential functions in testis development.

Odd-skipped maintains prohemocyte potency and blocks blood cell development in Drosophila

Studies using Drosophila have contributed significantly to our understanding of regulatory mechanisms that control stem cell fate choice. The Drosophila blood cell progenitor or prohemocyte shares important characteristics with mammalian hematopoietic stem cells, including quiescence, niche dependence, and the capacity to form all three fly blood cell types. This report extends our understanding of prohemocyte fate choice by showing that the zinc-finger protein Odd-skipped promotes multipotency and blocks differentiation. Odd-skipped was expressed in prohemocytes and downregulated in terminally differentiated plasmatocytes. Furthermore, Odd-skipped maintained the prohemocyte population and blocked differentiation of plasmatocytes and lamellocytes but not crystal cells. A previous study showed that Odd-skipped expression is downregulated by Decapentaplegic signaling. This report provides a functional basis for this regulator/target pair by suggesting that Decapentaplegic signaling limits Odd-skipped expression to promote prohemocyte differentiation. Overall, these studies are the basis for a gene regulatory model of prohemocyte cell fate choice.

JAK/STAT and the GATA factor Pannier control hemocyte maturation and differentiation in Drosophila

The lymph gland is the major site of hematopoiesis in Drosophila. During late larval stages three types of hemocytes are produced, plasmatocytes, crystal cells, and lamellocytes, and their differentiation is tightly controlled by conserved factors and signaling pathways. JAK/STAT is one of these pathways which have essential roles in vertebrate and fly hematopoiesis. We show that Stat has opposing cell-autonomous and non-autonomous functions in hemocyte differentiation. Using a clonal approach we established that loss of Stat in a set of prohemocytes in the cortical zone induces plasmatocyte maturation in adjacent hemocytes. Hemocytes lacking Stat fail to differentiate into plasmatocytes, indicating that Stat positively and cell-autonomously controls plasmatocyte differentiation. We also identified the GATA factor pannier (pnr) as a downstream target of Stat. By analyzing the phenotypes resulting from clonal loss and over-expression of pnr in lymph glands, we find that Pnr is positively regulated by Stat and specifically required for the differentiation of plasmatocytes. Stat and Pnr represent two essential factors controlling blood cell maturation in the developing lymph gland and exert their functions both in a cell-autonomous and non-cell-autonomous manner.

Drosophila models of cardiac disease

The fruit fly Drosophila melanogaster has emerged as a useful model for cardiac diseases, both developmental abnormalities and adult functional impairment. Using the tools of both classical and molecular genetics, the study of the developing fly heart has been instrumental in identifying the major signaling events of cardiac field formation, cardiomyocyte specification, and the formation of the functioning heart tube. The larval stage of fly cardiac development has become an important model system for testing isolated preparations of living hearts for the effects of biological and pharmacological compounds on cardiac activity. Meanwhile, the recent development of effective techniques to study adult cardiac performance in the fly has opened new uses for the Drosophila model system. The fly system is now being used to study long-term alterations in adult performance caused by factors such as diet, exercise, and normal aging. The fly is a unique and valuable system for the study of such complex, long-term interactions, as it is the only invertebrate genetic model system with a working heart developmentally homologous to the vertebrate heart. Thus, the fly model combines the advantages of invertebrate genetics (such as large populations, facile molecular genetic techniques, and short lifespan) with physiological measurement techniques that allow meaningful comparisons with data from vertebrate model systems. As such, the fly model is well situated to make important contributions to the understanding of complicated interactions between environmental factors and genetics in the long-term regulation of cardiac performance.