Differentiation In Drosophila Research Articles

Cytochrome c‐d regulates developmental apoptosis in the Drosophila retina

The role of cytochrome c (Cyt c) in caspase activation has largely been established from mammalian cell-culture studies, but much remains to be learned about its physiological relevance in situ. The role of Cyt c in invertebrates has been subject to considerable controversy. The Drosophila genome contains distinct cyt c genes: cyt c-p and cyt c-d. Loss of cyt c-p function causes embryonic lethality owing to a requirement of the gene for mitochondrial respiration. By contrast, cyt c-d mutants are viable but male sterile. Here, we show that cyt c-d regulates developmental apoptosis in the pupal eye. cyt c-d mutant retinas show a profound delay in the apoptosis of superfluous interommatidial cells and perimeter ommatidial cells. Furthermore, there is no apoptosis in mutant retinal tissues for the Drosophila homologues of apoptotic protease-activating factor 1 (Ark) and caspase 9 (Dronc). In addition, we found that cyt c-d--as with ark and dronc-regulates scutellar bristle number, which is known to depend on caspase activity. Collectively, our results indicate a role of Cyt c in caspase regulation of Drosophila somatic cells.

Role of senseless in late color photoreceptor differentiation in Drosophila

Role of senseless in late color photoreceptor differentiation in Drosophila

Enigmatic Flies: Is Drosophila in the "Evolution Canyon" A Model for Incipient Sympatric speciation?

Extensive studies of biota at "Evolution Canyon" (EC) on Mount Carmel (Nahal Oren Canyon, Israel) includeDrosophilaas one of the main model organisms. The microtopography of the EC permits interslope mixing by easy migration of the flies. Nevertheless, we found strong interslope differentiation inDrosophilapopulations derived from the opposite slopes involving habitat choice, as well as various aspects of induced changes in viability and longevity caused by short-term and lifetime high-temperature treatments. The most exciting findings were related to sexual behavior: interslope differences in mating propensity, sexual discrimination, reproductive activity, peculiarities in courtship song patterns, and significant positive assortative mating. Some of the foregoing effects were also confirmed inD. simulans.The evidence suggests that these populations are examples of ongoing divergence taking place regardless of gene flow. However, tests for interslope genetic differentiation inDrosophila, carried out in a number of laboratories, gave somewhat conflicting results. A possible explanation could be that adaptive differentiation can withstand destructive effects of interslope migration, but it should not necessarily be accompanied by differentiation for selectively neutral markers, unless the latter will be in linkage disequilibrium with selected loci. The last condition can also be maintained despite migration, but only under tight linkage and strong selection. For someDrosophilagenes, linkage disequilibrium is known to decay within just a few kilobases. Thus, differentiation for adaptive trait complexes and relevant candidate genes seems to be much better evidence for interslope divergent selection than that displayed by genetic distances estimated using molecular markers.

MicroRNA1 influences cardiac differentiation in Drosophila and regulates Notch signaling.

MicroRNAs (miRNAs) are genomically encoded small RNAs that hybridize with messenger RNAs, resulting in degradation or translational inhibition of targeted transcripts. The potential for miRNAs to regulate cell-lineage determination or differentiation from pluripotent progenitor or stem cells is unknown. Here, we show that microRNA1 (miR-1) is an ancient muscle-specific gene conserved in sequence and expression in Drosophila. Drosophila miR-1 (dmiR-1) is regulated through a serum response factor-like binding site in cardiac progenitor cells. Loss- and gain-of-function studies demonstrated a role for dmiR-1 in modulating cardiogenesis and in maintenance of muscle-gene expression. We provide in vivo evidence that dmiR-1 targets transcripts encoding the Notch ligand Delta, providing a potential mechanism for the expansion of cardiac and muscle progenitor cells and failure of progenitor cell differentiation in some dmiR-1 mutants. These findings demonstrate that dmiR-1 may "fine-tune" critical steps involved in differentiation of cardiac and somatic muscle progenitors and targets a pathway required for progenitor cell specification and asymmetric cell division.

Evidence for the involvement of dominant‐negative Notch molecules in the normal course of Drosophila development

Notch signaling is used to specify cell types during animal development. A high level specifies one cell type, whereas a low level specifies the alternate type. The effector of Notch signaling is the Notch intracellular domain. Upon its release from the plasma membrane in response to Delta binding the Notch extracellular domain, the Notch intracellular domain combines with the transcription factor Suppressor of Hairless and promotes the expression of target genes. Using a panel of antibodies made against different extracellular and intracellular regions of Notch, we show that cell types and tissues with low levels of Notch signaling are enriched for Notch molecules detected only by the extracellular domain antibodies. This enrichment often follows enrichment for Notch molecules detected only by antibodies made against the Suppressor of Hairless binding region. Notch molecules lacking most of the intracellular domain or containing only the Suppressor of Hairless binding region are produced during development. Such molecules are known to suppress Notch signaling, possibly by taking away Delta or Suppressor of Hairless from the full-length Notch. Thus, it is possible that dominant-negative Notch molecules are produced in the normal course of tissue differentiation in Drosophila as part of an auto-down-regulation mechanism.

Identification and expression analysis of putative mRNA‐like non‐coding RNA in Drosophila

One of the most surprising results to emerge from mammalian cDNA sequencing projects is that thousands of mRNA-like non-coding RNAs (ncRNAs) are expressed and constitute at least 10% of poly(A)(+) RNAs. In most cases, however, the functions of these RNA molecules remain unclear. To clarify the biological significance of mRNA-like ncRNAs, we computationally screened 11,691 Drosophila melanogaster full-length cDNAs. After eliminating presumable protein-coding transcripts, 136 were identified as strong candidates for mRNA-like ncRNAs. Although most of these putative ncRNAs are found throughout the Drosophila genus, predicted amino acid sequences are not conserved even in related species, suggesting that these transcripts are actually non-coding RNAs. In situ hybridization analyses revealed that 35 of the transcripts are expressed during embryogenesis, of which 27 were detected only in specific tissues including the tracheal system, midgut primordial cells, visceral mesoderm, germ cells and the central and peripheral nervous system. These highly regulated expression patterns suggest that many mRNA-like ncRNAs play important roles in multiple steps of organogenesis and cell differentiation in Drosophila. This is the first report that the majority of mRNA-like ncRNAs in a model organism are expressed in specific tissues and cell types.

Breast cancer, stem cells, and the stem cell niche

At least four cell types in mouse mammary epithelium, three in human, and three in cow are now known to be proliferation competent. Some evidence indicates that pregnancy may confer proliferative competency on a new cell type. These cells are widely seen as stem and progenitor cells that maintain the epithelium and produce lactational units during pregnancy. Evolutionarily conserved developmental signaling pathways active in germinal and neuronal stem cell proliferation and differentiation in drosophila and mammalian development are implicated in mammary tumorigenesis. In adult tissues this signaling is retained, is regulated by stem cell niches and operates to create new tissue and maintain tissue form and integrity. Disruption of this signaling may abrogate maintenance of the stem cell niche and lead to preneoplastic conditions.

The Dorsocross T-box genes are key components of the regulatory network controlling early cardiogenesis inDrosophila

Cardiac induction in Drosophila relies on combinatorial Dpp and Wg signaling activities that are derived from the ectoderm. Although some of the actions of Dpp during this process have been clarified, the exact roles of Wg, particularly with respect to myocardial cell specification, have not been well defined. Our present study identifies the Dorsocross T-box genes as key mediators of combined Dpp and Wg signals during this process. The Dorsocross genes are induced within the segmental areas of the dorsal mesoderm that receive intersecting Dpp and Wg inputs. Dorsocross activity is required for the formation of all myocardial and pericardial cell types, with the exception of the Eve-positive pericardial cells. In an early step, the Dorsocross genes act in parallel with tinman to activate the expression of pannier, a cardiogenic gene encoding a Gata factor. Our loss- and gain-of-function studies, as well as the observed genetic interactions among Dorsocross, tinman and pannier, suggest that co-expression of these three genes in the cardiac mesoderm, which also involves cross-regulation, plays a major role in the specification of cardiac progenitors. After cardioblast specification, the Dorsocross genes are re-expressed in a segmental subset of cardioblasts, which in the heart region develop into inflow valves (ostia). The integration of this new information with previous findings has allowed us to draw a more complete pathway of regulatory events during cardiac induction and differentiation in Drosophila.

Dimerization of Doublesex Is Mediated by a Cryptic Ubiquitin-associated Domain Fold: IMPLICATIONS FOR SEX-SPECIFIC GENE REGULATION

Male- and female-specific isoforms of the Doublesex (DSX) transcription factor regulate somatic sexual differentiation in Drosophila. The isoforms (DSX(M) and DSX(F)) share an N-terminal DNA binding domain (the DM motif), broadly conserved among metazoan sex-determining pathways. DM-DNA recognition is enhanced by a C-terminal dimerization domain. The crystal structure of this domain, determined at a resolution of 1.6 A, reveals a novel dimeric arrangement of ubiquitin-associated (UBA) folds. Although this alpha-helical motif is well characterized in pathways of DNA repair and subcellular trafficking, to our knowledge this is its first report in a transcription factor. Dimerization is mediated by a non-canonical hydrophobic interface extrinsic to the putative ubiquitin binding surface. Key side chains at this interface, identified by alanine scanning mutagenesis, are conserved among DSX homologs. The mechanism of dimerization is thus unrelated to the low affinity domain swapping observed among ubiquitin-associated CUE domains. The unexpected observation of a ubiquitin-associated fold in DSX extends the repertoire of alpha-helical dimerization elements in transcription factors. The possibility that the ubiquitination machinery participates in the regulation of sexual dimorphism is discussed.

Photoreceptor differentiation in Drosophila: From immature neurons to functional photoreceptors

How a pool of equipotent cells acquires a multitude of distinct fates is a major question in developmental biology. The study of photoreceptor (PR) cell differentiation in Drosophila has been used to address this question. PR differentiation is a process that extends over a period of 5 days: It begins in the larval eye imaginal disc when PRs are recruited and commit to particular PR fates, and it culminates in the pupal eye disc with the morphogenesis of the rhabdomeres and the initiation of rhodopsin expression. Several models for PR specification agree that the Ras and Notch signaling pathways are important for the specification of different PR subtypes (Freeman [1997] Development 124:261-270; Cooper and Bray [2000] Curr. Biol. 10:1507-1510; Tomlinson and Struhl [2001] Mol. Cell. 7:487-495). In the first part of this review, we briefly describe the different signaling pathways and transcription factors required for the specification and differentiation of the different PR subtypes in the larval eye disc. In the second part, we review the roles of several transcription factors, which are required for the terminal photoreceptor differentiation and rhodopsin expression.

Rab11 is required during Drosophila eye development

In an effort to identify the role of Rab11, a small GTP binding protein, during Drosophila differentiation, phenotypic manifestations associated with different alleles of Rab11 were studied. The phenotypes ranged from eye-defects, bristle abnormalities and sterility to lethality during various developmental stages. In this paper, our focus is targeted on eye defects caused by Rab11 mutations. A novel P-element insertion in the Rab11 locus, Rab11mo, displayed characteristic retinal anomalies, which could be reverted by P-element excision and expression of Rab11+ transgenes. During larval development, Rab11 is widely synthesized in photoreceptor cells and localizes to the rhabdomeres and lamina neuropil in adult eyes. Photoreceptors and associated bristles failed to be formed in homozygous clones generated in Rab11EP(3)3017 eyes. Decreased levels of Rab11 protein and increased cell death in Rab11mo third-instar larval eye-antennal discs suggest that the retinal defects originate during larval development. Our data indicate a requirement for Rab11 in ommatidial differentiation during Drosophila eye development.

Genetic control of epidermis differentiation in Drosophila.

Genetic control of epidermis differentiation in Drosophila.

Genetic control of epidermis differentiation in Drosophila.

In arthropods, the animal body is isolated from the external environment by a protective exoskeleton called the cuticle. The cuticle of young larvae has certainly been the most scrutinized structure in Drosophila and genetic studies of the pattern of cuticular extensions has provided the main source of our comprehension of the control of embryonic development. However, the complex structure of the cuticle remains poorly understood and analysis of the underlying epidermis has started only recently. Here I review different aspects of epidermis differentiation with the aim of presenting an integrated view of the organisation of the Drosophila integument. Although profound differences in epidermis organisation are observed across species, accumulated results suggest that epidermis formation and differentiation might share an unsuspected number of homologies between Drosophila and vertebrates.

The Ovo/Shavenbaby transcription factor specifies actin remodelling during epidermal differentiation in Drosophila

In Drosophila, differentiation of the epidermis results in a stereotyped array of cells with F-actin-based extensions at their apical face. We identified Ovo/Shavenbaby (Svb) as a transcription factor that governs changes in epidermal cell shape. Svb is required for the formation of apical extensions and cells deficient in svb differentiate a smooth surface. In both the embryo and the adult, we show that Svb is necessary and sufficient for the cells to grow extensions and that the tight regulation of ovo/ svb activity is critical for morphogenesis to occur correctly. We establish that Svb triggers early F-actin redistribution and is able to initiate the entire process of cytoskeletal remodelling, thereby defining it as a major regulator of epidermal differentiation.

Caspase Activity and a Specific Cytochrome C Are Required for Sperm Differentiation in Drosophila

The final stage of spermatid terminal differentiation involves the removal of their bulk cytoplasm in a process known as spermatid individualization. Here we show that apoptotic proteins play an essential role during spermatid individualization in Drosophila melanogaster. Several aspects of sperm terminal differentiation, including the activation of caspases, are reminiscent of apoptosis. Notably, caspase inhibitors prevent the removal of bulk cytoplasm in spermatids and block sperm maturation in vivo, causing male sterility. We further identified loss-of-function mutations in one of the two Drosophila cyt-c genes, cyt-c-d, which block caspase activation and subsequent spermatid terminal differentiation. Finally, a giant ubiquitin-conjugating enzyme, dBruce, is required to protect the sperm nucleus against hypercondensation and degeneration. These observations suggest that an apoptosis-like mechanism is required for spermatid differentiation in Drosophila.

The C. elegans che-1 gene encodes a zinc finger transcription factor required for specification of the ASE chemosensory neurons.

Chemotaxis to water-soluble chemicals such as NaCl is an important behavior of C. elegans when seeking food. ASE chemosensory neurons have a major role in this behavior. We show that che-1, defined by chemotaxis defects, encodes a zinc-finger protein similar to the GLASS transcription factor required for photoreceptor cell differentiation in Drosophila, and that che-1 is essential for specification and function of ASE neurons. Expression of a che-1::gfp fusion construct was predominant in ASE. In che-1 mutants, expression of genes characterizing ASE such as seven-transmembrane receptors, guanylate cyclases and a cyclic-nucleotide gated channel is lost. Ectopic expression of che-1 cDNA induced expression of ASE-specific marker genes, a dye-filling defect in neurons other than ASE and dauer formation.

Drosophila regulatory factor X is necessary for ciliated sensory neuron differentiation.

Ciliated neurons play an important role in sensory perception in many animals. Modified cilia at dendrite endings serve as sites of sensory signal capture and transduction. We describe Drosophila mutations that affect the transcription factor RFX and genetic rescue experiments that demonstrate its central role in sensory cilium differentiation. Rfx mutant flies show defects in chemosensory and mechanosensory behaviors but have normal phototaxis, consistent with Rfx expression in ciliated sensory neurons and neuronal precursors but not in photoreceptors. The mutant behavioral phenotypes are correlated with abnormal function and structure of neuronal cilia, as shown by the loss of sensory transduction and by defects in ciliary morphology and ultrastructure. These results identify Rfx as an essential regulator of ciliated sensory neuron differentiation in Drosophila.

Structure of the DNA Binding Region of Prospero Reveals a Novel Homeo-Prospero Domain

The Prospero transcription factor promotes neural differentiation in Drosophila, and its activity is tightly regulated by modulating its subcellular localization. Prospero is exported from the nucleus of neural precursors but imported into the nucleus of daughter cells, which is necessary for their proper differentiation. Prospero has a highly divergent putative homeodomain adjacent to a conserved Prospero domain; both are required for sequence-specific DNA binding. Here we show that the structure of these two regions consists of a single structural unit (a homeo-prospero domain), in which the Prospero domain region is in position to contribute to DNA binding and also to mask a defined nuclear export signal that is within the putative homeodomain region. We propose that the homeo-prospero domain coordinately regulates Prospero nuclear localization and DNA binding specificity.

Syntaxin 5 Is Required for Cytokinesis and Spermatid Differentiation in Drosophila

Syntaxin 5 is a Golgi-localized SNARE protein that has been shown to be required for ER–Golgi traffic in yeast and Golgi reassembly following cell division in mammalian cells. Here, we describe the characterization of the Drosophila ortholog of syntaxin 5, dSyx5, and show that, like its mammalian and yeast counterparts, the protein is localized to the Drosophila Golgi and binds to α-SNAP. Null mutations in dSyx5 are larval lethal and demonstrate impaired transport of a GFP-tagged membrane protein. A hypomorphic allele of dSyx5 caused by insertion of an EP element results in impenetrant lethality, and escaping adult flies are male sterile. The male sterility results both from failure of germ cells to complete cytokinesis and from defects in spermatid elongation and maturation. Ectopic expression of dSyx5 from the EP element can rescue the cytokinesis defect, but high levels of expression are required to restore maturation and fertility. Together, these results show that dSyx5 is required for the proper function of the Golgi apparatus and that an efficiently functioning Golgi apparatus is required for the steps leading to the completion of cytokinesis and formation of mature sperm.

Syntaxin 5 Is Required for Cytokinesis and Spermatid Differentiation in Drosophila

Syntaxin 5 is a Golgi-localized SNARE protein that has been shown to be required for ER–Golgi traffic in yeast and Golgi reassembly following cell division in mammalian cells. Here, we describe the characterization of the Drosophila ortholog of syntaxin 5, dSyx5, and show that, like its mammalian and yeast counterparts, the protein is localized to the Drosophila Golgi and binds to α-SNAP. Null mutations in dSyx5 are larval lethal and demonstrate impaired transport of a GFP-tagged membrane protein. A hypomorphic allele of dSyx5 caused by insertion of an EP element results in impenetrant lethality, and escaping adult flies are male sterile. The male sterility results both from failure of germ cells to complete cytokinesis and from defects in spermatid elongation and maturation. Ectopic expression of dSyx5 from the EP element can rescue the cytokinesis defect, but high levels of expression are required to restore maturation and fertility. Together, these results show that dSyx5 is required for the proper function of the Golgi apparatus and that an efficiently functioning Golgi apparatus is required for the steps leading to the completion of cytokinesis and formation of mature sperm.