A Drosophila genomic sequence with homology to human epidermal growth factor receptor

Genetic Screens to Analyze Pattern Formation of Egg and Embryo in Drosophila: A Personal History

In Drosophila development, the axes of the egg and future embryo are established during oogenesis. To learn about the underlying genetic and molecular pathways that lead to axis formation, I conducted a large-scale genetic screen at the beginning of my independent career. This led to the eventual understanding that both anterior-posterior and dorsal-ventral pattern information is transmitted from the oocyte to the surrounding follicle cells and in turn from the follicle cells back to the oocyte. How I came to conduct this screen and what further insights were gained by studying the mutants isolated in the screen are the topics of this autobiographical article.

Role of receptor tyrosine kinases during Drosophila development

In vertebrates, a tyrosine kinase activity has been identified as an integral component of growth factor receptors and the products of proto-oncogenes. Many of these receptor tyrosine kinases (RTKs) appear to play a key role in the regulation of cell growth. Recent analyses of several Drosophila genes encoding putative RTKs indicate that this class of proteins also plays an important role in decisions about cell fate that depend on cellular interactions during development. The sevenless RTK mediates the position-dependent specification of a particular photoreceptor cell type (R7) in the eye. The local specification of R7 cells requires a functional tyrosine kinase domain of the sevenless protein but does not depend on the spatially restricted expression of the sevenless gene. The Drosophila EGF receptor homologue serves multiple functions during development, some of which are clearly unrelated to regulation of cell growth. Finally, the torso gene encodes an RTK required for the specification of the terminal regions of the Drosophila larva. A number of other genes have been genetically identified that appear to function in the same developmental processes upstream or downstream of these three RTKs. These loci are excellent candidates for genes encoding other components of the signalling pathways, such as ligands or substrates of the RTKs.

Ancient mechanisms of visual sense organ development based on comparison of the gene networks controlling larval eye, ocellus, and compound eye specification in Drosophila

Key mechanisms of development are strongly constrained, and hence often shared in the formation of highly diversified homologous organs. This diagnostic is applied to uncovering ancient gene activities in the control of visual sense organ development by comparing the gene networks, which regulate larval eye, ocellus and compound eye specification in Drosophila. The comparison reveals a suite of shared aspects that are likely to predate the diversification of arthropod visual sense organs and, consistent with this, have notable similarities in the developing vertebrate visual system: (I) Pax-6 genes participate in the patterning of primordia of complex visual organs. (II) Primordium determination and differentiation depends on formation of a transcription factor complex that contains the products of the selector genes Eyes absent and Sine oculis. (III) The TGF-beta signaling factor Decapentaplegic exerts transcriptional activation of eyes absent and sine oculis. (IV) Canonical Wnt signaling contributes to primordium patterning by repression of eyes absent and sine oculis. (V) Initiation of determination and differentiation is controlled by hedgehog signaling. (VI) Egfr signaling drives retinal cell fate specification. (VII) The proneural transcription factor atonal regulates photoreceptor specification. (VII) The zinc finger gene glass regulates photoreceptor specification and differentiation.

Conservation of an inhibitor of the epidermal growth factor receptor, Kekkon1, in dipterans

Regulation of epidermal growth factor receptor (EGFR) signaling requires the concerted action of both positive and negative factors. While the existence of numerous molecules that stimulate EGFR activity has been well documented, direct biological inhibitors appear to be more limited in number and phylogenetic distribution. Kekkon1 (Kek1) represents one such inhibitor. Kek1 was initially identified in Drosophila melanogaster and appears to be absent from vertebrates and the invertebrate Caenorhabditis. To further investigate Kek1's function and evolution, we identified kek1 orthologs within dipterans. In D. melanogaster, kek1 is a transcriptional target of EGFR signaling during oogenesis, where it acts to attenuate receptor activity through an inhibitory feedback loop. The extracellular and transmembrane portion of Kek1 is sufficient for its inhibitory activity in D. melanogaster. Consistent with conservation of its role in EGFR signaling, interspecies comparisons indicate a high degree of identity throughout these regions. During formation of the dorsal-ventral axis Kek1 is expressed in dorsal follicle cells in a pattern that reflects the profile of receptor activation. D. virilis Kek1 (DvKek1) is also expressed dynamically in the dorsal follicle cells, supporting a conserved role in EGFR signaling. Confirming this, biochemical and transgenic assays indicate that DvKek1 is functionally interchangeable with DmKek1. Strikingly, we find that the cytoplasmic domain contains a region with the highest degree of conservation, which we have implicated in EGFR inhibition and dubbed the Kek tail (KT) box.

Insights into ErbB signaling from the structure of the ErbB2-pertuzumab complex

We have determined the 3.2 A X-ray crystal structure of the extracellular domain of the human epidermal growth factor receptor 2 (ErbB2 or HER2) in a complex with the antigen binding fragment of pertuzumab, an anti-ErbB2 monoclonal antibody also known as 2C4 or Omnitarg. Pertuzumab binds to ErbB2 near the center of domain II, sterically blocking a binding pocket necessary for receptor dimerization and signaling. The ErbB2-pertuzumab structure, combined with earlier mutagenesis data, defines the pertuzumab residues essential for ErbB2 interaction. To analyze the ErbB2 side of the interface, we have mutated a number of residues contacting pertuzumab and examined the effects of these mutations on pertuzumab binding and ErbB2-ErbB3 heterodimerization. We have also shown that conserved residues previously shown to be necessary for EGF receptor homodimerization may be dispensible for ErbB2-ErbB3 heterodimerization.

Developmental variation in epidermal growth factor receptor size and localization in the malaria mosquito, Anopheles gambiae

The AGER gene encoding the epidermal growth factor receptor (EGFR) of the malaria mosquito Anopheles gambiae was cloned and sequenced. It represents a canonical member of this family of tyrosine kinase proteins exhibiting many similarities to orthologues from other species, both on the level of genomic organization and protein structure. The mRNA can be detected throughout development. Western analysis with an antibody raised against the extracellular domain of the mosquito protein suggests developmental variation in protein size and location that may be involved in the function of EGFR in the mosquito.

Identification and characterization of DAlk: a novel Drosophila melanogaster RTK which drives ERK activation in vivo

BACKGROUND

The mammalian receptor protein tyrosine kinase (RTK), Anaplastic Lymphoma Kinase (ALK), was first described as the product of the t(2;5) chromosomal translocation found in non-Hodgkin's lymphoma. While the mechanism of ALK activation in non-Hodgkin's lymphoma has been examined, to date, no in vivo role for this orphan insulin receptor family RTK has been described.

RESULTS

We describe here a novel Drosophila melanogaster RTK, DAlk, which we have mapped to band 53 on the right arm of the second chromosome. Full-length DAlk cDNA encodes a phosphoprotein of 200 kDa, which shares homology not only with mammalian ALK but also with the orphan RTK LTK. Analysis of both mammalian and Drosophila ALK reveals that the ALK family of RTKs contains a newly identified MAM domain within their extracellular domains. Like its mammalian counterpart, DAlk appears to be expressed in the developing CNS by in situ analysis. However, in addition to expression of DAlk in the Drosophila brain, careful analysis reveals an additional early role for DAlk in the developing visceral mesoderm where its expression is coincident with activated ERK.

CONCLUSION

In this paper we describe a Drosophila melanogaster Alk RTK which is expressed in the developing embryonic mesoderm and CNS. Our data provide evidence for the existence of a DAlk RTK pathway in Drosophila. We show that ERK participates in this pathway, and that it is activated by DAlk in vivo. Expression patterns of dALK, together with activated ERK, suggest that DAlk fulfils the criteria of the missing RTK pathway, leading to ERK activation in the developing visceral mesoderm.

Mutant alleles of the Drosophila trithorax gene produce common and unusual homeotic and other developmental phenotypes

trithorax (trx) encodes chromosome-binding proteins required throughout embryogenesis and imaginal development for tissue- and cell-specific levels of transcription of many genes including homeotic genes of the ANT-C and BX-C. trx encodes two protein isoforms that contain conserved motifs including a C-terminal SET domain, central PHD fingers, an N-terminal DNA-binding homology, and two short motifs also found in the TRX human homologue, ALL1. As a first step to characterizing specific developmental functions of TRX, I examined phenotypes of 420 combinations of 21 trx alleles. Among these are 8 hypomorphic alleles that are sufficient for embryogenesis but provide different levels of trx function at homeotic genes in imaginal cells. One allele alters the N terminus of TRX, which severely impairs larval and imaginal growth. Hypomorphic alleles that alter different regions of TRX equivalently reduce function at affected genes, suggesting TRX interacts with common factors at different target genes. All hypomorphic alleles examined complement one another, suggesting cooperative TRX function at target genes. Comparative effects of hypomorphic genotypes support previous findings that TRX has tissue-specific interactions with other factors at each target gene. Some hypomorphic genotypes also produce phenotypes that suggest TRX may be a component of signal transduction pathways that provide tissue- and cell-specific levels of target gene transcription.

EGF receptor signaling in Drosophila oogenesis

The spatial regulation of Egfr activity in the follicular epithelium of the ovary is achieved by the localization of its ligand, Gurken, within the germline. The final distribution of Gurken within the oocyte appears to be specified both by the localization of the gurken RNA and by regulation of Gurken protein accumulation, possibly at the level of translation. Localized activation of the Egfr distinguishes certain subpopulations of follicle cells, thereby generating asymmetry within the follicular epithelium. In early oogenesis, Egfr activation in posterior follicle cells defines the AP polarity of the egg chamber, and in midoogenesis restriction of Egfr activity to dorsal follicle cells determines DV polarity. A number of factors required downstream of the Egfr have been identified, but the mechanism by which the observed patterning of the follicular epithelium is achieved remains unclear. The dynamic expression patterns of some of these targets suggest that the initial Gurken-Egfr signal at the dorsal side of the follicular epithelium mediates an initial distinction between dorsal and ventral follicle cells and also initiates subsequent refinement processes that determine the final pattern of cell fates. In the dorsal follicle cells, this refinement appears to involve interactions between Egfr targets and may also involve feedback regulation of Egfr activity such that the profile of Egfr activity is modulated over time. In addition, the initial Gurken-Egfr signal negatively regulates the functional domain of another patterning process that governs the establishment of the DV axis of the developing embryo.

Regulation of EGF receptor signaling establishes pattern across the developing Drosophila retina

Developing epithelia use a variety of patterning mechanisms to place individual cells into their correct positions. However, the means by which pattern elements are established are poorly understood. Here, we report evidence that regulation of Drosophila EGF receptor (DER) activity plays a central role in propagating the evenly spaced array of ommatidia across the developing Drosophila retina. DER activity is essential for establishing the first ommatidial cell fate, the R8 photoreceptor neuron. R8s in turn appear to signal through Rhomboid and Vein to create a patterned array of ‘proneural clusters’ which contain high levels of phosphorylated ERKA and the bHLH protein Atonal. Finally, secretion by the proneural clusters of Argos represses DER activity in less mature regions to create a new pattern of R8s. Propagation of this process anteriorly results in a retina with a precise array of maturing ommatidia.

In vivo analysis of Argos structure-function. Sequence requirements for inhibition of the Drosophila epidermal growth factor receptor

The Drosophila Argos protein is the only known extracellular inhibitor of the epidermal growth factor receptor (EGFR). It is structurally related to the activating ligands, in that it is a secreted protein with a single epidermal growth factor (EGF) domain. To understand the mechanism of Argos inhibition, we have investigated which regions of the protein are essential. A series of deletions were made and tested in vivo; furthermore, by analyzing chimeric proteins between Argos and the activating ligand, Spitz (a transforming growth factor-alpha-like factor), we have examined what makes one inhibitory and the other activating. Our results reveal that Argos has structural requirements that differ from all known EGFR activating ligands; domains flanking the EGF domain are essential for its function. We have also defined the important regions of the atypical Argos EGF domain. The extended B-loop is necessary, whereas the C-loop can be replaced with the equivalent Spitz region without substantially affecting Argos function. Comparison of the argos genes from Drosophila melanogaster and the housefly, Musca domestica, supports our structure-function analysis. These studies are a prerequisite for understanding how Argos inhibits the Drosophila EGFR and provide a basis for designing mammalian EGFR inhibitors.

windbeutel, a gene required for dorsoventral patterning in Drosophila, encodes a protein that has homologies to vertebrate proteins of the endoplasmic reticulum

The formation of the dorsoventral axis of the Drosophila embryo depends on cell-cell interactions that take place in the female ovary and involve the activation of transmembrane receptors by secreted ligands. The gene windbeutel functions in the somatic follicle cells of the ovary and is required for the generation of a signal that will determine the ventral side of the embryo. This signal originates in the follicle cells during oogenesis, but its actions are only manifested after fertilization, when the egg has already been laid. We have performed a molecular analysis of windbeutel. We have found that windbeutel encodes a putative resident protein of the endoplasmic reticulum, and has homologs in rats and humans. The gene is expressed for a brief period of time in the follicle cells of the ovary, at around the time when the dorsoventral axis of the egg chamber is first established. We propose that Windbeutel is responsible for the folding and/or modification of a specific factor that is secreted from the follicle cells and participates in the activation of the ventralizing signal.

maelstrom is required for an early step in the establishment of Drosophila oocyte polarity: posterior localization of grk mRNA

We describe a mutant, maelstrom, that disrupts a previously unobserved step in mRNA localization within the early oocyte, distinct from nurse-cell-to-oocyte RNA transport. Mutations in maelstrom disturb the localization of mRNAs for Gurken (a ligand for the Drosophila Egf receptor), Oskar and Bicoid at the posterior of the developing (stage 3–6) oocyte. maelstrom mutants display phenotypes detected in gurken loss-of-function mutants: posterior follicle cells with anterior cell fates, bicoid mRNA localization at both poles of the stage 8 oocyte and ventralization of the eggshell. These data are consistent with the suggestion that early posterior localization of gurken mRNA is essential for activation of the Egf receptor pathway in posterior follicle cells. Posterior localization of mRNA in stage 3–6 oocytes could therefore be one of the earliest known steps in the establishment of oocyte polarity. The maelstrom gene encodes a novel protein that has a punctate distribution in the cytoplasm of the nurse cells and the oocyte until the protein disappears in stage 7 of oogenesis.

Ectopic activation of torpedo/Egfr, a Drosophila receptor tyrosine kinase, dorsalizes both the eggshell and the embryo

The Drosophila gene torpedo/Egfr (top/Egfr) encodes a homolog of the vertebrate Epidermal Growth Factor receptor. This receptor is required several times during the life cycle of the fly for the transmisson of developmental cues. During oogenesis, Top/Egfr activation is required for the establishment of the dorsal/ventral axis of the egg and the embryo. To examine how ectopic Top/Egfr activation affects cell fate determination, we constructed an activated version of the protein. Expression of this activated form (lambda top) in the follicle cells of the ovary induces dorsal cell fates in both the follicular epithelium and the embryo. Different levels of expression resulted in different dorsal follicle cell fates. These dorsal cell fates were expanded in the anterior, but not the posterior, of the egg, even in cases where all the follicle cells covering the oocyte expressed lambda top. The expression of genes known to respond to top/Egfr activation, argos (aos), kekkon1 (kek 1) and rhomboid (rho), was also expanded in the presence of the lambda top construct. When lambda top was expressed in all the follicle cells covering the oocyte, kek 1 and argos expression was induced in follicle cells all along the anterior/posterior axis of the egg chamber. In contrast, rho RNA expression was only activated in the anterior of the egg chamber. These data indicate that the response to Top/Egfr signaling is regulated by an anterior/posterior prepattern in the follicle cells. Expression of lambda top in the entire follicular epithelium resulted in an embryo dorsalized along the entire anterior/posterior axis. Expression of lambda top in anterior or posterior subpopulations of follicle cells resulted in regionally autonomous dorsalization of the embryos. This result indicates that subpopulations of follicle cells along the anterior/posterior axis can respond to Top/Egfr activation independently of one another.

A point mutation in the extracellular domain activates LET-23, the Caenorhabditis elegans epidermal growth factor receptor homolog

The let-23 gene encodes a Caenorhabditis elegans homolog of the epidermal growth factor receptor (EGFR) necessary for vulval development. We have characterized a mutation of let-23 that activates the receptor and downstream signal transduction, leading to excess vulval differentiation. This mutation alters a conserved cysteine residue in the extracellular domain and is the first such point mutation in the EGFR subfamily of tyrosine kinases. Mutation of a different cysteine in the same subdomain causes a strong loss-of-function phenotype, suggesting that cysteines in this region are important for function and nonequivalent. Vulval precursor cells can generate either of two subsets of vulval cells (distinct fates) in response to sa62 activity. The fates produced depended on the copy number of the mutation, suggesting that quantitative differences in receptor activity influence the decision between these two fates.

G-protein-coupled receptors in insect cells

The main classes of transmembrane signaling receptor proteins are well conserved during evolution and are encountered in vertebrates as well as in invertebrates. All members of the G-protein-coupled receptor superfamily share a number of basic structural and functional characteristics. In both insects and mammals, this receptor class is involved in the perception and transduction of many important extracellular signals, including a great deal of paracrine, endocrine, and neuronal messengers and visual, olfactory and gustatory stimuli. Therefore, most of the receptor subclasses appear to have originated several hundred million years ago, before the divergence of the major animal Phyla took place. Nevertheless, many insect-specific molecular interactions are encountered and these could become interesting tools for future applications, e.g., in insect pest control. Insect cell lines are well suited for large-scale expression and characterization of cloned receptor genes. Furthermore, novel methods for the production of stably transformed insect cells may form a major breakthrough for insect signal transduction research.

The spitz gene is required for photoreceptor determination in the Drosophila eye where it interacts with the EGF receptor

Little is known about the mechanisms by which photoreceptors other than R7 are determined during Drosophila eye development. By looking for mutations that modify the phenotype caused by ectopic expression of the rhomboid gene in the eye, I have discovered that the spitz gene is required for photoreceptor determination. Mosaic analysis suggests that spitz, which encodes a TGF alpha homologue, produces a diffusible signal during ommatidial development. Other members of the spitz group and the EGF receptor also interact with sev-rho, in a pattern that suggests a model in which rhomboid can act as a mediator of a ligand-receptor interaction between spitz and Egfr in the developing eye. These data suggest that photoreceptors other than R7 use a Ras1 signalling pathway activated by the spitz/Egfr interaction, in a manner analogous to the Ras1 pathway activated by boss/sevenless in photoreceptor R7.

Conserved cis-elements bind a protein complex that regulates Drosophila ras2/rop bidirectional expression

The Drosophila ras2 promoter region exhibits bidirectional activity, as has been demonstrated for the human c-Ha-ras1 and the mouse c-Ki-ras. Here we address a unique case of ras regulation, as Drosophila ras2 provides the only example to date in which the flanking gene (rop) and its product have been isolated. A linking mechanism of control suggests a mutual interaction between the two gene products. Our studies indicate that the Drosophila ras2 promoter region shares with the human c-Ha-ras1 promoter a CACCC box and an AP-1-like sequence. A 14 bp promoter fragment which holds a CACCC element is demonstrated to interact with a specific transcription factor (factor B). This CACCC promoter element represents a stretch of imperfect palindrome. We present evidence that this factor can form a complex with another specific DNA-binding protein (factor A). The binding sites (A + B) for these protein factors are essential for 95% expression of both genes flanking the promoter (ras2 and rop). Region A consists of four overlapping consensus sequences: a TATA-like element, a DSE-like motif (the core sequence of the serum response element), a DRE octamer, which has been shown to play a role in cell proliferation, and a 5 bp direct repeat representing the GATA consensus sequence. Factor A has a very weak affinity to the full promoter region, but when complexed with factor B binding efficiency is enhanced. We also show that alterations of DNA-protein binding specificities can be achieved by supplementing the growth media with different sera.

Expression during Drosophila development of DER, a gene related to erbB-1 and neu: correlations with mutant phenotypes

We used in situ hybridization to study expression of the DER gene during Drosophila development. DER encodes a transmembrane cell-surface receptor with a cytoplasmic protein-tyrosine kinase domain, and resembles the vertebrate genes that encode the EGF receptor and the neu protein. We examined most stages of development in the Drosophila life cycle and found a substantial correlation between DER expression and the phenotypes associated with a variety of mutant alleles. Of particular note were high levels of expression in the primordia of the mouth parts, which are the embryonic tissues most sensitive to reductions in DER activity; discrete expression in a subset of neural cells essential for construction of the axonal scaffold, a structure that is deformed in mutant embryos; uneven expression in the eye disc, the development of which is abnormal in both mild hypomorphs and hypermorphs; and expression in the follicular epithelial cells of the ovary, which are responsible for producing the eggshell of developing oocytes and do so aberrantly in the mildest hypomorphs. However, DER transcripts were also detected in a subset of tissues that have not been reported to be abnormal in mutant organisms. Our findings agree with and extend recently reported results for the DER protein, indicating that DER is regulated primarily at the level of transcription, in contrast to previous suggestions. We conclude that the phenotypes displayed by recessive mutants can be attributed to loss of DER function in the affected tissues.

Receptor tyrosine kinases mediate cell-cell interactions during Drosophila development

In vertebrates, receptor tyrosine kinases (RTKs) have been identified as growth factor receptors and proto-oncogenes. Many of these RTKs appear to play a key role in the regulation of cell growth. Recent analyses of several Drosophila genes encoding putative RTKs indicate that this class of proteins also serves an important role in cell fate decisions which depend on cellular interactions during development. The sevenless RTK mediates the position-dependent specification of a particular photoreceptor cell type (R7) in the eye. The local specification of R7 cells requires a functional tyrosine kinase domain of the sevenless protein but does not depend on the spatially restricted expression of the sevenless gene. The Drosophila EGF receptor homolog serves multiple functions during development, some of which are clearly unrelated to regulation of cell growth. Finally, the torso gene encodes an RTK required for the specification of the terminal regions of the Drosophila larva. A number of other genes have been genetically identified that appear to function in the same developmental processes upstream or downstream of these three RTKs. These loci are excellent candidates for genes encoding other components of the signalling pathways such as ligands or substrates of the RTKs.

The maternal ventralizing locus torpedo is allelic to faint little ball, an embryonic lethal, and encodes the Drosophila EGF receptor homolog

The torpedo gene of Drosophila melanogaster is involved in the establishment of the dorsoventral pattern of eggshell and embryo. We have isolated new alleles of torpedo and have found that torpedo is allelic to the zygotic embryonic lethal faint little ball. We have shown that torpedo resides in subdivision 57F on the second chromosome--at the same location as the Drosophila homolog of the EGF receptor (DER). Using a cosmid that contains most of the DER coding region as a hybridization probe, we have shown that a cytologically small deficiency that eliminates torpedo activity also removes the DER gene, and that an inversion that was isolated as a strong torpedo allele breaks the coding region of the DER gene. We conclude that torpedo is the DER gene.

The Drosophila EGF receptor homolog (DER) gene is allelic to faint little ball, a locus essential for embryonic development

Recessive lethal mutations in the genetic locus of the Drosophila EGF receptor homolog (DER) were isolated. Identification of mutations in the gene is based on assays of DER protein autophosphorylation activity. Most DER alleles show little or no in vivo autophosphorylation. The ability to monitor these activities in vivo and in vitro offers a preliminary insight into the functional defects in the different mutant proteins. The identification of the DER locus was also confirmed by partial rescue of the mutant phenotype with a DER P-element construct. Homozygous DER mutants display a complex embryonic phenotype. Most notably, the anterior structures deteriorate, ventral denticle bands are missing, the germ band does not retract, and the central nervous system shows a collapse of commissure and midline pattern. Mutations in DER were shown to be allelic to the previously described locus faint little ball.

Tissue localization of Drosophila melanogaster insulin receptor transcripts during development

The Drosophila melanogaster insulin receptor (Drosophila insulin receptor homolog [dIRH]) is similar to its mammalian counterpart in deduced amino acid sequence, subunit structure, and ligand-stimulated protein tyrosine kinase activity. The function of this receptor in D. melanogaster is not yet known. However, a role in development is suggested by the observations that levels of insulin-stimulated kinase activity and expression of dIRH mRNA are maximal during Drosophila midembryogenesis. In this study, a 2.9-kilobase (kb) cDNA clone corresponding to both the dIRH tyrosine kinase domain and some of the 3' untranslated sequence was used to determine the tissue distribution of dIRH mRNA during development. Two principal mRNAs of 11 and 8.6 kb hybridized with the dIRH cDNA in Northern (RNA) blot analysis. The abundance of the 8.6-kb mRNA increased transiently in early embryos, whereas the 11-kb species was most abundant during midembryogenesis. A similar pattern of expression was previously determined by Northern analysis, using a dIRH genomic clone (L. Petruzzelli, R. Herrera, R. Arenas-Garcia, R. Fernandez, M. J. Birnbaum, and O. M. Rosen, Proc. Natl. Acad. Sci. USA 83:4710-4714, 1986). In situ hybridization revealed dIRH transcripts in the ovaries of adult flies, in which the transcripts appeared to be synthesized by nurse cells for eventual storage as maternal RNA in the mature oocyte. Throughout embryogenesis, dIRH transcripts were ubiquitously expressed, although after midembryogenesis, higher levels were detected in the developing nervous system. Nervous system expression remained elevated throughout the larval stages and persisted in the adult, in which the cortex of the brain and ganglion cells were among the most prominently labeled tissues. In larvae, the imaginal disk cells exhibited comparatively high levels of dIRH mRNA expression. The broad distribution of dIRH mRNA in embryos and imaginal disks is compatible with a role for dIRH in anabolic processes required for cell growth. The apparently elevated expression of dIRH mRNA in nervous tissue during mid- and late embryogenesis coincides with a period of active neurite outgrowth and suggests that dIRH may be involved in this process.

Tissue localization of Drosophila melanogaster insulin receptor transcripts during development

The Drosophila melanogaster insulin receptor (Drosophila insulin receptor homolog [dIRH]) is similar to its mammalian counterpart in deduced amino acid sequence, subunit structure, and ligand-stimulated protein tyrosine kinase activity. The function of this receptor in D. melanogaster is not yet known. However, a role in development is suggested by the observations that levels of insulin-stimulated kinase activity and expression of dIRH mRNA are maximal during Drosophila midembryogenesis. In this study, a 2.9-kilobase (kb) cDNA clone corresponding to both the dIRH tyrosine kinase domain and some of the 3' untranslated sequence was used to determine the tissue distribution of dIRH mRNA during development. Two principal mRNAs of 11 and 8.6 kb hybridized with the dIRH cDNA in Northern (RNA) blot analysis. The abundance of the 8.6-kb mRNA increased transiently in early embryos, whereas the 11-kb species was most abundant during midembryogenesis. A similar pattern of expression was previously determined by Northern analysis, using a dIRH genomic clone (L. Petruzzelli, R. Herrera, R. Arenas-Garcia, R. Fernandez, M. J. Birnbaum, and O. M. Rosen, Proc. Natl. Acad. Sci. USA 83:4710-4714, 1986). In situ hybridization revealed dIRH transcripts in the ovaries of adult flies, in which the transcripts appeared to be synthesized by nurse cells for eventual storage as maternal RNA in the mature oocyte. Throughout embryogenesis, dIRH transcripts were ubiquitously expressed, although after midembryogenesis, higher levels were detected in the developing nervous system. Nervous system expression remained elevated throughout the larval stages and persisted in the adult, in which the cortex of the brain and ganglion cells were among the most prominently labeled tissues. In larvae, the imaginal disk cells exhibited comparatively high levels of dIRH mRNA expression. The broad distribution of dIRH mRNA in embryos and imaginal disks is compatible with a role for dIRH in anabolic processes required for cell growth. The apparently elevated expression of dIRH mRNA in nervous tissue during mid- and late embryogenesis coincides with a period of active neurite outgrowth and suggests that dIRH may be involved in this process.

The Drosophila homolog of the mouse mammary oncogene int-1 is identical to the segment polarity gene wingless

We have isolated the Drosophila melanogaster homolog (Dint-1) of int-1, a conserved cellular oncogene implicated in viral mammary tumorigenesis in mice. The deduced Dint-1 protein sequence contains 468 amino acids and starts with a hydrophobic leader; it is 54% identical to the int-1 sequence, and all 23 cysteine residues are conserved. The putative Drosophila protein has an extra sequence of 85 amino acids, encoded on an additional exon. Dint-1 is expressed throughout development, but transcripts are barely detectable in adult flies. Hybridization in situ to embryos reveals a segmented pattern of expression. We show that Dint-1 and the segment polarity gene wingless are identical and map to the same location. The sequence of the gene suggests that the Dint-1/wingless protein functions in morphogenesis as a signal in cell-cell communication.

Primary sequence and developmental expression of a novel Drosophila melanogaster src gene

We have sequenced a cDNA clone for the Drosophila melanogaster gene Dsrc28C, a homolog of the vertebrate gene c-src. The cDNA contains a single open reading frame encoding a protein of 66 kilodaltons which contains features highly conserved within the src family of tyrosine protein kinases. Novel structural features of the Dsrc28C protein include a basic pI and a polyglycine domain near the amino terminus. Cell-free translation of in vitro-transcribed RNA yielded a protein of the predicted size which could be immunoprecipitated by anti-v-src antisera. RNA blot hybridization revealed that the gene is expressed predominantly during embryogenesis, in imaginal disks of third-instar larvae, and in adult females. In situ hybridization showed that expression in adult females is largely confined to nurse cells and developing oocytes.

Drosophila melanogaster homologs of the raf oncogene

A murine v-raf probe, representing the kinase domain, was used to identify two unique loci in Drosophila melanogaster DNA. The most closely related to v-raf was mapped by in situ hybridization to position 2F5-6 (Draf-1) on the X chromosome, whereas the other raf-related gene (Draf-2) was found at position 43A2-5 on chromosome 2. The nucleotide and amino acid homologies of Draf-1 to the kinase domain of v-raf are 61 and 65%, respectively. The large amount of a 3.2-kilobase Draf-1 transcript detected in eggs as a maternal message decreases during embryonic development, and significant steady-state levels are observed throughout the remainder of morphogenesis. We speculate that the Draf-1 locus plays an important role in early embryogenesis.

Primary sequence and developmental expression of a novel Drosophila melanogaster src gene

We have sequenced a cDNA clone for the Drosophila melanogaster gene Dsrc28C, a homolog of the vertebrate gene c-src. The cDNA contains a single open reading frame encoding a protein of 66 kilodaltons which contains features highly conserved within the src family of tyrosine protein kinases. Novel structural features of the Dsrc28C protein include a basic pI and a polyglycine domain near the amino terminus. Cell-free translation of in vitro-transcribed RNA yielded a protein of the predicted size which could be immunoprecipitated by anti-v-src antisera. RNA blot hybridization revealed that the gene is expressed predominantly during embryogenesis, in imaginal disks of third-instar larvae, and in adult females. In situ hybridization showed that expression in adult females is largely confined to nurse cells and developing oocytes.

Drosophila melanogaster homologs of the raf oncogene

A murine v-raf probe, representing the kinase domain, was used to identify two unique loci in Drosophila melanogaster DNA. The most closely related to v-raf was mapped by in situ hybridization to position 2F5-6 (Draf-1) on the X chromosome, whereas the other raf-related gene (Draf-2) was found at position 43A2-5 on chromosome 2. The nucleotide and amino acid homologies of Draf-1 to the kinase domain of v-raf are 61 and 65%, respectively. The large amount of a 3.2-kilobase Draf-1 transcript detected in eggs as a maternal message decreases during embryonic development, and significant steady-state levels are observed throughout the remainder of morphogenesis. We speculate that the Draf-1 locus plays an important role in early embryogenesis.

Sequence of the notch locus of Drosophila melanogaster: relationship of the encoded protein to mammalian clotting and growth factors

The Notch locus is essential for proper differentiation of the ectoderm in Drosophila melanogaster. Notch corresponds to a 37-kilobase transcription unit that codes for a major 10.4-kilobase polyadenylated RNA. The DNA sequence of this transcription unit is presented, except for portions of the two largest intervening sequences. DNA sequences also were obtained from three Notch cDNA clones, allowing the 5' and 3' ends of the gene to be mapped, and the structures and locations of nine RNA coding regions to be determined. The major Notch transcript encodes a protein of 2,703 amino acids. The protein is probably associated with cell surfaces and carries an extracellular domain composed of 36 cysteine-rich repeating units, each of about 38 amino acids. The gene appears to have evolved by repeated tandem duplications of the DNA coding for the 38-amino-acid-long protein segments, followed by insertion of intervening sequences. These repeating protein segments are quite homologous to portions of mammalian clotting factors IX and X and to the product of the Caenorhabditis elegans developmental gene lin-12. They are also similar to mammalian growth hormones, typified by epidermal growth factor.

Alternative 5' exons and tissue-specific expression of the Drosophila EGF receptor homolog transcripts

cDNA clones of the Drosophila epidermal growth factor receptor homolog (DER) gene were isolated and sequenced. The deduced amino acid sequence shows a similar degree of homology to the human epidermal growth factor receptor and to the rat and human neu proteins; the most striking difference is the addition of a third cysteine-rich extracellular domain in DER. The structure of the cDNA indicates the use of alternative 5' exons. Thus, the gene encodes three putative proteins differing at their N termini. The distribution of DER transcripts was analyzed by in situ hybridization. Transcripts are uniformly distributed in embryos, larval transcripts are primarily localized to proliferating tissues of the imaginal discs and brain cortex, and adult transcripts are detected mainly in the brain and ganglia. All three splicing alternatives show similar tissue distribution during development.

Sequence of the notch locus of Drosophila melanogaster: relationship of the encoded protein to mammalian clotting and growth factors

The Notch locus is essential for proper differentiation of the ectoderm in Drosophila melanogaster. Notch corresponds to a 37-kilobase transcription unit that codes for a major 10.4-kilobase polyadenylated RNA. The DNA sequence of this transcription unit is presented, except for portions of the two largest intervening sequences. DNA sequences also were obtained from three Notch cDNA clones, allowing the 5' and 3' ends of the gene to be mapped, and the structures and locations of nine RNA coding regions to be determined. The major Notch transcript encodes a protein of 2,703 amino acids. The protein is probably associated with cell surfaces and carries an extracellular domain composed of 36 cysteine-rich repeating units, each of about 38 amino acids. The gene appears to have evolved by repeated tandem duplications of the DNA coding for the 38-amino-acid-long protein segments, followed by insertion of intervening sequences. These repeating protein segments are quite homologous to portions of mammalian clotting factors IX and X and to the product of the Caenorhabditis elegans developmental gene lin-12. They are also similar to mammalian growth hormones, typified by epidermal growth factor.

Isolation of a Drosophila genomic sequence homologous to the kinase domain of the human insulin receptor and detection of the phosphorylated Drosophila receptor with an anti-peptide antibody

A Drosophila genomic fragment has been isolated with a deduced amino acid sequence that is strikingly homologous to that of the kinase domain of the human insulin receptor. The Drosophila DNA hybridizes with an 11-kilobase mRNA that is most prominent in 8- to 12-hr embryos. An anti-peptide antibody prepared to a sequence in the human insulin receptor kinase domain that is conserved in the Drosophila sequence immunoprecipitates a single 95-kDa Drosophila protein whose phosphorylation on tyrosine residues is dependent on insulin. We conclude that the DNA sequence is that of the kinase domain of the Drosophila insulin receptor and that the 95-kDa phosphoprotein is the autophosphorylated beta subunit of that receptor. The results are compatible with our previous reports demonstrating a specific insulin-binding Drosophila glycoprotein and an insulin-dependent tyrosine protein kinase whose activity is greatest during embryogenesis. The observations suggest a role for insulin-dependent protein tyrosine phosphorylation during embryogenesis.

Identification of a novel receptor in Drosophila for both epidermal growth factor and insulin

The notable amino acid homology among mammalian growth factor receptors with tyrosine-specific protein kinase activity has led to speculation that these receptors derived from a common evolutionary precursor. We report the identification of a novel growth factor receptor from Drosophila cell cultures that has dual binding specificity for both insulin and epidermal growth factor (EGF). This 100-kDa protein is also related antigenically to the mammalian receptors for EGF and possibly insulin but may not correspond to the mammalian counterpart of either receptor in Drosophila. The Drosophila protein is recognized by antisera directed against the mammalian receptor for EGF in immunoblot hybridizations. It can be affinity labeled with either 125I-labeled insulin or 125I-labeled EGF after immunoprecipitation with anti-EGF receptor antiserum. Excess unlabeled EGF or insulin will block the affinity labeling with either growth factor, suggesting that both EGF and insulin share a common binding site on the 100-kDa Drosophila receptor. This Drosophila protein, therefore, may be closely related to an evolutionary precursor of the mammalian receptors for insulin and EGF.