DNA sequence, structure, and tyrosine kinase activity of the Drosophila melanogaster Abelson proto-oncogene homolog

Gene mapping reveals the association between tyrosine protein kinase Abl1 and the silk yield of Bombyx mori

The Z chromosome of the silkworm contains a major gene that influences silk yield. This major locus on chromosome Z accounts for 35.10% of the phenotypic variance. The location and identification of the gene have been a focus of silkworm genetics research. Unfortunately, identification of this gene has been difficult. We used extreme phenotype subpopulations and selected from a backcross population, BC₁ M, which was obtained using the high-yield strain 872B and the low-yield strain IS-Dazao as parents, for mapping the gene on the chromosome Z. The candidate region was narrowed down to 134 kb at the tip of the chromosome. BmAbl1 in this region correlated with silk gland development by spatiotemporal expression analysis. This gene was differentially expressed in the posterior silk glands of the high- and low-yield strains. In BmAbl1, an insertion-deletion (indel) within the 10th exonic region and an SNP within the 6th intronic region were detected and shown to be associated with cocoon shell weight in 84 Bombyx mori strains with different yields. Nucleotide diversity analysis of BmAbl1 and its 50 kb flanking regions indicated that BmAbl1 has experienced strong artificial selection during silkworm domestication. This study is the first to identify the genes controlling silk yield in the major QTL of the Z chromosome using forward genetics.

Abl tyrosine kinases in T-cell signaling

Stimulation of the T-cell antigen receptor (TCR) leads to the activation of signaling pathways that are essential for T-cell development and the response of mature T cells to antigens. The TCR has no intrinsic catalytic activity, but TCR engagement results in tyrosine phosphorylation of downstream targets by non-receptor tyrosine kinases. Three families of tyrosine kinases have long been recognized to play critical roles in TCR-dependent signaling. They are the Src, zeta-associated protein of 70 kDa, and Tec families of kinases. More recently, the Abelson (Abl) tyrosine kinases have been shown to be activated by TCR engagement and to be required for maximal TCR signaling. Using T-cell conditional knockout mice deficient for Abl family kinases, Abl (Abl1) and Abl-related gene (Arg) (Abl2), it was recently shown that loss of Abl kinases results in defective T-cell development and a partial block in the transition to the CD4(+)CD8(+) stage. Abl/Arg double null T cells exhibit impaired TCR-induced signaling, proliferation, and cytokine production. Moreover, conditional knockout mice lacking Abl and Arg in T cells exhibit impaired CD8(+) T-cell expansion in vivo upon Listeria monocytogenes infection. Thus, Abl kinase signaling is required for both T-cell development and mature T-cell function.

A DNA damage signal activates and derepresses exon inclusion in Drosophila TAF1 alternative splicing

Signal-dependent alternative splicing is important for regulating gene expression in eukaryotes, yet our understanding of how signals impact splicing mechanisms is limited. A model to address this issue is alternative splicing of Drosophila TAF1 pre-mRNA in response to camptothecin (CPT)-induced DNA damage signals. CPT treatment of Drosophila S2 cells causes increased inclusion of TAF1 alternative cassette exons 12a and 13a through an ATR signaling pathway. To evaluate the role of TAF1 pre-mRNA sequences in the alternative splicing mechanism, we developed a TAF1 minigene (miniTAF1) and an S2 cell splicing assay that recapitulated key aspects of CPT-induced alternative splicing of endogenous TAF1. Analysis of miniTAF1 indicated that splice site strength underlies independent and distinct mechanisms that control exon 12a and 13a inclusion. Mutation of the exon 13a weak 5' splice site or weak 3' splice site to a consensus sequence was sufficient for constitutive exon 13a inclusion. In contrast, mutation of the exon 12a strong 5' splice site or moderate 3' splice site to a consensus sequence was only sufficient for constitutive exon 12a inclusion in the presence of CPT-induced signals. Analogous studies of the exon 13 3' splice site suggest that exon 12a inclusion involves signal-dependent pairing between constitutive and alternative splice sites. Finally, intronic elements identified by evolutionary conservation were necessary for full repression of exon 12a inclusion or full activation of exon 13a inclusion and may be targets of CPT-induced signals. In summary, this work defines the role of sequence elements in the regulation of TAF1 alternative splicing in response to a DNA damage signal.

four-jointed interacts with dachs, abelson and enabled and feeds back onto the Notch pathway to affect growth and segmentation in the Drosophila leg

The molecular basis of segmentation and regional growth during morphogenesis of Drosophila legs is poorly understood. We show that four-jointed is not only required for these processes, but also can direct ectopic growth and joint initiation when its normal pattern of expression is disturbed. These effects are non-autonomous, consistent with our demonstration of both transmembrane and secreted forms of the protein in vivo. The similarities between four-jointed and Notch phenotypes led us to further investigate the relationships between these pathways. Surprisingly, we find that although four-jointed expression is regulated downstream of Notch activation, four-jointed can induce expression of the Notch ligands, Serrate and Delta, and may thereby participate in a feedback loop with the Notch signaling pathway. We also show that four-jointed interacts with abelson, enabled and dachs, which leads us to suggest that one target of four-jointed signaling is the actin cytoskeleton. Thus, four-jointed may bridge the gap between the signals that direct morphogenesis and those that carry it out.

Identification of immune-related protein kinases from mosquitoes (Aedes aegypti)

Protein kinases are known to be involved in signal transduction for numerous physiological events. However, little is known about the roles of protein kinases in insect immunity. A fragment around 150 bp was amplified by polymerase chain reaction using cDNA templates from bacterial inoculated mosquitoes and primers corresponding to the conserved domain of protein kinases. Based on sequence analysis, 11 groups of protein kinases were characterized including 3 nonreceptor tyrosine kinases, 3 receptor tyrosine kinases, 3 serine/threonine kinases, and 2 novel protein kinases. The most abundant kinase obtained in this study reveals a high degree of similarity to human cholinesterase-related cell division controller (CHED) protein kinase. The expression of this mosquito CHED-like kinase is not detectable in normal female mosquitoes, but induced only after bacterial inoculation and trauma. A mosquito protein kinase was demonstrated to share homology with a plant Tousled gene, but has not yet been characterized in the animal system. In addition, analysis of the sequences of several protein kinases cloned from mosquitoes suggests that they might be involved in the regulation of cellular or humoral immunity.

Dominant effects of the bcr-abl oncogene on Drosophila morphogenesis

We targeted expression of human/fly chimeric Bcr-Abl proteins to the developing central nervous system (CNS) and eye imaginal disc of Drosophila melanogaster. Neural expression of human/fly chimeric P210 Bcr-Abl or P185 Bcr-Abl rescued abl mutant flies from pupal lethality, indicating that P210 and P185 Bcr-Abl can substitute functionally for Drosophila Abl during axonogenesis. However, increased levels of neurally expressed P210 or P185 Bcr-Abl but not Drosophila Abl produced CNS defects and lethality. Expression of P210 or P185 in the eye imaginal disc produced a dominant rough eye phenotype that was dependent on dosage of the transgene. Drosophila Enabled, previously identified as a suppressor of the abl mutant phenotype and substrate for Drosophila Abl kinase, had markedly increased phosphotyrosine levels in Bcr-Abl expressing Drosophila, indicating that it is a substrate for Bcr-Abl as well. Drosophila, therefore, is a suitable model system to identify Bcr-Abl interactions important for signal transduction and oncogenesis.

The making of an erythroid cell. Molecular control of hematopoiesis

The number of circulating red cells is regulated by the daily balance between two processes: the destruction of the old red cells in the liver and the generation of new cells in the bone marrow. The process during which hematopoietic stem cells generate new red cells is called erythropoiesis. This manuscript will describe the molecular mechanisms involved in the process of erythroid differentiation as we understand them today. In particular it will review how erythroid specific growth factor-receptor interactions activate specific transcription factors to turn on the expression of the genes responsible for the establishment of the erythroid phenotype.

Expression and immunolocalization of p59c-fyn tyrosine kinase in rat eggs

Fertilization overcomes meiotic arrest by triggering a series of biochemical events, resulting in activation of the egg. A small group of protein tyrosine kinases (PTKs) have been identified in eggs of invertebrates and lower vertebrates and inhibitor studies have suggested that they play a role in late events of egg activation. A recent study using the sea urchin system demonstrated that Fyn kinase was expressed in eggs and was activated within minutes of fertilization. In the present study, Western blot analysis as well as immune complex kinase assay demonstrated that p59(c-fyn) kinase was expressed in both unfertilized and fertilized rat eggs. Immunofluorescence confocal microscopy demonstrated that Fyn kinase was localized to the egg cortex but also to the polar body and the fertilizing cone which are elevated from the cortical cytoplasm of the activated egg. Surprisingly, Fyn was also found to be highly concentrated over the meiotic and mitotic spindles. To date, Fyn is the first PTK demonstrated to be present in the mammalian egg. Localization of Fyn to the egg cortex as well as the spindle microtubules indicates that this protein kinase may have multiple functions within the egg.

The segment-polarity gene fused is highly conserved in Drosophila

The segment polarity gene fused (fu) is involved in specification of positional information inside embryonic segments in Drosophila melanogaster (Dm). The predicted Fused (Fu) protein contains a serine/threonine kinase domain and a second domain with unknown function. We cloned and sequenced the fu homologous gene from Drosophila virilis (Dv) and made an interspecific DNA sequence comparison to identify regions that have been conserved during evolution. Comparison of the predicted amino acid (aa) sequences reveals two regions of strong homology, one corresponding to the kinase domain (268 aa), the other located in the third exon of the Dm fu gene, suggesting a functional importance for this region. Stretches of significantly conserved sequences are also observed in the 5' and 3' untranslated regions. Weak homology is seen in the intronic sequences although the adjacent exonic sequences are mostly conserved. These findings indicate a high conservation of the predicted Fu protein during the evolution of Drosophila.

BCR-ABL: an anti-apoptosis gene in chronic myelogenous leukemia

The expression of bcr-abl in chronic myelogenous leukemia leads to a large increase in the generation of mature myeloid cells. The key biochemical alteration in this disease is an increased Abl kinase activity. This up-regulation in activity is mediated through the binding of a portion of the Bcr molecule to the SH2 regulatory domain of the Abl protein. One effect of this alteration is a marked increase in resistance to drug induced cell death by apoptosis. This resistance can be overcome with the use of appropriate antisense oligonucleotides to the bcr-abl gene. The role and contribution of apoptosis to the development of the disease and the prospect of using antisense oligonucleotides as therapeutic agents is discussed.

The non-receptor tyrosine kinase Lyn is localised in the developing murine blood-brain barrier

The blood-brain barrier, formed by brain endothelium, is critical for brain function. The development of the blood-brain barrier involves brain angiogenesis and endothelial cell differentiation, processes which require active signal transduction pathways. The differentiation of brain endothelial cells to the "blood-brain-barrier phenotype" involves cytoskeletal changes which modulate the tightness of the barrier. In order to identify signal transduction proteins involved in blood-brain barrier development, cDNA from bovine and murine brain endothelial cells was used in a polymerase chain reaction for cloning of DNA encoding Src homology 3 domains. Src homology 3 domains are structural domains found in many signal transduction proteins. These domains often mediate interaction of signaling proteins with the cytoskeleton and therefore may play a role in the regulation of the cytoskeletal changes which occur during blood-brain-barrier development. Unexpectedly, all bovine and murine clones analyzed from polymerase chain reactions encoded the Src homology 3 domain of one protein, namely the non-receptor tyrosine kinase, Lyn, which is involved in signal transduction in cells of the hemopoietic system. In situ hybridization analyses confirmed the presence of lyn mRNA in developing blood vessels in embryonic and early post-natal mouse brain, but not in endothelium outside the brain. In bovine brain endothelial cells in primary culture, p53lyn is highly abundant and present in two forms which have different patterns of tyrosine phosphorylation. These data suggest that Lyn may be involved in transduction of growth and differentiation signals required for blood-brain-barrier development.

Protein phosphorylation pattern and role of products of c-erbB-1 and c-abl proto-oncogenes in murine preimplantation embryonic development

PROBLEM

To investigate the protein phosphorylation pattern and role of products of c-erbB-1 and c-abl proto-oncogenes with known tyrosine kinase activity in preimplantation embryonic development in mice.

METHOD

The protein phosphorylation pattern was studied by in vitro 32P metabolic labeling of murine ova/embryos as well as by in vitro kinase assay performed directly on various ova/embryos extracts. The role of products of c-erbB-1 (170 kDa, receptor for epidermal growth factor [EGF]) and c-abl proto-oncogenes (150 kDa) was examined by in vitro culturing murine embryos in the presence of monoclonal antibodies to respective protein products and by co-culturing with EGF, the ligand for EGF receptor (EGF-R).

RESULTS

In vitro metabolic labeling of murine ova/embryos showed 32P incorporation into at least two protein bands of murine ova (M(r) 81 and 36 kDa), six protein bands of two-cell (M(r) 81, 36; and 97, 52, 22 and 19 kDa, respectively), six protein bands of morula (M(r) 81, 36; 97, 22, and 19; and 33 kDa, respectively), and eight protein bands of blastocyst (81, 36; 97, 22, 19; and 115, 58, and 15 kDa, respectively), stage embryos; there were some specific bands in each stage. Prolonged labeling from 2 to 4 h not only resulted in a relative increase in 32P incorporation into these proteins but also revealed additional bands in morula (M(r) 133 and 115 kD) and blastocyst (M(r) 49, 33, and 31 kD) stage embryos. In vitro kinase assays performed directly on various ova/embryos extracts revealed at least three phosphoproteins (M(r) 58, 36 and 33, respectively) that were common to ova, two-cell, morula, and early/late blastocyst stage embryos. Additionally, three protein bands each in murine ova and two-cell embryos (M(r) 108, 81, 73 kDa, respectively), and four protein bands of late blastocyst (M(r) 108, 73; 133 and 18 kDa, respectively) stage embryos were also revealed. Culture of two-cell embryos in the presence of EGF, the ligand for EGF-receptor, resulted in a concentration dependent increase (P < .001) in the number of cells per blastocyst. Monoclonal antibody to c-erbB-1 170 kDa protein (receptor for EGF) did not affect development of in vitro cultured murine embryos from two-cell to morula, but significantly (P < .001) inhibited the in vitro development of morula to late blastocyst stage. Monoclonal antibody to c-abl protein inhibited the development of murine embryos from two-cell to morula (P < .017), as well as, from morula to late blastocyst stage (P < .002 to .01).

CONCLUSIONS

These results suggest that the stage-specific protein phosphorylation pattern and specific products of c-erB-1 and c-abl proto-oncogenes may have a role in preimplantation embryonic development in mice.

Identification of an abl-related protein tyrosine kinase in the cortex of the sea urchin egg: possible role at fertilization

Fertilization results in the tyrosine phosphorylation of several egg proteins within minutes of sperm-egg binding, although the identity of the kinase(s) involved and the mechanism of regulation is not known. In the present study, we have used site-directed antibodies based on the predicted amino acid sequence of a sea urchin egg transcript that shares significant homology with members of the ABL family of protein tyrosine kinases. These antibodies identified a 220-kDa protein kinase, highly enriched in the egg cortex, where it is tightly associated with detergent-insoluble cytoskeletal elements. The enzyme is capable of phosphorylating synthetic peptide substrates which were used to characterize the kinase activity in an immune-complex assay. Measurement of the protein tyrosine kinase activity immunoprecipitated at different times after fertilization revealed that the level of kinase activity is transiently elevated during the first few minutes postinsemination. Western blot analysis indicated that the amount of the 220-kDa protein did not increase significantly during this period, so the increased kinase activity probably results from activation of the enzyme. These in vitro studies indicate that the 220-kDa abl-related kinase is one of the protein kinases activated during fertilization and suggest that it may play a role in the egg activation process.

Proto-oncogenes and signaling processes in neural tissues

The study of ubiquitously expressed proto-oncogenes or tumor suppressor genes provided important insights into the second messenger signaling pathways common to neural and non-neural tissues. Therefore, it is expected that the analysis of proto-oncogenes expressed in neural tissues should probe into neurotrophic and neurotransmitter receptors, ion channels and other molecules involved in processes underlying basic physiological functions of the nervous system. This expectation is fulfilled by ample experimental evidence. Using the trk, abl and src families of tyrosine kinase encoded proto-oncogenes, we discuss here new insights into the structural and functional organization of neural tissues gained from the molecular and genetic analyses of these genes and their products. Special attention is given to the description of initial steps of signaling through the Trk receptors in response to neurotrophic factors of the Nerve Growth Factor family. The genetic analysis of the Drosophila abl gene product identified new gene products that interact with the Abl protein. This analysis illuminates the power of Drosophila genetics in dissecting components of a signal transduction pathway. The Src-family of non-receptor type protein-tyrosine kinases is discussed from the point of functional redundancy as revealed by targeted gene disruption and expression studies. The recent progress in the field of proto-oncogenes has been impressive and it is expected that proto-oncogenes will continue to provide valuable tools in the study of the complex signaling pathways that underlie the physiological functions of the central nervous system.

Abl tyrosine kinase in signal transduction and cell-cycle regulation

Although the biological function of the c-Abl tyrosine kinase remains unsolved, potentially productive avenues towards the elucidation of that function have been identified by recent progress. An F-actin binding and a sequence-specific DNA-binding domain have been discovered in c-Abl, and DNA binding has been shown to be cell-cycle regulated. Deletion of those two domains in the mouse c-Abl results in a loss of biological function despite the production of an active tyrosine kinase. These findings suggest a role for c-Abl in the regulation of processes occurring on F-actin and on specific DNA elements.

A human putative lymphocyte G0/G1 switch gene homologous to a rodent gene encoding a zinc-binding potential transcription factor

G0S24 is a member of a set of genes (putative G0/G1 switch regulatory genes) that are expressed transiently within 1-2 hr of the addition of lectin or cycloheximide to human blood mononuclear cells. Comparison of a full-length cDNA sequence with the corresponding genomic sequence reveals an open reading frame of 326 amino acids, distributed across two exons. Potential phosphorylation sites include the sequence PSPTSPT, which resembles an RNA polymerase II repeat reported to be a target of the cell cycle control kinase cdc2. Comparison of the derived protein sequence with those of rodent homologs allows classification into three groups. Group 1 contains G0S24 and the rat and mouse TIS11 genes (also known as TTP, Nup475, and Zfp36). Members of this group have three tetraproline repeats. Groups 1 and 2 have a serine-rich region and an "arginine element" (RRLPIF) at the carboxyl terminus. All groups contain cysteine- and histidine-rich putative zinc finger domains and a serine-phenylalanine "SFS" domain similar to part of the large subunit of eukaryotic RNA polymerase II. Comparison of group 1 human and mouse genomic sequences shows high conservation in the 5' flank and exons. A CpG island suggests expression in the germ line. G0S24 has potential sites for transcription factors in the 5' flank and intron; these include a serum response element. Protein and genomic sequences show similarities with those of a variety of proteins involved in transcription, suggesting that the G0S24 product has a similar role.

Increased levels of the Drosophila Abelson tyrosine kinase in nerves and muscles: subcellular localization and mutant phenotypes imply a role in cell-cell interactions

Mutations in the Drosophila Abelson tyrosine kinase have pleiotropic effects late in development that lead to pupal lethality or adults with a reduced life span, reduced fecundity and rough eyes. We have examined the expression of the abl protein throughout embryonic and pupal development and analyzed mutant phenotypes in some of the tissues expressing abl. abl protein, present in all cells of the early embryo as the product of maternally contributed mRNA, transiently localizes to the region below the plasma membrane cleavage furrows as cellularization initiates. The function of this expression is not yet known. Zygotic expression of abl is first detected in the post-mitotic cells of the developing muscles and nervous system midway through embryogenesis. In later larval and pupal stages, abl protein levels are also highest in differentiating muscle and neural tissue including the photoreceptor cells of the eye. abl protein is localized subcellularly to the axons of the central nervous system, the embryonic somatic muscle attachment sites and the apical cell junctions of the imaginal disk epithelium. Evidence for abl function was obtained by analysis of mutant phenotypes in the embryonic somatic muscles and the eye imaginal disk. The expression patterns and mutant phenotypes indicate a role for abl in establishing and maintaining cell-cell interactions.

Philadelphia chromosome-positive leukaemia: the translocated genes and their gene products

Overwhelming evidence indicates a role for the deregulated ABL protein tyrosine kinase in the aetiology of CML and Ph-positive acute leukaemia. These disorders are characterized by the generation of BCR/ABL fusion proteins with elevated tyrosine kinase activity. Although much is known concerning the transforming potential of ABL proteins in various systems, very little is understood of the normal function and mode of regulation of ABL activity. The mechanism of oncogenic activation is therefore also obscure. In spite of this, our understanding of the molecular details of these chromosomal translocations allows the design of therapies directed against their unique, leukaemia-specific proteins and RNA products.

Protein tyrosine kinases in nervous system development

Protein tyrosine kinases are important mediators of intracellular signaling during nervous system development. Activation of receptor protein tyrosine kinases by neurotrophic factors are initial events in the development of discrete cell populations. The patterns of expression and characterization of substrates for nonreceptor protein tyrosine kinases indicates that they also play a crucial role in neuronal development. The observed functional redundancy among protein tyrosine kinases and their associated intracellular signaling pathways underscores the need for further characterization of these novel interactions to elucidate the mechanisms regulating nervous system development.

Two Drosophila receptor-like tyrosine phosphatase genes are expressed in a subset of developing axons and pioneer neurons in the embryonic CNS

Two Drosophila receptor-like tyrosine phosphatase genes, DPTP99A and DPTP10D, were characterized. Protein products of these genes show distinct expression patterns specific to subsets of developing CNS axons. DPTP99A expression coincides with the onset of axonogenesis and is expressed in several pioneer neurons, including aCC and RP2, which pioneer the intersegmental nerve; its proteins are transiently expressed in the intersegmental and segmental nerves, arguing for a role in the establishment of these nerves. Both genes produce complex sets of transcripts, owing to the alternative utilization of exons and polyadenylation sites. Each gene produces alternative protein forms, which differ in their C-terminal tails. The deduced proteins possess extracellular FN-III repeats and intracellular PTPase domain(s). We discuss the implications of these results and the role of protein tyrosine dephosphorylation in axon outgrowth and guidance.

Kinase activity and genetic characterization of a growth related antigen of Drosophila

The Drosophila developmental antigen recognized by the monoclonal antibody F7D6 is expressed in dividing embryonic and imaginal cells but is lost from all differentiating tissues except electrogenic cells of the nervous system and spontaneously contracting muscles. The 63 kDa antigen is associated with the inner surface of plasma membranes and is expressed in several classes of tumorous mutants of Drosophila. The monoclonal antibody was used for immunoprecipitating the antigen for biochemical characterization and for screening expression vector cDNA libraries. Here we report that this oncodevelopmental antigen is a phosphoprotein and a serine-threonine specific protein kinase. A 1.6 kb cDNA isolated by immunological screening of an ovarian library hybridized to a single band on polytene chromosomes, localizing the gene to 72F on the left arm of the third chromosome. Immunofluorescence assays of deficiency stocks in the region confirmed the location of the gene and identity of the cDNA clone, and mapped the gene between the left breakpoints of Df(3L) st100.62 and Df(3L) stj7, i.e., between 72F3-7 and 73A1-2. The biochemical and genetic properties indicate that this is a novel growth-related kinase of Drosophila.

Temperature-sensitive mutants of Abelson murine leukemia virus deficient in protein tyrosine kinase activity

The effect of two missense mutations in abl on transformation by Abelson murine leukemia virus was evaluated. These mutations led to the substitution of a histidine for Tyr-590 and a glycine for Lys-536. Both changes gave rise to strains that were temperature dependent for transformation of both NIH 3T3 cells and lymphoid cells when expressed in the context of a truncated Abelson protein. In the context of the prototype P120 v-abl protein, the Gly-536 substitution generated a host range mutant that induced conditional transformation in lymphoid cells but had only a subtle effect on NIH 3T3 cells. The combination of both substitutions gave rise to a P120 strain that was temperature sensitive for both NIH 3T3 and lymphoid cell transformation. The Abelson proteins encoded by the temperature-sensitive strain displayed in vitro kinase activities that were reduced when compared with those of wild-type proteins. In vivo, levels of phosphotyrosine were reduced only at the restrictive temperature. Analysis of cells expressing either the wild-type P160 v-abl protein or the P210 bcr/abl protein and an Abelson protein encoded by a temperature-sensitive strain failed to correct this defect, suggesting either that tyrosine phosphorylation in vivo is an intramolecular reaction or that the protein encoded by the temperature-sensitive strain is a poor substrate for tyrosine phosphorylation in vivo. These results raise the possibility that tyrosine phosphorylation of Abelson protein plays a role in transformation.

Conservation of function of Drosophila melanogaster abl and murine v-abl proteins in transformation of mammalian cells

The Drosophila melanogaster abl and the murine v-abl genes encode tyrosine protein kinases (TPKs) whose amino acid sequences are highly conserved. To assess functional conservation between the two gene products, we constructed Drosophila abl/v-abl-chimeric Abelson murine leukemia viruses. In these chimeric Abelson murine leukemia viruses, the TPK and carboxy-terminal regions of v-abl were replaced with the corresponding regions of D. melanogaster abl. The chimeric Abelson murine leukemia viruses were able to mediate morphological and oncogenic transformation of NIH 3T3 cells and were able to abrogate the interleukin-3 dependence of a lymphoid cell line. We also found that a virus that contained both TPK and carboxy-terminal Drosophila abl regions had no in vitro transforming activity for primary bone marrow cells and lacked the ability to induce tumors in susceptible mice. A virus that replaced only a portion of the v-abl TPK region with that of Drosophila abl had low activity in in vitro bone marrow transformation and tumorigenesis assays. These results indicate that the transforming functions of abl TPKs are only partially conserved through evolution. These results also imply that the TPK region of v-abl is a major determinant of its efficient lymphoid cell-transforming activity.

Differential expression of alternate forms of a Drosophila src protein during embryonic and larval tissue differentiation

The Dsrc28C gene encodes two major proteins, p66 and p55, each of which contains a tyrosine kinase domain. Using monoclonal antibodies we have completed a detailed investigation of the spatial expression of Dsrc28C proteins during embryonic and larval development. Differentiation of a number of embryonic tissues is accompanied by the induction of Dsrc28C expression. With the exception of the developing salivary glands which express high levels of p66, developing tissues express the p55 form of Dsrc28C. Notable examples are cells of the and peripheral nervous systems which express p55 from the early stages of neurogenesis through the remainder of embryogenesis and pole cells which transiently express p55 during portions of embryonic stages 10 and 11. Nervous system expression includes the cell bodies and neuronal fibers of the central nervous system, the anterior sensory organs, and the peripheral sensory neurons. During larval development, p55 levels within the central nervous system remain high but substantial changes in the pattern of expression take place. p55 gradually disappears from the neuronal fibers of the central nervous system and from embryonic cell bodies. During the third larval instar, the birth of immature neuroblasts within the ventral and midbrain ganglia, but not within the optic ganglia, is marked by a transient high level of p55 expression. All imaginal cells that have been observed within the larva express the p66 protein. The patterns of expression that we have noted suggest that expression of the p55 form of Dsrc28C protein is an early event in the differentiation of neuronal cells, while expression of the p66 form is characteristic of cells committed to ectodermal cell differentiation.

Genetic analysis of a Drosophila neural cell adhesion molecule: interaction of fasciclin I and Abelson tyrosine kinase mutations

Drosophila fasciclin I is a homophilic cell adhesion molecule expressed in the developing embryo on the surface of a subset of fasciculating CNS axons, all PNS axons, and some nonneuronal cells. We have identified protein-null mutations in the fasciclin I (fas I) gene, and show that these mutants are viable and do not display gross defects in nervous system morphogenesis. The Drosophila Abelson (abl) proto-oncogene homolog encodes a cytoplasmic tyrosine kinase that is expressed during embryogenesis primarily in developing CNS axons; abl mutants show no gross defects in CNS morphogenesis. However, embryos doubly mutant for fas I and abl display major defects in CNS axon pathways, particularly in the commissural tracts where expression of these two proteins normally overlaps. The double mutant shows a clear defect in growth cone guidance; for example, the RP1 growth cone (normally fas I positive) does not follow its normal path across the commissure.

Homology of a yeast actin-binding protein to signal transduction proteins and myosin-I

In yeast, the cortical actin cytoskeleton seems to specify sites of growth of the cell surface. Because the actin-binding protein ABP1p is associated with the cortical cytoskeleton of Saccharomyces cerevisiae, it might be involved in the spatial organization of cell surface growth. ABP1p is localized to the cortical cytoskeleton and its overproduction causes assembly of the cortical actin cytoskeleton at inappropriate sites on the cell surface, resulting in delocalized surface growth. We have now cloned and sequenced the gene encoding ABP1p. ABP1p is a novel protein with a 50 amino-acid C-terminal domain that is very similar to the SH3 domain in the non-catalytic region of nonreceptor tyrosine kinases (including those encoded by the proto-oncogenes c-src and c-abl), in phospholipase C gamma and in alpha-spectrin. We also identified an SH3-related motif in the actin-binding tail domain of myosin-I. The identification of SH3 domains in a family of otherwise unrelated proteins that associate with the membrane cytoskeleton indicates that this domain might serve to bring together signal transduction proteins and their targets or regulators, or both, in the membrane cytoskeleton.

Drosophila abl tyrosine kinase in embryonic CNS axons: a role in axonogenesis is revealed through dosage-sensitive interactions with disabled

During Drosophila embryogenesis, the Abelson tyrosine kinase (abl) is localized in the axons of the central nervous system (CNS). Mutations in abl have no detectable effect on the morphology of the embryonic CNS, and the mutant animals survive to the pupal and adult stages. In the absence of abl function, however, heterozygous mutations or deletions of disabled (dab) exert dominant effects, disrupting axonal organization and shifting the lethal phase of the animals to embryonic and early larval stages. Embryos that are homozygous mutant for both abl and dab fail to develop any axon bundles in the CNS, although the peripheral nervous system and the larval cuticle appear normal. The genetic interaction between these two genes begins to define a process in which both the abl tyrosine kinase and the dab gene product participate in establishing axonal connections in the embryonic CNS of Drosophila.

The viral and cellular forms of the Abelson (abl) oncogene

The precision of molecular biology has allowed a better definition of the components of the Abelson system. We know the gene structures and gene products for the cellular and viral forms of this family of related tyrosine kinases. However, many basic issues first identified in the early biological observations of Abelson, Rabstein, and others remain unanswered. The precise pathway for transformation in biochemical terms remains unknown for Ab-MLV and all of its relatives. Relatively little can be said to explain the preferential growth stimulation for certain hematopoietic cell types by the viral and other altered forms of the oncogene, and no clear insights into the function of the normal cellular forms of the abl oncogene are available. Future progress will certainly depend on the intensive efforts by many workers in the broader field of cellular growth control mechanisms.