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

Ixodes scapularis Src tyrosine kinase facilitates Anaplasma phagocytophilum survival in its arthropod vector

Anaplasma phagocytophilum, the agent of human anaplasmosis, is an obligate intracellular bacterium that uses multiple survival strategies to persist in Ixodes scapularis ticks. Our previous study showed that A. phagocytophilum efficiently induced the tyrosine phosphorylation of several Ixodes proteins that includes extended phosphorylation of actin at tyrosine residue Y178. In order to identify the tyrosine kinase responsible for the A. phagocytophilum induced tyrosine phosphorylation of proteins, we combed the I. scapularis genome and identified a non-receptor Src tyrosine kinase ortholog. I. scapularis Src kinase showed high degree of amino acid sequence conservation with Dsrc from Drosophila melanogaster. We noted that at different developmental stages of I. scapularis ticks, larvae expressed significantly higher levels of src transcripts in comparison to the other stages. We found that A. phagocytophilum significantly reduced Src levels in unfed nymphs and in nymphs while blood feeding (48 h during feeding) in comparison to the levels noted to relative uninfected controls. However, A. phagocytophilum increased Src levels in fully engorged larvae and nymphs (48 h post feeding) and in vitro tick cells in comparison to the relative uninfected controls. Inhibition of Src kinase expression and activity by treatment with src-dsRNA or Src-inhibitor, respectively, significantly reduced A. phagocytophilum loads in ticks and tick cells. Overall, our study provides evidence for the important role of I. scapularis Src kinase in facilitating A. phagocytophilum colonization and survival in the arthropod vector.

Parcas, a regulator of non-receptor tyrosine kinase signaling, acts during anterior-posterior patterning and somatic muscle development in Drosophila melanogaster

We have isolated parcas (pcs) in a screen to identify novel regulators of muscle morphogenesis. Pcs is expressed in the ovary and oocyte during oogenesis and again in the embryo, specifically in the developing mesoderm, throughout muscle development. pcs is first required in the ovary during oogenesis for patterning and segmentation of the early Drosophila embryo due primarily to its role in the regulation of Oskar (Osk) levels. In addition to the general patterning defects observed in embryos lacking maternal contribution of pcs, these embryos show defects in Wingless (Wg) expression, causing losses of Wg-dependent cell types within the affected segment. pcs activity is required again later during embryogenesis in the developing mesoderm for muscle development. Loss and gain of function studies demonstrate that pcs is necessary at distinct times for muscle specification and morphogenesis. Pcs is predicted to be a novel regulator of non-receptor tyrosine kinase (NRTK) signaling. We have identified one target of Pcs regulation, the Drosophila Tec kinase Btk29A. While Btk29A appears to be regulated by Pcs during its early role in patterning and segmentation, it does not appear to be a major target of Pcs regulation during muscle development. We propose that Pcs fulfils its distinct roles during development by the regulation of multiple NRTKs.

Tec29 controls actin remodeling and endoreplication during invagination of the Drosophila embryonic salivary glands

Epithelial invagination is necessary for formation of many tubular organs, one of which is the Drosophila embryonic salivary gland. We show that actin reorganization and control of endocycle entry are crucial for normal invagination of the salivary placodes. Embryos mutant for Tec29, the Drosophila Tec family tyrosine kinase, showed delayed invagination of the salivary placodes. This invagination delay was partly the result of an accumulation of G-actin in the salivary placodes, indicating that Tec29 is necessary for maintaining the equilibrium between G- and F-actin during invagination of the salivary placodes. Furthermore, normal invagination of the salivary placodes appears to require the proper timing of the endocycle in these cells; Tec29 must delay DNA endoreplication in the salivary placode cells until they have invaginated into the embryo. Taken together, these results show that Tec29 regulates both the actin cytoskeleton and the cell cycle to facilitate the morphogenesis of the embryonic salivary glands. We suggest that apical constriction of the actin cytoskeleton may provide a temporal cue ensuring that endoreplication does not begin until the cells have finished invagination.

poirot,a new regulatory gene ofDrosophila oskaracts at the level of the short Oskar protein isoform

Embryonic germ cell formation and abdomen development in Drosophila requires localisation and site specific translation of oskar mRNA in the posterior part of the oocyte. Targeting of oskar function to the posterior pole of the oocyte needs a large set of proteins and RNAs, encoded by posterior group genes. Consequently, mutations in the posterior group genes can result in embryos without abdomens and/or germ cells. During a systematic hobo-mediated mutant isolation screen, we identified poirot, a novel posterior group gene, owing to its germ cell-less phenotype. We show that the lack of poirot activity dramatically decreases OSK protein levels, without affecting the oskar mRNA distribution. In poirot mutant oocytes, delocalised OSK protein is observed, indicating that wild-type poirot has a role in the anchoring process of the OSK protein at the posterior pole. Furthermore, we demonstrate that poirot acts in an isoform-specific manner, only the short OSK isoform is affected, while the long OSK isoform remains at wild-type levels in poirot mutants.

The Tec29 tyrosine kinase is required during Drosophila embryogenesis and interacts with Src64 in ring canal development

Tec29 encodes the only known Drosophila member of the Tec tyrosine kinases. By identifying the first mutations in Tec29 (formerly Src29A), we show that it is essential for head involution during embryogenesis and for ring canal development during oogenesis. Tec29 mutant egg chambers are defective in transfer of cytoplasm from the accessory nurse cells through the ring canals into the oocyte. Growth of the mutant ring canals is arrested, and they lack the strong phosphotyrosine localization seen in wild-type ring canals. Mutants lacking the Drosophila Src homolog Src64 show the same phenotype, and we show that Src64 is required for the localization of Tec29 to the ring canals. This interaction is similar to that between vertebrate Src and Tec kinases and suggests that Tec29 is an effector of Src64 that modifies ring canal components required for growth.

Tyrosine kinase signaling at fertilization

The unfertilized egg is a highly differentiated cell that retains unlimited developmental potential. The execution of that potential requires signal transduction pathways that release the egg from its quiescent metabolic state, direct the union of the maternal and paternal genome, and initiate a developmental program that will guide embryogenesis. The egg is equipped with an array of cytosolic as well as cell surface receptor protein tyrosine kinases as part of a preassembled signal transduction mechanism. These protein tyrosine kinases have been found to act at several points during this egg activation process, beginning as early as the initial sperm-egg interaction. While many of these kinase functions are common to all cells, several functions unique to fertilization demonstrate the versatility of this class of protein kinases.

High expression of the tec gene product in murine testicular germ cells and erythroblasts

Tec is a novel non-receptor-type protein tyrosine kinase that was originally identified from a murine liver cDNA library. While the function of Tec remains unknown, it was shown recently that two Tec-related kinases are involved directly in the growth and differentiation of bone marrow stem cells. As the localization of Tec protein has not been reported yet, immunohistochemical and immunochemical studies of various murine organs were conducted in the present study to clarify which cells express this kinase protein. An intense immunohistologic reaction was observed in neonatal and adult testicular germ cells, and neonatal and fetal hepatic erythroblasts. In addition, a clear immunostaining was noted in neonatal and adult tubal epithelial cells, hepatocytes, basal cells of the non-glandular stomach, foveolar epithelium of the glandular stomach, sebaceous cells of the skin and fetal cartilage. The immune reaction of germ cells and erythroblasts was observed in the cell membrane, although this protein does not have a transmembrane domain. Supportive western blotting of testis, adult liver, spleen and heart of adult C.B-17 mice with the use of anti-Tec antibody demonstrated a heavy 70 kDa band in the liver and testis, and a much weaker, small band in the heart and spleen. These results suggest that Tec protein has a specific role in testicular germ cells and erythroblasts.

Cell- and tissue-specific expression of putative protein kinase mRNAs in the embryonic leech, Hirudo medicinalis

Protein kinases play important roles in various cellular interactions underlying metazoan development. To complement existing analyses of protein kinase function in the development of members of the three phyla, Chordata, Arthropoda, and Nematoda, we have begun to examine the cell- and tissue-specific localization of protein kinases in another metazoan phylum, the Annelida. For this purpose, we used the polymerase chain reaction to amplify putative protein kinase catalytic domain cDNAs from the medicinal leech, Hirudo medicinalis. This strategy allowed us to identify 11 cytoplasmic and receptor tyrosine kinase catalytic domains, and 2 cytoplasmic serine/threonine kinase catalytic domains. Using these cDNAs as probes for nonradioactive whole-mount in situ hybridization, we examined the embryonic expression pattern of each of the corresponding putative kinase mRNAs. As has been found in other species, most of the Hirudo protein kinase mRNAs were expressed in a highly specific manner in certain embryonic cells and tissues. We found both neuron- and glia-specific kinases within the nervous system, as well as kinases expressed in non-nervous tissues, such as the haemocoelomic, muscular, and excretory systems. These kinase cDNAs encode proteins likely to be critical for proper development, and can be used as cell- and tissue-specific histological probes for the analysis of Hirudo embryogenesis.

Cytokine receptors and signal transduction

The past few years have seen an explosion in the identification, cloning and characterization of cytokines and their receptors. The pleiotropic effects of many of the growth factors and the considerable redundancy in the actions of growth factors have contributed to a mass of descriptive literature that often seems to defy summary. Only recently have common concepts begun to emerge. First, cytokines mediate their effects through a large family of receptors that have evolved from a common progenitor and retain structural and functional similarities. Within the haematopoietic system, the cytokines are not usually instructive in differentiation, but rather supportive, and may contribute to some differentiation-specific responses. The patterns of expression of cytokine receptors are therefore a product of differentiation and provide for changes in physiological regulation. The second important concept that is emerging is that the cytokines mediate their mitogenic effects through a common signal-transducing pathway involving tyrosine phosphorylation. Thus, although the cytokine receptor superfamily members do not have intrinsic protein tyrosine kinase activity, by coupling to activation of tyrosine phosphorylation they may affect cell growth by pathways that are common with the large family of growth factor receptors that contain intrinsic protein tyrosine kinase activity. The coupling of cytokine binding to tyrosine phosphorylation and mitogenesis requires a relatively small membrane-proximal domain of the receptors. This region has limited sequence similarity which may be required for the association of individual receptors with an appropriate kinase. Activation of kinase activity results from the dimerization or oligomerization of receptor homodimers or heterodimers. Again this requirement is similar to that seen with the growth factor receptors which have intrinsic protein tyrosine kinase activity. The protein tyrosine kinases that couple cytokine binding to tyrosine phosphorylation are members of the Jak family of kinases. The ubiquitous expression of these kinases provides a common cellular background on which the cytokine receptors can function and on which unique functionally distinct receptors have evolved. In particular, tyk2 is required for the responses initiated by IFN-alpha while Jak2 has been implicated in the responses to G-CSF, IL-3, EPO, growth hormone, prolactin and IFN-gamma.(ABSTRACT TRUNCATED AT 400 WORDS)

Protein-tyrosine kinase activity of alternate protein products of the Drosophila Dsrc28C locus

The Dsrc28C gene is a unique member of the extensive tyrosine kinase family. Two proteins, p66Dsrc28C and p55Dsrc28C, are encoded by the gene. Each contains a highly conserved tyrosine kinase domain and each lacks the usual amino-terminal myristylation signal. The protein-tyrosine kinase activity of the two proteins was investigated through a recombinant baculovirus expression system. p66Dsrc28C expressed from a recombinant baculovirus phosphorylated a large number of Sf9 cell proteins on tyrosine. A group of proteins of approximately 100 kDa were the preferred substrates. No evidence of p66Dsrc28C autophosphorylation was found. In contrast to p66Dsrc28C, p55Dsrc28C did not exhibit protein-tyrosine kinase activity when expressed from a recombinant baculovirus. A deletion derivative of p66Dsrc28C lacking the SH3 and SH2 domains also failed to phosphorylate Sf9 cell proteins. These results suggest that the protein-tyrosine kinase activity of Dsrc28C proteins is tightly regulated.

Characterization and spatial distribution of the ELAV protein during Drosophila melanogaster development

The embryonic lethal abnormal visual system (elav) gene of Drosophila melanogaster is required for the development and maintenance of the nervous system. Transcripts from this locus are distributed ubiquitously throughout the nervous system at all developmental stages. A product of this gene, the ELAV protein, has homology to known RNA binding proteins. The localization of the ELAV protein was studied in all developmental stages using antibodies that were generated against a hybrid protein made in Escherichia coli. In general, these data are consistent with previous results and demonstrate that (1) the ELAV protein is detected in the developing embryonic nervous system at a time coincident with the birth of the first neurons, (2) the ELAV protein is first detected in the majority of neurons of the central and peripheral nervous systems of embryos, larvae, pupae, and adults, (3) the ELAV protein appears to be localized to the nucleus, and (4) the ELAV protein is not detected in neuroblasts or identifiable glia. These data also provide new information concerning elav expression and show that (1) ELAV is not expressed in the ganglion mother cells (GMCs), (2) while the ELAV protein is localized to the nucleus, it is not uniformly distributed throughout this structure, and (3) other Drosophila species do express an ELAV-like antigen. We propose that the elav gene provides a neuronal-housekeeping function that is required for the successful posttranscriptional processing of transcripts from a set of genes the function of which is required for proper neuronal development and maintenance.

A gene related to the proto-oncogene fps/fes is expressed at diverse times during the life cycle of Drosophila melanogaster

The proto-oncogene fps/fes encodes a distinctive type of protein-tyrosine kinase. We identified a Drosophila gene (dfps85D) whose product resembles the proteins encoded by vertebrate fps/fes and the closely related gene fer. dfps85D is located at chromosomal position 85D10-13 and is unlikely to correspond to any previously defined genetic locus in Drosophila melanogaster. Expression of the gene is entirely zygotic in origin and occurs throughout the life cycle. But hybridization in situ revealed that the pattern of expression is specialized and evolves in a provocative manner. The most notable feature of expression is the diversity of developmental periods, tissues, and cells in which it occurs. In some tissues, expression is transient; in others, it is continuous. Expression occurs in both mitotic and terminally differentiated tissue and, at various times in development, is prominent in imaginal disks, gut, muscle, testes, ovaries, retina, and other neural tissues. It appears that the use of dfps85D is more diversified than that of other Drosophila protein-tyrosine kinases reported to date and contrasts sharply with the restricted expression of fps itself in vertebrates. The detailed description of expression provided here will help guide the search for mutants in dfps85D.

A gene related to the proto-oncogene fps/fes is expressed at diverse times during the life cycle of Drosophila melanogaster

The proto-oncogene fps/fes encodes a distinctive type of protein-tyrosine kinase. We identified a Drosophila gene (dfps85D) whose product resembles the proteins encoded by vertebrate fps/fes and the closely related gene fer. dfps85D is located at chromosomal position 85D10-13 and is unlikely to correspond to any previously defined genetic locus in Drosophila melanogaster. Expression of the gene is entirely zygotic in origin and occurs throughout the life cycle. But hybridization in situ revealed that the pattern of expression is specialized and evolves in a provocative manner. The most notable feature of expression is the diversity of developmental periods, tissues, and cells in which it occurs. In some tissues, expression is transient; in others, it is continuous. Expression occurs in both mitotic and terminally differentiated tissue and, at various times in development, is prominent in imaginal disks, gut, muscle, testes, ovaries, retina, and other neural tissues. It appears that the use of dfps85D is more diversified than that of other Drosophila protein-tyrosine kinases reported to date and contrasts sharply with the restricted expression of fps itself in vertebrates. The detailed description of expression provided here will help guide the search for mutants in dfps85D.