Phase-coherent sensing of the center-of-mass motion of trapped-ion crystals

Trapped ions are sensitive detectors of weak forces and electric fields that excite ion motion. Here measurements of the center-of-mass motion of a trapped-ion crystal that are phase coherent with an applied weak external force are reported. These experiments are conducted far from the trap motional frequency on a two-dimensional trapped-ion crystal of approximately 100 ions, and determine the fundamental measurement imprecision of our protocol free from noise associated with the center-of-mass mode. The driven sinusoidal displacement of the crystal is detected by coupling the ion crystal motion to the internal spin degree of freedom of the ions using an oscillating spin-dependent optical dipole force. The resulting induced spin precession is proportional to the displacement amplitude of the crystal, and is measured with near-projection-noise-limited resolution. A 49 pm displacement is detected with a signal-to-noise ratio of 1 in a single experimental determination, which is an order-of-magnitude improvement over prior phase-incoherent experiments. This displacement amplitude is 40 times smaller than the zero-point fluctuations. With our repetition rate, an8.4   pm / Hz displacement sensitivity is achieved, which implies12   ( yN/ion ) / Hz and77   ( μ V/m ) / Hz sensitivities to forces and electric fields, respectively. This displacement sensitivity, when applied on-resonance with the center-of-mass mode, indicates the possibility of weak force and electric field detection below 10-3 yN/ion and 1 nV/m, respectively.

Plasma Heating due to Cyclic Diffusion across a Separatrix

We observe plasma heating due to collisional diffusion across a separatrix when a magnesium ion column in a Penning-Malmberg trap is cyclically pushed back and forth across a partial trapping barrier. The barrier is an externally applied axisymmetric "squeeze" potential, which creates a velocity separatrix between trapped and passing particles. Weak ion-ion collisions then cause separatrix crossings, leading to irreversible heating. The heating rate scales as the square root of the oscillation rate times the collision frequency and thus can be dominant for low-collisionality plasmas. The particle velocity distribution function is measured with coherent laser induced fluorescence and shows passing and trapped particles having an out-of-phase response to the forced plasma oscillations.

Trapped Particle Effects in the Parametric Instability of Near-Acoustic Plasma Waves

Quantitative experiments on the parametric decay instability of near-acoustic plasma waves provide strong evidence that trapped particles reduce the instability threshold below fluid models. At low temperatures, the broad characteristics of the parametric instability are determined by the frequency detuning of the pump and daughter wave, and the wave-wave coupling strength, surprisingly consistent with cold fluid, three-wave theories. However, at higher temperatures, trapped particle effects dominate, and the pump wave becomes unstable at half the threshold pump wave amplitude with similar exponential growth rates as for a cold plasma.

First Test of Long-Range Collisional Drag via Plasma Wave Damping

This paper presents the first experimental confirmation of a new theory predicting enhanced drag due to long-range collisions in a magnetized plasma. The experiments measure damping of Langmuir waves in a multispecies pure ion plasma, which is dominated by interspecies collisional drag in certain regimes. The measured damping rates in these regimes exceed classical predictions of collisional drag damping by as much as an order of magnitude, but agree with the new theory.

Space charge frequency shifts of the cyclotron modes in multi-species ion plasmas

Shifts of the cyclotron frequency away from the "bare" cyclotron frequency are observed to be proportional to the total ion density through the E × B rotation frequency, and to the relative concentration of each ion species, in quantitative agreement with analytic theory. These shifts are measured at small excitation amplitudes on the typical center-of-mass m = 1 mode, and also on cyclotron modes with m = 0 and m = 2 azimuthal dependence. The frequency spacing between these modes is proportional to the rotation frequency of the ion cloud, which is controlled and measured using a "rotating wall" and laser-induced fluorescence. These cylindrical ion plasmas consist of Mg(+) isotopes, with H3 O (+) and O2 (+) impurities. It is observed that the shift in the m = 1 cyclotron frequency is larger for the minority species (25)Mg(+) and (26)Mg(+), than for the majority species (24)Mg(+). A simple center-of-mass model is presented, which is in quantitative agreement with these results. It is also shown that this model interprets and expands the intensity dependent calibration equation, (M/q) = A/f + B/f (2) + CI/f (2).

Compounds from Sichuan and Melegueta peppers activate, covalently and non-covalently, TRPA1 and TRPV1 channels

BACKGROUND AND PURPOSE

Oily extracts of Sichuan and Melegueta peppers evoke pungent sensations mediated by different alkylamides [mainly hydroxy-alpha-sanshool (alpha-SOH)] and hydroxyarylalkanones (6-shogaol and 6-paradol). We assessed how transient receptor potential ankyrin 1 (TRPA1) and TRP vanilloid 1 (TRPV1), two chemosensory ion channels, participate in these pungent sensations.

EXPERIMENTAL APPROACH

The structure-activity relationships of these molecules on TRPA1 and TRPV1 was measured by testing natural and synthetic analogues using calcium and voltage imaging on dissociated dorsal root ganglia neurons and human embryonic kidney 293 cells expressing the wild-type channels or specific cysteine mutants using glutathione trapping as a model to probe TRPA1 activation. In addition, using Trpv1 knockout mice, the compounds' aversive responses were measured in a taste brief-access test.

KEY RESULTS

For TRPA1 activation, the cis C6 double bond in the polyenic chain of alpha-SOH was critical, whereas no structural specificity was required for activation of TRPV1. Both 6-shogaol and 6-paradol were found to activate TRPV1 and TRPA1 channels, whereas linalool, an abundant terpene in Sichuan pepper, activated TRPA1 but not TRPV1 channels. Alkylamides and 6-shogaol act on TRPA1 by covalent bonding whereas none of these compounds activated TRPV1 through such interactions. Finally, TRPV1 mutant mice retained sensitivity to 6-shogaol but were not responsive to alpha-SOH.

CONCLUSIONS AND IMPLICATIONS

The pungent nature of components of Sichuan and Melegueta peppers was mediated via interactions with TRPA1 and TRPV1 channels and may explain the aversive properties of these compounds.

Specificity of FGF signaling in cell migration inDrosophila

We wanted to investigate the relationship between receptor tyrosine kinase (RTK) activated signaling pathways and the induction of cell migration. Using Drosophila tracheal and mesodermal cell migration as model systems, we find that the intracellular domain of the fibroblast growth factor receptors (FGFRs) Breathless (Btl) and Heartless (Htl) can be functionally replaced by the intracellular domains of Torso (Tor) and epidermal growth factor receptor (EGFR). These hybrid receptors can also rescue cell migration in the absence of Downstream of FGFR (Dof), a cytoplasmic protein essential for FGF signaling. These results demonstrate that tracheal and mesodermal cells respond during a specific time window to a receptor tyrosine kinase (RTK) signal with directed migration, independent of the presence or absence of Dof. We discuss our findings in the light of the recent findings that RTKs generate a generic signal that is interpreted in responding cells according to their developmental history.

A HOX complex, a repressor element and a 50 bp sequence confer regional specificity to a DPP-responsive enhancer

A central theme during development and homeostasis is the generation of cell type-specific responses to the action of a limited number of extant signaling cascades triggered by extracellular ligands. The molecular mechanisms by which information from such signals are integrated in responding cells in a cell-type specific manner remain poorly understood. We have undertaken a detailed characterization of an enhancer that is regulated by DPP signaling and by the homeotic protein Labial and its partners, Extradenticle and Homothorax. The expression driven by this enhancer (lab550) and numerous deletions and point mutants thereof was studied in wild-type and mutant Drosophila embryos as well as in cultured cells. We find that the lab550 enhancer is composed of two elements, a Homeotic Response Element (HOMRE) and a DPP Response Element (DPPRE) that synergize. None of these two elements can reproduce the expression of lab550, either with regard to expression level or with regard to spatial restriction. The isolated DPPRE of lab550 responds extremely weakly to DPP. Interestingly, we found that the inducibility of this DPPRE is weak because it is tuned down by the action of a repressor element. This repressor element and an additional 50 bp element appear to be crucial for the cooperation of the HOMRE and the DPPRE, and might tightly link the DPP response to the homeotic input. The cooperation between the different elements of the enhancer leads to the segmentally restricted activity of lab550 in the endoderm and provides a mechanism to create specific responses to DPP signaling with the help of a HOX protein complex.

Nuclear interpretation of Dpp signaling in Drosophila

Signaling by Decapentaplegic (Dpp), a member of the TGFbeta superfamily of signaling molecules similar to vertebrate BMP2 and BMP4, has been implicated in many developmental processes in Drosophila melanogaster. Notably, Dpp acts as a long-range morphogen during imaginal disc growth and patterning. Genetic approaches led to the identification of a number of gene products that constitute the core signaling pathway. In addition to the ligand-activated heteromeric receptor complex and the signal-transducing intracellular Smad proteins, Dpp signaling requires two nuclear proteins, Schnurri (Shn) and Brinker (Brk), to prime cells for Dpp responsiveness. A complex interplay between the nuclear factors involved in Dpp signaling appears to control the transcriptional readout of the Dpp morphogen gradient. It remains to be seen whether similar molecular mechanisms operate in the nucleus in vertebrate systems.

Genetic control of branching morphogenesis during Drosophila tracheal development

Branching morphogenesis is a widely used strategy to increase the surface area of a given organ. A number of tissues undergo branching morphogenesis during development, including the lung, kidney, vascular system and numerous glands. Until recently, very little has been known about the genetic principles underlying the branching process and about the molecules participating in organ specification and branch formation. The tracheal system of insects represents one of the best-characterised branched organs. The tracheal network provides air to most tissues and its development during embryogenesis has been studied intensively at the morphological and genetic level. More than 30 genes have been identified and ordered into sequential steps controlling branching morphogenesis. These studies have revealed a number of important principles that might be conserved in other systems.

Direct transcriptional control of the Dpp target omb by the DNA binding protein Brinker

The gradient morphogen Decapentaplegic (Dpp) organizes pattern by inducing the transcription of different target genes at distinct threshold concentrations during Drosophila development. An important, albeit indirect, mode by which Dpp controls the spatial extent of its targets is via the graded downregulation of brinker, whose product in turn negatively regulates the expression of these targets. Here we report the molecular dissection of the cis-regulatory sequences of optomotor-blind (omb), a Dpp target gene in the wing. We identify a minimal 284 bp Dpp response element and demonstrate that it is subject to Brinker (Brk) repression. Using this omb wing enhancer, we show that Brk is a sequence-specific DNA binding protein. Mutations in the high-affinity Brk binding site abolish responsiveness of this omb enhancer to Brk and also compromise the input of an unknown transcriptional activator. Our results therefore identify Brk as a novel transcription factor antagonizing Dpp signalling by directly binding target genes and repressing their expression.

Purification, cloning, and characterization of a second arylalkylamine N-acetyltransferase from Drosophila melanogaster

In insects, amine acetylation by the enzyme arylalkylamine N-acetyltransferase (AANAT) is involved in melatonin formation, sclerotization, and neurotransmitter inactivation. This wide spectrum of activities suggests that several AANAT enzymes are present. We recently purified a protein fraction with AANAT activity from Drosophila melanogaster and cloned the corresponding gene, aaNAT1. Following the same strategy, we now report the purification of an additional AANAT from D. melanogaster, AANAT2, and the cloning of the corresponding cDNA. The isolated protein differs from AANAT1a and AANAT1b in its molecular weight and isoelectric point. The AANAT2 shares about 30% identity with the products of the aaNAT1 gene. The enzyme does not follow one-site Michaelis-Menten kinetics when assayed with various concentrations of the arylalkylamine tryptamine and a constant concentration (0.5 mM) of the cofactor acetyl coenzyme A. The data can be interpreted in terms of an enzyme with two kinetic regimes (K(m1) = 7.2 microM, K(m2) = 0.6 mM, and v(max2) = 2.7 v(max1)) that are governed by binding of the substrate to a regulatory site (K(r) = 6.2 mM). These findings demonstrate the presence of a second expressed gene encoding an AANAT in D. melanogaster. Northern blot analysis revealed no diurnal variation of aaNAT2 transcription, similar to the results obtained for aaNAT1a and aaNAT1b.

Schnurri mediates Dpp-dependent repression of brinker transcription

Signalling by Decapentaplegic (Dpp), a member of the TGFbeta superfamily of signalling molecules, controls many aspects of Drosophila development by activating and repressing target genes. Several essential components of the Dpp signalling pathway have been identified, including the Dpp receptors Punt and Thick veins (Tkv) as well as the cytoplasmic mediators Mad and Medea. For target genes to be activated, Dpp signalling must suppress transcription of a repressor encoded by the brinker (brk) gene. Here we show that Schnurri (Shn), a large zinc-finger protein, is essential for Dpp-mediated repression of brk transcription; in contrast, Shn is not required for target-gene activation. Thus, the Dpp signalling pathway bifurcates, downstream of the signal-mediating SMAD proteins, into a Shn-dependent pathway leading to brk repression and a Shn-independent pathway leading to gene activation. The existence of several Shn-like proteins in vertebrates and the observation that Brk functions in BMP signalling in Xenopus indicates that a similar regulatory cascade may be conserved in higher organisms.

Expression of the blistered/DSRF gene is controlled by different morphogens during Drosophila trachea and wing development

The Drosophila serum response factor (DSRF) is expressed in the precursors of the terminal tracheal cells and in the future intervein territories of the third instar wing imaginal disc. Dissection of the DSRF regulatory region reveals that a single enhancer element, which is under the control of the fibroblast growth factor (FGF)-receptor signalling pathway, is sufficient to induce DSRF expression in the terminal tracheal cells. In contrast, two separate enhancers direct expression in distinct intervein sectors of the wing imaginal disc. One element is active in the central intervein sector and is induced by the Hedgehog signalling pathway. The other element is under the control of Decapentaplegic and is active in two separate territories, which roughly correspond to the intervein sectors flanking the central sector. Hence, each of the three characterized enhancers constitutes a molecular link between a specific territory induced by a morphogen signal and the localized expression of a gene required for the final differentiation of this territory.

Innate recognition of bacteria in human milk is mediated by a milk-derived highly expressed pattern recognition receptor, soluble CD14

Little is known about innate immunity to bacteria after birth in the hitherto sterile fetal intestine. Breast-feeding has long been associated with a lower incidence of gastrointestinal infections and inflammatory and allergic diseases. We found in human breast milk a 48-kD polypeptide, which we confirmed by mass spectrometry and sequencing to be a soluble form of the bacterial pattern recognition receptor CD14 (sCD14). Milk sCD14 (m-sCD14) concentrations were up to 20-fold higher than serum sCD14 from nonpregnant, pregnant, or lactating women. In contrast, lipopolysaccharide (LPS)-binding protein was at very low levels. Mammary epithelial cells produced 48-kD sCD14. m-sCD14 mediated activation by LPS and whole bacteria of CD14 negative cells, including intestinal epithelial cells, resulting in release of innate immune response molecules. m-sCD14 was undetectable in the infant formulas and commercial (cows') milk tested, although it was present in bovine colostrum. These findings indicate a sentinel role for sCD14 in human milk during bacterial colonization of the gut, and suggest that m-sCD14 may be involved in modulating local innate and adaptive immune responses, thus controlling homeostasis in the neonatal intestine.

Schnurri interacts with Mad in a Dpp-dependent manner

BACKGROUND

Decapentaplegic (Dpp) is a member of the transforming growth factor-beta superfamily. Dpp governs various developmental processes in Drosophila through the transcriptional regulation of a variety of genes. Signals of Dpp are transmitted from the cell membrane to the nucleus by Medea and Mad, both belonging to the Smad protein family. Mad was shown to bind to the Dpp-responsive element in genes such as vestigial, labial, and Ultrabithorax. The DNA binding affinity of Smad proteins is relatively low, and requires other nuclear factor(s) to form stable DNA binding complexes. schnurri (shn) was identified as a candidate gene acting downstream of Dpp receptors, but its relevance to Mad has remained unknown.

RESULTS

We characterized the biochemical functions of Shn. Shn forms homo-oligomers. Shn is localized in the nucleus, and is likely to have multiple nuclear localizing signals. Finally, we found that Shn interacts with Mad in a Dpp-dependent manner.

CONCLUSIONS

The present results argue that Shn may act as a nuclear component of the Dpp signalling pathway through direct interaction with Mad.

Regulation of Hox target genes by a DNA bound Homothorax/Hox/Extradenticle complex

To regulate their target genes, the Hox proteins of Drosophila often bind to DNA as heterodimers with the homeodomain protein Extradenticle (EXD). For EXD to bind DNA, it must be in the nucleus, and its nuclear localization requires a third homeodomain protein, Homothorax (HTH). Here we show that a conserved N-terminal domain of HTH directly binds to EXD in vitro, and is sufficient to induce the nuclear localization of EXD in vivo. However, mutating a key DNA binding residue in the HTH homeodomain abolishes many of its in vivo functions. HTH binds to DNA as part of a HTH/Hox/EXD trimeric complex, and we show that this complex is essential for the activation of a natural Hox target enhancer. Using a dominant negative form of HTH we provide evidence that similar complexes are important for several Hox- and exd-mediated functions in vivo. These data suggest that Hox proteins often function as part of a multiprotein complex, composed of HTH, Hox, and EXD proteins, bound to DNA.

The transcription factors KNIRPS and KNIRPS RELATED control cell migration and branch morphogenesis during Drosophila tracheal development

Cell migration during embryonic tracheal system development in Drosophila requires DPP and EGF signaling to generate the archetypal branching pattern. We show that two genes encoding the transcription factors KNIRPS and KNIRPS RELATED possess multiple and redundant functions during tracheal development. knirps/knirps related activity is necessary to mediate DPP signaling which is required for tracheal cell migration and formation of the dorsal and ventral branches. Ectopic knirps or knirps related expression in lateral tracheal cells respecifies their anteroposterior to a dorsoventral migration behavior, similar to that observed in the case of ectopic DPP expression. In dorsal tracheal cells knirps/knirps related activity represses the transcription factor SPALT; this repression is essential for secondary and terminal branch formation. However, in cells of the dorsal trunk, spalt expression is required for normal anteroposterior cell migration and morphogenesis. spalt expression is maintained by the EGF receptor pathway and, hence, some of the opposing activities of the EGF and DPP signaling pathways are mediated by spalt and knirps/knirps related. Furthermore, we provide evidence that the border between cells acquiring dorsal branch and dorsal trunk identity is established by the direct interaction of KNIRPS with a spalt cis-regulatory element.

Characterization of the prolyl dipeptidyl peptidase gene (dppIV) from the koji mold Aspergillus oryzae

The koji mold Aspergillus oryzae secretes a prolyl dipeptidyl peptidase (DPPIV) when the fungus is cultivated in a medium containing wheat gluten as the sole nitrogen and carbon source (MMWG). We cloned and sequenced the DPPIV gene from an A. oryzae library by using the A. fumigatus dppIV gene as a probe. Reverse transcriptase PCR experiments showed that the A. oryzae dppIV gene consists of two exons, the first of which is only 6 bp long. The gene encodes an 87.2-kDa polypeptide chain which is secreted into the medium as a 95-kDa glycoprotein. Introduction of this gene into A. oryzae leads to overexpression of prolyl dipeptidyl peptidase activity, while disruption of the gene abolishes all prolyl dipeptidyl peptidase activity in MMWG. The dppIV null mutants did not exhibit any change in phenotype other than the absence of prolyl dipeptidyl peptidase activity, suggesting that this activity is not essential. This loss of activity diminished the number of dipeptides and increased the number of larger peptides present in the MMWG culture broth. These effects were reversed by the addition of purified, recombinant DPPIV from the methylotrophic yeast expression vector Pichia pastoris. Our results suggest that the DPPIV enzyme may be of importance in industrial hydrolysis of what gluten-based substrates, which are rich in Pro residues.

Biochemical and biophysical characterization of refolded Drosophila DPP, a homolog of bone morphogenetic proteins 2 and 4

The mature C-terminal signaling domain of the Drosophila Decapentaplegic proprotein (DPP) can be efficiently refolded from chaotrope-solubilized inclusion bodies with the aid of a membrane protein-solubilizing detergent, high concentrations (0.75-2 M) of NaCl, and low temperatures (5-15 degreesC). The disulfide-linked homodimeric product contains N-terminal heparin-binding sites that were utilized as intrinsic affinity tags to obtain a highly enriched preparation in one chromatographic step. A subsequent C4 reverse phase high pressure liquid chromatography step provides high purity, salt-free protein that is amenable to biophysical and structural studies at a yield of approximately 3 mg/liter of bacterial culture. The dimeric protein is correctly folded as determined by electrophoretic, spectroscopic, chemical, and proteolytic analyses. Refolded DPP is also bioactive as shown by induction of chondrogenesis in embryonic chick limb bud cells and by high affinity binding to Noggin, an antagonist of bone morphogenetic protein signaling. In contrast to bone morphogenetic proteins extracted from demineralized bone or overexpressed in cell culture, the refolded Escherichia coli-expressed protein is not glycosylated at a conserved N-linked site and is therefore homogeneous. The C-terminal domain dimer is more hydrophobic and thus less soluble than its unfolded or partially folded forms, necessitating highly solubilizing conditions for recovery after folding in vitro. Hence solubilization of the mature ligand may be one of the principal roles of the large (250-400 amino acids) N-terminal prodomains of transforming growth factor-beta superfamily members, shown to act as intramolecular chaperones in vivo.

The Drosophila protein Dof is specifically required for FGF signaling

Receptor tyrosine kinases (RTKs) transmit signals to the cell nucleus via the MAP kinase (MAPK) cascade, using specific molecules to link the activated receptors to the MAPK cascade activator, Ras. We have identified a component of the FGF receptor (FGFR) signal transduction pathway, Downstream of FGFR (Dof). Dof is an intracellular protein that is essential for signal transmission by the FGFR and acts downstream of the receptor and upstream of Ras. Unlike other signaling molecules that act downstream of RTKs, Dof is not expressed ubiquitously but is present exclusively in cells that express FGFRs. Dof is needed in these cells for activation of the MAPK cascade via FGF signaling, but not for activation via other RTK ligands. Dof therefore appears to be committed exclusively to FGFR-mediated signal transduction.

Hox proteins meet more partners

The Hox genes are clustered sets of homeobox-containing genes that play a central role in animal development. Recent genetic and molecular data suggest that Hox proteins interact with pre-existing homeodomain protein complexes. These complexes may help to regulate Hox activity and Hox specificity, and help cells to interpret signaling cascades during development.

Molecular and biochemical characterization of the aaNAT1 (Dat) locus in Drosophila melanogaster: differential expression of two gene products

In insects, arylalkylamine N-acetyltransferases (AANATs) have been implicated in several physiological processes, including sclerotization, inactivation of certain neurotransmitters, and, similar to the function in vertebrates, catalysis of the rate-limiting step in melatonin biosynthesis. Here, we report an extensive biochemical and functional analysis of the products of the aaNAT1 gene of Drosophila melanogaster. The aaNAT1 gene generates two transcripts through alternative first-exon usage. These transcripts are under tissue-specific and developmental control and encode proteins which differ in their N-terminus with respect to their starting methionine. The more abundant isoform, AANATlb, is first expressed during late embryogenesis in the brain, the ventral nerve cord, and the midgut; in adults, AANATlb is still detectable in the brain and midgut. The less abundant isoform, AANATla, appears only during late pupal stages and in adults is found predominantly in the brain. We demonstrate that the mutation Dat(lo) represents a hypomorphic allele of aaNAT1b, in which an insertion of two transposable elements, MDG412 and blastopia, has occurred within the first intron of the gene. Using a deficiency which removes the aaNAT1 gene, we provide evidence that aaNAT1 is not essential for the process of sclerotization. Furthermore, neither of the two enzyme isoforms shows circadian regulation of RNA or protein levels. The differing levels of abundance and distinct developmental control of AANAT1a and AANAT1b suggest different in vivo functions for these two enzymes.

Synergistic activation of a Drosophila enhancer by HOM/EXD and DPP signaling

The homeotic proteins encoded by the genes of the Drosophila HOM and the vertebrate HOX complexes do not bind divergent DNA sequences with a high selectivity. In vitro, HOM (HOX) specificity can be increased by the formation of heterodimers with Extradenticle (EXD) or PBX homeodomain proteins. We have identified a single essential Labial (LAB)/EXD-binding site in a Decapentaplegic (DPP)-responsive enhancer of the homeotic gene lab which drives expression in the developing midgut. We show that LAB and EXD bind cooperatively to the site in vitro, and that the expression of the enhancer in vivo requires exd and lab function. In addition, point mutations in either the EXD or the LAB subsite compromise enhancer function, strongly suggesting that EXD and LAB bind to this site in vivo. Interestingly, we found that the activity of the enhancer is only stimulated by DPP signaling significantly upon binding of LAB and EXD. Thus, the enhancer appears to integrate positional information via the homeotic gene lab, and spatiotemporal information via DPP signaling; only when these inputs act in concert in an endodermal cell is the enhancer fully active. Our results illustrate how a tissue-specific response to DPP can be generated through synergistic effects on an enhancer carrying both DPP- and HOX-responsive sequences.

The cramped gene of Drosophila is a member of the Polycomb-group, and interacts with mus209, the gene encoding Proliferating Cell Nuclear Antigen

We have isolated and molecularly characterized the cramped (crm) gene of Drosophila melanogaster, and show that it can be classified as a Polycomb-group (Pc-G) gene. crm mutants exhibit typical Pc-G mutant phenotypes, reminiscent of ectopic homeotic gene expression, with additional sex comb teeth found on mesothoracic and metathoracic legs, and proximodistal transformations of the tarsal segments. crm encodes an 693 amino acids protein, with no significant homology to known proteins. We used polyclonal antibodies raised against bacterially expressed truncated CRM protein to show that the crm gene product is localized to the nucleus during embryogenesis. This nuclear localization appears to be restricted to S-phase nuclei, as CRM immunostaining disappears at mitosis. We found that this cell-cycle-dependent staining pattern was identical to that of Proliferating Cell Nuclear Antigen (PCNA). Furthermore, we provide evidence for co-localization of CRM and PCNA proteins in salivary gland polytene nuclei, and for a genetic interaction between crm and mus209, the Drosophila gene encoding PCNA. Together, our data suggest that these two proteins are involved in a common regulatory pathway and highlight possible interactions between Pc-G-mediated silencing and DNA replication in Drosophila.

DPP controls tracheal cell migration along the dorsoventral body axis of the Drosophila embryo

We report that DPP signaling is required for directed tracheal cell migration during Drosophila embryogenesis. The failure of tracheal cells to receive the DPP signal from adjacent dorsal and ventral cells results in the absence of dorsal and ventral migrations. Ectopic DPP signaling can reprogram cells in the center of the placode to adopt a dorsoventral migration behavior. The effects observed in response to ectopic DPP signaling are also observed upon the tracheal-specific expression of a constitutive active DPP type I receptor (TKV(Q253D)), indicating that the DPP signal is received and transmitted in tracheal cells to control their migration behavior. DPP signaling determines localized gene expression patterns in the developing tracheal placode, and is also required for the dorsal expression of the recently identified BRANCHLESS (BNL) guidance molecule, the ligand of the BREATHLESS (BTL) receptor. Thus, DPP plays a dual role during tracheal cell migration. It is required to control the dorsal expression of the BNL ligand; in addition, the DPP signal recruits groups of dorsal and ventral tracheal cells and programs them to migrate in dorsal and ventral directions.

Identification of the autophosphorylation sites of the Xenopus laevis Pim-1 proto-oncogene-encoded protein kinase

Pim-1 is an oncogene-encoded serine/threonine kinase expressed primarily in cells of the hematopoietic and germ line lineages. Previously identified only in mammals, pim-1 cDNA was cloned and sequenced from the African clawed frog Xenopus laevis. The coding region of Xenopus pim-1 encoded a protein of 324 residues, which exhibited 64% amino acid identity with the full-length human cognate. Xenopus Pim-1 was expressed in bacteria as a glutathione S-transferase (GST) fusion protein and in COS cells. Phosphoamino acid analysis revealed that recombinant Pim-1 autophosphorylated on serine and threonine and to a more limited extent on tyrosine. Electrospray ionization mass spectroscopy was undertaken to locate these phosphorylation sites, and the primary autophosphorylation site of GST-Pim-1 was identified as Ser-190 with Thr-205 and Ser-4 being minor sites. Ser-190, which immediately follows the high conserved Asp-Phe-Gly motif in catalytic subdomain VII, is also featured in more than 20 other protein kinases. To evaluate the importance of the Ser-190 site on the phosphotransferase activity of Pim-1, Ser-190 was mutated to either alanine or glutamic acid, and the constructs were expressed in bacteria as GST fusion proteins and in COS cells. These mutants confirmed that Ser-190 is a major autophosphorylation site of Pim-1 and indicated that phosphorylation of Pim-1 on the Ser-190 residue may serve to activate this kinase.

The Drosophila Serum Response Factor gene is required for the formation of intervein tissue of the wing and is allelic to blistered

The adult Drosophila wing is formed by an epithelial sheet, which differentiates into two non-neural tissues, vein or intervein. A large number of genes, many of them encoding components of an EGF-receptor signaling pathway, have previously been shown to be required for differentiation of vein tissue. Much less is known about the molecular control of intervein differentiation. Here we report that the Drosophila homolog of the mammalian Serum Response Factor gene (DSRF), which encodes a MADS-box containing transcriptional regulator, is expressed in the future intervein tissue of wing imaginal discs. In adult flies carrying only one functional copy of the DSRF gene, additional vein tissue develops in the wing, indicating that DSRF is required to spatially restrict the formation of veins. In mitotic clones lacking DSRF, intervein tissue fails to differentiate and becomes vein-like in appearance. Genetic and molecular evidence demonstrates that DSRF is encoded by the blistered locus, which produces ectopic veins and blistered wings when mutant. Our results show that DSRF plays a dual role during wing differentiation. It acts in a dosage-dependent [correction of dosage-dependant] manner to suppress the formation of wing veins and is required cell-autonomously to promote the development of intervein cells. We propose that DSRF acts at a key step between regulatory genes that define the early positional values in the developing wing disc and the subsequent localized expression of intervein-specific structural genes.

The pruned gene encodes the Drosophila serum response factor and regulates cytoplasmic outgrowth during terminal branching of the tracheal system

We identified a Drosophila gene, pruned, that regulates formation of the terminal branches of the tracheal (respiratory) system. These branches arise by extension of long cytoplasmic processes from terminal tracheal cells towards oxygen-starved tissues, followed by formation of a lumen within the processes. The pruned gene is expressed in terminal cells throughout the period of terminal branching. pruned encodes the Drosophila homologue of serum response factor (SRF), which functions with an ETS domain ternary complex factor as a growth-factor-activated transcription complex in mammalian cells. In pruned loss of function mutants, terminal cells fail to extend cytoplasmic projections. A constitutively activated SRF drives formation of extra projections that grow out in an unregulated fashion. An activated ternary complex factor has a similar effect. We propose that the Drosophila SRF functions like mammalian SRF in an inducible transcription complex, and that activation of this complex by signals from target tissues induces expression of genes involved in cytoplasmic outgrowth.

Recombinant gene expression and 1H NMR characteristics of the kringle (2 + 3) supermodule: spectroscopic/functional individuality of plasminogen kringle domains

The plasminogen kringle 2 (K2HPg) and kringle 3 (K3HPg) modules occur in tandem within the polypeptide segment that affords the heavy chain of plasmin. The K2HPg and K3HPg are unique among the plasminogen kringle domains in that they also are linked to each other via the Cys169-Cys297 (Cys4 of K2HPg to Cys43 of K3HPg, kringle numbering convention) disulfide bridge, thus generating a K2HPg-K3HPg "supermodule". The kringle (2 + 3) sequence of human plasminogen (r-EE[K2HPgK3HPg]DS) was expressed in Escherichia coli, using an expression vector containing the phage T5 promoter/operator N250PSN250P29 and the codons for an N-terminal hexahistidine tag to ensure the isolation of the recombinant protein by affinity chromatography on Ni(2+)-nitrilotriacetic acid/agarose under denaturing and reducing conditions. Kringle (2 + 3) was refolded in the presence of glutathione redox buffer. By taking advantage of the lysine affinity of kringle 2, the protein was purified by affinity chromatography on lysine-Bio-Gel. Recombinant kringle (2 + 3) was identified by amino acid composition, N-terminal sequence and mass determination. The 1H NMR spectrum shows that the intact r-K2HPgK3HPg is properly folded. By reference to spectra of the individual kringles, r-K2HPg and r-K3HPg, resonances of the K2HPg and K3HPg components in the spectrum of the intact r-K2HPgK3HPg can be readily distinguished. The strictly conserved Leu46 residue (kringle residue number convention) yields delta-methyl signals that are characteristic for K2HPg and K3HPg, exhibiting chemical shifts of -0.87 and -0.94 ppm, respectively, which are distinct from those of K1HPg, K4HPg, and K5HPg, (-1.04 to -1.05 ppm). Thus, the high-field Leu46 signals from K2HPg and K3HPg are well resolved from those of other kringles and can be identified unambiguously in spectra of the K1HPgK2HPgK3HPg elastolytic fragment of plasminogen as well as in spectra of Glu-plasminogen. Overall, r-K2HPgK3HPg exhibits broader resonance line widths than does the K1HPg component, consistent with a lesser mobility of the K2HPgK3HPg segment within the K1HPgK2HPgK3HPg fragment, a reflection of the extra structural constraint imposed by the disulfide bridge linking K2HPg to K3HPg. The ligand 6-aminohexanoic acid (6-AHA), which is known to interact with r-K2HPg but not with r-K3HPg, selectively perturbs K2 aromatic signals in the intact r-K2HPgK3HPg spectrum while leaving K3 resonances largely unaffected. Association constant (K(a)) values for 6-AHA determined from 1H NMR ligand titration experiments yield K(a) approximately 2.2 +/- 0.3 mM(-1) for the intact r-K2HPgK3HPg, comparable to K(a) approximately 2.3 +/- 0.2 mM(-1) determined for the isolated r-K2HPg, which demonstrates that the interactions of 6-AHA with the K2HPg ligand-binding site are not significantly affected by the neighboring K3HPg domain within the intact r-K2HPgK3HPg supermodule.

Comparison of the specificity of bacterially expressed cytoplasmic protein-tyrosine phosphatases SHP and SH-PTP2 towards synthetic phosphopeptide substrates

SHP and SH-PTP2 are related cytoplasmic protein-tyrosine phosphatases having two tandem amino-terminal src homology 2 domains linked to a single catalytic domain. There is growing evidence that these two molecules may exhibit opposing effects within specific signaling pathways. However, the relative contributions of the src homology 2 domains or the catalytic domains to these opposing effects are not well known. To evaluate the potential contribution of the catalytic domains, we compared the substrate specificity of the two phosphatases. As seen previously, the catalytic activities of bacterially expressed SHP and SH-PTP2 were regulated by the presence of the linked src homology 2 domains. In addition, we characterized a cryptic thrombin cleavage site within the carboxy-terminus of SHP that led to a striking increase in the activity of the catalytic domain. Employing a panel of phosphopeptide substrates whose sequences were modeled after intracellular phosphorylation sites, both SHP and SH-PTP2 demonstrated a similar specificity pattern. Similar to SH-PTP2, SHP failed to elicit detectable phosphate release from several phosphopeptide substrates, while displaying catalytic efficiencies that ranged over approximately 40-1.6 x 10(3) M-1 s-1 towards other substrates. In contrast, the PTP-1B phosphatase dephosphorylated all of the phosphopeptide substrates tested with approximately equal ease. The overall similarity demonstrated by the catalytic domains of SHP and SH-PTP2 suggested that differences in the in vivo behavior of these two molecules might not stem from differences in the substrate specificity of the catalytic domains, suggesting instead that the specificity of the src homology 2 domains is more important in this regard.

Schnurri is required for Drosophila Dpp signaling and encodes a zinc finger protein similar to the mammalian transcription factor PRDII-BF1

Cytokines of the TGF beta superfamily regulate many aspects of cellular function by activating receptor complexes consisting of two distantly related serine/threonine kinases. Previous studies have indicated that Drosophila dpp uses similar signaling complexes and strictly requires the punt and thick veins receptors to transduce the signal across the membrane. Here, we show that the schnurri (shn) gene is required for many aspects of dpp signaling. Genetic epistasis experiments indicate that shn functions downstream of the dpp signal and its receptors. The shn gene encodes a large protein similar to a family of mammalian zinc finger transcription factors. The shn protein might therefore act as a nuclear target in the dpp signaling pathway directly regulating the expression of dpp-responsive genes.

An absolute requirement for both the type II and type I receptors, punt and thick veins, for dpp signaling in vivo

TGF beta elicits diverse cellular responses by signaling through receptor complexes formed by two distantly related transmembrane serine/threonine kinases called type II and type I receptors. Previous studies have indicated that the product of the Drosophila thick veins (tkv) gene is a type I receptor for decapentaplegic (dpp). Here, we show that the Drosophila gene punt encodes a homolog of a vertebrate type II receptor, and we demonstrate that punt, like tkv, is essential in vivo for dpp-dependent patterning processes. Because no dpp-related signalling is apparent in the absence of either the punt or tkv receptor, we infer that both receptors act in concert to transduce the dpp signal and that their functions cannot be replaced by the other extant type II and I receptors.

Identification by electrospray ionization mass spectrometry of the sites of tyrosine phosphorylation induced in activated Jurkat T cells on the protein tyrosine kinase ZAP-70

We have developed a rapid and sensitive two capillary-column chromatography and mass spectrometry-based method for the determination of protein phosphorylation sites following recovery of individual phosphopeptides from two-dimensional phosphopeptide maps. With a standard phosphopeptide, we demonstrate detection sensitivity of at least 250 fmol for this system. We applied this technique to the analysis of in vitro sites of tyrosine phosphorylation induced on the T cell-specific protein tyrosine kinase ZAP-70 in the absence and presence of p56lck. We show that ZAP-70 has a primary autophosphorylation site at Tyr-292, with a secondary site at Tyr-126. We also show additional phosphorylation at Tyr-69, Tyr-178, Tyr-492, and Tyr-493 upon the addition of the protein tyrosine kinase, p56lck. By comparative two-dimensional phosphopeptide mapping, we show that ZAP-70 isolated from Jurkat T cells also autophosphorylates at Tyr-292 and Tyr-126. Similar analysis of 32P-labeled Jurkat cells stimulated with anti-T cell receptor antibodies reveals Tyr-492 and Tyr-493 as the principal sites of T cell antigen receptor-induced tyrosine phosphorylation, with additional phosphorylation at the Tyr-292, but not the Tyr-126 autophosphorylation site. The high degree of sensitivity achieved with this technology should greatly facilitate the direct biochemical determination of inducible protein phosphorylation events, an experimental strategy that until now has been both time consuming and difficult.

Evaluation of two-dimensional phosphopeptide maps by electrospray ionization mass spectrometry of recovered peptides

Intracellular signaling pathways are to a large extent regulated by reversible protein phosphorylation of pathway components. To fully investigate the regulation of these pathways, it is often necessary to identify the sites of protein phosphorylation induced on individual components. The low abundance of many of these molecules and the potentially low stoichiometry of phosphorylation means that conventional analytical techniques are incapable of identifying specific sites of modification inducible in vivo. The most common technique used is two-dimensional (2D) phosphopeptide mapping (electrophoresis, thin-layer chromatography) of peptides derived by proteolysis of a phosphoprotein. The number of spots detected is commonly interpreted as the number of sites of phosphorylation. Here we have achieved positive identification of phosphorylation sites by capillary high-performance liquid chromatography, with on-line mass spectrometric detection, of phosphopeptides recovered from 2D phosphopeptide maps. We demonstrate that the chemical composition of phosphopeptides is not altered during the 2D mapping procedure. By detailed analysis of the sites of phosphorylation induced in vitro on CD3-zeta by p56lck we demonstrate that interpretation of the sites of phosphorylation based on 2D phosphopeptide mapping alone is difficult. To minimize over- or misinterpretation of 2D phosphopeptide maps we therefore postulate rules that should be applied generally in cases in which protein phosphorylation sites are being evaluated by 2D phosphopeptide patterns alone.

Multiple requirements for the receptor serine/threonine kinase thick veins reveal novel functions of TGF beta homologs during Drosophila embryogenesis

Differentiation of distinct cell types at specific locations within a developing organism depends largely on the ability of cells to communicate. A major class of signalling proteins implicated in cell to cell communication is represented by members of the TGF beta superfamily. A corresponding class of transmembrane serine/threonine kinases has recently been discovered that act as cell surface receptors for ligands of the TGF beta superfamily. The product of the Drosophila gene decapentaplegic (dpp) encodes a TGF beta homolog that plays multiple roles during embryogenesis and the development of imaginal discs. Here we describe the complex expression pattern of thick veins (tkv), which encodes a receptor for dpp. We make use of tkv loss-of-function mutations to examine the consequences of the failure of embryonic cells to respond to dpp and/or other TGF beta homologs. We find that while maternal tkv product allows largely normal dorsoventral pattering of the embryo, zygotic tkv activity is indispensable for dorsal closure of the embryo after germ band retraction. Furthermore, tkv activity is crucial for patterning the visceral mesoderm; in the absence of functional tkv gene product, visceral mesoderm parasegment 7 cells fail to express Ultrabithorax, but instead accumulate Antennapedia protein. The tkv receptor is therefore involved in delimiting the expression domains of homeotic genes in the visceral mesoderm. Interestingly, tkv mutants fail to establish a proper tracheal network. Tracheal braches formed by cells migrating in dorsal or ventral directions are absent in tkv mutants. The requirements for tkv in dorsal closure, visceral mesoderm and trachea development assign novel functions to dpp or a closely related member of the TGF beta superfamily.

Activation and serine phosphorylation of the p56lck protein tyrosine kinase in response to antigen receptor cross-linking in B lymphocytes

We show that cross-linking the B cell AgR with anti-Ig Abs activates p56lck (Lck) in both the immature B cell line WEHI-231 and mature resting B cells from mouse spleen. Anti-Ig-stimulated Lck activity peaked after 1 to 2 min, but remained elevated for at least 15 min. Consistent with the proposed role for src family tyrosine kinases in AgR signaling, we found that Lck could phosphorylate the cytoplasmic tails of the Ig-alpha and Ig-beta components of the B cell AgR in vitro. Lck phosphorylated both of the tyrosines in the Ig-beta AgR homology motif and one of the two tyrosines in the Ig-alpha AgR homology motif. Finally, we show that AgR ligation in B cells caused a significant portion of the Lck to migrate with an apparent molecular mass of 60 kDa on SDS-PAGE gels. Conversion of p56lck to p60lck was maximal at 5 to 15 min, at which times Lck activity in the cells was decreasing. This Lck "band shift" has been observed previously in activated T cells and correlates with phosphorylation of Lck at serine 59. We show that the 60-kDa form of Lck induced by AgR cross-linking in B cells is also phosphorylated at serine 59. Phosphorylation of Lck at this site in vitro decreases its activity. Thus, in B cells, AgR cross-linking activates Lck and subsequently activates a kinase that phosphorylates Lck at serine 59, a potential negative regulatory site.

Activation and serine phosphorylation of the p56lck protein tyrosine kinase in response to antigen receptor cross-linking in B lymphocytes

We show that cross-linking the B cell AgR with anti-Ig Abs activates p56lck (Lck) in both the immature B cell line WEHI-231 and mature resting B cells from mouse spleen. Anti-Ig-stimulated Lck activity peaked after 1 to 2 min, but remained elevated for at least 15 min. Consistent with the proposed role for src family tyrosine kinases in AgR signaling, we found that Lck could phosphorylate the cytoplasmic tails of the Ig-alpha and Ig-beta components of the B cell AgR in vitro. Lck phosphorylated both of the tyrosines in the Ig-beta AgR homology motif and one of the two tyrosines in the Ig-alpha AgR homology motif. Finally, we show that AgR ligation in B cells caused a significant portion of the Lck to migrate with an apparent molecular mass of 60 kDa on SDS-PAGE gels. Conversion of p56lck to p60lck was maximal at 5 to 15 min, at which times Lck activity in the cells was decreasing. This Lck "band shift" has been observed previously in activated T cells and correlates with phosphorylation of Lck at serine 59. We show that the 60-kDa form of Lck induced by AgR cross-linking in B cells is also phosphorylated at serine 59. Phosphorylation of Lck at this site in vitro decreases its activity. Thus, in B cells, AgR cross-linking activates Lck and subsequently activates a kinase that phosphorylates Lck at serine 59, a potential negative regulatory site.

Receptor serine/threonine kinases implicated in the control of Drosophila body pattern by decapentaplegic

Members of the TGF beta superfamily of secreted signaling molecules regulate growth and cellular patterning during development and interact with specific type I and type II membrane receptors possessing a cytoplasmic serine/threonine kinase domain. We describe two members of the type I receptor family in Drosophila and demonstrate that they are encoded by the genes saxophone (sax) and thick veins (tkv). Further, we show that mutations that abolish sax or tkv activity cause phenotypes similar to partial or complete loss of activity, respectively, of the TGF beta homolog decapentaplegic (dpp). We propose that specification of distinct cell fates in response to different concentrations of dpp may be achieved combinatorially by the sax and tkv receptors.