An A-kinase anchoring protein is required for Protein kinase A regulatory subunit localization and morphology of actin structures during oogenesis inDrosophila

Regulation of oocyte maturation: Role of conserved ERK signaling

During oogenesis, oocytes arrest at meiotic prophase I to acquire competencies for resuming meiosis, fertilization, and early embryonic development. Following this arrested period, oocytes resume meiosis in response to species-specific hormones, a process known as oocyte maturation, that precedes ovulation and fertilization. Involvement of endocrine and autocrine/paracrine factors and signaling events during maintenance of prophase I arrest, and resumption of meiosis is an area of active research. Studies in vertebrate and invertebrate model organisms have delineated the molecular determinants and signaling pathways that regulate oocyte maturation. Cell cycle regulators, such as cyclin-dependent kinase (CDK1), polo-like kinase (PLK1), Wee1/Myt1 kinase, and the phosphatase CDC25 play conserved roles during meiotic resumption. Extracellular signal-regulated kinase (ERK), on the other hand, while activated during oocyte maturation in all species, regulates both species-specific, as well as conserved events among different organisms. In this review, we synthesize the general signaling mechanisms and focus on conserved and distinct functions of ERK signaling pathway during oocyte maturation in mammals, non-mammalian vertebrates, and invertebrates such as Drosophila and Caenorhabditis elegans.

The Nab2 RNA-binding protein patterns dendritic and axonal projections through a planar cell polarity-sensitive mechanism

RNA-binding proteins support neurodevelopment by modulating numerous steps in post-transcriptional regulation, including splicing, export, translation, and turnover of mRNAs that can traffic into axons and dendrites. One such RNA-binding protein is ZC3H14, which is lost in an inherited intellectual disability. The Drosophila melanogaster ZC3H14 ortholog, Nab2, localizes to neuronal nuclei and cytoplasmic ribonucleoprotein granules and is required for olfactory memory and proper axon projection into brain mushroom bodies. Nab2 can act as a translational repressor in conjunction with the Fragile-X mental retardation protein homolog Fmr1 and shares target RNAs with the Fmr1-interacting RNA-binding protein Ataxin-2. However, neuronal signaling pathways regulated by Nab2 and their potential roles outside of mushroom body axons remain undefined. Here, we present an analysis of a brain proteomic dataset that indicates that multiple planar cell polarity proteins are affected by Nab2 loss, and couple this with genetic data that demonstrate that Nab2 has a previously unappreciated role in restricting the growth and branching of dendrites that elaborate from larval body-wall sensory neurons. Further analysis confirms that Nab2 loss sensitizes sensory dendrites to the genetic dose of planar cell polarity components and that Nab2-planar cell polarity genetic interactions are also observed during Nab2-dependent control of axon projection in the central nervous system mushroom bodies. Collectively, these data identify the conserved Nab2 RNA-binding protein as a likely component of post-transcriptional mechanisms that limit dendrite growth and branching in Drosophila sensory neurons and genetically link this role to the planar cell polarity pathway. Given that mammalian ZC3H14 localizes to dendritic spines and controls spine density in hippocampal neurons, these Nab2-planar cell polarity genetic data may highlight a conserved path through which Nab2/ZC3H14 loss affects morphogenesis of both axons and dendrites in diverse species.

The crystal structure of yeast regulatory subunit reveals key evolutionary insights into Protein Kinase A oligomerization

Protein Kinase A (PKA) is a widespread enzyme that plays a key role in many signaling pathways from lower eukaryotes to metazoans. In mammals, the regulatory (R) subunits sequester and target the catalytic (C) subunits to proper subcellular locations. This targeting is accomplished by the dimerization and docking (D/D) domain of the R subunits. The activation of the holoenzyme depends on the binding of the second messenger cAMP. The only available structures of the D/D domain proceed from mammalian sources. Unlike dimeric mammalian counterparts, the R subunit from Saccharomyces cerevisiae (Bcy1) forms tetramers in solution. Here we describe the first high-resolution structure of a non-mammalian D/D domain. The tetramer in the crystals of the Bcy1 D/D domain is a dimer of dimers that retain the classical D/D domain fold. By using phylogenetic and structural analyses combined with site-directed mutagenesis, we found that fungal R subunits present an insertion of a single amino acid at the D/D domain that shifts the position of a downstream, conserved arginine. This residue participates in intra-dimer interactions in mammalian D/D domains, while due to this insertion it is involved in inter-dimer contacts in Bcy1, which are crucial for the stability of the tetramer. This surprising finding challenges well-established concepts regarding the oligomeric state within the PKAR protein family and provides important insights into the yet unexplored structural diversity of the D/D domains and the molecular determinants of R subunit oligomerization.

HtsRC-Mediated Accumulation of F-Actin Regulates Ring Canal Size During Drosophila melanogaster Oogenesis

Ring canals in the female germline of Drosophila melanogaster are supported by a robust filamentous actin (F-actin) cytoskeleton, setting them apart from ring canals in other species and tissues. Previous work has identified components required for the expansion of the ring canal actin cytoskeleton, but has not identified the proteins responsible for F-actin recruitment or accumulation. Using a combination of CRISPR-Cas9 mediated mutagenesis and UAS-Gal4 overexpression, we show that HtsRC-a component specific to female germline ring canals-is both necessary and sufficient to drive F-actin accumulation. Absence of HtsRC in the germline resulted in ring canals lacking inner rim F-actin, while overexpression of HtsRC led to larger ring canals. HtsRC functions in combination with Filamin to recruit F-actin to ectopic actin structures in somatic follicle cells. Finally, we present findings that indicate that HtsRC expression and robust female germline ring canal expansion are important for high fecundity in fruit flies but dispensable for their fertility-a result that is consistent with our understanding of HtsRC as a newly evolved gene specific to female germline ring canals.

Perineurial Barrier Glia Physically Respond to Alcohol in an Akap200-Dependent Manner to Promote Tolerance

Ethanol is the most common drug of abuse. It exerts its behavioral effects by acting on widespread neural circuits; however, its impact on glial cells is less understood. We show that Drosophila perineurial glia are critical for ethanol tolerance, a simple form of behavioral plasticity. The perineurial glia form the continuous outer cellular layer of the blood-brain barrier and are the interface between the brain and the circulation. Ethanol tolerance development requires the A kinase anchoring protein Akap200 specifically in perineurial glia. Akap200 tightly coordinates protein kinase A, actin, and calcium signaling at the membrane to control tolerance. Furthermore, ethanol causes a structural remodeling of the actin cytoskeleton and perineurial membrane topology in an Akap200-dependent manner, without disrupting classical barrier functions. Our findings reveal an active molecular signaling process in the cells at the blood-brain interface that permits a form of behavioral plasticity induced by ethanol.

Subcellular Specialization and Organelle Behavior in Germ Cells

Gametes, eggs and sperm, are the highly specialized cell types on which the development of new life solely depends. Although all cells share essential organelles, such as the ER (endoplasmic reticulum), Golgi, mitochondria, and centrosomes, germ cells display unique regulation and behavior of organelles during gametogenesis. These germ cell-specific functions of organelles serve critical roles in successful gamete production. In this chapter, I will review the behaviors and roles of organelles during germ cell differentiation.

AKAP200 promotes Notch stability by protecting it from Cbl/lysosome-mediated degradation in Drosophila melanogaster

AKAP200 is a Drosophila melanogaster member of the “A Kinase Associated Protein” family of scaffolding proteins, known for their role in the spatial and temporal regulation of Protein Kinase A (PKA) in multiple signaling contexts. Here, we demonstrate an unexpected function of AKAP200 in promoting Notch protein stability. In Drosophila, AKAP200 loss-of-function (LOF) mutants show phenotypes that resemble Notch LOF defects, including eye patterning and sensory organ specification defects. Through genetic interactions, we demonstrate that AKAP200 interacts positively with Notch in both the eye and the thorax. We further show that AKAP200 is part of a physical complex with Notch. Biochemical studies reveal that AKAP200 stabilizes endogenous Notch protein, and that it limits ubiquitination of Notch. Specifically, our genetic and biochemical evidence indicates that AKAP200 protects Notch from the E3-ubiquitin ligase Cbl, which targets Notch to the lysosomal pathway. Indeed, we demonstrate that the effect of AKAP200 on Notch levels depends on the lysosome. Interestingly, this function of AKAP200 is fully independent of its role in PKA signaling and independent of its ability to bind PKA. Taken together, our data indicate that AKAP200 is a novel tissue specific posttranslational regulator of Notch, maintaining high Notch protein levels and thus promoting Notch signaling.

AKAP200 belongs to a family of scaffolding proteins best known for their regulation of PKA localization. In this study, we have identified a novel role of AKAP200 in Notch protein stability and signaling. In Drosophila melanogaster, AKAP200’s loss and gain-of-function (LOF/GOF) phenotypes are characteristic of Notch signaling defects. Furthermore, we demonstrated genetic interactions between AKAP200 and Notch. Consistent with this, AKAP200 stabilizes the endogenous Notch protein and limits its ubiquitination. AKAP200 exerts its effects on Notch by antagonizing Cbl-mediated ubiquitination and thus lysosome targeting of Notch. Based on these data, we postulate a novel PKA independent mechanism of AKAP200 to achieve optimal Notch protein levels, with AKAP200 preventing Cbl-mediated lysosomal degradation of Notch.

Enhancer-trap flippase lines for clonal analysis in the Drosophila ovary

The Drosophila melanogaster genetic tool box includes many stocks for generating genetically mosaic tissue in which a clone of cells, related by lineage, contain a common genetic alteration. These tools have made it possible to study the postembryonic function of essential genes and to better understand how individual cells interact within intact tissues. We have screened through 201 enhancer-trap flippase lines to identify lines that produce useful clone patterns in the adult ovary. We found that approximately 70% of the lines produced clones that were present in the adult ovary and that many ovarian cell types were represented among the different clone patterns produced by these lines. We have also identified and further characterized five particularly useful enhancer-trap flippase lines. These lines make it possible to generate clones specifically in germ cells, escort cells, prefollicle cells, or terminal filament cells. In addition, we have found that chickadee is specifically upregulated in the posterior escort cells, follicle stem cells, and prefollicle cells that comprise the follicle stem cell niche region. Collectively, these studies provide several new tools for genetic mosaic analysis in the Drosophila ovary.

Developmental shaping of dendritic arbors in Drosophila relies on tightly regulated intra-neuronal activity of protein kinase A (PKA)

Dendrites develop morphologies characterized by multiple levels of complexity that involve neuron type specific dendritic length and particular spatial distribution. How this is developmentally regulated and in particular which signaling molecules are crucial in the process is still not understood. Using Drosophila class IV dendritic arborization (da) neurons we test in vivo the effects of cell-autonomous dose-dependent changes in the activity levels of the cAMP-dependent Protein Kinase A (PKA) on the formation of complex dendritic arbors. We find that genetic manipulations of the PKA activity levels affect profoundly the arbor complexity with strongest impact on distal branches. Both decreasing and increasing PKA activity result in a reduced complexity of the arbors, as reflected in decreased dendritic length and number of branching points, suggesting an inverted U-shape response to PKA. The phenotypes are accompanied by changes in organelle distribution: Golgi outposts and early endosomes in distal dendritic branches are reduced in PKA mutants. By using Rab5 dominant negative we find that PKA interacts genetically with the early endosomal pathway. We test if the possible relationship between PKA and organelles may be the result of phosphorylation of the microtubule motor dynein components or Rab5. We find that Drosophila cytoplasmic dynein components are direct PKA phosphorylation targets in vitro, but not in vivo, thus pointing to a different putative in vivo target. Our data argue that tightly controlled dose-dependent intra-neuronal PKA activity levels are critical in determining the dendritic arbor complexity, one of the possible ways being through the regulation of organelle distribution.

Capping protein beta is required for actin cytoskeleton organisation and cell migration during Drosophila oogenesis

Capping protein (CP) is a well-characterised actin-binding protein important for regulation of actin filament (AF) assembly. CP caps the barbed end of AFs, inhibiting the addition and loss of actin monomers. In Drosophila melanogaster, the gene encoding CP β-subunit is named capping protein beta (cpb; see Hopmann et al. [1996] J Cell Biol 133: 1293-305). The cpb level is reduced in the Drosophila bristle actin cytoskeleton and becomes disorganised with abnormal morphology. A reduced level of the CP protein in ovary results in disruption of oocyte determination, and disturbance of nurse cell (NC) cortical integrity and dumping. We describe novel defects appearing in cpb mutants during oogenesis, in which cpb plays an important role in border and centripetal follicle cell migration, ring canal development and cytoplasmic AF formation. The number of long cytoplasmic AFs was dramatically reduced in cpb hypomorphs and abnormal actin aggregates was seen on the inner side of NC membranes. A hypothesis to explain the formation of abnormal short-cut cytoplasmic AFs and actin aggregates in the cpb mutant NCs was proffered, along with a discussion of the reasons for 'dumpless' phenotype formation in the mutants.

Akap200 suppresses the effects of Dv-cbl expression in the Drosophila eye

The Drosophila melanogaster orthologue of the c-Cbl proto-oncogene acts to downregulate signalling from receptor tyrosine kinases by enhancing endocytosis of activated receptors. Expression of an analogue of the C-terminally truncated v-Cbl oncogene, Dv-cbl, in the developing Drosophila eye conversely leads to excess signalling and disruption to the well-ordered adult compound eye. Co-expression of activated Ras with Dv-cbl leads to a severe disruption of eye development. We have used a transposon-based inducible expression system to screen for molecules that can suppress the Dv-cbl phenotype and have identified an allele that upregulates the A-kinase anchoring protein, Akap200. Overexpression of Akap200 not only suppresses the phenotype caused by Dv-cbl expression, but also the severe disruption to eye development caused by the combined expression of Dv-cbl and activated Ras. Akap200 is also endogenously expressed in the developing Drosophila eye at a level that modulates the effects of excessive signalling caused by expression of Dv-cbl.

Novel regulators of planar cell polarity: a genetic analysis in Drosophila

Planar cell polarity (PCP) is a common feature of many epithelia and epithelial organs. Although progress has been made in the dissection of molecular mechanisms regulating PCP, many questions remain. Here we describe a screen to identify novel PCP regulators in Drosophila. We employed mild gain-of-function (GOF) phenotypes of two cytoplasmic Frizzled (Fz)/PCP core components, Diego (Dgo) and Prickle (Pk), and screened these against the DrosDel genome-wide deficiency collection for dominant modifiers. Positive genomic regions were rescreened and narrowed down with smaller overlapping deficiencies from the Exelixis collection and RNAi-mediated knockdown applied to individual genes. This approach isolated new regulators of PCP, which were confirmed with loss-of-function analyses displaying PCP defects in the eye and/or wing. Furthermore, knockdown of a subset was also sensitive to dgo dosage or dominantly modified a dishevelled (dsh) GOF phenotype, supporting a role in Fz/PCP-mediated polarity establishment. Among the new "PCP" genes we identified several kinases, enzymes required for lipid modification, scaffolding proteins, and genes involved in substrate modification and/or degradation. Interestingly, one of them is a member of the Meckel-Gruber syndrome factors, associated with human ciliopathies, suggesting an important role for cell polarity in nonciliated cells.

Drosophila spoonbill encodes a dual-specificity A-kinase anchor protein essential for oogenesis

spoonbill is a Drosophila female-sterile mutation, which interferes with normal egg patterning during oogenesis. Previous analyzes linked the mutation to a number of seemingly unrelated pathways, including GRK/EGFR and DPP, two major pathways essential for Drosophila and vertebrate development. Further work suggested that spoonbill may also function in actin polymerization and border-cell migration. Here we describe the molecular cloning of the spoonbill gene and characterize new mutant alleles, further demonstrating that spoonbill's function is essential during oogenesis. We found spoonbill to be allelic to CG3249 (also known as yu), which encodes the only known dual-specificity A-kinase anchor protein in Drosophila. Our data indicate that similar to mammalian AKAPs, Spoonbill protein contains a number of potential kinase and phosphatase binding motifs, and is targeted, in the ovary, to mitochondria and Golgi. Finally, we address some of spoonbill's mutant phenotypes from the perspective of the published data on the AKAP protein family.

Mechanisms of protein kinase A anchoring

The second messenger cyclic adenosine monophosphate (cAMP), which is produced by adenylyl cyclases following stimulation of G-protein-coupled receptors, exerts its effect mainly through the cAMP-dependent serine/threonine protein kinase A (PKA). Due to the ubiquitous nature of the cAMP/PKA system, PKA signaling pathways underlie strict spatial and temporal control to achieve specificity. A-kinase anchoring proteins (AKAPs) bind to the regulatory subunit dimer of the tetrameric PKA holoenzyme and thereby target PKA to defined cellular compartments in the vicinity of its substrates. AKAPs promote the termination of cAMP signals by recruiting phosphodiesterases and protein phosphatases, and the integration of signaling pathways by binding additional signaling proteins. AKAPs are a heterogeneous family of proteins that only display similarity within their PKA-binding domains, amphipathic helixes docking into a hydrophobic groove formed by the PKA regulatory subunit dimer. This review summarizes the current state of information on compartmentalized cAMP/PKA signaling with a major focus on structural aspects, evolution, diversity, and (patho)physiological functions of AKAPs and intends to outline newly emerging directions of the field, such as the elucidation of AKAP mutations and alterations of AKAP expression in human diseases, and the validation of AKAP-dependent protein-protein interactions as new drug targets. In addition, alternative PKA anchoring mechanisms employed by noncanonical AKAPs and PKA catalytic subunit-interacting proteins are illustrated.

A constant light-genetic screen identifies KISMET as a regulator of circadian photoresponses

Circadian pacemakers are essential to synchronize animal physiology and behavior with the day∶night cycle. They are self-sustained, but the phase of their oscillations is determined by environmental cues, particularly light intensity and temperature cycles. In Drosophila, light is primarily detected by a dedicated blue-light photoreceptor: CRYPTOCHROME (CRY). Upon light activation, CRY binds to the pacemaker protein TIMELESS (TIM) and triggers its proteasomal degradation, thus resetting the circadian pacemaker. To understand further the CRY input pathway, we conducted a misexpression screen under constant light based on the observation that flies with a disruption in the CRY input pathway remain robustly rhythmic instead of becoming behaviorally arrhythmic. We report the identification of more than 20 potential regulators of CRY-dependent light responses. We demonstrate that one of them, the chromatin-remodeling enzyme KISMET (KIS), is necessary for normal circadian photoresponses, but does not affect the circadian pacemaker. KIS genetically interacts with CRY and functions in PDF-negative circadian neurons, which play an important role in circadian light responses. It also affects daily CRY-dependent TIM oscillations in a peripheral tissue: the eyes. We therefore conclude that KIS is a key transcriptional regulator of genes that function in the CRY signaling cascade, and thus it plays an important role in the synchronization of circadian rhythms with the day∶night cycle.

In most organisms, intracellular molecular pacemakers called circadian clocks coordinate metabolic, physiological, and behavioral processes during the course of the day. For example, they determine when animals are active or resting. Circadian clocks are self-sustained oscillators, but their free-running period does not exactly match day length. Thus, they have to be reset by environmental inputs to stay properly phased with the day∶night cycle. The fruit fly Drosophila melanogaster relies primarily on CRYPTOCHROME (CRY)—a cell-autonomous blue-light photoreceptor—to synchronize its circadian clocks with the light∶dark cycle. With a genetic screen, we identified over 20 candidate genes that might regulate CRY function. kismet (kis) is among them: it encodes a chromatin remodeling factor essential for the development of Drosophila. We show that, in adult flies, KIS is expressed and functions in brain neurons that control daily behavioral rhythms. KIS determines how Drosophila circadian behavior responds to light, but not its free-running period. Moreover, manipulating simultaneously kis and cry activity demonstrates that these two genes interact to control molecular and behavioral circadian photoresponses. Our work therefore reveals that KIS regulates CRY signaling and thus determines how circadian clocks respond to light input.

JNK signaling controls border cell cluster integrity and collective cell migration

Collective cell movement is a mechanism for invasion identified in many developmental events. Examples include the movement of lateral-line neurons in Zebrafish, cells in the inner blastocyst, and metastasis of epithelial tumors [1]. One key model to study collective migration is the movement of border cell clusters in Drosophila. Drosophila egg chambers contain 15 nurse cells and a single oocyte surrounded by somatic follicle cells. At their anterior end, polar cells recruit several neighboring follicle cells to form the border cell cluster [2]. By stage 9, and over 6 hr, border cells migrate as a cohort between nurse cells toward the oocyte. The specification and directionality of border cell movement are regulated by hormonal and signaling mechanisms [3]. However, how border cells are held together while they migrate is not known. Here, we show that a negative-feedback loop controlling JNK activity regulates border cell cluster integrity. JNK signaling modulates contacts between border cells and between border cells and substratum to sustain collective migration by regulating several effectors including the polarity factor Bazooka and the cytoskeletal adaptor D-Paxillin. We anticipate a role for the JNK pathway in controlling collective cell movements in other morphogenetic and clinical models.

The AKAP Yu is required for olfactory long-term memory formation in Drosophila

Extensive neurogenetic analysis has shown that memory formation depends critically on cAMP-protein kinase A (PKA) signaling. Details of how this pathway is involved in memory formation, however, remain to be fully elucidated. From a large-scale behavioral screen in Drosophila, we identified the yu mutant to be defective in one-day memory after spaced training. The yu mutation disrupts a gene encoding an A-kinase anchoring protein (AKAP). AKAPs comprise a family of proteins, which determine the subcellular localization of PKAs and thereby critically restrict cAMP signaling within a cell. Further behavioral characterizations revealed that long-term memory (LTM) was disrupted specifically in the yu mutant, whereas learning, short-term memory and anesthesia-resistant memory all appeared normal. Another independently isolated mutation of the yu gene failed to complement the LTM defect associated with the yu mutation, and this phenotypic defect could be rescued by induced acute expression of a yu(+) transgene, suggesting that yu functions physiologically during memory formation. AKAP Yu is expressed preferentially in the mushroom body (MB) neuroanatomical structure, and expression of a yu(+) transgene to the MB, but not to other brain regions, is sufficient to rescue the LTM defect of the yu mutant. These observations lead us to conclude that proper localization of PKA by Yu AKAP in MB neurons is required for the formation of LTM.

A-kinase anchoring protein 150 in the mouse brain is concentrated in areas involved in learning and memory

A-kinase anchoring proteins (AKAPs) form large macromolecular signaling complexes that specifically target cAMP-dependent protein kinase (PKA) to unique subcellular compartments and thus, provide high specificity to PKA signaling. For example, the AKAP79/150 family tethers PKA, PKC and PP2B to neuronal membranes and postsynaptic densities and plays an important role in synaptic function. Several studies suggested that AKAP79/150 anchored PKA contributes to mechanisms associated with synaptic plasticity and memory processes, but the precise role of AKAPs in these processes is still unknown. In this study we established the mouse brain distribution of AKAP150 using two well-characterized AKAP150 antibodies. Using Western blotting and immunohistochemistry we showed that AKAP150 is widely distributed throughout the mouse brain. The highest AKAP150 expression levels were observed in striatum, cerebral cortex and several other forebrain regions (e.g. olfactory tubercle), relatively high expression was found in hippocampus and olfactory bulb and low/no expression in cerebellum, hypothalamus, thalamus and brain stem. Although there were some minor differences in mouse AKAP150 brain distribution compared to the distribution in rat brain, our data suggested that rodents have a characteristic AKAP150 brain distribution pattern. In general we observed that AKAP150 is strongly expressed in mouse brain regions involved in learning and memory. These data support its suggested role in synaptic plasticity and memory processes.

Dynamic anchoring of PKA is essential during oocyte maturation

In the final stages of ovarian follicular development, the mouse oocyte remains arrested in the first meiotic prophase, and cAMP-stimulated PKA plays an essential role in this arrest. After the LH surge, a decrease in cAMP and PKA activity in the oocyte initiates an irreversible maturation process that culminates in a second arrest at metaphase II prior to fertilization. A-kinase anchoring proteins (AKAPs) mediate the intracellular localization of PKA and control the specificity and kinetics of substrate phosphorylation. Several AKAPs have been identified in oocytes including one at 140 kDa that we now identify as a product of the Akap1 gene. We show that PKA interaction with AKAPs is essential for two sequential steps in the maturation process: the initial maintenance of meiotic arrest and the subsequent irreversible progression to the polar body extruded stage. A peptide inhibitor (HT31) that disrupts AKAP/PKA interactions stimulates oocyte maturation in the continued presence of high cAMP. However, during the early minutes of maturation, type II PKA moves from cytoplasmic sites to the mitochondria, where it associates with AKAP1, and this is shown to be essential for maturation to continue irreversibly.

The effects of disruption of A kinase anchoring protein-protein kinase A association on protein kinase A signalling in neuroendocrine melanotroph cells of Xenopus laevis

The secretory activity of melanotroph cells from Xenopus laevis is regulated by multiple neurotransmitters that act through adenylyl cyclase. Cyclic adenosine monophosphate (cAMP), acting on protein kinase A (PKA), stimulates the frequency of intracellular Ca(2+) oscillations and the secretory activity of the melanotroph cell. Anchoring of PKA near target proteins is essential for many PKA-regulated processes, and the family of A kinase anchoring proteins (AKAPs) is involved in the compartmentalisation of PKA type II (PKA II) regulatory subunits. In the present study, we determined to what degree cAMP signalling in Xenopus melanotrophs depends on compartmentalised PKA II. For this purpose, a membrane-permeable stearated form of Ht31 (St-Ht31), which dislodges PKA II from AKAP (thus disrupting PKA II signalling), was used. The effect of St-Ht31 on both secretion of radiolabelled peptides and intracellular Ca(2+) signalling by superfused Xenopus melanotrophs was assessed. St-Ht31 stimulated secretion but had no effect on Ca(2+) signalling. We conclude Xenopus melanotrophs possess a St-Ht31-sensitive PKA II that is associated with the exocytosis machinery and, furthermore, that Ca(2+) signalling is regulated by an AKAP-independent signalling system. Moreover, our results support a recent proposal that AKAP participates in regulating PKA activity independently from cAMP.

Misexpression screen for genes altering the olfactory map in Drosophila

Despite the identification of a number of guidance molecules, a comprehensive picture has yet to emerge to explain the precise anatomy of the olfactory map. From a misexpression screen of 1,515 P{GS} lines, we identified 23 genes that, when forcibly expressed in the olfactory receptor neurons, disrupted the stereotyped anatomy of the Drosophila antennal lobes. These genes, which have not been shown previously to control olfactory map development, encode novel proteins as well as proteins with known roles in axonal outgrowth and cytoskeletal remodeling. We analyzed Akap200, which encodes a Protein Kinase A-binding protein. Overexpression of Akap200 resulted in fusion of the glomeruli, while its loss resulted in misshapen and ectopic glomeruli. The requirement of Akap200 validates our screen as an effective approach for recovering genes controlling glomerular map patterning. Our finding of diverse classes of genes reveals the complexity of the mechanisms that underlie olfactory map development.

Gene expression patterns associated with blood-feeding in the malaria mosquito Anopheles gambiae

Background

Blood feeding, or hematophagy, is a behavior exhibited by female mosquitoes required both for reproduction and for transmission of pathogens. We determined the expression patterns of 3,068 ESTs, representing ~2,000 unique gene transcripts using cDNA microarrays in adult female Anopheles gambiae at selected times during the first two days following blood ingestion, at 5 and 30 min during a 40 minute blood meal and at 0, 1, 3, 5, 12, 16, 24 and 48 hours after completion of the blood meal and compared their expression to transcript levels in mosquitoes with access only to a sugar solution.

Results

In blood-fed mosquitoes, 413 unique transcripts, approximately 25% of the total, were expressed at least two-fold above or below their levels in the sugar-fed mosquitoes, at one or more time points. These differentially expressed gene products were clustered using k-means clustering into Early Genes, Middle Genes, and Late Genes, containing 144, 130, and 139 unique transcripts, respectively. Several genes from each group were analyzed by quantitative real-time PCR in order to validate the microarray results.

Conclusion

The expression patterns and annotation of the genes in these three groups (Early, Middle, and Late genes) are discussed in the context of female mosquitoes' physiological responses to blood feeding, including blood digestion, peritrophic matrix formation, egg development, and immunity.

Regulation of actin-based cell migration by cAMP/PKA

A wide variety of soluble signaling substances utilize the cyclic AMP-dependent protein kinase (PKA) pathway to regulate cellular behaviors including intermediary metabolism, ion channel conductivity, and transcription. A growing literature suggests that integrin-mediated cell adhesion may also utilize PKA to modulate adhesion-associated events such as actin cytoskeletal dynamics and migration. PKA is dynamically regulated by integrin-mediated cell adhesion to extracellular matrix (ECM). Furthermore, while some hallmarks of cell migration and cytoskeletal organization require PKA activity (e.g. activation of Rac and Cdc42; actin filament assembly), others are inhibited by it (e.g. activation of Rho and PAK; interaction of VASP with the c-Abl tyrosine kinase). Also, cell migration and invasion can be impeded by either inhibition or hyper-activation of PKA. Finally, a number of A-kinase anchoring proteins (AKAPs) serve to associate PKA with various components of the actin cytoskeleton, thereby enhancing and/or specifying cAMP/PKA signaling in those regions. This review discusses the growing literature that supports the hypothesis that PKA plays a central role in cytoskeletal regulation and cell migration.

Specific interactions of quercetin and other flavonoids with target proteins are revealed by elicited fluorescence

The fluorogenic properties of quercetin and similar flavonoids common in plants were exploited to analyse their interaction with target proteins. Quercetin produced a strong fluorescent signal upon binding to bovine serum albumin (BSA) and insulin. The fluorescent signal showed saturation kinetics with increasing flavonoid concentrations indicating the presence of defined peptide binding motifs. Other tested proteins showed no fluorescence with the flavonoids. In a comparative study including 22 flavonoids the compounds with fluorogenic properties were identified using our model proteins BSA and insulin and the structural requirements for the fluorogenic property were defined. Only flavones with a high degree of hydroxylation were able to elicit fluorescence. The emitted fluorescence was strongly enhanced at alkaline pH. Finally, an attempt was made to identify intracellular target molecules in live cells. Drosophila follicles showed a distinct staining pattern thus giving evidence that high concentrations of quercetin binding proteins are present in the nuclei and are associated with the ring canals. The presented biochemical and cytological data show that the interaction of the studied flavonoids with target proteins is specific and this finding opens up new experimental possibilities to systematically identify the cellular proteins with specific binding motifs for quercetin or other fluorogenic compounds of medical interest.