Protein tyrosine phosphatases and neural development

Impaired signaling pathways on Berardinelli-Seip congenital lipodystrophy macrophages during Leishmania infantum infection

Berardinelli-Seip congenital lipodystrophy (CGL), a rare autosomal recessive disorder, is characterized by a lack of adipose tissue. Infections are one of the major causes of CGL individuals' premature death. The mechanisms that predispose to infections are poorly understood. We used Leishmania infantum as an in vitro model of intracellular infection to explore mechanisms underlying the CGL infection processes, and to understand the impact of host mutations on Leishmania survival, since this pathogen enters macrophages through specialized membrane lipid domains. The transcriptomic profiles of both uninfected and infected monocyte-derived macrophages (MDMs) from CGL (types 1 and 2) and controls were studied. MDMs infected with L. infantum showed significantly downregulated expression of genes associated with infection-response pathways (MHC-I, TCR-CD3, and granzymes). There was a transcriptomic signature in CGL cells associated with impaired membrane trafficking and signaling in response to infection, with concomitant changes in the expression of membrane-associated genes in parasites (e.g. δ-amastins). We identified pathways suggesting the lipid storage dysfunction led to changes in phospholipids expression and impaired responses to infection, including immune synapse (antigen presentation, IFN-γ signaling, JAK/STAT); endocytosis; NF-kappaB signaling; and phosphatidylinositol biosynthesis. In summary, lipid metabolism of the host plays an important role in determining antigen presentation pathways.

The CNS/PNS Extracellular Matrix Provides Instructive Guidance Cues to Neural Cells and Neuroregulatory Proteins in Neural Development and Repair

Background. The extracellular matrix of the PNS/CNS is unusual in that it is dominated by glycosaminoglycans, especially hyaluronan, whose space filling and hydrating properties make essential contributions to the functional properties of this tissue. Hyaluronan has a relatively simple structure but its space-filling properties ensure micro-compartments are maintained in the brain ultrastructure, ensuring ionic niches and gradients are maintained for optimal cellular function. Hyaluronan has cell-instructive, anti-inflammatory properties and forms macro-molecular aggregates with the lectican CS-proteoglycans, forming dense protective perineuronal net structures that provide neural and synaptic plasticity and support cognitive learning. Aims. To highlight the central nervous system/peripheral nervous system (CNS/PNS) and its diverse extracellular and cell-associated proteoglycans that have cell-instructive properties regulating neural repair processes and functional recovery through interactions with cell adhesive molecules, receptors and neuroregulatory proteins. Despite a general lack of stabilising fibrillar collagenous and elastic structures in the CNS/PNS, a sophisticated dynamic extracellular matrix is nevertheless important in tissue form and function. Conclusions. This review provides examples of the sophistication of the CNS/PNS extracellular matrix, showing how it maintains homeostasis and regulates neural repair and regeneration.

Receptor protein tyrosine phosphatase σ binds to neurons in the adult mouse brain

The role of type IIA receptor protein tyrosine phosphatases (RPTPs), which includes LAR, RPTPσ and RPTPδ, in the nervous system is becoming increasingly recognized. Evidence supports a significant role for these RPTPs during the development of the nervous system as well as after injury, and mutations in RPTPs are associated with human disease. However, a major open question is the nature of the ligands that interact with type IIA RPTPs in the adult brain. Candidates include several different proteins as well as the glycosaminoglycan chains of proteoglycans. In order to investigate this problem, we used a receptor affinity probe assay with RPTPσ-AP fusion proteins on sections of adult mouse brain and to cultured neurons. Our results demonstrate that the major binding sites for RPTPσ in adult mouse brain are on neurons and are not proteoglycan GAG chains, as RPTPσ binding overlaps with the neuronal marker NeuN and was not significantly altered by treatments which eliminate chondroitin sulfate, heparan sulfate, or both. We also demonstrate no overlap of binding of RPTPσ with perineuronal nets, and a unique modulation of RPTPσ binding to brain by divalent cations. Our data therefore point to neuronal proteins, rather than CSPGs, as being the ligands for RPTPσ in the adult, uninjured brain.

Proteomic analysis of lithium-induced gene expression in the rat hypothalamus

The hypothalamic proteomes were analyzed 1 and 6 hr after an intraperitoneal injection of lithium chloride or sodium chloride (0.15 M, 12 ml/kg). Results showed that expression of 14 and 32 proteomes was increased consistently by 1 hr and 6 hr of lithium treatment, respectively. Among them, tentative implications of glial fibrillary acidic protein, receptor-type protein tyrosine phosphatase, spectrin, and glutamate dehydrogenase in the lithium-induced activation of the hypothalamic-pituitary-adrenal axis, and conditioned taste aversion have been discussed. The proteomes listed in this study will provide, at least, a new insight to understand the molecular mechanism of lithium's action in the brain.

Identification of Dlk1, Ptpru and Klhl1 as novel Nurr1 target genes in meso-diencephalic dopamine neurons

The orphan nuclear receptor Nurr1 is essential for the development of meso-diencephalic dopamine (mdDA) neurons and is required, together with the homeobox transcription factor Pitx3, for the expression of genes involved in dopamine metabolism. In order to elucidate the molecular mechanisms that underlie the neuronal deficits in Nurr1(-/-) mice, we performed combined gene expression microarrays and ChIP-on-chip analysis and thereby identified Dlk1, Ptpru and Klhl1 as novel Nurr1 target genes in vivo. In line with the previously described cooperativity between Nurr1 and Pitx3, we show that the expression of Ptpru and Klhl1 in mdDA neurons is also dependent on Pitx3. Furthermore, we demonstrate that Nurr1 interacts with the Ptpru promoter directly and requires Pitx3 for full expression of Ptpru in mdDA neurons. By contrast, the expression of Dlk1 is maintained in Pitx3(-/-) embryos and is even expanded into the rostral part of the mdDA area, suggesting a unique position of Dlk1 in the Nurr1 and Pitx3 transcriptional cascades. Expression analysis in Dlk1(-/-) embryos reveals that Dlk1 is required to prevent premature expression of Dat in mdDA neuronal precursors as part of the multifaceted process of mdDA neuronal differentiation driven by Nurr1 and Pitx3. Taken together, the involvement of Nurr1 and Pitx3 in the expression of novel target genes involved in important neuronal processes such as neuronal patterning, axon outgrowth and terminal differentiation, opens up new avenues to study the properties of mdDA neurons during development and in neuronal pathology as observed in Parkinson's disease.

A novel role for receptor like protein tyrosine phosphatase zeta in modulation of sensorimotor responses to noxious stimuli: evidences from knockout mice studies

Receptor like protein tyrosine phosphatase zeta (RPTPz) (also known as RPTPbeta or PTPxi) is a tyrosine phosphatase widely expressed in the nervous system, thought to play a role in cell-cell communication. However, knocking out RPTPz does not induce major neural abnormalities in mice. In order to better assess the potential role of RPTPz in various neural functions, we performed a comprehensive behavioural characterization of CNS/PNS functions in knockout mice (RPTPz -/-) confirming previously observed impaired working memory functions and further demonstrating an altered motor coordination. Moreover, RPTPz -/- mice displayed reduced responses to moderate thermal and tactile stimuli, both in baseline and under inflammatory conditions. These findings assign novel functional role of RPTPz in motor coordination and nociception.

A role for receptor protein tyrosine phosphatase lambda in midbrain development

The mid-hindbrain boundary (MHB) harbors an important organizing center for the adjacent brain regions. Here, we present evidence that the receptor protein tyrosine phosphatase lambda (RPTPlambda) is part of the complex molecular network that maintains and shapes the MHB region. RPTPlambda is expressed in a tight band of cells in the caudal midbrain, anterior to the transverse ring of Wnt1 expression. Forced expression of RPTPlambda across the mid-hindbrain region repressed expression of Wnt1, whereas RNA interference-mediated knock-down of RPTPlambda resulted in expansion and distortion of the Wnt1 domain. When ectopically expressed in the mesencephalon, RPTPlambda specifically inhibited the induction of Wnt1 expression after subsequent stimulation with Fgf8. Reduced Wnt1 expression after RPTPlambda transfection correlated with a decrease in Ras- mitogen-activated protein kinase activity at the MHB. We further show that in the embryonic midbrain, RPTPlambda can bind to beta-catenin, a central component of the canonical Wnt signaling pathway. Overexpression of RPTPlambda suppressed the activity of a beta-catenin responsive promoter in the midbrain and reduced progenitor cell proliferation. Cotransfection of Wnt1 or of a stabilized form of beta-catenin together with RPTPlambda partially rescued the RPTPlambda-mediated proliferation defect. Together, these data suggest that RPTPlambda may play a dual role in the control of midbrain development: as a negative modulator of Fgf8-induced Wnt1 expression at the MHB, which may help to confine the Wnt1 domain to it characteristic tight ring at the MHB; and as an inhibitor of canonical Wnt signaling through interaction with and presumably sequestration of beta-catenin.

The receptor protein tyrosine phosphatase PTP69D antagonizes Abl tyrosine kinase to guide axons in Drosophila

During Drosophila embryogenesis, both the cytoplasmic Abelson tyrosine kinase (Abl) and the membrane bound tyrosine phosphatase PTP69D are required for proper guidance of CNS and motor axons. We provide evidence that PTP69D modulates signaling by Abl and its antagonist, Ena. An Abl loss-of function mutation dominantly suppresses most Ptp69D mutant phenotypes including larval/pupal lethality and CNS and motor axon defects, while increased Abl and decreased Ena expression dramatically increase the expressivity of Ptp69D axonal defects. In contrast, Ptp69D mutations do not affect Abl mutant phenotypes. These results support the hypothesis that PTP69D antagonizes the Abl/Ena genetic pathway, perhaps as an upstream regulator. We also find that mutation of the gene encoding the cytoplasmic Src64B tyrosine kinase exacerbates Ptp69D phenotypes, suggesting that two different cytoplasmic tyrosine kinases, Abl and Src64B, modify PTP69D-mediated axon patterning in quite different ways.

Gene expression analyses of grade II gliomas and identification of rPTPbeta/zeta as a candidate oligodendroglioma marker

Grade II gliomas are morphologically and clinically heterogeneous tumors for which histopathological typing remains the major tool for clinical classification. To what extent the major histological subtypes - astrocytomas, oligodendrogliomas, and oligoastrocytomas - constitute true biological entities is largely unresolved. Furthermore, morphological classification is often ambiguous and would be facilitated by specific subtype markers. In this study, 23 grade II gliomas were expression-profiled and subjected to hierarchical clustering. All six oligodendrogliomas were grouped together in one of two major clusters; a significant correlation was thus observed between gene expression and histopathological subtype. Supervised analyses were performed to identify genes differentiating oligodendrogliomas from other grade II tumors. In a leave-one-out test using 10 features for classification, 20 out of 23 tumors were correctly classified. Among the most differentially expressed genes was rPTPbeta/zeta. The expression of the rPTP beta/zeta protein in oligodendrogliomas and astrocytomas was further validated by immunohistochemistry in an independent set of tumors. All 11 oligodendrogliomas of this set displayed strong staining. In contrast, neoplastic astrocytes were mostly negative for rPTPbeta/zeta staining. In summary, this study demonstrates a correlation between gene expression pattern and histological subtype in grade II gliomas. Furthermore, the results from the immunohistochemical analyses of rPTPbeta/zeta expression should prompt further evaluation of this protein as a novel oligodendroglioma marker.

Cell surface nucleolin on developing muscle is a potential ligand for the axonal receptor protein tyrosine phosphatase-sigma

Reversible tyrosine phosphorylation, catalyzed by receptor tyrosine kinases and receptor tyrosine phosphatases, plays an essential part in cell signaling during axonal development. Receptor protein tyrosine phosphatase-sigma has been implicated in the growth, guidance and repair of retinal axons. This phosphatase has also been implicated in motor axon growth and innervation. Insect orthologs of receptor protein tyrosine phosphatase-sigma are also implicated in the recognition of muscle target cells. A potential extracellular ligand for vertebrate receptor protein tyrosine phosphatase-sigma has been previously localized in developing skeletal muscle. The identity of this muscle ligand is currently unknown, but it appears to be unrelated to the heparan sulfate ligands of receptor protein tyrosine phosphatase-sigma. In this study, we have used affinity chromatography and tandem MS to identify nucleolin as a binding partner for receptor protein tyrosine phosphatase-sigma in skeletal muscle tissue. Nucleolin, both from tissue lysates and in purified form, binds to receptor protein tyrosine phosphatase-sigma ectodomains. Its expression pattern also overlaps with that of the receptor protein tyrosine phosphatase-sigma-binding partner previously localized in muscle, and nucleolin can also be found in retinal basement membranes. We demonstrate that a significant amount of muscle-associated nucleolin is present on the cell surface of developing myotubes, and that two nucleolin-binding components, lactoferrin and the HB-19 peptide, can block the interaction of receptor protein tyrosine phosphatase-sigma ectodomains with muscle and retinal basement membranes in tissue sections. These data suggest that muscle cell surface-associated nucleolin represents at least part of the muscle binding site for axonal receptor protein tyrosine phosphatase-sigma and that nucleolin may also be a necessary component of basement membrane binding sites of receptor protein tyrosine phosphatase-sigma.

Protein tyrosine and serine-threonine phosphatases in the sea urchin, Strongylocentrotus purpuratus: identification and potential functions

Protein phosphatases, in coordination with protein kinases, play crucial roles in regulation of signaling pathways. To identify protein tyrosine phosphatases (PTPs) and serine-threonine (ser-thr) phosphatases in the Strongylocentrotus purpuratus genome, 179 annotated sequences were studied (122 PTPs, 57 ser-thr phosphatases). Sequence analysis identified 91 phosphatases (33 conventional PTPs, 31 dual specificity phosphatases, 1 Class III Cysteine-based PTP, 1 Asp-based PTP, and 25 ser-thr phosphatases). Using catalytic sites, levels of conservation and constraint in amino acid sequence were examined. Nine of 25 receptor PTPs (RPTPs) corresponded to human, nematode, or fly homologues. Domain structure revealed that sea urchin-specific RPTPs including two, PTPRLec and PTPRscav, may act in immune defense. Embryonic transcription of each phosphatase was recorded from a high-density oligonucleotide tiling microarray experiment. Most RPTPs are expressed at very low levels, whereas nonreceptor PTPs (NRPTPs) are generally expressed at moderate levels. High expression was detected in MAP kinase phosphatases (MKPs) and numerous ser-thr phosphatases. For several expressed NRPTPs, MKPs, and ser-thr phosphatases, morpholino antisense-mediated knockdowns were performed and phenotypes obtained. Finally, to assess roles of annotated phosphatases in endomesoderm formation, a literature review of phosphatase functions in model organisms was superimposed on sea urchin developmental pathways to predict areas of functional activity.

Neural stem cells from protein tyrosine phosphatase sigma knockout mice generate an altered neuronal phenotype in culture

Background

The LAR family Protein Tyrosine Phosphatase sigma (PTPσ) has been implicated in neuroendocrine and neuronal development, and shows strong expression in specific regions within the CNS, including the subventricular zone (SVZ). We established neural stem cell cultures, grown as neurospheres, from the SVZ of PTPσ knockout mice and sibling controls to determine if PTPσ influences the generation and the phenotype of the neuronal, astrocyte and oligodendrocyte cell lineages.

Results

The neurospheres from the knockout mice acquired heterogeneous developmental characteristics and they showed similar morphological characteristics to the age matched siblings. Although Ptprs expression decreases as a function of developmental age in vivo, it remains high with the continual renewal and passage of the neurospheres. Stem cells, progenitors and differentiated neurons, astrocytes and oligodendrocytes all express the gene. While no apparent differences were observed in developing neurospheres or in the astrocytes and oligodendrocytes from the PTPσ knockout mice, the neuronal migration patterns and neurites were altered when studied in culture. In particular, neurons migrated farther from the neurosphere centers and the neurite outgrowth exceeded the length of the neuronal processes from age matched sibling controls.

Conclusion

Our results imply a specific role for PTPσ in the neuronal lineage, particularly in the form of inhibitory influences on neurite outgrowth, and demonstrate a role for tyrosine phosphatases in neuronal stem cell differentiation.

Protein tyrosine phosphatases of Toxoneuron nigriceps bracovirus as potential disrupters of host prothoracic gland function

The genomic sequence of the bracovirus associated with the wasp Toxoneuron nigriceps (Hymenoptera, Braconidae) (TnBV), an endophagous parasitoid of the tobacco budworm larvae, Heliothis virescens (Lepidoptera, Noctuidae), contains a large gene family coding for protein tyrosine phosphatases (PTPs). Here we report the characterization of cDNAs for two of the viral PTPs isolated by screening a cDNA library from haemocytes of parasitized host larvae. The two encoded proteins show 70% amino acid identity and are expressed in the fat body of parasitized hosts. In addition, one was expressed in inactivated prothoracic glands (PTGs), 24 h after parasitoid oviposition. The rapid block of ecdysteroidogenesis does not appear to be due to inhibition of general protein synthesis, as indirectly indicated by the unaltered S6 kinase activity in the cytosolic extracts of basal PTGs from parasitized host larvae. Rather, TnBV PTP over-expression in inactivated host PTGs suggests that gland function may be affected by the disruption of the phosphorylation balance of key proteins regulating points upstream from the ribosomal S6 phosphorylation in the PTTH signaling cascade.

A high throughput messenger RNA differential display screen identifies discrete domains of gene expression and novel patterning processes along the developing neural tube

BACKGROUND

During early development the vertebrate neural tube is broadly organized into the forebrain, midbrain, hindbrain and spinal cord regions. Each of these embryonic zones is patterned by a combination of genetic pathways and the influences of local signaling centres. However, it is clear that much remains to be learned about the complete set of molecular cues that are employed to establish the identity and intrinsic neuronal diversity of these territories. In order to address this, we performed a high-resolution messenger RNA differential display screen to identify molecules whose expression is regionally restricted along the anteroposterior (AP) neuraxis during early chick development, with particular focus on the midbrain and hindbrain vesicles.

RESULTS

This approach identified 44 different genes, with both known and unknown functions, whose transcription is differentially regulated along the AP axis. The identity and ontological classification of these genes is presented. The wide variety of functional classes of transcripts isolated in this screen reflects the diverse spectrum of known influences operating across these embryonic regions. Of these 44 genes, several have been selected for detailed in situ hybridization analysis to validate the screen and accurately define the expression domains. Many of the identified cDNAs showed no identity to the current databases of known or predicted genes or ESTs. Others represent genes whose embryonic expression has not been previously reported. Expression studies confirmed the predictions of the primary differential display data. Moreover, the nature of identified genes, not previously associated with regionalisation of the brain, identifies novel potential mechanisms in that process.

CONCLUSION

This study provides an insight into some of the varied and novel molecular networks that operate during the regionalization of embryonic neural tissue and expands our knowledge of molecular repertoire used during development.

Motheaten (me/me) mice deficient in SHP-1 are less susceptible to focal cerebral ischemia

We have demonstrated previously that the protein tyrosine phosphatase SHP-1 seems to play a role in glial development and is upregulated in non-dividing astrocytes after injury. The present study examines the effect of loss of SHP-1 on the CNS response to permanent focal ischemia. SHP-1 deficient (me/me) mice and wild-type littermates received a permanent middle cerebral artery occlusion (MCAO). At 1, 3, and 7 days after MCAO, infarct volume, neuronal survival and cell death, gliosis, and inflammatory cytokine levels were quantified. SHP-1 deficient me/me mice display smaller infarct volumes at 7 days post-MCAO, increased neuronal survival within the ischemic penumbra, and decreased numbers of cleaved caspase 3+ cells within the ischemic core compared with wild-type mice. In addition, me/me mice exhibit increases in GFAP+ reactive astrocytes, F4-80+ microglia, and a concomitant increase in the level of interleukin 12 (IL-12) over baseline compared with wild-type. Taken together, these results demonstrate that loss of SHP-1 results in greater healing of the infarct due to less apoptosis and more neuronal survival in the ischemic core and suggests that pharmacologic inactivation of SHP-1 may have potential therapeutic value in limiting CNS degeneration after ischemic stroke.

Effects of LAR and PTP-BL phosphatase deficiency on adult mouse retinal cells activated by lens injury

Using intact and lens-lesioned wildtype, leucocyte common antigen-related phosphatase deficient (LARDeltaP) and protein tyrosine phosphatase (PTP)-BAS-like phosphatase deficient (PTP-BLDeltaP) mice, we have evaluated the role of LAR and PTP-BL in retinal ganglion cell survival and neuritogenesis, and survival of activated retinal glia in vitro. There were no differences in in vitro retinal ganglion cell neuritogenesis and survival, as well as in activated retinal glia survival between intact wildtype and intact LARDeltaP or PTP-BLDeltaP mutant mice. In wildtype, LARDeltaP, and PTP-BLDeltaP retinal cultures, pre-conditioning by lens injury significantly increased retinal ganglion cell neuritogenesis and activated retinal glia numbers. However, in retinal cultures from lens-lesioned LARDeltaP and PTP-BLDeltaP mice, significantly smaller percentages of retinal ganglion cells grew neurites compared to lens-lesioned wildtype cultures. Significantly increased numbers of retinal ganglion cells survived in retinal cultures from lens-lesioned LARDeltaP mice compared to lens-lesioned wildtypes. PTP-BL phosphatase deficiency did not affect retinal ganglion cell survival in retinal cultures from lens-lesioned mice, though activated retinal glia numbers were significantly reduced in cultures from lens-lesioned PTP-BLDeltaP mice compared to lens-lesioned wildtypes. In summary, a functional phenotype was found in LARDeltaP and PTP-BLDeltaP mice, that was only obvious in lens lesion-stimulated retinal cultures. These observations suggest that LAR enhances retinal ganglion cell neurite initiation whilst suppressing retinal ganglion cell survival, and that PTP-BL facilitates both retinal ganglion cell neurite initiation and survival of activated retinal glia.

Protein tyrosine phosphatases: their role in insulin action and potential as drug targets

Protein tyrosine phosphatases (PTPases) are the enzymes responsible for the selective dephosphorylation of tyrosine residues. PTPases function to regulate a wide array of biological responses mediated by growth factors and other stimuli by balancing the cellular level of phosphotyrosine in concert with their counterparts, protein tyrosine kinases. The important roles which PTPases play in regulating intracellular signalling and, ultimately, biological function along with the recent availability of information regarding their structural features has highlighted them as potential targets for pharmacological modulation. This is demonstrated by the increased level of activity directed towards the identification of novel small-molecule PTPase inhibitors. The rationale and potential utility of this drug discovery approach is discussed here, with particular emphasis on its application for the treatment of insulin resistance and Type 2 diabetes.

Receptor protein tyrosine phosphatases regulate neural development and axon guidance

The regulation of tyrosine phosphorylation is recognized as an important developmental mechanism. Both addition and removal of phosphate moieties on tyrosine residues are tightly regulated during development. Originally, most attention focused on the role of tyrosine kinases during development, but more recently, the developmental importance of tyrosine phosphatases has been gaining interest. Receptor protein tyrosine phosphatases (RPTPs) are of particular interest to developmental biologists because the extracellular domains of RPTPs are similar to those of cell adhesion molecules (CAMs). This suggests that RPTPs may have functions in development similar to CAMs. This review focuses on the role of RPTPs in development of the nervous system in processes such as axon guidance, synapse formation, and neural tissue morphogenesis.

Mice lacking leukocyte common antigen-related (LAR) protein tyrosine phosphatase domains demonstrate spatial learning impairment in the two-trial water maze and hyperactivity in multiple behavioural tests

Leukocyte common antigen-related (LAR) protein is a cell adhesion molecule-like receptor-type protein tyrosine phosphatase. We previously reported that in LAR tyrosine phosphatase-deficient (LAR-Delta P) mice the number and size of basal forebrain cholinergic neurons as well as their innervation of the hippocampal area was reduced. With the hippocampus being implicated in behavioural activity aspects, including learning and memory processes, we assessed possible phenotypic consequences of LAR phosphatase deficiency using a battery of rodent behaviour tests. Motor function and co-ordination tests as well as spatial learning ability assays did not reveal any performance differences between wildtype and LAR-Delta P mice. A spatial learning impairment was found in the difficult variant of the Morris water maze. Exploration, nestbuilding and activity tests indicated that LAR-Delta P mice were more active than wildtype littermates. The observed hyperactivity in LAR-Delta P mice could not be explained by altered anxiety or curiosity levels, and was found to be persistent throughout the nocturnal period. In conclusion, behavioural testing of the LAR-Delta P mice revealed a spatial learning impairment and a significant increase in activity.

Receptor tyrosine phosphatase psi is required for Delta/Notch signalling and cyclic gene expression in the presomitic mesoderm

Segmentation in vertebrate embryos is controlled by a biochemical oscillator ('segmentation clock') intrinsic to the cells in the unsegmented presomitic mesoderm, and is manifested in cyclic transcription of genes involved in establishing somite polarity and boundaries. We show that the receptor protein tyrosine phosphatase psi (RPTPpsi) gene is essential for normal functioning of the somitogenesis clock in zebrafish. We show that reduction of RPTPpsi activity using morpholino antisense oligonucleotides results in severe disruption of the segmental pattern of the embryo, and loss of cyclic gene expression in the presomitic mesoderm. Analysis of cyclic genes in RPTPpsi morphant embryos indicates an important requirement for RPTPpsi in the control of the somitogenesis clock upstream of or in parallel with Delta/Notch signalling. Impairing RPTPpsi activity also interferes with convergent extension during gastrulation. We discuss this dual requirement for RPTPpsi in terms of potential functions in Notch and Wnt signalling.

Polydnavirus genes and genomes: emerging gene families and new insights into polydnavirus replication

Polydnavirus genome sequencing is providing new insights into viral genome organization and viral gene function. Sequence analyses demonstrate that the genomes of these viral mutualists are largely noncoding but maintain genes and gene families that are unrelated to other viral genes. Interestingly, these organizational patterns in polydnavirus genomes are evident in both the bracovirus and ichnovirus genera, even though these two genera are evolutionarily unrelated. The identity and function of some polydnavirus gene families are considered with some functions experimentally supported and others implied by homology relationships with known insect genes. The evidence relative to polydnavirus origins and evolution is considered but remains an area of speculation. However, sequencing of these viral genomes has been informative and provides opportunities for productive investigation of these unusual mutualistic insect viruses.

Chick receptor tyrosine phosphatase Psi is dynamically expressed during somitogenesis

To study the role of receptor tyrosine phosphatases in vertebrate development, in particular somitogenesis, we have cloned chick receptor tyrosine phosphatase Psi (cRPTPPsi). cRPTPPsi is expressed in a dynamic fashion in the somites to-be-formed and uniformly throughout the presomitic mesoderm. In differentiating somites, cRPTPPsi expression gets restricted to the dermomyotome. In addition cRPTPPsi is expressed in the developing intermediate mesoderm, in neurogenic and sensory organs, the limb bud and the developing heart.

Colocalisation of the protein tyrosine phosphatases PTP-SL and PTPBR7 with beta4-adaptin in neuronal cells

The mouse gene Ptprr encodes the neuronal protein tyrosine phosphatases PTP-SL and PTPBR7. These proteins differ in their N-terminal domains, with PTP-SL being a cytosolic, membrane-associated phosphatase and PTPBR7 a type I transmembrane protein. In this study, we further explored the nature of the PTP-SL-associated vesicles in neuronal cells using a panel of organelle markers and noted a comparable subcellular distribution for PTP-SL and the beta4-adaptin subunit of the AP4 complex. PTP-SL, PTPBR7 and beta4-adaptin are localised at the Golgi apparatus and at vesicles throughout the cytoplasm. Immunohistochemical analysis demonstrated that PTP-SL, PTPBR7 and beta4-adaptin are all endogenously expressed in brain. Interestingly, coexpression of PTP-SL and beta4-adaptin leads to an altered subcellular localisation for PTP-SL. Instead of the Golgi and vesicle-type staining pattern, still observable for beta4-adaptin, PTP-SL is now distributed throughout the cytoplasm. Although beta4-adaptin was found to interact with the phosphatase domain of PTP-SL and PTPBR7 in the yeast two-hybrid system, it failed to do so in transfected neuronal cells. Our data suggest that the tyrosine phosphatases PTP-SL and PTPBR7 may be involved in the formation and transport of AP4-coated vesicles or in the dephosphorylation of their transmembrane cargo molecules at or near the Golgi apparatus.

Dynamic Changes in the Expression of Protein Tyrosine Phosphatases During Preimplantation Mouse Development: Semi-Quantification by Real-Time PCR

Protein tyrosine phosphatase (PTP) expression was examined in preimplantation mouse embryos. We previously reported that SHP-2, LAR, PTPT9, SHP-1, and mRPTPB were expressed in preimplantation mouse embryos. Here, we examined changes in the expression levels of these PTPs during preimplantation development. cDNA was obtained by reverse transcription of embryo mRNA, amplified with 10 PCR cycles, and then subjected to real-time fluorescence-monitored PCR. Experiments with an mRNA dilution series revealed that the data obtained matched the quantities of mRNA used. The measurements obtained with real-time fluorescence-monitored PCR showed that the expression of each PTP mRNA changed dynamically, and that each had a different expression pattern. This suggests that PTPs are involved in the regulation of growth and differentiation during preimplantation development.

Inhibition of protein tyrosine/mitogen-activated protein kinase phosphatase activity is associated with D2 dopamine receptor supersensitivity in a rat model of Parkinson's disease

Previous work demonstrated that stimulation of D(2) dopamine receptors (D(2)DRs) in the unilaterally 6-hydroxydopamine (6-OHDA)-lesioned rat enhanced striatal extracellular signal-regulated kinase (ERK) activity ipsilateral to the lesion. The present work was designed to explore the mechanism underlying the activation of ERK in the denervated striatum. Stimulation of D(2)DR induced a 60% inhibition in protein tyrosine phosphatase (PTP) activity but not in PSP activity in lesioned striata. The D(2)DR antagonist spiperone blocked quinpirole-elicited PTP inhibition, and the D(1) receptor agonist 2,3,4,5-tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-benzazepine (SKF38393) did not inhibit PTP activity, indicating that PTP inhibition is a specific effect mediated by stimulation of D(2)DR. We further discovered that striatal mitogen-activated protein kinase phosphatase (MKP), a protein phosphatase that is responsible for ERK dephosphorylation, is inhibited in response to D(2)DR stimulation in 6-OHDA-lesioned rats. More specifically, MKP1 was identified to be the isozyme affected by D(2)DR stimulation. In PC12 cells that express D(2)DR, quinpirole elicited no change in PTP or MKP activity, whereas ERK was activated by D(2) dopamine receptor stimulation. The results indicate that 6-OHDA-induced striatal denervation leads to abnormal coupling between D(2)DR and PTP/MKP pathway. Moreover, unilateral inhibition of striatal PTP by an intrastriatal injection of vanadate induced contralateral rotation in control rats in response to D(2)DR stimulation, thus mimicking the response observed in the unilateral 6-OHDA-lesioned rat. The results indicate that attenuation of the PTP/MKP pathway may be responsible for the development of D(2)DR supersensitivity.

Convulsive disorder and the genetics of signal transduction; a study of a low molecular weight protein tyrosine phosphatase in a pediatric sample

Recent studies point to an involvement of kinases and phosphatases in ionic channel regulation and in physiopathologic mechanisms leading to convulsive disorders. Acid phosphatase locus 1 (ACP1), also named cytosolic low molecular weight phosphotyrosine phosphatase, is a highly polymorphic phosphatase that is especially abundant in the central nervous system and is known to be involved in several signal transduction pathways. We studied ACP1 in 122 children with idiopathic generalized tonic-clonic seizures, 80 children with febrile convulsions, and 417 controls from the population of Rome. Low activity phenotypes of ACP1 (*A/*A and *A/*B) were found to be over-represented while high activity phenotypes (*C/*C and *B/*C) were under-represented in generalized seizures cases compared to controls (P < 0.005). No significant difference was observed between febrile convulsion cases and controls. These observations suggest a protective role of the high activity ACP1 phenotypes against seizures in children.

A Drosophila homolog of cyclase-associated proteins collaborates with the Abl tyrosine kinase to control midline axon pathfinding

We demonstrate that Drosophila capulet (capt), a homolog of the adenylyl cyclase-associated protein that binds and regulates actin in yeast, associates with Abl in Drosophila cells, suggesting a functional relationship in vivo. We find a robust and specific genetic interaction between capt and Abl at the midline choice point where the growth cone repellent Slit functions to restrict axon crossing. Genetic interactions between capt and slit support a model where Capt and Abl collaborate as part of the repellent response. Further support for this model is provided by genetic interactions that both capt and Abl display with multiple members of the Roundabout receptor family. These studies identify Capulet as part of an emerging pathway linking guidance signals to regulation of cytoskeletal dynamics and suggest that the Abl pathway mediates signals downstream of multiple Roundabout receptors.

Protein tyrosine phosphatase-mu differentially regulates neurite outgrowth of nasal and temporal neurons in the retina

Cell adhesion molecules play an important role in the development of the visual system. The receptor-type protein tyrosine phosphatase, PTPmu is a cell adhesion molecule that mediates cell aggregation and may signal in response to adhesion. PTPmu is expressed in the chick retina during development and promotes neurite outgrowth from retinal ganglion cell (RGC) axons in vitro (Burden-Gulley and Brady-Kalnay, 1999). The axons of RGC neurons form the optic nerve, which is the sole output from the retina to the optic tectum in the chick. In this study, we observed that PTPmu expression in RGC axons occurs as a step gradient, with temporal axons expressing the highest level of PTPmu. PTPmu expression in the optic tectum occurred as a smooth descending gradient from anterior to posterior regions during development. Because temporal RGC axons innervate anterior tectal regions, PTPmu may regulate the formation of topographic projections to the tectum. In agreement with this hypothesis, a differential response of RGC neurites to a PTPmu substrate was also observed: RGCs of temporal retina were unable to extend neurites on PTPmu compared with neurites of nasal retina. When given a choice between PTPmu and a second substrate, the growth cones of temporal neurites clustered at the PTPmu border and stalled, thus avoiding additional growth on the PTPmu substrate. In contrast, PTPmu was permissive for growth of nasal neurites. Finally, application of soluble PTPmu to retinal cultures resulted in the collapse of temporal but not nasal growth cones. Therefore, PTPmu may specifically signal to temporal RGC axons to cease their forward growth after reaching the anterior tectum, thus allowing for subsequent innervation of deeper tectal layers.

c-SRC mediates neurite outgrowth through recruitment of Crk to the scaffolding protein Sin/Efs without altering the kinetics of ERK activation

SRC family kinases have been consistently and recurrently implicated in neurite extension events, yet the mechanism underlying their neuritogenic role has remained elusive. We report that epidermal growth factor (EGF) can be converted from a non-neuritogenic into a neuritogenic factor through moderate activation of endogenous SRC by receptor-protein-tyrosine phosphatase alpha (a physiological SRC activator). We show that such a qualitative change in the response to EGF is not accompanied by changes in the extent or kinetics of ERK induction in response to this factor. Instead, the pathway involved relies on increased tyrosine phosphorylation of, and recruitment of Crk to, the SRC substrate Sin/Efs. The latter is a scaffolding protein structurally similar to the SRC substrate Cas, tyrosine phosphorylation of which is critical for migration in fibroblasts and epithelial cells. Expression of a dominant negative version of Sin interfered with receptor-protein-tyrosine phosphatase alpha/EGF- as well as fibroblast growth factor-induced neurite outgrowth. These observations uncouple neuritogenic signaling in PC12 cells from sustained activation of ERK kinases and for the first time identify an effector of SRC function in neurite extension.

TheC. elegansLAR-like receptor tyrosine phosphatase PTP-3 and the VAB-1 Eph receptor tyrosine kinase have partly redundant functions in morphogenesis

Receptor-like protein-tyrosine phosphatases (RPTPs) form a diverse family of cell surface molecules whose functions remain poorly understood. The LAR subfamily of RPTPs has been implicated in axon guidance and neural development. Here we report the molecular and genetic analysis of the C. elegans LAR subfamily member PTP-3. PTP-3 isoforms are expressed in many tissues in early embryogenesis, and later become localized to neuronal processes and to epithelial adherens junctions. Loss of function in ptp-3 causes low-penetrance defects in gastrulation and epidermal development similar to those of VAB-1 Eph receptor tyrosine kinase mutants. Loss of function in ptp-3 synergistically enhances phenotypes of mutations in the C. elegans Eph receptor VAB-1 and a subset of its ephrin ligands, but does not show specific interactions with several other RTKs or morphogenetic mutants. The genetic interaction of vab-1 and ptp-3 suggests that LAR-like RPTPs and Eph receptors have related and partly redundant functions in C. elegans morphogenesis.

Tyrosine phosphatase STEP is a tonic brake on induction of long-term potentiation

The functional roles of protein tyrosine phosphatases (PTPs) in the developed CNS have been enigmatic. Here we show that striatal enriched tyrosine phosphatase (STEP) is a component of the N-methyl-D-aspartate receptor (NMDAR) complex. Functionally, exogenous STEP depressed NMDAR single-channel activity in excised membrane patches. STEP also depressed NMDAR-mediated synaptic currents whereas inhibiting endogenous STEP enhanced these currents. In hippocampal slices, administering STEP into CA1 neurons did not affect basal glutamatergic transmission evoked by Schaffer collateral stimulation but prevented tetanus-induced long-term potentiation (LTP). Conversely, inhibiting STEP in CA1 neurons enhanced transmission and occluded LTP induction through an NMDAR-, Src-, and Ca(2+)-dependent mechanism. Thus, STEP acts as a tonic brake on synaptic transmission by opposing Src-dependent upregulation of NMDARs.

Heparan sulfate proteoglycans are ligands for receptor protein tyrosine phosphatase sigma

RPTPsigma is a cell adhesion molecule-like receptor protein tyrosine phosphatase involved in nervous system development. Its avian orthologue, known as cPTPsigma or CRYPalpha, promotes intraretinal axon growth and controls the morphology of growth cones. The molecular mechanisms underlying the functions of cPTPsigma are still to be determined, since neither its physiological ligand(s) nor its substrates have been described. Nevertheless, a major class of ligand(s) is present in the retinal basal lamina and glial endfeet, the potent native growth substrate for retinal axons. We demonstrate here that cPTPsigma is a heparin-binding protein and that its basal lamina ligands include the heparan sulfate proteoglycans (HSPGs) agrin and collagen XVIII. These molecules interact with high affinity with cPTPsigma in vitro, and this binding is totally dependent upon their heparan sulfate chains. Using molecular modelling and site-directed mutagenesis, a binding site for heparin and heparan sulfate was identified in the first immunoglobulin-like domain of cPTPsigma. HSPGs are therefore a novel class of heterotypic ligand for cPTPsigma, suggesting that cPTPsigma signaling in axons and growth cones is directly responsive to matrix-associated cues.

Expression of receptor protein-tyrosine phosphatase alpha, sigma and LAR during development of the zebrafish embryo

Receptor protein-tyrosine phosphatases (RPTPs) are key players in Drosophila development. To study the role of RPTPs in vertebrate development, we have cloned zebrafish (zf) RPTPs, including RPTP alpha (RPTPalpha), RPTP sigma (RPTPsigma) and LAR. These three RPTPs are broadly transcribed in early development. At 24h post fertilisation (hpf), all three genes are expressed in the nervous system in partially overlapping patterns. At 3 days post fertilisation zf-RPTPalpha and zf-LAR show similar expression patterns in the central nervous system (CNS), the pharyngeal arches, the pectoral fins and the spinal cord. Interestingly, zf-LAR is uniquely expressed in the neuromast cells, whereas zf-RPTPsigma expression is confined to the central nervous system.

Factors controlling axonal and dendritic arbors

The sculpting and maintenance of axonal and dendritic arbors is largely under the control of molecules external to the cell. These factors include both substratum-associated and soluble factors that can enhance or inhibit the outgrowth of axons and dendrites. A large number of factors that modulate axonal outgrowth have been identified, and the first stages of the intracellular signaling pathways by which they modify process outgrowth have been characterized. Relatively fewer factors and pathways that affect dendritic outgrowth have been described. The factors that affect axonal arbors form an incompletely overlapping set with those that affect dendritic arbors, allowing selective control of the development and maintenance of these critical aspects of neuronal morphology.

The leukocyte common antigen-related protein tyrosine phosphatase receptor regulates regenerative neurite outgrowth in vivo

Drosophila and leech models of nervous system development demonstrate that protein tyrosine phosphatase (PTP) receptors regulate developmental neurite outgrowth. Whether PTP receptors regulate neurite outgrowth in adult systems or in regenerative states remains unknown. The leukocyte common antigen-related (LAR) receptor is known to be present in rodent dorsal root ganglion (DRG) neurons; therefore, the well established model of postcrush sciatic nerve regeneration was used to test the hypothesis that LAR is required for neurite outgrowth in the adult mammalian nervous system. In uninjured sciatic nerves, no differences in nerve morphology and sensory function were detected between wild-type and LAR-deficient littermate transgenic mice. Sciatic nerve crush resulted in increased LAR protein expression in DRG neurons. In addition, nerve injury led to an increase in the proportion of LAR protein isoforms known to have increased binding affinity to neurite-promoting laminin-nidogen complexes. Two weeks after nerve crush, morphological analysis of distal nerve segments in LAR-deficient transgenic mice demonstrated significantly decreased densities of myelinated fibers, decreased axonal areas, and increased myelin/axon area ratios compared with littermate controls. Electron microscopy analysis revealed a significant twofold reduction in the density of regenerating unmyelinated fibers in LAR-/- nerves distal to the crush site. Sensory testing at the 2 week time point revealed a corresponding 3 mm lag in the proximal-to-distal progression of functioning sensory fibers along the distal nerve segment. These studies introduce PTP receptors as a major new gene family regulating regenerative neurite outgrowth in vivo in the adult mammalian system.

A decrease in size and number of basal forebrain cholinergic neurons is paralleled by diminished hippocampal cholinergic innervation in mice lacking leukocyte common antigen-related protein tyrosine phosphatase activity

The leukocyte common antigen-related (LAR) receptor, composed of an extracellular region with three immunoglobulin-like and eight fibronectin type III-like domains, and a cytoplasmic region containing two protein tyrosine phosphatase domains, is thought to play a role in axonal outgrowth and guidance during neural development. LAR mutant mice were generated completely lacking the two cytoplasmic protein tyrosine phosphatase domains, resulting in the loss of ability to bind intracellular associating proteins, but (may be) still containing the ability to perform extracellular functions. A reduction in size of basal forebrain cholinergic neurons and diminished hippocampal innervation reported for knockout mice that contain a leaky gene trap inserted into the 5' part of the LAR gene [Yeo T. T. et al. (1997) J. Neurosci. Res. 47, 348-360] warranted a computer-assisted quantitative image analysis throughout the basal forebrain and hippocampus of our LAR mutant mice. The total number, longest diameter and cell body area were calculated for the choline acetyltransferase-positive neurons in the medial septum and vertical diagonal band, and optical density measurements were performed to determine the extent of acetyl cholinesterase-positive fibre innervation of the different layers in the dentate gyrus. In LAR mutant mice, the number of cholinergic cells was significantly reduced (approximately 25%) in the vertical diagonal band. Also, the cross-sectional area of the cholinergic neurons in the medial septum and vertical diagonal band was reduced (5%). These findings were paralleled by a diminished cholinergic innervation of the supragranular (18%) and molecular (4%) layers of the dentate gyrus. Thus, LAR protein tyrosine phosphatase activity appears crucial for size, number and target projection of basal forebrain cholinergic neurons, further strengthening a role for LAR in CNS development.

Receptor tyrosine phosphatases in axon growth and guidance

Receptor-like protein tyrosine phosphatases (RPTPs) continue to emerge as important signalling molecules in axons and their growth cones. Recent findings show that Drosophila RPTPs play key roles in guiding retinal axons and in preventing midline crossing of longitudinal axons. Vertebrate RPTPs are now implicated in controlling axon outgrowth, and preliminary evidence suggests that they too may influence axon guidance.

Glial tumor cell adhesion is mediated by binding of the FNIII domain of receptor protein tyrosine phosphatase beta (RPTPbeta) to tenascin C

The extracellular domain of receptor protein tyrosine phosphatase beta (RPTPbeta) is composed of several domains which mediate its interactions with distinct ligands present on the surface of either neurons or glial cells. Here, we demonstrate that the fibronectin type III domain (FNIII) of RPTPbeta binds to glial tumor-derived cell lines and primary astrocytes. We used affinity purification to isolate several proteins that specifically bind to the FNIII domain of RPTPbeta. One of these, a 240 kDa protein that was purified from U118MG glioblastoma cell, was identified as tenascin C based on the amino acid sequence of several tryptic peptides. The interaction of RPTPbeta with tenascin C was found to mediate cell adhesion. Adhesion and spreading of SF763T astrocytoma cells expressing RPTPbeta on tenascin C was specifically abolished by the addition of a soluble fragment containing the FNIII domain of the receptor. RPTPbeta-dependent cell adhesion was mediated by binding to the alternatively spliced FNIII repeats A1,2,4 (TnfnA1,2,4) of tenascin C. Furthermore, COS cells expressing RPTPbeta adhere to TnfnA1,2,4, while the parental cells did not. These results demonstrate that the FNIII domain of RPTPbeta binds to tenascin C and suggest that RPTPbeta present on glial tumor cells is a primary adhesion receptor system to the extracellular matrix.

Expression of receptor tyrosine phosphatase gamma during early development of the chick embryo

Studies in Drosophila suggest that receptor-tyrosine phosphatases are key regulators of neural development, however little is known about their expression or function in the nervous system of vertebrate embryos. In this report, we describe the expression pattern of RPTPgamma during early chick embryogenesis. Transcripts are largely restricted to the developing nervous system including oculomotor, trochlear and branchiomotor populations but are absent from spinal motor neurones. RPTPgamma is also detected in cells in the positions of hindbrain reticulospinal neurones, spinal commisural neurones and in cells with neuronal morphology in the ventral diencephalon. Within the peripheral nervous system transcripts are found in neuroblasts delaminating from epibranchial placodes and subsequently in placode-derived cranial ganglia. Outside the nervous system expression is detected in somites and transiently in the second branchial arch and the cranial mesenchyme.

Expression of receptor protein tyrosine phosphatases in embryonic chick spinal cord

Receptor-like protein tyrosine phosphatases potentially play a crucial role in axon growth and targeting. We focus here on their role within the embryonic avian spinal cord, in particular the development and outgrowth of motorneurons. We have used in situ mRNA hybridization to examine the spatiotemporal expression of eight receptor-like protein tyrosine phosphatases and find that it is both dynamic and highly varied, including novel, isoform-specific expression patterns. CRYP alpha 1 is expressed in all of the ventral motorneuron pools, whereas CRYP2, RPTP gamma, and RPTP alpha are only expressed in specific subsets of these neurons. CRYP alpha 2, RPTP psi, and RPTP delta are neuronally expressed elsewhere in the cord, but not in ventral motorneurons, whereas RPTP mu is unique in being restricted to capillaries. The developmentally regulated expression of these genes strongly suggests that the encoded phosphatases play numerous roles during neurogenesis and axonogenesis in the vertebrate spinal cord.

Possible role of the receptor protein tyrosine phosphatase HmLAR2 in interbranch repulsion in a leech embryonic cell

Accumulating evidence indicates that receptor protein tyrosine phosphatases (rPTPs) play major roles in growth cone migration. We have previously shown that the growth cones of the multiple parallel processes of an identified leech embryonic cell, the Comb cell (CC), express high levels of a leukocyte antigen-related (LAR)-like rPTP, HmLAR2. Embryonic injection of a polyclonal antibody to the receptor's ectodomain resulted in reduced process outgrowth and in processes crossing over each other, a behavior that is seldom observed in normal or control animals. Here we present results of injecting a soluble Fc-HmLAR2 ectodomain fusion protein into embryos in order to bind the endogenous ligands of HmLAR2. Single injections of the Fc-chimeric protein into the developing embryo resulted, 12 to 24 h postinjection, in clear morphological abnormalities, ranging from abnormally directed CC processes and crossovers to apparent growth cone collapse. At later times, 2 to 5 days post injection, growth cones appeared to have recovered and processes had continued to extend, but effects of the earlier guidance errors remained, with the CCs displaying a relatively high incidence of proximal guidance errors. When injected into the germinal plate of developing embryos, the fusion protein was found to bind selectively to the processes of the CCs themselves, in contrast to control injections of Fc alone or closely related Fc-tagged proteins, which did not decorate the CCs. Double-labeling experiments revealed an early phase of Fc-HmLAR2 labeling (within 20 min after application), during which the growth cones and filopodia of the CC showed significant binding of the receptor ectodomain, and a later phase (1-2 h after injection), when most of the label was redistributed away from the growth cones and into the proximal processes of the CC. In culture, HmLAR2-transfected COS cells were found to selectively bind the Fc-recombinant protein, but not Fc-tagged proteins bearing other closely related receptor ectodomains, demonstrating that the HmLAR2 ectodomain is capable of interacting homophilically. Together, our observations demonstrate that the rPTP HmLAR2 is critically involved in CC process extension through its participation in the regulation of growth cone structure, migration, and navigation. Moreover, since our experiments also indicate that HmLAR2 can bind to itself, we hypothesize that HmLAR2 has a key role in the mechanism of mutual repulsion that maintains the parallel growth of adjacent CC projections.

No obvious abnormality in mice deficient in receptor protein tyrosine phosphatase beta

The development of neurons and glia is governed by a multitude of extracellular signals that control protein tyrosine phosphorylation, a process regulated by the action of protein tyrosine kinases and protein tyrosine phosphatases (PTPs). Receptor PTPbeta (RPTPbeta; also known as PTPzeta) is expressed predominantly in the nervous system and exhibits structural features common to cell adhesion proteins, suggesting that this phosphatase participates in cell-cell communication. It has been proposed that the three isoforms of RPTPbeta play a role in regulation of neuronal migration, neurite outgrowth, and gliogenesis. To investigate the biological functions of this PTP, we have generated mice deficient in RPTPbeta. RPTPbeta-deficient mice are viable, are fertile, and showed no gross anatomical alterations in the nervous system or other organs. In contrast to results of in vitro experiments, our study demonstrates that RPTPbeta is not essential for neurite outgrowth and node formation in mice. The ultrastructure of nerves of the central nervous system in RPTPbeta-deficient mice suggests a fragility of myelin. However, conduction velocity was not altered in RPTPbeta-deficient mice. The normal development of neurons and glia in RPTPbeta-deficient mice demonstrates that RPTPbeta function is not necessary for these processes in vivo or that loss of RPTPbeta can be compensated for by other PTPs expressed in the nervous system.

PRL-1 PTPase expression is developmentally regulated with tissue-specific patterns in epithelial tissues

The mechanisms controlling tyrosine phosphorylation of cellular proteins are important in the regulation of many cellular processes, including development and differentiation. Protein tyrosine phosphatases (PTPases) may be as important as protein tyrosine kinases (PTKs) in these processes. PRL-1 is a distinct PTPase originally identified as an immediate-early gene in liver regeneration whose expression is associated with growth in some tissues but with differentiation in others. We now demonstrate that the PRL-1 protein is expressed during development in a number of digestive epithelial tissues. It is expressed at variable time points in the developing intestine, but its expression is limited to the developing villus enterocytes. In the gastric epithelium, PRL-1 expression in the adult is restricted to zymogen cells. PRL-1 is also expressed in the developing liver and esophagus and in the epithelia of the kidney and lung. In each of these contexts, the expression of PRL-1 is associated with terminal differentiation, suggesting that it may play a role in this important developmental process.

The Dopamine/D1 receptor mediates the phosphorylation and inactivation of the protein tyrosine phosphatase STEP via a PKA-dependent pathway

The striatal-enriched protein tyrosine phosphatase (STEP) family is expressed within dopaminoceptive neurons of the CNS and is particularly enriched within the basal ganglia and related structures. Alternative splicing produces several isoforms that are found in a number of subcellular compartments, including postsynaptic densities of medium spiny neurons. The variants include STEP(61), a membrane-associated protein, and STEP(46), a cytosolic protein. The C terminals of these two isoforms are identical, whereas the N-terminal domain of STEP(61) contains a novel 172 amino acid sequence that includes several structural motifs not present in STEP(46). Amino acid sequencing revealed a number of potential phosphorylation sites in both STEP isoforms. Therefore, we investigated the role of phosphorylation in regulating STEP activity. Both STEP(61) and STEP(46) are phosphorylated on seryl residues by a cAMP-dependent protein kinase (PKA)-mediated pathway in striatal homogenates. The specific residues phosphorylated in STEP(61) were identified by site-directed mutagenesis and tryptic phosphopeptide mapping as Ser160 and Ser221, whereas the major site of phosphorylation in STEP(46) was shown to be Ser49. Ser160 is located within the unique N terminal of STEP(61). Ser221 and Ser49 are equivalent residues present in STEP(61) and STEP(46), respectively, and are located at the center of the kinase-interacting motif that has been implicated in protein-protein interactions. Phosphorylation at this site decreases the activity of STEP in vitro by reducing its affinity for its substrate. In vivo studies using striatal slices demonstrated that the neurotransmitter dopamine leads to the phosphorylation of STEP via activation of D1 receptors and PKA.

The role of a LAR-like receptor tyrosine phosphatase in growth cone collapse and mutual-avoidance by sibling processes

Among the many cells or parts of cells that a growth cone may encounter during its embryonic migrations are other processes or parts of its parent cell. Such an event can be expected to be relatively frequent in the genesis of neuronal arbors, for instance, where the density of innervation of a target region can be quite high. Few experimental studies have addressed the very interesting question of whether a process "recognizes" siblings in some unique way, in a manner that can be distinguished from, say, how it interacts with unrelated cells. One example can be found in the leech, where sibling branches in the terminal fields of identified mechanosensory cells avoid each other strictly while permitting some significant continuing contact and overlap with homologues, a phenomenon that has been dubbed "self-avoidance." Another example has been reported in cultured Helisoma neurons, where severing a branch of a neuron allows sibling neurites to form electrical junctions with it, although normally sibling neurites do not do so. In both of these instances, coincidental activity was proposed as one means to achieve recognition of self and as possibly leading to the blocking of a continuing interaction among the parts, although alternative explanations were indeed considered possible.

Receptor tyrosine phosphatases in axon growth and guidance

The last 5 years has seen an explosion of evidence linking RPTPs to the regulation of axon growth and guidance. Important questions to be addressed include the ligand-receptor interactions involved in axon growth regulation, the signaling pathways controlled by RPTPs in neurons, and the manner in which different RPTPs within a class, and different classes of RPTPs, coordinate their functions to ensure appropriate axon growth. Are RPTPs signaling ligands, signaling receptors, or both? Do RPTPs function mainly by modifying adhesive preferences, or are they instructive in guidance decisions? Do specific types of RPTPs send specific signals to neurons, or do they work together to fine-tune levels of tyrosine phosphorylation? Whatever the outcome, it seems certain that the answers to these questions will come only from a combination of the powerful genetic approaches possible in Drosophila (and in mice) with the biochemical and cell biological approaches possible in the vertebrate systems.

Emerging issues in receptor protein tyrosine phosphatase function: lifting fog or simply shifting?

Transmembrane (receptor) tyrosine phosphatases are intimately involved in responses to cell-cell and cell-matrix contact. Several important issues regarding the targets and regulation of this protein family are now emerging. For example, these phosphatases exhibit complex interactions with signaling pathways involving SRC family kinases, which result from their ability to control phosphorylation of both activating and inhibitory sites in these kinases and possibly also their substrates. Similarly, integrin signaling illustrates how phosphorylation of a single protein, or the activity of a pathway, can be controlled by multiple tyrosine phosphatases, attesting to the intricate integration of these enzymes in cellular regulation. Lastly, we are starting to appreciate the roles of intracellular topology, tyrosine phosphorylation and oligomerization among the many mechanisms regulating tyrosine phosphatase activity.

Cellular signaling by neural cell adhesion molecules of the immunoglobulin superfamily

Neural cell adhesion molecules (CAMs) of the immunoglobulin superfamily nucleate and maintain groups of cells at key sites during early development and in the adult. In addition to their adhesive properties, binding of CAMs can affect intracellular signaling. Their ability to influence developmental events, including cell migration, proliferation, and differentiation can therefore result both from their adhesive as well as their signaling properties. This review focuses on the two CAMs for which the most information is known, the neural CAM, N-CAM, and L1. N-CAM was the first CAM to be characterized and, therefore, has been studied extensively. The binding of N-CAM to cells leads to a number of signaling events, some of which result in changes in gene expression. Interest in L1 derives from the fact that mutations in its gene lead to human genetic diseases including mental retardation. Much is known about modifications of the L1 cytoplasmic domain and its interaction with cytoskeletal molecules. The study of CAM signaling mechanisms has been assay-dependent rather than molecule-dependent, with particular emphasis on assays of neurite outgrowth and gene expression, an emphasis that is maintained throughout the review. The signals generated following CAM binding that lead to alterations in cell morphology and gene expression have been linked directly in only a few cases. We also review information on other CAMs, giving special consideration to those that are anchored in the membrane by a phospholipid anchor. These proteins, including a form of N-CAM, are presumed to be localized in lipid rafts, membrane substructures that include distinctive subsets of cytoplasmic signaling molecules such as members of the src-family of nonreceptor protein tyrosine kinases. In the end, these studies may reveal that what CAMs do after they bind cells together may have as profound consequences for the cells as the adhesive interactions themselves. This area will therefore remain a rich ground for future studies.