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Doppler radar detection of exceptional mass-migration of aphids into Finland.

Our objective was to detect mass migrations of insects of economic significance by insect traps and a Doppler weather radar. Migrants were sampled by suction traps, tow nets and light traps in the Helsinki region. We used radar to observe the migrating insects, and trajectories to backtrack mass migrations of aphids (Homoptera, Aphididae) in spring 1988. The aphid migrations were clearly observed in trap catches and by radar. The first migration, mainly involving Euceraphis betulae, occurred on 18 May and was tracked back to northern Poland. The second migration, mainly of Rhopalosiphum padi (a serious pest of small-grain cereals), occurred 3 days later and was tracked back to a large area covering Latvia and western Russia south of St Petersburg. The third migration included both E. betulae and R. padi, and took place on 30 May. It originated from Estonia. Neither trap nor radar data provide exact quantitative information on migrations. Trapping efficiency depends strongly on wind speed and insect size. Radar echo intensity is very strongly related to the sizes of insects in the large volume of air measured, and the sizes are not known accurately. Weather data, especially temperature, can be used in predicting the development of aphids, and air-parcel trajectories in estimating the source areas of migrants. These methods for forecasting aphid migrations, combined with radar observations, are useful for warning purposes and to intensify insect trapping. This would contribute to more efficient agricultural pest management.

Agriculture↗

Migration of medical image data archived using mini-PACS to full-PACS.

This study evaluated the migration to full-PACS of medical image data archived using mini-PACS at two hospitals of the Yonsei University Medical Center, Seoul, Korea. A major concern in the migration of medical data is to match the image data from the mini-PACS with the hospital OCS (Ordered Communication System). Prior to carrying out the actual migration process, the principles, methods, and anticipated results for the migration with respect to both cost and effectiveness were evaluated. Migration gateway workstations were established and a migration software tool was developed. The actual migration process was performed based on the results of several migration simulations. Our conclusions were that a migration plan should be carefully prepared and tailored to the individual hospital environment because the server system, archive media, network, OCS, and policy for data management may be unique.

Computer Systems↗

Platelet-derived growth factor in combination with collagen promotes the migration of human skin fibroblasts into a denuded area of a cell monolayer.

Since we have found previously that adult donor skin fibroblasts (TIG-114) migrated more slowly in serum-depleted medium than in medium supplemented with 10% FBS, we tried to identify a factor(s) which promotes fibroblast migration from the edge of a denuded area in a monolayer. In medium supplemented with 10% FBS, the effects of both suramin, a competitor of growth factors at the receptor level, and monensin, an inhibitor of the secretion of extracellular matrix, were examined. Both substances suppressed cell migration, suggesting that growth factors and matrix substances are important for cell migration. Then, we examined the effects of growth factors and extracellular matrix on fibroblast migration in serum-free medium. Platelet-derived growth factor (PDGF), basic fibroblast growth factor, acidic fibroblast growth factor, and transforming growth factor-beta did not stimulate cell migration. Type I collagen, plasma fibronectin, and heparin also did not promote cell migration. However, the combination of PDGF and type I collagen did promote cell migration. Addition of anti-PDGF antibody reduced the stimulatory effect induced by the combination of PDGF and type I collagen. These results suggest that the copresence of growth factors and extracellular matrix regulates fibroblast migration into a denuded area in a monolayer.

Adult↗

Migration of the myoelectric complex after interruption of the myenteric plexus: intestinal transection and regeneration of enteric nerves in the guinea pig.

The effects of surgical interruption of the myenteric plexus (myectomy), extrinsic denervation of a length of small intestine, or transection and reanastomosis of the intestinal wall on migration of phase III of the migrating myoelectric complex was studied in guinea pigs. In addition, the recovery of phase III migration and the regrowth of intestinal nerves and muscle across the reanastomosis was studied at various times up to 60 days after surgery. At 6-9 days after surgery, phase III did not migrate past the myectomy during 50%-60% of recorded migrating myoelectric complexes and transection and reanastomosis of the intestinal wall blocked aboral progression of phase III in 90% of cases. Extrinsic denervation did not alter phase III migration through the denervated segment. Phase III migration past the reanastomosis recovered with time after surgery; 80% recovery occurred by 60 days after surgery. Immunoreactivities for vasoactive intestinal peptide, gastrin-releasing peptide, and somatostatin were used as markers for intestinal nerves that were cut by transaction. Immunoreactivities for vasoactive intestinal peptide and gastrin-releasing peptide are contained in myenteric neurons that project in an oral to anal direction to other myenteric ganglia and to the circular muscle. Immunoreactivity for somatostatin is contained in nerve fibers projecting aborally to other myenteric ganglia. At 7-15 days after surgery, there were accumulations of immunoreactivities for vasoactive intestinal peptide, gastrin-releasing peptide, and somatostatin in nerve fibers on the oral side of the reanastomosis, but nerve fibers containing these peptides were not observed in myenteric ganglia or circular muscle close to the anal edge. At 23-28 days, immunoreactivities for vasoactive intestinal peptide, gastrin-releasing peptide, and somatostatin nerve fibers were traced across the reanastomosis and nerve terminals were detected in ganglia and muscle close to the lesion on the anal side. Nerve fibers traversed the lesion in all cases at 57-60 days and vasoactive intestinal peptide-, gastrin-releasing peptide-, and somatostatin-immunoreactive nerve terminals were detected in the first two to three rows of myenteric ganglia on the anal side. Regrowth of intestinal muscle followed a similar time-course to that observed for nerves. These data suggest that interruption of the myenteric plexus alone does not completely block phase III migration. In addition, recovery of phase III migration past a reanastomosis is associated with a restoration of both nervous and mechanical connections.

Animals↗

Effects of aging and dietary restriction on activity of monkey serum in promoting fibroblast migration.

In order to determine whether serum modified cellular aging in vivo, we previously studied the effects of serum from various mammals of different ages on cell functions such as proliferation and migration, and reported that cell migration was more greatly inhibited by serum from old donors than cell proliferation [1]. Moreover, since dietary restriction has been reported to extend lifespan and slow the aging rate of some animals [2], we wondered whether sera from dietary restricted and control monkeys of various ages might exhibit reduced aging effects on cell migration. When serum from young adult (3-5 years old) monkeys was added to plain medium, the migration of human fetal skin fibroblasts was very strongly inhibited compared to FBS. Surprisingly, sera from adult (6-11 years old) and old (more than 18 years old) monkeys caused significantly less migration-inhibitory activity than serum from young adult monkeys although sera from adult and old monkeys were much more inhibitory to cell migration than FBS. Dietary restriction only caused marginal effects on serum migration-promoting activity in a few monkey groups. The inhibition of cell migration caused by monkey serum was not brought about by cytotoxic effects since monkey serum stimulated cell proliferation as well as fetal bovine serum. These results indicate that the effects of aging on monkey serum migration-promoting activity are much more pronounced than those of dietary restriction.

Aging↗

Migration of dopaminergic neurons in the embryonic mesencephalon of mice.

Migration of dopamine (DA)-containing neurons and its guiding cues were histologically examined in the embryonic mesencephalon of normal mice. Cells immunoreactive (ir) for tyrosine hydroxylase (TH), a DA-synthesizing enzyme, were first detected on embryonic day 10 (E10) in the medio-basal part of the mesencephalon and were distributed throughout the entire length of the ventral mesencephalic wall at E12. By E14, TH-ir cells were located laterally along the ventral pial surface to form the primordia of the substantia nigra. Experiments with a single injection of bromodeoxyuridine, a thymidine analog, demonstrated that cells generated in the ventricular surface of the ventral mesencephalon at E11 migrated ventrally and then moved laterally to form the substantia nigra and the ventral tegmental area. Electron microscopic examination of the ventral mesencephalon of E12 mice disclosed that in the dorsal part ventrally migrating immature neurons made close contacts with the processes of radial glial cells. The expression of tenascin was transiently seen on radial glial processes between E10 and E13 coincident with the period of the ventral migration of mesencephalic DA neurons. By double immunostaining of E13 mesencephalon, ventrally migrating TH-ir cells were seen to be apposed to tenascin-bearing radial glial processes. On the other hand, laterally migrating neurons in the basal part of the mesencephalon were observed by electron microscopy to contact with tangentially arranged nerve fibers which were immunopositive for the 160 kDa neurofilament polypeptide at the light microscopic level from E10. Double immunostaining of E13 mesencephalon demonstrated that laterally migrating TH-ir cells were intermingled among neurofilament-ir fiber bundles. The cells of origin of the tangential nerve fibers were detected in the lateral part of the mesencephalon, when a fluorescent dye, 1,1'-dioctadecyl-3,3,3',3'-tetramethyl-indocarbocyanine perchlorate (DiI) was injected into the basal part of the mesencephalon of fixed E12 mice. The present results suggest that guiding cues of the radial migration of mesencephalic DA neurons represent processes of radial glial cells which express tenascin. On the other hand, tangentially arranged nerve fibers originating from the lateral part of the mesencephalon may provide a scaffolding along which the mesencephalic DA neurons subsequently migrate laterally to form the ventral tegmental area and the substantia nigra.

Animals↗

Lymphocyte migration into the CNS modelled in vitro.

We report on a series of experiments which examines the factors controlling lymphocyte adhesion to brain endothelium in vitro and the factors which control cell migration across the endothelium, using a new migration assay. Although lymphocyte adhesion preceded migration across the brain endothelium, the two processes are not identical. We noted that activated CD4+ T cells were particularly good at migrating across endothelia. CD8+ T cells and B cells did not migrate but adhered well to endothelia. Moreover, the endothelium maintained high levels of cell traffic without being disrupted and without exhausting the molecular systems which allowed migration. From the viewpoint of migration of dividing cells, the state of lymphocyte activation appeared to be the most important controlling factor--these cells migrated equally well across endothelium activated with cytokines or untreated endothelium. The kinetics of adhesion suggested that the LFA-1/ICAM-1 and VLA-4/VCAM combinations of adhesion molecules were important in controlling migration. With antibody blocking studies, the role of the LFA-1/ICAM-1 system was equivocal. While anti-LFA-1 blocked lymphocyte adhesion, anti-ICAM-1 did not, suggesting that the level of ICAM-1 was not critical.

Animals↗

Riding the glial monorail: a common mechanism for glial-guided neuronal migration in different regions of the developing mammalian brain.

In vitro studies from our laboratory indicate that granule neurons, purified from early postnatal mouse cerebellum, migrate on astroglial fibers by forming a 'migration junction' with the glial fiber along the length of the neuronal soma and extending a motile 'leading process' in the direction of migration. Similar dynamics are seen for hippocampal neurons migrating along hippocampal astroglial fibers in vitro. In heterotypic recombinations of neurons and glia from mouse cerebellum and rat hippocampus, neurons migrate on astroglial processes with a cytology and neuron-glia relationship identical to that of homotypic neuronal migration in vitro. In all four cases, the migrating neuron presents a stereotyped posture, speed and mode of movement, suggesting that glial fibers provide a generic pathway for neuronal migration in developing brain. Studies on the molecular basis of glial-guided migration suggest that astrotactin, a neuronal antigen that functions as a neuron-glia ligand, is likely to play a crucial role in the locomotion of the neuron along glial fibers. The navigation of neurons from glial fibers into cortical layers, in turn, is likely to involve neuron-neuron adhesion ligands.

Animals↗

Effects of anti-inflammatory agents on lymphocyte migration stimulated by the interferons, tumor necrosis factor and cutaneous inflammation.

Our goal was to examine the effect of anti-inflammatory agents on the migration of lymphocytes to cutaneous inflammatory sites and in response to cytokines. The accumulation of i.v. injected 111In-labelled peritoneal exudate lymphocytes in skin sites of rats injected with KLH to induce DTH reactions, LPS, poly I:C and the cytokines, IFN-gamma, IFN-alpha/beta and tumor necrosis factor was determined. Systemic dexamethasone (DEX) treatment strongly inhibited the migration of lymphocytes in response to all of the stimuli, however, the effective dose of DEX varied widely with the different recruiting agents. The lowest ED50 was observed with LPS, while IFN-alpha/beta was the least inhibited. DEX treatment increased lymphocyte accumulation in the bone marrow and spleen. Pretreatment of lymphocytes with DEX had no effect on their migration, while local i.d. hydrocortisone inhibited migration into the skin. Cyclosporin A treatment had no effect on lymphocyte recruitment in response to any of the cytokines or LPS but significantly inhibited migration to DTH reactions and poly I:C. Treatment of rats with indomethacin, ASA and BW755C produced only a marginal inhibition of lymphocyte migration in response to some of the stimuli tested. DEX is a potent inhibitor of lymphocyte migration to inflammation. In addition to suppressing cytokine production, it can suppress migration to cytokines, probably through inhibiting the effects of these agents on the vascular endothelium. Cyclosporin A decreases lymphocyte accumulation only through its ability to suppress lymphokine production, while inhibitors of arachidonate metabolism have little direct effect on lymphocyte migration.

Animals↗

Migrating neurons in the developing cerebral cortex of the mouse send callosal axons.

The presence of migrating callosal neurons during the development of the murine cerebral cortex was studied using biocytin and the lipophilic dye, 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate as retrograde tracers. After injections of biocytin in the presumptive somatosensory cortex of newborn mice which were analysed one day later, many anterogradely labelled fibres coursed towards the contralateral hemisphere through the corpus callosum. Retrogradely labelled callosal cells were also observed. Most callosal neurons corresponded to immature pyramidal cells. In addition, a few biocytin-labelled callosal neurons displayed extremely fusiform shapes, vertical orientation and a short, single process emerging from the apical side of the perikaryon. At the electron microscopic level, these cells had features identical to those described for migrating callosal neurons. Twenty-four hours after birth, these migrating neurons were almost exclusively observed in the upper, dense aspect of the cortical plate (presumptive layers II-III) and only very exceptionally in the infragranular layers. No retrogradely labelled cell resembling migrating neurons were noticed after injections on postnatal days 2 or 5. To study migrating callosal neurons at embryonic stages, crystals of the lipophilic dye were injected in the corpus callosum or the contralateral white matter in embryos aged 17, 18 and 19 days, corresponding to the initial development of the corpus callosum in mice. Whereas callosal migrating neurons were not detected at embryonic days 17 and 18, injections of the lipophilic dye on embryonic day 19 revealed the presence of labelled migrating neurons in the infragranular layers. To corroborate further that these cells are migrating neurons, [3H]thymidine was administered on embryonic days 16 and 17, and labelled mice were injected with biocytin on embryonic day 19 or the first postnatal day. Retrogradely labelled callosal neurons resembling migrating neurons were autoradiographically labelled. These results indicate that the specification of certain neuronal types and the emergence of their cell type-specific characteristics occur shortly after postmitotic neurons leave the ventricular zone, before being positioned within the cortical plate.

Animals↗

Induction of in vitro human lymphocyte migration by interleukin 3, interleukin 4, and interleukin 6.

The effects of interleukin 3 (IL 3), IL 4, IL 6, and interferon-gamma (IFN-gamma) on lymphocyte migration have been investigated and compared with those of transforming growth factor-beta 1 (TGF-beta 1), granulocyte colony stimulating factor (GCSF), and macrophage colony stimulating factor (MCSF). Potent, temperature-dependent stimulation of lymphocyte migration was obtained in response to IL 3 and IL 4 (ED50 less than 10(-11) M and less than 10(-13) M, respectively) and this migration was abolished in the presence of 3 micrograms ml-1 cytochalasin B. IL 6 and IFN-gamma were less active (ED50 greater than or equal to 10(-9) M and greater than or equal to 10(-8) M, respectively), maximal migration in response to IFN-gamma being only 30% above background as compared with approximately 250% for IL 3 and IL 4. TGF-beta 1, GCSF, and MCSF failed to stimulate lymphocyte migration in doses similar to those used for IL 3, IL 4, and IL 6. The presence of antisera to IL 3, IL 4, and IL 6 specifically inhibited lymphocyte migration induced by the corresponding cytokines (IC50 values being 1/10,000, greater than 1/30,000, and greater than 1/30,000 dilution of antibody, respectively). Cross-desensitization experiments using IL 3 and IL 4 demonstrated that neither IL 3 nor IL 4 were able to stimulate dose-related lymphocyte migration in cells preincubated with IL 3. Cells preincubated with IL 4 were only stimulated by a supraoptimal concentration of IL 4 (10(-11) M). The induction of lymphocyte migration by IL 3, IL 4, and IL 6 therefore appears to be a specific and potentially important effect of these cytokines. Cross-desensitization of lymphocytes by IL 3 and IL 4 raises the possibility that the induction of lymphocyte migration by these cytokines may occur through a common postreceptor signal transduction mechanism.

Chemotaxis, Leukocyte↗

Disruption of focal adhesion kinase slows transendothelial migration of AU-565 breast cancer cells.

Transendothelial migration of cancer cells from the vasculature into tissue stroma is a final step in the metastatic cascade, prior to formation of secondary tumors. Due to its role in 2-dimensional migration of cells on extracellular matrix proteins, we hypothesized that focal adhesion kinase (FAK) promotes transendothelial migration of cancer cells. AU-565 cells are weakly invasive metastatic breast adenocarcinoma cells that migrate through bovine lung microvessel endothelial cell monolayers. Electric cell-substrate impedance sensing detects a significant decrease in monolayer resistance upon addition of AU-565 cells. Immunofluorescence microscopy and filter-based migration assays demonstrate that this drop in resistance correlates with transendothelial migration. Transfection of AU-565 cells with FAK siRNA results in significantly diminished transendothelial migration of AU-565 cells within 15h. Expression of the dominant negative FAK inhibitor FAK-related non-kinase (FRNK) also results in delayed AU-565 transendothelial migration, whereas over-expression of wildtype FAK does not impact transendothelial migration substantially. These results demonstrate that FAK affects the rate of a key step in the metastatic cascade.

Animals↗

Assays for measuring extracellular GABA levels and cell migration rate in acute slices.

The postnatal subventricular zone (SVZ) contains the largest pool of dividing and migrating neural precursors in the adult rodent brain. Neuronal precursors migrate throughout the SVZ and along the rostral migratory stream (RMS) towards the olfactory bulb where they differentiate into interneurons. To facilitate the investigation of cell migration in the SVZ and RMS, an inexpensive migration assay was developed for use in acute brain slices. Acute sagittal slices were kept at 37 degrees C in 5% O2/95% CO2-saturated solution and migrating cells in the SVZ and RMS were visualized using an upright infrared-differential interference contrast microscope. Time-lapse movies were acquired to identify the direction and measure the speed of cell migration. The neurotransmitter GABA and inhibitors of GABA receptors or transporters can be bath applied to determine the function of endogenous GABA on the direction and speed of cell migration. In parallel, the levels of endogenous GABA released from acute SVZ or RMS explants were measured with mass spectrometry. Additional techniques such as electrophysiology and immunohistochemistry confirmed the identity of cells as neuronal precursors and characterized the expression of GABA receptors and transporters. This report describes how modulations in the direction and speed of neuronal precursor migration can be accurately monitored and how changes in local GABA levels can be measured. The described techniques can be used to identify the endogenous factors that regulate cell migration. Identifying such factors is essential for the future therapeutic use of SVZ cells to replace damaged or lost cells.

Animals↗

IL-18 enhances the migration ability of murine melanoma cells through the generation of ROI and the MAPK pathway.

Interleukin-18 (IL-18) has multiple effects on various cells that are involved in immune escape of murine melanoma cells and in the inflammatory responses. This study investigated the effect of IL-18 on the ability of murine melanoma cells to migrate by using B16F10 cells and the IL-18 antisense transfectants of B16F10 cells (the B16F10/IL-18 antisense transfectant). The B16F10 cells were more able to migrate than were the B16F10/IL-18 antisense transfectants. An exogenous IL-18 treatment improved the ability of the B16F10/IL-18 antisense transfectant cells to migrate, indicating that IL-18 enhanced the migration ability of melanoma cells. To determine the signaling mechanisms involved in IL-18-enhanced migration, we measured the ROI levels. It was found that the ROI levels were increased by IL-18, and an antioxidant, N-acetyl-l-cystein (NAC), blocked the effect of IL-18 on migration, suggesting the involvement of ROI in the signal transduction of IL-18-enhanced cell migration. IL-18-enhanced cell migration was also reduced by PD98059. In addition, the level of ERK1/2 phosphorylation was markedly increased by treating with exogenous IL-18 at 20 min. These results suggest that IL-18 enhances the ability of melanoma cells to migrate via the generation of ROI and the MAPK pathway.

Acetylcysteine↗

The role of phospholipase C and phosphatidylinositol 3-kinase in vascular smooth muscle cell migration and proliferation.

BACKGROUND: Vascular smooth muscle cell (SMC) proliferation and migration both contribute to the formation of intimal hyperplasia. Phospholipase C (PLC) and phosphatidylinositol 3-kinase (PI3-K) are ubiquitous signaling proteins that mediate multiple cellular events. In this study, we investigate the role of PLC and PI3-K in platelet-derived growth factor (PDGF) and extracellular matrix protein (ECM) induced SMC proliferation and migration. MATERIAL AND METHODS: Proliferation of human saphenous vein SMC was assessed by (3)H-thymidine incorporation. SMC migration was evaluated using a microchemotaxis chamber. U-73122 was used as a general inhibitor for PLC, and D609 and ET-18-OCH3, respectively, were used to block the isotypes of PLC, phosphatidylcholine- (PC-), and phosphatidylinositol- (PI-) specific PLC. PI3-K activity was inhibited using two selective inhibitors, LY-294002 and wortmannin. RESULTS: PDGF and Type 1 collagen (CN-I) stimulated SMC proliferation, whereas PDGF and four distinct extracellular matrix proteins CN-I, Type 4 collagen (CN-IV), fibronectin (FN), and laminin (LN) stimulated SMC migration. Both isotypes of PLC as well as PI3-K were necessary for PDGF- and CN-I-induced proliferation. Signaling for migration, however, was more specific. Of the various signaling proteins studied, only PI-PLC was necessary for PDGF-induced SMC migration. Conversely, PI3-K was the only signaling protein necessary for SMC migration in response to ECM proteins. CONCLUSION: The signaling pathways necessary for PDGF- and CN-I-induced SMC proliferation involve both isotypes of PLC as well as PI3-K. The signaling pathways used by growth factors and ECM to stimulate SMC migration are more selective. Understanding the intracellular signaling pathways required for SMC proliferation and migration may allow the development of tools to selectively block intimal hyperplasia.

Cell Division↗

Doublecortin is necessary for the migration of adult subventricular zone cells from neurospheres.

Mutations in human doublecortin (DCX) and knockdown of Dcx in rodents cause radial migration defects in the embryonic cerebral cortex. However, the brain phenotype of Dcx knockout mice is largely normal suggesting that Dcx is not necessary for most migration events. Adult subventricular zone (SVZ) cells migrate tangentially in the rostral migratory stream to the olfactory bulbs. Dcx is expressed in the SVZ but it is unknown if it is necessary for migration. We show that Dcx RNAi reduced SVZ cell migration in vitro, both cell autonomously and non-cell autonomously. Overexpression of Dcx rescued migration after knockdown, but did not increase migration by itself. Thus, Dcx is necessary not only for embryonic radial migration but also migration of adult SVZ cells.

3' Untranslated Regions↗

Dynamics of neural crest-derived cell migration in the embryonic mouse gut.

Neural crest-derived cells that form the enteric nervous system undergo an extensive migration from the caudal hindbrain to colonize the entire gastrointestinal tract. Mice in which the expression of GFP is under the control of the Ret promoter were used to visualize neural crest-derived cell migration in the embryonic mouse gut in organ culture. Time-lapse imaging revealed that GFP(+) crest-derived cells formed chains that displayed complicated patterns of migration, with sudden and frequent changes in migratory speed and trajectories. Some of the leading cells and their processes formed a scaffold along which later cells migrated. To examine the effect of population size on migratory behavior, a small number of the most caudal GFP(+) cells were isolated from the remainder of the population. The isolated cells migrated slower than cells in large control populations, suggesting that migratory behavior is influenced by cell number and cell-cell contact. Previous studies have shown that neurons differentiate among the migrating cell population, but it is unclear whether they migrate. The phenotype of migrating cells was examined. Migrating cells expressed the neural crest cell marker, Sox10, but not neuronal markers, indicating that the majority of migratory cells observed did not have a neuronal phenotype.

Animals↗

Notch and Numb are required for normal migration of peripheral glia in Drosophila.

A prominent feature of glial cells is their ability to migrate along axons to finally wrap and insulate them. In the embryonic Drosophila PNS, most glial cells are born in the CNS and have to migrate to reach their final destinations. To understand how migration of the peripheral glia is regulated, we have conducted a genetic screen looking for mutants that disrupt the normal glial pattern. Here we present an analysis of two of these mutants: Notch and numb. Complete loss of Notch function leads to an increase in the number of glial cells. Embryos hemizygous for the weak Notch(B-8X) allele display an irregular migration phenotype and mutant glial cells show an increased formation of filopodia-like structures. A similar phenotype occurs in embryos carrying the Notch(ts1) allele when shifted to the restrictive temperature during the glial cell migration phase, suggesting that Notch must be activated during glial migration. This is corroborated by the fact that cell-specific reduction of Notch activity in glial cells by directed numb expression also results in similar migration phenotypes. Since the glial migration phenotypes of Notch and numb mutants resemble each other, our data support a model where the precise temporal and quantitative regulation of Numb and Notch activity is not only required during fate decisions but also later during glial differentiation and migration.

Animals↗