Growth factors and taurine protect against excitotoxicity by stabilizing calcium homeostasis and energy metabolism

Taurine, brain derived neurotrophic factor (BDNF), and basic fibroblast growth factor (bFGF) are known to control the development of early postnatal cerebellar granule cells. This study attempted to investigate possible mechanisms of this control by determining neuronal survival, calcium homeostasis, and related calcium-mediated functions, as well as the site of action during glutamate-induced excitotoxicity in cultures of cerebellar granule cells. We report that stimulation of glutamate receptors induced a rapid increase in intracellular calcium concentrations ([Ca(2+)](i)) and a decrease in mitochondrial energy metabolism. These effects of glutamate were time- and concentration-dependent and could be specifically blocked by glutamate receptor antagonists. Taurine and bFGF but not BDNF differently regulated [Ca(2+)](i), and preserved the mitochondrial energy metabolism in the presence of glutamate. The regulation of [Ca(2+)](i) by bFGF and taurine required pretreatment of cells with these factors. Confocal microscope analysis of [Ca(2+)](i) and (45)Ca(2+) uptake studies showed that bFGF reduced the magnitude of glutamate-induced calcium uptake with no apparent regulation thereafter. Taurine, on the other hand, did not affect the level of calcium uptake induced by glutamate but rather the duration of the maximal response; this maximal response was transient and returned to basal levels approximately 10 min after glutamate receptor stimulation. We conclude from these data that bFGF and taurine prevent glutamate excitotoxicity through regulation of [Ca(2+)](i) and mitochondrial energy metabolism. Furthermore, the neuroprotective role of taurine and bFGF was enhanced by their collaboration.

Reduced number and altered morphology of microglial cells in colony stimulating factor-1-deficient osteopetrotic op/op mice

The numerical density of microglial cells is reduced by 47% in the corpus callosum, by 37% in the parietal cortex and by 34% in the frontal cortex of mice mutant at the op locus which are totally devoid of colony stimulating factor-1 (CSF-1), the major growth factor for macrophages. Moreover, microglia in the frontal cortex of the op/op mice are smaller and have shorter cytoplasmic processes compared to control mice. Study suggests that CSF-1 plays a role in vivo in the formation and maturation of microglia and has little or no effect on perivascular cells.

Identification of a candidate human spectrin Src homology 3 domain-binding protein suggests a general mechanism of association of tyrosine kinases with the spectrin-based membrane skeleton

Spectrin is a widely expressed protein with specific isoforms found in erythroid and nonerythroid cells. Spectrin contains an Src homology 3 (SH3) domain of unknown function. A cDNA encoding a candidate spectrin SH3 domain-binding protein was identified by interaction screening of a human brain expression library using the human erythroid spectrin (alphaI) SH3 domain as a bait. Five isoforms of the alphaI SH3 domain-binding protein mRNA were identified in human brain. Mapping of SH3 binding regions revealed the presence of two alphaI SH3 domain binding regions and one Abl-SH3 domain binding region. The gene encoding the candidate spectrin SH3 domain-binding protein has been located to human chromosome 10p11.2 --> p12. The gene belongs to a recently identified family of tyrosine kinase-binding proteins, and one of its isoforms is identical to e3B1, an eps8-binding protein (Biesova, Z., Piccoli, C., and Wong, W. T. (1997)Oncogene 14, 233-241). Overexpression of the green fluorescent protein fusion of the SH3 domain-binding protein in NIH3T3 cells resulted in cytoplasmic punctate fluorescence characteristic of the reticulovesicular system. This fluorescence pattern was similar to that obtained with the anti-human erythroid spectrin alphaI SigmaI/betaI SigmaI antibody in untransfected NIH3T3 cells; in addition, the anti-alphaI SigmaI/betaI SigmaI antibody also stained Golgi apparatus. Immunofluorescence obtained using antibodies against alphaI SigmaI/++betaI SigmaI spectrin and Abl tyrosine kinase but not against alphaII/betaII spectrin colocalized with the overexpressed green fluorescent protein-SH3-binding protein. Based on the conservation of the spectrin SH3 binding site within members of this protein family and published interactions, a general mechanism of interactions of tyrosine kinases with the spectrin-based membrane skeleton is proposed.

The regulation of phosphorylation of tau in SY5Y neuroblastoma cells: the role of protein phosphatases

In Alzheimer disease brain the microtubule associated protein (MAP) tau is abnormally hyperphosphorylated. The role of protein phosphatases (PP) in the regulation of phosphorylation of tau was studied in undifferentiated SY5Y cells. In cells treated with 10 nM okadaic acid (OA), a PP-2A/PP-1 inhibitor, the PP-1 and -2A activities decreased by 60% and 100% respectively and the activities of MAPKs, cdc2 kinase and cdk5, but not of GSK-3, increased. OA increased the phosphorylation of tau at Thr-231/Ser-235 and Ser-3961404, but not at Ser-262/356 or Ser-199/202. An increase in tyrosinated/detyrosinated tubulin ratio, a decrease in the microtubule binding activities of tau, MAP1b and MAP2, and cell death were observed. Treatment with 1 microm taxol partially inhibited the cell death. These data suggest (1) that OA induced hyperphosphorylation of tau is probably the result of activated MAPK and cdks in addition to decreased PP-2A and PP-1 activities and (2) that in SY5Y cells the OA induced cell death is associated with a decrease in stable microtubules.

Failed cell migration and death of purkinje cells and deep nuclear neurons in the weaver cerebellum

The mouse neurological mutant weaver has an atrophic cerebellar cortex with deficits in both Purkinje and granule cell number. Although granule cells are known to die postnatally shortly after their final cell division, the cause of the Purkinje cell deficit (cell death vs lack of production) is unknown. We report here a quantitative analysis of large cerebellar neurons of the weaver mutant during postnatal development. We explored the hypothesis that the cells of the entire cerebellar anlage were affected by the mutation by including in our study the neurons of the deep cerebellar nuclei (DCN). Our analysis reveals that in homozygous weaver mutants (1) the DCN are displaced laterally, display an abnormal anatomy, and suffer a 20-25% decrease in neuron number; (2) this numerical deficit is located in medial regions, similar to the localization of cortical deficits in both Purkinje and granule cells; (3) pyknotic figures are present in the juvenile DCN and in the Purkinje cell layer; and (4) the majority of cell death in these populations occurs not in medial regions where the numerical deficits are observed, but rather laterally where adult cell number is nearly normal. These results lead us to propose that the complete weaver phenotype includes a failure of the cell movements that lead to the fusion of the bilateral cerebellar anlage, and that this failure to migrate properly leaves some of the Purkinje cells and DCN neurons in a position where they are unable to make appropriate connections, leading to their death. In addition to implications for normal development, these observations suggest that weaver effects on the cerebellum can be unified into one consolidated model in which failure of cell movement affects all major cerebellar neurons.

Arrest of afferent axon extension by target neurons in vitro is regulated by the NMDA receptor

Cerebellar granule neurons in vitro specifically arrest the extension of their appropriate presynaptic axons, mossy fibers. This "stop-growing signal" may be an essential step in the formation and specificity of synapses. Here, we have tested whether ionotropic glutamate receptors are involved in the stop-growing signal. When explants of basilar pontine nuclei, a mossy fiber source, were cultured on granule neurons, most pontine neurites terminated <200 microm from their explant of origin, a criterion for the stop-growing signal. In contrast, treatment with the NMDA antagonist D(-)-2-amino-5-phosphonopentanoic acid (D-AP5) greatly increased the number of pontine neurites extending beyond 300 microm, whereas treatment with NMDA reduced the number of pontine neurites extending beyond 200 microm. A non-NMDA agonist (AMPA) and antagonist (6-cyano-7-nitroquinoxaline-2,3-dione) did not alter pontine neurite lengths. None of these agents affected neurite outgrowth from pontine explants in the absence of granule neurons, nor did any agent affect the survival of granule neurons. These results indicate that NMDA and D-AP5 specifically perturb an interaction between axons and target cells necessary for the stop-growing signal, and that NMDA receptors are critical for the development of a major cerebellar afferent system. These findings also suggest that NMDA-sensitive refinement of axon arbors during later development may involve the direct regulation of axon extension by target neurons.

Effect of K+- and kainate-mediated depolarization on survival and functional maturation of GABAergic and glutamatergic neurons in cultures of dissociated mouse cerebellum

The effect of the depolarizing agents, an elevated potassium concentration (25 mM) or kainic acid (50 microM) on neuronal survival and differentiation was investigated in cultures of dissociated neurons from cerebella of 7-day-old mice. When maintained in the presence of an antimitotic agent such cultures consist primarily of glutamatergic and GABAergic neurons. Cell survival was monitored by measurement of DNA, and differentiation by determining uptake and depolarization coupled release of glutamate (D-aspartate as label) and GABA. The depolarizing agents were added separately or together either from the start of the culture period (7-8 days) or at day 5 in culture. The main findings are that K+ depolarization is important for differentiation of glutamatergic neurons but not for GABAergic neurons. This depolarizing signal is important during the early phase of development in culture. For glutamatergic neurons, kainate may replace K+ as a depolarizing signal whereas in case of the GABAergic neurons, kainate was toxic particularly during the late phase of development. It was further observed that the glutamatergic neurons when maintained in a medium with 5 mM K+ during the first 5 days in culture became sensitive to kainate toxicity when this amino acid was added at day 5. This was not the case when the medium contained 25 mM K+ from the start of the culture period.

Balanced interaction of growth factors and taurine regulate energy metabolism, neuronal survival, and function of cultured mouse cerebellar cells under depolarizing conditions

The development of neuronal cells in a given cellular environment requires mechanisms that dynamically regulate the balanced interactions of multiple factors which are known to control maintenance and plasticity in function of neurons throughout constantly changing extracellular conditions. Periodic release of excitatory amino acids from both developing glial and neuronal cells into the extracellular environment and their uptake has been shown to stimulate neuronal function in concert with growth factors that control the degree of depolarization and, therefore, neuronal function. This study attempts to characterize the critical concentrations of these factors either alone or together in relation to energy metabolism, cell survival and function. We demonstrate a close correlation between energy metabolism of neuronal cells, controlled by the combination of growth-factors (beta FGF, BDNF), and glutamate-taurine as well as K+ in depolarizing concentrations (10-25 mM), during the balancing act of neuronal survival or death, and neuronal function. These functions depend on medium conditions (energy sources, ion composition), the ratio of glial cells versus neurons and cell density. Granule cell migration as a measure of developmental neuronal function was analyzed in the presence of various combinations of growth factors and taurine under various depolarizing conditions (glutamate, K+). We found that K+ concentrations > 7 mM in BME and 10% horse serum blocked migration in less than 30 min. Taurine did not prevent this effect. However, in the presence of HEPES as well as in F12-medium with HEPES, taurine restored granule cell migration. On the other hand, glutamate-or NMDA-mediated depolarization stopped migrating granule cells while NMDA antagonists extended the period of migration. Taurine amplified the stop-signal in the presence of glutamate agonists but increased the number of migrating cells in the absence of glutamate. Thus, the mechanisms of glutamate receptor mediated excitotoxicity, possibly by reducing Ca2+ influx under depolarizing conditions, but amplifies the stop-signal, Ca2+ levels may not control granule cell migration.

Increased proteolytic activity of the granule neurons may contribute to neuronal death in the weaver mouse cerebellum

The weaver mouse mutation is a genetic defect of unknown origin that leads to impairment of cerebellar granule neuronal migration and to neuronal cell death. We investigated laminin expression and proteolytic enzyme activity in this migration-deficient mouse mutant in vivo and in vitro to search for a molecular basis for the weaver defect. The weaver cerebellum showed a general increase in immunoreactivity for laminin, for a neurite outgrowth domain of the B2 chain of laminin, and for tissue plasminogen activator compared to the normal animals. Zymographic assays and immunocytochemistry confirmed that tissue plasminogen activator was the proteolytic enzyme synthesized in excess in the weaver mouse cerebellum in vivo. When placed in culture, the weaver granule neurons survived poorly on a laminin substratum, and failed to extend long neurites, unlike the normal cerebellar granule neurons. The cultured weaver granule neurons were proteolytically overactive and secreted excessive amounts of tissue plasminogen activator, which was likely to interfere with their neurite outgrowth potential on a laminin substratum. Indeed, the weaver granule neurons but not the normal neurons degraded laminin from their culture substratum and deposited a neurite outgrowth domain of the B2 chain of laminin onto their surfaces. Electrophysiology showed that the weaver granule neurons had poor resting membrane potentials (-38 V), whereas the normal neurons had normal resting membrane potentials of (-61 V). The resting membrane potentials of the weaver granule neurons were restored to near normal (-59 V) by a protease inhibitor, aprotinin. Aprotinin also rescued the weaver granule neurons from death on a laminin substratum and promoted their neurite outgrowth to the level of the normal animals. These results indicate that increased proteolytic activity accompanied with increased synthesis of laminin, and its B2 chain, distinguish the weaver mutation from the normal animals. These molecular changes may contribute to the impairment of granule neuronal migration and to the neuronal death, characteristic of the weaver mutation.

Abnormally phosphorylated tau in SY5Y human neuroblastoma cells

In Alzheimer disease (AD) the microtubule associated protein (MAP) tau is hyperphosphorylated at several sites. In the present study, like AD tau, tau in the human neuroblastoma SH-SY5Y was found to be hyperphosphorylated, at Ser-199/202, Thr-231, Ser-396 and Ser-404. However, in contrast to AD, the tau in SY5Y cells was not hyperphosphorylated at Ser-235 and there was only one tau isoform. Quantitative analysis revealed that approximately 80% of the SY5Y-tau was phosphorylated at Ser-199/202. The phosphorylated tau was deposited in perikarya and processes of the cells whereas most of the unphosphorylated (at Ser-199/202) tau was localized in the nucleus. Tau from the cell lysates did not bind to taxol-stabilized microtubules. In contrast, MAP1b and MAP2 from cell lysates bound to stabilized microtubules in vitro and were associated to the microtubule network in situ. Phosphorylation of tau at high levels, its inactivity with microtubules and its accumulation in SY5Y cells provide for the first time a cell model of cytoskeletal changes seen in AD.

Changes in expression of nonmuscle myosin heavy chain isoforms during muscle and nonmuscle tissue development

Anti-human platelet myosin antibodies and two anti-peptide antibodies, anti-peptide IIA and anti-peptide IIB, which recognize macrophage-type (MIIA) and brain-type (MIIB) isoforms of nonmuscle myosin heavy chain, respectively, were used to study expression of nonmuscle myosin isoforms in various tissues of mice during development. Tissue-specific changes in the relative isoform concentrations were observed by performing immunoblots of crude myosin extracts from nonmuscle and muscle tissues. In fetal and neonatal mouse tissues, the anti-peptide IIB antibodies stained a single band, called MIIB2, while the anti-peptide IIA and anti-platelet myosin antibodies stained a band that migrated faster than MIIB2. In brain, a slower moving band, MIIB1, started to appear at 2 weeks after birth, and in the adult cerebellum it was at least as abundant as MIIB2. In thymus, MIIB2 decreased selectively shortly after birth, while in liver both MIIB2 and MIIA rapidly disappeared, but the isoform(s) detected by anti-platelet myosin antibodies (MIIApla) remained constant. The MIIB2 and MIIA as well as MIIApla found in striated muscles from fetal and neonatal mice decreased to levels that were below the limit of detection by 3 weeks of age. In cryosections of skeletal and cardiac muscles, MIIB2 was localized within the muscle cells, while MIIA and MIIApla were primarily in the blood vessels and capillaries.

Neuronal migration in cerebellar microcultures is inhibited by antibodies against a neurite outgrowth domain of laminin

The functional role of laminin in neuronal migration was investigated by using polyclonal antibodies or their divalent (Fab')2 fragments to a neurite outgrowth promoting domain of the B2 chain of laminin in a cerebellar microculture system widely recognized as a model for neuronal migration. We show here that these antibodies or their (Fab')2 fragments totally inhibit migration of the mouse cerebellar granule cells along the glial and other neuronal cell processes. Antibodies to native laminin or other control antibodies have no inhibitory effect. Immunocytochemical analysis of the cerebellar microcultures indicates that the functional role of these antibodies may relate to the fact that the punctate deposits of laminin and its neurite outgrowth promoting domain accumulate in between the migrating neurons and the glial cells. These data provide the first direct evidence for the functional role of laminin and its neurite outgrowth domain in neuronal migration in the mammals. They further suggest that a neuronal cell surface contact with the extracellular deposits of a neurite outgrowth domain of the B2 chain of laminin may mediate neuronal-glial interactions.

The role of taurine in the survival and function of cerebellar cells in cultures of early postnatal cat

The role of taurine and beta-alanine was analyzed in kitten cerebellar cultures. Since in contrast to mouse, cats (and primates including man) cannot synthesize sufficient taurine to maintain their body pools, we considered the cat an ideal species for the analysis of the role of taurine during early postnatal cerebellar development under controlled conditions. Unexpectedly, we found that the presence of taurine was toxic to neurons but that compounds, considered to be competitors for the beta-amino acid uptake system, support cell survival and cell function in vitro, the opposite of the results found in mice. This could be explained by the finding that only minute amounts of [3H]taurine were taken up by both cat neurons and glial cells under optimal culture conditions but that in the presence of the taurine analogues beta-alanine and guanidinoethane sulfonic acid (GES) significant amounts of taurine were found in all cell types. These differences between mouse cerebellar cells and cat cerebellar cells in vitro suggest that a re-evaluation of the mechanisms that control taurine function in cats and primates is warranted.

Progressive loss of neuronal src protein in postnatal weaver and staggerer cerebellum

Two forms of the c-src protein-tyrosine kinase, pp60c-src, are detectable in the central nervous system. One form pp60+, appears to be exclusively expressed in neurons and is characterized by insertion of 6 amino acids compared to its non-neuronal counterpart, pp60. These 2 proteins were studied in the mutant mouse strains weaver and staggerer with postnatal loss of cerebellar granular neurons. We found a continuous postnatal decline of the neuronal form of pp60c-src, pp60+, in the cerebellum of both mutants concomitant with the degeneration of cerebellar granule cells. This indicates that granular neurons provide the main source for pp60+ in the cerebellar cortex.

Regional differences in cytoarchitecture of the weaver cerebellum suggest a new model for weaver gene action

This paper examines the structure and cytoarchitecture of the cerebellum of the weaver mutant mouse with particular emphasis on regional differences along the mediolateral and anterior-posterior axes. We have uncovered several, previously undescribed features of the weaver cerebellar phenotype. Perhaps the most dramatic example of our findings is the severe disruption of the folial structure of the hemispheres of the weaver cerebellum. A dorsal overgrowth of tissue occurs in the hemispheres that forms a finger-like projection superficial to an atrophic but structurally more normal cerebellar mass underneath. While this folial abnormality is most evident in the homozygote (wv/wv) the antecedents of its appearance are already apparent in the heterozygote (+/wv). At the level of the cytoarchitectonics of the mutant brain, we find substantial variation in the positioning, numbers and density of both Purkinje and granule cells. As a whole, Purkinje plus Golgi II cell numbers are down by over 40%, but this reduction occurs almost exclusively in the medial half of the cerebellum. The hemispheric region contains a nearly normal number of cells per sagittal section (although their positions are predominantly incorrect). The granule cells also show numerical variation; they are nearly absent at the midline, but a substantial number of them survive in the lateral cerebellar cortex. In the paraflocculus, for example, granule cells can be observed in a modest internal granule cell layer as late as 38 postnatal days. These results are discussed in terms of a model of wv gene action in which we propose that the effect of the mutation is a general disruption of cellular distribution in the cerebellar cortex, affecting both Purkinje and granule cells and beginning prenatally.

Mechanism of kainate toxicity to cerebellar neurons in vitro is analogous to reperfusion tissue injury

The neuroexcitotoxin kainate has been used as a selective lesioning agent to model the etiology of a number of neurodegenerative disorders. Although excitotoxins cause susceptible neurons to undergo prolonged or repeated depolarization, the proximate metabolic pathology responsible for neuronal necrosis has remained elusive. We report here that kainate-induced death of cerebellar neurons in culture is prevented by inhibiting the enzyme xanthine oxidase, a cellular source of cytotoxic superoxide radicals (O2-.). Moreover, neurons are also protected from excitotoxin-induced death by the addition to the culture medium of either superoxide dismutase or mannitol, which scavenge superoxide and hydroxyl radicals, respectively, or serine protease inhibitor, which forestalls formation of xanthine oxidase. These findings indicate that excitotoxin-induced neuronal degeneration is mediated by superoxide radicals generated by xanthine oxidase, a mechanism partially analogous to that proposed for tissue damage seen upon reperfusion of ischemic tissues.

Probable identity of NILE glycoprotein and the high-molecular-weight component of L1 antigen

We report here that anti-L1 antiserum, raised against material from embryonic brain, and anti-NILE antiserum, raised against purified NILE (nerve growth factor-inducible large external) glycoprotein of PC12 cells, immunoprecipitate from PC12 cells material of the same apparent molecular weight (230 kilodaltons) by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Furthermore, each of these immune reagents has the capacity to clear from a PC12 cell extract all of the 230-kilodalton antigen recognized by the other antiserum. Finally, in immunohistochemical staining of developing cerebellum the two antisera exhibit very similar staining patterns. We suggest that the NILE glycoprotein and the high-molecular-weight component of L1 antigen are closely related molecules, and probably the same.

Defective development of the thymus and immunological abnormalities in the neurological mouse mutation "staggerer"

The autosomal recessive mouse mutation "staggerer" (sg/sg), located on chromosome 9, has been recognized as a neurological mutant because of movement abnormalities and defective cerebellar development. We show here that the sg/sg mutation not only affects the development of the cerebellum, but also causes developmental and regulatory changes of the immune system: We observed, on gross inspection, a marked delay in the development of sg/sg thymus, generally enlarged lymph nodes, and undersized spleens. When immunized with SRBC, the sg/sg mouse generated, in normal proportions, helper T-cells in vivo and antibody-forming B-cells in vitro; however, a delay in terminating the response and a deficiency in generating suppressor cells was noted. This suggests the existence of a defect in regulatory feedback mechanisms. The marked delay in the growth of the thymus gland was associated with the prolonged existence of cell-surface carbohydrate patterns characteristic of immature thymocytes. The prolonged expression of embryonal cell-surface phenotypes was observed on the surface of cerebellum and thymus (and, to some extent, spleen) but not in cells from other organs.

Is cerebellar granule cell migration regulated by an internal clock?

We have studied the time course of migratory behavior of cerebellar granule cells in the microwell tissue culture system. [3H]Thymidine served as a marker for particular granule cell generations. When cultured 4 hr after [3H]thymidine injection for 6 days in microwell cultures, labeled granule cells were seen to migrate along fiber bundles expanding between reaggregates called "cables" for 3 to 4 days. After 5 and 6 days in vitro the percentage of labeled non-migrating cells found in clusters in reaggregates and on cables increased considerably. Whereas unlabeled cells continued to migrate. Comparable results were obtained when granule cells developed in vivo for various times after label and their developmental state was determined in vitro. Cells from cerebellar populations labeled 1 to 4 days before culture maintained their ability to migrate in vitro, even after granule cells had entered the internal granule cell layer. In contrast, the percentage of migrating cells labeled 5 and 6 days before culture was reduced significantly. The results suggest that the time span of granule cell migration is predetermined intrinsically rather than by external signals.

Development-dependent regulation of N-acetyl-beta-D-hexosaminidase of cerebellum and cerebrum of normal and staggerer mutant mice

Distinctive activities of various glycosidases were expressed in the cerebellum and cerebral cortex of mice during their development. In particular, N-acetyl-beta-D-hexosaminidase (EC 3.2.1.30) appeared to be developmentally regulated. A transient peak of enzyme activity at postnatal day 7 was characteristic for the cerebellum, whereas the activity in the cerebral cortex gradually increased through the 1st postnatal month and was maintained at a high level of activity throughout adulthood. The regulation of N-acetylhexosaminidase activity in the developing cerebellum of the staggerer mouse deviated clearly from enzyme activities in the wild-type, whereas the activity pattern in the staggerer cerebral cortex remained unaffected. In experiments mixing wild-type and staggerer cerebellum homogenates, the specific activity was additive. Thus, involvement of inhibitors or activating molecules can be excluded. This developmentally controlled regulation or disregulation in staggerer appears to be enzyme specific, sine beta-glucosidase, alpha-glucosidase, and beta-galactosidase did not exhibit such a pattern in either normal or staggerer mice. In the mutation weaver that, like staggerer, loses the majority of its cerebellar granule cells, N-acetyl-beta-hexosaminidase activity of the cerebellum was not elevated, indicating a specific defect in staggerer rather than a general effect on lysosomal enzymes due to cell death.

Changes in particulate neuraminidase activity during normal and staggerer mutant mouse development

The activity of particulate neuraminidase (sialidase, EC 3.2.1.18) in wild-type mice and the neurological mutant Staggerer was studied during development. Peak activity of this enzyme was observed at postnatal day 3 (P3) in three tissues of normal mice: cerebellum, cerebrum, and liver. In Staggerer, however, neuraminidase peak activity was observed at P27 in the cerebellum, whereas the activity was close to normal in Staggerer cerebrum and liver. Activities of the other glycosidases in Staggerer (alpha-glucosidase (pH 3.7), alpha-glucosidase (pH 6.0), N-acetyl-beta-hexosaminidase, beta-glucosidase, and beta-galactosidase) did not show significant variation compared with wild-type at P27 in any of the three tissues. This indicates that the late activity peak of particulate neuraminidase activity in the Staggerer cerebellum is neuraminidase-specific and not due to a general increase of lysosomal enzymes.

Histogenesis of mouse cerebellum in microwell cultures. Cell reaggregation and migration, fiber and synapse formation

A microwell culture system was developed for analysis of cell movements and interactions during nervous system histogenesis. Cells from trypsinized 7-day-old mouse cerebellum reaggregated within hours into clusters which later developed interconnections consisting of either sheets of migrating cells and cell processes or cables of fiber bundles with cells migrating along their surfaces. Granule cells in several stages of differentiation, basket and/or stellate neurons, some larger neurons, and two types of neuroglial cells were identified in reproducible, nonrandom patterns by scanning and transmission electron microscopy. Axonal and dendritic processes, both with growth cones, and numerous synapses were generated in vitro.

Microbial carbohydrate specific antibodies distinguish between different stages of differentiating mouse cerebellum

High titered anticarbohydrate antibodies were used to identify cell surface carbohydrates during different stages in histogenesis of mouse cerebellum in a micro tissue-culture system which mimics selected features of in vivo cerebellum development. Blockage of fiber formation within the first few days in vitro and inhibition of cell migrations by carbohydrate-specific antibodies served as an assay system for possible contributions of surface carbohydrates to the behavior of developing cerebellar cells. Microbial strains were selected on the basis of carbohydrate structures of their cell wall antigens, and anticarbohydrate antibodies were raised against treated whole bacteria and yeast in rabbits. We found that antibodies to mannan were active at all stages of development tested (embryonic day 13, E13; the day of birth, PO; and postnatal day 7, P7). Antibodies to sialic acids prepared against strains B and C of Neisseria meningitidis distinguish different subterminal structures: anti-B reacted with E13 and PO cerebellar cells, and anti-C mostly with cells older than P7. Antifetuin antibody recognized E13 and PO but not P7 cell populations. Pneumococcus C strain R36A-specific antibodies were effective only after coating cells to C type carbohydrate before application of the antibody. The results demonstrate that antimicrobiol carbohydrate antibodies cross-react with mammalian cell surface carbohydrate structures and therefore can be used as a powerful tool in tissue culture to analyse those structures which might control cell behaviors pertinent to cerebellar development.

Induction of antiphosphorylcholine antibody formation by anti-idiotypic antibodies

Anti-idiotypic antibodies have been used to mimic antigen in the mouse antiphosphorylcholine response in order to investigate the induction of precursors of antibody-forming cells. We have shown that interaction of anti-idiotype antibody with receptor antibody molecules induces the formation of antibodies that are specific for phosphorylcholine and carry the idiotypic determinants. This induction is dependent on the recognition of carrier determinants on the anti-idiotype antibody by helper T cells. We conclude that receptor antibody molecules on the surface of the precursors of antibody-forming cells deliver the antigenic signal for the induction of these cells.

The use of bacterial lipopolysaccharides to show that two signals are required for the induction of antibody synthesis

Evidence is presented that antigen-sensitive cells require two signals for induction. Normally these two signals are delivered to the cell via the recognition of two determinants on the immunogen: the first the receptor on the antigen-sensitive cell, and the second by the cooperating cell system. The special experimental situation described here depends upon the observation that bacterial lipopolysaccharides (LPS) render immunogenic a variety of haptens. When monovalent haptens (TNP-amino acids) are added to spleen cultures, specific antihapten responses are induced in the presence of LPS. After analyzing competing interpretations of this phenomenon, we propose that the antigenic signal is delivered as the consequence of a conformational change in the receptor upon interacting with antigen, and the second signal is delivered directly via the interaction of LPS with the membrane on the antigen-sensitive cell receiving the antigenic signal, or indirectly via the interaction of LPS with the cooperating cell population. These data imply LPS is not itself a mitogen, but merely completes an inductive stimulus to B cells. The experimental results from these and other studies indicate how these two signals may participate in inductive, suppressive, and paralytic stimuli to antigen-sensitive cells.

Quantitative analysis of cell types during growth and morphogenesis in Hydra

Tissue maceration was used to determine the absolute number and the distribution of cell types in Hydra. It was shown that the total number of cells per animal as well as the distribution of cells vary depending on temperature, feeding conditions, and state of growth. During head and foot regeneration and during budding the first detectable change in the cell distribution is an increase in the number of nerve cells at the site of morphogenesis. These results and the finding that nerve cells are most concentrated in the head region, diminishing in density down the body column, are discussed in relation to tissue polarity.