Monoclonal antibodies distinguish identifiable neurones in the leech

Pigment cells: Paragons of cellular development

Larvae of sea urchins have a population of conspicuous pigmented cells embedded in the outer surface epithelium. Pigment cells are a distinct mesodermal lineage that gives rise to a key component of the larval immune system. During cleavage, signaling from adjacent cells influences a small crescent of cells to initiate a network of genetic interactions that prepare the cells for morphogenesis and specializes them as immunocytes. The cells become active during gastrulation, detach from the epithelium, migrate through the blastocoel, and insert into the ectoderm where they complete their differentiation. Studies of pigment cell development have helped establish how cellular signaling controls networks of genetic interactions that bring about morphogenesis and differentiation. This review summarizes studies of pigment cell development and concludes that pigment cells are an excellent experimental model. Pigment cells provide several opportunities to further test and refine our understanding of the molecular basis of cellular development.

Spectral responses across a dorsal-ventral array of dermal sensilla in the medicinal leech

How do animals use visual systems to extract specific features of a visual scene and respond appropriately? The medicinal leech, Hirudo verbana, is a predatory, quasi-amphibious annelid with a rich sensorium that is an excellent system in which to study how sensory cues are encoded, and how key features of visual images are mapped into the CNS. The leech visual system is broadly distributed over its entire body, consisting of five pairs of cephalic eyecups and seven segmentally iterated pairs of dermal sensilla in each mid-body segment. Leeches have been shown to respond behaviorally to both green and near ultraviolet light (UV, 365–375 nm). Here, we used electrophysiological techniques to show that spectral responses by dermal sensilla are mapped across the dorsal–ventral axis, such that the ventral sensilla respond strongly to UV light, while dorsal sensilla respond strongly to visible light, broadly tuned around green. These results establish how key features of visual information are initially encoded by spatial mapping of photo-response profiles of primary photoreceptors and provide insight into how these streams of information are presented to the CNS to inform behavioral responses.

Progressions on the Coexistence of Neuronal and Glial Precursor Cells in the Cerebral Ventricular Zone

Heterogeneity is defined as the quality or state of being diverse in character or content. This article summarizes the natural progression from my studies, reported in the first issue of the Journal of Neuroscience, that identified molecular heterogeneity in precursor cells of the developing primate cerebral cortex to the current state in which differences defined at the molecular, cellular, circuit, and systems levels are building data encyclopedias. The emphasis on heterogeneity has impacted many contributors in the field of developmental neuroscience, who have led a quest to determine the extent to which there is diversity, when it appears developmentally, and what heritable and nonheritable factors mediate nervous system assembly and function. Since the appearance of the article on progenitor cell heterogeneity in the inaugural issue of the Journal of Neuroscience, there have been continuous advances in technologies and data analytics that are contributing to a much better understanding of the origins of neurobiological and behavioral heterogeneity.

The Development of Rapastinel (Formerly GLYX-13); A Rapid Acting and Long Lasting Antidepressant

Background

Rapastinel (GLYX-13) is a NMDA receptor modulator with glycine-site partial agonist properties. It is a robust cognitive enhancer and shows rapid and long-lasting antidepressant properties in both animal models and in humans.

Methods

Rapastinel was derived from a monoclonal antibody, B6B21, is a tetrapeptide (threonine-proline-proline-threonine-amide) obtained from amino acid sequence information obtained from sequencing one of the hypervariable regions of the light chain of B6B21. The in-vivo and in-vitro pharmacology of rapastinel was examined.

Results

Rapastinel was found to be a robust cognitive enhancer in a variety of learning and memory paradigms and shows marked antidepressant-like properties in multiple models including the forced swim (Porsolt), learned helplessness and chronic unpredictable stress. Rapastinel’s rapid-acting antidepressant properties appear to be mediated by its ability to activate NMDA receptors leading to enhancement in synaptic plasticity processes associated with learning and memory. This is further substantiated by the increase in mature dendritic spines found 24 hrs after rapastinel treatment in both the rat dentate gyrus and layer five of the medial prefrontal cortex. Moreover, ex vivo LTP studies showed that the effects of rapastinel persisted at least two weeks post-dosing.

Conclusion

These data suggest that rapastinel has significant effects on metaplasticity processes that may help explain the long lasting antidepressant effects of rapastinel seen in the human clinical trial results.

Generation of cell type-specific monoclonal antibodies for the planarian and optimization of sample processing for immunolabeling

BACKGROUND

Efforts to elucidate the cellular and molecular mechanisms of regeneration have required the application of methods to detect specific cell types and tissues in a growing cohort of experimental animal models. For example, in the planarian Schmidtea mediterranea, substantial improvements to nucleic acid hybridization and electron microscopy protocols have facilitated the visualization of regenerative events at the cellular level. By contrast, immunological resources have been slower to emerge. Specifically, the repertoire of antibodies recognizing planarian antigens remains limited, and a more systematic approach is needed to evaluate the effects of processing steps required during sample preparation for immunolabeling.

RESULTS

To address these issues and to facilitate studies of planarian digestive system regeneration, we conducted a monoclonal antibody (mAb) screen using phagocytic intestinal cells purified from the digestive tracts of living planarians as immunogens. This approach yielded ten antibodies that recognized intestinal epitopes, as well as markers for the central nervous system, musculature, secretory cells, and epidermis. In order to improve signal intensity and reduce non-specific background for a subset of mAbs, we evaluated the effects of fixation and other steps during sample processing. We found that fixative choice, treatments to remove mucus and bleach pigment, as well as methods for tissue permeabilization and antigen retrieval profoundly influenced labeling by individual antibodies. These experiments led to the development of a step-by-step workflow for determining optimal specimen preparation for labeling whole planarians as well as unbleached histological sections.

CONCLUSIONS

We generated a collection of monoclonal antibodies recognizing the planarian intestine and other tissues; these antibodies will facilitate studies of planarian tissue morphogenesis. We also developed a protocol for optimizing specimen processing that will accelerate future efforts to generate planarian-specific antibodies, and to extend functional genetic studies of regeneration to post-transcriptional aspects of gene expression, such as protein localization or modification. Our efforts demonstrate the importance of systematically testing multiple approaches to species-specific idiosyncracies, such as mucus removal and pigment bleaching, and may serve as a template for the development of immunological resources in other emerging model organisms.

Segmental and regional differences in neuronal expression of the leech Hox genes Lox1 and Lox2 during embryogenesis

Using double immunofluorescence experiments, we described the expression of the leech Hox genes, Lox1 and Lox2 by central neurons that stained for either serotonin or the leech-specific neuronal marker, Laz1-1. The goal is to determine whether the segmental boundaries of Lox1 and Lox2 expression in identified neurons coincide with segmental and regional differences in the differentiation of these cells. A number of neurons described here have been previously identified. The anteromedial serotonergic neurons are restricted to rostral ganglion 1 (R1) to midbody ganglion 3 (M3), but only express Lox1 in M2 and M3. The posteromedial serotonergic neurons which are situated in all segments as bilateral pairs early in development, but later become unpaired starting at M3, expressed Lox1 only in M2 and M3, and Lox2 in M8 to M21, in all paired and unpaired stages. The Retzius neurons, which stain for serotonin, express Lox2 in M7 to M21 where they exhibit different morphologies from their segmental homologs of the sex ganglia in M5 and M6. The Laz1-1 immunoreactive (Laz1-1+) heart accessory-like neurons express Lox1 in M4 and Lox2 in M7 to M17, but not in their segmental homologs of the heart accessory (HA) neurons located exclusively in M5 and M6. Also, Laz1-1+ neurons, which we named Lz3 expressed Lox1 in M4 to M8 where they are unpaired, but express Lox2 in M9 to M16 where they are bilaterally paired. Other Laz1-1 cells show more restricted and isolated Lox1 and Lox2 expression patterns. These results suggest a role of Lox1 and/or Lox2 in defining the anteroposterior boundaries of segmentally iterated neurons.

Phylogenetic conservation of the cell-type-specific Lan3-2 glycoepitope in Caenorhabditis elegans

The biological function of a cell-type-specific glycosylation of an adhesion molecule belonging to the L1CAM immunoglobulin superfamily was previously determined in the nervous system of the embryonic leech, Hirudo medicinalis. The Lan3-2 glycoepitope is a surface marker of sensory afferent neurons and is required for their appropriate developmental collateral branching and synaptogenesis in the CNS. The chemical structure of the Lan3-2 glycoepitope consists of beta-(1,4)-linked mannopyranose. Here, we show the conservation of the cell-type-specific expression of this mannose polymer in Caenorhabditis elegans. The Lan3-2 glycoepitope is expressed on the cell surface of a subset of dissociated embryonic neurons and, in the adult worm, by the pharyngeal motor neuron, M5, and the chemosensory afferents, the amphids. Additionally, the vulval epithelium expresses the Lan3-2 glycoepitope in late L4 larvae and in adult hermaphrodites. To investigate proteins carrying this restrictively expressed glycoepitope, worm extract was immunoaffinity purified with Lan3-2 monoclonal antibody and Western blotted. A polyclonal antibody reactive with the cytoplasmic tail of LAD-1/SAX-7, a C. elegans member of the L1CAM family, recognizes a 270 kDa protein band while Lan3-2 antibody also recognizes a 190 kDa glycoform, its putative Lan3-2 ectodomain. Thus, in C. elegans, as in leech, the Lan3-2 epitope is located on a L1CAM homologue. The cell-type-specific expression of the Lan3-2 glycoepitope shared by leech and C. elegans will be useful for understanding how cell-type-specific glycoepitopes mediate cell-cell interactions during development.

Effects of nerve injury and segmental regeneration on the cellular correlates of neural morphallaxis

Functional recovery of neural networks after injury requires a series of signaling events similar to the embryonic processes that governed initial network construction. Neural morphallaxis, a form of nervous system regeneration, involves reorganization of adult neural connectivity patterns. Neural morphallaxis in the worm, Lumbriculus variegatus, occurs during asexual reproduction and segmental regeneration, as body fragments acquire new positional identities along the anterior-posterior axis. Ectopic head (EH) formation, induced by ventral nerve cord lesion, generated morphallactic plasticity including the reorganization of interneuronal sensory fields and the induction of a molecular marker of neural morphallaxis. Morphallactic changes occurred only in segments posterior to an EH. Neither EH formation, nor neural morphallaxis was observed after dorsal body lesions, indicating a role for nerve cord injury in morphallaxis induction. Furthermore, a hierarchical system of neurobehavioral control was observed, where anterior heads were dominant and an EH controlled body movements only in the absence of the anterior head. Both suppression of segmental regeneration and blockade of asexual fission, after treatment with boric acid, disrupted the maintenance of neural morphallaxis, but did not block its induction. Therefore, segmental regeneration (i.e., epimorphosis) may not be required for the induction of morphallactic remodeling of neural networks. However, on-going epimorphosis appears necessary for the long-term consolidation of cellular and molecular mechanisms underlying the morphallaxis of neural circuitry.

Efficient production of monoclonal antibodies recognizing specific structures in Caenorhabditis elegans embryos using an antigen subtraction method

Monoclonal antibodies (mAbs) have been widely used to probe molecular components of specific cell types or cellular structures. We have developed a method to enrich antigens of low abundance in heterogeneous molecule mixtures by subtracting abundant antigens. The subtracted immunogen mixture is then used for immunization, which significantly increases the production of mAbs that exhibit specific staining patterns. By applying this "antigen subtraction" method to the embryonic extract of Caenorhabditis elegans, we have successfully isolated 35 mAbs that recognize specific structures, including P granules, muscles, the pharynx, and subsets of hypodermal cells; some of the mAbs revealed previously unreported cellular structures. This antigen subtraction approach can be used in various applications to produce mAbs against relatively scarce antigens in complex molecular mixtures. The mAbs will be useful tools for developmental and cell biological studies.

Systematic screening and identification of antigens recognized by monoclonal antibodies raised against the developing lateral olfactory tract

During development, olfactory bulb axons navigate a complex microenvironment composed of myriad molecules to construct a bundle called the lateral olfactory tract. The axons themselves also express thousands of different molecules. In the present study, we produced and characterized six monoclonal antibodies that label the lateral olfactory tract and its surroundings in a unique pattern. The labeling profiles suggested that the antigen molecules recognized by each antibody are heterogeneously distributed around the developing lateral olfactory tract. We developed an efficient screening method to identify the antigen molecules by combining expression of a cDNA library in COS-7 cells and the subsequent immunohistochemical staining of the cells. The systematic screening successfully identified specific cDNA clones for all of the monoclonal antibodies, which highly probably coded for the antigen molecules, and therefore unveiled the molecular nature of local components that embrace the developing lateral olfactory tract in mice.

Regeneration and asexual reproduction share common molecular changes: upregulation of a neural glycoepitope during morphallaxis in Lumbriculus

Neural morphallaxis is a regenerative process characterized by wide-spread anatomical and physiological changes in an adult nervous system. During segmental regeneration of the annelid worm, Lumbriculus variegatus, neural morphallaxis involved a reorganization of sensory, interneuronal, and motor systems as posterior fragments gained a more anterior body position. A monoclonal antibody, Lan 3-2, which labels a neural glyco-domain in the leech, was reactive in Lumbriculus. In the worm, this antibody labeled neural structures, particularly axonal tracts and giant fiber pathways of the central nervous system. A 60kDa protein, possessing a lumbriculid mannose-rich glycoepitope, was upregulated during neural morphallaxis, peaking in its expression at 3 weeks post-amputation. Peak upregulation of the Lan 3-2 epitope, or the protein possessing it, corresponded to the time of major neurobehavioral plasticity during regeneration. Analyses of asexually reproducing animals also revealed induction of the Lan 3-2 epitope. In this developmental context, Lan 3-2 epitope upregulation was also confined to segments expressing both changes in positional identity and neurobehavioral plasticity, but these molecular and behavioral changes occurred prior to body fragmentation. These results suggest that the lumbriculid Lan 3-2 glycoepitope and proteins that bear them have been co-opted for neural morphallactic programs, induced both in anticipation of reproductive fragmentation and in compensation for injury-induced fragmentation.

Leech filamin and Tractin: markers for muscle development and nerve formation

The Lan3-14 and Laz10-1 monoclonal antibodies recognize a 400 kDa antigen that is specifically expressed by all muscle cells in leech. We show that the antigen recognized by both antibodies is a member of the filamin family of actin binding proteins. Leech filamin has two calponin homology domains and 35 filamin/ABP-repeat domains. In addition, we used the Laz10-1 antibody to characterize the development of the segmentally iterated dorsoventral flattener muscles. We demonstrate that the dorsoventral flattener muscle develops as three discrete bundles of myofibers and that CNS axons pioneering the DP nerve extend only along the middle bundle. Interestingly, the middle dorsoventral muscle anlage is associated with only non-neuronal expression of the L1-family cell adhesion molecule Tractin. This expression is transient and occurs at the precise developmental stages when DP nerve formation takes place. Based on these findings we propose that the middle dorsoventral muscle anlagen provides a substrate for early axonal outgrowth and nerve formation and that this function may be associated with differential expression of distinct cell adhesion molecules.

Cell interactions that affect axonogenesis in the leech Theromyzon rude

The leech nervous system comprises a relatively simple network of longitudinal (connective) and transverse (segmental) nerves. We have followed the normal pattern of axon development in the glossiphoniid leech Theromyzon rude by immunostaining embryonic preparations with antibody to acetylated alpha-tubulin. The dependence of the normal pattern of axon growth on cells in the mesodermal (M) and ectodermal (N, O, P and Q) lineages was examined by selectively ablating subsets of these lineages in developing embryos. We found that ablating mesoderm severely disrupted overall axonogenesis, while various ectodermal ablations induced a range of more specific phenotypes. In particular, formation of the posterior segmental nerve (PP) was abnormal in embryos deficient in primary neuroectoderm (N lineage). More specific ablations demonstrated that a subset of N-derived cells were required for establishing the PP nerve root. Previous studies have shown that the PP nerve root is normally pioneered by an O lineage-derived neuron (PD). Our results suggest that the role of the N lineage-derived cells is to induce the migration of neuron P(D) to its normal position in the posterior compartment of the hemiganglion.

A monoclonal antibody specific to a song system nuclear antigen in estrildine finches

This paper describes a monoclonal antibody that recognizes a molecule whose expression is mostly restricted to some of the forebrain areas that control singing behavior in adult estrildine species studied, including the zebra, Bengalese, and spice finches. When the song system displays extreme sexual dimorphism, as in these species, antibody staining occurs only in the male's song nuclei. However, protein expression is identical in both sexes of estrildine finches, in which females also have a well-developed song system. Canaries appear to lack the protein, but it can be induced in female zebra finches by early estrogen treatment. Antibody staining patterns in the zebra finch show that the protein's expression is developmentally regulated to coincide with the abrupt increase in the volume and cell size of the male's or the estrogen-treated female's song system.

Is song special?

Akutagawa and Konishi (2001)([this issue of Neuron]) describe the spatial and temporal pattern of SNAg (song system nuclear antigen) expression within a subset of song-associated forebrain nuclei of grass finches. The timing and estrogen inducibility of SNAg expression suggest that it may function in establishing neural connections key to vocal learning.

Molecular identification and sequence analysis of Hillarin, a novel protein localized at the axon hillock

The monoclonal antibody Lan3-15 identifies a novel protein, Hillarin, that is localized to the axon hillock of leech neurons. Using this antibody we have identified a full length cDNA coding for leech Hillarin and determined its sequence. The gene encodes a 1274 residue protein with a predicted molecular mass of 144013 Da. Data base searches revealed that leech Hillarin has potential orthologues in fly and nematode and that these proteins share two novel protein domains. The W180 domain is characterized by five conserved tryptophans whereas the H domains share 21 invariant residues. In contrast to the arrangement in fly and nematode the cassette containing the W180 and H domains is repeated twice in leech Hillarin. This suggests that the leech Hillarin sequence originated from a duplication event of an ancestral protein with single cassette structure.

Neuronal growth and target recognition: lessons from the leech

The nervous system of the leech has been the subject of numerous studies since its "rediscovery" in the 1960s as a unique system for the study of the properties of glial cells. Subsequently, anatomical, physiological, and embryological studies of identified neurons have yielded a wealth of information about the differentiation of neuronal structure and function. In recent years, cellular approaches to the development of identified central and peripheral neurons have been complemented by molecular studies that promise to reveal the mechanisms by which neurons form their complex arbors and innervate specific targets.

Posttranslational processing and differential glycosylation of Tractin, an Ig-superfamily member involved in regulation of axonal outgrowth

Tractin is a novel member of the Ig-superfamily which has a highly unusual structure. It contains six Ig domains, four FNIII-like domains, an acidic domain, 12 repeats of a novel proline- and glycine-rich motif with sequence similarity to collagen, a transmembrane domain, and an intracellular tail with an ankyrin and a PDZ domain binding motif. By generating domain-specific antibodies, we show that Tractin is proteolytically processed at two cleavage sites, one located in the third FNIII domain, and a second located just proximal to the transmembrane domain resulting in the formation of four fragments. The most NH(2)-terminal fragment which is glycosylated with the Lan3-2, Lan4-2, and Laz2-369 glycoepitopes is secreted, and we present evidence which supports a model in which the remaining fragments combine to form a secreted homodimer as well as a transmembrane heterodimer. The extracellular domain of the dimers is mostly made up of the collagen-like PG/YG-repeat domain but also contains 11/2 FNIII domain and the acidic domain. The collagen-like PG/YG-repeat domain could be selectively digested by collagenase and we show by yeast two-hybrid analysis that the intracellular domain of Tractin can interact with ankyrin. Thus, the transmembrane heterodimer of Tractin constitutes a novel protein domain configuration where sequence that has properties similar to that of extracellular matrix molecules is directly linked to the cytoskeleton through interactions with ankyrin.

Ectopic CNS projections guide peripheral neuron axons along novel pathways in leech embryos

Previous studies have indicated that the formation of stereotyped segmental nerves in leech embryos depends on the interactions between CNS projections and ingrowing afferents from peripheral neurons. Especially, CNS-ablation experiments have suggested that CNS-derived guidance cues are required for the correct navigation of several groups of peripheral sensory neurons. In order to directly test this hypothesis we have performed transplantations of CNS ganglia into ectopic sites in segments from which the resident ganglia have been removed. We find that the transplanted ganglia extend numerous axons distributed roughly equally in all directions. When these CNS projections reach and make contact with peripheral sensory axons they are used as guides for peripheral neurons to grow toward and into the ectopic ganglia even when this means following novel pathways that cross the midline and/or segmental boundaries. The peripheral sensory axons turn and grow toward the ectopic ganglia only when in physical contact with CNS axons, suggesting that diffusible chemoattractants are not a factor. These results demonstrate that the guidance cues provided by ectopic CNS projections are both necessary and sufficient to steer peripheral sensory neuron axons into the CNS.

Sequential steps in synaptic targeting of sensory afferents are mediated by constitutive and developmentally regulated glycosylations of CAMs

Sensory afferents in the leech are labeled with both constitutive and developmentally regulated glycosylations (markers) of their cell adhesion molecules (CAMs). Their constitutive mannose marker, recognized by Lan3-2 monoclonal antibody (mAb), mediates the formation of their diffuse central arbors. We show that, at the ultrastructural level, these arbors consist of large, loosely organized axons rich with filopodia and synaptic vesicles. Perturbing the mannose-specific adhesion of this first targeting step leads to a gain in cell-cell contact but a loss of filopodia and synaptic vesicles. During the second targeting step, galactose markers divide afferents into different subsets. We focus on the subset labeled by the marker recognized by Laz2-369 mAb. Initially, the galactose marker appears where afferents contact central neurons. Subsequently it spreads proximally and distally, covering the entire afferent surface. Afferents now gain cell-cell contact, with central neurons and self-similar afferents, but lose filopodia and synaptic vesicles. Extant synaptic vesicles prevail where afferents are apposed to central neurons. These neurons develop postsynaptic densities and en passant synapses are forming. Perturbing the galactose-specific adhesion of this second targeting step causes a loss of cell-cell contact but a gain in filopodia and synaptic vesicles, essentially returning afferents to the first targeting step. The transformation of afferent growth, progressing from mannose- to galactose-specific adhesion, is consistent with a change from cell-matrix to cell-cell adhesion. By performing opposing functions in a temporal sequence, constitutive and developmentally regulated glycosylations of CAMs collaborate in the synaptogenesis of afferents and the consolidation of self-similar afferents.

Gliarin and macrolin, two novel intermediate filament proteins specifically expressed in sets and subsets of glial cells in leech central nervous system

Using monoclonal antibodies, we have identified two novel intermediate filament (IF) proteins, Gliarin and Macrolin, which are specifically expressed in the central nervous system of an invertebrate. The two proteins both contain the coiled-coil rod domain typical of the superfamily of IF proteins flanked by unique N- and C-terminal domains. Gliarin was found in all glial cells including macro- and microglial cells, whereas Macrolin was expressed in only a single pair of giant connective glial cells. The identification of Macrolin and Gliarin together with the characterization of the strictly neuronal IF protein Filarin in leech central nervous system demonstrate that multiple neuron- and glial-specific IFs are not unique to the vertebrate nervous system but are also found in invertebrates. Interestingly, phylogenetic analysis based on maximum parsimony indicated that the presence of neuron- and glial cell-specific IFs in coelomate protostomes as well as in vertebrates is not of monophyletic origin, but rather represents convergent evolution and appears to have arisen independently.

Mannose-specific recognition mediates two aspects of synaptic growth of leech sensory afferents: collateral branching and proliferation of synaptic vesicle clusters

The developmental role of carbohydrate markers in the genesis of neuronal networks was studied using leech sensory afferents as a model. Leech sensory afferents express a mannose-containing epitope on their cell surface that is recognized by monoclonal antibody Lan3-2. Previously, the elaboration of sensory arbors in the synaptic neuropil of CNS ganglia was experimentally shown to depend on this mannose marker. Sensory arbors were abolished by perturbing sensory afferents in the intact nervous system with Lan3-2 Fab fragments, a glycosidase, or mannose-BSA. To understand the cytological mechanisms underlying mannose-specific recognition for synaptogenesis, we have now studied the effects of antibody perturbation at the ultrastructural level in the sensory afferent target region. A characteristic signature of a normal sensory afferent is its profuse collateral branching, which, with ongoing development, is replaced by a single widened process, the sensory trunk, which possesses numerous synaptic vesicle clusters. The inhibition of mannose-specific recognition leads to a rapid, major reorganization of different stages of sensory afferent growth. Collateral branches at the distal growing region are reduced three- to fourfold. The pruned axons grow at an accelerated rate. Developmentally older sensory trunks experience a threefold reduction in synaptic vesicle clusters. These responses suggest that depriving sensory afferents of mannose-specific recognition aborts their synaptogenesis and causes them to resume behavior typical of tracking through axonal tracts. The current findings also suggest that the mannose marker, by promoting both collateral branching andthe proliferation of synaptic vesicle clusters, plays a critical role in two stages of sensory afferent synaptogenesis.

Differential glycosylation of tractin and LeechCAM, two novel Ig superfamily members, regulates neurite extension and fascicle formation

By immunoaffinity purification with the mAb Lan3-2, we have identified two novel Ig superfamily members, Tractin and LeechCAM. LeechCAM is an NCAM/FasII/ApCAM homologue, whereas Tractin is a cleaved protein with several unique features that include a PG/YG repeat domain that may be part of or interact with the extracellular matrix. Tractin and LeechCAM are widely expressed neural proteins that are differentially glycosylated in sets and subsets of peripheral sensory neurons that form specific fascicles in the central nervous system. In vivo antibody perturbation of the Lan3-2 glycoepitope demonstrates that it can selectively regulate extension of neurites and filopodia. Thus, these experiments provide evidence that differential glycosylation can confer functional diversity and specificity to widely expressed neural proteins.

Modulation and selection of neurotransmitter responses during synapse formation between identified leech neurons

1. Serotonin (5-HT) modulates two different responses in the pressure sensitive neurons (P) of the leech: an inhibitory, Cl- dependent synaptic response and a depolarizing extrasynaptic response. 2. Serotonergic Retzius cells (R) in vivo and in culture elicit inhibitory Cl- dependent responses in P neurons. Moreover, at discrete sites of contact between R and P cells, the excitatory response to 5-HT is gradually lost prior to synapse formation. This phenomenon is specifically mediated by R cells. 3. The extrasynaptic response is mediated by cation channels sensitive to protein kinase C (PKC). Cation channels are present at the sites of contact but they become insensitive to PKC. Moreover, cation channels from single P cells are no longer modulated by PKC if they are inserted (by cramming the patch pipette) into the cytoplasm of a P cell in contact with an R cell. 4. Blockers of tyrosine kinases prevent the uncoupling of cation channel modulation and inhibit synapse formation between the R and the P neurons. 5. We suggest that cell contact induces an intracellular, tyrosine kinase-dependent signal as part of the mechanism of neuronal recognition leading to synapse formation.

Initial formation and secondary condensation of nerve pathways in the medicinal leech

Invertebrates have proved to be important experimental systems for examining questions related to growth cone navigation and nerve formation, in large part because of their simpler nervous systems. However, such apparent simplicity can be deceiving because the final stereotyped patterns may be the result of multiple developmental mechanisms and not necessarily the sole consequence of the pathway choices of individual growth cones. We have examined the normal sequence of events that are involved in the formation of the major peripheral nerves in leech embryos by employing (1) an antibody directed against acetylated tubulin to label neurons growing out from the central nervous system, (2) the Lan3-2 antibody to label a specific population of peripheral neurons growing into the central nervous system, and (3) intracellular dye filling of single cells. We found that the mature pattern of nerves was characterized by a pair of large nerve roots, each of which branched into two major tracts. The earliest axonal projections did not, however, establish this pattern definitively. Rather, each of the four nerves initially formed as discrete, roughly parallel tracts without bifurcation, with the final branching pattern of the nerve roots being generated by a secondary condensation. In addition, we found that some of the nerves were pioneered in different ways and by different groups of neurons. One of the nerves was established by central neurons growing peripherally, another by peripheral neurons growing centrally. These results suggest that the formation of common nerves and neuronal pathfinding in the leech involves multiple sets of growth cone guidance strategies and morphogenetic mechanisms that belie its apparent simplicity.

Leech photoreceptors project their galectin-containing processes into the optic neuropils where they contact AP cells

We characterized a subset of leech sensory afferents, the photoreceptors, in terms of their molecular composition, anatomical distribution, and candidate postsynaptic partners. For reagents, we used an antiserum generated against purified LL35, a 35 kD leech lactose-binding protein (galectin); monoclonal antibody (mAb) Lan3-2, which is specific for a mannose-containing epitope common to the full set of sensory afferents; and dye injections. Photoreceptors differ from other types of sensory afferents by their abundant expression of galectin. However, photoreceptors share in common with other sensory modalities the mannose-containing epitope recognized by mAb Lan3-2. Photoreceptors from a given segment project their axons directly into the CNS ganglion innervating the same segment. They assemble in a target region, the optic neuropil, which is separate from the target regions of other sensory modalities. They also extend their axons as an optic tract into the connective to innervate optic neuropils of other CNS ganglia, thereby providing extensive intersegmental innervation for the 33 CNS ganglia comprising the leech nerve cord. Because of its intimate contact with the optic neuropil, a central neuron, the AP effector cell, is a strong candidate second order visual neuron. In confocal images, the AP cell projects its primary axon for about 100 microns alongside the optic neuropil. In electron micrographs, spines emanating from the axon of the AP cell make contact with vesicle laden nerve terminals of photoreceptors. Leech photoreceptors and their second order visual neurons represent a simple visual system for studying the mechanisms of axonal targeting.

Monoclonal antibodies as tools for studying the osteoblast lineage

Knowledge of the number and kinds of differentiation steps characterizing cells of the osteoblast lineage is inadequate. To analyze further osteoblast differentiation, a number of labs have generated monoclonal antibodies to osteogenic cells, derived from both normal bone and osteosarcomas. A variety of immunolabelling patterns on primary cell cultures, cell lines, and tissue sections has been reported, including cell surface, cytoplasmic, and extracellular matrix-associated patterns. Most of the antibodies selected recognize predominantly the mature osteoblast and osteocyte; in addition, however, antibodies have been generated that recognize pre-osteoblasts. Some recognize cells of both the osteoblast and chondroblast lineages and may contribute to a better understanding of the lineage and phenotypic relationships between these two cell types. In addition to recognition in vivo of cell subpopulations of discrete maturational stages, changes in the immunolabelling patterns in vitro have also documented a differentiation sequence in cells undergoing osteogenesis in cell and tissue cultures. In at least two cases, the antibodies have been used to isolate subpopulations of cells from bone, including relatively pure populations of osteocytes. With the exception of several antibodies that are against alkaline phosphatase or known matrix proteins including osteocalcin, the nature of the macromolecular species recognized by most of the antibodies generated to date are unknown. Recently, however, one antibody was used to clone the cDNA for the beta-galactoside-binding lectin, galectin 3 or epsilon binding protein (epsilon BP; IgE-binding protein; Mac-2), from a lambda gt11 osteoblast expression library; another was used to clone from an ROS 17/2.8-COS cell expression library the cDNA for OTS-8, a putative target gene of early response genes stimulated in response to phorbol esters in MC3T3-E1 cells. Neither of these macromolecules had previously been identified in bone cells, but the recent molecular and cellular analyses have shown them to be developmentally and/or hormonally regulated in osteoblastic cells. These antibodies extend the available markers and support earlier observations that a variety of molecules are differentially expressed by cells at different stages of the osteoblast lineage. This chapter will not be an exhaustive survey of all immunocytochemical and immunohistochemical analyses of osteogenic cells and tissues but will focus on the approach of eliciting novel monoclonal antibodies by the injection of osteogenic cells or crude bone extracts and its potential for establishing new markers of the osteoblast lineage. We have not included a large number of studies documenting the use of antibodies raised against several known bone matrix proteins; while these have been crucial in developing our current understanding of osteogenic differentiation, we sought rather to highlight the potential of the "random" injection approach.

Generating a phage display antibody library against an identified neuron

The generation of monoclonal antibodies by conventional hybridoma technology is limited by the diversity of the clones and the difficulties of screening the antibodies and of their large-scale production from isolated clones. As an alternative approach, we have investigated the suitability of phage display libraries for the production of recombinant antibodies against an identified neuron. Mice were immunized with isolated leech Retzius (R) neurons. The spleen poly A+ RNA was isolated and first-strand cDNA was prepared. The variable regions of light- and heavy-chain IgG molecules were amplified by the polymerase chain reaction (PCR) and separate libraries of each were constructed and combined in the pComb8 vector to yield a combinatorial library of approximately 10(7) transformants. Single R neurons that were plated in culture bound approximately 100 phages on a first screen and several thousand when the first batch was re-screened. Of these, 96 individual phage colonies were isolated and used for immunocytochemistry with leech CNS ganglia: 41 exhibited general staining, 20 showed no detectable staining and 30 stained selective subsets of neurons including (but not specific for) the R neuron. The phage display library approach thus simplifies the screening of large libraries with small numbers of (and even single) cells. However, the combinatorial antibodies with binding activity must still be tested individually by immunocytochemistry, which is further limited by their apparently low affinity.

Distribution of limbic system-associated membrane protein immunoreactivity in primate basal ganglia

The limbic system-associated membrane protein is a 64,000-68,000 mol.wt molecule known to be preferentially expressed by neurons in limbic structures of rats and cats. The present immunohistochemical study describes the distribution of this protein in the basal ganglia of Macaca fascicularis. The ventral striatum of the cynomolgus monkey displays a very intense immunostaining, whereas the dorsal striatum is much more weakly stained, except for some small zones scattered in the caudate nucleus and, to a lesser extent, in the putamen. These protein-rich zones are in register with striosomes, as visualized on adjacent sections immunostained for calbindin. At pallidal levels, immunostaining for the protein is observed only in the subcommissural regions, at the ventromedial tip of the internal pallidum, and in the caudoventral portion of the external pallidum. At nigral levels, the immunostaining is highly heterogeneous with a marked decreasing rostrocaudal gradient. The staining is most intense in nigral regions that receive striatal inputs and are enriched with calbindin. Nigral sectors populated by dopaminergic neurons, as visualized on adjacent sections immunostained for tyrosine hydroxylase, are largely devoid of immunoreactivity. In contrast, the immunostaining is uniformly intense in the ventral tegmental area. This study provides the first neuroanatomical evidence for teh existence of the limbic system-associated membrane protein in primate brain. It reveals that this glycoprotein is distributed in a highly heterogeneous manner in primate basal ganglia, where it preferentially labels regions that are anatomically and functionally linked to the limbic system.

Multiple strategies for directed growth cone extension and navigation of peripheral neurons

Leeches have a diverse constellation of peripheral neural elements that are challenged to extend growth cones in highly specific ways in a constantly changing embryonic environment. Two major systems are reviewed here. In one, peripheral afferents extend growth cones toward the central nervous system (CNS), forming common pathways, and then segregate into particular tracts within the CNS. A majority of these afferents depend on CNS-derived guidance cues and projections from the CNS to guide their way. However, not all of the nerves are established this way and at least one of the peripheral nerves is likely to be pioneered by sensillar sensory afferents. The distribution of particular antigens (such as the lan3-2 antigen) suggests the identity of molecules involved in homophilic adhesion along common pathways, whereas others (such as the lan4-2 and 3-6 antigens) are candidates for mediating specific pathway choices. In the second system, the myo-organizing Comb cell (C cell) projects multiple growth cones simultaneously along oblique trajectories not influenced by segmental or midline boundaries. Its parallel growth cones exhibit space-filling as well as directional growth and are guided by local cues to extend in discrete phases that are coordinated with the development of the environment. Both systems exhibit highly directed outgrowth orchestrated by a hierarchy of cues, establish patterns of neurites used to direct later migrating cells, and seem to be regulated temporally and spatially by interactions with the embryonic environment. These systems illustrate the strengths of examining neural development in vivo across several levels of analysis.

Synapse formation and function: insights from identified leech neurons in culture

Identified leech neurons in culture are providing novel insights to the signals underlying synapse formation and function. Identified neurons from the central nervous system of the leech can be removed individually and plated in culture, where they retain their characteristic physiological properties, grow neurites, and form specific synapses that are directly accessible by a variety of approaches. Synapses between cultured neurons can be chemical or electrical (either rectifying or not) or may not form, depending on the neuronal identities. Furthermore, the characteristics of these synapses depend on the regions of the cells that come into contact. The formation and physiology of synapses between the Retzius cell and its partners have been well characterized. Retzius cells form purely chemical, inhibitory synapses with pressure-sensitive (P) cells where serotonin (5-HT) is the transmitter. Retzius cells synthesize 5-HT, which is stored in vesicles that recycle after 5-HT is secreted on stimulation. The release of 5-HT is quantal, calcium-dependent, and shows activity-dependent facilitation and depression. Anterograde and retrograde signals during synapse formation modify calcium currents, responses to 5-HT, and neurite outgrowth. The nature of these synaptogenic signals is being elucidated. For example, contact specifically with Retzius cells induces a localized selection of transmitter responses in postsynaptic P cells. This effect is signaled by tyrosine phosphorylation prior to synapse formation.

Sequential steps in axonal targeting are mediated by carbohydrate markers

Mannose and hybrid/complex-type oligosaccharides serve as markers for both the full set of peripheral sensory afferent neurons in the leech and also for disjoint subsets of these neurons. We have shown that these various surface carbohydrates play crucial roles in the multistep process by which afferents meet their synaptic partners in the central nervous system (CNS). The carbohydrate marker common to all these afferents allows their projections (which are fasciculated as they enter the CNS) to disperse and search out target regions. Carbohydrate markers specific for subsets of these afferents subsequently allow each subset to consolidate the position of its projections in appropriate regions of the CNS where it contacts its synaptic partners.

Filarin, a novel invertebrate intermediate filament protein present in axons and perikarya of developing and mature leech neurons

The lan 3-8 monoclonal antibody recognizes a 63 kD antigen that is associated with the cytoskeleton in leech neurons. We have used this antibody to clone a novel invertebrate neuronal intermediate filament protein, filarin, by screening an expression vector library. A full-length clone of 2.2 kb identified by the antibody was isolated and sequenced. The protein contains a coiled-coil rod domain typical of the superfamily of intermediate filament proteins flanked by unique N- and C-terminal domains. The highest homology of filarin is to the alternatively spliced squid brain intermediate filament protein (Szaro et al., 1991, J. Biol. Chem. 266:15035-15041), the only other invertebrate neuronal intermediate filament in the data bank. However, apart from extensive homology in the two end regions of the rod domain, the similarity of the two proteins is limited to the general coiled-coil structure of intermediate filaments. Thus, filarin may represent a novel type of invertebrate neuronal intermediate filament protein. Filarin contains the extra 6 heptads characteristic of lamins and of all cytoplasmic invertebrate intermediate filaments analyzed so far. By Northern analysis, it appears that filarin is not alternatively spliced, since only a single transcript of 2.2 kb is recognized by the clone. Using the lan 3-8 antibody to follow its developmental expression, we found that filarin is present in all known neurons in the central and peripheral nervous system.

Calsensin: a novel calcium-binding protein expressed in a subset of peripheral leech neurons fasciculating in a single axon tract

The mAb lan3-6 recognizes a cytosolic antigen which is selectively expressed in the growth cones and axons of a small subset of peripheral sensory neurons fasciculating in a single tract common to all hirudinid leeches. We have used this antibody to clone a novel EF-hand calcium-binding protein, calsensin, by screening an expression vector library. A full-length clone of 1.1 kb identified by the antibody was isolated and sequenced. In situ hybridizations with calsensin probes and antibody staining using new polyclonal antisera generated against calsensin sequence demonstrate that calsensin indeed corresponds to the lan3-6 antigen. Calsensin consists of 83 residues with a calculated molecular mass of 9.1 kD that contains two helix-loop-helix domains. The calcium-binding domains are likely to be functional in vivo since a fusion protein derived from the calsensin clone binds 45Ca2+ in vitro. Immunoaffinity purification experiments with the lan3-6 antibody shows that a large 200,000 M(r) protein selectively copurifies with calsensin in two different leech species. These results suggest that calsensin may be functioning as a trigger protein which interacts with the larger protein. These data are consistent with the hypothesis that calsensin may mediate calcium-dependent signal transduction events in the growth cones and axons of this small group of sensory neurons which fasciculate in a single axon tract.

Targeting of neuronal subsets mediated by their sequentially expressed carbohydrate markers

The targeting of sensory afferent neurons in the leech CNS occurs in two discrete steps that are mediated via different carbohydrate recognitions, as shown by molecular perturbations of cultured embryos. A constitutive carbohydrate marker that is generic to all of these neurons mediates their initial defasciculation and arborization across the entire target region via mannose-specific recognition. Subsequently, two subsets of these same neurons can be differentiated by their expression of other markers that are located on hybrid or complex type carbohydrate chains. These developmentally regulated carbohydrate markers then mediate the target assembly of their respective neuronal subsets into discrete subregions. Thus, by performing opposing functions in a temporal sequence, constitutive and developmentally regulated carbohydrate markers collaborate in the targeting of neuronal subsets in the CNS.

Regeneration and post-metamorphic development of the central nervous system in the protochordate Ciona intestinalis: a study with monoclonal antibodies

In this study, we use three monoclonal antibodies that recognise antigens present in the central nervous system of the ascidian Ciona intestinalis to study regeneration and post-metamorphic development of the neural ganglion. We have also used bromodeoxyuridine labelling to study generation of the neuronal precursor cells. The first antibody, CiN 1, recognises all neurones in the ganglion, whereas the second, CiN 2, recognises only a subpopulation of the large cortical neurones. Western blotting studies show that CiN 2 recognises two membrane-bound glycoproteins of apparent Mr 129 and 100 kDa. CiN 1 is not reactive on Western blots. Immunocytochemical studies with these antibodies show that CiN 1-immunoreactive neurone-like cells are present at the site of regeneration as early as 5-7 days post-ablation, a sub-population of CiN 2-immunoreactive cells being detected by 9-12 days post-ablation. The third antibody, ECM 1, stains extracellular matrix components and recognises two diffuse bands on Western blots of whole-body and ganglion homogenates. The temporal and spatial pattern of appearance of CiN 1 and CiN 2 immunoreactivity both during post-metamorphic development and in regeneration occurs in the same sequence in both processes. Studies with bromodeoxyuridine show labelled nuclei in some neurones in the regenerating ganglion. Plausibly these originate from the dorsal strand, an epithelial tube that reforms by cell proliferation during the initial phases of regeneration. A second population of cells, the large cortical neurones, do not incorporate bromodeoxyuridine and thus must have been born prior to the onset of regeneration. This latter finding indicates a mechanism involving trans-differentiation of other cell types or differentiation of long-lived totipotent stem cells.

Target-induced neurogenesis in the leech CNS involves efferent projections to the target

During a critical period in leech embryogenesis, the sex nerves that connect the 5th and 6th midbody ganglia (MG5 and MG6) to the primordium of the male sexual organ carry a spatially localized signal that induces the birth of several hundred neurons specific to these ganglia. We examined particular cellular elements (afferents, efferents, non-neuronal components) within these nerves as potential conveyors of the inductive signal. We show that axons of peripheral sensory neurons in the male genitalia travel along the sex nerves and into MG5 and MG6, but reach the CNS after the critical period has elapsed and cannot, therefore, be involved in the induction. Of the six sex nerves, four contain non-neuronal cells that span the entire distance between the male genitalia and the sex ganglia. However, when male genitalia were transplanted to ectopic locations close to MG6, induction occurred frequently but only in MG6, mediated by ectopic nerves that do not contain these cells. Thus, non-neuronal cells specific to the normal sex nerves are not necessary for induction. In addition, dye injections into the target during the critical period failed to reveal migrating cells in the sex nerves that could convey the inductive signal to the CNS. Finally, we show that 11 pairs of central neurons in each ganglion project to the male organ early during the critical period. In the adult, at least 3 additional pairs of neurons in MG6 also innervate this target. We conclude that the only components of the sex nerves that connect the sex ganglia to the target during the critical period that could be associated with induced central mitogenesis are the axons of central neurons that innervate the male genitalia.

Specific pathway selection by the early projections of individual peripheral sensory neurons in the embryonic medicinal leech

In leech, the central annulus of each midbody segment possesses seven pairs of sensilla, which are mixed clusters of primary peripheral sensory neurons that extend their axons into the CNS where they segregate into distinct fascicles. Pathway selection by individual afferent growth cones of sensillar neurons was examined by double labeling using intracellular dye-filling with antibody labeling in early Hirudo medicinalis embryos. The monoclonal antibody Lan3-2 was used because sensillar neuronal tracts are specifically labeled by this antibody. Examining 68 individually filled neurons we found that sensillar neuron growth cones bifurcate within the CNS, that they project long filopodia capable of sampling the local environment, and that all of them appeared to choose a single particular CNS fascicle without apparent retraction or realignment of growth cones. Furthermore, each side of the bifurcating afferent growth cones always chose the same fascicle, implying a specific choice of a distinct labeled pathway. By dye-filling individual central neurons (P-cells), we show that there are centrally projecting axons present at the time sensillar afferents enter the ganglionic primordia and select a particular fascicle, and we confirm that at least the dorsal peripheral nerve is likely to be pioneered by central neurons, not by the peripheral afferents. In the sensillum studied here, we found examples of sensory neurons extending axons into one of all the available fascicles. Thus, an individual embryonic sensillum possesses a heterogeneous population of afferents with respect to the central fascicle chosen. This is consistent with the idea that segregation into distinct axon fascicles may be based upon functional differences between individual afferent neurons. Our findings argue strongly in favor of specific pathway selection by afferents in this system and are consistent with previous suggestions that there exists a hierarchy of cues, including surface glycoconjugates that mediate navigation of the sensillar growth cones and the fasciculation of their axons.

Early embryonic expression of a 60-kD glycoprotein in the developing nervous system of the lobster

To investigate the developmental processes that generate the crustacean nervous system, we used a monoclonal antibody that recognises an antigen that is expressed in the developing embryonic nervous system of the lobster, Homarus gammarus. Expression of this antigen commences early in embryogenesis, occurs in all parts of the embryonic central and peripheral nervous systems, and continues into adulthood. Initial expression in the central nervous system correlates with the onset of neuronal process outgrowth. Light microscopic analysis shows that the antigen is found surrounding the cell bodies and processes of all neurons. Biochemical analysis indicates that the antigen is a glycoprotein with an apparent molecular weight of 60 kD. Due to the early embryonic onset of its expression, this antigen is a useful cellular label for visualisation of pattern formation in the developing nervous system; this is documented in detail for the developing stomatogastric nervous system. The fact that the 60-kD antigen is expressed early in embryogenesis throughout the nervous system suggests that it might play an important role in the development of the lobster nervous system.

Cell surface contact mediates neuronal recognition and synapse formation between two identified leech neurons

An early event in the formation of the serotonergic synapse by the Retzius (R) onto the pressure-sensitive (P) neurons of the leech is the elimination of an extrasynaptic response to transmitter from sites of contact on the postsynaptic cell. This event during synapse formation is cell-specific in that it is elicited in vitro by contact with the presynaptic R cell but not with other neurons. In the study reported here, we investigated the nature of this interaction between R and P neurons. The loss of the extrasynaptic response of the P cell was elicited by contact with R cells fixed in a mild paraformaldehyde solution, but not by R cells treated with the proteolytic enzyme trypsin prior to fixation. As well, a variety of lectins were assayed for their ability to interfere with synapse formation. The transmitter responses of P cells plated on lectin-coated substrates were unaffected. However, exposure of the R cell to the lectin wheat germ agglutinin (WGA), but not to other lectins, prior to pairing prevented the loss of the extrasynaptic response in contacted P cells and blocked the formation of the R-P synapse in culture. We conclude that recognition by the P cell of the R cell during synapse formation may be mediated by an R cell-specific surface protein which binds wheat germ agglutinin.

Ultrastructure of an identified array of growth cones and possible substrates for guidance in the embryonic medicinal leech, Hirudo medicinalis

The oblique muscle organizer (Comb- or C-cell) in the embryonic medicinal leech, Hirudo medicinalis, provides an amenable situation to examine growth cone navigation in vivo. Each of the segmentally iterated C-cells extends an array of growth cones through the body wall along oblique trajectories. C-cell growth cones undergo an early, relatively slow period of extension followed by later, protracted and rapid directed outgrowth. During such transitions in extension, guidance might be mediated by a number of factors, including intrinsic constraints on polarity, spatially and temporally regulated cell and matrix interactions, physical constraints imposed by the environment, or guidance along particular cells in advance of the growth cones. Growth cones and their environment were examined by transmission electron microscopy to define those factors that might play a significant role in migration and guidance in this system. The ultrastructural examination has made the possibility very unlikely that simple, physical constraints play a prominent role in guiding C-cell growth cones. No anatomically defined paths or obliquely aligned channels were found in advance of these growth cones, and there were no identifiable physical boundaries, which might constrain young growth cones to a particular location in the body wall before rapid extension. There were diverse associations with many matrices and basement membranes located above, below, and within the layer in which growth cones appear to extend at the light level. Additionally, a preliminary examination of myocyte assembly upon processes proximal to the growth cones further implicates a role for matrix-associated interactions in muscle histogenesis as well as process outgrowth during embryonic development.

Monoclonal antibody labels olfactory and visual pathways in Drosophila and Apis brains

We employed a monoclonal antibody raised against Drosophila brain homogenate for a comparative immunocytochemical analysis of visual and olfactory pathways in brains of two insect species. On Western blots of Drosophila and Apis nervous tissue, antibody fb45 recognized an antigen with an apparent molecular weight higher than 180 kD. Application of the antibody to sections of Drosophila and Apis brain stained certain interneurons which conspicuously fasciculate in common tracts or neuropilar compartments. Both in Drosophila and in Apis, the antigen was also expressed on the perineural sheath and granular cell compartments in the majority of neuronal cell bodies. The antibody stained monopolar cells in the visual system of both species, and in Apis those fibers of the anterior superior optic tract which link the medulla with the mushroom bodies. In Drosophila, bundles of Kenyon cells of the mushroom bodies were stained. In worker bees and drones, the relay neurons of the median and lateral antennoglomerular tracts were labelled. Since the recognition of the antigen does not require fixation, the antibody can be employed to label selectively living neurons in dissociated cell culture. This opens up the possibility for future functional studies on the role of the antigen in vitro.

Axonal sprouting and laminin appearance after destruction of glial sheaths

Laminin, a large extracellular matrix molecule, is associated with axonal outgrowth during development and regeneration of the nervous system in a variety of animals. In the leech central nervous system, laminin immunoreactivity appears after axon injury in advance of the regenerating axons. Although studies of vertebrate nervous system in culture have implicated glial and Schwann cells as possible sources, the cells that deposit laminin at sites crucial for regeneration in the living animal are not known. We have made a direct test to determine whether, in the central nervous system of the leech, cells other than ensheathing glial cells can produce laminin. Ensheathing glial cells of adult leeches were ablated selectively by intracellular injection of a protease. As a result, leech laminin accumulated within 10 days in regions of the central nervous system where it is not normally found, and undamaged, intact axons began to sprout extensively. In normal leeches laminin immunoreactivity is situated only in the basement membrane that surrounds the central nervous system, whereas after ablation of ensheathing glia it appeared in spaces through which neurons grew. Within days of ablation of the glial cell, small mobile phagocytes, or microglia, accumulated in the spaces formerly occupied by the glial cell. Microglia were concentrated at precisely the sites of new laminin appearance and axon sprouting. These results suggest that in the animal, as in culture, leech laminin promotes sprouting and that microglia may be responsible for its appearance.

Molecules and cognition: the latterday lessons of levels, language, and lac. Evolutionary overview of brain structure and function in some vertebrates and invertebrates

The characteristics of the nervous systems of a number of organisms in different phyla are examined at the recombinant DNA, protein, neuroanatomic, neurophysiological, and cognitive levels. Among the invertebrates, special attention is paid to the advantages as well as the shortcomings of the fly Drosophila melanogaster, the worm Caenorhabditis elegans, the honey bee Apis mellifera, the sea hare Aplysia californica, the octopus Octopus vulgaris, and the squid Loligo pealei. Among vertebrates, the focus is on Homo sapiens, the mouse Mus musculus, the rat Rattus norvegicus, the cat Felis catus, the macaque monkey Macaca fascicularis, the barn owl Tyto alba, and the zebrafish Brachydanio rerio. Vertebrate nervous systems have also been compared in fossil vs. extant organisms. I conclude that complex nervous systems arose in the Early Cambrian via a big bang that was underpinned by a modular method of construction involving massive pleiotropy of gene circuits. This rapidity of construction had enormous implications for the degrees of freedom that were subsequently available to evolving nervous systems. I also conclude that at the level of neuronal populations and interactions of neuropiles there is no model system between phyla except at the basic macromolecular level. Further, I argue that to achieve a significant understanding of the functions of extant nervous systems we need to concentrate on fewer organisms in greater depth and manipulate genomes via transgenic technologies to understand the behavioral outputs that are possible from an organism. Finally, I analyze the concepts of "perceptual categorization" and "information processing" and the difficulties involved in the extrapolation of computer analogies to sophisticated nervous systems.