Heterogeneity of microtubule-associated protein (MAP2) in vertebrate brains

Genomic signatures of drift and selection driven by predation and human pressure in an insular lizard

Genomic divergence was studied in 10 small insular populations of the endangered Balearic Islands lizard (Podarcis lilfordi) using double digest restriction-site associated DNA sequencing. The objectives were to establish levels of divergence among populations, investigate the impact of population size on genetic variability and to evaluate the role of different environmental factors on local adaptation. Analyses of 72,846 SNPs supported a highly differentiated genetic structure, being the populations with the lowest population size (Porros, Foradada and Esclatasang islets) the most divergent, indicative of greater genetic drift. Outlier tests identified ~ 2% of loci as candidates for selection. Genomic divergence-Enviroment Association analyses were performed using redundancy analyses based on SNPs putatively under selection, detecting predation and human pressure as the environmental variables with the greatest explanatory power. Geographical distributions of populations and environmental factors appear to be fundamental drivers of divergence. These results support the combined role of genetic drift and divergent selection in shaping the genetic structure of these endemic island lizard populations.

Association of microtubule-associated protein (MAP1B) with growing axons in cultured hippocampal neurons

Microtubule-associated protein 1B (MAP1B) is a major constituent of the neuronal cytoskeleton early in development. This protein is present in embryonic brain and is composed of two isoforms that are the result of differential phosphorylation. We examined the distribution of MAP1B during the differentiation of cultured hippocampal neurons and compared it to that of MAP2 and tubulin. We demonstrated by immunofluorescent doublestaining that MAP1B and MAP2 are colocalized in cell bodies and the minor processes of hippocampal neurons during the early stages of development, before the establishment of neuronal polarity. Later, when neurons acquire axonal and dendritic characteristics, MAP1B is sorted into growing axons, including the growth cone, whereas MAP2 is restricted to dendrites and cell bodies. Unlike tubulin, the localization of MAP1B in growing axons is not uniform. Rather, the protein is found concentrated in the distal portion. During later stages of development, the neurons extend a network of fasciculating axonal and dendritic neurites in which the segregation of MAP1B and MAP2 is maintained. However, the staining of MAP1B in mature neuronal cultures decreases in a pattern that resembles the decline of this protein during brain development. These results support the association of MAP1B with growing axons and its correct developmental regulation in the hippocampal culture system.

A comparative study of MAP2 immunostaining in areas 9 and 17 in schizophrenia and Huntington chorea

Increasing evidence suggests that there may be significant morphological changes in the neuropil of the dorsolateral prefrontal cortex in schizophrenia. A controversial issue surrounding these deficits in the cortical neuropil is the confounding effects of antipsychotic (neuroleptic) medication as well as the question of generality to psychiatric disorders. To begin to address these issues we examined brains from Huntington's patients matched to a cohort of schizophrenics and controls. Many Huntington's patients take neuroleptics similar to schizophrenics; therefore, by comparing the two groups to controls we can begin to determine if neuroleptics play a role in the deficits reported in schizophrenia. Using MAP2 immunohistochemistry and thionin staining eight matched triplets of Huntington, schizophrenia and control, in areas 9 and 17 layers III and V were analyzed. Our results confirmed previous published data showing a schizophrenia-associated decrease in MAP2 in area 9 with no change in area 17. Similarly the Huntington's patients showed no change in area 9 layer III and no change in area 17. There was however, a modest decrease observed in layer V area 9 of the Huntington's patients. Neuron density measurements showed no change in either layer or brain region in any of the diagnostic categories. These observations suggest that antipsychotic medication may not be responsible for some of the morphological changes observed in the neuropil of the PFC in schizophrenia.

Evidence of altered neurogranin immunoreactivity in areas 9 and 32 of schizophrenic prefrontal cortex

Schizophrenia is a complex and poorly understood neuropsychiatric disorder. Much research has begun to implicate the prefrontal cortex in the disease. Using immunocytochemistry we determined if neurogranin, a protein found in dendrites, spines and cell bodies and an upstream regulator of calcium was altered in areas 9 and 32 of schizophrenic prefrontal cortex. We examined its expression in pyramidal cells in layers III and V. Tissues from 7 controls and 7 schizophrenics (from our original MAP2 study, Jones, L., Johnson, N., Byne, W., 2002. Alterations in MAP2 staining in area 9 and 32 of schizophrenic prefrontal cortex. Psych. Res. 114, 137-148) matched for age, sex and postmortem interval were examined. Using area fraction analysis we quantified the immunostaining. Additionally, we counted the number of positively stained pyramidal cells in the same 7 pairs. Neurogranin immunostaining was dramatically reduced in both layers III (72%) and V (50%) in area 9. In area 32 there was a more modest reduction in both layers III (36%) and V (40%). There was no difference in either brain region or layer in the density of positively stained pyramidal cells. These data confirm mounting evidence suggesting dendritic loss in the prefrontal cortex and suggest that the loss of protein does not appear to be due to a change in the number of cells producing the protein but rather in the amount of protein being produced. Additionally, these data suggest that the loss of neurogranin may alter the calcium-calmodulin dependent pathways due to its role as a regulator of calmodulin suggesting a link between structural and functional alterations of the pyramidal cells in the prefrontal cortex.

Alterations in MAP2 immunocytochemistry in areas 9 and 32 of schizophrenic prefrontal cortex

A variety of lines of converging evidence implicate the prefrontal cortex (PFC) in schizophrenia. Studies employing Nissl stains have suggested that PFC dendrites may be atrophic in schizophrenia; however, Nissl stains do not reveal dendrites. We employed MAP2 immunocytochemistry, which stains dendrites to examine cortical layers III and V in two areas of the PFC (areas 9 and 32). Occipital cortex (area 17) was examined as a control region. Tissues from seven schizophrenics and seven non-psychiatric controls were examined. Immunostaining was quantitated by area fraction analysis. MAP2 area fraction was decreased in both layers in both regions of PFC, but not in occipital cortex. Area 9 exhibited a 42% reduction in layer V and a 36% reduction in layer III. Area 32 exhibited a 31% reduction in layer V and a 36% reduction in layer III. Neither region exhibited a significant change in the density of pyramidal cells. These data are consistent with the hypothesis of a schizophrenia-associated decrease in dendritic material in the PFC.

Characterization of microtubule-associated proteins in teleosts

Although microtubules are known to play an important role in many cellular processes, they have been virtually neglected in fish. In this report, microtubule-associated proteins (MAPs) in fish (teleost) were characterized using antibodies (Abs) directed against the mammalian MAPs tau, MAP1A and B, and MAP 2. Two different populations of tau-like proteins (TLPs) were found in fish brain using the anti-tau Abs Tau-1, Tau-2, tau5', and tau3'. The TLPs that were recognized by Tau-1, Tau-2, and tau5' were (1) heat-stable; (2) the same molecular weight as mammalian TLPs: 59-62 kDa; (3) not enriched in microtubules prepared from catfish brain; and (4) localized to the cell body of neurons in fish brains. While the TLPs recognized by tau3' Abs were (1) heat-stable; (2) lower molecular weight than mammalian TLPs: 32-55 vs. 50-65 kDa; (3) enriched in microtubule fractions prepared from catfish brain, and (4) localized to the axons of neurons. These results are consistent with two different populations of TLPs being present in fish brains. While MAP2 was found to be approximately the same molecular weight, 250 kDa, in zebrafish and goldfish as in mammals and to be distributed to dendrites in the fish brain, both MAP1A and MAP1B were found to be about 25% the mass of their mammalian homologs. These results suggest that MAPS in fish have some characteristics similar to their mammalian counterparts, but also possess some unique properties that require further study to elucidate their function.

Tau-like proteins in the nervous system of goldfish

This report describes the presence of a group of tau-like proteins (TLPs) in goldfish central nervous system. The TLPs were immunoreactive with antibodies that recognized the carboxy-terminal domain of mammalian tau, but not with antibodies that recognized the amino-terminus. The TLPs of goldfish exhibited the basic properties of tau proteins including neuronal specificity, structural heterogeneity, heat stability and the ability to co-assemble with tubulin. We propose that TLPs may represent a precursor of tau, that share the microtubule binding domain and the carboxy-terminal domain with mammalian tau proteins. In contrast the amino-terminus of the TLPs is much shorter and may represent a more variable domain of tau proteins.

Restricted expression of the actin-regulatory protein, tropomyosin, defines distinct boundaries, evaginating neuroepithelium, and choroid plexus forerunners during early CNS development

In the hindbrain, rhombomeres represent morphological units that develop characteristic, segment-specific structures. Similar segments, known as prosomeres, have been proposed to exist in the forebrain. The neuroepithelial cells of the sharp boundary regions that form the borders between many segments often exhibit distinct shapes, reflecting unique cytoskeletal organization. The present investigation examined the expression of one family of actin-binding, regulatory proteins, the tropomyosins (TM), in boundaries. We found that high molecular weight TMs selectively concentrate in boundary cells and other neuroepithelial zones that exhibit unique cell shapes and movements. Specific TM expression is found at hindbrain boundaries as early as embryonic day 10 in the rat, whereas rhombomeres themselves were TM-negative. Highly restricted TM localization also defined some prosomere boundaries in the early forebrain, particularly those exhibiting unique cell shapes. Furthermore, several regions of the neuroepithelium that evaginate are TM-immunoreactive, including tuberal and preoptic neuroepithelium. Most striking, a subpopulation of neuroepithelial cells in the medial telencephalic wall expresses TM, apparently marking the neuroepithelial region that gives rise to the choroid plexus at least 2 d before its formation. This suggests that the medial cerebral wall is not entirely dedicated to generating cells that comprise allocortex. TM expression in the choroid plexus is maintained through initial evagination and appearance in all ventricles. The spatially restricted expression of TMs implicates that this actin-binding protein is involved in the dynamic regulation of cell shape or motility associated with boundary formation and morphogenesis of the neuroepithelium during critical stages of brain development.

Simultaneous detection of amplicon and HSV-1 helper encoded proteins reveals that neurons and astrocytoma cells do express amplicon-borne transgenes in the absence of synthesis of virus immediate early proteins

HSV-1 amplicon vectors were used to express either a cytoplasmic (beta-galactosidase) or a membrane targeted protein (TIMP-Thy1) in primary neuronal cultures, and a human astrocytoma cell line. Whereas some cells became infected by vector particles alone others were simultaneously infected by both vector and helper particles. Our results show that IEHCMV and HSV-1 IE3 promoters are able to direct transgene expression in these cells in the absence of synthesis of helper virus transacting proteins, and stress the need of monitoring expression from both partners of an amplicon population, in order to differentiate transgene expression in cells singly infected with amplicon particles, from those infected by both amplicon and helper particles.

Synaptogenesis and distribution of presynaptic axonal varicosities in low density primary cultures of neocortex: an immunocytochemical study utilizing synaptic vesicle-specific antibodies, and an electrophysiological examination utilizing whole cell recording

Low-density primary cultures of neocortical neurons were utilized to examine: (i) early interactions of growing neurites with morphological characteristics of axons with other neuronal elements, and (ii) the distribution of presynaptic axonal varicosities closely apposed to MAP-2 immunoreactive, putatively postsynaptic, dendrites. At the light microscopical level axonal varicosities, presumably presynaptic terminals, were identified using immunocytochemistry incorporating antibodies specific for the synaptic vesicle antigens synaptophysin and synapsin. The presence of synaptophysin- and synapsin-immunoreactive swellings along axonal processes was first detected at 5 days post-plating and was also apparent in axons growing in isolation. At 5-7 days in vitro, immunolabelled axonal varicosities in close apposition to putative postsynaptic dendrites (MAP-2 immunoreactive) dendrites were detected. Electrophysiologically active synaptic contacts can also readily be detected at this stage. After 3 weeks in vitro presynaptic contacts do appear to be distributed heterogeneously along postsynaptic dendrites of many neurons in culture. As the culture matures a higher number of presynaptic profiles can be seen along dendrites, with a centrifugal distribution, e.g. a higher density of presynaptic axonal terminals in close apposition to more distal regions of larger dendrites, putatively considered to be apical dendrites of pyramidal-like neurons. In our cultures, the overall increase in the density and the pattern of distribution of presynaptic axon terminals immunoreactive for synaptic vesicle antigens closely apposed to putative post-synaptic structures mimics the general postnatal increase of synaptic density in the neocortex in vivo. Thus, low density primary cultures of neocortical neurons offer a valuable system to explore and manipulate (i) the molecular and cellular basis of neocortical synaptogenesis, and (ii) the pharmacology of neocortical synaptic transmission.

Expression and distribution of phosphorylated MAP1B in growing axons of cultured hippocampal neurons

Microtubule associated proteins (MAPs) interact with tubulin to modulate neurite stability and growth during development. The phosphorylated form of one of these MAPs, MAP1B (MAP1B-P) is hypothesized to be of particular importance for the regulation of neurite outgrowth. To investigate the mechanisms by which MAP1B and MAP1B-P contribute to this regulation, we used a new antibody against an isoform of MAP1B-P to determine its pattern of expression during neuronal development in vitro. We examined cultured hippocampal neurons because these provide a well-established system to evaluate the development of axons and dendrites. MAP1B, MAP1B-P and MAP2 colocalized to the cell bodies and minor processes during the first 24 hours of culture, but MAP1B-P also extended well into the growth cones. As neurite outgrowth and differentiation proceeded, MAP1B and MAP1B-P became localized to the cell bodies and axons, and MAP2 to the cell bodies and dendrites. After 3 days, MAP1B-P declined in the cell body and was segregated to the distal axon; MAP1B remained in the cell body, but was also concentrated in the distal axon. Over 5-9 days in culture, MAP1B-P levels decreased and became undetectable; MAP1B levels decreased later (19-23 days). MAP2 levels, however, remained high through the entire culture period in cell bodies and dendrites. These results are consistent with the hypothesis that MAP1B-P plays an important role in the initiation and elongation of axons by regulating the dynamics of microtubules near the growth cone: MAP1B-P expression is greatest during the period of active neurite extension, is particularly prominent in growth cones where axon outgrowth is most active, and decreases along with the decline in active axon extension.

Different stability of posttranslationally modified brain microtubules isolated from cold-temperate fish

Microtubule proteins were isolated by a temperature-dependent assembly-disassembly method from brain tissue of for cold-temperature fish; one fresh water fish (Oncorhynchus mykiss), and three marine fish (Labrus berggylta, Zoarces viviparus and Gadus morhua). The alpha-tubulins from all four fish species were acetylated. The alpha-tubulins from the marine fish were composed of a mixture of tyrosinated and detyrosinated tubulin, while the fresh water fish tubulin only reacted with an antibody against detyrosinated tubulin. The isolated microtubules had a similar MAP composition. A 400 kD protein and a MAP2-like protein were found, but MAP1 was missing. All microtubules disassembled upon cooling to 0 degrees C. In spite of these common characteristics, the assembly of microtubules from Labrus berggylta was inhibited by colchicine and calcium, in contrast to the assembly of microtubules from Oncorhynchus mykiss and Zoarces viviparus. For the latter, colchicine was not completely inhibitory even at a concentration as high as 1 mM, and calcium induced the formation of both loosely and densely coiled ribbons. The effects of calcium and colchicine on microtubules from Oncorhynchus mykiss and Zoarces viviparus were modulated by either fish or cow MAPs, indicating that the effects are due to intrinsic properties of the fish tubulins and not the MAPs. In view of these findings, our results suggest that there is no correlation between colchicine sensitivity, inability of calcium to inhibit microtubule assembly, and acetylation and detyrosination.

Purification and immunological characterization of acid beta-galactosidase from dog liver

1. Dog liver acid beta-galactosidase was isolated in high yield and purified to homogeneity using a series of chromatographies on Con A-Sepharose, decyl-agarose, anion-exchange HPLC and gel-filtration HPLC. 2. Non-denaturing gel filtration by HPLC gave a single homogeneous peak corresponding to molecular mass of 180-190 kDa. During SDS-PAGE analysis, the single peak dissociated into a major band corresponding to molecular mass of 32 kDa with minor bands at 18 and 13 kDa. 3. Polyclonal antibodies raised against the purified enzyme immunoprecipitated beta-galactosidase activity specifically from dog liver extracts and recognized a single 32 kDa band in Western blot analysis of dog tissue homogenates. This antibody did not crossreact with any protein band in tissue homogenates from other species examined except cat. 4. Western blot analysis of tissue extracts from dogs affected with GM1-gangliosidosis showed the presence of a 32 kDa band similar to that of controls.

Calpain-mediated proteolysis of microtubule associated proteins MAP1B and MAP2 in developing brain

Microtubule associated proteins MAP1B and MAP2 are important components of the neuronal cytoskeleton. During early development of the brain, MAP1B (340 kDa) is present as two isoforms that differ in their level of phosphorylation, while MAP2 is expressed as a single high molecular weight isoform (MAP2B, 280 kDa) and a low molecular weight form (MAP2C, 70 kDa). In this study we examined and compared the sensitivities of MAP1B and MAP2, obtained from MT preparations and brain homogenates of young rats, to degradation by calcium-activated neutral protease, calpain II. We found that in MAPs prepared from microtubules the two isoforms of MAP1B had comparable sensitivity to calpain-mediated proteolysis. Similarly, the high and low molecular weight forms of MAP2 were equally sensitive to digestion by calpain. However, although both MAPs were very susceptible to calpain-mediated proteolysis, MAP1B was more resistant to degradation by calpain than MAP2. Furthermore, the endogenous degradation of MAPs in neonate brain homogenates was calcium-dependent and inhibited by leupeptin, and the pattern of degradation products for MAP1B and MAP2 was similar to that of calpain-mediated proteolysis. These data suggest that calpain can play a role in the regulation of MAPs levels during brain development, in relation to normal neuronal differentiation and disorders associated with neurodegeneration.

Regulation of microtubule associated protein 2 (MAP2) expression by nerve growth factor in PC12 cells

In the presence of nerve growth factor (NGF), PC12 cells cease to divide and differentiate, extending long microtubule-containing neurites. We showed by immunoblot analysis that MAP2 was detectable in PC12 after 4 days of NGF treatment and that its levels increased five- to sevenfold after 12 days of NGF treatment. The apparent molecular weight of MAP2 in PC12 cells was similar to that of rat brain MAP2 (280,000), with a doublet representing the MAP2 isoforms. However, the relative levels of MAP2 in differentiated PC12 cells were 5-10% of those found in rat brain. Immunofluorescence analysis of NGF-treated PC12 cells revealed that MAP2 co-localized with tubulin and was present in cell bodies and neurites. Northern blot analysis showed that the levels of MAP2 mRNA increased in PC12 cells during NGF-treatment in a pattern that paralleled the protein levels, suggesting that MAP2 expression is transcriptionally regulated.

The phylogenic expression of plasmolipin in the vertebrate nervous system

Plasmolipin is a plasma membrane proteolipid is a major myelin membrane component (Cochary et al., 1990). In this study we report the phylogenic expression of plasmolipin in the vertebrate nervous system. Using Western blot analysis with polyclonal antibodies, we have analyzed membrane fractions, including myelin, from elasmobranchs, teleosts, amphibians, reptiles, birds and mammals. On the basis of immune detection, plasmolipin appears to be restricted to the mammalian nervous system. Comparison of the central and peripheral nervous systems of mammals showed only minor differences in the level of plasmolipin in these two regions. Within mammals, little quantitative differences were observed when rat, human and bovine membrane fractions were compared. The late evolutionary expression of plasmolipin which results in its restriction to mammals makes it unique among the (major) myelin proteins. The potential physiologic significance of these data are discussed.

Early in vitro genesis and differentiation of axons and dendrites by hippocampal neurons analyzed quantitatively with neurofilament-H and microtubule-associated protein 2 antibodies

Differentiating neurons initially extend neurites that are the precursors of axons and dendrites. The temporal pattern of neurite outgrowth has been studied extensively, but mostly qualitative analyses have been used to study this phenomenon. We have examined neurite outgrowth of hippocampal neurons in primary cultures using a polyclonal antibody against microtubule-associated protein 2 (MAP2) and a novel monoclonal antibody against the phosphorylated form of high neurofilament subunit (NF-H). These antibodies serve as markers for dendrites and axons, respectively. The neurite staining patterns were quantified during the first 10 days in culture and the analysis revealed that primary processes undergo three phases of differentiation: (i) in the first 24 h, the majority of primary neurites express MAP2 only and a small percentage express both MAP2 and NF-H; (ii) between 24 and 48 h, NF-H expression increases and it is coexpressed with MAP2 in many neurites as they begin to lengthen; and (iii) between 48 h and 4 days, MAP2 and NF-H protein expression occurs in separate populations of neurites. While most of the earliest forming primary neurites appear to be dendritic (MAP2 only), the coexpression of dendritic and axonal protein markers in a group of early forming processes suggests that these neurites may not be predetermined to become a dendrite or an axon. Our data also indicate that NF-H is detectable early in primary neurite development and that, based on in vivo localization and morphology of cultured neurites, the phosphorylated form of NF-H is concentrated in axons.

Turnover of cytoskeletal proteins in vivo

The turnover of the microtubule-associated proteins 1B and 2 (MAP1B and MAP2), tubulin, high molecular weight neurofilament protein (NF-H), and spectrin were studied by in vivo labeling. Radiolabeled [35S]methionine was injected intracranially to 10-day-old rats and the rate of turnover was measured for total and specific brain proteins. The turnover of total brain proteins was biphasic and consisted of a fast and a slow component with half lives of 6.5 +/- 0.4 and 14.2 +/- 0.7 (mean +/- S.E.M.) days, respectively. The turnover of individual cytoskeletal brain proteins was also biphasic. The fast decay rates of MAP1B, MAP2, tubulin and spectrin were 5.8 +/- 0.7, 6.9 +/- 0.3, 4.8 +/- 0.5 and 4.9 +/- 0.4 days, respectively, while the slow decay rates of these proteins were 12.0 +/- 1.3, 12.4 +/- 1.7, 15.0 +/- 0.5 and 16.0 +/- 1.2 days, respectively. In addition, the Triton X-100 insoluble fraction of MAP1B, tubulin, spectrin and NF-H showed monophasic decay rates of 29.0 +/- 2.3, 15.0 +/- 1.4, 16.0 +/- 0.9 and 18.5 +/- 1.5 days, respectively, which were similar to their slow decay rates in whole brain homogenates, suggesting that incorporation of these proteins into the cytoskeletal lattice increases their stability.

Microtubule associated protein (MAP1B) is present in cultured oligodendrocytes and co-localizes with tubulin

Differentiation of oligodendrocytes is accompanied by the extension of processes and the assembly of the myelin membrane. It is likely that the cytoskeleton plays an important role in this process in terms of changes in cell shape, transport of myelin components, and organization of the myelin membrane. Oligodendrocytes contain microtubules (MT) which associate with other components of the cytoskeleton, and microtubule associated proteins (MAPs) may mediate some of these interactions. In this study we have shown the presence of MAP1B in oligodendrocytes grown in primary glial cultures by double-label immunofluorescence using antibodies to galactocerebroside (GC) and MAP1B. The staining of the cultures showed that GC-positive oligodendrocytes were also stained with MAP1B antibodies. However, MAP1B stain was limited to cell bodies and processes, whereas GC stain was also seen in flattened membrane sheets and punctate staining in processes. MAP1B staining was also compared with that of myelin proteolipid (PLP), myelin basic protein (MBP) and beta-tubulin in secondary glial cultures that were enriched for oligodendrocytes. The results showed a typical staining of cell bodies and membranous profiles using PLP antibodies, and the staining of cell bodies and flattened regions of membranous sheets by MBP antibodies. In contrast, both polyclonal and monoclonal antibodies to MAP1B showed a uniform diffuse staining of cell bodies, major processes, and fine interconnected processes. Double-labeling of the cells showed that MAP1B was co-localized with tubulin, but was not present in glial fibrillary acidic protein (GFAP)-positive astrocytes. Western and Northern blot analyses of primary glial cultures showed that MAP1B had a molecular mass of 320 kDa and a mRNA of 10 kb. These values are identical to those previously reported for brain MAP1B (Safaei and Fischer, 1989) and demonstrate the presence of MAP1B in oligodendrocytes.

Changes in microtubule-associated protein MAP1B phosphorylation during rat brain development

Microtubule-associated protein MAP1B from neonatal rat brain was separated on sodium dodecyl sulfate-containing polyacrylamide gels into two isoforms (high and low MAP1B), both of which were recognized by a panel of monoclonal and polyclonal antibodies against MAP1B. In addition, SMI31, a monoclonal antibody directed against phosphorylated epitopes of the neurofilament proteins, showed phosphatase-sensitive reactivity against the high isoform of MAP1B. The antigenic relationship between the phosphorylated isoform of MAP1B and neurofilaments was confirmed by the reactivity of SMI31 with the immunoprecipitated MAP1B protein. After dephosphorylation of MAP1B with alkaline phosphatase, the higher-molecular-weight isoform of MAP1B was no longer detectable with phosphate-insensitive anti-MAP1B antibodies, whereas there was a significant increase in the immunoreactivity of the lower-molecular-weight MAP1B isoform. These data suggest that the structural microheterogeneity of MAP1B is due to differences in phosphorylation. The two isoforms were present in all brain regions of the young rat. During brain development, the general decrease in MAP1B levels was accompanied by changes in the relative amount of the two isoforms. In particular, the phosphorylated isoform of MAP1B decreased dramatically to almost undetectable levels in adult brain. This conclusion was further supported by immunoblotting analysis that showed the disappearance of phosphorylated epitopes of MAP1B early during brain development. In addition, dephosphorylation experiments demonstrated the phosphatase sensitivity of the phosphorylated isoform throughout development.

Synthesis, axonal transport, and turnover of the high molecular weight microtubule-associated protein MAP 1A in mouse retinal ganglion cells: tubulin and MAP 1A display distinct transport kinetics

Microtubule-associated proteins (MAPs) in neurons establish functional associations with microtubules, sometimes at considerable distances from their site of synthesis. In this study we identified MAP 1A in mouse retinal ganglion cells and characterized for the first time its in vivo dynamics in relation to axonally transported tubulin. A soluble 340-kD polypeptide was strongly radiolabeled in ganglion cells after intravitreal injection of [35S]methionine or [3H]proline. This polypeptide was identified as MAP 1A on the basis of its co-migration on SDS gels with MAP 1A from brain microtubules; its co-assembly with microtubules in the presence of taxol or during cycles of assembly-disassembly; and its cross-reaction with well-characterized antibodies against MAP 1A in immunoblotting and immunoprecipitation assays. Glial cells of the optic nerve synthesized considerably less MAP 1A than neurons. The axoplasmic transport of MAP 1A differed from that of tubulin. Using two separate methods, we observed that MAP 1A advanced along optic axons at a rate of 1.0-1.2 mm/d, a rate typical of the Group IV (SCb) phase of transport, while tubulin moved 0.1-0.2 mm/d, a group V (SCa) transport rate. At least 13% of the newly synthesized MAP 1A entering optic axons was incorporated uniformly along axons into stationary axonal structures. The half-residence time of stationary MAP 1A in axons (55-60 d) was 4.6 times longer than that of MAP 1A moving in Group IV, indicating that at least 44% of the total MAP 1A in axons is stationary. These results demonstrate that cytoskeletal proteins that become functionally associated with each other in axons may be delivered to these sites at different transport rates. Stable associations between axonal constituents moving at different velocities could develop when these elements leave the transport vector and incorporate into the stationary cytoskeleton.

Developmental regulation of microtubule-associated protein 2 expression in regions of mouse brain

The relative levels of microtubule-associated protein 2(MAP2) were determined during postnatal development of the mouse in six different discrete brain regions: cerebellum, cortex, hippocampus, olfactory bulb, brainstem, and hypothalamus. Brain homogenates were electrophoresed on sodium dodecyl sulfate-containing gels and analyzed by immunoblotting with MAP2-specific antibodies. The levels of MAP2 in each region were determined using radiolabeled secondary antibodies and densitometric quantification of the autoradiograms over a range that was determined to have a linear response. The results indicated that in all regions and at all ages there was only one high-molecular-weight polypeptide of MAP2, which did not change in electrophoretic mobility after dephosphorylation. In most regions, the levels of MAP2 increased during the first 2 postnatal weeks. However, there were differences in the time course and relative levels of MAP2 between regions. In addition, all regions of the brain expressed the low-molecular-weight form of MAP2 (MAP2c) that was present at birth as a heterogeneous group of polypeptides with an apparent molecular weight of 70K. Most of the heterogeneity of MAP2c, however, was eliminated after dephosphorylation. The levels of MAP2c decreased dramatically after 2 weeks postnatally, except for the olfactory bulb, where the levels of MAP2c remained relatively high even in adults.

An immunohistochemical characterization of the primitive and maturing neuroepithelial components in the OTT-6050 transplantable mouse teratoma

The neuroepithelial component of the OTT-6050 mouse teratoma has previously been characterized as an experimental system for the study of differentiation and cytologic maturation in embryonal tumours of the human central nervous system. A number of transplantable tumours composed of primitive stem cells and of a neuroepithelial component displaying a spectrum of differentiation were previously produced by centrifugal elutriation of the dissociated OTT-6050 teratoma. These tumours have provided a reproducible cell population that has permitted the study of both the early and later stages of neoplastic neurocytogenesis. The purpose of the present study was to detect, by immunohistochemistry, the earliest stages of neurocytogenesis in these tumours as shown by the expression of neuron-associated microtubule proteins. This was correlated to the appearance and localization of other markers associated with neuronal and glial differentiation. The primitive neuroepithelial structures resembling neural tubes (medulloepithelial rosettes) contained single or small groups of cells which reacted with the monoclonal antibody TUJ1, specific for the neuron-associated class III beta-tubulin isotype. Immature neuroblasts and maturing polar neurons also showed immunoreactivity with TUJ1, whereas reactivity for microtubule-associated protein 2 (MAP2), tau, the 200 kilodalton isoform of neurofilament protein, neuron-specific enolase and synaptophysin was primarily seen in maturing neurons. By comparison, both medulloepithelial and ependymoblastic rosettes, neuroblasts and glial cells were immunopositive with monoclonal antibody TU27, which defines an antigenic site shared by most mammalian beta-tubulin isotypes. Astroglia were reactive with antisera to glial fibrillary acidic and S-100 proteins, but not with monoclonal antibody (MAb) TUJ1, or with MAbs to the other neuron-associated cytoskeletal proteins, MAP2, tau and the 200 kilodalton subunit of neurofilament protein. Our findings suggest that (1) expression of the class III beta-tubulin isotype is an early event during neoplastic neurocytogenesis, (2) this isotype is subsequently preserved in maturing neuronal populations, and (3) it is not present at detectable levels in stem cells or glial cells. The observation that morphologically undifferentiated neuroepithelial cells express a neuron-associated beta-tubulin isotype signifies the value of examining tubulin isotype expression in the characterization of normal and neoplastic neuroepithelial differentiation.

Regulation of microtubule-associated protein 2 (MAP2) mRNA expression during rat brain development

The expression of MAP2 during rat brain development was studied by using specific antibodies and cDNA probes. MAP2 cDNAs were isolated from a rat brain lambda gt11 library, and their identity was confirmed by the reactivity of their fusion proteins with several independent monoclonal antibodies that recognize MAP2. Northern blot analyses of the RNA prepared from whole brains, cerebral cortex, hypothalamus, brain stem, olfactory bulbs, and cerebellum showed that the levels of MAP2 mRNA increase during the initial phase of development, reach a maximum between postnatal weeks 2 and 3, and then decrease in the adult. The time course and the kinetics of this change varied between different brain regions and appeared to reflect the pattern of morphological changes in these regions. RNA blots were also analyzed with beta-tubulin and beta-actin cDNA probes to ensure the quality and the quantity of the RNA. The levels of MAP2 mRNA and protein showed similar changes during the initial part of brain development and suggested a transcriptional control. However, while MAP2 protein levels remained high throughout development, MAP2 mRNA levels decreased in adulthood. We suggest that the increased stability of the MAP2 molecule may be a contributing factor in the developmental regulation of steady-state levels of MAP2.

Distribution of phosphate-independent MAP2 epitopes revealed with monoclonal antibodies in microwave-denatured human nervous system tissues

In contrast with results obtained in experimental animals, antibodies to microtubule associated protein-2 (MAP2) preferentially label abnormal structures in human nervous system tissue samples, but the normal sites at which MAP2 is expressed are not well-defined. To determine the distribution of MAP2 in the human central (CNS) and peripheral (PNS) nervous systems, we prepared monoclonal antibodies (MAbs) specific to MAP2, and compared the localization of this MAP in postmortem bovine and human tissues as well as in several human neural cell lines that express either neurofilament (NF) or glial filament (GF) proteins. Eight MAbs specific for phosphate-independent epitopes in bovine and human MAP2 were obtained, and those that performed well in tissues produced immunoreactivity confined to the somatodendritic domain of neurons in bovine and human CNS and PNS tissues. Other neural cells (e.g. astrocytes) did not express MAP2 immunoreactivity using these MAbs. Postmortem delays of less than 24 h prior to tissue denaturation did not affect the distribution of MAP2 immunoreactivity. However, microwave denaturation of these tissues preserved MAP2 immunoreactivity better than fixation with Bouin's solution or formalin. Microwave treatment also improved the immunoreactivity of several MAbs for NF and GF proteins. Finally, MAP2 was not detected in human neural cell lines that express NF (2) or GF (1) proteins. We conclude that microwave denaturation provides an effective means to preserve the immunoreactivity of normal human neuronal cytoskeletal proteins, and that this method of tissue denaturation allows the normal distribution of MAP2 to be defined in postmortem samples of human CNS and PNS tissues.

Cloning of a cDNA encoding MAP1B in rat brain: regulation of mRNA levels during development

This article describes the isolation of a microtubule-associated protein 1B (MAP1B) cDNA clone from a rat brain lambda gt11 library and the study of MAP1B mRNA expression during brain development. On Northern blots, the cDNA hybridized with an mRNA of greater than 10 kilobases which was present only in the brain. The identity of the cDNA was confirmed by the characterization of the antiserum against the fusion protein, and also by comparing both the original antibody and the anti-fusion protein antiserum with a panel of well-studied monoclonal antibodies against different forms of MAP1 and MAP2. The regulation of MAP1B mRNA during development was studied in whole brain, cerebral cortex, hypothalamus, brainstem, and olfactory bulbs. The steady-state levels of MAP1B mRNA in all tissues examined were relatively low in the adult compared to developing brains. This decrease varied in different brain regions, and its time course appeared to coincide with the pattern of postnatal developmental and morphological events. The developmental patterns of the MAP1B mRNA and protein in the brain were similar, suggesting that expression of this protein is under transcriptional control. The RNA blots were also probed with beta-actin and beta-tubulin to compare the levels of MAP1B mRNA with other cytoskeletal elements and as controls for the quality of the RNA.

Age-dependent expression of microtubule-associated protein 2 in the ventromedial nucleus of the hypothalamus

A distinctive developmental pattern of microtubule-associated protein 2 (MAP2) was detected in the ventromedial hypothalamus of rats. A region of more intense MAP2 immunoreactivity in this nucleus was present at birth, became prominent in a ringed appearance by postnatal day 4 and disappeared in the third postnatal week. This period of selective MAP2 expression in particular subcortical regions may signify important functions of MAP2 in the stabilization of developing dendritic structure.

Sex- and hormone-dependent antigen immunoreactivity in developing rat hypothalamus

Morphological sex differences in adults can result from differential gonadal steroid exposure during critical perinatal periods. This study describes the use of a monoclonal antibody we have developed to study mechanisms of sexual differentiation of brain structure and function. Used as a marker in immunocytochemistry, antibody AB-2 revealed subsets of cells, including radial glia, transiently during the perinatal period. Peak reactivity in radial glia was on embryonic day 19 in males and on postnatal day 1 in females. On postnatal day 1, AB-2 immunoreactivity in radial glia was 2-fold greater in females than in males. Greater activity was detected in males on one side of the brain than the other (2- to 4-fold, depending on the region). To test the hormone dependence of this sex difference, pregnant rats were injected with testosterone propionate to expose fetal females to androgen on embryonic day 18. This resulted in lower levels of AB-2 immunoreactivity in radial glia of the treated female offspring on postnatal day 1 relative to control females, and the pattern was bilaterally asymmetric, approaching that of males. Thus the difference between sexes in immunoreactivity with AB-2 as a marker was hormone dependent in a predictable manner. Whether this marker is revealing a sex difference in accessibility of antigen by immunocytochemistry or a sex difference in intrinsic antigen levels is not yet resolved. In either case these results support the hypothesis that certain hormone-dependent molecular events occur transiently during development.