Cell-surface antigens of developing rat cerebellar neurons: identification with monoclonal antibodies

Receptor for mouse hepatitis virus is a member of the carcinoembryonic antigen family of glycoproteins

The receptor for mouse hepatitis virus (MHV), a murine coronavirus, is a 110- to 120-kDa glycoprotein on intestinal brush border membranes and hepatocyte membranes. The N-terminal 25-amino acid sequence of immunoaffinity-purified MHV receptor was identical to the predicted mature N termini of two mouse genes related to human carcinoembryonic antigen (CEA) and was strongly homologous to the N termini of members of the CEA family in humans and rats. Polyclonal antibodies to human CEA recognized the immunoaffinity-purified MHV receptor and the MHV receptor in liver membranes and intestinal brush border membranes from MHV-susceptible mouse strains. In membranes from MHV-resistant SJL/J mice, the anti-CEA antibodies recognized a homologous glycoprotein that failed to bind MHV. The MHV receptor glycoprotein was detected in membranes of BALB/c colon, small intestine, and liver, which are the principal targets for MHV replication in vivo. The MHV receptor glycoprotein resembled members of the human CEA family in molecular weight, acidic pI, extensive glycosylation, solubility in perchloric acid, and tissue distribution. Thus, the MHV receptor is, to our knowledge, the first member of the CEA family of glycoproteins to be identified as a virus receptor.

Distribution and developmental expression of the nerve terminal protein NT75 in the rat cerebellum

Previous studies of the nerve terminal protein NT75 in the developing spinal cord have suggested an association between the appearance of NT75 immunoreactivity and the process of synaptogenesis. To examine the time course of NT75 expression further, the current study compared the localization of NT75 and the synaptic vesicle protein synaptophysin in the adult and developing rat cerebellum and in cerebellar tissue cultures. In the adult cerebellum, dense NT75 staining is confined to the molecular layer, where it is associated with parallel fiber endings of cerebellar granule cells. During development, NT75 immunoreactivity is first detectable in the cerebellar cortex as a dense band of staining in the deepest portion of the molecular layer at postnatal day 10. The stained zone expands to occupy a progressively greater portion of the molecular layer until about postnatal day 20. Synaptophysin staining occurs in granule cell processes earlier than NT75 and is found throughout the molecular layer by postnatal day 7. Quantitatively, rapid increases in both NT75 and synaptophysin occur in the first three postnatal weeks, with NT75 activity reaching levels exceeding the adult value by 50% over postnatal days 20 through 30, whereas synaptophysin plateaus at near adult levels by postnatal day 20. In cerebellar cultures, NT75 staining in neurites develops over several days, increasing coincidentally with development of synaptic contacts, whereas synaptophysin staining is already present in most neurites after only 1 day in vitro. The results indicate that NT75 expression in developing cerebellar granule cell nerve terminals is closely associated with the appearance of mature nerve terminals, suggesting that the protein may have a role in the formation/stabilization of the synaptic ending or in the mechanisms of synaptic transmission.

Rat olfactory cells and a central nervous system neuronal subpopulation share a cell surface antigen

Using the monoclonal antibody (Mab) 6B7, a cell surface component found in adult rat central nervous system membrane preparations and on the surfaces of a subpopulation of neurons in cultures of embryonic rat forebrain has been identified. This Mab was derived from mice immunized with a rat forebrain synaptic plasma membrane preparation. High levels of Mab 6B7 binding are observed with membrane preparations from rat forebrain and olfactory bulb but no detectable binding is observed with membranes from the non-neural adult rat tissues heart, kidney, liver, lung and testes. Binding to dorsal root ganglia preparations was 5-fold lower than to forebrain. In immunofluorescence analyses, Mab 6B7 binds to the surface of a significant proportion of neurons in cultures of embryonic day 14 rat forebrain. However, it is absent from GFAP-positive astrocytes, oligodendrocytes, Schwann cells and fibroblastic cells in rat neural cultures. Due to the high levels of binding in olfactory tissue, the distribution of the 6B7 antigen in the olfactory epithelium was characterized in greater detail. In cryostat sections, 6B7 appears to react with a cell population of the basal layer of the adult rat epithelium, but is absent from the cell bodies of the more mature neuronal population which lies higher in the epithelium. This result suggests that within the olfactory epithelium Mab 6B7 may be useful as a marker for the proliferative basal cells which are the neuronal precursors in the epithelium. In summary, the 6B7 antigen may be useful in identifying and analyzing cell subpopulations in both the central nervous system and olfactory epithelium.

Smooth muscle cells transiently express NCAM

NCAM (neural cell adhesion molecule) polypeptides were first detected on neuronal cells and were subsequently found to be expressed at least transiently by a number of other cell types including skeletal and cardiac but not smooth muscle. We report here that rat smooth muscle expresses NCAM in vitro and transiently in vivo. Using a monoclonal antibody 3F4 which reacts with most rat NCAM polypeptides, NCAM was found on the surface of cultured rat aortic smooth muscle lines A10 and A7r5 and mouse smooth muscle like line BC3H1 in abundances equal to or greater than those of cardiac muscle, skeletal muscle, and neuronal cell lines. The major NCAM polypeptide of muscle cells was Mr = 140 kDa with lesser amounts of the 120 kDa form. Consistent with these results, a major NCAM mRNA of 6.7 kb was detected in Northern analyses with lesser amounts of the 4.3 and 2.9 kb mRNA size classes. The relative abundance of NCAM mRNA was similar in RNA prepared from smooth muscle A7r5 cells, L6 skeletal muscle cells, and 9-day-old rat brain. NCAM was distributed across the entire surface of cultured smooth muscle cells in a highly punctate manner. Cryostat sections of rat aorta, intestine and bladder were examined by immunofluorescence to determine if NCAM is also expressed on smooth muscle in vivo. In each case NCAM was found to be transiently expressed by the smooth muscle cells of these tissues. Highest NCAM levels were observed at embryonic day 17 which then declined to undetectable levels in tissues from adults. These results extend previous observations to indicate all muscle types transiently express NCAM in development.

The cellular neurobiology of neuronal development: the cerebellar granule cell

Cerebellar granule cells in vivo and in vitro have been widely used in the study of the cellular neurobiology of neuronal development. We have described the basic neuroanatomical data on the granule cell in the developing and mature cerebellum. The importance of the cytoskeleton in determining the morphology of the granule cell and in process outgrowth and cell migration has been described. Extensive information is now available on the composition of the granule cell cytoskeleton. Cell surface glycoproteins are thought to be involved in the control of cell adhesion and cellular interactions during development. A number of surface molecules belonging to either the N-CAM or the Ng-CAM groups of glycoproteins have been studied in detail in the cerebellum. The role of these proteins in cell adhesion and in granule cell-astroglial interactions during granule cell migration has been reviewed. The survival and differentiation of neurones is controlled by soluble trophic factors. Several factors have been described which act as trophic factors for granule cells in vitro and may do the same in vivo. The numerous studies that have been carried out on the cerebellar granule cell have allowed us to describe certain aspects of the cellular neurobiology of this class of neurones as an example with general significance for the understanding of neuronal differentiation and function.

Tubulin: a factor necessary for the synthesis of both Sendai virus and vesicular stomatitis virus RNAs

Tubulin acts as a positive transcription factor for in vitro RNA synthesis by two different negative-strand viruses: Sendai virus, a paramyxovirus; vesicular stomatitis virus (VSV), a rhabdovirus. A monoclonal antibody directed against beta-tubulin completely inhibited not only mRNA synthesis and RNA replication catalyzed in vitro by extracts of cells infected with either virus but also mRNA synthesis by detergent-disrupted purified virions. The synthesis of both a leader-like RNA and the NP mRNA directed by detergent-disrupted purified Sendai virions was shown to be totally dependent on the addition of purified tubulin. The addition of purified tubulin, although not required, also stimulated mRNA synthesis directed by detergent-disrupted VSV virions 2- to 7-fold. Finally, there appears to be an association between tubulin and the L protein of VSV, since both monoclonal and polyclonal anti-tubulin antisera specifically immunoprecipitated not only tubulin but also the L protein of two different VSV serotypes from the soluble protein fraction of infected cells.

Individual neural cell types express immunologically distinct N-CAM forms

The neural cell adhesion molecules, or N-CAMs, are a group of structurally and immunologically related glycoproteins found in vertebrate neural tissues. Adult brain N-CAMs have apparent molecular weights of 180,000, 140,000, and 120,000. In this article we identify, using monoclonal antibody (Mab) 3G6.41, an immunologically distinct adult rat N-CAM form and show that this form is selectively expressed by some clonal neural cell lines. Consecutive immunoprecipitation experiments indicate that rabbit anti-N-CAM can remove from solubilized cerebellar neuron primary cultures all 180,000- and 140,000-mol-wt N-CAM molecules that react with Mab 3G6.41. However Mab 3G6.41 cannot remove all N-CAM molecules that react with rabbit anti-N-CAM. Rabbit anti-N-CAM binds to and immunoprecipitates N-CAM forms from the rat neuronal cell lines B35, B65, and B104, the glial lines B12 and C6, and L6 myoblasts. Mab 3G6.41 does not bind to or immunoprecipitate N-CAM from the B12 and B65 lines but does react with the other four lines by both criteria. Many cells in primary cultures of postnatal rat that express glial fibrillary acidic protein also bind Mab 3G6.41. Thus a unique form of rat N-CAM recognized by Mab 3G6.41 is found on some but not all neuronal, glial, and muscle cells.