Characterization of amalgam: a member of the immunoglobulin superfamily from Drosophila

Characterization of cDNA clones defining variant forms of human neural cell adhesion molecule N-CAM

The neural cell adhesion molecule N-CAM has been identified in a number of species and comprises at least three major cell surface polypeptides of different molecular structures and tissue distributions. We report here the isolation and characterization of cDNA clones encoding two of the three major forms of N-CAM from a human neuroblastoma cDNA library. One of the clones, NII-6, provides the first complete sequence of a small cytoplasmic domain (140 kDa) form of the molecule in humans and differs in a number of respects from cDNA clones derived from human muscle. These differences include the presence of a 30-bp insert in the fourth immunoglobulin-like domain of N-CAM, a 3-bp insert in the extracellular portion of the molecule, and an additional 6 bp in the middle of the membrane-spanning segment. Based on the analysis of a genomic DNA clone spanning these regions of N-CAM, the first two differences arise by alternate splicing of RNA and occur in some, but not all clones; the additional 6 bp may reflect a genetic polymorphism. A second cDNA clone, NI-10, encodes the complete sequence of a segment that is specific to the large cytoplasmic domain (180 kDa) polypeptide of human N-CAM and is very similar to corresponding segments of mouse, chicken, and rat N-CAM. This sequence also arises by alternative splicing of RNA. In addition, we have identified a genomic DNA segment encoding sequences specific to the third, small surface domain (120 kDa) polypeptide of N-CAM. The data presented here and previously define the DNA sequences of the membrane-bound forms and known variants of human N-CAM. From these sequences, a wide variety of probes can be generated for investigating the expression of particular N-CAM polypeptides in normal and pathological tissues.

The axonal glycoprotein TAG-1 is an immunoglobulin superfamily member with neurite outgrowth-promoting activity

Pathfinding of axons in the developing nervous system is thought to be mediated by glycoproteins expressed on the surface of embryonic axons and growth cones. One molecule suggested to play a role in axonal growth is TAG-1, a 135 kd glycoprotein expressed transiently on the surface of subsets of neurons in the developing mammalian nervous system. We isolated a full-length cDNA clone encoding rat TAG-1. TAG-1 has six immunoglobulin-like domains and four fibronectin type III-like repeats and is structurally similar to other immunoglobulin-like proteins expressed on developing axons. Neurons maintained in vitro on a substrate of TAG-1 extend long neurites, suggesting that this protein plays a role in the initial growth and guidance of axons in vivo. TAG-1 is anchored to the neuronal membrane via a glycosyl phosphatidylinositol linkage and is also released from neurons, suggesting that TAG-1 also functions as a substrate adhesion molecule when released into the extracellular environment.

PECAM-1 (CD31) cloning and relation to adhesion molecules of the immunoglobulin gene superfamily

An antibody to a platelet integral membrane glycoprotein was found to cross-react with the previously identified CD31 myelomonocytic differentiation antigen and with hec7, an endothelial cell protein that is enriched at intercellular junctions. This antibody identified a complementary DNA clone from an endothelial cell library. The 130-kilodalton translated sequence contained six extracellular immunoglobulin (Ig)-like domains and was most similar to the cell adhesion molecule (CAM) subgroup of the Ig superfamily. This is the only known member of the CAM family on platelets. Its cell surface distribution suggests participation in cellular recognition events.

The MHC molecules of nonmammalian vertebrates

There is very little known about the long-term evolution of the MHC and MHC-like molecules. This is because both the theory (the evolutionary questions and models) and the practice (the animals systems, functional assays and reagents to identify and characterize these molecules) have been difficult to develop. There is no molecular evidence yet to decide whether vertebrate immune systems (and particularly the MHC molecules) are evolutionarily related to invertebrate allorecognition systems, and the functional evidence can be interpreted either way. Even among the vertebrates, there is great heterogeneity in the quality and quantity of the immune response. The functional evidence for T-lymphocyte function in jawless and cartilagenous fish is poor, while the bony fish seem to have many characteristics of a mammalian immune system. The organization and sequence of fish Ig genes also indicate that important events in the evolution of the immune system and the MHC occurred in the fish, but thus far there is no molecular evidence for recognizable MHC-like molecules in any fish. There is clearly an MHC in amphibians and birds with many characteristics like the MHC of mammals (a single genetic region encoding polymorphic class I and class II molecules) and evidence for polymorphic class I and class II molecules in reptiles. However, many details differ from the mammals, and it is not clear whether these reflect historical accident or selection for different lifestyles or environment. For example, the adult frog Xenopus has a vigorous immune system with many similarities to mammals, a ubiquitous class I molecule, but a much wider class II tissue distribution than human, mouse and chicken. The Xenopus tadpole has a much more restricted immune response, no cell surface class I molecules and a mammalian class II distribution. The axolotl has a very poor immune response (as though there are no helper T cells), a wide class II distribution and, for most animals, no cell surface class I molecule. It would be enlightening to understand both the mechanisms for the regulation of the MHC molecules during ontogeny and the consequences for the immune system and survival of the animals. These animals also differ markedly in the level of MHC polymorphism. Another difference from mammals is the presence of previously uncharacterized molecules. In Xenopus and reptiles, there are two populations of class I alpha chain on the surface of erythrocytes, those in association with beta 2m and those in association with a disulfide-linked homodimer.(ABSTRACT TRUNCATED AT 400 WORDS)

Adhesion molecules and animal development

In recent years considerable progress has been made in the identification and characterization of molecules that mediate cell adhesion during animal development. This review attempts to pick out from the vast amount of information in this rapidly expanding field some of the key features of adhesion molecules, to present ideas about their role in development, and to indicate the directions in which the field is now moving.

Identification of a chromosome 18q gene that is altered in colorectal cancers

Allelic deletions involving chromosome 18q occur in more than 70 percent of colorectal cancers. Such deletions are thought to signal the existence of a tumor suppressor gene in the affected region, but until now a candidate suppressor gene on this chromosomal arm had not been identified. A contiguous stretch of DNA comprising 370 kilobase pairs (kb) has now been cloned from a region of chromosome 18q suspected to reside near this gene. Potential exons in the 370-kb region were defined by human-rodent sequence identities, and the expression of potential exons was assessed by an "exon-connection" strategy based on the polymerase chain reaction. Expressed exons were used as probes for cDNA screening to obtain clones that encoded a portion of a gene termed DCC; this cDNA was encoded by at least eight exons within the 370-kb genomic region. The predicted amino acid sequence of the cDNA specified a protein with sequence similarity to neural cell adhesion molecules and other related cell surface glycoproteins. While the DCC gene was expressed in most normal tissues, including colonic mucosa, its expression was greatly reduced or absent in most colorectal carcinomas tested. Somatic mutations within the DCC gene observed in colorectal cancers included a homozygous deletion of the 5' end of the gene, a point mutation within one of the introns, and ten examples of DNA insertions within a 0.17-kb fragment immediately downstream of one of the exons. The DCC gene may play a role in the pathogenesis of human colorectal neoplasia, perhaps through alteration of the normal cell-cell interactions controlling growth.

The unc-5, unc-6, and unc-40 genes guide circumferential migrations of pioneer axons and mesodermal cells on the epidermis in C. elegans

Three known genes guide circumferential migrations of pioneer axons and mesodermal cells on the nematode body wall. unc-5 affects dorsal migrations, unc-40 primarily affects ventral migrations, and unc-6 affects migrations in both directions. Circumferential movements still occur, but are misdirected whereas longitudinal movements are normal in these mutants. Pioneer growth cones migrating directly on the epidermis are affected; growth cones migrating along established axon fascicles are normal. Thus these genes affect cell guidance and not cell motility per se. We propose that two opposite, adhesive gradients guide circumferential migrations on the epidermis. unc-5, unc-6, and unc-40 may encode these adhesion molecules or their cellular receptors. Neurons have access to the basal lamina and the basolateral surfaces of the epidermis, but mesodermal cells contact only the basal lamina. These genes probably identify molecular cues on the basal lamina that guide mesodermal migrations. The same basal lamina cues, or perhaps related molecules on the epidermal cell surfaces, guide pioneer neurons.

MUC18, a marker of tumor progression in human melanoma, shows sequence similarity to the neural cell adhesion molecules of the immunoglobulin superfamily

The MUC18 antigen is an integral membrane glycoprotein of 113 kDa whose expression on primary human melanomas correlates with poor prognosis and the development of metastatic disease. MUC18 is expressed only sporadically in benign melanocytic nevi and thin primary melanomas that have a low probability of metastasizing. However, with increasing tumor thickness, MUC18 expression becomes more frequent and it is found on 80% of advanced primary tumors and metastases. MUC18-encoding cDNA clones were obtained by screening a human melanoma phage lambda expression library with monoclonal antibodies produced against the denatured antigen. The deduced sequence of 603 amino acids consists of a signal peptide, five immunoglobulin-like domains, a transmembrane region, and a short cytoplasmic tail. The highest sequence similarity is with a group of nervous system cell adhesion molecules, which includes neural cell adhesion molecule (N-CAM). The close structural relationship with these molecules suggests that MUC18 may also be a developmentally regulated cell adhesion molecule.

Drosophila neuroglian: a member of the immunoglobulin superfamily with extensive homology to the vertebrate neural adhesion molecule L1

Drosophila neuroglian is an integral membrane glycoprotein that is expressed on a variety of cell types in the Drosophila embryo, including expression on a large subset of glial and neuronal cell bodies in the central and peripheral nervous systems and on the fasciculating axons that extend along them. Neuroglian cDNA clones were isolated by expression cloning. cDNA sequence analysis reveals that neuroglian is a member of the immunoglobulin superfamily. The extracellular portion of the protein consists of six immunoglobulin C2-type domains followed by five fibronectin type III domains. Neuroglian is closely related to the immunoglobulin-like vertebrate neural adhesion molecules and, among them, shows most extensive homology to mouse L1. Its homology to L1 and its embryonic localization suggest that neuroglian may play a role in neural and glial cell adhesion in the developing Drosophila embryo. We report here on the identification of a lethal mutation in the neuroglian gene.

Fasciclin III: a novel homophilic adhesion molecule in Drosophila

Drosophila fasciclin III is an integral membrane glycoprotein that is expressed on a subset of neurons and fasciculating axons in the developing CNS, as well as in several other tissues during development. Here we report on the isolation of a full-length cDNA encoding an 80 kd form of fasciclin III. We have used this cDNA, under heat shock control, to transfect the relatively nonadhesive Drosophila S2 cell line. Examination of these transfected cells indicates that fasciclin III is capable of mediating adhesion in a homophilic, Ca2+-independent manner. Sequence analysis reveals that fasciclin III encodes a transmembrane protein with no significant homology to any known protein, including the previously characterized families of vertebrate cell adhesion molecules. The distribution of this adhesion molecule on subsets of fasciculating axons and growth cones during Drosophila development suggests that fasciclin III plays a role in growth cone guidance.

A genetic and developmental analysis of mutations in labial, a gene necessary for proper head formation in Drosophila melanogaster

We have undertaken a developmental genetic analysis of labial (lab), the most proximal gene in the Antennapedia complex (ANT-C) of Drosophila melanogaster. The terminal phenotype of mutant embryos was examined in cuticle preparations, in thin sections, and by scanning electron microscopy. These preparations revealed a failure of head involution and the loss or disruption of several head structures, including the salivary glands and the H-piece and ventral arm of the cephalopharyngeal apparatus. Although these structures are presumed to derive from the gnathocephalic segments, we argue that the observed defects are likely to be a secondary consequence of a failure of head involution. A function for lab in the development of the adult head was inferred from the phenotype of animals bearing hypomorphic alleles and from clones of lab- tissue generated by mitotic recombination. Two aspects of the mutant phenotype were manifested. Ventrally, a deletion and/or disruption of tissue occurred in the maxillary palp and vibrissae regions. Dorsally, the posterior head appeared to be transformed to a thoracic-like identity. Mutations in lab, like those in the Deformed and proboscipedia loci of the ANT-C, reveal a homoeotic phenotype only in the adult stage of the life cycle.

Selective recognition between embryonic afferent neurons of grasshopper appendages in vitro

Selective affinity between afferent neurons has been proposed as a major mechanism underlying the assembly of the insect peripheral nervous system during development. Afferent insect neurons establish adhesive interactions in vivo that are resistant to proteolytic degradation by elastase and independent of the basal lamina. We have tested whether afferent neurons express selective affinity for one another under more simplified and controlled conditions in vitro. We report here that (1) afferent neurons from dissociated embryonic tissue selectively aggregate within 80 min when incubated with rotation, (2) afferent axons establish and maintain fasciculation in vitro, and (3) afferent neuronal processes in vitro preferentially contact the somata of other afferent neurons in a mixed field of cells.

The mouse neuronal cell surface protein F3: a phosphatidylinositol-anchored member of the immunoglobulin superfamily related to chicken contactin

Several members of the Ig superfamily are expressed on neural cells where they participate in surface interactions between cell bodies and processes. Their Ig domains are more closely related to each other than to Ig variable and constant domains and have been grouped into the C2 set. Here, we report the cloning and characterization of another member of this group, the mouse neuronal cell surface antigen F3. The F3 cDNA sequence contains an open reading frame that could encode a 1,020-amino acid protein consisting of a signal sequence, six Ig-like domains of the C2 type, a long premembrane region containing two segments that exhibit sequence similarity to fibronectin type III repeats and a moderately hydrophobic COOH-terminal sequence. The protein does not contain a typical transmembrane segment but appears to be attached to the membrane by a phosphatidylinositol anchor. Antibodies against the F3 protein recognize a prominent 135-kD protein in mouse brain. In fetal brain cultures, they stain the neuronal cell surface and, in cultures maintained in chemically defined medium, most prominently neurites and neurite bundles. The mouse f3 gene maps to band F of chromosome 15. The gene transcripts detected in the brain by F3 cDNA probes are developmentally regulated, the highest amounts being expressed between 1 and 2 wk after birth. The F3 nucleotide and deduced amino acid sequence show striking similarity to the recently published sequence of the chicken neuronal cell surface protein contactin. However, there are important differences between the two molecules. In contrast to F3, contactin has a transmembrane and a cytoplasmic domain. Whereas contactin is insoluble in nonionic detergent and is tightly associated with the cytoskeleton, about equal amounts of F3 distribute between buffer-soluble, nonionic detergent-soluble, and detergent-insoluble fractions. Among other neural cell surface proteins, F3 most resembles the neuronal cell adhesion protein L1, with 25% amino acid identity between their extracellular domains. Based on its structural similarity with known cell adhesion proteins of nervous tissue and with L1 in particular, we propose that F3 mediates cell surface interactions during nervous system development.

Structure and distribution of the Notch protein in developing Drosophila

Antibodies to Notch show that it is a stable, high-molecular-weight transmembrane glycoprotein, with epidermal growth factor (EGF)-like elements exposed on the cell surface. The protein is phosphorylated variably on serines of the cytoplasmic domain. Individual Notch polypeptide chains appear to be associated with one another by disulfide bonds, suggesting that homotypic interaction of these proteins is required for function. Immunocytochemistry has revealed striking features of Notch expression that might clarify its function: Cells of the ventral neurogenic ectoderm become conspicuously labeled with the protein prior to embryonic neurogenesis, and Notch appears to be associated with cells destined for both neural and epidermal lineages. High levels of Notch become restricted to neuroblasts as they delaminate from the embryonic ectoderm and are apposed to mesoderm. Mesodermal cells express Notch also, suggesting a possible involvement in neurogenesis, or an unknown role in mesoderm differentiation. In larvae and pupae, a correlation of expression and neuroblast mitotic activity is seen for many cells. Notch produced by a dividing neuroblast may persist on derivative cells, including terminally differentiated neurons and nerve processes. In the larval eye imaginal disk, strong Notch expression appears in the morphogenetic furrow, uniformly on cell surfaces as they cluster to form ommatidia. Expression persists on ommatidia after release from the furrow. These patterns suggest a role for Notch in position-dependent development in both initiation and maintenance of cell-surface interactions. In the eye and embryonic ectoderm, uniform expression on cells interacting to produce different developmental lineages from a single primordium suggests that Notch alone may not be sufficient to elaborate cell fates.

Drosophila abl tyrosine kinase in embryonic CNS axons: a role in axonogenesis is revealed through dosage-sensitive interactions with disabled

During Drosophila embryogenesis, the Abelson tyrosine kinase (abl) is localized in the axons of the central nervous system (CNS). Mutations in abl have no detectable effect on the morphology of the embryonic CNS, and the mutant animals survive to the pupal and adult stages. In the absence of abl function, however, heterozygous mutations or deletions of disabled (dab) exert dominant effects, disrupting axonal organization and shifting the lethal phase of the animals to embryonic and early larval stages. Embryos that are homozygous mutant for both abl and dab fail to develop any axon bundles in the CNS, although the peripheral nervous system and the larval cuticle appear normal. The genetic interaction between these two genes begins to define a process in which both the abl tyrosine kinase and the dab gene product participate in establishing axonal connections in the embryonic CNS of Drosophila.

Neural cell recognition molecule F11: homology with fibronectin type III and immunoglobulin type C domains

We report here the complete cDNA sequence of F11 130 kd polypeptide, a chick neural cell surface-associated glycoprotein implicated in neurite fasciculation and elongation. The predicted protein sequence of 1010 amino acids includes an amino-terminal signal peptide and a carboxy-terminal hydrophobic stretch, which is compatible with the consensus motif for covalent attachment of glycosyl-phosphatidylinositol. Accordingly, F11 lacks an intracellular domain, which is consistent with evidence obtained from protease protection experiments on isolated microsomes. In addition, the molecule comprises six domains related to the immunoglobulin domain type C and four resembling fibronectin repeat type III. Both types of repeats resemble those present in neural cell adhesion molecules L1 and N-CAM. The possible identity of F11 with the chick neural glycoprotein contactin is discussed.

Growth cone guidance in insects: fasciclin II is a member of the immunoglobulin superfamily

The cellular cues that guide neuronal growth cones toward their targets are highly conserved in such diverse organisms as insects and vertebrates. Evidence presented here suggests that the molecular mechanisms underlying these events may be equally conserved. This article describes the structure and function of fasciclin II, a glycoprotein expressed on a subset of fasciculating axons in the grasshopper embryo. Antibody perturbation experiments suggest that fasciclin II functions in mediating one form of neuronal recognition: selective fasciculation. Fasciclin II is a member of the immunoglobulin gene superfamily and is homologous in structure and function to the neural cell adhesion molecule N-CAM and to several other vertebrate cell adhesion molecules.