Cloning and sequencing of a cDNA encoding bovine intercellular adhesion molecule 3 (ICAM-3)

A cDNA encoding a putative bovine intercellular adhesion molecule (ICAM)-3, a ligand of the leukocyte integrin LFA-1 (CD11a/CD18), was sequenced and compared with human ICAM sequences. The 1635-bp bovine sequence codes for a protein of 544 amino acids (aa). This putative bovine ICAM-3 has five immunoglobulin (Ig)-like domains similar to human ICAM-1 and ICAM-3, and belongs to the Ig gene superfamily. The overall identities of the deduced aa sequence with those of human ICAM-3 and ICAM-1 are 61% and 58%, respectively. The predicted number and positions of Cys residues are all conserved between the bovine and human ICAM 3 aa sequences.     

Molecular characterization of the murine argininosuccinate synthetase locus.

The cDNA and gene encoding murine argininosuccinate synthetase were cloned and characterized. The cDNA sequence predicts a peptide of 412 amino acids (aa) including the initiator methionine. There is 98% identity with the aa sequence of the human enzyme. The 3'-untranslated region of the cDNA includes two regions of sequence which are conserved between mouse, rat, human and cow. The murine gene contains 16 exons with the start codon occurring in exon 3. Although alternative splicing occurs in primates to include or exclude exon 2, exon 2 sequences were included in the murine mRNA in all tissues and developmental stages examined. The inclusion of exon 2 in murine mRNA, compared to the usual exclusion in human mRNA, may be explained by differences in the donor splice sequences for exon 2.     

Cloning of cDNAs encoding human interphotoreceptor retinoid-binding protein (IRBP) and comparison with bovine IRBP sequences

We have determined the sequence of the human interphotoreceptor retinoid-binding protein mRNA from three separately isolated cDNAs. The sequence is 4.28 kb long and encodes a protein of 1247 amino acids (aa) including a putative signal peptide and propeptide. The sequence is shorter (by about 1.67 kb) than the bovine mRNA with the major difference in the lengths located in the 3'-untranslated region. We suggest that this resulted from an insertion in the bovine gene or a large deletion from the human gene. The insertion/deletion is flanked on either side by sequences that are similar in the bovine and human sequences. Like the bovine polypeptide, the deduced protein sequence from the human cDNA contains a fourfold repeat, with each repeat containing about 300 aa. Among the four repeats, the identity is about 30-40%. The identity between the complete bovine and human polypeptide sequences is 84%. The identity between the nucleotide sequences is 83% (excluding the major insertion/deletion). Comparison with the bovine gene indicates that the human sequence may lack about 5-10 bp at the 5' end of the cDNA; it, however, includes a poly(A) tail at the 3' end. Thus, the human sequence is virtually full length, is similar to the bovine sequence, and contains a striking fourfold repeat.     

CD14 is a member of the family of leucine-rich proteins and is encoded by a gene syntenic with multiple receptor genes.

We have isolated and characterized genomic and cDNA clones encoding the murine homolog of the human monocyte/granulocyte cell surface glycoprotein, CD14. As in man, the expression of murine CD14 is limited to the myeloid lineage. The murine and human CD14 genes are highly conserved in their intron-exon organization and nucleotide sequence. Their deduced protein sequences show 66% amino acid identity. In both mouse and man, the CD14 protein contains a repeating (10 times) leucine-rich motif (LXXLXLX) that is also found in a group of heterogeneous proteins from phylogenetically distant species. The CD14 gene has been mapped to mouse chromosome 18 which also contains at least five genes encoding receptors (Pdgfr, Adrb2r, li, Grl-1, Fms). Thus CD14 and the receptor genes form a conserved syntenic group localized on mouse chromosome 18 and human chromosome 5. The inclusion of CD14 in the family of leucine-rich proteins, its expression profile and the murine chromosomal localization support the hypothesis that CD14 may function as a receptor.     

Identification of fetal liver tyrosine kinase 3 (flt3) ligand domain required for receptor binding and function using naturally occurring ligand isoforms

We used a comparative approach to identify the fetal liver tyrosine kinase 3 (flt3) ligand structure required for binding and function. Two conserved bovine flt3 ligand isoforms, which differ in a defined region within the extracellular domain, were identified and shown to be uniformly transcribed in individuals with diverse MHC haplotypes. Notably, at the amino acid level, the extracellular domain of the bovine flt3 ligand isoform 1 is 81 and 72% identical with the extracellular domains of the human and murine flt3 ligands, respectively, whereas isoform-2 has a deletion within this domain. Bovine flt3 ligand isoform 1, but not 2, bound the human flt3 receptor and stimulated murine pro B cells transfected with the murine flt3 receptor. This retention of binding and function allowed definition of key residues by identifying sequences conserved among species. We have shown that a highly conserved, 18 aa sequence within the flt3 ligand extracellular domain is required for flt3 receptor binding and function. However, a peptide representing this sequence is insufficient for receptor binding as demonstrated by its failure to inhibit the bovine flt3 ligand isoform 1 binding to the human flt3 receptor. The requirement for flanking structure was confirmed by testing bovine flt3 ligand isoform 1 constructs truncated at specific residues outside the 18 aa sequence. Overall, the flt3 ligand structure required for function is markedly similar to that of the related hemopoietic growth factors, CSF-1 and steel factor. This definition of the required flt3 ligand structure will facilitate development of agonists to enhance dendritic cell recruitment for vaccines and immunotherapy.     

Characterization of the caprine (Capra hircus) beta-2 integrin CD18-encoding cDNA and identification of mutations potentially responsible for the ruminant-specific virulence of Mannheimia haemolytica

The leukocyte integrins play a critical role in a great number of cellular adhesive interactions during the immune response. We describe here the isolation and characterization of the caprine beta(2) (CD18) sub-unit, common to the leukocyte beta(2)-integrin family. The deduced 770-amino-acid sequence reveals a transmembrane protein with 80, 81, 83, 96 and 99% identity with its canine, murine, human, bovine and ovine homologues respectively. Analysis of CD18 sequences emphasizes the functional importance of the beta(2) sub-unit I-like domain, and included metal ion-dependent adhesion site-like motif and confirms that of the cytoplasmic tail. Moreover, comparisons of ruminant versus non-ruminant CD18 sequences allowed the identification of 16 potential mutation sites that could be held responsible for the unique virulence of Mannheimia haemolytica for ruminants. Mannheimiosis is known to be the major respiratory disease among ruminants, whereas it is not pathogenic for other mammals, an observation that has been attributed to a specific interaction between M. haemolytica leukotoxin and ruminants' CD18. Therefore, the data provided here offer the possibility to explore new avenues in studies based on the caprine model and provide key information for future studies aimed at elucidating the molecular mechanisms underlying the ruminant-specific virulence of M. haemolytica.     

Structure and domain organization of the CD19 antigen of human, mouse, and guinea pig B lymphocytes. Conservation of the extensive cytoplasmic domain.

The CD19 molecule is a 95,000 Mr cell-surface protein of human B lymphocytes with two extracellular Ig-like domains and a 240 amino acid cytoplasmic tail. cDNA encoding human CD19 and the cytoplasmic domain of the mouse CD19 Ag were previously isolated. In this report, those cDNA were used to isolate cDNA or genomic DNA encoding the complete mCD19 protein and a portion of CD19 from the guinea pig. Mouse pre-B and B cell lines expressed two CD19 mRNA species of 2.7 and 2.2 kb, whereas myeloma cell lines were negative as were T cell lines. Similarly, among mouse organs, only spleen contained detectable CD19 mRNA. These results suggest that only B cells express CD19 in mouse, as in man. Sequence determination revealed substantial conservation, with hCD19 and mCD19 being 66% and hCD19 and gpCD19 being 73% identical in amino acid sequence. The cytoplasmic region of CD19 was most highly conserved with human/mouse being 73% identical and human/guinea pig being 83% identical in amino acid sequence. Isolation of the hCD19 and mCD19 genes and determination of exon/intron boundaries revealed that both genes were structurally similar and were composed of at least 15 exons, 4 encoded extracellular domains, and 9 encoded cytoplasmic domains. Six of the exons that encoded cytoplasmic domains were essentially identical in sequence in all three species indicating that these regions have undergone considerable selective pressure to conserve sequences. Thus, CD19 appears to be well conserved in structure and expression through recent mammalian evolution and the highly conserved cytoplasmic domains may play a critical role in the transduction of CD19-mediated signals.     

The murine gene encoding the highly conserved Sm B protein contains a nonfunctional alternative 3' splice site.

The cDNA and partial genomic nucleotide (nt) sequences were derived for the mouse Sm B polypeptide and compared to the cDNA and genomic sequences encoding human Sm B. The deduced amino acid (aa) sequences from the mouse and human genes are identical with the exception of a single conserved aa substitution, accounting for the ability of anti-Sm antibodies to recognize the Sm polypeptides from a broad range of species. The genomic sequence of mouse B gene is similar to the human B genomic locus that extends from exon 6 to exon 7. These loci include conservation of both 3' alternative splice sites and putative branch points required to process B and B' mRNAs in human cells. However, the nt sequence downstream from the putative distal 3' splice junction and single nt flanking the 3' splice site consensus sequence, differ between mouse and human B. This results in a murine mRNA with a different predicted secondary structure around the distal 3' splice site when compared to humans. Thus, secondary structural constraints in the mRNA or changes in the exon sequence might prevent recognition of this alternative splice site to form B' mRNA in murine tissues.     

Isolation of a cDNA encoding a putative SPARC from the brine shrimp, Artemia franciscana

SPARC (Secreted protein, acidic, rich in cysteine) is an extracellular matrix-associated and anti-adhesive glycoprotein extensively studied in vertebrates. Its presence among invertebrates has been reported in nematodes and flies. We cloned a cDNA containing a complete open reading frame for SPARC from the brine shrimp, Artemia franciscana. The amino acid sequence identity between the Artemia and the fly SPARCs was 55%, whereas that of the Artemia and the nematode proteins was 45%. Artemia and vertebrates exhibited a sequence identity of 30% in the predicted aa sequences. The SPARC consisted of four domains commonly found among reported SPARCs. The protein comprised 291 amino acids, having a signal peptide, a follistatin-like domain, one N-glycosylation site and one calcium-binding EF-hand motif. Fourteen cysteine residues conserved among all the secreted forms of SPARCs were present in the Artemia SPARC, and four extra cysteine residues were also found in it. The extra residues were conserved among SPARCs of the arthropods and the nematode. Phylogenetic analyses showed that the sequences of SPARCs were grouped into those of vertebrates and invertebrates. Though the structural organization of SPARC was conserved among all the species studied, SPARC within a group was highly conserved within that group, but divergent between the two. Northern blots revealed the presence of a 1.1 kb mRNA, which was faintly expressed in embryos and considerably detected in prenauplii and nauplii. The isolation of a SPARC cDNA from Artemia franciscana provides intriguing features of the divergent protein, SPARC.     

A cross-species analysis of the cystic fibrosis transmembrane conductance regulator. Potential functional domains and regulatory sites.

To help elucidate the function of the cystic fibrosis transmembrane conductance regulator (CFTR), we have undertaken a cross-species analysis of the DNA sequence which encodes this protein. We have isolated and characterized the cDNA of the bovine homologue of CFTR. The deduced amino acid sequence shows high overall identity with the published sequences from human and mouse, although there is marked variability between the different potential functional domains. The region around human amino acid 508, which is deleted in 70% of cystic fibrosis chromosomes, is highly conserved across species; of the missense cystic fibrosis mutations reported to date, all of the amino acids in the normal human sequence are conserved in the bovine and mouse sequences. A single amino acid encoded by the human cDNA (Ser-434) is missing in the bovine sequence, and there are two amino acids encoded by the bovine sequence which are absent in the human. These all stem from in-frame 3-base omissions within the sequences. In addition to the cow, we amplified the DNA sequences encoding a portion of the R-domain from sheep, monkey, rabbit, and guinea pig. These sequences show relatively low overall sequence identity (63%), but nearly all of the potential protein kinase A and protein kinase C phosphorylation sites are conserved over all of the species examined. Our results suggest functional significance for certain highly conserved residues and putative domains within CFTR.     

Characterization of the caprine (Capra hircus) beta-2 integrin CD18-encoding cDNA and identification of mutations potentially responsible for the ruminant-specific virulence of Mannheimia haemolytica

The leukocyte integrins play a critical role in a great number of cellular adhesive interactions during the immune response. We describe here the isolation and characterization of the caprine β₂ (CD18) sub-unit, common to the leukocyte β₂-integrin family. The deduced 770-amino-acid sequence reveals a transmembrane protein with 80, 81, 83, 96 and 99% identity with its canine, murine, human, bovine and ovine homologues respectively. Analysis of CD18 sequences emphasizes the functional importance of the β₂ sub-unit I-like domain, and included metal ion-dependent adhesion site-like motif and confirms that of the cytoplasmic tail. Moreover, comparisons of ruminant versus non-ruminant CD18 sequences allowed the identification of 16 potential mutation sites that could be held responsible for the unique virulence of Mannheimia haemolytica for ruminants. Mannheimiosis is known to be the major respiratory disease among ruminants, whereas it is not pathogenic for other mammals, an observation that has been attributed to a specific interaction between M.?haemolytica leukotoxin and ruminants’ CD18. Therefore, the data provided here offer the possibility to explore new avenues in studies based on the caprine model and provide key information for future studies aimed at elucidating the molecular mechanisms underlying the ruminant-specific virulence of M. haemolytica.     

Comparative sequence analysis of the hexon gene in the entire spectrum of human adenovirus serotypes: phylogenetic, taxonomic, and clinical implications

The adenovirus (AdV) hexon constitutes the major virus capsid protein. The epitopes located on the hexon protein are targets of neutralizing antibodies in vivo, serve in the recognition by cytotoxic T cells, and provide the basis for the classification of adenoviruses into the 51 serotypes known to date. We have sequenced the entire hexon gene from human serotypes with incomplete or no sequence information available (n = 34) and performed a comparative analysis of all sequences. The overall sequence divergence between the 51 human serotypes ranged from 0.7 to 25.4% at the protein level. The sequence information has been exploited to assess the phylogeny of the adenovirus family, and protein distances between the six AdV species (A to F) and among individual serotypes within each species were calculated. The analysis revealed that the differences among serotypes within individual species range from 0.3 to 5.4% in the conserved regions (765 amino acids [aa]) and from 1.5 to 59.6% in the variable regions (154 to 221 aa). Serotypes of different species showed an expectedly greater divergence both in the conserved (5.9 to 12.3%) and variable (49.0 to 74.7%) regions. Construction of a phylogenetic tree revealed three major clades comprising the species B+D+E, A+F, and C, respectively. For serotypes 50 and 51, the original assignment to species B and D, respectively, is not in accordance with the hexon DNA and protein sequence data, which placed serotype 50 within species D and serotype 51 within species B. Moreover, the hexon gene of serotype 16, a member of species B, was identified as the product of recombination between sequences of species B and E. In addition to providing a basis for improved molecular diagnostics and classification, the elucidation of the complete hexon gene sequence in all AdV serotypes yields information on putative epitopes for virus recognition, which may have important implications for future treatment strategies permitting efficient targeting of any AdV serotype.     

The murine homologue of the T lymphocyte antigen CD28. Molecular cloning and cell surface expression

The human T lymphocyte Ag CD28 (Tp44) is a homodimeric glycoprotein expressed on the surface of a majority of human peripheral T cells and thymocytes. Although exposure of T cells to anti-CD28 mAb does not activate T cells, stimulation of CD28 can synergize with signals transmitted through the TCR or other stimuli to augment proliferation and lymphokine production. We have used a portion of the human CD28 cDNA to isolate a homologous murine cDNA from an EL4 T lymphoma library. The murine clone has 61% nucleotide identity with the human cDNA. Both human and murine sequences exhibit homology with members of the Ig supergene family and CTLA-4, a T cell specific murine gene. Many characteristics of the human CD28 molecule are conserved within the putative murine CD28 polypeptide. The murine cDNA sequence encodes a polypeptide of 218 amino acids that has 68% identity with the human sequence. Both the murine and human molecules are integral membrane glycoproteins with hydrophobic signal peptide sequences and transmembrane region. All five potential N-linked glycosylation sites are conserved and six of the seven cysteine residues of the mouse protein are found in the human CD28 polypeptide. The murine cDNA is encoded by a single copy nonrearranging gene whose expression at the mRNA level is restricted to T cells. A rabbit antiserum was raised against a synthetic peptide corresponding to a hydrophilic portion of the translated murine cDNA sequence. This antiserum identifies an 80-kDa homodimer consisting of disulfide-bonded subunits of 40 kDa that is expressed on splenic T cells, thymocytes, and several T cell tumors, but not on B cells. deglycosylation studies indicate that four of the five N-linked glycosylation sites are used and that the mature core protein has a molecular mass of 25 kDa, close to that predicted by the cDNA sequence. Transfection of the murine cDNA into Chinese hamster ovary cells resulted in the expression of an 80-kDa dimeric molecule that was immunoprecipitated by the antipeptide antiserum. Taken together, these data provide strong support that we have identified the murine homologue of CD28.