Complete genome structure of the nitrogen-fixing symbiotic bacterium Mesorhizobium loti

The complete nucleotide sequence of the genome of a symbiotic bacterium Mesorhizobium loti strain MAFF303099 was determined. The genome of M. loti consisted of a single chromosome (7,036,071 bp) and two plasmids, designated as pMLa (351,911 bp) and pMLb (208, 315 bp). The chromosome comprises 6752 potential protein-coding genes, two sets of rRNA genes and 50 tRNA genes representing 47 tRNA species. Fifty-four percent of the potential protein genes showed sequence similarity to genes of known function, 21% to hypothetical genes, and the remaining 25% had no apparent similarity to reported genes. A 611-kb DNA segment, a highly probable candidate of a symbiotic island, was identified, and 30 genes for nitrogen fixation and 24 genes for nodulation were assigned in this region. Codon usage analysis suggested that the symbiotic island as well as the plasmids originated and were transmitted from other genetic systems. The genomes of two plasmids, pMLa and pMLb, contained 320 and 209 potential protein-coding genes, respectively, for a variety of biological functions. These include genes for the ABC-transporter system, phosphate assimilation, two-component system, DNA replication and conjugation, but only one gene for nodulation was identified.

Sequence and analysis of chromosome 3 of the plant Arabidopsis thaliana

Arabidopsis thaliana is an important model system for plant biologists. In 1996 an international collaboration (the Arabidopsis Genome Initiative) was formed to sequence the whole genome of Arabidopsis and in 1999 the sequence of the first two chromosomes was reported. The sequence of the last three chromosomes and an analysis of the whole genome are reported in this issue. Here we present the sequence of chromosome 3, organized into four sequence segments (contigs). The two largest (13.5 and 9.2 Mb) correspond to the top (long) and the bottom (short) arms of chromosome 3, and the two small contigs are located in the genetically defined centromere. This chromosome encodes 5,220 of the roughly 25,500 predicted protein-coding genes in the genome. About 20% of the predicted proteins have significant homology to proteins in eukaryotic genomes for which the complete sequence is available, pointing to important conserved cellular functions among eukaryotes.

Human desmocollin 1a transiently expressed in COS-7 cells and NIH 3T3-3 cells is reacted by IgG4 antibodies in a pemphigus foliaceus serum

Human desmocollin (Dsc) 1 is an autoantigen in the subcorneal pustular dermatosis type of IgA pemphigus. Moreover, Dscs, particularly bovine Dscs, are recognized by IgG antibodies in certain sera of various types of pemphigus by immunoblotting. In this study, 10 pemphigus sera were examined by immunofluorescence for IgG antibodies to human Dsc1a, Dsc2a and Dsc3a transiently expressed in COS-7 and NIH 3T3-3 cells using two different transfection methods. IgG antibodies in a number of sera showed a strong background staining with untransfected COS-7 and NIH 3T3-3 cells. Using COS-7 cells, a pemphigus foliaceus serum, which did not stain untransfected COS-7 cells, was found to contain IgG antibodies reactive exclusively with Dsc1a. This serum showed the same reactivity in studies using NIH 3T3-3 cells. Moreover, this pemphigus foliaceus serum contained IgG4, but not IgG1 antibodies, to Dscla expressed in the NIH 3T3-3 cells. These results indicate that autoantibody response in pemphigus foliaceus might be more heterogenous than hitherto supposed.

Envoplakin and periplakin are the paraneoplastic pemphigus antigens

Paraneoplastic pemphigus (PNP) sera have been reported to immunoprecipitate multiple proteins, including the 250 kDa and 210 kDa proteins believed to correspond to desmoplakins I/II, BP230, and two unidentified proteins of 190 kDa and 170 kDa. We have recently provided evidence that the presence of the 210 kDa and 190 kDa proteins is the most prominent feature of PNP, and have suggested that the major 210 kDa antigen may not correspond to desmoplakin II. Using immunoprecipitation and immunoblotting, we found that some PNP sera identified a doublet protein migrating at 210 kDa, with the larger protein corresponding to desmoplakin II, and the smaller protein corresponding to envoplakin, a recently described precursor of the keratinocyte cornified envelope. In contrast to desmoplakin II, envoplakin was detected by all PNP sera analyzed. Using immunoblotting and immunoprecipitation, we further showed that the 190 kDa PNP antigen is identical to periplakin, another recently identified envelope precursor that can form complexes with envoplakin. Like desmoplakin and BP230, envoplakin and periplakin belong to the plakin family of proteins.

Bullous pemphigoid showing unusual ocular changes

We describe a 68-year-old Japanese woman with erythematous and bullous skin lesions. Antibasement membrane zone antibodies of IgG class were detected in the serum, which reacted with the 230 kDa and 180 kDa bullous pemphigoid antigens on immunoblot analysis. The patient later developed corneal opacity in both eyes and a detachment of the epithelium in the centre of the cornea. However, no change was seen in the conjunctiva. These ocular lesions are different from those of cicatricial pemphigoid. The ocular lesions could be reproduced by injection of IgG from this patient into the stroma of the corneas of rabbits. Both the cutaneous and ocular lesions responded well to oral corticosteroid therapy. We diagnosed this patient as having bullous pemphigoid associated with a unique ocular lesion.

Analysis of antigens targeted by circulating IgG and IgA autoantibodies in 50 patients with cicatricial pemphigoid

In this study we investigated sera from 50 typical cicatricial pemphigoid (CP) patients. By indirect immunofluorescence on 1 M NaCl-split human skin sections, IgG of 17 sera and IgA of 22 sera reacted with the epidermal side of the split, while IgG of two sera reacted with the dermal side. These latter two sera were later confirmed to be anti-epiligrin CP. By immunoblotting of epidermal extracts, IgG of 14 sera reacted with the 230 kD bullous pemphigoid (BP) antigen (BP230). IgG of 15 sera and IgA of 11 sera reacted with the 180 kD BP antigen (BP180). Interestingly, a bacterial fusion protein containing the BP180 NC16a domain was recognized by IgG of 18 sera but not by IgA of any sera. Fusion proteins containing the C-terminal region of BP180 were recognized by IgG of 20 sera, but it was detected by IgA of only two sera. Our results suggest that, although CP sera show very low titers of autoantibodies, a considerable number of sera contain IgG antibodies to BP180 (either NC16a or C-terminal domain), confirming previous studies. In addition, we showed that greater numbers of IgA antibodies react with BP180, seemingly with different types of epitopes from those for IgG antibodies. Because the specificity of IgG antibodies is not very different from those in BP, IgA antibodies may play a specific role for the development of characteristic clinical features in CP. Future studies should elucidate the pathogenic role of the IgA antibodies in CP.

Human desmocollin 1 (Dsc1) is an autoantigen for the subcorneal pustular dermatosis type of IgA pemphigus

IgA pemphigus showing IgA anti-keratinocyte cell surface autoantibodies is divided into subcorneal pustular dermatosis (SPD) and intraepidermal neutrophilic IgA dermatosis (IEN) types. We previously showed by immunoblotting that IgA from some IgA pemphigus patients reacted with bovine desmocollins (Dsc), but not human Dsc. To determine the antigen for IgA pemphigus, we focused on conformation-dependent epitopes of Dsc, because sera of patients with classical pemphigus recognize conformation-sensitive epitopes of desmogleins. We constructed mammalian expression vectors containing the entire coding sequences of human Dsc1, Dsc2, and Dsc3 and transiently transfected them into COS7 cells by lipofection. Immunofluorescence of COS7 cells transfected with single human Dscs showed that IgA antibodies of all six SPD-type IgA pemphigus cases reacted with the surface of cells expressing Dsc1, but not with cells expressing Dsc2 or Dsc3. In contrast, none of seven IEN-type IgA pemphigus cases reacted with cells transfected with any Dscs. These results convincingly indicate that human Dsc1 is an autoantigen for SPD-type IgA pemphigus, suggesting the possibility of an important role for Dsc1 in the pathogenesis of this disease. This study shows that a Dsc can be an autoimmune target in human skin disease.

Apoptosis identified by DNA fragmentation in epidermal neoplasms

In the previous study, we demonstrated apoptotic cells in basal cell carcinomas by means of terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling (TUNEL). Positive staining cells were present at the peripheries and centers of the nests. The number of positive cells increased in cases showing deep infiltration. We also stained other epidermal neoplasms using this modified TUNEL method. In squamous cell carcinomas, many positive cells were observed in poorly differentiated types, but only a few cells were stained in well-differentiated types. TUNEL positive cells were rare in Bowen's disease. No positive cells were seen in seborrheic keratosis or verruca vulgaris. Our studies showed that apoptotic cells were more common in rapid growth neoplasms than in slow growth neoplasms.