Assay of the heat-labile enterotoxin of Escherichia coli in infant rabbits.

Infant rabbits were shown to respond to Escherichia coli heat-labile enterotoxin by a consistent increase in intestinal fluid content, which was maximal 5 h after oral dosing. Infant rabbits could be used in a simple quantitative assay for heat-labile E. coli enterotoxin based on the ratios of gut weight to remaining body weight 5 h after oral dosing. Infant rabbits remained responsive to heat-labile enterotoxin up to 14 days of age, after which their gastric pH became low enough to destroy the enterotoxin. Rabbits that had been deprived of food before being dosed had a reduced gastric pH and a reduced response to the enterotoxin. Lincomycin andmitomycin C were found not to increase th e yield of heat-labile enterotoxin from E. coli strain P307.

Tandem arrangement of the closely linked desmoglein genes on human chromosome 18.

The desmogleins, together with the desmocollins, both members of the cadherin superfamily, are the adhesive proteins of the desmosome type of cell junction, characteristically found in epithelial cells. Three different human desmoglein isoforms are encoded by separate genes (DSG1, DSG2, and DSG3) located on chromosome 18q12.1. DSG2 has been shown to be the most widely expressed in all desmosome-containing tissues, whereas DSG1 and DSG3 are expressed only in certain tissues, mostly stratified squamous epithelia. The desmoglein isoforms are expressed in a stratification-related manner in human epidermis, DSG1 being suprabasally expressed and DSG3 at a lower level, while DSG2 expression is weak and basal. Yeast artificial chromosome clones carrying all three known human desmoglein genes have now been isolated. The smallest clone containing all three DSG genes was 275 kb, and the three desmoglein genes were clustered within a region of less than 150 kb. From the types of clone obtained and from restriction enzyme analysis the order of the DSG genes and their orientation was deduced to be 5'-DSG1-DSG3-DSG2-3'. There thus appears to be some correspondence between the order of DSG genes and their expression within tissues, raising the intriguing possibility that the organization of the desmoglein gene cluster is required for properly regulated gene expression.

A YAC contig joining the desmocollin and desmoglein loci on human chromosome 18 and ordering of the desmocollin genes.

The desmocollins and desmogleins are members of the cadherin family of adhesive proteins present in the desmosome type of cell-cell junction. All of the known desmoglein and desmocollin isoforms, which have differing tissue and developmental distributions, are coded by very closely linked genes at 18q12.1. We have previously described YAC clones carrying all three known desmoglein (DSG) genes. We have now isolated YAC clones that carry all three known desmocollin genes (DSC1, 2, and 3) from two libraries and also isolated clones that join the DSC locus to the DSG locus, forming a complete contig for the region. Absence of chimeric ends for some of the YACs was confirmed by isolating Vectorette PCR products for the YAC ends and mapping the derived DNA sequences back to other YACs from CEPH. The whole DSC/DSG gene complex occupies no more than about 700 kb, and the genes are arranged in the order cen-3'-DSC3-DSC2-DSC1-5'-5'-DSG1-DSG3-D SG2-3'-tel, so that the two gene clusters are transcribed outward from the interlocus region. A P1 clone carrying part of DSC2 and DSC3 confirmed the relative orientation of transcription of these two genes. The conservation of close genetic linkage may be of trivial importance related to the recent duplication of these genes or may be because there is a region within the locus that is involved in coordinating the expression of the desmoglein and desmocollin genes.

Biological evaluation of a methanol-soluble, heat-stable Escherichia coli enterotoxin in infant mice, pigs, rabbits, and calves.

Escherichia coli P16 was shown to produce two heat-stable toxins (ST) with differing biological activity. The toxins were separated by methanol extraction, and the first, STa, was methanol soluble, partially heat stable, active in neonatal piglets (1 to 3 days old) and infant mice, but inactive in weaned pigs (7 to 9 weeks old); the second, STb, was methanol insoluble, active in weaned pigs and rabbit ligated loops, but inactive in infant mice. It is therefore suggested that use of suckling mice as indicators of ST production will fail to identify certain ST-producing strains.

Exon-intron organization of the human type 2 desmocollin gene (DSC2): desmocollin gene structure is closer to "classical" cadherins than to desmogleins.

The cadherins are a superfamily of calcium-dependent glycoproteins that are cell adhesion molecules. Two families of cadherins, the desmocollins (Dsc) and desmogleins (Dsg), are found only in the desmosome type of cell-cell junction. They are each present in at least three different isoforms with differing spatial and temporal distributions and are specified by two clusters of closely linked genes on human chromosome 18q12.1. The human DSC2 gene, coding for the most widely distributed form of the desmocollins, has been found to consist of more than 32 kb of DNA. By using PCR we have determined the exon-intron organization. The gene is arranged into 17 exons ranging in size from 46 to 258 bp; exon 16 is alternatively spliced, giving rise to the a and b forms of the protein. This has revealed a remarkable degree of conservation of intron position with other cadherins. The desmocollin exon-intron organization is more similar to the so-called classical cadherins than to the desmogleins, especially in the cytoplasmic domain. Intron 1 is the largest in DSC2, as it is in the desmogleins, in contrast to the classical cadherins, where intron 2 is extremely large; this latter intron is missing from the desmogleins.