Intracellular expression of the truncated extracellular domain of c-erbB-3/HER3.

The ERBB3 gene is expressed as a 6.2- and a 1.4-kb transcript. The former encodes the full-length transmembrane protein and the latter a truncated extracellular fragment consisting of 140 amino acids of the c-erbB-3 protein followed by 43 unique residues. We have examined the expression of the two ERBB3 transcripts by Northern blotting in cancer cell lines and normal human fetal and adult tissues. We expressed the truncated receptor fragment and showed that it was glycosylated, probably with a single N-linked complex sugar chain, and that the protein was a 58-kDa disulphide-linked dimer. We were able to crosslink iodinated neuregulin (NRG)-1beta to the full-length solubilised receptor but not to the truncated dimeric protein. Using Western blot analysis, the truncated protein was shown to be present in cell lysates and, using immunoelectron microscopy, in vesicular structures within cells and associated with the plasma cell membrane.

Brachydactyly and mental retardation: an Albright hereditary osteodystrophy-like syndrome localized to 2q37.

We report five patients with a combination of brachymetaphalangia and mental retardation, similar to that observed in Albright hereditary osteodystrophy (AHO). Four patients had cytogenetically visible de novo deletions of chromosome 2q37. The fifth patient was cytogenetically normal and had normal bioactivity of the alpha subunit of Gs (Gs alpha), the protein that is defective in AHO. In this patient, we have used a combination of highly polymorphic molecular markers and FISH to demonstrate a microdeletion at 2q37. The common region of deletion overlap involves the most telomeric 2q marker, D2S125, and extends proximally for a maximum distance of 17.6 cM. We suggest this represents a consistent phenotype associated with some deletions at 2q37 and that genes important for skeletal and neurodevelopment lie within this region. Screening for deletions at this locus should be considered in individuals with brachymetaphalangia and mental retardation. Furthermore, 2q37 represents a candidate region for type E brachydactyly.

PAX3 gene structure and mutations: close analogies between Waardenburg syndrome and the Splotch mouse.

The human PAX3 gene contains a paired box and a paired-type homeobox, and is believed to play a role in pattern formation in the embryo. We describe the exon-intron structure of the homeobox-containing part of PAX3, complementing earlier descriptions of the 5' part of the gene. Mutations in PAX3 have been described in patients with Type 1 Waardenburg syndrome, who have hearing loss and pigmentary abnormalities, while Splotch mice have mutations in the homologous mouse Pax-3 gene. We describe a series of patients who have previously unidentified PAX3 mutations. These include a chromosomal deletion, a splice-site mutation and an amino acid substitution which closely correspond to the molecular changes seen in the Splotch-retarded, Splotch and Splotch-delayed mouse mutants respectively. These mutations confirm that Waardenburg syndrome is produced by gene dosage effects and show that the phenotypic differences between Splotch mice and humans with Waardenburg syndrome are caused by differences in genetic background rather than different primary effects of the mutations.

Transcription of a stem/loop region of a tumour-amplified sequence induces bacterial aggregation.

A sequence of human DNA, amplified in a lung tumour, was shown to induce expression-dependent effects on Escherichia coli phenotype. Previous studies have demonstrated the induction of abnormal plasmid supercoiling and bacterial aggregation in host strains harbouring various constructs encoding this region. Subcloning identified a short stretch of 50 bp crucial for these effects. This study details further characterization of the active sequence. Computer analysis of the region predicted the formation of a stem/loop structure in transcribed RNA. Transcription, in the absence of translation, of a 22 bp sequence comprising this structure was sufficient to induce bacterial aggregation. Site-directed and random mutagenesis of the sub-region were carried out in order to identify critical factors in the induction of this phenotypic shift. It was found that changes in the loop sequence modulated activity, and mutations increasing predicted stem stability produced more active constructs. The wild-type sequence induced high level aggregation in only a limited number of strains but using the mutagenesis data, a sequence was synthesized that induced high level aggregation in most E. coli strains tested.