Tumour-suppressor activity of H19 RNA

Loss of heterozygosity in certain human embryonal tumours implicates a tumour-suppressor gene at chromosome 11p15.5 and selective loss of maternal alleles suggests that this gene is paternally imprinted. The human H19 gene maps to 11p15.5, is expressed in differentiating fetal cells and is paternally imprinted. We report here that two embryonal tumour cell lines, RD and G401, showed growth retardation and morphological changes when transfected with an H19 expression construct. More importantly, clonogenicity in soft agar and tumorigenicity in nude mice were abrogated in the G401-H19 transfectants. In addition to demonstrating its tumour-suppressor potential, this transfection system should help structural and functional studies of the enigmatic H19 gene.

Apoptosis: final common pathway of photoreceptor death in rd, rds, and rhodopsin mutant mice

Mutations in the retinal degeneration, retinal degeneration slow(/peripherin) and rhodopsin genes cause photoreceptor degeneration in humans and mice. Although the phenotypes arising from these mutations are different, suggesting different mechanisms of pathogenesis, we present evidence that apoptosis may be the final common pathway of the disease process linking genotype to phenotype. We observed internucleosomal cleavage of retinal DNA by gel electrophoresis and fragmented DNA at the single cell level by labeling the nicked DNA ends with biotinylated poly(dU). In retinal degeneration mice, DNA fragmentation occurred during the period of photoreceptor degeneration. In retinal degeneration slow mice and in transgenic mice expressing a mutant (Pro347Ser) rhodopsin gene, DNA fragmentation occurred after normal histogenetic cell death (also apoptosis) had ceased. Since DNA fragmentation by internucleosomal cleavage is a cardinal feature of apoptosis, our data suggest that all three of these genetic mutations lead to apoptosis.

Cellular interactions implicated in the mechanism of photoreceptor degeneration in transgenic mice expressing a mutant rhodopsin gene

Photoreceptors of transgenic mice expressing a mutant rhodopsin gene (Pro347-->Ser) slowly degenerate. The mechanism of degeneration was studied by aggregation of embryos of normal and transgenic mice to form chimeras. In these chimeras, mosaicism was observed in the coat color, retinal pigment epithelium, and retina. In the retina, the genotype of adjacent patches of normal and transgenic photoreceptors was determined by in situ hybridization with a transgene-specific RNA probe. Photoreceptors in the chimeric retina degenerated uniformly, independent of the genotype and similar to the photoreceptors in transgenic mice. However, the chimeric retinas showed varying proportions of normal and transgenic cells. The chimeric retina with a nearly even proportion of normal and transgenic photoreceptors displayed uniform but slower degeneration than that observed in a transgenic mouse of the same age. Our results demonstrate non-autonomy of gene action for the mutated rhodopsin gene and imply that cellular interactions between photoreceptors in the retina probably play a role in degeneration.

Imprinting of human H19: allele-specific CpG methylation, loss of the active allele in Wilms tumor, and potential for somatic allele switching

Genomic imprinting and monoallelic gene expression appear to play a role in human genetic disease and tumorigenesis. The human H19 gene, at chromosome 11p15, has previously been shown to be monoallelically expressed. Since CpG methylation has been implicated in imprinting, we analyzed methylation of H19 DNA. In fetal and adult organs the transcriptionally silent H19 allele was extensively hypermethylated through the entire gene and its promoter, and, consistent with a functional role for DNA methylation, expression of an H19 promoter-reporter construct was inhibited by in vitro methylation. Gynogenetic ovarian teratomas were found to contain only hypomethylated H19 DNA, suggesting that the expressed H19 allele might be maternal. This was confirmed by analysis of 11p15 polymorphisms in a patient with Wilms tumor. The tumor had lost the maternal 11p15, and H19 expression in the normal kidney was exclusively from this allele. Imprinting of human H19 appears to be susceptible to tissue-specific modulation in somatic development; in one individual, cerebellar cells were found to express only the otherwise silent allele. Implications of these findings for the role of DNA methylation in imprinting and for H19 as a candidate imprinted tumor-suppressor gene are discussed.

DNA content and estrogen receptors in primary carcinoma of the breast

DNA content and estrogen-receptor status were studied in 54 consecutive patients with primary breast carcinoma. Estrogen-receptor determinations were performed by immunohistochemical assay on frozen sections with a monoclonal antibody against the estrogen-receptor molecule and by biochemical analysis with a dextran-coated charcoal method. Nuclear DNA content was measured by flow cytometry performed on formalin-fixed, paraffin-embedded sections. Seventy-two percent of tumours were positive for estrogen receptors by immunohistochemical assay and 67% by biochemical assay. Comparison of the qualitative results of immunohistochemical and biochemical estrogen-receptor determinations revealed a strong correlation between the two assays, with agreement in 90% of the cases (p less than 0.001). Regression analysis showed only a weak relationship between the quantitative results of the two assays. DNA analysis was performed in 51 cases, and 54% demonstrated aneuploid stemlines by flow cytometry. An association was demonstrated between aneuploidy and low levels of estrogen receptor. The association was highly significant with the immunohistochemical assay but not with the biochemical assay. The authors' results suggest that immunohistologic determinations of estrogen receptor status may better reflect the biologic features of the tumour cells. However, improved standardization in reporting the results is necessary if the test is to have widespread use.

A simple method for the preparation of human serum albumin

A simple method, based on ethanol fractionation, for the preparation of highly purified human serum albumin with a higher yield than that of the conventional ethanol procedures is described. It consists of two purification steps, namely, precipitation of most of the other plasma proteins from a 3-fold diluted plasma with ethanol at 42% concentration, pH 5.75 and -5 degrees C, leaving over 96% pure albumin in the supernatant, followed by isoelectric precipitation of albumin from the supernatant at pH 4.8 and -5 degrees C. The paste thus obtained was processed to the final albumin solution according to the conventional methods. The yield of the final albumin with a purity of over 99% was equivalent to 29.5 g/l of plasma representing a recovery of over 93%. The possibility of recovering other plasma proteins and the suitability for large scale preparation are also discussed.