In situ hybridization of messenger RNA sequences

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.

Detection of gastrin and its messenger RNA in Zollinger-Ellison tumors by non-radioactive in situ hybridization and immunocytochemistry

Gastrin immunocytochemistry and non-radioactive in situ hybridization, using biotinylated oligonucleotide probes, for gastrin mRNA have been used for studying a retrospective material of six gastrin-producing (Zollinger-Ellison) tumors. Hybridization results for gastrin mRNA were positive in all six, while gastrin immunoreactivity could be detected in five tumors. In one of the patients, different areas of the same tumor displayed differences in immunoreactivity to gastrin, but were uniformly hybridization positive. Weak hybridization signals were detected in liver metastases from a necropsy case, while the gastrin immunostaining was more pronounced. The results show that non-radioactive hybridization methods are applicable to routine clinical specimens stored for as long as 16 years and that in situ hybridization may be a useful complement to immunocytochemical diagnosis, particularly in cases where high synthesis and little storage of hormonal products occur.

In situ hybridisation of albumin mRNA in normal liver and hepatocellular carcinoma with a digoxigenin labelled oligonucleotide probe

AIMS

To study the localisation and distribution of albumin mRNA in normal liver and hepatocellular carcinoma by in situ hybridisation with an oligonucleotide probe.

METHODS

A 51 base oligonucleotide was synthesised from a sequence at the 5' end of the human albumin gene and the probe was labelled at its 3' end with digoxigenin 11-dUTP. Formalin fixed, wax embedded sections of liver biopsy specimens were used to study the localisation and distribution of albumin mRNA. After in situ hybridisation the bound probe was visualised using a digoxigenin antibody conjugated with alkaline phosphatase.

RESULTS

In normal liver albumin mRNA was detected in hepatocytes and no positive signal was observed in biliary epithelium, vascular endothelium, or Kupffer cells. In 75% (9/12) of the hepatocellular carcinomas studied a positive hybridisation signal was observed in tumour cells.

CONCLUSIONS

Albumin mRNA can be detected in sections of formalin fixed, wax embedded liver, a digoxigenin labelled probe is ideally suited for in situ hybridisation of liver because there is no background from the detection system. The identification of albumin mRNA may be a useful marker of hepatocellular carcinoma, and the demonstration of albumin mRNA by in situ hybridisation overcomes the potential background problem associated with albumin immunohistochemistry.

Quantitative non-radioactive in situ hybridization. Model studies and studies on pituitary proopiomelanocortin cells after adrenalectomy

Non-radioactive in situ hybridization using biotinylated oligodeoxynucleotides and a detection protocol involving monoclonal antibiotin antibodies and the alkaline phosphatase-anti-alkaline phosphatase system was employed for quantitation by image analysis. Calibrations of the image analysis system with neutral density filters revealed that the grey levels recorded were strongly linearly correlated to the absorbance (r2 = 0.97) in the range studied in tissue specimens (0-0.8 optical density or absorbance units). Several methodological parameters, including light source stability, section thickness, probe concentration and development time were initially optimized. Model systems revealed that the grey level measured varied linearly with the logarithm of the target concentration. Moreover, histophysiological studies on adrenalectomized and sham-operated rats documented that previous biochemical data on an 8- to 10-fold increase in anterior lobe proopiomelanocortin (POMC) mRNA levels 8 days after adrenalectomy are accounted for both by an increased ACTH cell concentration and content of POMC mRNA, as well as by increases in ACTH cell sizes and cell numbers. Also in agreement with biochemical data, image analysis did not reveal significant differences between OD's of melanotrophs in adrenalectomized and sham-operated animals. To our knowledge, these data are the first to document that non-radioactive in situ hybridization can be employed for relative quantitation. A particular advantage of this approach is the good morphological definition which permits parallel analyses of densitometric values, cell sizes and cell areas/cell numbers.