Li Wang, Wei Lu, Yuan-Gen Chen, Xiao-Mei Zhou, Jian-Ren Gu, ¹Department of Gastroenterology, Huashan Hospital, Shanghai Medical University, Shanghai 200040, China
²National Laboratory for Oncogene and Related Genes, Shanghai Cancer Insti tute, Shanghai 200032, China
Dr. Li Wang, female, born on 1996-11-24 in Jingjiang, Jiangsu Province , Han nationality, graduated from Shanghai Medical University as a Ph.D. fellow in 1999, attending doctor of gastroenterology, majoring in molecular biol ogy research of gastroenterology, having 12 papers published.
Supported by the National Natural Science Foundation of China, N o.39470329
Correspondence to: Dr. Li Wang, Department of Gastroenterology, Huashan Hospital, 12 Wu Lu Mu Qi Zhong Road, Shanghai 200040, China
Telephone: +86-21-62489999 Ext.274
Email.Wangli＠shtel.net.cn
Received: 1999-04-08

Subject headings: colonic mucosa; colonic neoplasms; RNA, mess enger; gene expression

Wang L, Lu W, Chen YG, Zhou XM, Gu JR. Comparison of gene expression between normal colon mucosa and colon carcinoma by means of messenger RNA differential display. World J Gastroentero, 1999;5(6):533-534

INTRODUCTION
Messenger RNA differential display technique, developed by Dr. Liang in 1992^［1］, is a powerful new tool for identifying and cloning differentially expressed genes in a certain type of cell line, tissue or a special developing stage. Using this method, large amounts of molecular biological information can be obtained easily and quickly. In our study, this technique was used to compare genes expressed differentially between normal colon mucosa and colon carcinomas, in order to understand the molecular biological basis of colon cancer.

MATERIALS AND METHODS
Samples
Fifteen samples of colon carcinoma were obtained from radical colectomy, samples of normal colon mucosa were obtained 8cm-10cm apart from colon carc inoma.

Reagents
Guanidine thiocyanate and β-mercaptoethanol were purchased fro m BRL (America); T₁₂MN primer and AP primer were presented by the National Laboratory for Oncogene and Related Genes, Shanghai Cancer Institute.

Experimental procedures
RNA preparation Total RNA was isolated from normal colon mucosa and colon carcinoma using single-step method of guanidine thiocyanate describe d by Chomczynski^［2,3］, some steps had been modified.

Reverse transcription DNA-free RNA was reversely transcribed using the oligo-dT primer T₁₂MN in the presence of [α-³²P]dATP.

PCR amplification Using cDNA products as temples, PCR reaction s were performed in the presence of ［γ-³⁵S］ dATP, the primer combination was T₁₂MN and AP. Following denaturation for 30 sec onds at 94℃, the PCR steps consisted of 30 seconds at 94℃, 2 minutes at 40℃, 30 seconds at 72℃ for 40 cycles, followed by 5 minutes at 72℃. Amplified PCR p roducts from normal colon mucosa and colon carcinomas were separated side by sid e on a 7.5M urea/6% polyacrylamide gel.

Recovery of differentially expressed bands After autoradiograp hy, the cDNA bands representing differently expressed mRNAs were excised from the gel. For each band, extracted cDNA was reamplified for 30 cycles with t he same primers and the same PCR conditions used in the initial PCR, except that no radioactive dNTP was included. After PCR, the product was run on 1.5% low m elt agarose gel and stained with ethidium bromide.

Northern blot analysis PCR bands of the expected size were cut from the gel, purified and used as probes. DNA probes were radio-labeled by t he random prime labeling method, hybridized with RNA from pre samples and other RNA samples respectively.

RESULTS
Total RNAs from normal colon mucosa and colon carcinomas were isolated using single-step method of guanidine thiocyanate, then reversely transcribed into first string of cDNA, T₁₂MA, T₁₂MC, T₁₂MT and T₁₂MG were used as oligo-dT primer individually. The result of alkaline denatured electrophoresis indicated that cDNA molecules were in the range of 0.5kb-5kb. cDNAs were amplified by PCR reaction using the primer combination. T₁₂MN and AP₂, AP₄, PCR products were separated by 6% polyacrylamide gel electrophoresis. Fourteen bands were obtained which were differentially displayed between normal colon mucosa and colon carcinoma. Eight bands (T₁-T₈) were highly expressed in carcinomas, and the other 6 bands were expressed only in normal tissues. T₁ band was verified to be highly expressed in tumor, but had no expression in normal tissues by Northern blot. This cDNA band would be used for cloning and sequencing.

DISCUSSION
The technique of mRNA differential display, by means of combinating T₁₂MN and arbitrary primer AP, can detect all expressed genes in mammalian cells and recover their molecular biological information. These cDNA fragments can be used as probes to isolate target genes from genomic DNA or cDNA library for intensive molecular biological identification. The technique has several advantages over other methods, such as simplicity, sensitivity, reproducibility, versatility and speed, so that it has been used in researches of many diseases, especially in m olecular biological study of malignant tumors. We screened 14 cDNA fragments by mea ns of mRNA DD, one of these bands (T₁) was highly expressed in the colon carci noma which was used for differential display. Using T₁ band as probe, we foun d that it was also highly expressed in many other colon carcinomas (12/15). In the further study, this DNA fragment can be used for cloning and sequencing. Ch ecking the database of Genebank, if the sequence of this cDNA band has no homology to the sequences of other nucleic acids, it can be considered as partial cDNA fragment of a new colon carcinoma-related gene. By screening the genomic DNA o r a certain cDNA library, the full-length cDNA can be cloned, which may be help ful in the study of the molecular biology of colon carcinoma.

REFERENCES
1    Liang P, Pardee AB. Differential display of eukaryotic mRNAs by means of the polymerase chain reaction.
      Science,1992;257:967-971
2    Chomczynski P, Sacchi N. Single-step method of RNA isolation by acid guanidium thiocyanate phenol chloroform 
      extraction. Anal Biochem, 1987;162:156-159
3    Sibert PD, Chenchik A. Modified and guanidinium thiocyanate phenol chloroform RNA extraction method which greatly
      reduced DNA containation. Nucleic Acid Res, 1993;21:2019-2020 

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