CN109486920B - Internal reference gene hsa _ circ _0000284 of human tissue/cell specimen circular RNA and application thereof - Google Patents

Abstract

The invention discloses a human tissue/cell specimen circular RNA fluorescence quantitative PCR (RT-qPCR) internal reference gene hsa _ circ _0000284, and a primer and application thereof. The invention firstly screens in a high-throughput sequencing result, then verifies in various cells of a human body by using RT-qPCR, and confirms the accuracy and stability of the obtained reference gene and the specific primer thereof used for relative expression analysis of the human body, and the expression level is not influenced by experimental conditions such as chemotherapeutic drugs, hypoxia and the like.

Description

Internal reference gene hsa _ circ _0000284 of human tissue/cell specimen circular RNA and application thereof

Technical Field

The invention belongs to the technical field of molecular biology, and particularly relates to an RT-qPCR (reverse transcription-quantitative polymerase chain reaction) internal reference gene hsa _ circ _0000284 of human tissue/cell specimen circular RNA, and a primer and application thereof.

Background

Circular RNAs (circular RNAs) are molecules with a single-stranded closed circular structure formed by covalent bonds, have no 5 'end cap and 3' end poly (A) tail, and are relatively stable in structure and are not influenced by ribonuclease R (RNase R). In 1976, humans have discovered the presence of circular RNA molecules, but have been thought to be false cleavage products, or mediators of escape intron noose delimbination. In recent years, with the development of high throughput sequencing technologies and the updating of analytical methods, a large number of circular RNA molecules have been identified. More and more researches show that the circular RNA molecule is not a gene shearing byproduct, but a molecule with certain functions, wherein the main functions comprise competitive adsorption of miRNA, binding of protein to influence the function of protein, translation of protein, competition of linear shearing of mRNA, regulation of RNA polymerase II activity and serving as a biomarker of diseases.

RT-qPCR has been widely used for gene expression analysis as a sensitive method for detecting RNA. When the expression level of a target gene is detected by using the RT-qPCR technology, in order to reduce the possible differences of a detection sample in RNA yield, quality and reverse transcription efficiency, the internal reference gene is required to be standardized and corrected. The accuracy of the RT-qPCR result is determined to a great extent by the internal reference gene, so that finding the gene which can be stably expressed under all samples and experimental conditions as the internal reference gene is the key for correctly implementing the RT-qPCR technology.

Currently, researchers still use linear β -actin or GAPDH as reference genes when detecting the expression level of circular RNA. Since the circular RNA has the same sequence as its parent linear gene, back-to-back primers (divergent primers) need to be designed for the circular RNA in order to prevent interference of the parent linear gene. Although back-to-back primers exclude some degree of interference from the parent linear gene, interference from linear splicing isoforms with the same linker (back-splice) sequence as the circular RNA cannot be excluded. It is best to use RNase R to remove the interference of these linear splicing isoforms, however, this also removes beta-actin or GAPDH as reference genes, so that these linear reference genes can no longer be used to correct the expression of the target gene. The RNA is divided into two equal parts, one part is treated by RNase R for amplification of circular RNA, the other part is treated by RNase R for amplification of internal reference gene, and the correction is carried out by Mg in RNase R buffer²⁺The interference of (2). Therefore, in the field of research of circular RNA, there is an urgent need to develop an internal reference gene that can be standardized as circular RNA.

Disclosure of Invention

The invention aims to provide an RT-qPCR internal reference gene hsa _ circ _0000284 of human tissue/cell specimen circular RNA, a primer and an application thereof aiming at the defects of the prior art, wherein the internal reference gene hsa _ circ _0000284 is also circular RNA, can tolerate the treatment of RNase R, and overcomes the problem that no internal reference exists after the RNase R is treated in the circular RNA detection in the prior art.

The first purpose of the invention is to provide an RT-qPCR reference gene of human tissue/cell specimen circular RNA, the sequence of which is shown as SEQ ID NO. 1.

The second purpose of the invention is to provide the specific primers of the RT-qPCR internal reference gene hsa _ circ _0000284 of the human tissue/cell sample circular RNA, wherein the forward primer and the reverse primer are respectively shown as SEQ ID NO.2 and SEQ ID NO. 3.

The third purpose of the invention is to provide the application of the internal reference gene or the specific primer in the preparation of the RT-qPCR kit.

Further, the kit also comprises conventional PCR reagents.

The internal reference gene hsa _ circ _0000284 is used as the RT-qPCR internal reference gene of human tissue/cell specimen circular RNA.

The specific primer is applied as the RT-qPCR specific primer of the human tissue/cell specimen circular RNA.

The invention provides hsa _ circ _0000284 as an internal reference gene for amplifying circular RNA genes of human tissues/cell samples, and the hsa _ circ _0000284 gene is also circular RNA, so the gene is tolerant to the treatment of RNase R, and the problem that no internal reference exists after the RNase R is treated in circular RNA detection is solved. The invention firstly screens in a high-throughput sequencing result, then verifies in various cells of a human body by using RT-qPCR, and proves the accuracy and stability of hsa _ circ _0000284 and the primer thereof used for relative expression analysis of the human body, and the expression level of the hsa _ circ _0000284 is not influenced by experimental conditions such as chemotherapeutic drugs, hypoxia and the like. hsa _ circ _0000284 can be used as a separate reference gene and can be used without combination with other reference genes.

Drawings

FIG. 1a is a melting curve of the reference gene hsa _ circ _0000284 in example 2.

FIG. 1b is an electrophoretogram of all candidate reference genes of example 2, wherein: m is marker, 1 is hsa _ circ _0000471, 2 is hsa _ circ _0000284, 3 is hsa _ circ _0002484, 4 is hsa _ circ _0001445, 5 is hsa _ circ _0000944, 6 is hsa _ circ _0000567, 7 is GAPDH, 8 is 18s rRNA, 9 is β -actin.

Detailed Description

The technical solution of the present invention is further illustrated by the following specific examples.

Example 1

1. Screening of candidate reference genes for circular RNA

The Gene Expression Omnibus (GEO) website (https:// www.ncbi.nlm.nih.gov/GEO /) was logged to download a GSE 77661-numbered data set (GSE77661_ circuit _ srpbm _ union _ samples _ loci.txt.gz) comprising 6 healthy human specimens (brain, colon, heart, liver, lung and stomach) and 7 circular RNA sequencing results for cancer and paracancerous human tissue specimens (bladder, breast, colorectal, gastric, liver, clear cell, and prostate).

The data processing method comprises the following steps:

(1) and 50 circular RNAs were obtained in total, with only the circular RNAs expressed in all samples being retained.

(2) The stability of 50 circular RNAs in tissue specimens analyzed by geNorm, NormFinder and BestKeeper, respectively, 10 circular RNAs with the best stability were taken for each method, and then the intersection was taken from the 3 data sets obtained to obtain 6 circular RNAs.

2. Further screening of stable candidate reference genes in cell samples

RT-qPCR amplification primers were designed for 6 candidate circular RNAs using circPrimer software, as shown in Table 1.

TABLE 1 primers used for RT-qPCR amplification

Collecting human tumor or normal cell specimen shown in Table 2, extracting Total RNA with RNAscope Total RNA Kit according to the instruction, taking 500ng Total RNA, using Thermo Scientific reverse Aid First Strand cDNA Synthesis Kit with random primer as reverse transcription primer to synthesize First Strand cDNA, diluting 5 times, taking 1 uL cDNA as template, and using Light

480SYBR Green I Master (Roche, IN, USA) was used for amplification reaction under the following conditions: 10 minutes at 95 ℃; denaturation at 95 ℃ for 8 seconds, annealing at 58 ℃ for 8 seconds, 40 cycles. And (3) collecting signals in an annealing stage, and collecting melting curve fluorescence signals at the temperature of 60-95 ℃. Another 2. mu.g of total RNA was treated with 6U of RNase R at 37 ℃ for 15 minutes to remove linear RNA, and 500ng of the RNA after the removal of the linear RNA was reverse transcribed and amplified according to the above procedure.

TABLE 2 cell lines for screening candidate genes

In addition to the above-mentioned untreated human cells, the expression of each candidate reference gene in the cell lines treated with different reagents was examined. Specifically, MCF-7 cells were treated with different concentrations of doxorubicin (10, 50 and 250nM), ammonium chloride (25, 50 and 100. mu.M) and alkannin (5, 10 and 15. mu.M) for 24 hours, and then RNA was extracted, linear RNA was removed, reverse transcription and detection were performed according to the above procedure.

According to the RT-PCR amplification results before and after the linear RNA of all cell strains is removed, the RT-qPCR results of 22 non-drug-added cell strains are analyzed firstly, and the stability evaluation result of the internal reference gene is obtained, and is shown in Table 3; then, the RT-qPCR results of all cell lines (containing the drug-treated MCF-7 cells) were analyzed again, and the results of evaluating the stability of the reference gene were obtained as shown in Table 4. Because the final output of the geonorm algorithm is the two most stable genes, hsa _ circ _0000284 and hsa _ circ _0000471 are the most stable in this example. According to the Normfinder algorithm, hsa _ circ _0000284 and hsa _ circ _0000471 are also the two genes with the best stability. Based on the results of the evaluation by BestKeeper, Table 3 shows that hsa _ circ _0001445 is most stable in the RNA samples that were not linearized, but its standard deviation and coefficient of variation are much greater than those of the other genes, and furthermore hsa _ circ _0000471 is most stable in the results of the evaluation of the other two groups of samples in Table 3; the results in Table 4 show that hsa _ circ _0000284 and hsa _ circ _0000471 are the two genes that are most stable.

TABLE 3 results of evaluation of stability of candidate genes based on RT-qPCR results of 22 cell lines

Genes are ranked from high to low in stability

TABLE 4 evaluation results of candidate Gene stability based on RT-qPCR results of 22 cells and MCF-7 cells after drug addition

Genes are ranked from high to low in stability

Example 2

Specificity and amplification efficiency evaluation of hsa _ circ _0000284

The results of RT-qPCR showed that the dissolution curve for hsa _ circ _0000284 was unimodal (shown in FIG. 1 a), indicating the absence of non-specific amplification. To confirm the amplification without non-specific bands, the amplification products were electrophoresed on 2% agarose gel, and the results are shown in FIG. 1b, in which no bands were observed.

To obtain the amplification efficiency of hsa _ circ _0000284, the template was first diluted by fold and then amplified on the machine. After obtaining the amplification result, the result is fitted with a straight line to obtain a slope (slope), and then the amplification efficiency is calculated by the following formula:

E(％)＝(2^-1/slope-1)×100

finally, the amplification efficiency of hsa _ circ _0000284 was found to be 94.89%.

Sequence listing

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Claims (1)

1. The application of the circular RNA hsa _ circ _0000284 as an RT-qPCR reference gene of the circular RNA of human tissue/cell specimens, wherein the sequence of the circular RNA hsa _ circ _0000284 is shown in SEQ ID NO. 1.

Images