Antonio Tugores and Juan Carlos Izpfsua Belmonte 1 Introduction

Arbitrarily primed PCR is a method that was initially developed to analyze and compare genome complexity (1,2). By using arbitrary primers, an array of stochastic sequences can be amplified using the polymerase chain reaction (PCR) and resolved by denaturing acrylamide gels, generating a characteristic pattern or fingerprint. This technique can be readily applied for the analysis of differentially expressed genes in two different cell types by simply converting the mRNA into cDNA (3,4). A different fingerprint pattern will then reflect differential gene expression between the cell types analyzed. The number and intensity of the fingerprints depend largely on two parameters: the abundance of the original RNAs, and how well the primers match the primary sequence so that efficient amplification can take place. Taking this into consideration, the method appears to be more suitable for the comparison of cell types where a large number of differentially expressed genes are anticipated. A major advantage of this method when compared to other strategies used for the isolation of differentially expressed genes is that a very small amount of RNA is required. This makes the method very suitable for embryological studies, where sometimes the quantity of tissue that can be collected is limiting.

At least two major approaches can be taken to generate and amplify cDNA (Fig. 1). We will designate them as (1) arbitrarily primed PCR of RNA (RAP-PCR [3]), and (2) differential display of mRNA 5' ends (4).

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