Sarah Pollock

Systematic identification of abundant A-to-I editing sites in the human transcriptome

RNA editing by members of the ADAR (adenosine deaminases acting on RNA) family leads to site-specific conversion of adenosine to inosine (A-to-I) in precursor messenger RNAs. Editing by ADARs is believed to occur in all metazoa, and is essential for mammalian development. Currently, only a limited number of human ADAR substrates are known, whereas indirect evidence suggests a substantial fraction of all pre-mRNAs being affected. Here we describe a computational search for ADAR editing sites in the human transcriptome, using millions of available expressed sequences. We mapped 12,723 A-to-I editing sites in 1,637 different genes, with an estimated accuracy of 95%, raising the number of known editing sites by two orders of magnitude. We experimentally validated our method by verifying the occurrence of editing in 26 novel substrates. A-to-I editing in humans primarily occurs in noncoding regions of the RNA, typically in Alu repeats. Analysis of the large set of editing sites indicates the role of editing in controlling dsRNA stability.

Metabolism of soluble sugars in developing melon fruit: a global transcriptional view of the metabolic transition to sucrose accumulation

The sweet melon fruit is characterized by a metabolic transition during its development that leads to extensive accumulation of the disaccharide sucrose in the mature fruit. While the biochemistry of the sugar metabolism pathway of the cucurbits has been well studied, a comprehensive analysis of the pathway at the transcriptional level allows for a global genomic view of sugar metabolism during fruit sink development. We identified 42 genes encoding the enzymatic reactions of the sugar metabolism pathway in melon. The expression pattern of the 42 genes during fruit development of the sweet melon cv Dulce was determined from a deep sequencing analysis performed by 454 pyrosequencing technology, comprising over 350,000 transcripts from four stages of developing melon fruit flesh, allowing for digital expression of the complete metabolic pathway. The results shed light on the transcriptional control of sugar metabolism in the developing sweet melon fruit, particularly the metabolic transition to sucrose accumulation, and point to a concerted metabolic transition that occurs during fruit development.

Use of Non-Normalized, Non-Amplified cDNA for 454-Based RNA Sequencing of Fleshy Melon Fruit

The melon (Cucumis melo L.) fruit is an important crop and model system for the genomic study of both fleshy fruit development and the Cucurbitaceae family. To obtain an accurate representation of the melon fruit transcriptome based on expressed sequence tag (EST) abundance in 454‐pyrosequencing data, we prepared double‐stranded complementary DNA (cDNA) of melon without the usual amplification and normalization steps. A purification step was also included to eliminate small fragments. Complementary DNAs were obtained from 14 individual fruit libraries derived from two genotypes, separated into flesh and peel tissues, and sampled throughout fruit development. Pyrosequencing was performed using Genome Sequencer FLX (GS FLX) technology, resulting in 1,215,359 reads, with mean length of >200 nucleotides. The global digital expression data was validated by comparative reverse transcription quantitative real‐time polymerase chain reaction (RT‐qPCR) of 40 selected genes and expression patterns were similar for the two methods. The results indicate that high‐quality, nonbiased cDNA for next‐generation sequencing can be prepared from mature, fleshy fruit, which are notorious for difficulties in ribonucleic acid (RNA) preparation.