Adult Drosophila melanogaster apterous[56f] strain flies were obtained from Carolina Biological Supply (Burlington, NC). Flies were quick frozen on dry ice and total RNA was extracted (Andrews et al, Genome Research 10:2030-2043) using Trizol reagent (GibcoBRL, Gaithersburg, MD). Probes were labeled with Cy3 (Probe 1) or Cy5 (Probe 2). To synthesize probes, mRNA was isolated by a single round of poly(A) selection using Oligotex resin (Qiagen, Valencia, CA). The purified mRNA was quantified using RiboGreen dye (Molecular Probes) in a fluorescent assay. RiboGreen dye was diluted 1:200 (v/v final) and mixed with known RNA concentrations (determined by absorbance at 260 nm) ranging from 1 to 5000 ng/ml. A Millennium RNA size ladder (Ambion, Austin, TX) was used to generate standard curves and unknown samples were diluted as necessary. Fluorescence was measured in 96-well plates with a FLUOstar fluorometer (BMG Lab Technologies, Germany) fitted with 485 nm (excitation) and 520 nm (emission) filters. Between 25 and 100 ng mRNA were separated on an Agilent 2100 Bioanalyzer (Agilent Technologies, Palo Alto, CA), to examine the mRNA size distribution. 200 ng of purified mRNA were converted to either a Cy3- or Cy5-labeled cDNA probe using a custom labeling kit (Incyte Genomics). Each reaction contained 50 mM Tris–HCl pH 8.3, 75 mM KCl, 15 mM MgCl2, 4 mM DTT, 2 mM dNTPs (0.5 mM each), 2 µg Cy3 or Cy5 random 9mer (Trilink, San Diego, CA), 20 U RNase inhibitor (Ambion), 200 U MMLV RNase H-free reverse transcriptase (Promega, Madison, WI) and mRNA. Correspondingly labeled Cy3 and Cy5 cDNA products were combined and purified on a size exclusion column, concentrated by ethanol precipitation and resuspended in hybridization buffer. Probes were added between two subarray slides and developed as described (Yue et al.2001, NAR. 29:e41). Microarrays were scanned on a GenePix 4000A scanner (Axon Instruments, Foster City, CA) at 535 nm. Signal intensities were initially stored and analyzed using GEMTools software (Incyte Genomics, Palo Alto CA). Background corrections were done by calculating the average Cy3/Cy5 signal to produce a balanced coefficient (Yue et al., 2001).
Ratio of uncorrected Probe 1/Probe 2 signal intensity.
VALUE
Ratio of uncorrected Probe 1/balanced Probe 2 signal intensity
Probe 1Signal
Raw signal intensity data from Cy3 (Probe 1) channel.
Probe 1S/B
Probe 1 signal minus background/background.
Probe 1Area%
Percentage of area read from element spot.
Probe 2 BalancedSignal
Raw signal intensity data from Cy5 channel balanced against Probe 1 signal. Intensity is adjusted by a balancing coefficient that takes the average Cy3 signal on an array/the average Cy5 signal on the array.
Probe 2Signal
Raw signal intensity data from Cy5 (Probe 2) channel.
