Glyoxal fixation facilitates transcriptome analysis after antigen staining and cell sorting by flow cytometry
Fig 2
Determination of RNA-compatible fixation and permeabilisation conditions.
A: 1x106 COLO205 cells were either unfixed (lane 1), fixed with 70% ethanol on ice for 15 minutes (lane 2) or fixed with 4% formaldehyde on ice for 15 minutes (lane 3). Unfixed cells were dissolved immediately in TRI Reagent, fixed cells were washed once in PBS by centrifugation at 2000 x g for 3 minutes at 4°C before RNA extraction with TRI Reagent. 20% of RNA obtained was separated on a 1.2% glyoxal gel and imaged by ethidium bromide staining. B: COLO205 cells were either unfixed (lane 1), fixed with 70% ethanol on ice for 15 minutes (lane 2) or fixed with 100% methanol on ice for 15 minutes (lane 3). Unfixed cells were dissolved immediately in TRI Reagent, fixed cells were washed once in PBS by centrifugation at 2000 x g for 3 minutes at 4°C before RNA extraction with TRI Reagent. RNA was analysed as in A. C: COLO205 cells were fixed with glyoxal fixation mix (pH4) either without or with 20% ethanol and incubated on ice for 15 minutes and washed once in PBS by centrifugation at 2000 x g for 3 minutes at 4°C. RNA was extracted and analysed as in A. D: COLO205 cells were either unfixed (lane 1), fixed with glyoxal fixation mix (pH4) with 20% ethanol (lane 2) or with 4% formaldehyde on ice for 15 minutes (lane 3). Cells were washed once in PBS by centrifugation at 2000 x g for 3 minutes at 4°C and incubated on ice for 1 hour in 100 μl PBS followed by centrifugation at 2000 x g for 3 minutes at 4°C before RNA extraction with an RNeasy mini kit. E: 100 ng RNA per reaction from D was subjected to one-step combined reverse transcription and quantitative PCR reactions for ACT1B, GAPDH and PGK1. The RNA yield from formaldehyde-fixed RNA cells was <<100ng and therefore control and formaldehyde-fixed reactions were performed on cell equivalents of extracted RNA solution. Ct is the cycle number at which the fluorescence exceeded threshold. 3 technical replicates for each RT-qPCR reaction were performed. F: COLO205 cells were either unfixed (lane 1) or fixed with glyoxal fixation mix (pH4) with 20% ethanol on ice for 15 minutes and permeabilised in 100% methanol on ice for 30 minutes (lane 2), or 0.5% saponin on ice for 30 minutes (lane 3) or 0.3% Triton X-100 on ice for 30 minutes (lane 4). RNA was analysed as in A. G: COLO205 cells were either unfixed (lane 1) or fixed with glyoxal fixation mix (pH4) with 20% ethanol on ice for 15 minutes, permeabilised in 100% methanol on ice for 30 minutes followed by incubation in primary antibody for 1 hour on ice and secondary antibody for 30 minutes on ice in dark (lane 2). RNA was analysed as in A.
