2.3. Quantitative analysis of gene expression levels in the liver of grass
carp
Total RNA was isolated from 30–50 mg liver tissue of grass carp
using SV Total RNA Isolation System (Promega, USA) by following the
manufacturer's protocol. The extracted RNA was resuspended in 50 μl
RNase-free water and quantified using Eppendorf Biophotometer
(Germany). One microgram of total RNA was used for reverse transcription
with ReverTra Ace qPCR RT Kit (ToYoBo, Japan) according to the
manufacturer's recommendations. Based on the results obtained,
beta-actin level was stable that differences of the mean Cq between
the two groups were 0.3366 at 30 days and 0.215 at 60 days, and therefore
it was used as the internal control gene for the quantitative RT-PCR
assay.