if the ratio of gene isoforms changed, how to determine whether it's a result of alternative splicing change or one mRNA isoform is specificly degraded?
For distinguishing RNA degradation from change in alternative splicing, you can design two primers (Forward and Reverse) on 5' and 3' ends of your RNA of interest and do RT-PCR by using these two primers. If PCR product is changed in its length that is spliced. but when it results in no PCR product, that is RNA degradation.