This function returns the pcs from the obtained RangedSummarizedExperiment object of selected transcripts
getPCs(rse_tx, assayname = "tpm")
Ranged Summarizeed Experiment with only trancsripts selected for qsva
character string specifying the name of the assay desired in rse_tx
prcomp object generated by taking the pcs of degraded transcripts
getPCs(rse_tx, "tpm")