passages.id: split_5_test_1701_passage
passages.type: progene_text
passages.text: To investigate possible defects in cell - cycle regulation in PV , the expression of Rb and CDK inhibitor gene messenger RNAs ( mRNAs ) in highly purified human erythroid colony - forming cells ( ECFCs ) was screened using an RNase protection assay ( RPA ) and 11 gene probes .