Intricate combinatorial patterns of exon splicing generate multiple Rh-related isoforms in human erythroid cells

The Rhesus (Rh) blood group system shows complex polymorphisms in the human. Some of the heterogeneity may be generated by alternative RNA splicing. For a systematic analysis of Rh-related mRNA isoforms expressed in reticulocytes, we isolated mRNA, which was then reverse transcribed and amplified by the polymerase chain reaction (PCR) to give Rh-related cDNAs of two segments of 704 bp and 975 bp. The PCR amplification of the 5'-region yielded a single PCR product, whereas a complex electrophoretic pattern of PCR bands was derived from the 3'-region. A highly reproducible ladder of multiple additional bands migrated below the PCR products corresponding to the full-size cDNAs for RhPI and RhPII and encoding two different Rh polypeptides. Eleven and five truncated isoforms of the RhPI and RhPII cDNAs, respectively, were identified in the PCR products. These isoforms appear to be generated by combinatorial splicing of six RhPI and three RhPII exons. Our results suggest that the Rh-related polypeptides consist of a mixture of RhPI and RhPII polypeptide isoforms differing at the C terminus. Multiple RNA splicing pathways are thus operative in the two Rh-related genes even within a single cell lineage of human erythroid cells.