Analysis of transgene expression in bone marrow–derived stromal cells from Sl/Sl^d,Sl/Sl^d-S, andSl/Sl^d-MR mice. Total cellular RNA was extracted as described in Materials and Methods. SCF-specific primers (upper panel) were used that recognize only the full-length transcript of SCF. As a loading control actin specific primers (lower panel) were used on the same RNA sample as described in Materials and Methods. RT-PCR products were examined on 1% ethidium bromide containing agarose gel and subsequently probed with SCF and actin specific probes. Upper arrow, SCF-specific primers (733 bp); lower panel, actin-specific primers (732 bp). Molecular weight (MW) marker is shown on the left.