Erythroblasts express 2 isoforms of ICAM-4.

RT/PCR analysis of mRNA isolated from erythroblasts obtained from Friend virus–infected mice and further differentiated in culture. Using primers binding to exon 1 and exon 3, products of 594 bp and 456 bp were amplified. At the 0 hour initiation of culture, cells were 98% proerythroblasts. After 44 hours in culture, cells were well hemoglobinized. Actin was amplified at each time point so that densitometry measurements of ICAM-4 and ICAM-4S could be normalized to actin. Normalization ratios for ICAM-4/actin were 0.189, 0.326, 0.513, and 0.484 for 0, 17, 32, and 44 hours, respectively. Normalization ratios for ICAM-4S/actin were 0.103, 0.133, 0.231, and 0.247 for 0, 17, 32, and 44 hours, respectively.