Expression of human membrane proteins 4.1a and 4.1b in reticulocytes and mature erythrocytes.

The erythrocyte membrane protein of band 4.1 is an essential protein of the erythrocyte cytoskeleton. Two isoforms have been detected in human erythrocytes, and six in nucleated avian erythrocytes. Multiple alternative splicing of human reticulocyte mRNA for protein 4.1 implies the possibility of even more isoforms. Structural and functional dissimilarities between isoforms, and their differential expression during the course of erythropoiesis are not well understood. Here, we show that only protein 4.1b is present in the immature reticulocytes of anaemic patients. The ratio of 4.1a to 4.1b in mature reticulocytes of healthy individuals was 1.25. This ratio was 2.0 in healty mature erythrocytes, and 0.7 in peripheral red blood cells from anaemic patients. Taking into account these and other available data, we speculate that the steady state levels of protein 4.1 isoforms change gradually in the terminal stages of erythropoiesis.