Mutations in the murine erythroid α-spectrin gene alter spectrin mRNA and protein levels and spectrin incorporation into the red blood cell membrane skeleton

Tetramers of αand β-spectrin heterodimers, linked via intermediary proteins to transmembrane proteins, stabilize the red blood cell cytoskeleton. Deficiencies of either αor β-spectrin can result in severe hereditary spherocytosis or elliptocytosis (HS/HE) in mice and humans. Four mouse mutations, sph, sph, sph, and sph, affect the erythroid αspectrin gene, Spna1, on Chromosome 1 and cause severe HS or HE. Here, we describe the molecular alterations in α-spectrin and their consequences in sph/sph and sph/sph erythrocytes. sph is a splicing mutation that initiates skipping of exon 41 and premature protein termination prior to the site required for dimerization of α-spectrin with βspectrin. sph is a nonsense mutation in exon 52 that eliminates the COOH-terminal 13 amino acids. Both defects result in instability of the red cell membrane and loss of membrane surface area. In sph/sph , barely perceptible levels of messenger RNA and consequent decreased synthesis of α-spectrin protein are primarily responsible for the resultant hemolysis. By contrast, sph/sph mice synthesize the truncated α-spectrin in which the 13-terminal amino acids are deleted at higher levels than normal but cannot retain this mutant protein in the cytoskeleton. The sph deletion is near the 4.1/actin binding region at the junctional complex providing new evidence that this 13 amino acid segment at the COOH-terminus of α-spectrin is crucial to the stability of the junctional complex. For personal use only. at PENN STATE UNIVERSITY on March 1, 2013. bloodjournal.hematologylibrary.org From