The murine mutation jaundiced is caused by replacement of an arginine with a stop codon in the mRNA encoding the ninth repeat of beta-spectrin.

Birkenmeier

Bodine

et al. 2003

Tetramers of ␣-and ␤-spectrin heterodimers, linked by intermediary proteins to transmembrane proteins, stabilize the red blood cell cytoskeleton. Deficiencies of either ␣-or ␤-spectrin can result in severe hereditary spherocytosis (HS) or hereditary elliptocytosis (HE) in mice and humans. Four mouse mutations, sph, sph Dem , sph 2BC , and sph J , affect the erythroid ␣-spectrin gene, Spna1, on chromosome 1 and cause severe HS and HE. Here we describe the molecular alterations in ␣-spectrin and their consequences in sph 2BC /sph 2BC and sph J /sph J erythrocytes. A splicing mutation, sph 2BC initiates the skipping of exon 41 and premature protein termination before the site required for dimerization of ␣-spectrin with ␤-spectrin. A nonsense mutation in exon 52, sph J eliminates the COOHterminal 13 amino acids. Both defects result in instability of the red cell membrane and loss of membrane surface area. In sph 2BC /sph 2BC , barely perceptible levels of messenger RNA and consequent decreased synthesis of ␣-spectrin protein are primarily responsible for the resultant hemolysis. By contrast, sph J /sph J mice synthesize the truncated ␣-spectrin in which the 13-terminal amino acids are deleted at higher levels than normal, but they cannot retain this mutant protein in the cytoskeleton. The sph J 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 ␣-spectrin is crucial to the stability of the junctional complex. IntroductionMice with mutations in genes encoding membrane skeletal proteins are important models for hereditary spherocytosis (HS). 1 Gene mapping and disrupted protein levels 2,3 identified the affected product and became the basis for the subsequent cloning and sequencing of ␣-spectrin (Spna1), ␤-spectrin (Spnb1), and ankyrin (Ank1) from mouse 4-6 and human DNA. 7-10 ␤-Spectrin is a pivotal protein that provides binding sites for ankyrin, the linker between spectrin and the transmembrane protein band 3; ␣-spectrin heterodimerization; tetramerization of heterodimers 11 ; and 4.1, a protein that joins spectrin tetramers to the transmembrane protein glycophorin C at junctional complexes. 12 Anchoring of the spectrinbased cytoskeleton to the transmembrane proteins band 3 and glycophorin C is essential for red blood cell stability. The nucleotide alterations described for the mouse beta spectrin (ja/ ja), 13 ankyrin (nb/nb), 14 and ␣-spectrin (sph/sph, sph Dem /sph Dem ) 4,15 mutations provide an explanation for the instability of red cells in these mutants and clues to the functional consequences of alterations in specific amino acids. Assessing functional effects of mutations in humans is more difficult because the secondary genetic diversity affects results, mutations are heterogeneous, and clinical severity may vary among patients with the same mutation.The murine ␣-spectrin mutations sph, sph 2BC , and sph J result in severe HS, whereas sph Dem is a unique model for hereditary elliptocytosis (HE). 16 ␣-Spect...

Section: Introductionmentioning

confidence: 99%

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

Birkenmeier

Bodine

et al. 2003

“…29 ␤-Spectrindeficient ja/ja mice have a nonsense mutation in ␤-spectrin repeat 9, causing complete deficiency of both ␣-and ␤-spectrin. 4 Three ␣-spectrin mouse mutants, sph/sph, sph 2BC /sph 2BC , and sph J /sph J , have HS. The sph 2BC and sph J mutations are in the 3Ј end of ␣-spectrin, distant from the self-association site, 30 and do not affect tetramerization (Figure 2).…”

Section: Discussionmentioning

confidence: 99%

“…2 To date, all spontaneous mutations in ␣-spectrin (Spna1 sph , Spna1 sph-2BC , and Spna1 sph-J , hereafter, sph, sph 2BC , and sph J ) and ␤-spectrin (Spnb1 ja , hereafter, ja) that affect the RBC cytoskeleton in mice cause severe HS. 3 These mice have been instrumental in elucidating the genetic basis of the disease, 3 the distribution of red cell proteins, 4 and potential therapeutic measures. 5 Recently, we have shown that, as adults, the mutant mice develop thrombosis in many tissues.…”

Section: Introductionmentioning

confidence: 99%

Defective spectrin integrity and neonatal thrombosis in the first mouse model for severe hereditary elliptocytosis

Roesch

Hamblen

et al. 2001

Mutations affecting the conversion of spectrin dimers to tetramers result in hereditary elliptocytosis (HE), whereas a deficiency of human erythroid ␣-or ␤-spectrin results in hereditary spherocytosis (HS). All spontaneous mutant mice with cytoskeletal deficiencies of spectrin reported to date have HS. Here, the first spontaneous mouse mutant, sph Dem / sph Dem , with severe HE is described. The sph Dem mutation is the insertion of an intracisternal A particle element in intron 10 of the erythroid ␣-spectrin gene. This causes exon skipping, the inframe deletion of 46 amino acids from repeat 5 of ␣-spectrin and alters spectrin dimer/tetramer stability and osmotic fragility. The disease is more severe in sph Dem /sph Dem neonates than in ␣-spectrin-deficient mice with HS. Thrombosis and infarction are not, as in the HS mice, limited to adults but occur soon after birth. Genetic background differences that exist between HE and HS mice are suspect, along with red blood cell morphology differences, as modifiers of thrombosis timing. sph Dem

“…11 Reticulocytes compose 75% to 95% of the total circulating erythroid cells; mean cell volume (MCV) is increased, reflecting the larger, immature cells in the circulation. [13][14][15] Spleen and liver, sources of newly generated RBCs in anemic mice, are grossly enlarged. [13][14][15] Iron deposits accumulate in the kidney and liver.…”

Section: Introductionmentioning

confidence: 99%

“…[13][14][15] Spleen and liver, sources of newly generated RBCs in anemic mice, are grossly enlarged. [13][14][15] Iron deposits accumulate in the kidney and liver. 11 Mice with HS are much more severely affected than most humans with HS, many of whom are not diagnosed until an unrelated health crisis arises.…”

Section: Introductionmentioning

confidence: 99%

Reduced incidence of thrombosis in mice with hereditary spherocytosis following neonatal treatment with normal hematopoietic cells

Lee

Deveau

et al. 2001

Thrombosis is a life-threatening complication of hemolytic anemia in humans. Cardiac thrombi are present in all adult ␣-spectrin-deficient (sph/sph) mice with severe hereditary spherocytosis, providing a model for events preceding thrombosis. The current study evaluated (1) the timing of thrombosis initiation and (2) the effect of postnatal transplantation of normal cells on life span and thrombotic incidence in adult mice. Thrombi are detected histologically following necropsy in untreated sph/sph mice of various ages and are not observed until 6 weeks of age. Thrombotic incidence increases from 50% at 6 to 7 weeks of age to 100% at 9 weeks of age. As a potential therapy, nonablated sph/sph neonates were transfused with either genetically marked normal peripheral blood (PB), bone marrow (BM) , IntroductionOne of the more serious complications of heritable hemolytic anemias in humans is thrombosis. Thrombotic events affect approximately 20% of patients with sickle cell disease, 5% to 10% of patients with ␤-thalassemia, and a small number of patients with hereditary spherocytosis (HS). [1][2][3][4][5][6][7][8][9][10] In adult mice with severe hemolytic anemia caused by deficiency of red blood cell (RBC) cytoskeletal components, cardiac thrombi are prevalent. 11,12 The mutant mice have severe HS typified by misshapen RBCs that are destroyed within a single day of entry into the peripheral blood (PB). 11 Reticulocytes compose 75% to 95% of the total circulating erythroid cells; mean cell volume (MCV) is increased, reflecting the larger, immature cells in the circulation. [13][14][15] Spleen and liver, sources of newly generated RBCs in anemic mice, are grossly enlarged. [13][14][15] Iron deposits accumulate in the kidney and liver. 11 Mice with HS are much more severely affected than most humans with HS, many of whom are not diagnosed until an unrelated health crisis arises.There are few models for thrombosis in experimental animals with hemolytic anemia. The mice with HS adequately fill that void. The incidence of coronary thrombosis is highest (85% to 100%) in HS mice with mutations in ␣-spectrin (Spna1), and lowest (15% to 22%) in HS mice with ␤-spectrin and ankyrin mutations. 11,12 These mice, except for the mutation they carry, share identical genetic backgrounds and environments, permitting comparative analyses. Adult Spna1 sph / Spna1 sph (hereafter, sph/sph) mice have the highest incidence (100%) of thrombosis. They provide a model for determining thrombus ontogeny, pathological consequences, precipitating agents, and efficacy of therapeutic interventions. Death of 30% of untreated sph/sph mice occurs before 3 weeks of age; the average life span of the survivors is 26.8 weeks. It is not clear whether the postnatal deaths are caused by thrombosis or other pathology. Here, the temporal development of thrombosis is established in sph/sph mice.To date, we have shown that bone marrow (BM) hematopoietic cells transplanted from sph/sph mice to normal recipients are sufficient for thrombogenesis 12 and that inversi...