Disease relevance of beta-Spec

• This variant represents both the first point mutation and the first beta spectrin mutation demonstrated in autosomal dominant hereditary spherocytosis [1].

High impact information on beta-Spec

• We analyzed the DNA sequence of the cDNA encoding the NH2 terminal region of beta spectrin from members of a kindred with autosomal dominant hereditary spherocytosis associated with defective protein 4.1 binding [1].
• We found a point mutation at codon 202 within the 272 amino acid NH2-terminal region of beta spectrin [1].
• Mechanistically, beta-Spectrin is required for the localization of alpha-Spectrin and Ankyrin to the postsynaptic membrane [2].
• We use transgenic double-stranded RNA to selectively eliminate alpha-Spectrin, beta-Spectrin, or Ankyrin [2].
• (1) Removal of the pleckstrin homology domain blocked polarized spectrin assembly in midgut epithelial cells and was usually lethal [3].

Biological context of beta-Spec

• Here we used a genetic approach to directly test the requirement for the beta subunit of the alphabeta spectrin molecule in morphogenesis and function of epithelial cells in Drosophila. beta Spectrin mutations were lethal during late embryonic/early larval development and they produced subtle defects in midgut morphology and stomach acid secretion [4].
• Here, we demonstrate that Drosophila karussell mutations affect beta-spectrin and lead to distinct axonal patterning defects in the embryonic CNS. karussell mutants display a slit-sensitive axonal phenotype characterized by axonal looping in stage-13 embryos [5].
• We used a transgene rescue strategy in Drosophila melanogaster to test contributions of four specific functional sites in beta spectrin to its assembly and function [3].
• Elimination of beta(H) prevents the stable recruitment of alpha-spectrin to the apical domain, but does not result in a loss of apicobasal polarity, as would be predicted from current models describing the role of spectrin in the establishment of cell polarity [6].
• The primary amino acid sequence of each spectrin subunit is dominated by tandemly repeated 106-residue motifs [7].

Anatomical context of beta-Spec

• alpha- and beta-Spectrin are major components of a submembrane cytoskeletal network connecting actin filaments to integral plasma membrane proteins [8].
• The C-terminal extremity of the erythroid beta-chain is also of great interest, since tissue-specific differential processing of 3'beta-spectrin gene pre-mRNA generates a beta spectrin-isoform with a unique C-terminus in human skeletal muscle [9].
• Surprisingly, elimination of alpha-spectrin from follicle cells does not appear to prevent the assembly of conventional beta-spectrin and ankyrin at the lateral domain of the follicle cell plasma membrane [10].
• Spectrin functions upstream of ankyrin in a spectrin cytoskeleton assembly pathway [3].
• However, all cells that lack PAR-1 accumulate spectrin and F-actin laterally, and show a strong increase in the density of microtubules [11].

Associations of beta-Spec with chemical compounds

• Paramagnetic spin label-induced NMR resonance broadening shows that helix C', the partial domain involved in alpha- and beta-spectrin association, exhibits little interaction with the structural domain [12].
• Mutation of a highly conserved isoleucine disrupts hydrophobic interactions in the alpha beta spectrin self-association binding site [13].

Regulatory relationships of beta-Spec

• It was previously shown that ankyrin and beta spectrin are recruited to sites of cell-cell contact in Drosophila S2 cells expressing the homophilic adhesion molecule neuroglian [14].

Other interactions of beta-Spec

• Drosophila beta spectrin functions independently of alpha spectrin to polarize the Na,K ATPase in epithelial cells [4].
• The results suggest that beta-Spectrin contributes to midline repulsion through the regulation of Slit-Robo pathway components [8].
• The results establish a role for beta spectrin in determining the subcellular distribution of the Na, K ATPase and, unexpectedly, this role is independent of alpha spectrin [4].
• This region is closely related to the N-terminal segment of several src-tyrosine kinases and to a domain of phospholipase C. Like the spectrin alpha-chain, the major central part of the spectrin beta-chain is made up of repeat units of 106 amino-acids [9].
• A beta-spectrin isoform from Drosophila (beta H) is similar in size to vertebrate dystrophin [15].

Analytical, diagnostic and therapeutic context of beta-Spec

• Immunoprecipitation assays using protein fragments synthesized in vitro from recombinant DNA showed that interchain binding at the head end was mediated by segment 0-1 of alpha-spectrin and segment 18 of beta-spectrin [16].

References