Hereditary elliptocytosis associated with spectrin Le Puy in a Japanese family: ultrastructural aspect of the red cell skeleton

Influence of network topology on the elasticity of the red blood cell membrane skeleton

A finite-element network model is used to investigate the influence of the topology of the red blood cell membrane skeleton on its macroscopic mechanical properties. Network topology is characterized by the number of spectrin oligomers per actin junction (phi a) and the number of spectrin dimers per self-association junction (phi s). If it is assumed that all associated spectrin is in tetrameric form, with six tetramers per actin junction (i.e., phi a = 6.0 and phi s = 2.0), then the topology of the skeleton may be modeled by a random Delaunay triangular network. Recent images of the RBC membrane skeleton suggest that the values for these topological parameters are in the range of 4.2 < phi a < 5.5 and 2.1 < phi s < 2.3. Model networks that simulate these realistic topologies exhibit values of the shear modulus that vary by more than an order of magnitude relative to triangular networks. This indicates that networks with relatively sparse nontriangular topologies may be needed to model the RBC membrane skeleton accurately. The model is also used to simulate skeletal alterations associated with hereditary spherocytosis and Southeast Asian ovalocytosis.

Spectrin mutations in hereditary elliptocytosis and hereditary spherocytosis

Hereditary elliptocytosis (HE), its aggravated form hereditary pyropoikilocytosis (HPP), and hereditary spherocytosis (HS) designate a set of congenital hemolytic syndromes. The responsible mutations lie in several genes encoding proteins of the red cell membrane. In particular, they involve the SPTA1 and SPTB genes that encode erythroid spectrin alpha- and beta-chains, respectively. In situ, spectrin is a alpha 2 beta 2 fibrillar tetramer resulting from the head-to-head self-association of two alpha beta dimers. In HE, the 24 known alpha-chain mutations lie in the self-association site or its vicinity, whereas the 17 beta-chain mutations occur in the self-association site itself (record of November 30, 1995). Allele alpha LELY (LELY: Low Expression LYon) is found in ethnic groups remote from one another with a uniform frequency (20-30% of all alpha-alleles). It allows an expanded expression of any HE alpha-allele located in trans and results in severe HE or in HPP. In HS, a number of spectrin mutations have been recorded recently. Allele alpha LEPRA (LEPRA: Low Expression PRAgue) would occur in a recurrent fashion.

A surface replica method: a useful tool for studies of the cytoskeletal network in red cell membranes of normal subjects and patients with a beta-spectrin mutant (spectrin Le Puy: beta 220/214)

Visualization of the components of the red cell membranes, and especially the structure of cytoskeletal proteins in situ, has become a requisite in studies of red cell membrane disorders. There has been a search for a consistent and dependable method for detecting these structures. In the present study, the surface replica method was used with transmission electron microscopy to examine the cytoskeletal network of the red cell ghosts of a normal control and patients with a beta-spectrin mutant (beta-spectrin Le Puy). The surface replica method is well-suited to observation of the cytoskeletal network of the membranes in a nearly native in situ condition. Immunogold labelling with anti-membrane protein antibodies is easily applicable to the identification of each component of the cytoskeletal proteins. The findings obtained under normal and pathological conditions using the surface replica method corresponded with those made by the quick-freeze, deep-etching method.

A deletional frameshift mutation in spectrin beta-gene associated with hereditary elliptocytosis in spectrin Napoli

We studied a clinically manifest, dominantly transmitted elliptocytosis in an Italian family. We found a new spectrin variant, designated spectrin Napoli. Its beta-chain was truncated in its C-terminal region (apparent MW 216 kD). It displayed a low expression level (15%). There was a 8 nt deletion: CTTTTGAGAAGT-->CTGT (nt 6255-6262), starting after codon 2053. This deletion was followed by a 54 nt (18 amino acids) missense sequence and terminated by the TGA triplet which normally overlaps codons 2074 and 2075 (CTTGAG). The overall length of the mutated beta-chain was comparable to that found in spectrin Nice, spectrin Tokyo and spectrin Tandil, which are other variants with truncated beta-chains; however, a distinct nonsense codon was used in spectrin Napoli.