Protein 4.1R–deficient mice are viable but have erythroid membrane skeleton abnormalities

Abstract

A diverse family of protein 4.1R isoforms is encoded by a complex gene on human chromosome 1. Although the prototypical 80-kDa 4.1R in mature erythrocytes is a key component of the erythroid membrane skeleton that regulates erythrocyte morphology and mechanical stability, little is known about 4.1R function in nucleated cells. Using gene knockout technology, we have generated mice with complete deficiency of all 4.1R protein isoforms. These 4.1R-null mice were viable, with moderate hemolytic anemia but no gross abnormalities. Erythrocytes from these mice exhibited abnormal morphology, lowered membrane stability, and reduced expression of other skeletal proteins including spectrin and ankyrin, suggesting that loss of 4.1R compromises membrane skeleton assembly in erythroid progenitors. Platelet morphology and function were essentially normal, indicating that 4.1R deficiency may have less impact on other hematopoietic lineages. Nonerythroid 4.1R expression patterns, viewed using histochemical staining for lacZ reporter activity incorporated into the targeted gene, revealed focal expression in specific neurons in the brain and in select cells of other major organs, challenging the view that 4.1R expression is widespread among nonerythroid cells. The 4.1R knockout mice represent a valuable animal model for exploring 4.1R function in nonerythroid cells and for determining pathophysiological sequelae to 4.1R deficiency.

Protein 4.1R, a Microtubule-associated Protein Involved in Microtubule Aster Assembly in Mammalian Mitotic Extract

“…4.1R might stabilize the interaction among NuMA, dynein, dynactin, and microtubules in a manner analogous to its role in the stabilization of the association of spectrin, actin, and integral proteins in red blood cells. Viable homozygous 4.1R knockout mice have been generated (47). The viability of these mice is perplexing, given the wide tissue distribution of 4.1R and its possible involvement in cell division.…”

Protein 4.1 tumor suppressors: getting a FERM grip on growth regulation

“…A decrease in 4.1R expression as a consequence of a chromosomal mutation results in hereditary elliptocytosis, a disorder characterized by pronounced hemolysis, splenomegaly and abnormally shaped red blood cells (Tchernia et al, 1981). This abnormal erythrocyte phenotype has also been documented in Protein 4.1R null mice (Shi et al, 1999). Consistent with a role in membrane stabilization, the FERM, SABD and CTD domains have been shown to mediate membrane-cytoskeleton interactions through interactions with integral membrane proteins.…”

Interaction between protein 4.1R and spectrin heterodimers

“…Spectrin tetramers associated in a hexagonal array connect the membrane via junctional complexes by interacting with actin filaments, protein 4.1R, and glycophorin C, among which 4.1R plays a crucial role in regulating the junctional complexes by stabilizing the spectrin-actin network and anchoring it to the membrane (14). Studies with mouse models suggest that deficiency of 4.1R in RBCs results in a considerable reduction in actin filaments and significant loss of cytoskeletal structure and membrane proteins (15)(16)(17). Deficiency of 4.1R in human RBCs leads to the pronounced disruption of cytoskeletal meshwork, which is closely associated with anemia and elliptocytosis (18)(19)(20)(21).…”