HGNC Approved Gene Symbol: MFSD2BCytogenetic location: 2p23.3 Genomic coordinates (GRCh38): 2:24,010,084-24,026,774 (from NCBI)▼ DescriptionMFSD2B appears to...
HGNC Approved Gene Symbol: MFSD2B
Cytogenetic location: 2p23.3 Genomic coordinates (GRCh38): 2:24,010,084-24,026,774 (from NCBI)
MFSD2B appears to function as an active cation-dependent transporter for sphingosine-1-phosphate (S1P) in red blood cells (RBCs) and platelets (Vu et al., 2017).
▼ Cloning and Expression
By searching databases for sequences similar to mouse Mfsd2a (614397), Angers et al. (2008) identified mouse and human MFSD2B. The deduced proteins contain 494 and 497 amino acid, respectively, and both have 12 predicted transmembrane domains. Northern blot analysis detected high Mfsd2b expression in mouse spleen, with lower expression in lung, testis, and ovary, and little to no expression in other tissues examined.
Using Western blot analysis, Vu et al. (2017) found that Mfsd2b was highly expressed in mouse RBCs and platelets, but was absent in lymphoid lineages. Human and mouse MFSD2B localized on the plasma membrane of transfected HEK293 cells.
▼ Gene Function
Vu et al. (2017) demonstrated that MFSD2B is essential for sphingosine-1-phosphate (S1P) export from red blood cells and platelets. Comprehensive lipidomic analysis indicated a dramatic and specific accumulation of S1P species in Mfsd2b knockout red blood cells and platelets compared with that of wildtype controls. Consistently, biochemical assays from knockout red blood cells, platelets, and cell lines overexpressing human and mouse Mfsd2b proteins demonstrated that Mfsd2b actively exports S1P. Plasma S1P level in knockout mice was significantly reduced by 42 to 54% of wildtype levels, indicating that the Mfsd2b pathway contributes approximately half of the plasma S1P pool. The reduction of plasma S1P in knockout mice was insufficient to cause blood vessel leakiness, but it did render the mice more sensitive to anaphylactic shock. Stress-induced erythropoiesis significantly increased plasma S1P levels, and knockout mice were sensitive to these treatments. Surprisingly, knockout mice exhibited hemolysis associated with red blood cell stomatocytes, and the hemolytic phenotype was severely increased with signs of membrane fragility under stress erythropoiesis. Vu et al. (2017) concluded that S1P secretion by Mfsd2b is critical for red blood cell morphology, and that their data revealed an unexpected physiologic role of red blood cells in sphingolipid metabolism in circulation.
By genomic sequence analysis, Angers et al. (2008) mapped the human and mouse MFSD2B genes to chromosomes 2p23 and 12A1.1, respectively.
Hartz (2018) mapped the MFSD2B gene to chromosome 2p23.3 based on an alignment of the MFSD2B sequence (GenBank BC033385) with the genomic sequence (GRCh38).
▼ Animal Model
Vu et al. (2017) found that Mfsd2b -/- mice were born at the expected mendelian ratio, appeared normal, and thrived. Mfsd2b -/- mice had reduced RBC count, elevated reticulocyte and stomatocyte counts, and mild splenomegaly. Mfsd2b -/- RBCs were unable to secrete S1P and accumulated high S1P levels. Similarly, Mfsd2b -/- platelets were unable to secrete S1P under basal or stimulated conditions.