|Blood Group Antigen Gene Mutation Database|
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John Milton Hagen Blood Group System
Gene locus - SEMA7A
Semaphorin 7A, the antigen for the JMH blood groups system, is an 80 kd glycoprotein, bound to the cell membrane via a glycosylphosphatidylinositol (GPI) linkage. It is expressed on the surface of erythrocytes and activated lymphocytes and is a member of semaphorin family of proteins that play a major role in regulation of the immune response and certain neuronal functions. The deduced sequence of the protein consists of 666 amino acids, showing a signal peptide, a GPI anchor motif and 5 potential glycosylation sites. An immunoglobulin-like and an RGD motifs are also present.
Chromosomal location of SEMA7A is 15q22.3-q23. The coding sequence is 2061bp organized in 14 exons.
Function of proteins
Function is not known on the surface of erythrocytes although a recent report suggests that a variant allele Sema7A 1381T, in contrast to the wild-type, may cause differential regulation of T-cell response (Gras et al.PMID 22845496) In the immune system, Sema7A expressed on activated T cells stimulates macrophages to produce proinflammatory cytokines through the alpha1beta1 integrin. Thus, integrin-mediated signaling is a common mechanism by which Sema7A functions in both the nervous and immune systems. (Suzuki K et al.Nature Immunology 2008 9 17-23).
Expressed on erythrocytes and peripheral blood lymphocytes. Northern analysis detected their presence in various tissues of the nervous system, in placenta, testis, spleen.
Not known. JMH antigen is not present on complement-sensitive erythrocytes of patients with paroxysmal nocturnal hemoglobinuria (PNH).
The JMH antigen can be acquired by erythrocytes and thus, its level of expression may vary or be transient.
Four alleles of SEMA7A gene were recently documented based on variant JMH serological phenotypes (Seltsam et al. Transfusion 2007 47 133-146). Two other phenotypes observed within a group of 44 individuals examined, namely a JMH- weak and JMH-negative phenotypes, were characterized by a reduction or loss of Sema7A expression on the surface of erythocytes. So far no molecular explanation is forthcoming for the occurrence of these phenotypes, as full-length transcripts and no changes in the coding sequence were observed. Clearly, factors or mechanisms other than coding sequence changes of SEMA7A may affect the surface expression of Semaphorin 7A protein.
Other database IDs and links
Yamada et al. Molecular cloning of CDw108. J Immunol. 1999. 162(7):4094-100.Pubmed
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Olga O. Blumenfeld
Dept. of Biochemistry
Albert Einstein College of Medicine
New York, NY 10461, USA
Contributors for specific alleles are listed with the alleles.
Updated 2012-08-20 13:51:36.087