Cloning of a complementary DNA encoding a new mouse B lymphocyte differentiation antigen, homologous to the human B1 (CD20) antigen, and localization of the gene to chromosome 19.
The human B1 (CD20) molecule is a differentiation Ag found only on the surface of B lymphocytes. This structurally unique phosphoprotein plays a role in the regulation of human B cell proliferation and differentiation. In order to determine whether this structure is also expressed by murine B cells, cDNA clones that encode the mouse equivalent of the B1 molecule were isolated. The longest murine cDNA clone isolated, pmB1-1, contained a 1.4-kb insert with an 873 base pair open reading frame that encodes a protein of 32 kDa. The predicted mouse B1 protein contains three hydrophobic domains that may span the membrane four times and shares a 73% amino acid sequence homology with the human B1 protein. The pmB1-1 cDNA probe was used to examine mB1 mRNA expression. Northern blot analysis indicated that pmB1-1 hybridized with two mRNA species of 2.3 and 3.0 kb that were expressed only in murine spleen lymphocytes, in B lineage cell lines representing mature B cells, and were weakly expressed in one of two plasmacytoma cell lines. pmB1-1 failed to hybridize with RNA isolated from murine T cell lines, thymus, and nonlymphoid tissues. Southern blot analysis indicated that mB1 was encoded by a single copy gene. In situ hybridization localized the mB1 gene to chromosome 19 band B, a region that also contains the genes that encode the Ly-1, Ly-10, and Ly-12 Ag. These results suggest that only B cells express this heretofore undescribed murine cell-surface protein that is structurally homologous with the membrane-embedded human B1 Ag.
Tedder
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TF
Division of Tumor Immunology, Dana-Farber Cancer Institute, Boston, MA 02115.
Klejman
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Disteche
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Adler
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DA
Schlossman
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Saito
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H
D000595:Amino Acid Sequence; D000818:Animals; D018951:Antigens, CD20; D000944:Antigens, Differentiation, B-Lymphocyte / Q000235:genetics*; D000950:Antigens, Ly / Q000235:genetics*; D001483:Base Sequence; D015139:Blotting, Southern; D002874:Chromosome Mapping; D003001:Cloning, Molecular; D004247:DNA / Q000302:isolation & purification*; D006801:Humans; D051379:Mice; D008807:Mice, Inbred BALB C; D008969:Molecular Sequence Data; D012333:RNA, Messenger / Q000302:isolation & purification; D012689:Sequence Homology, Nucleic Acid
D018951:Antigens, CD20; D000944:Antigens, Differentiation, B-Lymphocyte; D000950:Antigens, Ly; C057962:LY 44 antigen; D012333:RNA, Messenger; D004247:DNA