Wilson G L, Najfeld V, Kozlow E, Menniger J, Ward D, Kehrl J H
Laboratory of Immunoregulation, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, MD 20892.
J Immunol. 1993 Jun 1;150(11):5013-24.
The human CD22 gene is expressed specifically in B lymphocytes and likely has an important function in cell-cell interactions. A nearly full length human CD22 cDNA clone was used to isolate genomic clones that span the CD22 gene. The CD22 gene is spread over 22 kb of DNA and is composed of 15 exons. The first exon contains the major transcriptional start sites. The translation initiation codon is located in exon 3, which also encodes a portion of the signal peptide. Exons 4 to 10 encode the seven Ig domains of CD22, exon 11 encodes the transmembrane domain, exons 12 to 15 encode the intracytoplasmic domain of CD22, and exon 15 also contains the 3' untranslated region. A minor form of CD22 mRNA likely results from splicing of exon 5 to exon 8, skipping exons 6 and 7. A 4.6-kb XbaI fragment of the CD22 gene was used to map the chromosomal location of CD22 by fluorescence in situ hybridization. The hybridization locus was identified by combining fluorescent images of the probe with the chromosomal banding pattern generated by an Alu probe. The results demonstrate that CD22 is located within the band region q13.1 of chromosome 19. Two closely clustered major transcription start sites and several minor start sites were mapped by primer extension. Similarly to many other lymphoid-specific genes, the CD22 promoter lacks an obvious TATA box. Approximately 4 kb of DNA 5' of the transcription start sites were sequenced and found to contain multiple Alu elements. Potential binding sites for the transcriptional factors NF-kappa B, AP-1, and Oct-2 are located within 300 bp 5' of the major transcription start sites. A 400-bp fragment (bp -339 through +71) of the CD22 promoter region was subcloned into a pGEM-chloramphenicol acetyltransferase vector and after transfection into B and T cells was found to be active in both B and T cells. Further studies of the CD22 gene should lead to a greater understanding of the expression of CD22 during B cell development and differentiation.
人类CD22基因特异性表达于B淋巴细胞，可能在细胞间相互作用中发挥重要功能。利用一个近乎全长的人类CD22 cDNA克隆分离出跨越CD22基因的基因组克隆。CD22基因分布在22 kb的DNA上，由15个外显子组成。第一个外显子包含主要转录起始位点。翻译起始密码子位于外显子3中，该外显子还编码信号肽的一部分。外显子4至10编码CD22的7个免疫球蛋白结构域，外显子11编码跨膜结构域，外显子12至15编码CD22的胞质内结构域，外显子15还包含3'非翻译区。一种较小形式的CD22 mRNA可能是由于外显子5与外显子8拼接，跳过了外显子6和7。利用CD22基因的一个4.6 kb XbaI片段通过荧光原位杂交来定位CD22的染色体位置。通过将探针的荧光图像与由Alu探针产生的染色体带型相结合来鉴定杂交位点。结果表明CD22位于19号染色体的q13.1带区。通过引物延伸定位了两个紧密聚集的主要转录起始位点和几个次要起始位点。与许多其他淋巴特异性基因类似，CD22启动子缺乏明显的TATA盒。对转录起始位点5'端约4 kb的DNA进行测序，发现其中含有多个Alu元件。转录因子NF-κB、AP-1和Oct-2的潜在结合位点位于主要转录起始位点5'端300 bp范围内。将CD22启动子区域的一个400 bp片段（-339至+71 bp）亚克隆到pGEM-氯霉素乙酰转移酶载体中，转染到B细胞和T细胞后发现其在这两种细胞中均有活性。对CD22基因的进一步研究应有助于更深入了解CD22在B细胞发育和分化过程中的表达情况。
