Ogg S L, Komaragiri M V, Mather I H
Department of Animal Sciences, University of Maryland, College Park 20742, USA.
Mamm Genome. 1996 Dec;7(12):900-5. doi: 10.1007/s003359900265.
Butyrophilin is a glycoprotein of the immunoglobulin superfamily that is secreted in association with the milk-fat-globule membrane from mammary epithelial cells. As a first step towards determining the possible function(s) of this protein in lactation, the mouse butyrophilin gene (Btn) has been cloned from a 129-ES cell genomic library. Over 14 kb of DNA was sequenced, including the entire transcriptional unit of the gene, and 4.6 kb and 1.1 kb of the 5' and 3' flanking region, respectively. In addition, the overall structure of the bovine gene (BTN) was determined by amplification of genomic DNA by the polymerase chain reaction. Both Btn and BTN comprise seven exons and six introns. The signal sequence and two immunoglobulin-like folds of the exoplasmic domain and the membrane anchor are encoded by separate exons, and the cytoplasmic domain is encoded by two short exons and a large terminal exon that also includes 3' untranslated sequence. The butyrophilin gene appears to have evolved from a subset of genes in the immunoglobulin superfamily and genes encoding the B30.2 domain, which is conserved in a family of zinc-finger proteins. Murine butyrophilin mRNA was detected specifically in the mammary gland by RNase protection analysis. Expression increased during the last half of pregnancy and was maximal during lactation. The 5' flanking region of Btn was analyzed for putative regulatory elements and is different from the promoters of other mammary-specific genes. Btn should be useful for determining the mechanisms underlying mammary-specific gene expression and potentially for the production of heterologous proteins in the milk of transgenic animals.
嗜乳脂蛋白是免疫球蛋白超家族的一种糖蛋白，它与乳腺上皮细胞分泌的乳脂肪球膜相关联而分泌。作为确定该蛋白在泌乳过程中可能功能的第一步，从小鼠129-ES细胞基因组文库中克隆了小鼠嗜乳脂蛋白基因（Btn）。对超过14 kb的DNA进行了测序，包括该基因的整个转录单元，以及分别位于5'和3'侧翼区域的4.6 kb和1.1 kb。此外，通过聚合酶链反应扩增基因组DNA确定了牛基因（BTN）的整体结构。Btn和BTN都由七个外显子和六个内含子组成。信号序列、胞外结构域的两个免疫球蛋白样结构域以及膜锚定结构由单独的外显子编码，而胞质结构域由两个短外显子和一个大的末端外显子编码，该末端外显子还包括3'非翻译序列。嗜乳脂蛋白基因似乎是从免疫球蛋白超家族中的一组基因以及编码B30.2结构域的基因进化而来，B30.2结构域在锌指蛋白家族中是保守的。通过核糖核酸酶保护分析在乳腺中特异性检测到小鼠嗜乳脂蛋白mRNA。在妊娠后半期表达增加，在泌乳期达到最大值。对Btn的5'侧翼区域进行了推定调控元件分析，它与其他乳腺特异性基因的启动子不同。Btn对于确定乳腺特异性基因表达的潜在机制以及在转基因动物乳汁中生产异源蛋白可能是有用的。
