Beigneux Anne P, Vergnes Laurent, Qiao Xin, Quatela Steven, Davis Ryan, Watkins Steven M, Coleman Rosalind A, Walzem Rosemary L, Philips Mark, Reue Karen, Young Stephen G
Division of Cardiology, Department of Internal Medicine, University of California, Los Angeles, CA 90095, USA.
J Lipid Res. 2006 Apr;47(4):734-44. doi: 10.1194/jlr.M500556-JLR200. Epub 2006 Jan 31.
In analyzing the sequence tags for mutant mouse embryonic stem (ES) cell lines in BayGenomics (a mouse gene-trapping resource), we identified a novel gene, 1-acylglycerol-3-phosphate O-acyltransferase (Agpat6), with sequence similarities to previously characterized glycerolipid acyltransferases. Agpat6's closest family member is another novel gene that we have provisionally designated Agpat8. Both Agpat6 and Agpat8 are conserved from plants, nematodes, and flies to mammals. AGPAT6, which is predicted to contain multiple membrane-spanning helices, is found exclusively within the endoplasmic reticulum (ER) in mammalian cells. To gain insights into the in vivo importance of Agpat6, we used the Agpat6 ES cell line from BayGenomics to create Agpat6-deficient (Agpat6-/-) mice. Agpat6-/- mice lacked full-length Agpat6 transcripts, as judged by northern blots. One of the most striking phenotypes of Agpat6-/- mice was a defect in lactation. Pups nursed by Agpat6-/- mothers die perinatally. Normally, Agpat6 is expressed at high levels in the mammary epithelium of breast tissue, but not in the surrounding adipose tissue. Histological studies revealed that the aveoli and ducts of Agpat6-/- lactating mammary glands were underdeveloped, and there was a dramatic decrease in the size and number of lipid droplets within mammary epithelial cells and ducts. Also, the milk from Agpat6-/- mice was markedly depleted in diacylglycerols and triacylglycerols. Thus, we identified a novel glycerolipid acyltransferase of the ER, AGPAT6, which is crucial for the production of milk fat by the mammary gland.
在分析BayGenomics（一个小鼠基因捕获资源库）中突变小鼠胚胎干细胞（ES细胞）系的序列标签时，我们鉴定出一个新基因，即1-酰基甘油-3-磷酸O-酰基转移酶（Agpat6），其序列与先前鉴定的甘油脂质酰基转移酶相似。Agpat6最接近的家族成员是另一个我们暂命名为Agpat8的新基因。从植物、线虫、果蝇到哺乳动物，Agpat6和Agpat8都是保守的。预测AGPAT6含有多个跨膜螺旋，在哺乳动物细胞中仅在内质网（ER）中发现。为了深入了解Agpat6在体内的重要性，我们使用来自BayGenomics的Agpat6 ES细胞系培育出Agpat6基因缺陷（Agpat6-/-）小鼠。通过Northern印迹法判断，Agpat6-/-小鼠缺乏全长Agpat6转录本。Agpat6-/-小鼠最显著的表型之一是泌乳缺陷。由Agpat6-/-母亲哺育的幼崽在围产期死亡。正常情况下，Agpat6在乳腺组织的乳腺上皮中高水平表达，但在周围脂肪组织中不表达。组织学研究表明，Agpat6-/-泌乳乳腺的腺泡和导管发育不全，乳腺上皮细胞和导管内脂质小滴的大小和数量显著减少。此外，Agpat6-/-小鼠的乳汁中甘油二酯和甘油三酯明显减少。因此，我们鉴定出一种新的内质网甘油脂质酰基转移酶AGPAT6，它对乳腺产生乳脂肪至关重要。
