Wooding F B Peter, Mather Ian H
Physiology Neuroscience and Development Department, Cambridge University, Cambridge, CB2 3EG, UK.
Department of Animal and Avian Sciences, University of Maryland, College Park, MD20742, USA.
Cell Tissue Res. 2017 Feb;367(2):283-295. doi: 10.1007/s00441-016-2505-8. Epub 2016 Sep 27.
This paper reports a detailed ultrastructural and immunocytochemical investigation of the structure of the milk fat globule membrane (MFGM) in a variety of species. The process follows the same pattern in all mammals so far investigated. The initial (or primary) MFGM immediately on release from the mammary cell is a continuous unit membrane with a thin underlying layer of cytoplasmic origin and a monolayer of phospholipid separating it from the core lipid. This structure changes rapidly as the milk fat globule (MFG) moves into the alveolar lumen. The unit membrane plus the underlying layer of cytoplasm modifies drastically into discontinuous patches and networks. These are superimposed upon a continuous apparently structureless sheet of electron dense material stabilising the MFG and similar to that which bounded the lipid in the cell. The underlying layer of the patches increases in electron density and immunocytochemistry demonstrates localisation of MFGM proteins in this layer. In four species, the dense material shows ordered paracrystalline molecular arrays in section and en face views. All the arrays show the same basic pattern and unit size as determined by optical diffraction. Similar patches, networks and arrays are present on the surface of expressed MFG. Negative staining of lipid-extracted expressed MFGs shows similar patches and networks of membrane. These also occasionally show the crystalline arrays and label with MFGM protein antibodies. Similar networks and strands of plasma membrane on the MFG surface are shown by our CLSM examination of unfixed expressed MFG from mice genetically modified to express a fluorescent molecule as a normal plasma membrane constituent.
本文报道了对多种物种乳脂肪球膜（MFGM）结构的详细超微结构和免疫细胞化学研究。到目前为止，在所有已研究的哺乳动物中，该过程遵循相同的模式。刚从乳腺细胞释放出来的初始（或初级）MFGM是一层连续的单位膜，其下方有一层薄的细胞质起源层，还有一层磷脂单分子层将其与核心脂质分隔开。随着乳脂肪球（MFG）移入肺泡腔，这种结构会迅速改变。单位膜加上下方的细胞质层会剧烈地转变为不连续的斑块和网络。这些斑块和网络叠加在一层连续的、看似无结构的电子致密物质薄片上，该物质稳定了MFG，并且与细胞内界定脂质的物质相似。斑块的下层电子密度增加，免疫细胞化学显示MFGM蛋白定位于该层。在四个物种中，致密物质在切片和正面视图中显示出有序的准晶体分子阵列。所有阵列都显示出与通过光学衍射确定的相同基本模式和单位尺寸。在挤出的MFG表面也存在类似的斑块、网络和阵列。对脂质提取后的挤出MFG进行负染色显示出类似的膜斑块和网络。这些偶尔也会显示出晶体阵列并用MFGM蛋白抗体标记。我们通过共聚焦激光扫描显微镜（CLSM）对经基因改造以表达荧光分子作为正常质膜成分的小鼠未固定挤出MFG进行检查，显示出MFG表面类似的网络和质膜链。
