Vinot Stéphanie, Le Tran, Ohno Shigeo, Pawson Tony, Maro Bernard, Louvet-Vallée Sophie
Laboratoire de Biologie Cellulaire du Développement, UMR 7622, CNRS, Université Pierre et Marie Curie, 9 Quai St Bernard, 75252 Paris cedex 05, France.
Dev Biol. 2005 Jun 15;282(2):307-19. doi: 10.1016/j.ydbio.2005.03.001.
In many organisms, like Caenorhabditis elegans and Drosophila melanogaster, establishment of spatial patterns and definition of cell fate are driven by the segregation of determinants in response to spatial cues, as early as oogenesis or fertilization. In these organisms, a family of conserved proteins, the PAR proteins, is involved in the asymmetric distribution of cytoplasmic determinants and in the control of asymmetric divisions. In the mouse embryo, it is only at the 8-cell stage during compaction that asymmetries, leading to cellular diversification and blastocyst morphogenesis, are first observed. However, it has been suggested that developmentally relevant asymmetries could be established already in the oocyte and during fertilization. This led us to study the PAR proteins during the early stages of mouse development. We observed that the homologues of the different members of the PAR/aPKC complex and PAR1 are expressed in the preimplantation mouse embryo. During the first embryonic cleavages, before compaction, PARD6b and EMK1 are observed on the spindle. The localization of these two proteins becomes asymmetric during compaction, when blastomeres flatten upon each other and polarize. PARD6b is targeted to the apical pole, whereas EMK1 is distributed along the baso-lateral domain. The targeting of EMK1 is dependent upon cell-cell interactions while the apical localization of PARD6b is independent of cell contacts. At the 16-cell stage, aPKCzeta colocalizes with PARD6b and a colocalization of the three proteins (PARD6b/PARD3/aPKCzeta can occur in blastocysts, only at tight junctions. This choreography suggests that proteins of the PAR family are involved in the setting up of blastomere polarity and blastocyst morphogenesis in the early mammalian embryo although the interactions between the different players differ from previously studied systems. Finally, they reinforce the idea that the first developmentally relevant asymmetries are set up during compaction.
在许多生物体中，如秀丽隐杆线虫和黑腹果蝇，早在卵子发生或受精时，空间模式的建立和细胞命运的定义就由决定因子响应空间线索的分离所驱动。在这些生物体中，一类保守蛋白家族，即PAR蛋白，参与细胞质决定因子的不对称分布以及不对称分裂的控制。在小鼠胚胎中，只有在致密化的8细胞阶段才首次观察到导致细胞多样化和囊胚形态发生的不对称性。然而，有人提出，与发育相关的不对称性可能在卵母细胞和受精过程中就已建立。这促使我们研究小鼠发育早期阶段的PAR蛋白。我们观察到PAR/aPKC复合物和PAR1不同成员的同源物在植入前的小鼠胚胎中表达。在第一次胚胎分裂期间，在致密化之前，纺锤体上可观察到PARD6b和EMK1。当卵裂球彼此扁平化并极化时，这两种蛋白的定位在致密化过程中变得不对称。PARD6b靶向顶端极，而EMK1沿基底外侧区域分布。EMK1的靶向依赖于细胞间相互作用，而PARD6b的顶端定位则独立于细胞接触。在16细胞阶段，aPKCzeta与PARD6b共定位，并且这三种蛋白（PARD6b/PARD3/aPKCzeta）的共定位仅在囊胚的紧密连接处发生。这种编排表明，PAR家族蛋白参与早期哺乳动物胚胎中卵裂球极性的建立和囊胚形态发生，尽管不同参与者之间的相互作用与先前研究的系统不同。最后，它们强化了这样一种观点，即第一个与发育相关的不对称性是在致密化过程中建立的。
