|
Centrosomes are the major microtubule organizing center (MTOC) in mammalian cells. Failure of centrosome regulation can cause mistakes in chromosome segregation and is associated with aneuploidy. A centrosome is composed of two orthogonal cylindrical proteins, called centrioles, which are surrounded by an electron dense and protein dense amorphous cloud of pericentriolar matrix, often abbreviated as "PCM". The PCM is essential for nucleation and organization of microtubules.〔 The centrosome cycle is important to ensure that daughter cells receive a centrosome after cell division. As the cell cycle progresses, the centrosome undergoes a series of morphological and functional changes. Initiation of the centrosome cycle occurs early in the cell cycle, so that by the time mitosis occurs there are two centrosomes. The centrosome cycle consists of four phases that are synchronized to cell cycle. These include: centrosome duplication during the G1 phase and S Phase, centrosome maturation in the G2 phase, centrosome separation in the mitotic phase, and centrosome disorientation in the late mitotic phase—G1 phase. ==Centriole synthesis== Centrioles are generated in new daughter cells through duplication of preexisting centrioles in the mother cells. Each daughter cell inherits two centrioles (one centrosome) surrounded by pericentriolar material as a result of cell division. The two centrioles are of different ages, though. One centriole originates from the mother cell and the other is replicated from the mother centriole during the cell cycle. It is possible to distinguish between the two preexisting centrioles, because the mother and daughter centriole differ in both shape and function. For example, the mother centriole can nucleate and organize microtubules, whereas the daughter centriole can only nucleate. First, procentrioles begin to form near each preexisting centriole as the cell moves from the G1 phase to the S phase. During S and G2 phase of the cell cycle, the procentrioles elongate until they reach the length of the older mother and daughter centrioles(which takes on characteristics of a mother centriole). Once they reach full length, the new centriole and its mother centriole form a diplosome. A diplosome is a rigid complex formed by an orthogonal mother and newly formed centriole (now a daughter centriole) that aids in the processes of mitosis. As mitosis occurs, the distance between mother and daughter centriole increases until, congruent with anaphase, the diplosome breaks down and each centriole is surrounded by its own pericentriolar material.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Centrosome cycle」の詳細全文を読む スポンサード リンク
|