Molecular Biology of the Cell

無駄をそぎ落とした細胞 : リボソームも 小胞体も ゴルジ体もない ( 復習 : 図 1.3) つまり 蛋白質は合成されない 教科書 9.2.1 核 (DNA が詰まっている しかし DNA の転写は止められている ) ATP( エネルギー ) 合成装置 : ミトコン DNA は消滅する運命 Figure 21-27 Molecular Biology of the Cell ( Garland Science 2008) 1

ハムスター卵とヒト精子 : 生殖能力診断 教科書 9.2.1 10% 以上進入すれば正常 実際の受精は 1/300,000,000 (3 億分の 1) Figure 21-32 Molecular Biology of the Cell ( Garland Science 2008) 2

カルシウムイメージング : 本学では白川英樹先生がご専門 教科書 9.2.1 21.3 Calcium Wave During Fertilization When a sperm cell fuses with this sea urchin egg cell, calcium ions begin rushing into the cell at the site of fusion. In these experiments, calcium concentrations are visualized and measured with a fluorescent dye that becomes increasingly brighter the more calcium is present. Brightness is then translated into a color scale, and, in this three-dimensional display, into peak heights, where red and high peaks represent the highest calcium concentrations. A second rise of the calcium concentration can be observed after fertilization. It occurs during the movement カルシウム濃度の上昇が引き金となって酵素を包んでいる顆粒がポップコーンのようにはじける 酵素が働き 2 つ目の精子が入らないようにバリアを作る ( 次の動画で詳しく ) 3

21.4 Sea Urchin Fertilization 発展教科書 9.2.1 A sea urchin egg during fertilization is visualized here simultaneously by phase contrast microscopy and by fluorescence microscopy. The egg contains a fluorescent dye that becomes brighter in the presence of calcium ions. When a sperm cell fuses with the egg, the fluorescence image shows a wave of calcium ions that sweeps through the cytosol, starting from the initial point of sperm egg fusion. Following the path of the calcium wave, we see a membrane, called the fertilization envelope, rising from the cell surface. The fertilization envelope protects the fertilized egg from the outside environment, and prevents the entry of additional sperm. The rise in cytosolic calcium triggers an elevation of the fertilization envelope through the process of exocytosis. Exocytosis releases hydrolytic enzymes stored in vesicles. Action of the released hydrolases causes a swelling of material surrounding the cell, which in turn elevates the fertilization envelope. Exocytosis can be visualized directly in this system. For this purpose, the plasma membrane is labeled with a fluorescent dye, seen on the right. Each time a vesicle fuses, it leaves a depression in the plasma membrane which, in the optical sections shown, appears as a ring of increased fluorescent staining. On the left, differential interference contrast microscopy is used to directly view the exocytic vesicles that underlie the plasma membrane. The vesicles are visible here, because they are densely packed with protein and consequently have a different refractive index from the surrounding material. Each time a vesicle exocytoses, it disperses its contents and disappears from the image. This effect is best seen when we step back and forth between adjacent frames of the movie. 4

ウニの胞胚 教科書 9.2.2 と図 9.1 原腸 Figure 22-3 (part 1 of 3) Molecular Biology of the Cell ( Garland Science 2008) 5

教科書 9.2 と図 9.1 と 9.2 内胚葉 中胚葉細胞 口 腸管 骨 Figure 22-3 (part 2 of 3) Molecular Biology of the Cell ( Garland Science 2008) お尻の穴 6

動物の体の基本設計図 : 口とお尻が貫通した図 教科書 9.2.3 ( 外胚葉 ) ( 内胚葉 ) 口 お尻の穴 Figure 22-3 (part 3 of 3) Molecular Biology of the Cell ( Garland Science 2008) ( 中胚葉 ) 7

教科書 9.2.3 と図 9.2 22.3 Gastrulation ( 原腸胚形成 ) During gastrulation, cells of this developing frog embryo rearrange in a dramatic ballet of orchestrated cell movements. In a continuous motion, cells from the outer layer of the embryo ( 胚 ) sweep towards the vegetal pole and start invaginating, forming a deep cavity in the interior. The paths of the cells and the topology of these rearrangements are best seen in this animation of an embryo that has been sliced open. The different cell layers that are formed in this way have very different fates. Cells that line the newly formed cavity, called the endoderm, develop into the lining of the gut( 腸 ) and many internal organs such as liver, pancreas, and lung. Cells in the middle layer, called the mesoderm, give rise to muscle and connective tissue. Cells remaining on the outside, called the ectoderm, go on to form the outer layer of the skin, as well as the nervous system. 8

ここまでのまとめの動画 教科書図 9.1 と 9.2 22.2 Developing Egg Cells This frog egg cell has been fertilized and starts dividing. The first cell divisions occur very rapidly. Cells divide every thirty minutes. This timing is very precise. Egg cells that have been fertilized at the same time divide and develop in almost perfect synchrony. After a day or two, embryonic development ( 胚発生 )is completed and tadpoles hatch from the eggs. 9

オーガナイザーを切り取って 別の胚に移植する実験 教科書 9.2.4 細胞塊 ( 宿主となる ) 胚に移植 Figure 22-6b Molecular Biology of the Cell ( Garland Science 2008) 発生途上の体構造を再編成 10

22.4 Spemann s Organizer 教科書 9.2.4 Hans Spemann and Hilde Mangold were pioneers of developmental biology. They showed how the pattern of the embryo is created by interactions between one group of cells and another. In 1924 they made a famous discovery. They found that a small piece of tissue called the Organiser, taken from a specific site in the early frog embryo and transplanted to another embryo, could control the behavior of neighboring cells and direct the formation of an entire body axis. The key experiment is re-enacted here by a modern developmental biologist, using the frog Xenopus Lavis. Two Xenopus embryos are maneuvered under the dissecting microscope. The embryos are beginning to gastrulate. The blastopore, where cells are tucking into the interior, is visible as a dark crescent in the embryo on the left. The dorsal lip of the blastopore contains the Organizer cells. With a pair of forceps and a fine tungsten needle, a block of Organizer tissue is cut from the embryo on the left. Using a hair plucked from a human eyebrow, the block of tissue is gently pushed into a site on the ventral side of the other embryo. An hour later, the graft has healed into the host embryo and the organizer cells have been integrated at an atopic site. Two days later, the host embryo has developed into conjoined twins. The grafted Organizer has caused the host cells around the graft to form a second 11 body axis, complete with central nervous system, eyes, somites, and other structures.

教科書 9.3.1 発生の一番最初には 大雑把に前後 左右 上下を決めるための遺伝子が働き それぞれの場所に別々の蛋白質を合成して 目印とする うしろ前末端背と腹 セントラルドグマの復習 : うしろ遺伝子 ( うしろ DNA) うしろ mrna(nanos) うしろ蛋白質 Figure 22-32 Molecular Biology of the Cell ( Garland Science 2008) 12

頭胸 お腹 教科書 9.3 Figure 22-26 Molecular Biology of the Cell ( Garland Science 2008) 13

教科書 9.3.2 前 うしろ まずはおおまかに体の前後 左右 上下を決めてから細部 ( 節 ) を決める Figure 22-38 Molecular Biology of the Cell ( Garland Science 2008) ホメオティック遺伝子は体節間の違いを決める 14

教科書 9.3.2 と 9.3.3 遺伝子の並んでいる順番と翻訳されてできる蛋白質の空間的位置とは対応している Figure 22-44 Molecular Biology of the Cell ( Garland Science 2008) 15

昆虫と哺乳類それぞれの Hox 遺伝子群 体の領域への対応付け 教科書 9.3.2 と 9.3.3 ハエの DNA 共通祖先の DNA 人間の DNA ハエも人間も 対応する Hox 遺伝子の配列や順番は似ている Figure 22-46 Molecular Biology of the Cell ( Garland Science 2008) 16

ここまでのまとめの動画 22.5 Drosophila Development( 発生 ) 教科書 9.3 During development, a Drosophila embryo( 胚 ) undergoes many complex morphological changes. We first see migration of pole cells from the posterior end. These cells are destined to become the germ cells of the fly. A crest develops which separates a region that will develop into the head, mouth parts, and fore gut. At this stage, the future tail end of the body is folded over on the dorsal side. Body segments then become defined. The first three segments will give rise to the head and mouth parts, the next three to the thorax, and the remaining ones to the abdomen. Eventually, the rear end of the embryo will retract back onto the ventral side and straighten out the embryo. Development to this stage takes about 10 hours. We can appreciate the complexity of these events by morphing a series of individual scanning electron micrographs into a continuous temporal sequence: migration of pole cells; development of various surface indentations, including openings to the air ducts, or tracheal tubes; segmentation, and tail retraction. A similar sequence viewed from the top or the dorsal side. Pole cells migrate and then move into the interior as the hind gut invaginates. The rear end is temporarily folded over onto the dorsal side and eventually starts retracting to straighten out the embryo. Early in development when seen from the bottom or ventral side a deep groove forms during gastrulation( 原腸胚形成 ), as mesodermal cells migrate inward, where they become the precursor cells for many internal organs. The groove then seals 17 off as the cells that remain exterior zipper up.

非対称分裂 教科書 9.4 と図 9.3 幹細胞 幹細胞 外因的要因 ( 細胞外で特定の分子が偏る ) 内因的要因 ( 細胞内で特定の分子が偏る ) Figure 23-6 Molecular Biology of the Cell ( Garland Science 2008) 18

造血系 :( ほぼ ) 骨髄でのできごと リンパ球も赤血球も 元々は同じ幹細胞から分裂したもの! リンパ球前駆細胞 教科書 9.5.3 リンパ球 ( 例外 : 胸腺で ) 造血幹細胞 造血前駆細胞 好中球好酸球 ( 例外 ) 骨髄球前駆細胞 Figure 23-42 Molecular Biology of the Cell ( Garland Science 2008) 巨核球赤血球 19

骨髄 教科書 9.5.1 好中球 ( 未熟 ) 赤血球の前駆細胞 巨核球 ( 未熟 ) 好酸球 ( 未熟 ) 単球 ( 未熟 ) 赤血球 Figure 23-39b Molecular Biology of the Cell ( Garland Science 2008) リンパ球 ( 未熟 ) 20

教科書 9.5.2 と図 9.4 皮脂腺 幹細胞 Figure 23-2 Molecular Biology of the Cell ( Garland Science 2008) 21

教科書 9.5.5 脂肪細胞 神経細胞 白血球 筋肉細胞 ES 細胞 : 受精卵からできた胚を壊して作ることが倫理的に問題とされている Figure 23-68 Molecular Biology of the Cell ( Garland Science 2008) 22

教科書 9.5.5 23.14 Embryonic Stem Cells Embryonic stem cells, or ES cells, are able to differentiate into any cell type in the body. ES cells derived from an embryo can be grown in culture. Upon exposure to an appropriate cocktail of signal molecules, the cells differentiate into specific cell types. In this experiment, ES cells were exposed to signal molecules, inducing the differentiation program that specifies the development of heart muscle cells. After a few days in culture, the previously homogeneous, undifferentiated cells, organize into groups of highly specialized cells. Remarkably, the cells in these groups start contracting rhythmically, indicating they have formed a fully functional contractile apparatus, characteristic of muscle cells. Examining GFP that has been expressed from a heart-muscle specific promoter, shows that the appropriate gene expression programs have been activated selectively in the beating cells. 23

本日のまとめ : 1. 受精 初期胚形成 胚発生 個体 2. もともと 1 つの細胞 ( 受精卵 ) が分化して別々の細胞になる 3. 分化し切った細胞を補充するのが再生 例 : 皮膚のけががなおる など この場合 皮膚幹細胞が分化することで補充している 4. 個体をまるごと作れる全能性幹細胞 (ES 細胞など ) がある 朝日新聞 2012.07.21 24