第15章 细胞分化与胚胎发育.

Presentation on theme: "第15章 细胞分化与胚胎发育."— Presentation transcript:

1 第15章 细胞分化与胚胎发育

2 Main content Cell differentiation Developmental cell differentiation
Basic conception Cell tortipotency Stem cell The facors affecting cell differentiation Developmental cell differentiation

3 Section 1: cell differentiation
脊椎动物细胞分化示意图

4 一、Basic conception of cell differentiation
The process of the cell from multicellular organism be able to differentiate into a specific cell type, in addtion, maitains its choice through many subsequent generations. 在个体发育中，由一种相同的细胞类型经由细胞分裂后逐渐在形态，结构和功能上形成稳定性差异，产生不同细胞类群的过程称为细胞分化。

5 （一）Cell differentiation results from gene differential expression
分子杂交技术检测基因及其mRNA 的表达 输卵管 细胞 成红细胞 胰岛β细胞 卵清蛋白基因探针 + - β-珠蛋白基因探针 胰岛素基因探针 实验方法 Southern杂交 Northern杂交

6 （二）House keeping gene and tissue specific gene
RT-PCR of XRRA1 and a house-keeping gene G3PDH from HCT116 clones treated with X-radiation, various cancer and normal cells, and normal tissues/organs 甘油醛-3-磷酸脱氢酶 House keeping gene (管 家基因) Expressed in all cells, their gene products are essential for cell metabolism. Replicated during the early S phase. G3PDH或GAPDH是甘油醛-3-磷酸脱氢酶（ glyceraldehyde-3-phosphate dehydrogenase ）的英文缩写。该酶是三梭酸循环途径中的一个酶，该酶基因为管家（house keeping）基因，几乎在所有组织中都高水平表达，且它不受含有的部分识别位点、佛波脂等的诱导物质的影响而保持恒定，故被广泛用作抽提total RNA，poly(A)+ RNA，Western blot等实验操作的标准化的内参。

7 （二）House keeping gene and tissue specific gene
Differential expressed in tissues thus keep their specific morphology, structure and function. Replicated during the early S phase in the cell where the gene is expressed. Repliacted during the late S phase in the cell where the gene is not expressed. RT-PCR of XRRA1 and a house-keeping gene G3PDH from HCT116 clones treated with X-radiation, various cancer and normal cells, and normal tissues/organs 不同类型细胞中特异性表达的基因，其产物赋予各种类型细胞特异的形 态结构特征与 特异的功能 G3PDH或GAPDH是甘油醛-3-磷酸脱氢酶（ glyceraldehyde-3-phosphate dehydrogenase ）的英文缩写。该酶是三梭酸循环途径中的一个酶，该酶基因为管家（house keeping）基因，几乎在所有组织中都高水平表达，且它不受含有的部分识别位点、佛波脂等的诱导物质的影响而保持恒定，故被广泛用作抽提total RNA，poly(A)+ RNA，Western blot等实验操作的标准化的内参。 甘油醛-3-磷酸脱氢酶 7

8 （三）Combinatorial gene control creates many different cell types in Eucaryotes

9 （四）The single gene regulatory protein can trigger the formation of an entire organ
MyoD is a protein with a key role in regulating muscle differentiation. MyoD belongs to a family of proteins known as myogenic regulatory factors (MRFs) sharing bHLH (basic helix loop helix) structures as transcription factors.

10 The life cycle of the slime molds
（五）cell differentiation also be employed for the protozoan to adjust the environment The life cycle of the slime molds The life cycle of the slime molds (Margulis' phylum Rhizopoda, Pr-2) gives a fascinating example of something that seems half-way between a colony and a multi-celled animal (Figure 3)10. At one stage of the life cycle, it is independent single-celled amoebas. At another stage the amoebas swarm to form a "slug". The slug looks and moves like a multi-cellular animal -- including a slimy cellulose "skin", but in fact each of the component amoebas retains its individual identity. In the reproductive stage the "slug" grows into a fruiting body -- a stalk with a round cap that bursts into a shower of spores that produce the next generation amoebas. At this point some of the original amoebas undergo programmed death to form the stalks and other specialized portions of the fruiting body. In the aggregated stages, the individual amoebas appear to use chemical signalling to initiate the various stages in the life cycle and coordinate the movements of the aggregation. 黏菌繁殖过程示意

11 （六）Transdifferentiation
Transdifferentialtion(转分化): 一种分化类型的细胞转变成另一种类型的分化细胞的现象称为转分化。 去分化： 分化细胞失去其特有结构与功能变成为未分化细胞细胞特征过程。 再分化：未分化细胞重新特化过程。

12 （七） Regeneration Regeneration (再生）
广义再生涉及细胞，组织，器官以及个体水平。一般指生物体缺失部分后重建过程。 蝾螈肢体的切除再生

13 Main content Cell differentiation Developmental cell differentiation
Basic conception Cell tortipotency Stem cell The facors affecting cell differentiation Developmental cell differentiation

14 二, cell totipotency Cell totipotency:
The cell’s capacity to form an entire organism. e.g.: Human development begins when a sperm fertilizes an egg and creates a single totipotent cell. In the first hours after fertilization, this cell divides into identical totipotent cells. Approximately four days after fertilization and after several cycles of cell division, these totipotent cells begin to specialize. 细胞经分裂和分化后仍具有形成完整有机体的潜能或特性。

15 Plant cell totipotency

16 nucleus totipotency-爪蟾核移植实验
全能性细胞核 （totipotent nucleus） 终末分化细胞的细胞核仍 然具有全能性 Nuclear transfer experiment 证明细胞核的全能性

17 nucleus totipotency- 哺乳动物体细胞核移植

18 Main content Cell differentiation Developmental cell differentiation
Basic conception Cell tortipotency Stem cell The facors affecting cell differentiation Developmental cell differentiation

19 三, Stem cell Defining properties: 1, not terminally differentiated 2, divide without limit 3, its two daughter cells with the choices to be remain stem cell or be terminal differentiated

20 Category of stem cell Differential potential Totipotent stem cell
Pluripotent stem cell Unipotent stem cell Differential potential

21 Category of stem cell Totipotent stem cell (全能干细胞)：
具分化产生三个胚层中的各种类型的细胞，能发育成胚盘组织，产生子代个体。 如哺乳动物全能干细胞：受精卵与卵裂早期细胞。

22 Category of stem cell Differential potential Tortipotent stem cell
Pluripotent stem cell Unipotent stem cell Differential potential

23 Category of stem cell Pluripotent stem cell (多能干细胞)：
在一定条件下，能分化产生3个胚层中的各种类型的细胞并形成器官的一类干细胞，如胚胎干细胞和生殖嵴干细胞。

24 Category of stem cell Differential potential Tortipotent stem cell
Pluripotent stem cell Unipotent stem cell Differential potential

25 Category of stem cell Unipotent stem cell (单能干细胞)： 能分化产生一种或几种类型的细胞。
神经元 寡突胶质细胞 星形胶质细胞

26 Category of stem cell Embryonic Stem (ES) cell : 胚胎干细胞
Sources difference Adult Stem (AS) cell: 成体干细胞

27 Embryonic Stem Cell 人胚胎干细胞建系示意
人胚胎干细胞建系示意

28 Embryonic Stem Cell 人胚胎干细胞定向诱导分化
人的胚胎干细胞诱导分化成胰岛β 细胞：A. 体外诱导产生的经3 种特异标志蛋白染色的胰岛β 细胞。B. 将这些细胞移植到糖尿病模型小鼠体内，一周后，小鼠的血糖趋于正常。移植后6 周取出移植物（箭头所指），结果血糖明显升高。 人胚胎干细胞定向诱导分化

29 Producing stem cells from embryos and somatic cell nuclear transfer

30 somatic cell nuclear transfer derived stem cell
人类的治疗性克隆与再生医学的设想

31 Comparison of ESC and ASC

32 Induced Pluripotent Stem Cell (iPS)

33 Induced Pluripotent Stem Cell (iPS)
Oct4 Sox2 c-myc KLF4 诱导多能干细胞： 性质类似胚胎干细胞, 具多样分化潜能。 33

34 Cell engineering 生殖性克隆 治疗性克隆 再生医学 组织工程 人类的治疗性克隆与再生医学的设想

35 Main content Cell differentiation Developmental cell differentiation
Basic conception Cell tortipotency Stem cell The facors affecting cell differentiation Developmental cell differentiation

36 四, the factors affecting cell differentiation

37 （一）Cytoplasm nonhomogeneity from the fertilized egg for cell differentiation
隐蔽mRNA 决定子 （determinent） 果蝇卵在受精后2小时内只进行核分裂, 胞质不分裂，形成合胞体胚胎。随后核向卵边缘迁移，细胞的分化命运决定于核迁入不同的细胞质区域。迁入卵后端生殖质（germplasm）中的最终分化为生殖细胞。 证明了果蝇卵细胞后端存在决定生殖细胞分化的细胞质成分即生殖质就是 种质细胞的决定子 Figure 22-28a Molecular Biology of the Cell (© Garland Science 2008)

38 （二）extracellular signals for cell differentiation
近端组织的相互作用（promixate tissue interaction）主要通过细胞旁分泌产生信号分子来实现 细胞分化的共性： 胚胎细胞，尤其是后口动物胚胎细胞的分化过程中，尽管细胞分化的最终命运大相径庭，但对分化，尤其是早期分化起主要调控作用的都是少数几种相同的信号途径，它们按照极其相似的方式调控发育过程

39 胚胎诱导（embryonic induction）
胚胎诱导(embryonic induction)动物在一定的胚胎发育时期, 一部分细胞影响相邻细胞使其向一定方向分化的作用称为胚胎诱导, 或称为分化诱导。能对其他细胞的分化起诱导作用的细胞称为诱导者或组织者。如脊索可诱导其顶部的外胚层发育成神经板，神经沟和神经管。这种诱导是通过信号来实现的，其中有些诱导信号是短距离的，仅限于相互接触的细胞间；有些是长距离的，通过扩散作用于靶细胞。通常把响应诱导信号的同类细胞叫做形态发生场（morphogenetic field）。除了上述的典型的诱导方式外，还有其它一些方式，如：级联信号（cascade signaling）、梯度信号（gradient signaling）、拮抗信号（antagonistic signaling）、组合信号（combinatorial signaling）、侧向信号（lateral signaling）等。

40 （三）cell- cell interaction and position effect
细胞所处的位置不同对细胞分化命运的影响 位置信息（sonic hedgehog信号）在翅膀发育中的作用

41 （四）cell memory and determination
Cell determination: 一个细胞接受了指令，在发育中这一细胞及其子代细胞将区别于其他细胞而分化成某种特定细胞类型。

42 （四）cell memory and determination
果蝇幼虫成虫盘：一些未分化的细胞群，在幼虫变态过程中，不同的成 虫盘发育为成虫不同的器官。

43 （四）cell memory and determination
成虫盘移植实验 果蝇成虫盘细胞决定状态的移植实验

44 （四）cell memory and determination
细胞记忆 正反馈途径（positive feedback loop），即细胞接受信号刺激后 ，激活转录调节因子， 该因子不仅诱导自身基因表达，还诱导其 他组织特异性基因的表达 染色体结构变化（DNA 与蛋白质 相互作用及其修饰）信息传到子 代细胞

45 （五）environment for sex determination
环境因素对细胞分化 可产生影响，并进而 影响到生物个体发育 通过细胞自身的遗传 机构发挥作用 Fig. 1. Temperature-dependent sex determination in the American alligator (Alligator mississippiensis), the red-eared slider turtle (Trachemys scripta elegans), and the alligator snapping turtle (Macroclemys temminckii). Animal Reproduction Science, 1998, 53: 77–86

46 （六）chromatin change and gene rearrangement
细胞分化过程中，胞内染色体会部分丢失，如红细胞以及马蛔虫卵裂。 基因重排是细胞分化一种特殊方式，在B淋巴细胞中，其DNA经历断裂丢失与重排进而利用有限基因资源表达极丰富抗体。

47 Main content Cell differentiation Developmental cell differentiation
Basic conception Cell tortipotency Stem cell The facors affecting cell differentiation Developmental cell differentiation

48 Section 2：Developmental cell differention

49 一、 Germ cell differentiation
BBA-Gene Regulatory Mechanisms, 2012, 1819(6): 616–630 性细胞从体细胞中分化出来，被认为是后生动物起源的重要标志。 高度分化的精子卵子一旦结合，所有既有分化标记会消失，成为新生命起点。 Fig. 2. Germ cell differentiation in mice. (A) Schematic representation of spermatogenesis in seminiferous tubules of the adult mouse testis (AdMT). Male germ cell differentiation occurs within the seminiferous epithelium formed by Sertoli cells that are connected laterally by tight junctions and features incomplete cytokinesis so that the cytoplasm of clonal siblings remains connected. Spermatogenesis begins with the differentiation and mitotic proliferation of spermatogonia (2n) which are in contact with the basement membrane. They enter meiosis and form primary spermatocytes (4n) which undergo genetic recombination before becoming secondary spermatocytes (2n) following the first meiotic division which is closely followed by the second meiotic division which generates round spermatids (n). Spermiogenesis is the process by which these cells undergo nuclear and head reshaping and develop a tail as elongating spermatids, forming the spermatozoa which are finally released as individualized cells into the tubule lumen. (B) Immunohistochemical detection of KPNA4 in the AdMT (Abcam ab6039, as in [27]) reveals intense staining in nuclei of pachytene spermatocytes (Sc), round spermatids (Rs) and Sertoli cells (Se) and in the cytoplasm of Leydig cells (Ly). Asterisk, Seminiferous tubule lumen. Es, elongating spermatids. (C) Predominant subcellular localization of the three importin α proteins from immunohistochemistry is shown in AdMT: KPNA2, red; KPNA3, blue; KPNA4, green. Solid lines represent nucleoplasmic localization, and dotted lines represent cytoplasmic localization. The data are obtained from and . (D) Schematic representation of mouse oocyte maturation in adults. Oocytes are arrested in meiotic prophase in fetal life and typically resume meiosis only after puberty. After germinal vesicle breakdown (GVBD), microtubules (green) polymerize around the mass of chromosomes (blue) and the meiotic spindle begins to migrate to the cortex. The first polar body (PB) is extruded in the axis of spindle migration, and the oocyte chromosomes progress to metaphase of the second meiotic division then undergo a second arrest until fertilization. Germ cell differentiation in mice 49

50 性别分化实际上是性腺细胞的分化 性腺是一个极为特殊的器官 大多数器官的发育进程，其细 胞分化都仅有一个方向
性腺是一个极为特殊的器官 大多数器官的发育进程，其细 胞分化都仅有一个方向 性腺的分化却具有两个截然不 同的方向——睾丸或卵巢 性腺原基中每个细胞都具备这 两种分化潜能，要么分化为睾 丸细胞，要么分化为卵巢细胞 从种系的发生来看，专司生殖功能的性细胞（germ line）从体细胞（somatic cell）分化出来，被认为是后生生物起源的重要标志，并且随着进化水平的提高，生殖细胞的分化程度也呈现不断提高的趋势。 Differentiation of ovaries and testes from bipotential gonads 50

51 哺乳动物Y染色体携带男性性别决定的关键基因：睾丸决 定因子
---- 只有一条X染色体没有Y染色体的人发育成女性 ---- 具有多个X染色体，同时具有Y染色体的个体发育成男性 ---- 在XX-XY嵌合体的性腺发育中，首先分化的是睾丸支持细胞， 该细胞核型是 XY。 从种系的发生来看，专司生殖功能的性细胞（germ line）从体细胞（somatic cell）分化出来，被认为是后生生物起源的重要标志，并且随着进化水平的提高，生殖细胞的分化程度也呈现不断提高的趋势。 Differentiation of ovaries and testes from bipotential gonads An XX sex-reversed mouse (33.13) with SRY gene is phenotypically male 51

52 睾丸决定因子：SRY: sex-determining region of the Y chromosome
---这个基因它被发现于XY男性和极少的XX男性。 ---通过分析XX男性和XY女性的DNA,睾丸决定基因被进一步缩小到Y染色体短臂上一个35kb碱基对的区域。 ---Sry基因在XY小鼠性腺体细胞刚分化为sertoli cell之前的体细胞中表达, 随后消失。 转基因(SRY)小鼠实验： ---将Sry基因14kb区域取下，显微注射到刚受精的小鼠合子原核中(XX型)。注射过含有Sry序列的小鼠胚胎发育出睾丸、雄性的附属器官和阴茎。 --- 但无法形成具功能的精子。

53 SRY: sex-determining region of the Y chromosome
在这个区域中发现一个男性特异的 DNA序列， 编码223氨基酸的肽. 这 个肽含有一个HMG (high mobility group) box的DNA结合域，它可诱导 与它结合的DNA区域发生弯曲。 在性腺早期分化过程中，FGF9、SRY和sox9构成了一个调控网络：SRY的表达，启动了sox9的表达，而sox9作为转录因子，激活FGF9； FGF9蛋白分泌到细胞外，作为信号分子，起两方面的作用：一是通过信号转导过程作用于本身的sox9基因，维持其表达，同时也作用于邻近细胞，使前体细胞向睾丸支持细胞分化过程中sox9的表达水平保持相对平衡，保证分化的同步。 Figure 1. Model of gene regulatory networks in mammalian sex determination. Sex-determining genetic activity in the XY pre-Sertoli cell (PSC) is dominated by SRY-SOX9-FGF9/FGFR2. This genetic pathway is stabilized by mutually positive (curved arrows) interactions between SOX9 and FGF9, resulting in continued expression of SOX9 in the Sertoli cell lineage, in combination with antagonism (hammered lines) of ovary-determining genes/proteins (shown in red). Only a short period of SRY expression is required to upregulate Sox9 from its basal levels in the bipotential gonad. FGF9 and PGD2 support paracrine signaling (arrows exiting from lower cell), resulting in the recruitment of additional supporting cell precursors (upper PSC) that express SRY and/or SOX9 to the Sertoli cell lineage. The secreted molecules FGF9 and desert hedgehog (DHH) also function in masculinizing the germ cell and steroidogenic cell lineages, respectively. This testis-determining gene regulatory network and its downstream targets (‘testis genes’) initiate a variety of morphogenetic processes, including the migration of endothelial cells from the adjacent mesonephros, which are crucial to the formation of testis cords and the associated coelomic blood vessel. In the female (XX) gonad, the absence of SRY in pregranulosa cells (PGC) results in successful antagonism of SOX9/FGF9 by ovary-determining gene products. This causes commitment to the granulosa cell lineage and permits retinoic acid (RA) to drive ovarian germ cells into meiosis. Note the linear core of the testis-determining pathway and the somewhat more modular appearance of the ovary-determining network. Note also that NR5A1 functions at distinct stages—this is likely to be true of several molecules included. Question marks indicate missing components or uncertainty in terms of regulatory relationships. IR = INSR, INSRR, and IGF1R. Figure Developmental Biology (© Sinauer Associates,Inc. 2010) 53

54 原生殖细胞迁移 性腺是生殖细胞发育场所。原生殖细胞（PGC）形成于胚胎发育早期，（人类第四周，小鼠受精后第7天），来自胚外中胚层的细胞首先聚集在尿囊和后肠的交界处，然后沿卵黄囊的尾部进入后肠向背部迁移，PGC在迁移过程中快速分裂。

55 SRY与性腺细胞分化 人类胚胎发育中，原生殖细胞到达生殖嵴在第六周，直到第七周，男女两性生殖嵴及其相关附属结构未有任何差别。SRY于胚胎发育第41天表达，与原生殖细胞细胞到达生殖嵴一致。

56 SRY启动Sox9表达，开启保守‘精巢形成途径’
* 常染色体上的睾丸决定基因， 含HMG box的转录因子。 * Sry在胚胎中，可能仅有几小时活性，但它的主要作用可能是激活Sox9. * 人(XX)有额外拷贝的SOX9基因发育为雄性，即使没有SRY基因存在。 * 在小鼠中SOX9基因仅表达于雄性生殖嵴中。同时，它与Sry都表达于同样的生殖嵴细胞中，但其表达时间稍晚。 * 敲除Sox9基因在XY小鼠性腺中的表达，发生性逆转。 * Sox9转基因XX小鼠---形成精巢，缺乏精子。 Figure Developmental Biology (© Sinauer Associates,Inc. 2010)

57 SRY启动Sox9表达，开启保守‘精巢形成途径’
--- Sox9基因在所有脊椎动物中表达。Sry基因似乎仅存在于哺乳动物中。Sox9才是脊椎动物中核心的雄性决定因子。 --- 在哺乳动物中， Sry激活Sox9; --- 但在鸟类、两栖类、鱼类， 它似乎由Dmrt1的激活。 --- Sox9在sertoli前体细胞中的表达可受Sry和Sf1的共同调节。 Figure Developmental Biology (© Sinauer Associates,Inc. 2010)

58 Sox9：保守的‘精巢形成途径’的决定因子
---- 结合自己的启动子，维持其表达。 ---- 阻止β-catenin诱导卵巢形成 结合许多精巢形成必须的基因上游调控元件，调节其表达。 ---- 结合AMH(anti-mullerian duct hormone)的启动子区，调节其表达 ---- Sox9激活Fgf9的表达；而Fgf9又可维持 Sox9的转录，建立正反馈环路，驱动性腺发育。 Figure Developmental Biology (© Sinauer Associates,Inc. 2010)

59 Sox 9 持续表达依赖胞外信号分子FGF9 FGF9： * FGF9敲除小鼠，突变体均为雌性。 * Sox9可激活FGF9表达。
--- 可引起sertoli cell的前体细胞增殖、分化。 --- 激活邻近中肾(mesonephros)的内皮细胞(endothelial cell)迁入XY性腺。这些细胞构成精巢的主要动脉并诱导sertoli cell前体形成睾丸索。

60 Wnt4在卵巢发育中起重要作用 * Wnt在发育过程中的各个阶段都发挥着重要作用，在性别决定之前，Wnt4在两性的生殖嵴中都有表达；
*在性别决定发生时（小鼠12.5天），Wnt4的表达仅限于XX个体，在雄性生殖嵴中的表达大大下降。 *在缺失Wnt4的转基因小鼠中，卵巢不能正常形成。 (C. Logan and R. Nusse, 2004) 经典Wnt信号通路

61 Wnt4 与FGF9 有颉颃作用，是卵巢形成必需的。
性腺细胞分化中的信号途径 Wnt4 与FGF9 有颉颃作用，是卵巢形成必需的。 性腺细胞分化中的信号途径：SRY 在上游基因的诱导下表达， 激活了Sox9 ，后者又激活FGF9 的表达；FGF9 蛋白分泌到细胞外，通过信号转导过程维持本身的Sox9 基因表达，同时也作用于邻近细胞，保证分化的同步，并触发睾丸的形成。Sox9 蛋白还促使穆勒氏管退化。Wnt4 与FGF9 有颉颃作用，是卵巢形成必需的。 在性腺早期分化过程中，FGF9、SRY和sox9构成了一个调控网络：SRY的表达，启动了sox9的表达，而sox9作为转录因子，激活FGF9； FGF9蛋白分泌到细胞外，作为信号分子，起两方面的作用：一是通过信号转导过程作用于本身的sox9基因，维持其表达，同时也作用于邻近细胞，使前体细胞向睾丸支持细胞分化过程中sox9的表达水平保持相对平衡，保证分化的同步。 Wnt4 (wingless-related MMTV integration site 4) 编码一种生长因子，是Wnt（wingless-type）家族的成员。Wnt在发育过程中的各个阶段都发挥着重要作用，在性别决定之前，Wnt4在两性的生殖嵴中都有表达；在性别决定发生时（小鼠12.5天），Wnt4的表达仅限于XX个体，在雄性生殖嵴中的表达大大下降。在小鼠中敲除（knock out）Wnt4，突变体的性腺部分分化为睾丸样结构，穆勒氏管退化，性激素分泌受阻，生殖细胞发生凋亡。可见Wnt4在雌性性别决定的若干步骤都有作用。 在性别决定过程中，Wnt4和FGF9这两种分泌性信号分子具有明显的颉颃作用。在XY性腺中，SRY启动Sox9和FGF9之间的反馈回路，使FGF9表达量提高，同时阻遏Wnt4的表达，性腺朝睾丸方向分化；在XX的性腺中消除Wnt4的表达，足以导致FGF9和sox9表达的上升，尽管这些细胞中并不存在SRY基因。

62 Nature Reviews Genetics 13, 163-174 (March 2012)
其他脊椎动物的性别决定 哺乳动物中， Dmrt1位于常染色体上。在小鼠中，Dmrt1对性别不起决定作用；但可影响到Sertoli cell分化和Germ cell存活。 在Medaka fish中(Matsuda et al, 2002)，Y染色体上的Dmrt1表达于发育精巢的体细胞中，对精巢发育极为重要。可能会激活Sox9基因。 在家鸡中，Z染色体上的Dmrt1是雄性决定基因。 Figure 2 | Diverse roles of DMRT1 orthologues in vertebrate sex determination. Blue shading indicates masculinizing function and pink indicates feminizing function. a | In mammals, expression of the X‑chromosome-linked sex-determining region of chromosome Y (SRY) gene in the fetal gonad triggers male development by activating SOX9 transcription during a crucial period and, in the absence of SOX9 activation, ovarian development ensues. DMRT1 is expressed in the fetal gonad in mammals before sex determination but is required only after gonadal sex is determined. b | In medaka, a Y‑chromosome-linked, recently duplicated Dmrt1 gene, DM domain on Y (Dmy; also known as Dmrt1by), has a role that is analogous to that of SRY, triggering testis development in XY fish. c | In birds, Dmrt1 is Z‑chromosome-linked and thus genetic males have two copies, whereas females have one. Dmrt1 expression is much higher in the genital ridge of ZZ birds, and Dmrt1 is required for testis determination, suggesting that testis fate requires a critical threshold of Dmrt1 activity. d | In the frog Xenopus laevis, a duplicated and truncated Dmrt1 gene (dm-w) is found on the female-specific W chromosome and appears to block the ability of the autosomal Dmrt1 gene to determine testis fate. In medaka, birds and X. laevis, the autosomal Dmrt1 genes also are believed to function in testicular differentiation after gonadal sex is determined, similar to the situation for their mammalian counterparts. Nature Reviews Genetics 13, (March 2012) Diverse roles of DMRT1 orthologues in vertebrate sex determination 62

63 二、早期胚胎发育过程中的细胞分化 "for their discoveries concerning the genetic control of early embryonic development"

64 三、果蝇胚胎早期发育中的细胞分化 无论是母体mRNA的作用 还是细胞间相互作用，其 结果是启动特定基因表达
卵受精后，首先表达的是 母体基因；母体基因产物 沿胚前后轴形成浓度梯度， 决定了胚的前后位置和头 尾区域；控制其它基因的 表达 母体基因→ 裂隙基因→ 成对规则基因→体节极性 基因→同源异形基因 图15－18 果蝇体节形成中的基因调控 bicoid 等母体基因的mRNA 和蛋白在受精卵中形成浓度梯度，调控裂隙基因的表达，形成各自特异的表达区域；裂隙基因再调控成对规则基因，各形成7 条横纹状分布的表达区；成对规则基因调控其下游的体节极性基因，形成14 条表达横纹，相当于14 个副体节的位置。体节的不同特征则是由同源异型基因决定的。（Markus Noll 博士惠赠） 1)母体效应基因(maternal-effect gene) 这些基因决定果蝇的极性，即果蝇的头部、尾部、背部-腹部的轴。 2)体节基因(segmentation genes) 这些基因控制着果蝇体节的数量 3)同源异形选择基因( homeotic selector genes) 此类基因负责各种节的同一性，它们的突变将造成身体的一部分结构转变成另一部分结构

65 本章小结 细胞分化具个性 任何一种细胞的分化、任何组织的形成以及每个器官的构建，都 是一系列复杂信号联合作用的结果，都有其本身的特性——特定 的局部环境、特定的一组诱导者和特定的信号途径 细胞分化具共性 在任何胚胎，尤其是脊椎动物胚胎细胞的分化过程中，都可以见 到FGF、Wnt、TGF－β、RA和Shh等信号途径，它们按照极其相 似的方式调控发育过程 FGF信号途径 Wnt信号途径 BMP信号途径 RA信号途径 Shh信号途径

66 Thank you!