医学精品课件生殖细胞发育

1、Chapter 2 The development of germ cells2021/7/16 星期五1一、生殖细胞（一）精子发生和成熟1. 睾丸中发生： 精原细胞初级精母细胞次级精母细胞 精子细胞精子 结果：染色体数减半；DNA量减半； 核型为23, X 或23, Y2. 附睾内成熟：获得运动和受精能力。3. 女性生殖道内获能和顶体反应2021/7/16 星期五2(二）、卵子发育过程： 出生前完成 排卵前完成卵原细胞初级卵母细胞 受精时完成 次级卵母细胞成熟卵细胞结果：一个初级卵母细胞发育形成一个成熟卵细胞 成熟卵细胞的染色体数目减半，DNA量减半。 2021/7/16 星期五3JMCB：

2、利用胚胎干细胞诱导功能性精子细胞蒋杰 近日，上海交通大学冯立新研究小组报道一个全新的体外诱导精子和卵子的方法。冯立新研究员采用的方法可从雄性胚胎干细胞（XY 染色体）在体外同时生成游动的精子和卵子。更为重要的是他们的研究进一步阐明了从胚胎干细胞生成精子和卵子分子机理，是这一领域研究的重大突破。之前，科学家们已经证明了胚胎干细胞（ESC）能在体外分化出胚性生殖细胞，冯立新研究小组体外诱导分化并不经过类胚体形成，通过利用转基因技术直 接从胚胎干细胞转化为生殖细胞。Dazl基因是表达生殖细胞特异RNA结合蛋白的基因，人和多种动物的Dazl基因是精子发生的重要调控因子，Dazl基 因突变或表达缺乏将导

3、致精子发生过程减数分裂障碍和雄性不育。研究者通过Dazl基因的异位表达，最终在体外将小鼠胚胎干细胞同时诱导出了游动的精子和卵 子。此外， Dazl基因的瞬时过量表达使Nanog受到抑制，但是小鼠胚胎干细胞核抗原被诱导成生殖细胞。Dazl基因敲低导致了生殖细胞部分标记物基因表达降低， 比如说Stella，MVH和Prdm1等。冯立新研究小组不仅证明了Dazl基因是控制生殖细胞分化的一个主要控制基因，而且通过Dazl基因异位表达 诱导出小鼠胚胎干细胞在体外分化成了生殖细胞精子和卵子。2009年10月28日，斯坦福大学人类胚胎干细胞及再生组织医学研究小组Kehkooi Kee 等在Nature发表了

4、他们最新的研究成果，研究者在实验室通过人体干细胞制造出人工精子和卵子，这一研究成果进一步证实了冯立新研究团队所做的工作的前 沿性和重要性，同时也表明我国在体外诱导干细胞生成精子和卵子研究处于国际领先地位。（生物谷B）2021/7/16 星期五4Journal of Molecular Cell Biology (2009), 111 doi:10.1093/jmcb/mjp026Dazl Promotes Germ Cell Differentiation from Embryonic Stem CellsZhuo Yu1, Ping Ji1, Jinping Cao1, Shu Zhu1,

5、Yao Li2, Lin Zheng3, Xuejin Chen2, and Lixin Feng1,*1 Laboratory for Germ Cell Research, Institute of Medical Sciences, Shanghai Jiao Tong University School of Medicine, Shanghai 200025, China2 Department of Laboratory Animal Sciences, Shanghai Jiao Tong University School of Medicine, Shanghai 20002

6、5, China3 Department of Pathology, Shanghai Jiao Tong University School of Medicine, Shanghai 200025, ChinaIt has been demonstrated that through the formation of embryoid bodies (EBs) germ cells can be derived from embryonic stem (ES) cells. Here, we describe a transgene expression approach to deriv

7、e germ cells directly from ES cells in vitro without EB formation. Through the ectopic expression of Deleted in Azoospermia-Like (Dazl), a germ cell-specific RNA-binding protein,both motile tailed-sperm and oocytes were induced from mouse ES (mES) cells in culture. Furthermore, transient overexpress

8、ion of Dazl led to suppression of Nanog but induced germ cell nuclear antigen in mES cells. Dazl knockdown resulted in reduction in the expression of germ cell markers including Stella, MVH and Prdm1. Our study indicates that Dazl is a master gene controlling germ cell differentiation and that ectop

9、ic expression of Dazl promotes the dynamic differentiation of mouse ES cells into gametes in vitro.2021/7/16 星期五5Nature：利用干细胞培育出人工精子卵子美国科学家在实验室中通过人体干细胞制造出人工精子和卵子，在为无数不孕不育症夫妇带来福音的同时，也为人类的亲子关系带来无穷争论。这项研究由美国政府资助。加州斯坦福大学的科学家将化学药物和维生素混合，成功诱使干细胞变成了精子和卵子。他们培育出的精子有头部和短小的尾部，被认为发育成熟，完全能够使卵子受精。而卵子培育还处于研究初期，但仍然

10、比其他科学家取得的成果要进步得多。精子和卵子的培育进展发表于自然杂志，为不孕症男女有朝一日培育出自己的精卵用于试管婴儿疗法带来了希望。美国的科研团队利用生长了几天的胚胎干细胞完成了实验，但他们希望进一步利用人体表皮细胞复制精子和卵子的培育过程。表皮细胞将首先放入一种混合物中，该混合物会使表皮细胞的生物钟回溯到胚胎干细胞状态。然后再将其培育成精子和卵子。而使用某人自己的皮肤意味着实验室培育出的精子或卵子不会与其身体出现排斥反应。未来的科学研究也可能会利用男性皮肤培育出“雄性卵子”，或者利用女性皮肤培育出“雌性精子”。这将帮助同性恋夫妇拥有遗传学上的亲生子女。但是，很多科学家质疑，由于女性细胞中缺

11、少男性的Y染色体，因此从中培育出精子是不可能的”根据世界卫生组织公布的数字，全世界不孕症患者人数约为8000万1.1亿，还有很多育龄夫妇由于癌症治疗而无法生育。最新的实验成果会帮助他们 成功生育出至少从生物学的角度是他们自己的子女。然而，这同时也引发了巨大的道德和伦理争论，因为这可能会制作出完全的人工婴儿，众多男女也会逐渐退出哺 育后代的行列。反对者认为肆意改变人类生育过程是错误的，并警告说治疗不育症的进展有可能引发家庭成员关系的扭曲和破坏。（生物谷B）2021/7/16 星期五6Nature advance online publication 28 October 2009 | doi:1

12、0.1038/nature08562Human DAZL, DAZ and BOULE genes modulate primordial germ-cell and haploid gamete formationKehkooi Kee1, Vanessa T. Angeles1, Martha Flores1, Ha Nam Nguyen1 & Renee A. Reijo Pera1Center for Human Embryonic Stem Cell Research and Education, Institute for Stem Cell Biology & Regenerat

13、ive Medicine, Department of Obstetrics and Gynecology, Stanford University School of Medicine, Stanford University, Palo Alto, California 94305, USACorrespondence to: Renee A. Reijo Pera1 Correspondence and requests for materials should be addressed to R.A.R.P.The leading cause of infertility in men

14、 and women is quantitative and qualitative defects in human germ-cell (oocyte and sperm) development. Yet, it has not been possible to examine the unique developmental genetics of human germ-cell formation and differentiation owing to inaccessibility of germ cells during fetal development. Although

15、several studies have shown that germ cells can be differentiated from mouse and human embryonic stem cells, human germ cells differentiated in these studies generally did not develop beyond the earliest stages1, 2, 3, 4, 5, 6, 7, 8. Here we used a germ-cell reporter to quantify and isolate primordia

16、l germ cells derived from both male and female human embryonic stem cells. By silencing and overexpressing genes that encode germ-cell-specific cytoplasmic RNA-binding proteins (not transcription factors), we modulated human germ-cell formation and developmental progression. We observed that human D

17、AZL (deleted in azoospermia-like) functions in primordial germ-cell formation, whereas closely related genes DAZ and BOULE (also called BOLL) promote later stages of meiosis and development of haploid gametes. These results are significant to the generation of gametes for future basic science and po

18、tential clinical applications.2021/7/16 星期五7FASEBJournal：找到控制雄性产生精子关键基因娜娜 美国实验生物学会联合会杂志（FASEB Journal）12 月刊上刊登了一篇研究报告称，科学家已经发现睾丸中的雄性激素控制精子生成和男性生育的机理，男性可能采用和女性类似的方式避孕。这个发现同时也给那些精 子数量少和无生育能力的男性带来了希望。虽然上述结果只在小鼠上进行了验证，在其它哺乳动物例如人类身上也可能得到类似结果。米歇尔威尔士（Michelle Welsh）博士是论文的合著者，他来自英国爱丁堡的女王医学研究院生殖生育学中心，他说：“这项研

19、究给我们提供了一个新的机会，让我们可以了解雄性激素 是如何控制精子产生的，这机理可以为男性不育治疗提供新的思路，同时，为研制出新型男性避孕药提供新的启示。”威尔士和同事用两组老鼠来进行了研究。第一组老鼠是正常鼠群。第二组老鼠睾丸管周肌样细胞中缺少一个基因，这个基因是用来为男性荷尔蒙受体编码的，相比拥有正常基因组的老鼠来说，缺少基因组老鼠精子产生量将大幅减少，并导致不育。医学博士杰拉德韦斯曼（Gerald Weissmann）是美国实验生物学会联合会杂志的主编，他说：“尽管女性避孕药在60年代以来就已经开始使用，而类似的男性避孕药却一直没有研究 出来。这个新研究结果不仅是针对雄性激素和它们的细胞

20、而得到的新型男性避孕药，它同时有望发现新的方法来促进精子生成。2021/7/16 星期五8The FASEB Journal. 2009;23:4218-4230.doi: 10.1096/fj.09-138347.Androgen action via testicular peritubular myoid cells is essential for male fertilityMichelle Welsh*, Philippa T. K. Saunders*, Nina Atanassova, Richard M. Sharpe* and Lee B. Smith*,1* Medica

21、l Research Council Human Reproductive Sciences Unit, Centre for Reproductive Biology, The Queens Medical Research Institute, Edinburgh, UK; and theInstitute of Experimental Morphology and Anthropology with Museum, Bulgarian Academy of Sciences, Sofia, BulgariaAndrogens are essential for normal sperm

22、atogenesis and male fertility, but how androgens exert this effect remains uncertain. Androgen receptors (ARs) are expressed in several testicular cell types, but continuing uncertainty exists over which cell type mediates androgen control of spermatogenesis. Androgen signaling via Sertoli cells (SC

23、s) is essential for complete spermatogenesis, but the role for androgen signaling via peritubular myoid (PTM) cells is contentious. To address this controversy, we generated PTM-specific AR-knockout (PTM-ARKO) mice in which gross reproductive development was normal, but all PTM-ARKO males were azoos

24、permic and infertile. Testis weight was reduced beyond puberty, and in adulthood there was an 86% reduction in germ cells, compared with wild-type littermates. These changes were not explained by any deficits in testosterone, luteinizing hormone, or follicle-stimulating hormone concentrations. SC fu

25、nction was impaired in PTM-ARKO males, indicated by reduced seminiferous tubule fluid production and reduced expression of some androgen-dependent SC genes. Androgen action via PTM cells is therefore essential for normal testis function, spermatogenesis, and fertility in males. This study also provi

26、des the first direct evidence for the importance of androgen-driven stromal-epithelial interactions underpinning the regulation of spermatogenesis; PTM-ARKO mice will enable identification of the new molecular pathways involved.Welsh, M., Saunders, P. T. K., Atanassova, N., Sharpe, R. M., Smith, L.

27、B. Androgen action via testicular peritubular myoid cells is essential for male fertility.2021/7/16 星期五9SCD：利用人类胚胎干细胞造出人造精子唐宁 生物学家卡里姆调制出一种化学物质和维生素构成的“鸡尾酒”，在这种“鸡尾酒”培养环境下，人体干细胞转变成精子。 通过显微镜观测，科学家清晰地看到了这种人造精子有头和尾，并能像正常的精子一样游动。体外受精诊所，届时可以使成千上万的不育男性拥有自己的“基因”儿女。而这仅需要患者的一小点皮肤组织即可。据今天的干细胞研究及进展(Stem Cells and

28、 Development)刊文介绍，英国纽卡斯尔大学的科研人员 致力于人体干细胞研究，并且首次造出人造精子。生物学家卡里姆调制出一种化学物质和维生素构成的“鸡尾酒”，在这种“鸡尾酒”培养环境下，人体干细胞转变 成精子。通过显微镜观测，科学家清晰地看到了这种人造精子有头和尾，并能像正常的精子一样游动。卡里姆教授表示相信这种人造精子能够使卵子受孕，并能制造出 健康的小宝宝。卡里姆教授还将进行进一步研究，以确定该项成果的安全性，并申请监管部门许可，利用人造精子开展实验室人工受孕研究。科研人员也曾试图利用女性胚胎制造出精子，但是实验失败了。这表明在繁衍后代方面，男性占有主导地位。但是有朝一日科学家也许

29、会通过女性干细胞制造出人造卵子，届时人造精子和人造卵子结合，将会诞生完全人造的婴儿。（生物谷B）2021/7/16 星期五102021/7/16 星期五11Stem Cells and Development doi:10.1089/scd.2009.0063.In Vitro Derivation of Human Sperm from Embryonic Stem CellsKarim Nayernia, Jae Ho Lee, Majlinda Lako, Lyle Armstrong, Mary Herbert, Manyu Li, Wolfgang Engel, David Elli

30、ott, Miodrag Stojkovic, John Parrington, Alison Murdoch, Tom Strachan, Xin ZhangDifferentiation of human embryonic stem cells (hESCs) to specific cell types can be achieved using methods that mimic in vivo embryonic developmental programs. Human egg and sperm cells (gametes) are derived from a found

31、er population of germline stem cells (GSCs), primordial germ cells (PGCs), that are set aside early in embryogenesis which give raise to gonocytes in males. After birth, gonocytes differentiate to adult male germline stem cells, spermatogonial stem cells (SSCs), which can self-renew and generate spe

32、rm cells, are unique stem cells in that they are solely dedicated to transmit genetic information from generation to generation. Understanding the mechanisms of germ cell specification, development and its differentiation to sperm is important for elucidating the causes of male infertility. Here, we

33、 developed an in vitro strategy for establishing of male GSCs from human embryonic stem cells. These in vitro derived GSCs express markers which are specific for PGCs, SSCs, meiotic and postmeiotic germ cells indicating maturation of the primordial germ cells to haploid male gametes. In vitro derive

34、d germ cells are able to enter meiosis and generate haploid motile sperm-like cells in vitro. While full potential of the human ES derived germ cells and sperm remains to be demonstrated, this in vitro modeling of human gametogenesis provides a new approach for studying biology of human germ cells a

35、nd establishment of therapeutic approaches in reproductive medicine.2021/7/16 星期五12来源 搜狐 2007-4-16 8:41:33 女性可制造精子自行受孕未来女同性恋生育将成可能生物谷 北京时间4月13日消息，英国12日发布的一项前沿研究显示女性将能够制造精子，这使得女同性恋生子成为可能。 纽卡斯尔大学教授卡里姆-纳耶里纳表示，利用骨髓组织制造精子细胞将可以治疗男性不育，另一方面从女性骨髓组织中提取的干细胞也可以通过某种诱骗机制使其分化成为精子细胞。 不过，从女性身体中分化出的精子细胞将只有X染色体，因此她们的后

36、代只可能是女儿。 研究表示，未来甚至可以出现仅由女性构成的世界。纳耶里纳表示：“从理论上说这是完全可能的。问题是制造出的精子是否具备完整的功能。我认为只要这一过程 是安全的，就不存在伦理学上的障碍。我们目前正在申请伦理学许可，并准备直接利用纽卡斯尔这里的骨髓干细胞库。” 如果精子细胞能够从女性骨髓组织中分化，那么随后将在实验室中进行培育，并测试其是否能够穿透鼠类卵子的外壁，从而验证受精的可能性。纳耶里纳表示：“我 们测试用这种方式制造出的男性和女性精子。”不过他同时表示，目前没有计划用这种精子让人类卵子受精，因为这一行为需要多个主管部门的批准。 不需要男人，女人自己也可以制造精子生孩子，这样的

37、情景大概只有科幻小说上才会出现，但是英国科学家却说，在不久的将来，他们可能会将这样的想法变成现实。 只能生女儿？ 研究者称，他们此前已经从男子的骨髓组织中成功提取并且培育出了精子细胞，他们相信这样的技术应该同样也适用于女性。如此一来，那些长期受不育症困扰的男性将可能从此摆脱烦恼，而那些女同性恋者也可以不需要借助男人而拥有自己的孩子。 不过，科学家表示，从女性身体中提取并培育出精子将意味着她们只能生女儿，因为生男孩所需的Y染色体只能从男性精子那里获得。2021/7/16 星期五132005-1-6 1:51:00 细胞：精子干细胞成为新的“万能细胞”日本京都大学教授筱原隆司领导的研究小组最近通过

38、动物实验，用精子干细胞制成像胚胎干细胞一样可生成各种器官和组织的细胞，作为又一种“万能细胞”引起了广泛关注。据读卖新闻29日报道，筱原教授在实验中培养刚诞生的幼鼠的精囊细胞，约一个月后出现了和胚胎干细胞形状相似的细胞，筱原教授用培养胚胎干细胞的条件对这种细胞继续加以培养，发现这种细胞不但发生了分化，而且还出现了增殖现象，细胞的性质与功能和胚胎干细胞相似。一旦改变培养条件，就会分化成血液、心肌和血管细胞等。2021/7/16 星期五142010-1-21 10:55:11 Nature：同源精子会抱团前进美国哈佛大学研究人员报告说，如果将两种实验鼠的精子混合在一起，那么相同来源的精子就会利用其头

39、部的钩状物互相连接起来，协力向前游动，这样一列“精子火车”的速度比单个精子要快约50，四分之三相同来源的精子都会加入这样的队列中。2021/7/16 星期五15Competition drives cooperation among closely related sperm of deer miceHeidi S. Fisher1,2 &Among the extraordinary adaptations driven by sperm competition is the cooperative behaviour of spermatozoa1. By forming cooperat

40、ive groups, sperm can increase their swimming velocity and thereby gain an advantage in intermale sperm competition1, 2. Accordingly, selection should favour cooperation of the most closely related sperm to maximize fitness3. Here we show that sperm of deer mice (genus Peromyscus) form motile aggreg

41、ations, then we use this system to test predictions of sperm cooperation. We find that sperm aggregate more often with conspecific than heterospecific sperm, suggesting that individual sperm can discriminate on the basis of genetic relatedness. Next, we provide evidence that the cooperative behaviou

42、r of closely related sperm is driven by sperm competition. In a monogamous species lacking sperm competition, Peromyscus polionotus, sperm indiscriminately group with unrelated conspecific sperm. In contrast, in the highly promiscuous deer mouse, Peromyscus maniculatus, sperm are significantly more

43、likely to aggregate with those obtained from the same male than with sperm from an unrelated conspecific donor. Even when we test sperm from sibling males, we continue to see preferential aggregations of related sperm in P. maniculatus. These results suggest that sperm from promiscuous deer mice dis

44、criminate among relatives and thereby cooperate with the most closely related sperm, an adaptation likely to have been driven by sperm competition.2021/7/16 星期五162009-9-15 11:00:47 BiologicalReviews：男性超级精子游动过快可能导致不孕一项最新的研究显示，有些人当不上父亲可能是因为他们产生的是超级精子，它们游动得太快太有力。进化生物学家奥伦哈森相信，这些超级精子会有效越过女性身体的防卫，以致于不只一个精

45、子刺破同一个卵子。这种状况叫多精入卵，结果毁了卵子和卵子的受精机会。该研究发表在生物学评论杂志上2021/7/16 星期五172010-5-25 9:39:40 Science：首次发现可发育成卵的干细胞日本一个研究小组日前发现，在雌鳉鱼的卵巢内存在可发育成鳉鱼卵的干细胞。有关成果已经刊登在最新一期的美国科学杂志网络版上。研究小组对雌性鳉鱼进行基因操作，使其卵巢内的卵发出红光，结果发现了很多即将发育为卵的细胞。利用绿色荧光蛋白质给这些细胞做上标记以后，研究人员发现许多新形成的卵也会发出绿色荧光，这说明这些细胞的确发育成了卵，因此这些细胞就是干细胞。 2021/7/16 星期五182 生殖细胞发

46、生2.1 生殖细胞的起源与分化2.2 精子发生2.3 卵子发生2021/7/16 星期五192.1生殖细胞的起源与分化原始生殖细胞（primordial germ cell,PGC）-迁移（migration)-生殖嵴（genital ridge)-germ cells2.1.1 生殖质与生殖细胞分化ZygotecleavageAB cells and P1 cellsP1-P2-P3-P4-germ cells Genes: Pie-1,maternal-effect gene,oskar gene,etc.2021/7/16 星期五202.2 原生殖细胞的迁移两栖类通过卵裂进行迁移，植物极

47、-分裂沟-内胚层-背肠系膜-生殖嵴哺乳动物起源原肠作用胚胎外层-原条后部-尿囊后肠交接处-卵黄囊-沿背肠系膜-左右侧生殖嵴鸟类和爬行动物起源新月区-血液循环-生殖嵴2021/7/16 星期五21精子发生（spermatogenesis）2021/7/16 星期五22男性生殖系统组成功能：睾丸生殖管道附属腺外生殖器产生精子分泌雄激素2021/7/16 星期五23生精小管白膜鞘膜脏层鞘膜腔睾丸网直精小管一、睾丸（testis）睾丸的一般结构：白膜睾丸纵隔睾丸小叶生精小管直精小管睾丸网2021/7/16 星期五24(一)生精小管（seminiferous tubules）(二)睾丸间质2021/7/

48、16 星期五25（一）生 精 小 管 （ seminiferous tubules ）生精上皮 基膜 肌样细胞2021/7/16 星期五26生 精 上 皮 ( spermatogenic epithelium )生 精 细 胞( Spermatogenic cell )支 持 细 胞(sustentacular cell )2021/7/16 星期五271、生 精 细 胞( Spermatogenic cell ) ：(1)精原细胞(2)初级精母细胞(3)次级精母细胞(4)精子细胞(5)精子2021/7/16 星期五281、生 精 细 胞： (1)精原细胞(spermatogonium)A型B

49、型Ad型n Ad型Ad型Ap型B型2021/7/16 星期五291、生 精 细 胞： (1)精原细胞(spermatogonium) (2)初级精母细胞(Primary spermatocyte)A型(Ad, Ap )B型2021/7/16 星期五30精母细 胞 成 熟 分 裂减数分裂(meiosis)2021/7/16 星期五311、生 精 细 胞： (1)精原细胞(spermatogonium) (2)初级精母细胞(Primary spermatocyte) (3)次级精母细胞(secondary spermatocyte)A型(Ad, Ap )B型2021/7/16 星期五321、生 精

50、 细 胞： (1)精原细胞(spermatogonium) (2)初级精母细胞(Primary spermatocyte) (3)次级精母细胞(secondary spermatocyte) (4)精子细胞 ( spermatid )A型(Ad, Ap )B型2021/7/16 星期五33 精 子 形 成（ spermiogenesis ） (4)精子细胞 ( spermatid )2021/7/16 星期五34(5)精子（spermatozoon）2021/7/16 星期五35(5)精子（spermatozoon）头部：胞核顶体顶体酶尾部：轴丝线粒体鞘2021/7/16 星期五36精 子 发

51、 生Ad型精原细胞初级精母细胞次级精母细胞B型精原细胞精子细胞精子组蛋白精核蛋白Ap型精原细胞胞质桥2021/7/16 星期五37精子发生 SpermatogenesisGrowthMitosis I,Cytoplasmic divisionMeiosis II,Cytoplasmic divisionspermatids (haploid)secondary spermatocytes (haploid)primary spermatocyte (diploid)spermato-gonium (diploid male reproductive cell)2021/7/16 星期五38卵子

52、发生OogenesisGrowthMeiosis I,Cytoplasmic divisionMeiosis II,Cytoplasmic division卵子(n) ovum (haploid)初级卵母细胞 (2n) primary oocyte (diploid)卵原细胞 (2n) oogonium (diploid reproductive cell)次级卵母细胞 (n) secondary oocyte (haploid)第一极体(n) first polar body (haploid)三个极体(n) 3 polar bodies (haploid)2021/7/16 星期五3920

53、21/7/16 星期五402021/7/16 星期五412021/7/16 星期五422021/7/16 星期五432021/7/16 星期五442021/7/16 星期五452021/7/16 星期五462021/7/16 星期五472021/7/16 星期五482021/7/16 星期五492021/7/16 星期五502021/7/16 星期五512021/7/16 星期五522021/7/16 星期五532021/7/16 星期五542021/7/16 星期五552021/7/16 星期五562021/7/16 星期五572021/7/16 星期五582021/7/16 星期五5920

54、21/7/16 星期五602021/7/16 星期五612021/7/16 星期五622021/7/16 星期五632021/7/16 星期五642021/7/16 星期五652021/7/16 星期五662021/7/16 星期五672021/7/16 星期五682021/7/16 星期五692021/7/16 星期五702.1 Generation of germ cell 1.Overview of germ line specification(特化）2.Germ-line specification in Drosophlia3.Germ-line specification in

55、elegans4.Specification of vetebrate germ line2021/7/16 星期五711.Overview of germ line specification(特化） In animals that set aside a germ line in early development ,germ-cell specification occurs during cleavage or gastrulation. In many cases, this involoves a special area of cytoplasm ,the germ plasm,

56、 which is distinguishable in the egg. In such animals ,the formation of germ plasm is dependent on asymmetrically distributed maternal gene products. In birds and mammals, the germ line is not specified by cytoplasmic determinants,but by inductive interactions controlled by zygotic genes.2021/7/16 星

57、期五723.Germ-line specification in elegans（线虫）The first four cleavage divisions of the C.elegans embryo are reminiscent暗示的of stem cell divisions, each producing the founder of a somatic cell lineage and another stem cell（a-P cell). The fourth division produces a somatic founder cell and the P4 cell, w

58、hich is the source of the germ line. The unfertilized egg contains germ cell determinants called P-granules. These are initially distributed uniformly in the egg, but become restricted to the P-cells during cleavage and are eventually restricted to the P4 cell. Mutations that disrupt the embryonic c

59、leavage pattern also affect germ line specification, while other mutations block germ cells specification without influencing embryonic polarity. 2021/7/16 星期五732.Germ-line specification in Drosophlia（果蝇） In Drosophila, the germ plasm located at the posterior pole the egg, and undergoes cellularizat

60、ion a few divisions before the somatic cells are formed. This produces about 15 primordial germ cells called pole cells. The pole plasm is distinguishable because it contains distinct polar granules, comprising a number of proteins that control localization of the pole plasm and germ cell specificat