V動物身體圖式的模式建成II實用教案

1、Patterning the body plan in animals1 Development of the Drosophila body plan1.1 Specification of the antero-posterior and dorso-ventral axis in Drosophila oocyte1.2 Setting up the body axes in Drosophila1.3 Patterning the Drosophila embryo2 Patterning the vertebrate body plan2.1 Specification and se

2、tting up of the body axes in amphibians (Xenopus)2.2 Somite formation and antero-posterior patterning2.3 Patterning the vertebrate nervous system2.4 Specifying the left-right axis (left-right asymmetry of internal organs)第1頁/共63頁第一頁，共64頁。All vertebrates, despite their many outward differences, have

3、a similar basic body planThe skeleton of a mouse embryo illustrates the vertebrate body plan The AP axis: head, trunk with paired appendages (vertebral column脊柱(jzh) and the post-anal tailThe vertebral column is divided into cervical (neck), thoracic (chest), lumbar (lower back), and sacral (hip and

4、 lower) regionsThe DV axis: the mouth defining the ventral side and the spinal cord the dorsal side第2頁/共63頁第二頁，共64頁。第3頁/共63頁第三頁，共64頁。Patterning the body plan in vertebratesn Early development in Drosophila is largely under the control of maternal factors that sequentially activate a different sets o

5、f the embryos own genes (zygotic genes) to pattern the body plan. n Vertebrate axes do not form from localized determinants, as in Drosophila. Rather, they arise progressively through a sequence of inductive interactions between neighboring cells. Amphibian axis formation is an example of this regul

6、ative development. n The experiments of Hans Spemann and his students showed there exists an embryonic organizer, Spemann organizer that determines the amphibian axis formation and patterns the embryo along the body axes through inducing such inductive interactions.第4頁/共63頁第四頁，共64頁。Patterning the bo

7、dy plan in animals1 Development of the Drosophila body plan1.1 Specification of the antero-posterior and dorso-ventral axis in Drosophila oocyte1.2 Setting up the body axes in Drosophila1.3 Patterning the Drosophila embryo2 Patterning the vertebrate body plan2.1 Specification and setting up of the b

8、ody axes in amphibians (Xenopus)2.2 Somite formation and antero-posterior patterning2.3 Patterning the vertebrate nervous system2.4 Specifying the left-right axis (left-right asymmetry of internal organs)第5頁/共63頁第五頁，共64頁。In the transplantation experiments, Hans Spemann and Hilde Mangold showed that

9、the dorsal lip of the blastopore can induce the hosts ventral tissues to form a second embryo with clear antero-posterior and dorso-ventral body axes. Spemann refered the dorsal lip as the organizer.The discovery of the Spemann organizer第6頁/共63頁第六頁，共64頁。Dr Hans Spemann-the Nobel Laureate in Physiolo

10、gy or Medicine 1935For his discovery of the organizer effect in embryonic development第7頁/共63頁第七頁，共64頁。Mechanisms underlying role of the Spemann organizer in development of the body plann How was the organizer specified and formed? What caused the dorsal blastopore lip to differ from any other region

11、 of the embryo?n What factors were being secreted from the organizer to create the antero-posterior and dorso-ventral axes?n How did the patterning of the embryo along the body axes become accompanied?第8頁/共63頁第八頁，共64頁。Mechanisms underlying role of the Spemann organizer in development of the body pla

12、nn How was the organizer specified and formed? What caused the dorsal blastopore lip to differ from any other region of the embryo?n What factors were being secreted from the organizer to create the antero-posterior and dorso-ventral axes?n How did the patterning of the embryo along the body axes be

13、come accompanied?第9頁/共63頁第九頁，共64頁。The developmentally important maternal factors are differentially localized along the animal-vegetal axis in the Xenopus unfertilized eggsThe Xenopus egg possesses a distinct animal-vegetal axis, with most of the developmentally important maternal products (mRNA/pro

14、teins) localized in the vegetal region第10頁/共63頁第十頁，共64頁。Vg-1 is a member of TGF-beta family of signaling proteins第11頁/共63頁第十一頁，共64頁。The cortical rotation upon sperm entry can both specify the dorsal side of the amphibian embryo, and induce formation of the Spemann organizerThe cortical rotation relo

15、cates those maternal factors , such as Wnt-11 and Dishevelled protein originally located at the vegetal pole to a site approximately opposite to the sperm entry. These factors called dorsalizing factors specify their new location as the future dorsal side of the embryo, thus conferring the dorsal-ve

16、ntral axis第12頁/共63頁第十二頁，共64頁。第13頁/共63頁第十三頁，共64頁。Model of the mechanism by which the Disheveled protein stabilizes beta-catenin in the dorsal portion of the amphibian egg第14頁/共63頁第十四頁，共64頁。The role of Wnt pathway proteins in dorsal-ventral axis specification (I)E: Blocking the endogenous GSK-3 in the

17、 ventral cells of the early embryo leads to formation of a second set of body axis第15頁/共63頁第十五頁，共64頁。The role of Wnt pathway proteins in dorsal-ventral axis specification (II)第16頁/共63頁第十六頁，共64頁。Model of the induction of the Spemann organizer in the dorsal mesodermLocalization of stablized beta-caten

18、in in the dorsal side of the embryoActivation of Wnt signaling activates genes encoding proteins such as SiamoisSiamois and TGF-beta signaling pathway function together to activate the goosecoid gene in the dorsal portionGoosecoid as a transcription factor activates genes whose proteins are responsi

19、ble for induction of the Spemann organizer in the dorsal mesoderm第17頁/共63頁第十七頁，共64頁。n How was the organizer specified and formed? What caused the dorsal blastopore lip to differ from any other region of the embryo?n What factors were being secreted from the organizer to create the dorso-ventral and

20、antero-posterior axes?n How did the patterning of the embryo along the body axes become accompanied?Mechanisms underlying role of the Spemann organizer in development of the body plan第18頁/共63頁第十八頁，共64頁。The functions of the Spemann organizer (I)n The ability to self-differentiate dorsal mesoderm into

21、 prechordal plate, chordamesoderm (notochord脊索(j su) etcn The ability to dorsalize the surrounding mesoderm into paraxial (somite-forming) mesoderm (When it would otherwise form ventral mesoderm)n The ability to dorsalize the ectoderm, inducing the formation of the neural tuben The ability to initia

22、te the movements of gastrulation. Once the dorsal portion of the embryo is established, the movement of the involuting mesoderm establishes the AP axis. In Xenopus (and other vertebrates), the formation of the AP axis follows the formation of the DV axis第19頁/共63頁第十九頁，共64頁。The functions of the Speman

23、n organizer (II)n The Organizer functions in setting up the dorsal-ventral axis by secreting diffusible proteins (Noggin, chordin, and follistatin) that antagonize/block the BMP signal. These diffusible proteins generate a gradient of BMP signaling that specifies the DV axisn The Organizer is able t

24、o secret the Wnt blockers Cerberus, Dickkopf and Frzb in the anterior portion of the embryo that generate a gradient of Wnt signaling. Thus, the Wnt signaling gradient specifies the AP axis.第20頁/共63頁第二十頁，共64頁。第21頁/共63頁第二十一頁，共64頁。第22頁/共63頁第二十二頁，共64頁。第23頁/共63頁第二十三頁，共64頁。The diffusible signal proteins

25、secreted by the Spemann organizer (I)The Organizer functions in setting up the dorsal-ventral axis by secreting diffusible proteins (Noggin, Chordin, and Follistatin) that antagonize/block the BMP signal. These diffusible proteins generate a gradient of BMP signaling that specifies the DV axis第24頁/共

26、63頁第二十四頁，共64頁。Localization of noggin mRNA in the organizer tissueAt gastrulation, noggin is expressed in the dorsal blastopore lipDuring convergent extension, noggin is expressed in the dorsal mesoderm (the notochord, prechordal plate etc )第25頁/共63頁第二十五頁，共64頁。Noggin protein is important for developm

27、ent of the dorsal and anterior structures of the Xenopus embryoRescue of dorsal structures by Noggin proteinMost top: The embryo lacks dorsal structures due to exposure to the UVThe 2nd-4th panel: the rescued embryos with dorsal structures in a dosage-related fasion, when the defect embryo is inject

28、ed with noggin mRNAThe bottom: If too much noggin mRNA is injected, the embryo produces dorsal tissues at the expense of ventral and posterior tissue, becoming little more than a head.第26頁/共63頁第二十六頁，共64頁。Model for the action of the Organizer in specifying the DV axisP-Smad1 antibody staining shows t

29、he gradient of the BMP signaling along the DV axis in an early gastrulating Xenopus embryoA gradient of BMP4 signaling elicits the expression of different genes in a concentration-dependent fasion 第27頁/共63頁第二十七頁，共64頁。The diffusible signal proteins secreted by the Spemann organizer (II)The Organizer

30、is able to secret the Wnt blockers Cerberus, Dickkopf and Frzb in the anterior portion of the embryo that generate a gradient of Wnt signaling. Thus, the Wnt signaling gradient specifies the AP axis.第28頁/共63頁第二十八頁，共64頁。Cerberus, a secreted protein from the organizer is important for development of t

31、he most anterior head structuresInjection of Cerberus mRNA into a vegetal ventral Xenopus blastomere at the 32-cell stage induce ectopic head structures第29頁/共63頁第二十九頁，共64頁。Frzb, another secreted protein from the organizer is important for development of the most anterior head structuresThe frzb is e

32、xpressed in the head endomesoderm of the organizerThe frzb mRNA: dark blueThe chordin mRNA: brownMicroinjection of frzb mRNA into the marginal zone leads to the inhibition of trunk formation, due to inactivation of the Wnt signaling第30頁/共63頁第三十頁，共64頁。The organizer is able to secret different sets of

33、 signal proteins that antagonize/block BMP and (or) Wnt signaling第31頁/共63頁第三十一頁，共64頁。第32頁/共63頁第三十二頁，共64頁。Mechanisms underlying role of the Spemann organizer in the body axis formationn How was the organizer specified and formed? What caused the dorsal blastopore lip to differ from any other region o

34、f the embryo?n What factors were being secreted from the organizer to create the antro-posterior and dorso-ventral axes?n How did the patterning of the embryo along the body axes become accompanied?第33頁/共63頁第三十三頁，共64頁。第34頁/共63頁第三十四頁，共64頁。The trunk mesoderm of a neurula-stage embryo can be subdivided

35、 into four regions along the dorso-ventral axis 第35頁/共63頁第三十五頁，共64頁。The trunk mesoderm of a neurula-stage embryo can be subdivided into four regions along the dorso-ventral axis Patterning the mesoderm along the dorso-ventral axis (subdivision of the mesoderm) is controlled by the gradient of BMP4 s

36、ignaling. High doses of BMP4 activate those genes (, Xvent1) for development of the lateral plate mesoderm Intermediate levels of BMP4 instruct formation of the intermediate mesoderm Low doses of BMP4 regulate the paraxial mesoderm differentiation through activating myf5 et al The mesoderm becomes n

37、otochord tissue when no BMP4 activity is present in the most dorsal region第36頁/共63頁第三十六頁，共64頁。The antero-posterior axial patterning in vertebratesPatterning of the vertebrate embryo along the AP axis will be focused on:Patterning of the dorsal mesoderm that forms the somites, the blocks of mesoderma

38、l cells that give rise to the skeleton and muscles of the trunkPatterning of the ectoderm that will develop into the nervous system. 第37頁/共63頁第三十七頁，共64頁。Patterning the body plan in animals1 Development of the Drosophila body plan1.1 Specification of the antero-posterior and dorso-ventral axis in Dro

39、sophila oocyte1.2 Setting up the body axes in Drosophila1.3 Patterning the Drosophila embryo2 Patterning the vertebrate body plan2.1 Specification and setting up of the body axes in amphibians (Xenopus)2.2 Somite formation and antero-posterior patterning2.3 Patterning the vertebrate nervous system2.

40、4 Specifying the left-right axis (left-right asymmetry of internal organs)第38頁/共63頁第三十八頁，共64頁。Neural tube and somites seen by scanning electron microscopy第39頁/共63頁第三十九頁，共64頁。Patterning of the somite-forming mesoderm along the antero-posterior axisn Somites are blocks of mesodermal tissue that are fo

41、rmed after gastrulation. They forms sequentially in pairs on either side of the notochord, starting at the anterior end of the embryo or head end. The somites give rise to the vertebrae, to the muscles of the trunk and limbs, and to the dermis of the skin.n Somites differentiate into particular axia

42、l structures depending on their position along the AP axis. The anterior-most somites skullThose posterior to them cervical vertebraeMore posterior ones thoracic vertebrae with ribs第40頁/共63頁第四十頁，共64頁。n The pre-somatic mesoderm is patterned along its AP axis before somite formation begins during gast

43、rulation.n The positional identity of the somites is specified by the combinatorial expression of genes of the Hox complexs along the AP axis, from the hindbrain to the posterior end, with the order of expression of these genes along the axis corresponding to their order in the cluster along the chr

44、omosomen Mutations or overexpression of a Hox gene results, in general, in localized defects in the region in which the gene is expressed, and cause homeotic transformations（同源(tn yun)異型轉(zhuǎn)化）.Somites are formed in a well-defined order along the antero-posterior axis第41頁/共63頁第四十一頁，共64頁。Specification of

45、 the pre-somitic mesoderm by position along the antero-posterior axis has occurred before somite formation begins during gastrulation 第42頁/共63頁第四十二頁，共64頁。Identity of somites along the antero-posterior axis is specified by Hox gene expression (I)n The Hox (Homeobox) genes of vertebrates encode a larg

46、e group of gene regulatory proteins that all contain a similar DNA-binding region of around 60 amino acids known as the homeodomain. The homeodomain is encoded by a DNA motif of around 180 base pairs termed the homeobox, a name that came originally from the fact that this gene family was discovered

47、through mutations that produce a homeotic transformationa mutation in which one structure replaces another. For example, the four-winged fly. n Hox genes that specify positional identity along the AP axis were originally identified in Drosophila and it turned out that related genes are involved in p

48、atterning the vertebrate axis 第43頁/共63頁第四十三頁，共64頁。Identity of somites along the antero-posterior axis is specified by Hox gene expression (II)n All the Hox genes whose functions are known encode transcriptional factors. Most vertebrates have four separate clusters of Hox genes. n A particular featur

49、e of the Hox gene expression in both insects and vertebrates is that the genes in each cluster are expressed in a temporal and spatial order that reflects their order on the chromosome. That is-a spatial pattern of genes on a chromosome corresponds to a spatial expression pattern in the embryo (The

50、order of the genes in each cluster from 3，to 5，in the DNA is the order in which they are expressed along the AP axis). n The overall pattern suggests that the combination of Hox genes provides positional identity for each somite. In the cervical region, for example, each somite, and thus each verteb

51、ra, could be specified by a unique pattern of Hox gene expression 第44頁/共63頁第四十四頁，共64頁。Specification of the identity (characteristic strucutre) of each segment is accomplished by the homeotic selector (同源同源(tn yun)異型選擇者異型選擇者) geneslab and Dfd-the head segmentsScr and Antp- the thoracic segmentsUbx -

52、the third thoracic segment AbdA and AbdB-the abdominal segmentsHomeotic gene expression in DrosophilaThere are 2 clusters of the homeotic genes encoding the Antennapedia and bithorax complexes第45頁/共63頁第四十五頁，共64頁。Loss-of-function mutations in the Ultrabithorax gene can transform the 3rd thoracic segm

53、ent into another 2nd thoracic segment, producing a four-winged fly 第46頁/共63頁第四十六頁，共64頁。第47頁/共63頁第四十七頁，共64頁。第48頁/共63頁第四十八頁，共64頁。Almost every region in the mesoderm along the antero-posterior axis is characterized by a particular set of expressed Hox genes第49頁/共63頁第四十九頁，共64頁。第50頁/共63頁第五十頁，共64頁。Pattern

54、ing the body plan in animals1 Development of the Drosophila body plan1.1 Specification of the antero-posterior and dorso-ventral axis in Drosophila oocyte1.2 Setting up the body axes in Drosophila1.3 Patterning the Drosophila embryo2 Patterning the vertebrate body plan2.1 Specification and setting u

55、p of the body axes in amphibians (Xenopus)2.2 Somite formation and antero-posterior patterning2.3 Patterning the vertebrate nervous system2.4 Specifying the left-right axis (left-right asymmetry of internal organs)第51頁/共63頁第五十一頁，共64頁。The ectoderm lying along the dorsal midline of the embryo becomes

56、specified as neuroectoderm, the neural plate, during gastrulationDuring the stage of neurulation, the neural plate forms the neural tube, which eventually differentiates into the central nervous system第52頁/共63頁第五十二頁，共64頁。第53頁/共63頁第五十三頁，共64頁。Rhombomere: 菱腦節(jié)Branchial arches: 鰓弓第54頁/共63頁第五十四頁，共64頁。Patt

57、erning the nervous system along the AP axisn Hox genes are expressed in the mouse embryo hindbrain in a well-defined pattern, which closely correlates with the segmental pattern. Thus, Hox gene expression may provide a molecular basis for the identities of both rhombomeres (菱腦節(jié)) and the neural crest

58、 at the different positions in the hindbrain.n Both gene mis-expression or gene knock-outs in mice have alreadly shown that change in the Hox gene expression causes a partial or complete homeotic transformation of one segment into another in the hindbrain. Thus, the Hox genes determine patterning of

59、 the hindbrain region along the AP axis第55頁/共63頁第五十五頁，共64頁。第56頁/共63頁第五十六頁，共64頁。Patterning the nervous system along the AP axisn Hox genes are involved in patterning the hindbrain, but Hox gene expression can not be detected in the most anterior neural tissues of the mousethe midbrain and forebrain.

60、n Instead, homeodomain transcriptional factors such as Otx and Emc are expressed anterior to the hindbrain and specify pattern in the anterior brain in a manner similar to the Hox gene more posteriorly. In mice, Otx1 and Otx2 are expressed in overlapping domains in the developing forebrain and hindb