Gastrulation2amphibian

1、15. Amphibian Gastrulation 2Fate maps of the blastula of the Xenopus爪蟾胚胎原基分布圖爪蟾胚胎原基分布圖 Superficial layer of animal hemisphereSuperficial layer of animal hemisphere ectoderm ectoderm Superficial layer of vegetal hemisphere Superficial layer of vegetal hemisphere endodermendoderm The cells beneath the

2、 surface in the equatorial The cells beneath the surface in the equatorial (marginal region) (marginal region) mesoderm mesoderm3原腸腔原腸腔囊胚腔囊胚腔4(1) Cell movements during (1) Cell movements during amphibian gastrulationamphibian gastrulation The The invaginationinvagination of cells below the of cells

3、below the equator in the equator in the gray crescentgray crescent（灰色新月（灰色新月區(qū)）區(qū)） initiates the gastrulationinitiates the gastrulation. . The next phase involves the The next phase involves the involutioninvolution of the of the marginal zone cellsmarginal zone cells（邊緣帶細邊緣帶細胞）胞）. .Marginal zoneMargi

4、nal zone: the zone surrounding the equator of the : the zone surrounding the equator of the blastula, where the animal and vegetal hemispheres meet.blastula, where the animal and vegetal hemispheres meet.While the animal cells undergo epibolyWhile the animal cells undergo epiboly and and cover the e

5、ntire embryo .cover the entire embryo .5The formation of LB (Lip of the blastopore : 胚孔唇）6 Firstly: dorsal lip Then: the dorsal lip expands laterally to form lateral lips. Finally: a ventral lip develops over which additional mesodermal and endodermal precursors cells pass. 7Xenopus8Lip of the blast

6、opore (LB: 胚孔唇） The first cells to compose the dLBThe first cells to compose the dLB( (背唇背唇): ): the bottle cells that invaginatedthe bottle cells that invaginated to form to form the endoderm later.the endoderm later. Then: cells that involuteThen: cells that involute to become the to become the he

7、ad mesoderm later.head mesoderm later. Next: chordamesodermNext: chordamesoderm ( (脊索中胚層脊索中胚層) cells.) cells.The cells constituting the dLBThe cells constituting the dLB are constantly are constantly changing: changing: 9(2) Positioning the blastopore(2) Positioning the blastoporeThe entry of sperm

8、causes the rotating 30 of cytoplasm toward upward, which activates the cytoplasm opposite the point of sperm entry, enabling it to initiate gastrulation. 10The factors that initiate gastrulation is in the internal cytoplasm.第一次卵裂進入到第一次卵裂進入到4050時，時，30g 4分鐘分鐘11(3) Invagination(3) Invagination and invo

9、lution and involution12Bottle cells（瓶狀細胞）（瓶狀細胞）:The main body of each cell goes toward the inside while the cell maintains contact with the outside surface by way of a slender (微微細的）細的）neck. The outer-inner length of these cells greatly increase to yield the “bottle” shape. 13Vegetal rotationIMZ14 V

10、egetal rotation: at least 2 hours before the bottle cells form, internal cell movements propel（推動）（推動）the cells of the dorsal floor of the blastocoel to be immediately above the involuting mesoderm. Vegetal rotation push the pharyngeal endoderm（咽內胚層）（咽內胚層）forward, driving the mesoderm passively（被動地）

11、（被動地） into the embryo. The involution is led by the pharyngeal endoderm and head mesoderm.Vegetal rotation(植物植物極旋轉極旋轉)15Removal of the bottle cells does not affect the involution, while removal of the deep involuting marginal zone (深深層內卷邊緣帶，層內卷邊緣帶，dIMZ) cells stops archenteron formation.16The conver

12、gent extension（集聚延伸） of the dorsal mesoderm17 Shortly before the involution, the several layers of deep IMZ cells intercalate（插入）. This intercalation causes a convergent extension along the mediolateral axis（中側（中側軸）軸） that integrates（整合）（整合）several mesodermal streams to form a long, narrow band. As

13、gastrulation continues, the deep marginal cells flatten（變平）（變平）, the formerly superficial cells form the wall of the archenteron(原來的表原來的表層細胞內卷形成原腸頂部的壁層細胞內卷形成原腸頂部的壁). 1819(4) Migration of the involuting mesoderm The mesodermal cells entering through the dorsal lip give rise to the notochord and somit

14、es脊索和體節(jié)脊索和體節(jié). The other mesoderm enters through the ventral and lateral lips to create the mesodermal mantle. 2021 In many amphibians, the involuting mesodermal precursors migrate toward the animal pole on a fibronectin lattice（纖連蛋白架子）（纖連蛋白架子）secreted by the cells of the blastocoel roof.22(5) The formation of endoderm The endoderm derived from the superficial IMZ（表層表層內卷邊緣帶）內卷邊緣帶）cells form the archenteron roof. The endoderm from the subblastoporal （胚孔下）（胚孔下） vegetal cells become the archenteron floor.23(6) Epiboly of the ectoderm The animal cap and noninvoluting MZ（NIMZ: 非內卷邊緣帶）非內卷邊緣帶）cells