Gastrulation

Question 1

Morphogenesis 3 movements

Answer 1

1. Internalization
   - invagination/involution
   - ingression
2. Convergence and Extension
   - mediolateral intercalation
   - directed migration
3. Epiboly
   - radial intercalation
   - cell shape changes

Question 2

How do differentiated cells move and reorganize during development to generate the body plan and a functional organism?

Answer 2

Through morphogenesis

Question 3

is the point in embryogenesis where the basic organization of the organism is established.

Answer 3

Gastrulation

Question 4

Events in gastrulation:

Answer 4

1. Establishment of the three basic germ layers;
2. Groups of cells that will give rise to specific organ systems and tissues are moved into the right position;
3. Groups of cells that will influence each other’s differentiation are positioned so they can have an effect on each other.

Question 5

2-Fold Process in Amniotes:

Primary Gastrulation
Secondary Gastrulation

Question 6

is the point in embryogenesis where there are MORPHOGENETIC MOVEMENTS

Answer 6

Gastrulation

Question 7

Gastrulation changes:

Answer 7

1. Cell shape
2. Cell adhesion

Question 8

Contraction of the ________ drives apical constriction

Answer 8

adhesion belt

Question 9

Cytoskeletal events drive CELL SHAPE changes

Answer 9

Microtubules elongate, causing cells to become columnar -> Apical actin-filament bundles contract, narrowing the cells at their apices

Question 10

A transcription factor that represses E-cadherin, a protein crucial for cell-cell adhesion.

Answer 10

Snail

Question 11

E-Cadherin & Epithelial-Mesenchymal Transformation

Columnar epithelial cells = E-Cadherin -> Bottle cell = Loss of E-Cadherin -> Mesenchyme cell = No E-Cadherin

Question 12

is a gradual, multifactorial process in which different cellular requirements can be independently regulated.

Answer 12

epithelial-mesenchymal transition (EMT)

Question 13

4 Evolutionary Conserved Morphogenetic Movements in Gastrulation

Answer 13

1. Emboly (internalization)
2. Epiboly
3. Convergence
4. Extension

Question 14

Emboly (internalization)
The first process in gastrulation.
* Invagination
* Involution
* Ingression/Delamination

Question 15

“a form of cell spreading in which cells flatten out to cover a much larger surface area”

Answer 15

Epiboly

Question 16

Local inward buckling of an epithelium

Answer 16

Invagination

Question 17

Inward movement of a cell layer around a point or edge

Answer 17

Involution

Question 18

Movement of individual cells or small groups from an epithelium into a cavity

Answer 18

Ingression

Question 19

Splitting layers of cells (coordinated ingression)

Answer 19

Delamination

Question 20

Spread of an outside cell layer (as a unit) to envelop a yolk mass or deeper layer

Answer 20

Epiboly

Question 21

Movement of individual cells over other cells or matrix

Answer 21

Migration

Question 22

Elongates the nascent germ layers from head to tail and narrows them from back to belly

Answer 22

Convergence & Extension

Question 23

Summary of body axis elongation and driving mechanisms

Tissue level
Convergent extension
Inter-tissue flow
Intra-tissue flow
Growth
Swelling

Cell level
Intercalation
Specification
Movement
Proliferation
Differentiation

Question 24

Gastrulation in Drosophila

Mesoderm morphogen
Endoderm morphogen

Answer 24

Spatzle
Trunk

Question 25

Gastrulation in Sea urchin:

Answer 25

1. Primary Mesenchyme cells (PMCs) ingress (driven by changes in cell adhesion) 1a.Invaginating PMCs migrate on the extracellular matrix lining the blastocoel using filopodia 1b. PMCs eventually fuse and form the spicules (skeletal rods) 2. Apical constriction and changes in the extracellular matrix create a dome-shaped invagination (archenteron) 3. Cell intercalation (convergent extension) converts the dome (archenteron) into an elongated tube 4. Secondary mesenchyme cells (SMCs) at the leading edge of the gut tube use filopodia to look for cues at the animal pole and pull themselves to that site

Question 26

Changes in cell adhesion drive the first step of gastrulation

Question 27

Xenopus laevis embryo

Answer 27

Ectoderm Neuro-ectoderm Dorsal mesoderm Ventral mesoderm Spemann's organizer Nieuwkoop centre

Question 28

Blastocoel prevents cells from interacting too soon and allows space for cell migration

Question 29

Gastrulation in Frog: Apical Constriction of _______ drives blastopore invagination

Answer 29

bottle cells

Question 30

Gastrulation in Frog: 1. Blastopore formation 2. Involution of Marginal Zone Cells ➢ movement of inside MZ cells dependent on ectoderm cells of blastocoel roof secreting fibronectin 3. Formation of the Archenteron = Convergent extension of dorsal mesoderm 4. Epiboly of ectoderm

Question 31

is essential for mesodermal cell involution during gastrulation

Answer 31

Fibronectin

Question 32

Gastrulation in Chick: 1. Appearance of primitive streak - Formation of 2-layered blastoderm - Ingression of epiblast cells in to subgerminal space - Migration of marginal zone cells to form hypoblast - Epiboly of ectoderm –yolk becomes enclosed by ectoderm

Question 33

Cells passing __________ form the head structure

Answer 33

Hensen's node

Question 34

Gastrulation in Mammals * begins at the posterior end of the embryo * _______control cell migration and specification -–downregulate E-cadherin; regulate ______, ______ and _______ (genes that influence specification)

Answer 34

FGFs; snail; Brachury; Tbx6

Question 35

Time line of early human development

Answer 35

Fertilization -> Cleavage (1 day) -> Blastocyst (6 days) -> Implantation -> (14 days) -> Gastrulation begins (17 days) -> Neurulation begins (22 days) -> Gastrulation complete (23 days) -> Neurulation complete & Differentiation begins (>24 days)

Question 36

Human Gastrulation: Formation of Epiblast and Hypoblast (ICM) Delamination occurs prior to implantation

Question 37

Human Gastrulation: Tissue Formation Cells entering the node become

Answer 37

notochord

Question 38

Human Gastrulation: Tissue Formation 1st cells entering primitive streak become

Answer 38

endoderm

Question 39

Human Gastrulation: Tissue Formation Later cells entering primitive streak become

Answer 39

mesoderm

Question 40

Human Gastrulation: Tissue Formation Cells that don't enter the primitive streak become

Answer 40

ectoderm

Question 41

Differentiation of Primary Germ Layers (from the gastrula) Ectoderm - Nervous system - Epidermis of skin Mesoderm - Skeleton - Muscles - Circulatory system - Gonads Endoderm - Digestive tract - Respiratory system - Liver, pancreas, bladder

Question 42

Human disorders attributed to abnormal gastrulation

Answer 42

Conjoined twinning Chordoma Caudal agenesis

Question 43

Do plants undergo GASTRULATION?

Answer 43

No

Question 44

Plants, like animals, develop 3 basic tissue systems (_____, ________, and _______), but do not rely on gastrulation to establish this layered system of tissues.

Answer 44

dermal; ground; vascular

Question 45

“It is not birth, marriage or death but GASTRULATION, which is truly the most important time in your life.” - Lewis Wolpert (1986)