W12

Question 1

What is the difference between pattern forming (Musterbildung) and morphogenesis (Morphogenese- Gestaltbildung)?

Answer 1

Pattern forming is setting up the patterns for development. Morphogenesis changes the 3 dimensional organisation.

Question 2

How are the 3D changes of morphogenesis brought about?

Answer 2

1. Cell growth and proliferation 2. Cell death 3. Cell shape 4. Cell adhesion 5. Cell migration (plants only 1-3)

Question 3

What are the 3 stages of foetus development?

Answer 3

1. Cleavage (includes morula and blastula) 2. Gastrulation (Ectoderm, mesoderm and endoderm develop) 3. Neurulation

Question 4

What are the individual egg cells at the cleavage stage?

Answer 4

blastomeres At this stage cleavage is not accompanied by cell growth, because the egg cell is already big. This enables very fast division.

Question 5

What happens with very yolky eggs in the cleavage stage?

Answer 5

Cytokinesis during the cleavage cycle is either incomplete (zebra fish, chicken) or doesn’t occur (D. malanogaster)

Question 6

Stages of cleavage in Drosophila.

Answer 6

1. 30 min - fusion of sperm and egg nuclei 2. 70 min - nuclear division creating syncytium 3. 90 min - nuclei migrate to periphery of cytoplasm 4. 2h - syncytial blastoderm 5. 3h - cellular blastoderm

Question 7

Why is the axis of cell division important?

Answer 7

1. control tissue outgrowth 2. control asymmetric cell division e.g. C. elegans. AB and P1 cells divide along different axes.

Question 8

What is a mammalian embryo at the blastula stage called and what are its components?

Answer 8

Blastocyst 1. inner cell mass (becomes animal) 2. blastocoel 3. trophectoderm (becomes placenta)

Question 9

What are the morphogenetic processes and mechanisms of blastocyst formation?

Answer 9

Processes: compaction (morula), blastocoel formation Mechanisms: cell adhesion, cell polarization, oriented cell division

Question 10

How does compaction occur?

Answer 10

By minimizing the cell surface not touching another cell. This affects cell polarity as well, the outer apical cell surface being different from the basolateral surface.

Question 11

What are the two types of cleavage of a polarized cell, and what are their effects?

Answer 11

1. radial cleavage - 2 polarized cells 2. tangential cleavage - 1 polarized cell, 1 nonpolarized cell

Question 12

What is the effect of cell polarization in the formation of the blastocyte?

Answer 12

Sodium ions are transported more towards the inside, increasing the hydrostatic pressure, generates blastocoel. 2. tangential cleavage in one region generates inner cell mass.

Question 13

What are the molecular mechanisms of cell adhesion?

Answer 13

1. cell-cell adhesion: cadherins (Ca2+ dependent), immunoglobulin super family proteins (e.g. N-CAM: neural cell adhesion molecule) 2. cell-matrix adhesion: integrins (transmembrane proteins) - laminin (protein of extracellular matrix)

Question 14

What is the important cell adhesion factor for the development of morula?

Answer 14

E-cadherin

Question 15

What is the cause of the phenomenon seen in the sorting out experiment?

Answer 15

Different cell types have distinct cell adhesion characteristics. This allowed the identification of cell adhesion molecules.

Question 16

Processes of neurulation in Xenopus.

Answer 16

Morphogenetic processes: separation of the neuroectoderm/neural plate from ectoderm and formation of neural tube. Morphogenitic mechanisms: different cell adhesion molecules promotes two cell groups - future neurons: N-Cadherin and N-CAM - future epithelial cells: E-Cadherin

Question 17

mRNAs responsible for separation of epidermal and neural cells?

Answer 17

E-cadherin (E for epidermal) N-cadherin (N for neural)

Question 18

What are the two different types of development of the blostopore?

Answer 18

protostomes: blastopore becomes the mouth e.g. insects deuterostomes: blastopore becomes anus e.g. vertebrates

Question 19

3 stages of development. 1. before fertilization. 2. before gastrulation 3. after gastrulation

Answer 19

1. zygote 2. blastula 3. gastrula

Question 20

Ectoderm develops into…

Answer 20

skin, nervous system

Question 21

Mesoderm develops into…

Answer 21

notochord, skeleton, muscle, kidney, heart, blood

Question 22

Endoderm develops into…

Answer 22

gut, liver, lungs

Question 23

Molecular mechanisms of cell shape change…

Answer 23

actin filaments and their interaction with myosin motor proteins. Many actin-interacting proteins control the formation and quality of the actin filaments.

Question 24

Mesoderm invagination during gastrulation in D. melanogaster.

Answer 24

Twist and Snail are expressed in the prospective mesoderm. Mesoderm invagination starts by an apical constriction in prospective mesodermal cells becasue of gene expression changes by Twist and Snail.

Question 25

Mesoderm invagination is one of the first processes during Drosophila gastrulation. What is it followed by?

Answer 25

1. **EMT** (epithelia to mesenchyme transition) Twist and snail also control a change from E- to N-cadherin expression and **cell migration** towards the dorsal midline. 2. Endoderm invagination and **anterior and posterior midgut invagination**. 3. **Germband is extended by lateral cell intercalation**

Question 26

How is **cell interaction** used to change the form of tissue?

Answer 26

1. Germ band extension during Drosophila gastrulation involves cell intercalation. 2. convergent extension - cell intercalation observed in mesoderm during vertebrate gastrulation.

Question 27

Which spatial cues orient cell intercalation in vertebrate gastrulation?

Answer 27

**Planar epithelial cell polarity** is important and involves non-canonical Wnt signaling. frizzled\>Wnt

Question 28

What are the 3 important stages of Xenopus gastrulation?

Answer 28

* involution: rolling in of the endoderm and mesoderm at the blastopore * epiboly: spreading of the ectoderm over the invaginating endoderm and mesoderm (radial cell intercalation) * convergent extension: Tightening of the mesoderm into an elongated domain along the A-P axis(medio-lateral intercalation)

Question 29

Hensen's node and notochord in chick.

Answer 29

1. Hensen's node moves backwards 2. cells which migrate through the node condense into the notochord 3. notochord important for the formation of somites and neural tube and neural crest cells. 4. notochord charachteristic feature of chordates

Question 30

What are some structures that apoptosis builds?

Answer 30

1. cavity formation 2. separation of digits 3. **wolffian duct, m**üllerian duct (difference between man and woman) 4. loss of tail 5. refining neuronal connections

Question 31

Neural crest cells develop into a diversity of different cell types. How are these specified?

Answer 31

1. 1. Hox code 2. 2. signals provided by other cells on the migratory pathway