What is the difference between pattern forming (Musterbildung) and morphogenesis (Morphogenese- Gestaltbildung)?
Pattern forming is setting up the patterns for development. Morphogenesis changes the 3 dimensional organisation.
How are the 3D changes of morphogenesis brought about?
1. Cell growth and proliferation 2. Cell death 3. Cell shape 4. Cell adhesion 5. Cell migration (plants only 1-3)
What are the 3 stages of foetus development?
1. Cleavage (includes morula and blastula) 2. Gastrulation (Ectoderm, mesoderm and endoderm develop) 3. Neurulation
What are the individual egg cells at the cleavage stage?
blastomeres At this stage cleavage is not accompanied by cell growth, because the egg cell is already big. This enables very fast division.
What happens with very yolky eggs in the cleavage stage?
Cytokinesis during the cleavage cycle is either incomplete (zebra fish, chicken) or doesn't occur (D. malanogaster)
Stages of cleavage in Drosophila.
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
Why is the axis of cell division important?
1. control tissue outgrowth 2. control asymmetric cell division e.g. C. elegans. AB and P1 cells divide along different axes.
What is a mammalian embryo at the blastula stage called and what are its components?
Blastocyst 1. inner cell mass (becomes animal) 2. blastocoel 3. trophectoderm (becomes placenta)
What are the morphogenetic processes and mechanisms of blastocyst formation?
Processes: compaction (morula), blastocoel formation Mechanisms: cell adhesion, cell polarization, oriented cell division
How does compaction occur?
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.
What are the two types of cleavage of a polarized cell, and what are their effects?
1. radial cleavage - 2 polarized cells 2. tangential cleavage - 1 polarized cell, 1 nonpolarized cell
What is the effect of cell polarization in the formation of the blastocyte?
Sodium ions are transported more towards the inside, increasing the hydrostatic pressure, generates blastocoel. 2. tangential cleavage in one region generates inner cell mass.
What are the molecular mechanisms of cell adhesion?
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)
What is the important cell adhesion factor for the development of morula?
What is the cause of the phenomenon seen in the sorting out experiment?
Different cell types have distinct cell adhesion characteristics. This allowed the identification of cell adhesion molecules.
Processes of neurulation in Xenopus.
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
mRNAs responsible for separation of epidermal and neural cells?
E-cadherin (E for epidermal) N-cadherin (N for neural)
What are the two different types of development of the blostopore?
protostomes: blastopore becomes the mouth e.g. insects deuterostomes: blastopore becomes anus e.g. vertebrates
3 stages of development. 1. before fertilization. 2. before gastrulation 3. after gastrulation
1. zygote 2. blastula 3. gastrula
Ectoderm develops into...
skin, nervous system
Mesoderm develops into...
notochord, skeleton, muscle, kidney, heart, blood
Endoderm develops into...
gut, liver, lungs
Molecular mechanisms of cell shape change...
actin filaments and their interaction with myosin motor proteins. Many actin-interacting proteins control the formation and quality of the actin filaments.
Mesoderm invagination during gastrulation in D. melanogaster.
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.
Mesoderm invagination is one of the first processes during Drosophila gastrulation. What is it followed by?
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
How is cell interaction used to change the form of tissue?
Germ band extension during Drosophila gastrulation involves cell intercalation.
convergent extension - cell intercalation observed in mesoderm during vertebrate gastrulation.
Which spatial cues orient cell intercalation in vertebrate gastrulation?
Planar epithelial cell polarity is important and involves non-canonical Wnt signaling.
What are the 3 important stages of Xenopus gastrulation?
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)
Hensen's node and notochord in chick.
Hensen's node moves backwards
cells which migrate through the node condense into the notochord
notochord important for the formation of somites and neural tube and neural crest cells.
notochord charachteristic feature of chordates
What are some structures that apoptosis builds?
separation of digits
wolffian duct, müllerian duct (difference between man and woman)
loss of tail
refining neuronal connections
Neural crest cells develop into a diversity of different cell types. How are these specified?