cell migration during tissue formation

Question 1

similarities and differences in cytoskeletal organisation in epithelial and mesenchymal cells

Answer 1

mesenchymal cells -
at real, myoli is located in stress fires
composed of actin and myosin bundles
GTPare RhoA needed to build stress fibres, RhoA activated by down stream effector ROCK
ROCK inhibition reduces stress fibre tension
contractility of the rear mediated by local phosphorylation of myoll by RhoA-ROCK pathway
epithelial cells -
morphogenic process dependent on myoll distribution and tensile activity in the cell
activation of myoll relies on activation of RhoA to apical domain
apical localisation requires RhoA and ROCK

Question 2

what is needed for chemotactic movement

Answer 2

actin extension of pseudopadoia in the direction of signal, cells polarise and move directionally

Question 3

chemotactic migration of the primordial germ cells in zebra fish

Answer 3

cells detect changing SDF1 signal 2hrs after fertilisation through serpentine CXCR4 receptors
cells move by blebbing
cells correct motion during migration using a run and tumble mechanism
SDF1 is secreted into extracellular matrix by tissue cells in areas which germ cells migrate to in sebrafish
CXCR4 is sdf1s receptor, found on the surface of primordial germ cells
SDF1 expresssion causes PGC to migrate posteriorly
PCG polarisation is a response to chempkine signalling during apolar tumbling stage, stochastic loacal increase in calcium at various points at the cell periphery induces contraction of myosin associated with the actin nerve

Question 4

what is FGF receptor required for

Answer 4

mesoderm induction

Question 5

gastrulation movements in chick embryo

Answer 5

epiblast cells converge on the primitive streak and pass through it as individual cells, spreading out underneath the surface forming the bottom layer of the endoderm and middle layer of mesoderm
cells become specified as endo and meso during passage through the streak, cells remaining on the surface stay ectoderm

Question 6

mesoderm cell migration is controlled by attractive repulsive contractions

Answer 6

mesoderm cells migrate out of the streak at various anterior and posterior positions in the cells
cells move out of the streak under influences of a repulsive FGF8 signal
anterior mesoderm cells move anteriorly in response to FGF4 produced by the forming head process and notochord, cells in the posterior streak move into the extra embryonic area to form blood islands in response to VEGF
PDGF signalling in the epiblast controls N-cadherin expression of migrating mesoderm cells and lays out a migration domain for mesoderm cells

Question 7

gradient formation by differential receptor mediated ligand clearance

Answer 7

CXCR4 and CXCR7 receptors bind SDF1 but mainly CXCR4 transduces a movement signal
CXCR4 bind at the end closest to the direction of movement

Question 8

epithelial to mesenchymal transition

Answer 8

in epithelium, adherens junctions hold cells tightly together to form a continuous sheet
mesenchyme has a much looser arragnement
- some cases lack mature adhesive junctions
- offer partly surrounded by extracellular matrix and contact each other through thin contacts
- becomes connected by gap junctions - protein pores in adjacent cell membranes
epithelia are present within early embryos as dynamic and transient structures
epithelia are the starting tissue from which other cells emerge
EMT = dissolution of adherens junctions between epithelial cells

Question 9

neural crest cells form during the formation of the neural tube

Answer 9

neural crest cells are induced at the neural plate border by intermediate levels of BMP signalling and high levels of Wnt, FGF and RA signalling
signals induce several transcription factors whose co-expression defines the neural crest cell territory and controls delamination
neural crest cells differentiate into a plethora of different cell types
- no other embyonic cell population can generate such a diversity of cells
neural crest cells forming in the hind brain innervate the branchial arches
- migration is confined by repulsive signalling via Semaphorins detected by neutrophilins
- dispersal of cells controlled by contact inhibition of locomotion and chemotaxis

Question 10

what regulates collective cell migration of cephalic neural crest cells

Answer 10

cell to cell interactions and external signals

Question 11

collective cell movement

Answer 11

cells are mostly in a mesenchymal state
cells move in cohorts in close contact with other cells
movement can be influenced by chemotaxis and chemokines
cell dependent destruction of ligand may create gradients that help disperse cells
cells may disperse as a result of contact inhibition of locomotion
mechanisms are complex and can only be studied in vivo