Block B Lecture 1.3 - Gradients & Differentiation

Describe differentiation?

they start off as pluripotent stem cells in the blastocyst but, over time, become more specialised until reaching their terminally differentiated form

Does the process of specialisation follow a process?

yes, their is a ‘programmed’ path to their specified final form/fate

Is the process of specialisation reversible?

no - not naturally

Stages of cell differentiation that are reversible?

-pluripotent

-other

-heman gioblast

-multipotent hemato-poietic

-myeloid progenitor (mesoderm)

STEM cells early on in development?

-cells haven’t been programmed yet

-single cell has all the info & ability to become the adult organism (e.g. plankton)

What are STEM cells able to do when transplanted before becoming specialised?

able to adopt the appropriate form for their new home (everything is kind of equal at this stage..) (e.g. toad)

STEM cells later on?

cells taken from different parts of an embryo remember where they came from and differentiate accordingly: they have already become ‘specified’

What processes must be occurring in a 3D embryo?

-local cellular interactions

-long-range morphogen signals

=> cellular responses

What do local cellular interactions do?

organise tissues

What do long-range morphogens signals do?

determine the orientation of the embryo & its specific regions

What do these 2 signals cause (response) to be irreversibly started?

-migration process

-specific differentiation process

What happens when you mix different cell types?

they will organise themselves into regional embryo-like structures… sorting like-with-like

What does cell adhesion often drive?

cell organisation

How does cell adhesion drive cell organisation?

-proteins expressed on the surface of cells that like to stick to the same molecules on other cells

What type of binding/interactions is involved in cell adhesion?

homophilic

What is a way used to generate an axis (head-tail)?

morphogen gradients

What is a morphogen?

a molecule that is secreted that induces cell fate decisions in recipient cells in a concentration gradient-dependent long-range manner

What do morphogen gradients require?

-production from a point source

-long-range distribution

-reception & interpretation (contact-dependent) by cell

Worplet’s “French flag” model 1?

the cells closest to the morphogen signal (receive high conc.) causing them to respond one way

Worplet’s “French flag” model 2?

same idea as the first but instead cells will read multiple signals and will have more of a logic response