47.3 Cell Fate Blog Post

Cell Fate Specification

Definitions:

• Differentiation—changes involved in the progressive diversification of the structure and function of cells Acquisition of the characteristics that allow different cell types to perform their functions.
• Cell fate—what a cell will become (if left alone).
• Potency—what a cell could become
• Commitment—restriction in potency
• Specification—labile state where a cell has reversibly acquired fate (potency > fate)
• Determination—state where a cell has irreversibly acquired fate (potency = fate)
• Determinant—a molecule that regulates cell fate
• Morphogen—a molecule forms a gradient and regulates cell fate in a concentration dependent manner. 

I. Types of Specificaton

1. Autonomous Specification 
• Remove a cell and the cell types normally derived from that cell will not form.
• Isolate a cell and it will form the cell types it normally would have.
2. Conditional Specification
• Remove a cell and the cell types normally formed by that cell will be contributed by other cells (compensation) 
3. Syncitial Specification
• Important in insects

II. Autonomous Specification 

• Asymmetric distribution and inheritance of determinants 
• Determinants typically cytoplasmic 
• Determinants usually RNAs or proteins
1. MACHO mRNA localized in yellow cytoplasm of tunicate embryo 
• Antisense blocks muscle formation (=necessary)
• Injected mRNA induces animal pole to form muscle (=sufficient) 
2. SKN-1 protein localized in C. elegans EMS cell (pharynx derived from EMS) 
• skn-1 loss-of-function mutant produces no pharynx (necessary)
• Fucus contains cell wall determinants (handout)

III. Conditional Specification 

• A cell’s fate is determined by its environment 

A. Cell interactions.

• Contact with neighboring cells influence cell fate e.g. sea urchin 
• Animal pole cells alone produce ectoderm only
• Animal pole cells plus micromeres produce cell types normally derived from vegetal pole cells 
• Stem Cells—cells that divide to maintain a self-renewing population, and contribute daughters that will differentiate. Can get progressive commitment.