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 - a labile state where a cell has reversibly acquired fate (potency > fate)

Determination - a 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 Specification

A. 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.

B. Conditional Specification

• Remove a cell and the cell types normally formed by that cell will be contributed by other cells (compensation)

C. Syncitial Specification

• Important in insects

Autonomous Specification

• Asymmetric distribution and inheritance of determinants
• Determinants typically cytoplasmic (Fig. 3.10).
• Determinants usually RNAs or proteins e.g. 1. MACHO mRNA localized in yellow cytoplasm of the tunicate embryo
• Antisense blocks muscle formation (=necessary)
• Injected mRNA induces animal pole to form muscle (=sufficient) e.g. 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)

Conditional Specification 

• A cell’s fate is determined by its environment

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.