Cell fate determination

Cell fate determination is the programming of a cell to follow a specified path of cell differentiation. Often, cells are discussed in terms of their terminal differentiation state. During development, fates of some few cells may be specified at certain times. When referring to developmental fate or cell fate, one is talking about everything that happens to that cell and its progeny after that point in development.

The process of a cell to be committed to a certain state can be divided into two stages: specification and determination. Specification is not a permanent stage and cells can be reversed based upon different cues. In contrast, determination refers to when cells are irreversibly committed to a particular fate. This is a process influenced by the action of the extracellular environment and the contents of the cell's genome. Determination is not something that is visible under the microscope- cells do not change their appearance when they become determined. Determination is followed by differentiation, the actual changes in biochemistry, structure, and function that result in cells of different types. Differentiation often involves a change in appearance as well as function.

The state of commitment of a cell is also known as its developmental potential. When the developmental potential is less than or equal to the developmental fate, the cell is exhibiting mosaic behavior. When the developmental potential is greater than the developmental fate, the cell is exhibiting regulative behavior.

Embryos can use a combination of methods and exhibit a combination of behaviors throughout its development.

Types of specification
There are three major ways that developmental fates become specified: autonomous specification, conditional specification and syncytial specification.

Autonomous specification
This type of specification results from cell-intrinsic properties; it gives rise to mosaic development. The cell-intrinsic properties arise from a cleavage of a cell with asymmetric cytoplasmic determinants or morphogenetic determinants. Thus, the fate of the cell depends on factors segregated into the cytoplasm during cleavage. Early examples of autonomous specification came from the work of Whittaker in tunicate embryos.

Conditional specification
In contrast to the autonomous specification, this type of specification is a cell-extrinsic process that relies on cues and interactions between cells or from concentration-gradients of morphogens. These interactions can be either stimulatory or inhibitory. This type of specification was discovered from the result of transplantation experiments and isolation experiments.

Syncytial specification
This type of a specification is a hybrid of the autonomous and conditional that occurs in insects. This method involves the action of morphogen gradients within the syncytium. As there are no cell boundaries in the syncytium, these morphogens can influence nuclei in a concentration-dependent manner.

Link to: Cellular determination