Positive-Feedback Loops

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Two types of positive-feedback loops are used in maintaining patterning decisions: intracellular and intercellular.

Intracellular Positive-Feedback Loops

In intracellular positive-feedback loops, protein being expressed binds to an enhancer on its own gene, thereby maintaining its own transcription.

An example of this is the positive-feedback loop used for Sxl splicing in the female developmental pathway.

Here, the transcription factor binds to an enhancer of its own gene, maintaining its transcription.

Intercellular Positive-Feedback Loops

Another mechanism uses cell-cell interactions to create a mutal positive-feedback loop between cells.

Each adjacent cell sends out a signal that activates receptors, signal transduction pathways, and transcription-factor expression in the other cell.