Genes, Regulation, and the Control of Cellular Activity
Cells do not simply possess genes; they regulate their use. Networks of DNA elements, transcription factors, chromatin states, and RNA-related processes help determine which genes are active in particular cells and circumstances.
The Investigative Question
How do cells control when, where, and how strongly genetic information is used?
What We Observe
A multicellular organism contains many kinds of cells with very different structures and activities even though those cells generally contain essentially the same genome.
The difference lies largely in which genes are active, when they are active, and how strongly they are expressed.
Gene expression is therefore controlled rather than being a simple automatic reading of every gene in the genome.
Scientific Background
Gene regulation occurs at several levels. DNA sequences such as promoters and enhancers can interact with transcription factors. Chromatin structure influences access to DNA. RNA molecules and RNA-binding proteins can affect processing, stability, localization, and translation.
Regulatory interactions can operate together in networks. A regulatory protein produced by one gene may influence several other genes, whose products may in turn affect still others.
These systems allow cells to respond to development, nutrients, stress, signaling molecules, and changing environmental conditions.
Why It Matters
Genetic information is useful only when a cell can access and employ it appropriately.
A gene needed during embryonic development may be harmful if activated at the wrong time. A protein useful in one tissue may be unnecessary in another. Cells therefore require mechanisms that connect stored genetic information with circumstances and cellular identity.
This makes regulation an essential part of biological information processing.
What Is Known
Gene expression is controlled through interacting mechanisms involving regulatory DNA, transcription factors, chromatin, RNA processing, RNA stability, and other cellular systems.
Large genomic projects have identified extensive patterns of cell- and tissue-specific regulatory activity.
Changes in regulatory sequences can produce important biological and evolutionary effects even when protein-coding sequences remain unchanged.
What Is Proposed
Regulatory networks can evolve through changes in transcription-factor binding sites, gene duplication, modification of regulatory proteins, recruitment of existing components into new relationships, and other evolutionary mechanisms.
Evolutionary developmental biology investigates how changes in gene regulation can produce differences in form and development among organisms.
What Remains Uncertain
The complete regulatory architecture of complex genomes is not yet known.
Individual regulatory elements may operate differently among cell types, developmental stages, and environmental conditions. Many apparent regulatory associations still require experimental confirmation of their precise functions.
Scientists also continue to investigate how large regulatory networks originated and changed during evolutionary history.
Key Numbers
ENCODE phase III integrated nearly 6,000 new experiments and reported regulatory information across hundreds of human and mouse cell and tissue contexts.
Design Relevance
Gene regulation is relevant to Intelligent Design because it reveals that biological information involves more than possessing useful sequences. Cells must also coordinate their use.
Networks capable of activating, suppressing, and adjusting genetic activity can appear strongly organized toward biological function.
At the same time, evolutionary biology provides mechanisms by which regulatory relationships can be modified and co-opted. The design question therefore concerns the origin and cumulative organization of the system, not merely the existence of an individual regulatory switch.
Assessment
Modern genomics has replaced the simple picture of genes acting independently with a much richer picture of regulated genomic activity.
The resulting networks are central to development and cellular function. Their existence deserves investigation both in terms of the mechanisms by which they operate and the historical processes by which those mechanisms arose.